[release-branch.go1.23] go1.23.5

Change-Id: I849328cf93adf24c223f103f5b834635970ea652
Reviewed-on: https://go-review.googlesource.com/c/go/+/643137
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Gopher Robot <gobot@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

VERSION

@@ -0,0 +1,2 @@
+go1.23.5
+time 2025-01-10T16:44:59Z

codereview.cfg

@@ -1 +1,2 @@
-branch: master
+branch: release-branch.go1.23
+parent-branch: master

src/cmd/cgo/gcc.go

@@ -2579,6 +2579,11 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 		if dt.BitSize > 0 {
 			fatalf("%s: unexpected: %d-bit int type - %s", lineno(pos), dt.BitSize, dtype)
 		}
+
+		if t.Align = t.Size; t.Align >= c.ptrSize {
+			t.Align = c.ptrSize
+		}
+
 		switch t.Size {
 		default:
 			fatalf("%s: unexpected: %d-byte int type - %s", lineno(pos), t.Size, dtype)
@@ -2595,9 +2600,8 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 				Len: c.intExpr(t.Size),
 				Elt: c.uint8,
 			}
-		}
+			// t.Align is the alignment of the Go type.
-		if t.Align = t.Size; t.Align >= c.ptrSize {
+			t.Align = 1
-			t.Align = c.ptrSize
 		}
 
 	case *dwarf.PtrType:
@@ -2826,6 +2830,11 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 		if dt.BitSize > 0 {
 			fatalf("%s: unexpected: %d-bit uint type - %s", lineno(pos), dt.BitSize, dtype)
 		}
+
+		if t.Align = t.Size; t.Align >= c.ptrSize {
+			t.Align = c.ptrSize
+		}
+
 		switch t.Size {
 		default:
 			fatalf("%s: unexpected: %d-byte uint type - %s", lineno(pos), t.Size, dtype)
@@ -2842,9 +2851,8 @@ func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Typ
 				Len: c.intExpr(t.Size),
 				Elt: c.uint8,
 			}
-		}
+			// t.Align is the alignment of the Go type.
-		if t.Align = t.Size; t.Align >= c.ptrSize {
+			t.Align = 1
-			t.Align = c.ptrSize
 		}
 
 	case *dwarf.VoidType:
@@ -3110,10 +3118,11 @@ func (c *typeConv) Struct(dt *dwarf.StructType, pos token.Pos) (expr *ast.Struct
 		}
 
 		// Round off up to talign, assumed to be a power of 2.
+		origOff := off
 		off = (off + talign - 1) &^ (talign - 1)
 
 		if f.ByteOffset > off {
-			fld, sizes = c.pad(fld, sizes, f.ByteOffset-off)
+			fld, sizes = c.pad(fld, sizes, f.ByteOffset-origOff)
 			off = f.ByteOffset
 		}
 		if f.ByteOffset < off {

src/cmd/cgo/internal/test/cgo_test.go

@@ -70,6 +70,7 @@ func Test31891(t *testing.T)                 { test31891(t) }
 func Test42018(t *testing.T)                 { test42018(t) }
 func Test45451(t *testing.T)                 { test45451(t) }
 func Test49633(t *testing.T)                 { test49633(t) }
+func Test69086(t *testing.T)                 { test69086(t) }
 func TestAlign(t *testing.T)                 { testAlign(t) }
 func TestAtol(t *testing.T)                  { testAtol(t) }
 func TestBlocking(t *testing.T)              { testBlocking(t) }

src/cmd/cgo/internal/test/test.go

@@ -940,6 +940,19 @@ typedef struct {
 } issue67517struct;
 static void issue67517(issue67517struct* p) {}
 
+// Issue 69086.
+// GCC added the __int128 type in GCC 4.6, released in 2011.
+typedef struct {
+	int a;
+#ifdef __SIZEOF_INT128__
+	unsigned __int128 b;
+#else
+	uint64_t b;
+#endif
+	unsigned char c;
+} issue69086struct;
+static int issue690861(issue69086struct* p) { p->b = 1234; return p->c; }
+static int issue690862(unsigned long ul1, unsigned long ul2, unsigned int u, issue69086struct s) { return (int)(s.b); }
 */
 import "C"
 
@@ -2349,3 +2362,24 @@ func issue67517() {
 		b: nil,
 	})
 }
+
+// Issue 69086.
+func test69086(t *testing.T) {
+	var s C.issue69086struct
+
+	typ := reflect.TypeOf(s)
+	for i := 0; i < typ.NumField(); i++ {
+		f := typ.Field(i)
+		t.Logf("field %d: name %s size %d align %d offset %d", i, f.Name, f.Type.Size(), f.Type.Align(), f.Offset)
+	}
+
+	s.c = 1
+	got := C.issue690861(&s)
+	if got != 1 {
+		t.Errorf("field: got %d, want 1", got)
+	}
+	got = C.issue690862(1, 2, 3, s)
+	if got != 1234 {
+		t.Errorf("call: got %d, want 1234", got)
+	}
+}

src/cmd/cgo/internal/testcarchive/carchive_test.go

@@ -33,7 +33,7 @@ import (
 	"unicode"
 )
 
-var globalSkip = func(t *testing.T) {}
+var globalSkip = func(t testing.TB) {}
 
 // Program to run.
 var bin []string
@@ -59,12 +59,12 @@ func TestMain(m *testing.M) {
 
 func testMain(m *testing.M) int {
 	if testing.Short() && os.Getenv("GO_BUILDER_NAME") == "" {
-		globalSkip = func(t *testing.T) { t.Skip("short mode and $GO_BUILDER_NAME not set") }
+		globalSkip = func(t testing.TB) { t.Skip("short mode and $GO_BUILDER_NAME not set") }
 		return m.Run()
 	}
 	if runtime.GOOS == "linux" {
 		if _, err := os.Stat("/etc/alpine-release"); err == nil {
-			globalSkip = func(t *testing.T) { t.Skip("skipping failing test on alpine - go.dev/issue/19938") }
+			globalSkip = func(t testing.TB) { t.Skip("skipping failing test on alpine - go.dev/issue/19938") }
 			return m.Run()
 		}
 	}
@@ -1291,8 +1291,8 @@ func TestPreemption(t *testing.T) {
 	}
 }
 
-// Issue 59294. Test calling Go function from C after using some
+// Issue 59294 and 68285. Test calling Go function from C after with
-// stack space.
+// various stack space.
 func TestDeepStack(t *testing.T) {
 	globalSkip(t)
 	testenv.MustHaveGoBuild(t)
@@ -1350,6 +1350,53 @@ func TestDeepStack(t *testing.T) {
 	}
 }
 
+func BenchmarkCgoCallbackMainThread(b *testing.B) {
+	// Benchmark for calling into Go fron C main thread.
+	// See issue #68587.
+	//
+	// It uses a subprocess, which is a C binary that calls
+	// Go on the main thread b.N times. There is some overhead
+	// for launching the subprocess. It is probably fine when
+	// b.N is large.
+
+	globalSkip(b)
+	testenv.MustHaveGoBuild(b)
+	testenv.MustHaveCGO(b)
+	testenv.MustHaveBuildMode(b, "c-archive")
+
+	if !testWork {
+		defer func() {
+			os.Remove("testp10" + exeSuffix)
+			os.Remove("libgo10.a")
+			os.Remove("libgo10.h")
+		}()
+	}
+
+	cmd := exec.Command("go", "build", "-buildmode=c-archive", "-o", "libgo10.a", "./libgo10")
+	out, err := cmd.CombinedOutput()
+	b.Logf("%v\n%s", cmd.Args, out)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	ccArgs := append(cc, "-o", "testp10"+exeSuffix, "main10.c", "libgo10.a")
+	out, err = exec.Command(ccArgs[0], ccArgs[1:]...).CombinedOutput()
+	b.Logf("%v\n%s", ccArgs, out)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	argv := cmdToRun("./testp10")
+	argv = append(argv, fmt.Sprint(b.N))
+	cmd = exec.Command(argv[0], argv[1:]...)
+
+	b.ResetTimer()
+	err = cmd.Run()
+	if err != nil {
+		b.Fatal(err)
+	}
+}
+
 func TestSharedObject(t *testing.T) {
 	// Test that we can put a Go c-archive into a C shared object.
 	globalSkip(t)

src/cmd/cgo/internal/testcarchive/testdata/libgo10/a.go

@@ -0,0 +1,12 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "C"
+
+//export GoF
+func GoF() {}
+
+func main() {}

src/cmd/cgo/internal/testcarchive/testdata/libgo9/a.go

@@ -6,9 +6,29 @@ package main
 
 import "runtime"
 
+// extern void callGoWithVariousStack(int);
 import "C"
 
 func main() {}
 
 //export GoF
-func GoF() { runtime.GC() }
+func GoF(p int32) {
+	runtime.GC()
+	if p != 0 {
+		panic("panic")
+	}
+}
+
+//export callGoWithVariousStackAndGoFrame
+func callGoWithVariousStackAndGoFrame(p int32) {
+	if p != 0 {
+		defer func() {
+			e := recover()
+			if e == nil {
+				panic("did not panic")
+			}
+			runtime.GC()
+		}()
+	}
+	C.callGoWithVariousStack(C.int(p));
+}

src/cmd/cgo/internal/testcarchive/testdata/main10.c

@@ -0,0 +1,22 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "libgo10.h"
+
+int main(int argc, char **argv) {
+	int n, i;
+
+	if (argc != 2) {
+		perror("wrong arg");
+		return 2;
+	}
+	n = atoi(argv[1]);
+	for (i = 0; i < n; i++)
+		GoF();
+
+	return 0;
+}

src/cmd/cgo/internal/testcarchive/testdata/main9.c

@@ -6,19 +6,27 @@
 
 void use(int *x) { (*x)++; }
 
-void callGoFWithDeepStack() {
+void callGoFWithDeepStack(int p) {
 	int x[10000];
 
 	use(&x[0]);
 	use(&x[9999]);
 
-	GoF();
+	GoF(p);
 
 	use(&x[0]);
 	use(&x[9999]);
 }
 
-int main() {
+void callGoWithVariousStack(int p) {
-	GoF();                  // call GoF without using much stack
+	GoF(0);                  // call GoF without using much stack
-	callGoFWithDeepStack(); // call GoF with a deep stack
+	callGoFWithDeepStack(p); // call GoF with a deep stack
+	GoF(0);                  // again on a shallow stack
+}
+
+int main() {
+	callGoWithVariousStack(0);
+
+	callGoWithVariousStackAndGoFrame(0); // normal execution
+	callGoWithVariousStackAndGoFrame(1); // panic and recover
 }

src/cmd/compile/internal/escape/solve.go

@@ -318,9 +318,10 @@ func containsClosure(f, c *ir.Func) bool {
 		return false
 	}
 
-	// Closures within function Foo are named like "Foo.funcN..."
+	for p := c.ClosureParent; p != nil; p = p.ClosureParent {
-	// TODO(mdempsky): Better way to recognize this.
+		if p == f {
-	fn := f.Sym().Name
+			return true
-	cn := c.Sym().Name
+		}
-	return len(cn) > len(fn) && cn[:len(fn)] == fn && cn[len(fn)] == '.'
+	}
+	return false
 }

src/cmd/compile/internal/importer/gcimporter_test.go

@@ -582,6 +582,23 @@ func TestIssue25596(t *testing.T) {
 	compileAndImportPkg(t, "issue25596")
 }
 
+func TestIssue70394(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// This package only handles gc export data.
+	if runtime.Compiler != "gc" {
+		t.Skipf("gc-built packages not available (compiler = %s)", runtime.Compiler)
+	}
+
+	pkg := compileAndImportPkg(t, "alias")
+	obj := lookupObj(t, pkg.Scope(), "A")
+
+	typ := obj.Type()
+	if _, ok := typ.(*types2.Alias); !ok {
+		t.Fatalf("type of %s is %s, wanted an alias", obj, typ)
+	}
+}
+
 func importPkg(t *testing.T, path, srcDir string) *types2.Package {
 	pkg, err := Import(make(map[string]*types2.Package), path, srcDir, nil)
 	if err != nil {

src/cmd/compile/internal/importer/testdata/alias.go

@@ -0,0 +1,7 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package testdata
+
+type A = int32

src/cmd/compile/internal/importer/ureader.go

@@ -9,6 +9,7 @@ import (
 	"cmd/compile/internal/syntax"
 	"cmd/compile/internal/types2"
 	"cmd/internal/src"
+	"internal/buildcfg"
 	"internal/pkgbits"
 )
 
@@ -30,9 +31,7 @@ func ReadPackage(ctxt *types2.Context, imports map[string]*types2.Package, input
 
 		ctxt:        ctxt,
 		imports:     imports,
-		// Currently, the compiler panics when using Alias types.
+		enableAlias: true,
-		// TODO(gri) set to true once this is fixed (issue #66873)
-		enableAlias: false,
 
 		posBases: make([]*syntax.PosBase, input.NumElems(pkgbits.RelocPosBase)),
 		pkgs:     make([]*types2.Package, input.NumElems(pkgbits.RelocPkg)),
@@ -411,6 +410,14 @@ func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types2.Package, string) {
 			panic("weird")
 
 		case pkgbits.ObjAlias:
+			if buildcfg.Experiment.AliasTypeParams && len(r.dict.bounds) > 0 {
+				// Temporary work-around for issue #68526: rather than panicking
+				// with an non-descriptive index-out-of-bounds panic when trying
+				// to access a missing type parameter, instead panic with a more
+				// descriptive error. Only needed for Go 1.23; Go 1.24 will have
+				// the correct implementation.
+				panic("importing generic type aliases is not supported in Go 1.23 (see issue #68526)")
+			}
 			pos := r.pos()
 			typ := r.typ()
 			return newAliasTypeName(pr.enableAlias, pos, objPkg, objName, typ)

src/cmd/compile/internal/ir/func.go

@@ -51,6 +51,8 @@ import (
 // the generated ODCLFUNC, but there is no
 // pointer from the Func back to the OMETHVALUE.
 type Func struct {
+	// if you add or remove a field, don't forget to update sizeof_test.go
+
 	miniNode
 	Body Nodes
 
@@ -76,6 +78,9 @@ type Func struct {
 	// Populated during walk.
 	Closures []*Func
 
+	// Parent of a closure
+	ClosureParent *Func
+
 	// Parents records the parent scope of each scope within a
 	// function. The root scope (0) has no parent, so the i'th
 	// scope's parent is stored at Parents[i-1].
@@ -512,6 +517,7 @@ func NewClosureFunc(fpos, cpos src.XPos, why Op, typ *types.Type, outerfn *Func,
 
 	fn.Nname.Defn = fn
 	pkg.Funcs = append(pkg.Funcs, fn)
+	fn.ClosureParent = outerfn
 
 	return fn
 }

src/cmd/compile/internal/ir/sizeof_test.go

@@ -20,7 +20,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{Func{}, 176, 296},
+		{Func{}, 180, 304},
 		{Name{}, 96, 168},
 	}
 

src/cmd/compile/internal/rangefunc/rangefunc_test.go

@@ -2099,3 +2099,27 @@ func TestTwoLevelReturnCheck(t *testing.T) {
 		t.Errorf("Expected y=3, got y=%d\n", y)
 	}
 }
+
+func Bug70035(s1, s2, s3 []string) string {
+	var c1 string
+	for v1 := range slices.Values(s1) {
+		var c2 string
+		for v2 := range slices.Values(s2) {
+			var c3 string
+			for v3 := range slices.Values(s3) {
+				c3 = c3 + v3
+			}
+			c2 = c2 + v2 + c3
+		}
+		c1 = c1 + v1 + c2
+	}
+	return c1
+}
+
+func Test70035(t *testing.T) {
+	got := Bug70035([]string{"1", "2", "3"}, []string{"a", "b", "c"}, []string{"A", "B", "C"})
+	want := "1aABCbABCcABC2aABCbABCcABC3aABCbABCcABC"
+	if got != want {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}

src/cmd/compile/internal/types2/alias.go

@@ -134,10 +134,10 @@ func (check *Checker) newAlias(obj *TypeName, rhs Type) *Alias {
 // newAliasInstance creates a new alias instance for the given origin and type
 // arguments, recording pos as the position of its synthetic object (for error
 // reporting).
-func (check *Checker) newAliasInstance(pos syntax.Pos, orig *Alias, targs []Type, ctxt *Context) *Alias {
+func (check *Checker) newAliasInstance(pos syntax.Pos, orig *Alias, targs []Type, expanding *Named, ctxt *Context) *Alias {
 	assert(len(targs) > 0)
 	obj := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil)
-	rhs := check.subst(pos, orig.fromRHS, makeSubstMap(orig.TypeParams().list(), targs), nil, ctxt)
+	rhs := check.subst(pos, orig.fromRHS, makeSubstMap(orig.TypeParams().list(), targs), expanding, ctxt)
 	res := check.newAlias(obj, rhs)
 	res.orig = orig
 	res.tparams = orig.tparams

src/cmd/compile/internal/types2/api_test.go

@@ -2900,20 +2900,46 @@ func TestFileVersions(t *testing.T) {
 	}{
 		{"", "", ""},                    // no versions specified
 		{"go1.19", "", "go1.19"},        // module version specified
-		{"", "go1.20", ""},             // file upgrade ignored
+		{"", "go1.20", "go1.21"},        // file version specified below minimum of 1.21
-		{"go1.19", "go1.20", "go1.20"}, // file upgrade permitted
+		{"go1", "", "go1"},              // no file version specified
-		{"go1.20", "go1.19", "go1.20"}, // file downgrade not permitted
+		{"go1", "goo1.22", "go1"},       // invalid file version specified
-		{"go1.21", "go1.19", "go1.19"}, // file downgrade permitted (module version is >= go1.21)
+		{"go1", "go1.19", "go1.21"},     // file version specified below minimum of 1.21
+		{"go1", "go1.20", "go1.21"},     // file version specified below minimum of 1.21
+		{"go1", "go1.21", "go1.21"},     // file version specified at 1.21
+		{"go1", "go1.22", "go1.22"},     // file version specified above 1.21
+		{"go1.19", "", "go1.19"},        // no file version specified
+		{"go1.19", "goo1.22", "go1.19"}, // invalid file version specified
+		{"go1.19", "go1.20", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.19", "go1.21", "go1.21"},  // file version specified at 1.21
+		{"go1.19", "go1.22", "go1.22"},  // file version specified above 1.21
+		{"go1.20", "", "go1.20"},        // no file version specified
+		{"go1.20", "goo1.22", "go1.20"}, // invalid file version specified
+		{"go1.20", "go1.19", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.20", "go1.20", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.20", "go1.21", "go1.21"},  // file version specified at 1.21
+		{"go1.20", "go1.22", "go1.22"},  // file version specified above 1.21
+		{"go1.21", "", "go1.21"},        // no file version specified
+		{"go1.21", "goo1.22", "go1.21"}, // invalid file version specified
+		{"go1.21", "go1.19", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.21", "go1.20", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.21", "go1.21", "go1.21"},  // file version specified at 1.21
+		{"go1.21", "go1.22", "go1.22"},  // file version specified above 1.21
+		{"go1.22", "", "go1.22"},        // no file version specified
+		{"go1.22", "goo1.22", "go1.22"}, // invalid file version specified
+		{"go1.22", "go1.19", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.22", "go1.20", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.22", "go1.21", "go1.21"},  // file version specified at 1.21
+		{"go1.22", "go1.22", "go1.22"},  // file version specified above 1.21
 
 		// versions containing release numbers
 		// (file versions containing release numbers are considered invalid)
 		{"go1.19.0", "", "go1.19.0"},         // no file version specified
-		{"go1.20", "go1.20.1", "go1.20"},     // file upgrade ignored
+		{"go1.20.1", "go1.19.1", "go1.20.1"}, // invalid file version
-		{"go1.20.1", "go1.20", "go1.20.1"},   // file upgrade ignored
+		{"go1.20.1", "go1.21.1", "go1.20.1"}, // invalid file version
-		{"go1.20.1", "go1.21", "go1.21"},     // file upgrade permitted
+		{"go1.21.1", "go1.19.1", "go1.21.1"}, // invalid file version
-		{"go1.20.1", "go1.19", "go1.20.1"},   // file downgrade not permitted
+		{"go1.21.1", "go1.21.1", "go1.21.1"}, // invalid file version
-		{"go1.21.1", "go1.19.1", "go1.21.1"}, // file downgrade not permitted (invalid file version)
+		{"go1.22.1", "go1.19.1", "go1.22.1"}, // invalid file version
-		{"go1.21.1", "go1.19", "go1.19"},     // file downgrade permitted (module version is >= go1.21)
+		{"go1.22.1", "go1.21.1", "go1.22.1"}, // invalid file version
 	} {
 		var src string
 		if test.fileVersion != "" {

src/cmd/compile/internal/types2/check.go

@@ -327,7 +327,6 @@ func (check *Checker) initFiles(files []*syntax.File) {
 		check.errorf(files[0], TooNew, "package requires newer Go version %v (application built with %v)",
 			check.version, go_current)
 	}
-	downgradeOk := check.version.cmp(go1_21) >= 0
 
 	// determine Go version for each file
 	for _, file := range check.files {
@@ -336,33 +335,18 @@ func (check *Checker) initFiles(files []*syntax.File) {
 		// unlike file versions which are Go language versions only, if valid.)
 		v := check.conf.GoVersion
 
-		fileVersion := asGoVersion(file.GoVersion)
+		// If the file specifies a version, use max(fileVersion, go1.21).
-		if fileVersion.isValid() {
+		if fileVersion := asGoVersion(file.GoVersion); fileVersion.isValid() {
-			// use the file version, if applicable
+			// Go 1.21 introduced the feature of allowing //go:build lines
-			// (file versions are either the empty string or of the form go1.dd)
+			// to sometimes set the Go version in a given file. Versions Go 1.21 and later
-			if pkgVersionOk {
+			// can be set backwards compatibly as that was the first version
-				cmp := fileVersion.cmp(check.version)
+			// files with go1.21 or later build tags could be built with.
-				// Go 1.21 introduced the feature of setting the go.mod
-				// go line to an early version of Go and allowing //go:build lines
-				// to “upgrade” (cmp > 0) the Go version in a given file.
-				// We can do that backwards compatibly.
 			//
-				// Go 1.21 also introduced the feature of allowing //go:build lines
+			// Set the version to max(fileVersion, go1.21): That will allow a
-				// to “downgrade” (cmp < 0) the Go version in a given file.
+			// downgrade to a version before go1.22, where the for loop semantics
-				// That can't be done compatibly in general, since before the
+			// change was made, while being backwards compatible with versions of
-				// build lines were ignored and code got the module's Go version.
+			// go before the new //go:build semantics were introduced.
-				// To work around this, downgrades are only allowed when the
+			v = string(versionMax(fileVersion, go1_21))
-				// module's Go version is Go 1.21 or later.
-				//
-				// If there is no valid check.version, then we don't really know what
-				// Go version to apply.
-				// Legacy tools may do this, and they historically have accepted everything.
-				// Preserve that behavior by ignoring //go:build constraints entirely in that
-				// case (!pkgVersionOk).
-				if cmp > 0 || cmp < 0 && downgradeOk {
-					v = file.GoVersion
-				}
-			}
 
 			// Report a specific error for each tagged file that's too new.
 			// (Normally the build system will have filtered files by version,
@@ -377,6 +361,13 @@ func (check *Checker) initFiles(files []*syntax.File) {
 	}
 }
 
+func versionMax(a, b goVersion) goVersion {
+	if a.cmp(b) > 0 {
+		return a
+	}
+	return b
+}
+
 // A bailout panic is used for early termination.
 type bailout struct{}
 

src/cmd/compile/internal/types2/instantiate.go

@@ -11,6 +11,7 @@ import (
 	"cmd/compile/internal/syntax"
 	"errors"
 	"fmt"
+	"internal/buildcfg"
 	. "internal/types/errors"
 )
 
@@ -126,8 +127,9 @@ func (check *Checker) instance(pos syntax.Pos, orig genericType, targs []Type, e
 		res = check.newNamedInstance(pos, orig, targs, expanding) // substituted lazily
 
 	case *Alias:
-		// TODO(gri) is this correct?
+		if !buildcfg.Experiment.AliasTypeParams {
 			assert(expanding == nil) // Alias instances cannot be reached from Named types
+		}
 
 		tparams := orig.TypeParams()
 		// TODO(gri) investigate if this is needed (type argument and parameter count seem to be correct here)
@@ -138,7 +140,7 @@ func (check *Checker) instance(pos syntax.Pos, orig genericType, targs []Type, e
 			return orig // nothing to do (minor optimization)
 		}
 
-		return check.newAliasInstance(pos, orig, targs, ctxt)
+		return check.newAliasInstance(pos, orig, targs, expanding, ctxt)
 
 	case *Signature:
 		assert(expanding == nil) // function instances cannot be reached from Named types

src/cmd/compile/internal/types2/issues_test.go

@@ -1121,3 +1121,23 @@ func f(x int) {
 		t.Errorf("got: %s want: %s", got, want)
 	}
 }
+
+func TestIssue68877(t *testing.T) {
+	const src = `
+package p
+
+type (
+	S struct{}
+	A = S
+	T A
+)`
+
+	conf := Config{EnableAlias: true}
+	pkg := mustTypecheck(src, &conf, nil)
+	T := pkg.Scope().Lookup("T").(*TypeName)
+	got := T.String() // this must not panic (was issue)
+	const want = "type p.T struct{}"
+	if got != want {
+		t.Errorf("got %s, want %s", got, want)
+	}
+}

src/cmd/compile/internal/types2/named.go

@@ -282,7 +282,7 @@ func (t *Named) cleanup() {
 		if t.TypeArgs().Len() == 0 {
 			panic("nil underlying")
 		}
-	case *Named:
+	case *Named, *Alias:
 		t.under() // t.under may add entries to check.cleaners
 	}
 	t.check = nil

src/cmd/compile/internal/types2/subst.go

@@ -115,7 +115,7 @@ func (subst *subster) typ(typ Type) Type {
 		// that has a type argument for it.
 		targs, updated := subst.typeList(t.TypeArgs().list())
 		if updated {
-			return subst.check.newAliasInstance(subst.pos, t.orig, targs, subst.ctxt)
+			return subst.check.newAliasInstance(subst.pos, t.orig, targs, subst.expanding, subst.ctxt)
 		}
 
 	case *Array:

src/cmd/compile/internal/types2/typeset.go

@@ -131,8 +131,8 @@ func (s *_TypeSet) underIs(f func(Type) bool) bool {
 	}
 	for _, t := range s.terms {
 		assert(t.typ != nil)
-		// x == under(x) for ~x terms
+		// Unalias(x) == under(x) for ~x terms
-		u := t.typ
+		u := Unalias(t.typ)
 		if !t.tilde {
 			u = under(u)
 		}

src/cmd/go.mod

@@ -9,7 +9,7 @@ require (
 	golang.org/x/mod v0.19.0
 	golang.org/x/sync v0.7.0
 	golang.org/x/sys v0.22.0
-	golang.org/x/telemetry v0.0.0-20240717194752-0b706e19b701
+	golang.org/x/telemetry v0.0.0-20240828213427-40b6b7fe7147
 	golang.org/x/term v0.20.0
 	golang.org/x/tools v0.22.1-0.20240618181713-f2d2ebe43e72
 )

src/cmd/go.sum

@@ -16,8 +16,8 @@ golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
 golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
 golang.org/x/sys v0.22.0 h1:RI27ohtqKCnwULzJLqkv897zojh5/DwS/ENaMzUOaWI=
 golang.org/x/sys v0.22.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
-golang.org/x/telemetry v0.0.0-20240717194752-0b706e19b701 h1:+bltxAtk8YFEQ61B/lcYQM8e+7XjLwSDbpspVaVYkz8=
+golang.org/x/telemetry v0.0.0-20240828213427-40b6b7fe7147 h1:Lj8KbuZmoFUbI6pQ28G3Diz/5bRYD2UY5vfAmhrLZWo=
-golang.org/x/telemetry v0.0.0-20240717194752-0b706e19b701/go.mod h1:amNmu/SBSm2GAF3X+9U2C0epLocdh+r5Z+7oMYO5cLM=
+golang.org/x/telemetry v0.0.0-20240828213427-40b6b7fe7147/go.mod h1:amNmu/SBSm2GAF3X+9U2C0epLocdh+r5Z+7oMYO5cLM=
 golang.org/x/term v0.20.0 h1:VnkxpohqXaOBYJtBmEppKUG6mXpi+4O6purfc2+sMhw=
 golang.org/x/term v0.20.0/go.mod h1:8UkIAJTvZgivsXaD6/pH6U9ecQzZ45awqEOzuCvwpFY=
 golang.org/x/text v0.16.0 h1:a94ExnEXNtEwYLGJSIUxnWoxoRz/ZcCsV63ROupILh4=

src/cmd/link/internal/ld/elf.go

@@ -805,13 +805,19 @@ func elfwritefreebsdsig(out *OutBuf) int {
 	return int(sh.Size)
 }
 
-func addbuildinfo(val string) {
+func addbuildinfo(ctxt *Link) {
+	val := *flagHostBuildid
 	if val == "gobuildid" {
 		buildID := *flagBuildid
 		if buildID == "" {
 			Exitf("-B gobuildid requires a Go build ID supplied via -buildid")
 		}
 
+		if ctxt.IsDarwin() {
+			buildinfo = uuidFromGoBuildId(buildID)
+			return
+		}
+
 		hashedBuildID := notsha256.Sum256([]byte(buildID))
 		buildinfo = hashedBuildID[:20]
 
@@ -821,11 +827,13 @@ func addbuildinfo(val string) {
 	if !strings.HasPrefix(val, "0x") {
 		Exitf("-B argument must start with 0x: %s", val)
 	}
-
 	ov := val
 	val = val[2:]
 
-	const maxLen = 32
+	maxLen := 32
+	if ctxt.IsDarwin() {
+		maxLen = 16
+	}
 	if hex.DecodedLen(len(val)) > maxLen {
 		Exitf("-B option too long (max %d digits): %s", maxLen, ov)
 	}

src/cmd/link/internal/ld/macho.go

@@ -297,6 +297,8 @@ func getMachoHdr() *MachoHdr {
 	return &machohdr
 }
 
+// Create a new Mach-O load command. ndata is the number of 32-bit words for
+// the data (not including the load command header).
 func newMachoLoad(arch *sys.Arch, type_ uint32, ndata uint32) *MachoLoad {
 	if arch.PtrSize == 8 && (ndata&1 != 0) {
 		ndata++
@@ -849,6 +851,20 @@ func asmbMacho(ctxt *Link) {
 			}
 		}
 
+		if ctxt.IsInternal() && len(buildinfo) > 0 {
+			ml := newMachoLoad(ctxt.Arch, LC_UUID, 4)
+			// Mach-O UUID is 16 bytes
+			if len(buildinfo) < 16 {
+				buildinfo = append(buildinfo, make([]byte, 16)...)
+			}
+			// By default, buildinfo is already in UUIDv3 format
+			// (see uuidFromGoBuildId).
+			ml.data[0] = ctxt.Arch.ByteOrder.Uint32(buildinfo)
+			ml.data[1] = ctxt.Arch.ByteOrder.Uint32(buildinfo[4:])
+			ml.data[2] = ctxt.Arch.ByteOrder.Uint32(buildinfo[8:])
+			ml.data[3] = ctxt.Arch.ByteOrder.Uint32(buildinfo[12:])
+		}
+
 		if ctxt.IsInternal() && ctxt.NeedCodeSign() {
 			ml := newMachoLoad(ctxt.Arch, LC_CODE_SIGNATURE, 2)
 			ml.data[0] = uint32(codesigOff)

src/cmd/link/internal/ld/macho_update_uuid.go

@@ -42,7 +42,7 @@ func uuidFromGoBuildId(buildID string) []byte {
 	// to use this UUID flavor than any of the others. This is similar
 	// to how other linkers handle this (for example this code in lld:
 	// https://github.com/llvm/llvm-project/blob/2a3a79ce4c2149d7787d56f9841b66cacc9061d0/lld/MachO/Writer.cpp#L524).
-	rv[6] &= 0xcf
+	rv[6] &= 0x0f
 	rv[6] |= 0x30
 	rv[8] &= 0x3f
 	rv[8] |= 0xc0

src/cmd/link/internal/ld/main.go

@@ -95,6 +95,7 @@ var (
 	flagN             = flag.Bool("n", false, "no-op (deprecated)")
 	FlagS             = flag.Bool("s", false, "disable symbol table")
 	flag8             bool // use 64-bit addresses in symbol table
+	flagHostBuildid   = flag.String("B", "", "set ELF NT_GNU_BUILD_ID `note` or Mach-O UUID; use \"gobuildid\" to generate it from the Go build ID")
 	flagInterpreter   = flag.String("I", "", "use `linker` as ELF dynamic linker")
 	flagCheckLinkname = flag.Bool("checklinkname", true, "check linkname symbol references")
 	FlagDebugTramp    = flag.Int("debugtramp", 0, "debug trampolines")
@@ -196,7 +197,6 @@ func Main(arch *sys.Arch, theArch Arch) {
 	flag.Var(&ctxt.LinkMode, "linkmode", "set link `mode`")
 	flag.Var(&ctxt.BuildMode, "buildmode", "set build `mode`")
 	flag.BoolVar(&ctxt.compressDWARF, "compressdwarf", true, "compress DWARF if possible")
-	objabi.Flagfn1("B", "add an ELF NT_GNU_BUILD_ID `note` when using ELF; use \"gobuildid\" to generate it from the Go build ID", addbuildinfo)
 	objabi.Flagfn1("L", "add specified `directory` to library path", func(a string) { Lflag(ctxt, a) })
 	objabi.AddVersionFlag() // -V
 	objabi.Flagfn1("X", "add string value `definition` of the form importpath.name=value", func(s string) { addstrdata1(ctxt, s) })
@@ -294,6 +294,10 @@ func Main(arch *sys.Arch, theArch Arch) {
 		*flagBuildid = "go-openbsd"
 	}
 
+	if *flagHostBuildid != "" {
+		addbuildinfo(ctxt)
+	}
+
 	// enable benchmarking
 	var bench *benchmark.Metrics
 	if len(*benchmarkFlag) != 0 {

src/cmd/trace/gstate.go

@@ -257,6 +257,10 @@ func (gs *gState[R]) stop(ts trace.Time, stack trace.Stack, ctx *traceContext) {
 	if gs.lastStopStack != trace.NoStack {
 		stk = ctx.Stack(viewerFrames(gs.lastStopStack))
 	}
+	var endStk int
+	if stack != trace.NoStack {
+		endStk = ctx.Stack(viewerFrames(stack))
+	}
 	// Check invariants.
 	if gs.startRunningTime == 0 {
 		panic("silently broken trace or generator invariant (startRunningTime != 0) not held")
@@ -270,6 +274,7 @@ func (gs *gState[R]) stop(ts trace.Time, stack trace.Stack, ctx *traceContext) {
 		Dur:      ts.Sub(gs.startRunningTime),
 		Resource: uint64(gs.executing),
 		Stack:    stk,
+		EndStack: endStk,
 	})
 
 	// Flush completed ranges.

src/cmd/vendor/golang.org/x/telemetry/internal/configstore/download.go

@@ -16,6 +16,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"sync/atomic"
 
 	"golang.org/x/telemetry/internal/telemetry"
 )
@@ -29,12 +30,22 @@ const (
 // creation flag.
 var needNoConsole = func(cmd *exec.Cmd) {}
 
+var downloads int64
+
+// Downloads reports, for testing purposes, the number of times [Download] has
+// been called.
+func Downloads() int64 {
+	return atomic.LoadInt64(&downloads)
+}
+
 // Download fetches the requested telemetry UploadConfig using "go mod
 // download". If envOverlay is provided, it is appended to the environment used
 // for invoking the go command.
 //
 // The second result is the canonical version of the requested configuration.
 func Download(version string, envOverlay []string) (*telemetry.UploadConfig, string, error) {
+	atomic.AddInt64(&downloads, 1)
+
 	if version == "" {
 		version = "latest"
 	}

src/cmd/vendor/golang.org/x/telemetry/internal/crashmonitor/monitor.go

@@ -21,12 +21,12 @@ import (
 	"golang.org/x/telemetry/internal/counter"
 )
 
-// Supported reports whether the runtime supports [runtime.SetCrashOutput].
+// Supported reports whether the runtime supports [runtime/debug.SetCrashOutput].
 //
 // TODO(adonovan): eliminate once go1.23+ is assured.
 func Supported() bool { return setCrashOutput != nil }
 
-var setCrashOutput func(*os.File) error // = runtime.SetCrashOutput on go1.23+
+var setCrashOutput func(*os.File) error // = runtime/debug.SetCrashOutput on go1.23+
 
 // Parent sets up the parent side of the crashmonitor. It requires
 // exclusive use of a writable pipe connected to the child process's stdin.

src/cmd/vendor/golang.org/x/telemetry/internal/upload/run.go

@@ -112,10 +112,25 @@ func newUploader(rcfg RunConfig) (*uploader, error) {
 	logger := log.New(logWriter, "", log.Ltime|log.Lmicroseconds|log.Lshortfile)
 
 	// Fetch the upload config, if it is not provided.
-	config, configVersion, err := configstore.Download("latest", rcfg.Env)
+	var (
+		config        *telemetry.UploadConfig
+		configVersion string
+	)
+
+	if mode, _ := dir.Mode(); mode == "on" {
+		// golang/go#68946: only download the upload config if it will be used.
+		//
+		// TODO(rfindley): This is a narrow change aimed at minimally fixing the
+		// associated bug. In the future, we should read the mode only once during
+		// the upload process.
+		config, configVersion, err = configstore.Download("latest", rcfg.Env)
 		if err != nil {
 			return nil, err
 		}
+	} else {
+		config = &telemetry.UploadConfig{}
+		configVersion = "v0.0.0-0"
+	}
 
 	// Set the start time, if it is not provided.
 	startTime := time.Now().UTC()

src/cmd/vendor/golang.org/x/telemetry/start.go

@@ -206,7 +206,8 @@ func startChild(reportCrashes, upload bool, result *StartResult) {
 	fd, err := os.Stat(telemetry.Default.DebugDir())
 	if err != nil {
 		if !os.IsNotExist(err) {
-			log.Fatalf("failed to stat debug directory: %v", err)
+			log.Printf("failed to stat debug directory: %v", err)
+			return
 		}
 	} else if fd.IsDir() {
 		// local/debug exists and is a directory. Set stderr to a log file path
@@ -214,23 +215,31 @@ func startChild(reportCrashes, upload bool, result *StartResult) {
 		childLogPath := filepath.Join(telemetry.Default.DebugDir(), "sidecar.log")
 		childLog, err := os.OpenFile(childLogPath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0600)
 		if err != nil {
-			log.Fatalf("opening sidecar log file for child: %v", err)
+			log.Printf("opening sidecar log file for child: %v", err)
+			return
 		}
 		defer childLog.Close()
 		cmd.Stderr = childLog
 	}
 
+	var crashOutputFile *os.File
 	if reportCrashes {
 		pipe, err := cmd.StdinPipe()
 		if err != nil {
-			log.Fatalf("StdinPipe: %v", err)
+			log.Printf("StdinPipe: %v", err)
+			return
 		}
 
-		crashmonitor.Parent(pipe.(*os.File)) // (this conversion is safe)
+		crashOutputFile = pipe.(*os.File) // (this conversion is safe)
 	}
 
 	if err := cmd.Start(); err != nil {
-		log.Fatalf("can't start telemetry child process: %v", err)
+		// The child couldn't be started. Log the failure.
+		log.Printf("can't start telemetry child process: %v", err)
+		return
+	}
+	if reportCrashes {
+		crashmonitor.Parent(crashOutputFile)
 	}
 	result.wg.Add(1)
 	go func() {

src/cmd/vendor/modules.txt

@@ -45,7 +45,7 @@ golang.org/x/sync/semaphore
 golang.org/x/sys/plan9
 golang.org/x/sys/unix
 golang.org/x/sys/windows
-# golang.org/x/telemetry v0.0.0-20240717194752-0b706e19b701
+# golang.org/x/telemetry v0.0.0-20240828213427-40b6b7fe7147
 ## explicit; go 1.20
 golang.org/x/telemetry
 golang.org/x/telemetry/counter

src/crypto/tls/handshake_client_test.go

@@ -852,6 +852,7 @@ func testResumption(t *testing.T, version uint16) {
 		MaxVersion:   version,
 		CipherSuites: []uint16{TLS_RSA_WITH_RC4_128_SHA, TLS_ECDHE_RSA_WITH_RC4_128_SHA},
 		Certificates: testConfig.Certificates,
+		Time:         testTime,
 	}
 
 	issuer, err := x509.ParseCertificate(testRSACertificateIssuer)
@@ -868,6 +869,7 @@ func testResumption(t *testing.T, version uint16) {
 		ClientSessionCache: NewLRUClientSessionCache(32),
 		RootCAs:            rootCAs,
 		ServerName:         "example.golang",
+		Time:               testTime,
 	}
 
 	testResumeState := func(test string, didResume bool) {
@@ -914,7 +916,7 @@ func testResumption(t *testing.T, version uint16) {
 
 	// An old session ticket is replaced with a ticket encrypted with a fresh key.
 	ticket = getTicket()
-	serverConfig.Time = func() time.Time { return time.Now().Add(24*time.Hour + time.Minute) }
+	serverConfig.Time = func() time.Time { return testTime().Add(24*time.Hour + time.Minute) }
 	testResumeState("ResumeWithOldTicket", true)
 	if bytes.Equal(ticket, getTicket()) {
 		t.Fatal("old first ticket matches the fresh one")
@@ -922,13 +924,13 @@ func testResumption(t *testing.T, version uint16) {
 
 	// Once the session master secret is expired, a full handshake should occur.
 	ticket = getTicket()
-	serverConfig.Time = func() time.Time { return time.Now().Add(24*8*time.Hour + time.Minute) }
+	serverConfig.Time = func() time.Time { return testTime().Add(24*8*time.Hour + time.Minute) }
 	testResumeState("ResumeWithExpiredTicket", false)
 	if bytes.Equal(ticket, getTicket()) {
 		t.Fatal("expired first ticket matches the fresh one")
 	}
 
-	serverConfig.Time = func() time.Time { return time.Now() } // reset the time back
+	serverConfig.Time = testTime // reset the time back
 	key1 := randomKey()
 	serverConfig.SetSessionTicketKeys([][32]byte{key1})
 
@@ -945,11 +947,11 @@ func testResumption(t *testing.T, version uint16) {
 	testResumeState("KeyChangeFinish", true)
 
 	// Age the session ticket a bit, but not yet expired.
-	serverConfig.Time = func() time.Time { return time.Now().Add(24*time.Hour + time.Minute) }
+	serverConfig.Time = func() time.Time { return testTime().Add(24*time.Hour + time.Minute) }
 	testResumeState("OldSessionTicket", true)
 	ticket = getTicket()
 	// Expire the session ticket, which would force a full handshake.
-	serverConfig.Time = func() time.Time { return time.Now().Add(24*8*time.Hour + time.Minute) }
+	serverConfig.Time = func() time.Time { return testTime().Add(24*8*time.Hour + 2*time.Minute) }
 	testResumeState("ExpiredSessionTicket", false)
 	if bytes.Equal(ticket, getTicket()) {
 		t.Fatal("new ticket wasn't provided after old ticket expired")
@@ -957,7 +959,7 @@ func testResumption(t *testing.T, version uint16) {
 
 	// Age the session ticket a bit at a time, but don't expire it.
 	d := 0 * time.Hour
-	serverConfig.Time = func() time.Time { return time.Now().Add(d) }
+	serverConfig.Time = func() time.Time { return testTime().Add(d) }
 	deleteTicket()
 	testResumeState("GetFreshSessionTicket", false)
 	for i := 0; i < 13; i++ {
@@ -968,7 +970,7 @@ func testResumption(t *testing.T, version uint16) {
 	// handshake occurs for TLS 1.2. Resumption should still occur for
 	// TLS 1.3 since the client should be using a fresh ticket sent over
 	// by the server.
-	d += 12 * time.Hour
+	d += 12*time.Hour + time.Minute
 	if version == VersionTLS13 {
 		testResumeState("ExpiredSessionTicket", true)
 	} else {
@@ -984,6 +986,7 @@ func testResumption(t *testing.T, version uint16) {
 		MaxVersion:   version,
 		CipherSuites: []uint16{TLS_RSA_WITH_RC4_128_SHA, TLS_ECDHE_RSA_WITH_RC4_128_SHA},
 		Certificates: testConfig.Certificates,
+		Time:         testTime,
 	}
 	serverConfig.SetSessionTicketKeys([][32]byte{key2})
 
@@ -1009,6 +1012,7 @@ func testResumption(t *testing.T, version uint16) {
 			CurvePreferences: []CurveID{CurveP521, CurveP384, CurveP256},
 			MaxVersion:       version,
 			Certificates:     testConfig.Certificates,
+			Time:             testTime,
 		}
 		testResumeState("InitialHandshake", false)
 		testResumeState("WithHelloRetryRequest", true)
@@ -1018,6 +1022,7 @@ func testResumption(t *testing.T, version uint16) {
 			MaxVersion:   version,
 			CipherSuites: []uint16{TLS_RSA_WITH_RC4_128_SHA, TLS_ECDHE_RSA_WITH_RC4_128_SHA},
 			Certificates: testConfig.Certificates,
+			Time:         testTime,
 		}
 	}
 
@@ -1736,6 +1741,7 @@ func testVerifyConnection(t *testing.T, version uint16) {
 		serverConfig := &Config{
 			MaxVersion:   version,
 			Certificates: []Certificate{testConfig.Certificates[0]},
+			Time:         testTime,
 			ClientCAs:    rootCAs,
 			NextProtos:   []string{"protocol1"},
 		}
@@ -1749,6 +1755,7 @@ func testVerifyConnection(t *testing.T, version uint16) {
 			RootCAs:            rootCAs,
 			ServerName:         "example.golang",
 			Certificates:       []Certificate{testConfig.Certificates[0]},
+			Time:               testTime,
 			NextProtos:         []string{"protocol1"},
 		}
 		test.configureClient(clientConfig, &clientCalled)
@@ -1791,8 +1798,6 @@ func testVerifyPeerCertificate(t *testing.T, version uint16) {
 	rootCAs := x509.NewCertPool()
 	rootCAs.AddCert(issuer)
 
-	now := func() time.Time { return time.Unix(1476984729, 0) }
-
 	sentinelErr := errors.New("TestVerifyPeerCertificate")
 
 	verifyPeerCertificateCallback := func(called *bool, rawCerts [][]byte, validatedChains [][]*x509.Certificate) error {
@@ -2038,7 +2043,7 @@ func testVerifyPeerCertificate(t *testing.T, version uint16) {
 			config.ServerName = "example.golang"
 			config.ClientAuth = RequireAndVerifyClientCert
 			config.ClientCAs = rootCAs
-			config.Time = now
+			config.Time = testTime
 			config.MaxVersion = version
 			config.Certificates = make([]Certificate, 1)
 			config.Certificates[0].Certificate = [][]byte{testRSACertificate}
@@ -2055,7 +2060,7 @@ func testVerifyPeerCertificate(t *testing.T, version uint16) {
 		config := testConfig.Clone()
 		config.ServerName = "example.golang"
 		config.RootCAs = rootCAs
-		config.Time = now
+		config.Time = testTime
 		config.MaxVersion = version
 		test.configureClient(config, &clientCalled)
 		clientErr := Client(c, config).Handshake()
@@ -2368,7 +2373,7 @@ func testGetClientCertificate(t *testing.T, version uint16) {
 		serverConfig.RootCAs = x509.NewCertPool()
 		serverConfig.RootCAs.AddCert(issuer)
 		serverConfig.ClientCAs = serverConfig.RootCAs
-		serverConfig.Time = func() time.Time { return time.Unix(1476984729, 0) }
+		serverConfig.Time = testTime
 		serverConfig.MaxVersion = version
 
 		clientConfig := testConfig.Clone()
@@ -2539,6 +2544,7 @@ func testResumptionKeepsOCSPAndSCT(t *testing.T, ver uint16) {
 		ClientSessionCache: NewLRUClientSessionCache(32),
 		ServerName:         "example.golang",
 		RootCAs:            roots,
+		Time:               testTime,
 	}
 	serverConfig := testConfig.Clone()
 	serverConfig.MaxVersion = ver

src/crypto/tls/handshake_server_test.go

@@ -501,6 +501,7 @@ func testCrossVersionResume(t *testing.T, version uint16) {
 	serverConfig := &Config{
 		CipherSuites: []uint16{TLS_RSA_WITH_AES_128_CBC_SHA},
 		Certificates: testConfig.Certificates,
+		Time:         testTime,
 	}
 	clientConfig := &Config{
 		CipherSuites:       []uint16{TLS_RSA_WITH_AES_128_CBC_SHA},
@@ -508,6 +509,7 @@ func testCrossVersionResume(t *testing.T, version uint16) {
 		ClientSessionCache: NewLRUClientSessionCache(1),
 		ServerName:         "servername",
 		MinVersion:         VersionTLS12,
+		Time:               testTime,
 	}
 
 	// Establish a session at TLS 1.3.

src/crypto/tls/handshake_test.go

@@ -491,9 +491,10 @@ func testHandshake(t *testing.T, clientConfig, serverConfig *Config) (serverStat
 		if got := string(buf); got != sentinel {
 			t.Errorf("read %q from TLS connection, but expected %q", got, sentinel)
 		}
-		if err := cli.Close(); err != nil {
+		// We discard the error because after ReadAll returns the server must
-			t.Errorf("failed to call cli.Close: %v", err)
+		// have already closed the connection. Sending data (the closeNotify
-		}
+		// alert) can cause a reset, that will make Close return an error.
+		cli.Close()
 	}()
 	server := Server(s, serverConfig)
 	err = server.Handshake()
@@ -518,6 +519,11 @@ func fromHex(s string) []byte {
 	return b
 }
 
+// testTime is 2016-10-20T17:32:09.000Z, which is within the validity period of
+// [testRSACertificate], [testRSACertificateIssuer], [testRSA2048Certificate],
+// [testRSA2048CertificateIssuer], and [testECDSACertificate].
+var testTime = func() time.Time { return time.Unix(1476984729, 0) }
+
 var testRSACertificate = fromHex("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")
 
 var testRSACertificateIssuer = fromHex("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")

src/crypto/tls/tls_test.go

@@ -1112,8 +1112,6 @@ func TestConnectionState(t *testing.T) {
 	rootCAs := x509.NewCertPool()
 	rootCAs.AddCert(issuer)
 
-	now := func() time.Time { return time.Unix(1476984729, 0) }
-
 	const alpnProtocol = "golang"
 	const serverName = "example.golang"
 	var scts = [][]byte{[]byte("dummy sct 1"), []byte("dummy sct 2")}
@@ -1129,7 +1127,7 @@ func TestConnectionState(t *testing.T) {
 		}
 		t.Run(name, func(t *testing.T) {
 			config := &Config{
-				Time:         now,
+				Time:         testTime,
 				Rand:         zeroSource{},
 				Certificates: make([]Certificate, 1),
 				MaxVersion:   v,
@@ -1760,7 +1758,7 @@ func testVerifyCertificates(t *testing.T, version uint16) {
 			var serverVerifyPeerCertificates, clientVerifyPeerCertificates bool
 
 			clientConfig := testConfig.Clone()
-			clientConfig.Time = func() time.Time { return time.Unix(1476984729, 0) }
+			clientConfig.Time = testTime
 			clientConfig.MaxVersion = version
 			clientConfig.MinVersion = version
 			clientConfig.RootCAs = rootCAs

src/crypto/x509/name_constraints_test.go

@@ -1607,6 +1607,23 @@ var nameConstraintsTests = []nameConstraintsTest{
 		leaf:          leafSpec{sans: []string{"dns:.example.com"}},
 		expectedError: "cannot parse dnsName \".example.com\"",
 	},
+	// #86: URIs with IPv6 addresses with zones and ports are rejected
+	{
+		roots: []constraintsSpec{
+			{
+				ok: []string{"uri:example.com"},
+			},
+		},
+		intermediates: [][]constraintsSpec{
+			{
+				{},
+			},
+		},
+		leaf: leafSpec{
+			sans: []string{"uri:http://[2006:abcd::1%25.example.com]:16/"},
+		},
+		expectedError: "URI with IP",
+	},
 }
 
 func makeConstraintsCACert(constraints constraintsSpec, name string, key *ecdsa.PrivateKey, parent *Certificate, parentKey *ecdsa.PrivateKey) (*Certificate, error) {

src/crypto/x509/verify.go

@@ -11,6 +11,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"net/netip"
 	"net/url"
 	"reflect"
 	"runtime"
@@ -434,8 +435,10 @@ func matchURIConstraint(uri *url.URL, constraint string) (bool, error) {
 		}
 	}
 
-	if strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]") ||
+	// netip.ParseAddr will reject the URI IPv6 literal form "[...]", so we
-		net.ParseIP(host) != nil {
+	// check if _either_ the string parses as an IP, or if it is enclosed in
+	// square brackets.
+	if _, err := netip.ParseAddr(host); err == nil || (strings.HasPrefix(host, "[") && strings.HasSuffix(host, "]")) {
 		return false, fmt.Errorf("URI with IP (%q) cannot be matched against constraints", uri.String())
 	}
 

src/database/sql/sql.go

@@ -1368,8 +1368,8 @@ func (db *DB) conn(ctx context.Context, strategy connReuseStrategy) (*driverConn
 
 			db.waitDuration.Add(int64(time.Since(waitStart)))
 
-			// If we failed to delete it, that means something else
+			// If we failed to delete it, that means either the DB was closed or
-			// grabbed it and is about to send on it.
+			// something else grabbed it and is about to send on it.
 			if !deleted {
 				// TODO(bradfitz): rather than this best effort select, we
 				// should probably start a goroutine to read from req. This best
@@ -3594,6 +3594,7 @@ type connRequestAndIndex struct {
 // and clears the set.
 func (s *connRequestSet) CloseAndRemoveAll() {
 	for _, v := range s.s {
+		*v.curIdx = -1
 		close(v.req)
 	}
 	s.s = nil

src/database/sql/sql_test.go

@@ -4920,6 +4920,17 @@ func TestConnRequestSet(t *testing.T) {
 			t.Error("wasn't random")
 		}
 	})
+	t.Run("close-delete", func(t *testing.T) {
+		reset()
+		ch := make(chan connRequest)
+		dh := s.Add(ch)
+		wantLen(1)
+		s.CloseAndRemoveAll()
+		wantLen(0)
+		if s.Delete(dh) {
+			t.Error("unexpected delete after CloseAndRemoveAll")
+		}
+	})
 }
 
 func BenchmarkConnRequestSet(b *testing.B) {

src/encoding/gob/decode.go

@@ -911,8 +911,11 @@ func (dec *Decoder) decOpFor(wireId typeId, rt reflect.Type, name string, inProg
 var maxIgnoreNestingDepth = 10000
 
 // decIgnoreOpFor returns the decoding op for a field that has no destination.
-func (dec *Decoder) decIgnoreOpFor(wireId typeId, inProgress map[typeId]*decOp, depth int) *decOp {
+func (dec *Decoder) decIgnoreOpFor(wireId typeId, inProgress map[typeId]*decOp) *decOp {
-	if depth > maxIgnoreNestingDepth {
+	// Track how deep we've recursed trying to skip nested ignored fields.
+	dec.ignoreDepth++
+	defer func() { dec.ignoreDepth-- }()
+	if dec.ignoreDepth > maxIgnoreNestingDepth {
 		error_(errors.New("invalid nesting depth"))
 	}
 	// If this type is already in progress, it's a recursive type (e.g. map[string]*T).
@@ -938,7 +941,7 @@ func (dec *Decoder) decIgnoreOpFor(wireId typeId, inProgress map[typeId]*decOp,
 			errorf("bad data: undefined type %s", wireId.string())
 		case wire.ArrayT != nil:
 			elemId := wire.ArrayT.Elem
-			elemOp := dec.decIgnoreOpFor(elemId, inProgress, depth+1)
+			elemOp := dec.decIgnoreOpFor(elemId, inProgress)
 			op = func(i *decInstr, state *decoderState, value reflect.Value) {
 				state.dec.ignoreArray(state, *elemOp, wire.ArrayT.Len)
 			}
@@ -946,15 +949,15 @@ func (dec *Decoder) decIgnoreOpFor(wireId typeId, inProgress map[typeId]*decOp,
 		case wire.MapT != nil:
 			keyId := dec.wireType[wireId].MapT.Key
 			elemId := dec.wireType[wireId].MapT.Elem
-			keyOp := dec.decIgnoreOpFor(keyId, inProgress, depth+1)
+			keyOp := dec.decIgnoreOpFor(keyId, inProgress)
-			elemOp := dec.decIgnoreOpFor(elemId, inProgress, depth+1)
+			elemOp := dec.decIgnoreOpFor(elemId, inProgress)
 			op = func(i *decInstr, state *decoderState, value reflect.Value) {
 				state.dec.ignoreMap(state, *keyOp, *elemOp)
 			}
 
 		case wire.SliceT != nil:
 			elemId := wire.SliceT.Elem
-			elemOp := dec.decIgnoreOpFor(elemId, inProgress, depth+1)
+			elemOp := dec.decIgnoreOpFor(elemId, inProgress)
 			op = func(i *decInstr, state *decoderState, value reflect.Value) {
 				state.dec.ignoreSlice(state, *elemOp)
 			}
@@ -1115,7 +1118,7 @@ func (dec *Decoder) compileSingle(remoteId typeId, ut *userTypeInfo) (engine *de
 func (dec *Decoder) compileIgnoreSingle(remoteId typeId) *decEngine {
 	engine := new(decEngine)
 	engine.instr = make([]decInstr, 1) // one item
-	op := dec.decIgnoreOpFor(remoteId, make(map[typeId]*decOp), 0)
+	op := dec.decIgnoreOpFor(remoteId, make(map[typeId]*decOp))
 	ovfl := overflow(dec.typeString(remoteId))
 	engine.instr[0] = decInstr{*op, 0, nil, ovfl}
 	engine.numInstr = 1
@@ -1160,7 +1163,7 @@ func (dec *Decoder) compileDec(remoteId typeId, ut *userTypeInfo) (engine *decEn
 		localField, present := srt.FieldByName(wireField.Name)
 		// TODO(r): anonymous names
 		if !present || !isExported(wireField.Name) {
-			op := dec.decIgnoreOpFor(wireField.Id, make(map[typeId]*decOp), 0)
+			op := dec.decIgnoreOpFor(wireField.Id, make(map[typeId]*decOp))
 			engine.instr[fieldnum] = decInstr{*op, fieldnum, nil, ovfl}
 			continue
 		}

src/encoding/gob/decoder.go

@@ -35,6 +35,8 @@ type Decoder struct {
 	freeList     *decoderState                           // list of free decoderStates; avoids reallocation
 	countBuf     []byte                                  // used for decoding integers while parsing messages
 	err          error
+	// ignoreDepth tracks the depth of recursively parsed ignored fields
+	ignoreDepth int
 }
 
 // NewDecoder returns a new decoder that reads from the [io.Reader].

src/encoding/gob/gobencdec_test.go

@@ -806,6 +806,8 @@ func TestIgnoreDepthLimit(t *testing.T) {
 	defer func() { maxIgnoreNestingDepth = oldNestingDepth }()
 	b := new(bytes.Buffer)
 	enc := NewEncoder(b)
+
+	// Nested slice
 	typ := reflect.TypeFor[int]()
 	nested := reflect.ArrayOf(1, typ)
 	for i := 0; i < 100; i++ {
@@ -819,4 +821,16 @@ func TestIgnoreDepthLimit(t *testing.T) {
 	if err := dec.Decode(&output); err == nil || err.Error() != expectedErr {
 		t.Errorf("Decode didn't fail with depth limit of 100: want %q, got %q", expectedErr, err)
 	}
+
+	// Nested struct
+	nested = reflect.StructOf([]reflect.StructField{{Name: "F", Type: typ}})
+	for i := 0; i < 100; i++ {
+		nested = reflect.StructOf([]reflect.StructField{{Name: "F", Type: nested}})
+	}
+	badStruct = reflect.New(reflect.StructOf([]reflect.StructField{{Name: "F", Type: nested}}))
+	enc.Encode(badStruct.Interface())
+	dec = NewDecoder(b)
+	if err := dec.Decode(&output); err == nil || err.Error() != expectedErr {
+		t.Errorf("Decode didn't fail with depth limit of 100: want %q, got %q", expectedErr, err)
+	}
 }

src/go/build/constraint/expr.go

@@ -16,6 +16,10 @@ import (
 	"unicode/utf8"
 )
 
+// maxSize is a limit used to control the complexity of expressions, in order
+// to prevent stack exhaustion issues due to recursion.
+const maxSize = 1000
+
 // An Expr is a build tag constraint expression.
 // The underlying concrete type is *[AndExpr], *[OrExpr], *[NotExpr], or *[TagExpr].
 type Expr interface {
@@ -151,7 +155,7 @@ func Parse(line string) (Expr, error) {
 		return parseExpr(text)
 	}
 	if text, ok := splitPlusBuild(line); ok {
-		return parsePlusBuildExpr(text), nil
+		return parsePlusBuildExpr(text)
 	}
 	return nil, errNotConstraint
 }
@@ -201,6 +205,8 @@ type exprParser struct {
 	tok   string // last token read
 	isTag bool
 	pos   int // position (start) of last token
+
+	size int
 }
 
 // parseExpr parses a boolean build tag expression.
@@ -249,6 +255,10 @@ func (p *exprParser) and() Expr {
 // On entry, the next input token has not yet been lexed.
 // On exit, the next input token has been lexed and is in p.tok.
 func (p *exprParser) not() Expr {
+	p.size++
+	if p.size > maxSize {
+		panic(&SyntaxError{Offset: p.pos, Err: "build expression too large"})
+	}
 	p.lex()
 	if p.tok == "!" {
 		p.lex()
@@ -388,7 +398,13 @@ func splitPlusBuild(line string) (expr string, ok bool) {
 }
 
 // parsePlusBuildExpr parses a legacy build tag expression (as used with “// +build”).
-func parsePlusBuildExpr(text string) Expr {
+func parsePlusBuildExpr(text string) (Expr, error) {
+	// Only allow up to 100 AND/OR operators for "old" syntax.
+	// This is much less than the limit for "new" syntax,
+	// but uses of old syntax were always very simple.
+	const maxOldSize = 100
+	size := 0
+
 	var x Expr
 	for _, clause := range strings.Fields(text) {
 		var y Expr
@@ -414,19 +430,25 @@ func parsePlusBuildExpr(text string) Expr {
 			if y == nil {
 				y = z
 			} else {
+				if size++; size > maxOldSize {
+					return nil, errComplex
+				}
 				y = and(y, z)
 			}
 		}
 		if x == nil {
 			x = y
 		} else {
+			if size++; size > maxOldSize {
+				return nil, errComplex
+			}
 			x = or(x, y)
 		}
 	}
 	if x == nil {
 		x = tag("ignore")
 	}
-	return x
+	return x, nil
 }
 
 // isValidTag reports whether the word is a valid build tag.

src/go/build/constraint/expr_test.go

@@ -222,7 +222,7 @@ var parsePlusBuildExprTests = []struct {
 func TestParsePlusBuildExpr(t *testing.T) {
 	for i, tt := range parsePlusBuildExprTests {
 		t.Run(fmt.Sprint(i), func(t *testing.T) {
-			x := parsePlusBuildExpr(tt.in)
+			x, _ := parsePlusBuildExpr(tt.in)
 			if x.String() != tt.x.String() {
 				t.Errorf("parsePlusBuildExpr(%q):\nhave %v\nwant %v", tt.in, x, tt.x)
 			}
@@ -319,3 +319,66 @@ func TestPlusBuildLines(t *testing.T) {
 		})
 	}
 }
+
+func TestSizeLimits(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		expr string
+	}{
+		{
+			name: "go:build or limit",
+			expr: "//go:build " + strings.Repeat("a || ", maxSize+2),
+		},
+		{
+			name: "go:build and limit",
+			expr: "//go:build " + strings.Repeat("a && ", maxSize+2),
+		},
+		{
+			name: "go:build and depth limit",
+			expr: "//go:build " + strings.Repeat("(a &&", maxSize+2),
+		},
+		{
+			name: "go:build or depth limit",
+			expr: "//go:build " + strings.Repeat("(a ||", maxSize+2),
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := Parse(tc.expr)
+			if err == nil {
+				t.Error("expression did not trigger limit")
+			} else if syntaxErr, ok := err.(*SyntaxError); !ok || syntaxErr.Err != "build expression too large" {
+				if !ok {
+					t.Errorf("unexpected error: %v", err)
+				} else {
+					t.Errorf("unexpected syntax error: %s", syntaxErr.Err)
+				}
+			}
+		})
+	}
+}
+
+func TestPlusSizeLimits(t *testing.T) {
+	maxOldSize := 100
+	for _, tc := range []struct {
+		name string
+		expr string
+	}{
+		{
+			name: "+build or limit",
+			expr: "// +build " + strings.Repeat("a ", maxOldSize+2),
+		},
+		{
+			name: "+build and limit",
+			expr: "// +build " + strings.Repeat("a,", maxOldSize+2),
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := Parse(tc.expr)
+			if err == nil {
+				t.Error("expression did not trigger limit")
+			} else if err != errComplex {
+				t.Errorf("unexpected error: got %q, want %q", err, errComplex)
+			}
+		})
+	}
+}

src/go/parser/parser.go

@@ -1676,6 +1676,8 @@ func (p *parser) parseElementList() (list []ast.Expr) {
 }
 
 func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
+	defer decNestLev(incNestLev(p))
+
 	if p.trace {
 		defer un(trace(p, "LiteralValue"))
 	}

src/go/parser/parser_test.go

@@ -598,10 +598,11 @@ var parseDepthTests = []struct {
 	{name: "chan2", format: "package main; var x «<-chan »int"},
 	{name: "interface", format: "package main; var x «interface { M() «int» }»", scope: true, scopeMultiplier: 2}, // Scopes: InterfaceType, FuncType
 	{name: "map", format: "package main; var x «map[int]»int"},
-	{name: "slicelit", format: "package main; var x = «[]any{«»}»", parseMultiplier: 2},             // Parser nodes: UnaryExpr, CompositeLit
+	{name: "slicelit", format: "package main; var x = []any{«[]any{«»}»}", parseMultiplier: 3},      // Parser nodes: UnaryExpr, CompositeLit
-	{name: "arraylit", format: "package main; var x = «[1]any{«nil»}»", parseMultiplier: 2},         // Parser nodes: UnaryExpr, CompositeLit
+	{name: "arraylit", format: "package main; var x = «[1]any{«nil»}»", parseMultiplier: 3},         // Parser nodes: UnaryExpr, CompositeLit
-	{name: "structlit", format: "package main; var x = «struct{x any}{«nil»}»", parseMultiplier: 2}, // Parser nodes: UnaryExpr, CompositeLit
+	{name: "structlit", format: "package main; var x = «struct{x any}{«nil»}»", parseMultiplier: 3}, // Parser nodes: UnaryExpr, CompositeLit
-	{name: "maplit", format: "package main; var x = «map[int]any{1:«nil»}»", parseMultiplier: 2},    // Parser nodes: CompositeLit, KeyValueExpr
+	{name: "maplit", format: "package main; var x = «map[int]any{1:«nil»}»", parseMultiplier: 3},    // Parser nodes: CompositeLit, KeyValueExpr
+	{name: "element", format: "package main; var x = struct{x any}{x: «{«»}»}"},
 	{name: "dot", format: "package main; var x = «x.»x"},
 	{name: "index", format: "package main; var x = x«[1]»"},
 	{name: "slice", format: "package main; var x = x«[1:2]»"},

src/go/types/alias.go

@@ -137,10 +137,10 @@ func (check *Checker) newAlias(obj *TypeName, rhs Type) *Alias {
 // newAliasInstance creates a new alias instance for the given origin and type
 // arguments, recording pos as the position of its synthetic object (for error
 // reporting).
-func (check *Checker) newAliasInstance(pos token.Pos, orig *Alias, targs []Type, ctxt *Context) *Alias {
+func (check *Checker) newAliasInstance(pos token.Pos, orig *Alias, targs []Type, expanding *Named, ctxt *Context) *Alias {
 	assert(len(targs) > 0)
 	obj := NewTypeName(pos, orig.obj.pkg, orig.obj.name, nil)
-	rhs := check.subst(pos, orig.fromRHS, makeSubstMap(orig.TypeParams().list(), targs), nil, ctxt)
+	rhs := check.subst(pos, orig.fromRHS, makeSubstMap(orig.TypeParams().list(), targs), expanding, ctxt)
 	res := check.newAlias(obj, rhs)
 	res.orig = orig
 	res.tparams = orig.tparams

src/go/types/api_test.go

@@ -2906,20 +2906,46 @@ func TestFileVersions(t *testing.T) {
 	}{
 		{"", "", ""},                    // no versions specified
 		{"go1.19", "", "go1.19"},        // module version specified
-		{"", "go1.20", ""},             // file upgrade ignored
+		{"", "go1.20", "go1.21"},        // file version specified below minimum of 1.21
-		{"go1.19", "go1.20", "go1.20"}, // file upgrade permitted
+		{"go1", "", "go1"},              // no file version specified
-		{"go1.20", "go1.19", "go1.20"}, // file downgrade not permitted
+		{"go1", "goo1.22", "go1"},       // invalid file version specified
-		{"go1.21", "go1.19", "go1.19"}, // file downgrade permitted (module version is >= go1.21)
+		{"go1", "go1.19", "go1.21"},     // file version specified below minimum of 1.21
+		{"go1", "go1.20", "go1.21"},     // file version specified below minimum of 1.21
+		{"go1", "go1.21", "go1.21"},     // file version specified at 1.21
+		{"go1", "go1.22", "go1.22"},     // file version specified above 1.21
+		{"go1.19", "", "go1.19"},        // no file version specified
+		{"go1.19", "goo1.22", "go1.19"}, // invalid file version specified
+		{"go1.19", "go1.20", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.19", "go1.21", "go1.21"},  // file version specified at 1.21
+		{"go1.19", "go1.22", "go1.22"},  // file version specified above 1.21
+		{"go1.20", "", "go1.20"},        // no file version specified
+		{"go1.20", "goo1.22", "go1.20"}, // invalid file version specified
+		{"go1.20", "go1.19", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.20", "go1.20", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.20", "go1.21", "go1.21"},  // file version specified at 1.21
+		{"go1.20", "go1.22", "go1.22"},  // file version specified above 1.21
+		{"go1.21", "", "go1.21"},        // no file version specified
+		{"go1.21", "goo1.22", "go1.21"}, // invalid file version specified
+		{"go1.21", "go1.19", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.21", "go1.20", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.21", "go1.21", "go1.21"},  // file version specified at 1.21
+		{"go1.21", "go1.22", "go1.22"},  // file version specified above 1.21
+		{"go1.22", "", "go1.22"},        // no file version specified
+		{"go1.22", "goo1.22", "go1.22"}, // invalid file version specified
+		{"go1.22", "go1.19", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.22", "go1.20", "go1.21"},  // file version specified below minimum of 1.21
+		{"go1.22", "go1.21", "go1.21"},  // file version specified at 1.21
+		{"go1.22", "go1.22", "go1.22"},  // file version specified above 1.21
 
 		// versions containing release numbers
 		// (file versions containing release numbers are considered invalid)
 		{"go1.19.0", "", "go1.19.0"},         // no file version specified
-		{"go1.20", "go1.20.1", "go1.20"},     // file upgrade ignored
+		{"go1.20.1", "go1.19.1", "go1.20.1"}, // invalid file version
-		{"go1.20.1", "go1.20", "go1.20.1"},   // file upgrade ignored
+		{"go1.20.1", "go1.21.1", "go1.20.1"}, // invalid file version
-		{"go1.20.1", "go1.21", "go1.21"},     // file upgrade permitted
+		{"go1.21.1", "go1.19.1", "go1.21.1"}, // invalid file version
-		{"go1.20.1", "go1.19", "go1.20.1"},   // file downgrade not permitted
+		{"go1.21.1", "go1.21.1", "go1.21.1"}, // invalid file version
-		{"go1.21.1", "go1.19.1", "go1.21.1"}, // file downgrade not permitted (invalid file version)
+		{"go1.22.1", "go1.19.1", "go1.22.1"}, // invalid file version
-		{"go1.21.1", "go1.19", "go1.19"},     // file downgrade permitted (module version is >= go1.21)
+		{"go1.22.1", "go1.21.1", "go1.22.1"}, // invalid file version
 	} {
 		var src string
 		if test.fileVersion != "" {

src/go/types/check.go

@@ -349,7 +349,6 @@ func (check *Checker) initFiles(files []*ast.File) {
 		check.errorf(files[0], TooNew, "package requires newer Go version %v (application built with %v)",
 			check.version, go_current)
 	}
-	downgradeOk := check.version.cmp(go1_21) >= 0
 
 	// determine Go version for each file
 	for _, file := range check.files {
@@ -358,33 +357,19 @@ func (check *Checker) initFiles(files []*ast.File) {
 		// unlike file versions which are Go language versions only, if valid.)
 		v := check.conf.GoVersion
 
-		fileVersion := asGoVersion(file.GoVersion)
+		// If the file specifies a version, use max(fileVersion, go1.21).
-		if fileVersion.isValid() {
+		if fileVersion := asGoVersion(file.GoVersion); fileVersion.isValid() {
-			// use the file version, if applicable
-			// (file versions are either the empty string or of the form go1.dd)
-			if pkgVersionOk {
-				cmp := fileVersion.cmp(check.version)
 			// Go 1.21 introduced the feature of setting the go.mod
 			// go line to an early version of Go and allowing //go:build lines
-				// to “upgrade” (cmp > 0) the Go version in a given file.
+			// to set the Go version in a given file. Versions Go 1.21 and later
-				// We can do that backwards compatibly.
+			// can be set backwards compatibly as that was the first version
+			// files with go1.21 or later build tags could be built with.
 			//
-				// Go 1.21 also introduced the feature of allowing //go:build lines
+			// Set the version to max(fileVersion, go1.21): That will allow a
-				// to “downgrade” (cmp < 0) the Go version in a given file.
+			// downgrade to a version before go1.22, where the for loop semantics
-				// That can't be done compatibly in general, since before the
+			// change was made, while being backwards compatible with versions of
-				// build lines were ignored and code got the module's Go version.
+			// go before the new //go:build semantics were introduced.
-				// To work around this, downgrades are only allowed when the
+			v = string(versionMax(fileVersion, go1_21))
-				// module's Go version is Go 1.21 or later.
-				//
-				// If there is no valid check.version, then we don't really know what
-				// Go version to apply.
-				// Legacy tools may do this, and they historically have accepted everything.
-				// Preserve that behavior by ignoring //go:build constraints entirely in that
-				// case (!pkgVersionOk).
-				if cmp > 0 || cmp < 0 && downgradeOk {
-					v = file.GoVersion
-				}
-			}
 
 			// Report a specific error for each tagged file that's too new.
 			// (Normally the build system will have filtered files by version,
@@ -399,6 +384,13 @@ func (check *Checker) initFiles(files []*ast.File) {
 	}
 }
 
+func versionMax(a, b goVersion) goVersion {
+	if a.cmp(b) < 0 {
+		return b
+	}
+	return a
+}
+
 // A bailout panic is used for early termination.
 type bailout struct{}
 

src/go/types/instantiate.go

@@ -14,6 +14,7 @@ import (
 	"errors"
 	"fmt"
 	"go/token"
+	"internal/buildcfg"
 	. "internal/types/errors"
 )
 
@@ -129,8 +130,9 @@ func (check *Checker) instance(pos token.Pos, orig genericType, targs []Type, ex
 		res = check.newNamedInstance(pos, orig, targs, expanding) // substituted lazily
 
 	case *Alias:
-		// TODO(gri) is this correct?
+		if !buildcfg.Experiment.AliasTypeParams {
 			assert(expanding == nil) // Alias instances cannot be reached from Named types
+		}
 
 		tparams := orig.TypeParams()
 		// TODO(gri) investigate if this is needed (type argument and parameter count seem to be correct here)
@@ -141,7 +143,7 @@ func (check *Checker) instance(pos token.Pos, orig genericType, targs []Type, ex
 			return orig // nothing to do (minor optimization)
 		}
 
-		return check.newAliasInstance(pos, orig, targs, ctxt)
+		return check.newAliasInstance(pos, orig, targs, expanding, ctxt)
 
 	case *Signature:
 		assert(expanding == nil) // function instances cannot be reached from Named types

src/go/types/issues_test.go

@@ -1131,3 +1131,23 @@ func f(x int) {
 		t.Errorf("got: %s want: %s", got, want)
 	}
 }
+
+func TestIssue68877(t *testing.T) {
+	const src = `
+package p
+
+type (
+	S struct{}
+	A = S
+	T A
+)`
+
+	t.Setenv("GODEBUG", "gotypesalias=1")
+	pkg := mustTypecheck(src, nil, nil)
+	T := pkg.Scope().Lookup("T").(*TypeName)
+	got := T.String() // this must not panic (was issue)
+	const want = "type p.T struct{}"
+	if got != want {
+		t.Errorf("got %s, want %s", got, want)
+	}
+}

src/go/types/named.go

@@ -285,7 +285,7 @@ func (t *Named) cleanup() {
 		if t.TypeArgs().Len() == 0 {
 			panic("nil underlying")
 		}
-	case *Named:
+	case *Named, *Alias:
 		t.under() // t.under may add entries to check.cleaners
 	}
 	t.check = nil

src/go/types/subst.go

@@ -118,7 +118,7 @@ func (subst *subster) typ(typ Type) Type {
 		// that has a type argument for it.
 		targs, updated := subst.typeList(t.TypeArgs().list())
 		if updated {
-			return subst.check.newAliasInstance(subst.pos, t.orig, targs, subst.ctxt)
+			return subst.check.newAliasInstance(subst.pos, t.orig, targs, subst.expanding, subst.ctxt)
 		}
 
 	case *Array:

src/go/types/typeset.go

@@ -134,8 +134,8 @@ func (s *_TypeSet) underIs(f func(Type) bool) bool {
 	}
 	for _, t := range s.terms {
 		assert(t.typ != nil)
-		// x == under(x) for ~x terms
+		// Unalias(x) == under(x) for ~x terms
-		u := t.typ
+		u := Unalias(t.typ)
 		if !t.tilde {
 			u = under(u)
 		}

src/internal/abi/type.go

@@ -177,6 +177,15 @@ func TypeOf(a any) *Type {
 	return (*Type)(NoEscape(unsafe.Pointer(eface.Type)))
 }
 
+// TypeFor returns the abi.Type for a type parameter.
+func TypeFor[T any]() *Type {
+	var v T
+	if t := TypeOf(v); t != nil {
+		return t // optimize for T being a non-interface kind
+	}
+	return TypeOf((*T)(nil)).Elem() // only for an interface kind
+}
+
 func (t *Type) Kind() Kind { return t.Kind_ & KindMask }
 
 func (t *Type) HasName() bool {

src/internal/poll/sendfile_bsd.go

@@ -32,28 +32,46 @@ func SendFile(dstFD *FD, src int, pos, remain int64) (written int64, err error,
 		if int64(n) > remain {
 			n = int(remain)
 		}
+		m := n
 		pos1 := pos
 		n, err = syscall.Sendfile(dst, src, &pos1, n)
 		if n > 0 {
 			pos += int64(n)
 			written += int64(n)
 			remain -= int64(n)
-		}
+			// (n, nil) indicates that sendfile(2) has transferred
-		if err == syscall.EINTR {
+			// the exact number of bytes we requested, or some unretryable
+			// error have occurred with partial bytes sent. Either way, we
+			// don't need to go through the following logic to check EINTR
+			// or fell into dstFD.pd.waitWrite, just continue to send the
+			// next chunk or break the loop.
+			if n == m {
 				continue
+			} else if err != syscall.EAGAIN &&
+				err != syscall.EINTR &&
+				err != syscall.EBUSY {
+				// Particularly, EPIPE. Errors like that would normally lead
+				// the subsequent sendfile(2) call to (-1, EBADF).
+				break
 			}
+		} else if err != syscall.EAGAIN && err != syscall.EINTR {
 			// This includes syscall.ENOSYS (no kernel
 			// support) and syscall.EINVAL (fd types which
 			// don't implement sendfile), and other errors.
 			// We should end the loop when there is no error
 			// returned from sendfile(2) or it is not a retryable error.
-		if err != syscall.EAGAIN {
 			break
 		}
+		if err == syscall.EINTR {
+			continue
+		}
 		if err = dstFD.pd.waitWrite(dstFD.isFile); err != nil {
 			break
 		}
 	}
-	handled = written != 0 || (err != syscall.ENOSYS && err != syscall.EINVAL)
+	if err == syscall.EAGAIN {
+		err = nil
+	}
+	handled = written != 0 || (err != syscall.ENOSYS && err != syscall.EINVAL && err != syscall.EOPNOTSUPP && err != syscall.ENOTSUP)
 	return
 }

src/internal/poll/sendfile_linux.go

@@ -50,6 +50,9 @@ func SendFile(dstFD *FD, src int, remain int64) (written int64, err error, handl
 			break
 		}
 	}
+	if err == syscall.EAGAIN {
+		err = nil
+	}
 	handled = written != 0 || (err != syscall.ENOSYS && err != syscall.EINVAL)
 	return
 }

src/internal/poll/sendfile_solaris.go

@@ -61,6 +61,9 @@ func SendFile(dstFD *FD, src int, pos, remain int64) (written int64, err error,
 			break
 		}
 	}
+	if err == syscall.EAGAIN {
+		err = nil
+	}
 	handled = written != 0 || (err != syscall.ENOSYS && err != syscall.EINVAL)
 	return
 }

src/internal/types/testdata/check/go1_20_19.go

@@ -14,4 +14,4 @@ type Slice []byte
 type Array [8]byte
 
 var s Slice
-var p = (Array)(s /* ok because Go 1.20 ignored the //go:build go1.19 */)
+var p = (Array)(s /* ok because file versions below go1.21 set the langage version to go1.21 */)

src/internal/types/testdata/check/go1_21_19.go

@@ -14,4 +14,4 @@ type Slice []byte
 type Array [8]byte
 
 var s Slice
-var p = (Array)(s /* ERROR "requires go1.20 or later" */)
+var p = (Array)(s /* ok because file versions below go1.21 set the langage version to go1.21 */)

src/internal/types/testdata/check/go1_21_22.go

@@ -0,0 +1,16 @@
+// -lang=go1.21
+
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Check Go language version-specific errors.
+
+//go:build go1.22
+
+package p
+
+func f() {
+	for _ = range /* ok because of upgrade to 1.22 */ 10 {
+	}
+}

src/internal/types/testdata/check/go1_22_21.go

@@ -0,0 +1,16 @@
+// -lang=go1.22
+
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Check Go language version-specific errors.
+
+//go:build go1.21
+
+package p
+
+func f() {
+	for _ = range 10 /* ERROR "requires go1.22 or later" */ {
+	}
+}

src/internal/types/testdata/fixedbugs/issue66285.go

@@ -1,14 +1,9 @@
-// -lang=go1.21
+// -lang=go1.13
 
 // Copyright 2024 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Note: Downgrading to go1.13 requires at least go1.21,
-//       hence the need for -lang=go1.21 at the top.
-
-//go:build go1.13
-
 package p
 
 import "io"

src/internal/types/testdata/fixedbugs/issue68903.go

@@ -0,0 +1,24 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type A = [4]int
+type B = map[string]interface{}
+
+func _[T ~A](x T) {
+	_ = len(x)
+}
+
+func _[U ~A](x U) {
+	_ = cap(x)
+}
+
+func _[V ~A]() {
+	_ = V{}
+}
+
+func _[W ~B](a interface{}) {
+	_ = a.(W)["key"]
+}

src/internal/types/testdata/fixedbugs/issue68935.go

@@ -0,0 +1,26 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+type A = struct {
+	F string
+	G int
+}
+
+func Make[T ~A]() T {
+	return T{
+		F: "blah",
+		G: 1234,
+	}
+}
+
+type N struct {
+	F string
+	G int
+}
+
+func _() {
+	_ = Make[N]()
+}

src/internal/weak/pointer_test.go

@@ -5,9 +5,12 @@
 package weak_test
 
 import (
+	"context"
 	"internal/weak"
 	"runtime"
+	"sync"
 	"testing"
+	"time"
 )
 
 type T struct {
@@ -128,3 +131,82 @@ func TestPointerFinalizer(t *testing.T) {
 		t.Errorf("weak pointer is non-nil even after finalization: %v", wt)
 	}
 }
+
+// Regression test for issue 69210.
+//
+// Weak-to-strong conversions must shade the new strong pointer, otherwise
+// that might be creating the only strong pointer to a white object which
+// is hidden in a blackened stack.
+//
+// Never fails if correct, fails with some high probability if incorrect.
+func TestIssue69210(t *testing.T) {
+	if testing.Short() {
+		t.Skip("this is a stress test that takes seconds to run on its own")
+	}
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer cancel()
+
+	// What we're trying to do is manufacture the conditions under which this
+	// bug happens. Specifically, we want:
+	//
+	// 1. To create a whole bunch of objects that are only weakly-pointed-to,
+	// 2. To call Strong while the GC is in the mark phase,
+	// 3. The new strong pointer to be missed by the GC,
+	// 4. The following GC cycle to mark a free object.
+	//
+	// Unfortunately, (2) and (3) are hard to control, but we can increase
+	// the likelihood by having several goroutines do (1) at once while
+	// another goroutine constantly keeps us in the GC with runtime.GC.
+	// Like throwing darts at a dart board until they land just right.
+	// We can increase the likelihood of (4) by adding some delay after
+	// creating the strong pointer, but only if it's non-nil. If it's nil,
+	// that means it was already collected in which case there's no chance
+	// of triggering the bug, so we want to retry as fast as possible.
+	// Our heap here is tiny, so the GCs will go by fast.
+	//
+	// As of 2024-09-03, removing the line that shades pointers during
+	// the weak-to-strong conversion causes this test to fail about 50%
+	// of the time.
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		for {
+			runtime.GC()
+
+			select {
+			case <-ctx.Done():
+				return
+			default:
+			}
+		}
+	}()
+	for range max(runtime.GOMAXPROCS(-1)-1, 1) {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for {
+				for range 5 {
+					bt := new(T)
+					wt := weak.Make(bt)
+					bt = nil
+					time.Sleep(1 * time.Millisecond)
+					bt = wt.Strong()
+					if bt != nil {
+						time.Sleep(4 * time.Millisecond)
+						bt.t = bt
+						bt.a = 12
+					}
+					runtime.KeepAlive(bt)
+				}
+				select {
+				case <-ctx.Done():
+					return
+				default:
+				}
+			}
+		}()
+	}
+	wg.Wait()
+}

src/net/http/client.go

@@ -614,7 +614,8 @@ func (c *Client) do(req *Request) (retres *Response, reterr error) {
 
 		// Redirect behavior:
 		redirectMethod        string
-		includeBody    bool
+		includeBody           = true
+		stripSensitiveHeaders = false
 	)
 	uerr := func(err error) error {
 		// the body may have been closed already by c.send()
@@ -681,7 +682,12 @@ func (c *Client) do(req *Request) (retres *Response, reterr error) {
 			// in case the user set Referer on their first request.
 			// If they really want to override, they can do it in
 			// their CheckRedirect func.
-			copyHeaders(req)
+			if !stripSensitiveHeaders && reqs[0].URL.Host != req.URL.Host {
+				if !shouldCopyHeaderOnRedirect(reqs[0].URL, req.URL) {
+					stripSensitiveHeaders = true
+				}
+			}
+			copyHeaders(req, stripSensitiveHeaders)
 
 			// Add the Referer header from the most recent
 			// request URL to the new one, if it's not https->http:
@@ -744,7 +750,7 @@ func (c *Client) do(req *Request) (retres *Response, reterr error) {
 // makeHeadersCopier makes a function that copies headers from the
 // initial Request, ireq. For every redirect, this function must be called
 // so that it can copy headers into the upcoming Request.
-func (c *Client) makeHeadersCopier(ireq *Request) func(*Request) {
+func (c *Client) makeHeadersCopier(ireq *Request) func(req *Request, stripSensitiveHeaders bool) {
 	// The headers to copy are from the very initial request.
 	// We use a closured callback to keep a reference to these original headers.
 	var (
@@ -758,8 +764,7 @@ func (c *Client) makeHeadersCopier(ireq *Request) func(*Request) {
 		}
 	}
 
-	preq := ireq // The previous request
+	return func(req *Request, stripSensitiveHeaders bool) {
-	return func(req *Request) {
 		// If Jar is present and there was some initial cookies provided
 		// via the request header, then we may need to alter the initial
 		// cookies as we follow redirects since each redirect may end up
@@ -796,12 +801,15 @@ func (c *Client) makeHeadersCopier(ireq *Request) func(*Request) {
 		// Copy the initial request's Header values
 		// (at least the safe ones).
 		for k, vv := range ireqhdr {
-			if shouldCopyHeaderOnRedirect(k, preq.URL, req.URL) {
+			sensitive := false
+			switch CanonicalHeaderKey(k) {
+			case "Authorization", "Www-Authenticate", "Cookie", "Cookie2":
+				sensitive = true
+			}
+			if !(sensitive && stripSensitiveHeaders) {
 				req.Header[k] = vv
 			}
 		}
-
-		preq = req // Update previous Request with the current request
 	}
 }
 
@@ -977,9 +985,7 @@ func (b *cancelTimerBody) Close() error {
 	return err
 }
 
-func shouldCopyHeaderOnRedirect(headerKey string, initial, dest *url.URL) bool {
+func shouldCopyHeaderOnRedirect(initial, dest *url.URL) bool {
-	switch CanonicalHeaderKey(headerKey) {
-	case "Authorization", "Www-Authenticate", "Cookie", "Cookie2":
 	// Permit sending auth/cookie headers from "foo.com"
 	// to "sub.foo.com".
 
@@ -997,9 +1003,6 @@ func shouldCopyHeaderOnRedirect(headerKey string, initial, dest *url.URL) bool {
 	dhost := idnaASCIIFromURL(dest)
 	return isDomainOrSubdomain(dhost, ihost)
 }
-	// All other headers are copied:
-	return true
-}
 
 // isDomainOrSubdomain reports whether sub is a subdomain (or exact
 // match) of the parent domain.

src/net/http/client_test.go

@@ -1536,6 +1536,55 @@ func testClientCopyHeadersOnRedirect(t *testing.T, mode testMode) {
 	}
 }
 
+// Issue #70530: Once we strip a header on a redirect to a different host,
+// the header should stay stripped across any further redirects.
+func TestClientStripHeadersOnRepeatedRedirect(t *testing.T) {
+	run(t, testClientStripHeadersOnRepeatedRedirect)
+}
+func testClientStripHeadersOnRepeatedRedirect(t *testing.T, mode testMode) {
+	var proto string
+	ts := newClientServerTest(t, mode, HandlerFunc(func(w ResponseWriter, r *Request) {
+		if r.Host+r.URL.Path != "a.example.com/" {
+			if h := r.Header.Get("Authorization"); h != "" {
+				t.Errorf("on request to %v%v, Authorization=%q, want no header", r.Host, r.URL.Path, h)
+			}
+		}
+		// Follow a chain of redirects from a to b and back to a.
+		// The Authorization header is stripped on the first redirect to b,
+		// and stays stripped even if we're sent back to a.
+		switch r.Host + r.URL.Path {
+		case "a.example.com/":
+			Redirect(w, r, proto+"://b.example.com/", StatusFound)
+		case "b.example.com/":
+			Redirect(w, r, proto+"://b.example.com/redirect", StatusFound)
+		case "b.example.com/redirect":
+			Redirect(w, r, proto+"://a.example.com/redirect", StatusFound)
+		case "a.example.com/redirect":
+			w.Header().Set("X-Done", "true")
+		default:
+			t.Errorf("unexpected request to %v", r.URL)
+		}
+	})).ts
+	proto, _, _ = strings.Cut(ts.URL, ":")
+
+	c := ts.Client()
+	c.Transport.(*Transport).Dial = func(_ string, _ string) (net.Conn, error) {
+		return net.Dial("tcp", ts.Listener.Addr().String())
+	}
+
+	req, _ := NewRequest("GET", proto+"://a.example.com/", nil)
+	req.Header.Add("Cookie", "foo=bar")
+	req.Header.Add("Authorization", "secretpassword")
+	res, err := c.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer res.Body.Close()
+	if res.Header.Get("X-Done") != "true" {
+		t.Fatalf("response missing expected header: X-Done=true")
+	}
+}
+
 // Issue 22233: copy host when Client follows a relative redirect.
 func TestClientCopyHostOnRedirect(t *testing.T) { run(t, testClientCopyHostOnRedirect) }
 func testClientCopyHostOnRedirect(t *testing.T, mode testMode) {
@@ -1702,43 +1751,39 @@ func testClientAltersCookiesOnRedirect(t *testing.T, mode testMode) {
 // Part of Issue 4800
 func TestShouldCopyHeaderOnRedirect(t *testing.T) {
 	tests := []struct {
-		header     string
 		initialURL string
 		destURL    string
 		want       bool
 	}{
-		{"User-Agent", "http://foo.com/", "http://bar.com/", true},
-		{"X-Foo", "http://foo.com/", "http://bar.com/", true},
-
 		// Sensitive headers:
-		{"cookie", "http://foo.com/", "http://bar.com/", false},
+		{"http://foo.com/", "http://bar.com/", false},
-		{"cookie2", "http://foo.com/", "http://bar.com/", false},
+		{"http://foo.com/", "http://bar.com/", false},
-		{"authorization", "http://foo.com/", "http://bar.com/", false},
+		{"http://foo.com/", "http://bar.com/", false},
-		{"authorization", "http://foo.com/", "https://foo.com/", true},
+		{"http://foo.com/", "https://foo.com/", true},
-		{"authorization", "http://foo.com:1234/", "http://foo.com:4321/", true},
+		{"http://foo.com:1234/", "http://foo.com:4321/", true},
-		{"www-authenticate", "http://foo.com/", "http://bar.com/", false},
+		{"http://foo.com/", "http://bar.com/", false},
-		{"authorization", "http://foo.com/", "http://[::1%25.foo.com]/", false},
+		{"http://foo.com/", "http://[::1%25.foo.com]/", false},
 
 		// But subdomains should work:
-		{"www-authenticate", "http://foo.com/", "http://foo.com/", true},
+		{"http://foo.com/", "http://foo.com/", true},
-		{"www-authenticate", "http://foo.com/", "http://sub.foo.com/", true},
+		{"http://foo.com/", "http://sub.foo.com/", true},
-		{"www-authenticate", "http://foo.com/", "http://notfoo.com/", false},
+		{"http://foo.com/", "http://notfoo.com/", false},
-		{"www-authenticate", "http://foo.com/", "https://foo.com/", true},
+		{"http://foo.com/", "https://foo.com/", true},
-		{"www-authenticate", "http://foo.com:80/", "http://foo.com/", true},
+		{"http://foo.com:80/", "http://foo.com/", true},
-		{"www-authenticate", "http://foo.com:80/", "http://sub.foo.com/", true},
+		{"http://foo.com:80/", "http://sub.foo.com/", true},
-		{"www-authenticate", "http://foo.com:443/", "https://foo.com/", true},
+		{"http://foo.com:443/", "https://foo.com/", true},
-		{"www-authenticate", "http://foo.com:443/", "https://sub.foo.com/", true},
+		{"http://foo.com:443/", "https://sub.foo.com/", true},
-		{"www-authenticate", "http://foo.com:1234/", "http://foo.com/", true},
+		{"http://foo.com:1234/", "http://foo.com/", true},
 
-		{"authorization", "http://foo.com/", "http://foo.com/", true},
+		{"http://foo.com/", "http://foo.com/", true},
-		{"authorization", "http://foo.com/", "http://sub.foo.com/", true},
+		{"http://foo.com/", "http://sub.foo.com/", true},
-		{"authorization", "http://foo.com/", "http://notfoo.com/", false},
+		{"http://foo.com/", "http://notfoo.com/", false},
-		{"authorization", "http://foo.com/", "https://foo.com/", true},
+		{"http://foo.com/", "https://foo.com/", true},
-		{"authorization", "http://foo.com:80/", "http://foo.com/", true},
+		{"http://foo.com:80/", "http://foo.com/", true},
-		{"authorization", "http://foo.com:80/", "http://sub.foo.com/", true},
+		{"http://foo.com:80/", "http://sub.foo.com/", true},
-		{"authorization", "http://foo.com:443/", "https://foo.com/", true},
+		{"http://foo.com:443/", "https://foo.com/", true},
-		{"authorization", "http://foo.com:443/", "https://sub.foo.com/", true},
+		{"http://foo.com:443/", "https://sub.foo.com/", true},
-		{"authorization", "http://foo.com:1234/", "http://foo.com/", true},
+		{"http://foo.com:1234/", "http://foo.com/", true},
 	}
 	for i, tt := range tests {
 		u0, err := url.Parse(tt.initialURL)
@@ -1751,10 +1796,10 @@ func TestShouldCopyHeaderOnRedirect(t *testing.T) {
 			t.Errorf("%d. dest URL %q parse error: %v", i, tt.destURL, err)
 			continue
 		}
-		got := Export_shouldCopyHeaderOnRedirect(tt.header, u0, u1)
+		got := Export_shouldCopyHeaderOnRedirect(u0, u1)
 		if got != tt.want {
-			t.Errorf("%d. shouldCopyHeaderOnRedirect(%q, %q => %q) = %v; want %v",
+			t.Errorf("%d. shouldCopyHeaderOnRedirect(%q => %q) = %v; want %v",
-				i, tt.header, tt.initialURL, tt.destURL, got, tt.want)
+				i, tt.initialURL, tt.destURL, got, tt.want)
 		}
 	}
 }

src/net/http/internal/testcert/testcert.go

@@ -10,56 +10,56 @@ import "strings"
 // LocalhostCert is a PEM-encoded TLS cert with SAN IPs
 // "127.0.0.1" and "[::1]", expiring at Jan 29 16:00:00 2084 GMT.
 // generated from src/crypto/tls:
-// go run generate_cert.go  --rsa-bits 2048 --host 127.0.0.1,::1,example.com --ca --start-date "Jan 1 00:00:00 1970" --duration=1000000h
+// go run generate_cert.go  --rsa-bits 2048 --host 127.0.0.1,::1,example.com,*.example.com --ca --start-date "Jan 1 00:00:00 1970" --duration=1000000h
 var LocalhostCert = []byte(`-----BEGIN CERTIFICATE-----
-MIIDOTCCAiGgAwIBAgIQSRJrEpBGFc7tNb1fb5pKFzANBgkqhkiG9w0BAQsFADAS
+MIIDSDCCAjCgAwIBAgIQEP/md970HysdBTpuzDOf0DANBgkqhkiG9w0BAQsFADAS
 MRAwDgYDVQQKEwdBY21lIENvMCAXDTcwMDEwMTAwMDAwMFoYDzIwODQwMTI5MTYw
 MDAwWjASMRAwDgYDVQQKEwdBY21lIENvMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8A
-MIIBCgKCAQEA6Gba5tHV1dAKouAaXO3/ebDUU4rvwCUg/CNaJ2PT5xLD4N1Vcb8r
+MIIBCgKCAQEAxcl69ROJdxjN+MJZnbFrYxyQooADCsJ6VDkuMyNQIix/Hk15Nk/u
-bFSW2HXKq+MPfVdwIKR/1DczEoAGf/JWQTW7EgzlXrCd3rlajEX2D73faWJekD0U
+FyBX1Me++aEpGmY3RIY4fUvELqT/srvAHsTXwVVSttMcY8pcAFmXSqo3x4MuUTG/
-aUgz5vtrTXZ90BQL7WvRICd7FlEZ6FPOcPlumiyNmzUqtwGhO+9ad1W5BqJaRI6P
+jCX3Vftj0r3EM5M8ImY1rzA/jqTTLJg00rD+DmuDABcqQvoXw/RV8w1yTRi5BPoH
-YfouNkwR6Na4TzSj5BrqUfP0FwDizKSJ0XXmh8g8G9mtwxOSN3Ru1QFc61Xyeluk
+DFD/AWTt/YgMvk1l2Yq/xI8VbMUIpjBoGXxWsSevQ5i2s1mk9/yZzu0Ysp1tTlzD
-POGKBV/q6RBNklTNe0gI8usUMlYyoC7ytppNMW7X2vodAelSu25jgx2anj9fDVZu
+qOPa4ysFjBitdXiwfxjxtv5nXqOCP5rheKO0sWLk0fetMp1OV5JSJMAJw6c2ZMkl
-h7AXF5+4nJS4AAt0n1lNY7nGSsdZas8PbQIDAQABo4GIMIGFMA4GA1UdDwEB/wQE
+U2WMqAEpRjdE/vHfIuNg+yGaRRqI07NZRQIDAQABo4GXMIGUMA4GA1UdDwEB/wQE
 AwICpDATBgNVHSUEDDAKBggrBgEFBQcDATAPBgNVHRMBAf8EBTADAQH/MB0GA1Ud
-DgQWBBStsdjh3/JCXXYlQryOrL4Sh7BW5TAuBgNVHREEJzAlggtleGFtcGxlLmNv
+DgQWBBQR5QIzmacmw78ZI1C4MXw7Q0wJ1jA9BgNVHREENjA0ggtleGFtcGxlLmNv
-bYcEfwAAAYcQAAAAAAAAAAAAAAAAAAAAATANBgkqhkiG9w0BAQsFAAOCAQEAxWGI
+bYINKi5leGFtcGxlLmNvbYcEfwAAAYcQAAAAAAAAAAAAAAAAAAAAATANBgkqhkiG
-5NhpF3nwwy/4yB4i/CwwSpLrWUa70NyhvprUBC50PxiXav1TeDzwzLx/o5HyNwsv
+9w0BAQsFAAOCAQEACrRNgiioUDzxQftd0fwOa6iRRcPampZRDtuaF68yNHoNWbOu
-cxv3HdkLW59i/0SlJSrNnWdfZ19oTcS+6PtLoVyISgtyN6DpkKpdG1cOkW3Cy2P2
+LUwc05eOWxRq3iABGSk2xg+FXM3DDeW4HhAhCFptq7jbVZ+4Jj6HeJG9mYRatAxR
-+tK/tKHRP1Y/Ra0RiDpOAmqn0gCOFGz8+lqDIor/T7MTpibL3IxqWfPrvfVRHL3B
+Y/dEpa0D0EHhDxxVg6UzKOXB355n0IetGE/aWvyTV9SiDs6QsaC57Q9qq1/mitx5
-grw/ZQTTIVjjh4JBSW3WyWgNo/ikC1lrVxzl4iPUGptxT36Cr7Zk2Bsg0XqwbOvK
+2GFBoapol9L5FxCc77bztzK8CpLujkBi25Vk6GAFbl27opLfpyxkM+rX/T6MXCPO
-5d+NTDREkSnUbie4GeutujmX3Dsx88UiV6UY/4lHJa6I5leHUNOHahRbpbWeOfs/
+6/YBacNZ7ff1/57Etg4i5mNA6ubCpuc4Gi9oYqCNNohftr2lkJr7REdDR6OW0lsL
-WkBKOclmOV2xlTVuPw==
+rF7r4gUnKeC7mYIH1zypY7laskopiLFAfe96Kg==
 -----END CERTIFICATE-----`)
 
 // LocalhostKey is the private key for LocalhostCert.
 var LocalhostKey = []byte(testingKey(`-----BEGIN RSA TESTING KEY-----
-MIIEvAIBADANBgkqhkiG9w0BAQEFAASCBKYwggSiAgEAAoIBAQDoZtrm0dXV0Aqi
+MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQDFyXr1E4l3GM34
-4Bpc7f95sNRTiu/AJSD8I1onY9PnEsPg3VVxvytsVJbYdcqr4w99V3AgpH/UNzMS
+wlmdsWtjHJCigAMKwnpUOS4zI1AiLH8eTXk2T+4XIFfUx775oSkaZjdEhjh9S8Qu
-gAZ/8lZBNbsSDOVesJ3euVqMRfYPvd9pYl6QPRRpSDPm+2tNdn3QFAvta9EgJ3sW
+pP+yu8AexNfBVVK20xxjylwAWZdKqjfHgy5RMb+MJfdV+2PSvcQzkzwiZjWvMD+O
-URnoU85w+W6aLI2bNSq3AaE771p3VbkGolpEjo9h+i42TBHo1rhPNKPkGupR8/QX
+pNMsmDTSsP4Oa4MAFypC+hfD9FXzDXJNGLkE+gcMUP8BZO39iAy+TWXZir/EjxVs
-AOLMpInRdeaHyDwb2a3DE5I3dG7VAVzrVfJ6W6Q84YoFX+rpEE2SVM17SAjy6xQy
+xQimMGgZfFaxJ69DmLazWaT3/JnO7RiynW1OXMOo49rjKwWMGK11eLB/GPG2/mde
-VjKgLvK2mk0xbtfa+h0B6VK7bmODHZqeP18NVm6HsBcXn7iclLgAC3SfWU1jucZK
+o4I/muF4o7SxYuTR960ynU5XklIkwAnDpzZkySVTZYyoASlGN0T+8d8i42D7IZpF
-x1lqzw9tAgMBAAECggEABWzxS1Y2wckblnXY57Z+sl6YdmLV+gxj2r8Qib7g4ZIk
+GojTs1lFAgMBAAECggEAIYthUi1lFBDd5gG4Rzlu+BlBIn5JhcqkCqLEBiJIFfOr
-lIlWR1OJNfw7kU4eryib4fc6nOh6O4AWZyYqAK6tqNQSS/eVG0LQTLTTEldHyVJL
+/4yuMRrvS3bNzqWt6xJ9MSAC4ZlN/VobRLnxL/QNymoiGYUKCT3Ww8nvPpPzR9OE
-dvBe+MsUQOj4nTndZW+QvFzbcm2D8lY5n2nBSxU5ypVoKZ1EqQzytFcLZpTN7d89
+sE68TUL9tJw/zZJcRMKwgvrGqSLimfq53MxxkE+kLdOc0v9C8YH8Re26mB5ZcWYa
-EPj0qDyrV4NZlWAwL1AygCwnlwhMQjXEalVF1ylXwU3QzyZ/6MgvF6d3SSUlh+sq
+7YFyZQpKsQYnsmu/05cMbpOQrQWhtmIqRoyn8mG/par2s3NzjtpSE9NINyz26uFc
-XefuyigXw484cQQgbzopv6niMOmGP3of+yV4JQqUSb3IDmmT68XjGd2Dkxl4iPki
+k/3ovFJQIHkUmTS7KHD3BgY5vuCqP98HramYnOysJ0WoYgvSDNCWw3037s5CCwJT
-6ZwXf3CCi+c+i/zVEcufgZ3SLf8D99kUGE7v7fZ6AQKBgQD1ZX3RAla9hIhxCf+O
+gCKuM+Ow6liFrj83RrdKBpm5QUGjfNpYP31o+QNP4QKBgQDSrUQ2XdgtAnibAV7u
-3D+I1j2LMrdjAh0ZKKqwMR4JnHX3mjQI6LwqIctPWTU8wYFECSh9klEclSdCa64s
+7kbxOxro0EhIKso0Y/6LbDQgcXgxLqltkmeqZgG8nC3Z793lhlSasz2snhzzooV5
-uI/GNpcqPXejd0cAAdqHEEeG5sHMDt0oFSurL4lyud0GtZvwlzLuwEweuDtvT9cJ
+5fTy1y8ikXqjhG0nNkInFyOhsI0auE28CFoDowaQd+5cmCatpN4Grqo5PNRXxm1w
-Wfvl86uyO36IW8JdvUprYDctrQKBgQDycZ697qutBieZlGkHpnYWUAeImVA878sJ
+HktfPEgoP11NNCFHvvN5fEKbbQKBgQDwVlOaV20IvW3IPq7cXZyiyabouFF9eTRo
-w44NuXHvMxBPz+lbJGAg8Cn8fcxNAPqHIraK+kx3po8cZGQywKHUWsxi23ozHoxo
+VJka1Uv+JtyvL2P0NKkjYHOdN8gRblWqxQtJoTNk020rVA4UP1heiXALy50gvj/p
-+bGqeQb9U661TnfdDspIXia+xilZt3mm5BPzOUuRqlh4Y9SOBpSWRmEhyw76w4ZP
+hMcybPTLYSPOhAGx838KIcvGR5oskP1aUCmFbFQzGELxhJ9diVVjxUtbG2DuwPKd
-OPxjWYAgwQKBgA/FehSYxeJgRjSdo+MWnK66tjHgDJE8bYpUZsP0JC4R9DL5oiaA
+tD9TLxT2OQKBgQCcdlHSjp+dzdgERmBa0ludjGfPv9/uuNizUBAbO6D690psPFtY
-brd2fI6Y+SbyeNBallObt8LSgzdtnEAbjIH8uDJqyOmknNePRvAvR6mP4xyuR+Bv
+JQMYaemgSd1DngEOFVWADt4e9M5Lose+YCoqr+UxpxmNlyv5kzJOFcFAs/4XeglB
-m+Lgp0DMWTw5J9CKpydZDItc49T/mJ5tPhdFVd+am0NAQnmr1MCZ6nHxAoGABS3Y
+PHKdgNW/NVKxMc6H54l9LPr+x05sYdGlEtqnP/3W5jhEvhJ5Vjc8YiyVgQKBgQCl
-LkaC9FdFUUqSU8+Chkd/YbOkuyiENdkvl6t2e52jo5DVc1T7mLiIrRQi4SI8N9bN
+zwjyrGo+42GACy7cPYE5FeIfIDqoVByB9guC5bD98JXEDu/opQQjsgFRcBCJZhOY
-/3oJWCT+uaSLX2ouCtNFunblzWHBrhxnZzTeqVq4SLc8aESAnbslKL4i8/+vYZlN
+M0UsURiB8ROaFu13rpQq9KrmmF0ZH+g8FSzQbzcbsTLg4VXCDXmR5esOKowFPypr
-s8xtiNcSvL+lMsOBORSXzpj/4Ot8WwTkn1qyGgECgYBKNTypzAHeLE6yVadFp3nQ
+Sm667BfTAGP++D5ya7MLmCv6+RKQ5XD8uEQQAaV2kQKBgAD8qeJuWIXZT0VKkQrn
-Ckq9yzvP/ib05rvgbvrne00YeOxqJ9gtTrzgh7koqJyX1L4NwdkEza4ilDWpucn0
+nIhgtzGERF/6sZdQGW2LxTbUDWG74AfFkkEbeBfwEkCZXY/xmnYqYABhvlSex8jU
-xiUZS4SoaJq6ZvcBYS62Yr1t8n09iG47YL8ibgtmH3L+svaotvpVxVK+d7BLevA/
+supU6Eea21esIxIub2zv/Np0ojUb6rlqTPS4Ox1E27D787EJ3VOXpriSD10vyNnZ
-ZboOWVe3icTy64BT3OQhmg==
+jel6uj2FOP9g54s+GzlSVg/T
 -----END RSA TESTING KEY-----`))
 
 func testingKey(s string) string { return strings.ReplaceAll(s, "TESTING KEY", "PRIVATE KEY") }

src/net/sendfile_unix_alt.go

@@ -53,6 +53,9 @@ func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
 		if err != nil {
 			return 0, err, false
 		}
+		if fi.Mode()&(fs.ModeSymlink|fs.ModeDevice|fs.ModeCharDevice|fs.ModeIrregular) != 0 {
+			return 0, nil, false
+		}
 
 		remain = fi.Size()
 	}

src/net/sendfile_unix_test.go

@@ -0,0 +1,86 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build unix
+
+package net
+
+import (
+	"internal/testpty"
+	"io"
+	"os"
+	"sync"
+	"syscall"
+	"testing"
+)
+
+// Issue 70763: test that we don't fail on sendfile from a tty.
+func TestCopyFromTTY(t *testing.T) {
+	pty, ttyName, err := testpty.Open()
+	if err != nil {
+		t.Skipf("skipping test because pty open failed: %v", err)
+	}
+	defer pty.Close()
+
+	// Use syscall.Open so that the tty is blocking.
+	ttyFD, err := syscall.Open(ttyName, syscall.O_RDWR, 0)
+	if err != nil {
+		t.Skipf("skipping test because tty open failed: %v", err)
+	}
+	defer syscall.Close(ttyFD)
+
+	tty := os.NewFile(uintptr(ttyFD), "tty")
+	defer tty.Close()
+
+	ln := newLocalListener(t, "tcp")
+	defer ln.Close()
+
+	ch := make(chan bool)
+
+	const data = "data\n"
+
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		conn, err := ln.Accept()
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		defer conn.Close()
+
+		buf := make([]byte, len(data))
+		if _, err := io.ReadFull(conn, buf); err != nil {
+			t.Error(err)
+		}
+
+		ch <- true
+	}()
+
+	conn, err := Dial("tcp", ln.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer conn.Close()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		if _, err := pty.Write([]byte(data)); err != nil {
+			t.Error(err)
+		}
+		<-ch
+		if err := pty.Close(); err != nil {
+			t.Error(err)
+		}
+	}()
+
+	lr := io.LimitReader(tty, int64(len(data)))
+	if _, err := io.Copy(conn, lr); err != nil {
+		t.Error(err)
+	}
+}

src/os/copy_test.go

@@ -0,0 +1,154 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package os_test
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"math/rand/v2"
+	"net"
+	"os"
+	"runtime"
+	"sync"
+	"testing"
+
+	"golang.org/x/net/nettest"
+)
+
+// Exercise sendfile/splice fast paths with a moderately large file.
+//
+// https://go.dev/issue/70000
+
+func TestLargeCopyViaNetwork(t *testing.T) {
+	const size = 10 * 1024 * 1024
+	dir := t.TempDir()
+
+	src, err := os.Create(dir + "/src")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer src.Close()
+	if _, err := io.CopyN(src, newRandReader(), size); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := src.Seek(0, 0); err != nil {
+		t.Fatal(err)
+	}
+
+	dst, err := os.Create(dir + "/dst")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer dst.Close()
+
+	client, server := createSocketPair(t, "tcp")
+	var wg sync.WaitGroup
+	wg.Add(2)
+	go func() {
+		defer wg.Done()
+		if n, err := io.Copy(dst, server); n != size || err != nil {
+			t.Errorf("copy to destination = %v, %v; want %v, nil", n, err, size)
+		}
+	}()
+	go func() {
+		defer wg.Done()
+		defer client.Close()
+		if n, err := io.Copy(client, src); n != size || err != nil {
+			t.Errorf("copy from source = %v, %v; want %v, nil", n, err, size)
+		}
+	}()
+	wg.Wait()
+
+	if _, err := dst.Seek(0, 0); err != nil {
+		t.Fatal(err)
+	}
+	if err := compareReaders(dst, io.LimitReader(newRandReader(), size)); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func compareReaders(a, b io.Reader) error {
+	bufa := make([]byte, 4096)
+	bufb := make([]byte, 4096)
+	for {
+		na, erra := io.ReadFull(a, bufa)
+		if erra != nil && erra != io.EOF {
+			return erra
+		}
+		nb, errb := io.ReadFull(b, bufb)
+		if errb != nil && errb != io.EOF {
+			return errb
+		}
+		if !bytes.Equal(bufa[:na], bufb[:nb]) {
+			return errors.New("contents mismatch")
+		}
+		if erra == io.EOF && errb == io.EOF {
+			break
+		}
+	}
+	return nil
+}
+
+type randReader struct {
+	rand *rand.Rand
+}
+
+func newRandReader() *randReader {
+	return &randReader{rand.New(rand.NewPCG(0, 0))}
+}
+
+func (r *randReader) Read(p []byte) (int, error) {
+	var v uint64
+	var n int
+	for i := range p {
+		if n == 0 {
+			v = r.rand.Uint64()
+			n = 8
+		}
+		p[i] = byte(v & 0xff)
+		v >>= 8
+		n--
+	}
+	return len(p), nil
+}
+
+func createSocketPair(t *testing.T, proto string) (client, server net.Conn) {
+	t.Helper()
+	if !nettest.TestableNetwork(proto) {
+		t.Skipf("%s does not support %q", runtime.GOOS, proto)
+	}
+
+	ln, err := nettest.NewLocalListener(proto)
+	if err != nil {
+		t.Fatalf("NewLocalListener error: %v", err)
+	}
+	t.Cleanup(func() {
+		if ln != nil {
+			ln.Close()
+		}
+		if client != nil {
+			client.Close()
+		}
+		if server != nil {
+			server.Close()
+		}
+	})
+	ch := make(chan struct{})
+	go func() {
+		var err error
+		server, err = ln.Accept()
+		if err != nil {
+			t.Errorf("Accept new connection error: %v", err)
+		}
+		ch <- struct{}{}
+	}()
+	client, err = net.Dial(proto, ln.Addr().String())
+	<-ch
+	if err != nil {
+		t.Fatalf("Dial new connection error: %v", err)
+	}
+	return client, server
+}

src/os/dir.go

@@ -132,15 +132,18 @@ func ReadDir(name string) ([]DirEntry, error) {
 // CopyFS copies the file system fsys into the directory dir,
 // creating dir if necessary.
 //
-// Newly created directories and files have their default modes
+// Files are created with mode 0o666 plus any execute permissions
-// where any bits from the file in fsys that are not part of the
+// from the source, and directories are created with mode 0o777
-// standard read, write, and execute permissions will be zeroed
+// (before umask).
-// out, and standard read and write permissions are set for owner,
-// group, and others while retaining any existing execute bits from
-// the file in fsys.
 //
-// Symbolic links in fsys are not supported, a *PathError with Err set
+// CopyFS will not overwrite existing files. If a file name in fsys
-// to ErrInvalid is returned on symlink.
+// already exists in the destination, CopyFS will return an error
+// such that errors.Is(err, fs.ErrExist) will be true.
+//
+// Symbolic links in fsys are not supported. A *PathError with Err set
+// to ErrInvalid is returned when copying from a symbolic link.
+//
+// Symbolic links in dir are followed.
 //
 // Copying stops at and returns the first error encountered.
 func CopyFS(dir string, fsys fs.FS) error {
@@ -174,7 +177,7 @@ func CopyFS(dir string, fsys fs.FS) error {
 		if err != nil {
 			return err
 		}
-		w, err := OpenFile(newPath, O_CREATE|O_TRUNC|O_WRONLY, 0666|info.Mode()&0777)
+		w, err := OpenFile(newPath, O_CREATE|O_EXCL|O_WRONLY, 0666|info.Mode()&0777)
 		if err != nil {
 			return err
 		}

src/os/example_test.go

@@ -61,7 +61,7 @@ func ExampleFileMode() {
 		log.Fatal(err)
 	}
 
-	fmt.Printf("permissions: %#o\n", fi.Mode().Perm()) // 0400, 0777, etc.
+	fmt.Printf("permissions: %#o\n", fi.Mode().Perm()) // 0o400, 0o777, etc.
 	switch mode := fi.Mode(); {
 	case mode.IsRegular():
 		fmt.Println("regular file")

src/os/exec_posix.go

@@ -35,10 +35,11 @@ func startProcess(name string, argv []string, attr *ProcAttr) (p *Process, err e
 		}
 	}
 
+	attrSys, shouldDupPidfd := ensurePidfd(attr.Sys)
 	sysattr := &syscall.ProcAttr{
 		Dir: attr.Dir,
 		Env: attr.Env,
-		Sys: ensurePidfd(attr.Sys),
+		Sys: attrSys,
 	}
 	if sysattr.Env == nil {
 		sysattr.Env, err = execenv.Default(sysattr.Sys)
@@ -63,7 +64,7 @@ func startProcess(name string, argv []string, attr *ProcAttr) (p *Process, err e
 	// For Windows, syscall.StartProcess above already returned a process handle.
 	if runtime.GOOS != "windows" {
 		var ok bool
-		h, ok = getPidfd(sysattr.Sys)
+		h, ok = getPidfd(sysattr.Sys, shouldDupPidfd)
 		if !ok {
 			return newPIDProcess(pid), nil
 		}

src/os/file.go

@@ -366,7 +366,7 @@ func Open(name string) (*File, error) {
 }
 
 // Create creates or truncates the named file. If the file already exists,
-// it is truncated. If the file does not exist, it is created with mode 0666
+// it is truncated. If the file does not exist, it is created with mode 0o666
 // (before umask). If successful, methods on the returned File can
 // be used for I/O; the associated file descriptor has mode O_RDWR.
 // If there is an error, it will be of type *PathError.
@@ -602,11 +602,11 @@ func UserHomeDir() (string, error) {
 // On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and
 // ModeSticky are used.
 //
-// On Windows, only the 0200 bit (owner writable) of mode is used; it
+// On Windows, only the 0o200 bit (owner writable) of mode is used; it
 // controls whether the file's read-only attribute is set or cleared.
 // The other bits are currently unused. For compatibility with Go 1.12
-// and earlier, use a non-zero mode. Use mode 0400 for a read-only
+// and earlier, use a non-zero mode. Use mode 0o400 for a read-only
-// file and 0600 for a readable+writable file.
+// file and 0o600 for a readable+writable file.
 //
 // On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive,
 // and ModeTemporary are used.

src/os/os_test.go

@@ -1376,8 +1376,7 @@ func TestChtimes(t *testing.T) {
 	t.Parallel()
 
 	f := newFile(t)
-
+	// This should be an empty file (see #68687, #68663).
-	f.Write([]byte("hello, world\n"))
 	f.Close()
 
 	testChtimes(t, f.Name())
@@ -1395,12 +1394,9 @@ func TestChtimesOmit(t *testing.T) {
 func testChtimesOmit(t *testing.T, omitAt, omitMt bool) {
 	t.Logf("omit atime: %v, mtime: %v", omitAt, omitMt)
 	file := newFile(t)
-	_, err := file.Write([]byte("hello, world\n"))
+	// This should be an empty file (see #68687, #68663).
-	if err != nil {
-		t.Fatal(err)
-	}
 	name := file.Name()
-	err = file.Close()
+	err := file.Close()
 	if err != nil {
 		t.Error(err)
 	}
@@ -3358,6 +3354,14 @@ func TestCopyFS(t *testing.T) {
 		t.Fatal("comparing two directories:", err)
 	}
 
+	// Test whether CopyFS disallows copying for disk filesystem when there is any
+	// existing file in the destination directory.
+	if err := CopyFS(tmpDir, fsys); !errors.Is(err, fs.ErrExist) {
+		t.Errorf("CopyFS should have failed and returned error when there is"+
+			"any existing file in the destination directory (in disk filesystem), "+
+			"got: %v, expected any error that indicates <file exists>", err)
+	}
+
 	// Test with memory filesystem.
 	fsys = fstest.MapFS{
 		"william":    {Data: []byte("Shakespeare\n")},
@@ -3395,6 +3399,14 @@ func TestCopyFS(t *testing.T) {
 	}); err != nil {
 		t.Fatal("comparing two directories:", err)
 	}
+
+	// Test whether CopyFS disallows copying for memory filesystem when there is any
+	// existing file in the destination directory.
+	if err := CopyFS(tmpDir, fsys); !errors.Is(err, fs.ErrExist) {
+		t.Errorf("CopyFS should have failed and returned error when there is"+
+			"any existing file in the destination directory (in memory filesystem), "+
+			"got: %v, expected any error that indicates <file exists>", err)
+	}
 }
 
 func TestCopyFSWithSymlinks(t *testing.T) {

src/os/pidfd_linux.go

@@ -8,20 +8,28 @@
 //  v5.3: pidfd_open syscall, clone3 syscall;
 //  v5.4: P_PIDFD idtype support for waitid syscall;
 //  v5.6: pidfd_getfd syscall.
+//
+// N.B. Alternative Linux implementations may not follow this ordering. e.g.,
+// QEMU user mode 7.2 added pidfd_open, but CLONE_PIDFD was not added until
+// 8.0.
 
 package os
 
 import (
 	"errors"
 	"internal/syscall/unix"
+	"runtime"
 	"sync"
 	"syscall"
 	"unsafe"
 )
 
-func ensurePidfd(sysAttr *syscall.SysProcAttr) *syscall.SysProcAttr {
+// ensurePidfd initializes the PidFD field in sysAttr if it is not already set.
+// It returns the original or modified SysProcAttr struct and a flag indicating
+// whether the PidFD should be duplicated before using.
+func ensurePidfd(sysAttr *syscall.SysProcAttr) (*syscall.SysProcAttr, bool) {
 	if !pidfdWorks() {
-		return sysAttr
+		return sysAttr, false
 	}
 
 	var pidfd int
@@ -29,23 +37,33 @@ func ensurePidfd(sysAttr *syscall.SysProcAttr) *syscall.SysProcAttr {
 	if sysAttr == nil {
 		return &syscall.SysProcAttr{
 			PidFD: &pidfd,
-		}
+		}, false
 	}
 	if sysAttr.PidFD == nil {
 		newSys := *sysAttr // copy
 		newSys.PidFD = &pidfd
-		return &newSys
+		return &newSys, false
 	}
 
-	return sysAttr
+	return sysAttr, true
 }
 
-func getPidfd(sysAttr *syscall.SysProcAttr) (uintptr, bool) {
+// getPidfd returns the value of sysAttr.PidFD (or its duplicate if needDup is
+// set) and a flag indicating whether the value can be used.
+func getPidfd(sysAttr *syscall.SysProcAttr, needDup bool) (uintptr, bool) {
 	if !pidfdWorks() {
 		return 0, false
 	}
 
-	return uintptr(*sysAttr.PidFD), true
+	h := *sysAttr.PidFD
+	if needDup {
+		dupH, e := unix.Fcntl(h, syscall.F_DUPFD_CLOEXEC, 0)
+		if e != nil {
+			return 0, false
+		}
+		h = dupH
+	}
+	return uintptr(h), true
 }
 
 func pidfdFind(pid int) (uintptr, error) {
@@ -126,14 +144,21 @@ func pidfdWorks() bool {
 
 var checkPidfdOnce = sync.OnceValue(checkPidfd)
 
-// checkPidfd checks whether all required pidfd-related syscalls work.
+// checkPidfd checks whether all required pidfd-related syscalls work. This
-// This consists of pidfd_open and pidfd_send_signal syscalls, and waitid
+// consists of pidfd_open and pidfd_send_signal syscalls, waitid syscall with
-// syscall with idtype of P_PIDFD.
+// idtype of P_PIDFD, and clone(CLONE_PIDFD).
 //
 // Reasons for non-working pidfd syscalls include an older kernel and an
 // execution environment in which the above system calls are restricted by
 // seccomp or a similar technology.
 func checkPidfd() error {
+	// In Android version < 12, pidfd-related system calls are not allowed
+	// by seccomp and trigger the SIGSYS signal. See issue #69065.
+	if runtime.GOOS == "android" {
+		ignoreSIGSYS()
+		defer restoreSIGSYS()
+	}
+
 	// Get a pidfd of the current process (opening of "/proc/self" won't
 	// work for waitid).
 	fd, err := unix.PidFDOpen(syscall.Getpid(), 0)
@@ -159,5 +184,27 @@ func checkPidfd() error {
 		return NewSyscallError("pidfd_send_signal", err)
 	}
 
+	// Verify that clone(CLONE_PIDFD) works.
+	//
+	// This shouldn't be necessary since pidfd_open was added in Linux 5.3,
+	// after CLONE_PIDFD in Linux 5.2, but some alternative Linux
+	// implementations may not adhere to this ordering.
+	if err := checkClonePidfd(); err != nil {
+		return err
+	}
+
 	return nil
 }
+
+// Provided by syscall.
+//
+//go:linkname checkClonePidfd
+func checkClonePidfd() error
+
+// Provided by runtime.
+//
+//go:linkname ignoreSIGSYS
+func ignoreSIGSYS()
+
+//go:linkname restoreSIGSYS
+func restoreSIGSYS()

src/os/pidfd_linux_test.go

@@ -6,8 +6,10 @@ package os_test
 
 import (
 	"errors"
+	"internal/syscall/unix"
 	"internal/testenv"
 	"os"
+	"os/exec"
 	"syscall"
 	"testing"
 )
@@ -57,3 +59,93 @@ func TestFindProcessViaPidfd(t *testing.T) {
 		t.Fatalf("Release: got %v, want <nil>", err)
 	}
 }
+
+func TestStartProcessWithPidfd(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	t.Parallel()
+
+	if err := os.CheckPidfdOnce(); err != nil {
+		// Non-pidfd code paths tested in exec_unix_test.go.
+		t.Skipf("skipping: pidfd not available: %v", err)
+	}
+
+	var pidfd int
+	p, err := os.StartProcess(testenv.GoToolPath(t), []string{"go"}, &os.ProcAttr{
+		Sys: &syscall.SysProcAttr{
+			PidFD: &pidfd,
+		},
+	})
+	if err != nil {
+		t.Fatalf("starting test process: %v", err)
+	}
+	defer syscall.Close(pidfd)
+
+	if _, err := p.Wait(); err != nil {
+		t.Fatalf("Wait: got %v, want <nil>", err)
+	}
+
+	// Check the pidfd is still valid
+	err = unix.PidFDSendSignal(uintptr(pidfd), syscall.Signal(0))
+	if !errors.Is(err, syscall.ESRCH) {
+		t.Errorf("SendSignal: got %v, want %v", err, syscall.ESRCH)
+	}
+}
+
+// Issue #69284
+func TestPidfdLeak(t *testing.T) {
+	testenv.MustHaveExec(t)
+	exe, err := os.Executable()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Find the next 10 descriptors.
+	// We need to get more than one descriptor in practice;
+	// the pidfd winds up not being the next descriptor.
+	const count = 10
+	want := make([]int, count)
+	for i := range count {
+		var err error
+		want[i], err = syscall.Open(exe, syscall.O_RDONLY, 0)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// Close the descriptors.
+	for _, d := range want {
+		syscall.Close(d)
+	}
+
+	// Start a process 10 times.
+	for range 10 {
+		// For testing purposes this has to be an absolute path.
+		// Otherwise we will fail finding the executable
+		// and won't start a process at all.
+		cmd := exec.Command("/noSuchExecutable")
+		cmd.Run()
+	}
+
+	// Open the next 10 descriptors again.
+	got := make([]int, count)
+	for i := range count {
+		var err error
+		got[i], err = syscall.Open(exe, syscall.O_RDONLY, 0)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// Close the descriptors
+	for _, d := range got {
+		syscall.Close(d)
+	}
+
+	t.Logf("got %v", got)
+	t.Logf("want %v", want)
+
+	// Allow some slack for runtime epoll descriptors and the like.
+	if got[count-1] > want[count-1]+5 {
+		t.Errorf("got descriptor %d, want %d", got[count-1], want[count-1])
+	}
+}

src/os/pidfd_other.go

@@ -8,11 +8,11 @@ package os
 
 import "syscall"
 
-func ensurePidfd(sysAttr *syscall.SysProcAttr) *syscall.SysProcAttr {
+func ensurePidfd(sysAttr *syscall.SysProcAttr) (*syscall.SysProcAttr, bool) {
-	return sysAttr
+	return sysAttr, false
 }
 
-func getPidfd(_ *syscall.SysProcAttr) (uintptr, bool) {
+func getPidfd(_ *syscall.SysProcAttr, _ bool) (uintptr, bool) {
 	return 0, false
 }
 

src/os/readfrom_linux_test.go

@@ -14,15 +14,12 @@ import (
 	"net"
 	. "os"
 	"path/filepath"
-	"runtime"
 	"strconv"
 	"strings"
 	"sync"
 	"syscall"
 	"testing"
 	"time"
-
-	"golang.org/x/net/nettest"
 )
 
 func TestCopyFileRange(t *testing.T) {
@@ -784,41 +781,3 @@ func testGetPollFDAndNetwork(t *testing.T, proto string) {
 		t.Fatalf("server Control error: %v", err)
 	}
 }
-
-func createSocketPair(t *testing.T, proto string) (client, server net.Conn) {
-	t.Helper()
-	if !nettest.TestableNetwork(proto) {
-		t.Skipf("%s does not support %q", runtime.GOOS, proto)
-	}
-
-	ln, err := nettest.NewLocalListener(proto)
-	if err != nil {
-		t.Fatalf("NewLocalListener error: %v", err)
-	}
-	t.Cleanup(func() {
-		if ln != nil {
-			ln.Close()
-		}
-		if client != nil {
-			client.Close()
-		}
-		if server != nil {
-			server.Close()
-		}
-	})
-	ch := make(chan struct{})
-	go func() {
-		var err error
-		server, err = ln.Accept()
-		if err != nil {
-			t.Errorf("Accept new connection error: %v", err)
-		}
-		ch <- struct{}{}
-	}()
-	client, err = net.Dial(proto, ln.Addr().String())
-	<-ch
-	if err != nil {
-		t.Fatalf("Dial new connection error: %v", err)
-	}
-	return client, server
-}

src/runtime/cgo/gcc_stack_unix.c

@@ -31,10 +31,11 @@ x_cgo_getstackbound(uintptr bounds[2])
 	pthread_attr_get_np(pthread_self(), &attr);
 	pthread_attr_getstack(&attr, &addr, &size); // low address
 #else
-	// We don't know how to get the current stacks, so assume they are the
+	// We don't know how to get the current stacks, leave it as
-	// same as the default stack bounds.
+	// 0 and the caller will use an estimate based on the current
-	pthread_attr_getstacksize(&attr, &size);
+	// SP.
-	addr = __builtin_frame_address(0) + 4096 - size;
+	addr = 0;
+	size = 0;
 #endif
 	pthread_attr_destroy(&attr);
 

src/runtime/cgocall.go

@@ -231,34 +231,6 @@ func cgocall(fn, arg unsafe.Pointer) int32 {
 func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) {
 	g0 := mp.g0
 
-	inBound := sp > g0.stack.lo && sp <= g0.stack.hi
-	if mp.ncgo > 0 && !inBound {
-		// ncgo > 0 indicates that this M was in Go further up the stack
-		// (it called C and is now receiving a callback).
-		//
-		// !inBound indicates that we were called with SP outside the
-		// expected system stack bounds (C changed the stack out from
-		// under us between the cgocall and cgocallback?).
-		//
-		// It is not safe for the C call to change the stack out from
-		// under us, so throw.
-
-		// Note that this case isn't possible for signal == true, as
-		// that is always passing a new M from needm.
-
-		// Stack is bogus, but reset the bounds anyway so we can print.
-		hi := g0.stack.hi
-		lo := g0.stack.lo
-		g0.stack.hi = sp + 1024
-		g0.stack.lo = sp - 32*1024
-		g0.stackguard0 = g0.stack.lo + stackGuard
-		g0.stackguard1 = g0.stackguard0
-
-		print("M ", mp.id, " procid ", mp.procid, " runtime: cgocallback with sp=", hex(sp), " out of bounds [", hex(lo), ", ", hex(hi), "]")
-		print("\n")
-		exit(2)
-	}
-
 	if !mp.isextra {
 		// We allocated the stack for standard Ms. Don't replace the
 		// stack bounds with estimated ones when we already initialized
@@ -266,26 +238,37 @@ func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) {
 		return
 	}
 
-	// This M does not have Go further up the stack. However, it may have
+	inBound := sp > g0.stack.lo && sp <= g0.stack.hi
-	// previously called into Go, initializing the stack bounds. Between
+	if inBound && mp.g0StackAccurate {
-	// that call returning and now the stack may have changed (perhaps the
+		// This M has called into Go before and has the stack bounds
-	// C thread is running a coroutine library). We need to update the
+		// initialized. We have the accurate stack bounds, and the SP
-	// stack bounds for this case.
+		// is in bounds. We expect it continues to run within the same
+		// bounds.
+		return
+	}
+
+	// We don't have an accurate stack bounds (either it never calls
+	// into Go before, or we couldn't get the accurate bounds), or the
+	// current SP is not within the previous bounds (the stack may have
+	// changed between calls). We need to update the stack bounds.
 	//
 	// N.B. we need to update the stack bounds even if SP appears to
-	// already be in bounds. Our "bounds" may actually be estimated dummy
+	// already be in bounds, if our bounds are estimated dummy bounds
-	// bounds (below). The actual stack bounds could have shifted but still
+	// (below). We may be in a different region within the same actual
-	// have partial overlap with our dummy bounds. If we failed to update
+	// stack bounds, but our estimates were not accurate. Or the actual
-	// in that case, we could find ourselves seemingly called near the
+	// stack bounds could have shifted but still have partial overlap with
-	// bottom of the stack bounds, where we quickly run out of space.
+	// our dummy bounds. If we failed to update in that case, we could find
+	// ourselves seemingly called near the bottom of the stack bounds, where
+	// we quickly run out of space.
 
 	// Set the stack bounds to match the current stack. If we don't
 	// actually know how big the stack is, like we don't know how big any
 	// scheduling stack is, but we assume there's at least 32 kB. If we
 	// can get a more accurate stack bound from pthread, use that, provided
-	// it actually contains SP..
+	// it actually contains SP.
 	g0.stack.hi = sp + 1024
 	g0.stack.lo = sp - 32*1024
+	mp.g0StackAccurate = false
 	if !signal && _cgo_getstackbound != nil {
 		// Don't adjust if called from the signal handler.
 		// We are on the signal stack, not the pthread stack.
@@ -296,12 +279,16 @@ func callbackUpdateSystemStack(mp *m, sp uintptr, signal bool) {
 		asmcgocall(_cgo_getstackbound, unsafe.Pointer(&bounds))
 		// getstackbound is an unsupported no-op on Windows.
 		//
+		// On Unix systems, if the API to get accurate stack bounds is
+		// not available, it returns zeros.
+		//
 		// Don't use these bounds if they don't contain SP. Perhaps we
 		// were called by something not using the standard thread
 		// stack.
 		if bounds[0] != 0 && sp > bounds[0] && sp <= bounds[1] {
 			g0.stack.lo = bounds[0]
 			g0.stack.hi = bounds[1]
+			mp.g0StackAccurate = true
 		}
 	}
 	g0.stackguard0 = g0.stack.lo + stackGuard
@@ -319,6 +306,8 @@ func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) {
 	}
 
 	sp := gp.m.g0.sched.sp // system sp saved by cgocallback.
+	oldStack := gp.m.g0.stack
+	oldAccurate := gp.m.g0StackAccurate
 	callbackUpdateSystemStack(gp.m, sp, false)
 
 	// The call from C is on gp.m's g0 stack, so we must ensure
@@ -338,9 +327,14 @@ func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) {
 	// stack. However, since we're returning to an earlier stack frame and
 	// need to pair with the entersyscall() call made by cgocall, we must
 	// save syscall* and let reentersyscall restore them.
+	//
+	// Note: savedsp and savedbp MUST be held in locals as an unsafe.Pointer.
+	// When we call into Go, the stack is free to be moved. If these locals
+	// aren't visible in the stack maps, they won't get updated properly,
+	// and will end up being stale when restored by reentersyscall.
 	savedsp := unsafe.Pointer(gp.syscallsp)
 	savedpc := gp.syscallpc
-	savedbp := gp.syscallbp
+	savedbp := unsafe.Pointer(gp.syscallbp)
 	exitsyscall() // coming out of cgo call
 	gp.m.incgo = false
 	if gp.m.isextra {
@@ -372,9 +366,15 @@ func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) {
 	osPreemptExtEnter(gp.m)
 
 	// going back to cgo call
-	reentersyscall(savedpc, uintptr(savedsp), savedbp)
+	reentersyscall(savedpc, uintptr(savedsp), uintptr(savedbp))
 
 	gp.m.winsyscall = winsyscall
+
+	// Restore the old g0 stack bounds
+	gp.m.g0.stack = oldStack
+	gp.m.g0.stackguard0 = oldStack.lo + stackGuard
+	gp.m.g0.stackguard1 = gp.m.g0.stackguard0
+	gp.m.g0StackAccurate = oldAccurate
 }
 
 func cgocallbackg1(fn, frame unsafe.Pointer, ctxt uintptr) {

src/runtime/coro.go

@@ -208,6 +208,18 @@ func coroswitch_m(gp *g) {
 	// directly if possible.
 	setGNoWB(&mp.curg, gnext)
 	setMNoWB(&gnext.m, mp)
+
+	// Synchronize with any out-standing goroutine profile. We're about to start
+	// executing, and an invariant of the profiler is that we tryRecordGoroutineProfile
+	// whenever a goroutine is about to start running.
+	//
+	// N.B. We must do this before transitioning to _Grunning but after installing gnext
+	// in curg, so that we have a valid curg for allocation (tryRecordGoroutineProfile
+	// may allocate).
+	if goroutineProfile.active {
+		tryRecordGoroutineProfile(gnext, nil, osyield)
+	}
+
 	if !gnext.atomicstatus.CompareAndSwap(_Gwaiting, _Grunning) {
 		// The CAS failed: use casgstatus, which will take care of
 		// coordinating with the garbage collector about the state change.

src/runtime/export_test.go

@@ -1886,3 +1886,30 @@ func (m *TraceMap) PutString(s string) (uint64, bool) {
 func (m *TraceMap) Reset() {
 	m.traceMap.reset()
 }
+
+func SetSpinInGCMarkDone(spin bool) {
+	gcDebugMarkDone.spinAfterRaggedBarrier.Store(spin)
+}
+
+func GCMarkDoneRestarted() bool {
+	// Only read this outside of the GC. If we're running during a GC, just report false.
+	mp := acquirem()
+	if gcphase != _GCoff {
+		releasem(mp)
+		return false
+	}
+	restarted := gcDebugMarkDone.restartedDueTo27993
+	releasem(mp)
+	return restarted
+}
+
+func GCMarkDoneResetRestartFlag() {
+	mp := acquirem()
+	for gcphase != _GCoff {
+		releasem(mp)
+		Gosched()
+		mp = acquirem()
+	}
+	gcDebugMarkDone.restartedDueTo27993 = false
+	releasem(mp)
+}

src/runtime/gc_test.go

@@ -6,6 +6,8 @@ package runtime_test
 
 import (
 	"fmt"
+	"internal/testenv"
+	"internal/weak"
 	"math/bits"
 	"math/rand"
 	"os"
@@ -787,3 +789,78 @@ func TestMemoryLimitNoGCPercent(t *testing.T) {
 func TestMyGenericFunc(t *testing.T) {
 	runtime.MyGenericFunc[int]()
 }
+
+func TestWeakToStrongMarkTermination(t *testing.T) {
+	testenv.MustHaveParallelism(t)
+
+	type T struct {
+		a *int
+		b int
+	}
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
+	defer debug.SetGCPercent(debug.SetGCPercent(-1))
+	w := make([]weak.Pointer[T], 2048)
+
+	// Make sure there's no out-standing GC from a previous test.
+	runtime.GC()
+
+	// Create many objects with a weak pointers to them.
+	for i := range w {
+		x := new(T)
+		x.a = new(int)
+		w[i] = weak.Make(x)
+	}
+
+	// Reset the restart flag.
+	runtime.GCMarkDoneResetRestartFlag()
+
+	// Prevent mark termination from completing.
+	runtime.SetSpinInGCMarkDone(true)
+
+	// Start a GC, and wait a little bit to get something spinning in mark termination.
+	// Simultaneously, fire off another goroutine to disable spinning. If everything's
+	// working correctly, then weak.Strong will block, so we need to make sure something
+	// prevents the GC from continuing to spin.
+	done := make(chan struct{})
+	go func() {
+		runtime.GC()
+		done <- struct{}{}
+	}()
+	go func() {
+		time.Sleep(100 * time.Millisecond)
+
+		// Let mark termination continue.
+		runtime.SetSpinInGCMarkDone(false)
+	}()
+	time.Sleep(10 * time.Millisecond)
+
+	// Perform many weak->strong conversions in the critical window.
+	var wg sync.WaitGroup
+	for _, wp := range w {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			wp.Strong()
+		}()
+	}
+
+	// Make sure the GC completes.
+	<-done
+
+	// Make sure all the weak->strong conversions finish.
+	wg.Wait()
+
+	// The bug is triggered if there's still mark work after gcMarkDone stops the world.
+	//
+	// This can manifest in one of two ways today:
+	// - An exceedingly rare crash in mark termination.
+	// - gcMarkDone restarts, as if issue #27993 is at play.
+	//
+	// Check for the latter. This is a fairly controlled environment, so #27993 is very
+	// unlikely to happen (it's already rare to begin with) but we'll always _appear_ to
+	// trigger the same bug if weak->strong conversions aren't properly coordinated with
+	// mark termination.
+	if runtime.GCMarkDoneRestarted() {
+		t.Errorf("gcMarkDone restarted")
+	}
+}

src/runtime/lockrank.go

@@ -17,6 +17,7 @@ const (
 	lockRankDefer
 	lockRankSweepWaiters
 	lockRankAssistQueue
+	lockRankStrongFromWeakQueue
 	lockRankSweep
 	lockRankTestR
 	lockRankTestW
@@ -90,6 +91,7 @@ var lockNames = []string{
 	lockRankDefer:               "defer",
 	lockRankSweepWaiters:        "sweepWaiters",
 	lockRankAssistQueue:         "assistQueue",
+	lockRankStrongFromWeakQueue: "strongFromWeakQueue",
 	lockRankSweep:               "sweep",
 	lockRankTestR:               "testR",
 	lockRankTestW:               "testW",
@@ -169,6 +171,7 @@ var lockPartialOrder [][]lockRank = [][]lockRank{
 	lockRankDefer:               {},
 	lockRankSweepWaiters:        {},
 	lockRankAssistQueue:         {},
+	lockRankStrongFromWeakQueue: {},
 	lockRankSweep:               {},
 	lockRankTestR:               {},
 	lockRankTestW:               {},
@@ -180,11 +183,11 @@ var lockPartialOrder [][]lockRank = [][]lockRank{
 	lockRankPollDesc:            {},
 	lockRankWakeableSleep:       {},
 	lockRankHchan:               {lockRankSysmon, lockRankScavenge, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankWakeableSleep, lockRankHchan},
-	lockRankAllocmR:         {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan},
+	lockRankAllocmR:             {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan},
-	lockRankExecR:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan},
+	lockRankExecR:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan},
-	lockRankSched:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR},
+	lockRankSched:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR},
-	lockRankAllg:            {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched},
+	lockRankAllg:                {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched},
-	lockRankAllp:            {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched},
+	lockRankAllp:                {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched},
 	lockRankNotifyList:          {},
 	lockRankSudog:               {lockRankSysmon, lockRankScavenge, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankWakeableSleep, lockRankHchan, lockRankNotifyList},
 	lockRankTimers:              {lockRankSysmon, lockRankScavenge, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankTimers},
@@ -196,29 +199,29 @@ var lockPartialOrder [][]lockRank = [][]lockRank{
 	lockRankUserArenaState:      {},
 	lockRankTraceBuf:            {lockRankSysmon, lockRankScavenge},
 	lockRankTraceStrings:        {lockRankSysmon, lockRankScavenge, lockRankTraceBuf},
-	lockRankFin:             {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankFin:                 {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankSpanSetSpine:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankSpanSetSpine:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankMspanSpecial:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankMspanSpecial:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankTraceTypeTab:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankTraceTypeTab:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankGcBitsArenas:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankMspanSpecial},
+	lockRankGcBitsArenas:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankMspanSpecial},
-	lockRankProfInsert:      {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankProfInsert:          {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankProfBlock:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankProfBlock:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankProfMemActive:   {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
+	lockRankProfMemActive:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings},
-	lockRankProfMemFuture:   {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankProfMemActive},
+	lockRankProfMemFuture:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankProfMemActive},
-	lockRankGscan:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture},
+	lockRankGscan:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture},
-	lockRankStackpool:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
+	lockRankStackpool:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
-	lockRankStackLarge:      {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
+	lockRankStackLarge:          {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
-	lockRankHchanLeaf:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankHchanLeaf},
+	lockRankHchanLeaf:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankHchanLeaf},
-	lockRankWbufSpans:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
+	lockRankWbufSpans:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan},
-	lockRankMheap:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans},
+	lockRankMheap:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans},
-	lockRankMheapSpecial:    {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap},
+	lockRankMheapSpecial:        {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap},
-	lockRankGlobalAlloc:     {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap, lockRankMheapSpecial},
+	lockRankGlobalAlloc:         {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap, lockRankMheapSpecial},
-	lockRankTrace:           {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap},
+	lockRankTrace:               {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap},
-	lockRankTraceStackTab:   {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap, lockRankTrace},
+	lockRankTraceStackTab:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankDefer, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollCache, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR, lockRankExecR, lockRankSched, lockRankAllg, lockRankAllp, lockRankNotifyList, lockRankSudog, lockRankTimers, lockRankTimer, lockRankNetpollInit, lockRankRoot, lockRankItab, lockRankReflectOffs, lockRankUserArenaState, lockRankTraceBuf, lockRankTraceStrings, lockRankFin, lockRankSpanSetSpine, lockRankMspanSpecial, lockRankGcBitsArenas, lockRankProfInsert, lockRankProfBlock, lockRankProfMemActive, lockRankProfMemFuture, lockRankGscan, lockRankStackpool, lockRankStackLarge, lockRankWbufSpans, lockRankMheap, lockRankTrace},
 	lockRankPanic:               {},
 	lockRankDeadlock:            {lockRankPanic, lockRankDeadlock},
 	lockRankRaceFini:            {lockRankPanic},
-	lockRankAllocmRInternal: {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankAllocmW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR},
+	lockRankAllocmRInternal:     {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankAllocmW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankAllocmR},
-	lockRankExecRInternal:   {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankExecR},
+	lockRankExecRInternal:       {lockRankSysmon, lockRankScavenge, lockRankForcegc, lockRankSweepWaiters, lockRankAssistQueue, lockRankStrongFromWeakQueue, lockRankSweep, lockRankTestR, lockRankTimerSend, lockRankExecW, lockRankCpuprof, lockRankPollDesc, lockRankWakeableSleep, lockRankHchan, lockRankExecR},
 	lockRankTestRInternal:       {lockRankTestR, lockRankTestW},
 }

src/runtime/map.go

@@ -1209,6 +1209,11 @@ func (h *hmap) sameSizeGrow() bool {
 	return h.flags&sameSizeGrow != 0
 }
 
+//go:linkname sameSizeGrowForIssue69110Test
+func sameSizeGrowForIssue69110Test(h *hmap) bool {
+	return h.sameSizeGrow()
+}
+
 // noldbuckets calculates the number of buckets prior to the current map growth.
 func (h *hmap) noldbuckets() uintptr {
 	oldB := h.B
@@ -1668,7 +1673,16 @@ func moveToBmap(t *maptype, h *hmap, dst *bmap, pos int, src *bmap) (*bmap, int)
 }
 
 func mapclone2(t *maptype, src *hmap) *hmap {
-	dst := makemap(t, src.count, nil)
+	hint := src.count
+	if overLoadFactor(hint, src.B) {
+		// Note: in rare cases (e.g. during a same-sized grow) the map
+		// can be overloaded. Make sure we don't allocate a destination
+		// bucket array larger than the source bucket array.
+		// This will cause the cloned map to be overloaded also,
+		// but that's better than crashing. See issue 69110.
+		hint = int(loadFactorNum * (bucketShift(src.B) / loadFactorDen))
+	}
+	dst := makemap(t, hint, nil)
 	dst.hash0 = src.hash0
 	dst.nevacuate = 0
 	// flags do not need to be copied here, just like a new map has no flags.

src/runtime/mgc.go

@@ -190,6 +190,7 @@ func gcinit() {
 	work.markDoneSema = 1
 	lockInit(&work.sweepWaiters.lock, lockRankSweepWaiters)
 	lockInit(&work.assistQueue.lock, lockRankAssistQueue)
+	lockInit(&work.strongFromWeak.lock, lockRankStrongFromWeakQueue)
 	lockInit(&work.wbufSpans.lock, lockRankWbufSpans)
 }
 
@@ -418,6 +419,26 @@ type workType struct {
 		list gList
 	}
 
+	// strongFromWeak controls how the GC interacts with weak->strong
+	// pointer conversions.
+	strongFromWeak struct {
+		// block is a flag set during mark termination that prevents
+		// new weak->strong conversions from executing by blocking the
+		// goroutine and enqueuing it onto q.
+		//
+		// Mutated only by one goroutine at a time in gcMarkDone,
+		// with globally-synchronizing events like forEachP and
+		// stopTheWorld.
+		block bool
+
+		// q is a queue of goroutines that attempted to perform a
+		// weak->strong conversion during mark termination.
+		//
+		// Protected by lock.
+		lock mutex
+		q    gQueue
+	}
+
 	// cycles is the number of completed GC cycles, where a GC
 	// cycle is sweep termination, mark, mark termination, and
 	// sweep. This differs from memstats.numgc, which is
@@ -800,6 +821,19 @@ func gcStart(trigger gcTrigger) {
 // This is protected by markDoneSema.
 var gcMarkDoneFlushed uint32
 
+// gcDebugMarkDone contains fields used to debug/test mark termination.
+var gcDebugMarkDone struct {
+	// spinAfterRaggedBarrier forces gcMarkDone to spin after it executes
+	// the ragged barrier.
+	spinAfterRaggedBarrier atomic.Bool
+
+	// restartedDueTo27993 indicates that we restarted mark termination
+	// due to the bug described in issue #27993.
+	//
+	// Protected by worldsema.
+	restartedDueTo27993 bool
+}
+
 // gcMarkDone transitions the GC from mark to mark termination if all
 // reachable objects have been marked (that is, there are no grey
 // objects and can be no more in the future). Otherwise, it flushes
@@ -842,6 +876,10 @@ top:
 	// stop the world later, so acquire worldsema now.
 	semacquire(&worldsema)
 
+	// Prevent weak->strong conversions from generating additional
+	// GC work. forEachP will guarantee that it is observed globally.
+	work.strongFromWeak.block = true
+
 	// Flush all local buffers and collect flushedWork flags.
 	gcMarkDoneFlushed = 0
 	forEachP(waitReasonGCMarkTermination, func(pp *p) {
@@ -872,6 +910,10 @@ top:
 		goto top
 	}
 
+	// For debugging/testing.
+	for gcDebugMarkDone.spinAfterRaggedBarrier.Load() {
+	}
+
 	// There was no global work, no local work, and no Ps
 	// communicated work since we took markDoneSema. Therefore
 	// there are no grey objects and no more objects can be
@@ -910,6 +952,8 @@ top:
 		}
 	})
 	if restart {
+		gcDebugMarkDone.restartedDueTo27993 = true
+
 		getg().m.preemptoff = ""
 		systemstack(func() {
 			// Accumulate the time we were stopped before we had to start again.
@@ -936,6 +980,11 @@ top:
 	// start the world again.
 	gcWakeAllAssists()
 
+	// Wake all blocked weak->strong conversions. These will run
+	// when we start the world again.
+	work.strongFromWeak.block = false
+	gcWakeAllStrongFromWeak()
+
 	// Likewise, release the transition lock. Blocked
 	// workers and assists will run when we start the
 	// world again.

src/runtime/mheap.go

@@ -2049,8 +2049,19 @@ func internal_weak_runtime_registerWeakPointer(p unsafe.Pointer) unsafe.Pointer
 func internal_weak_runtime_makeStrongFromWeak(u unsafe.Pointer) unsafe.Pointer {
 	handle := (*atomic.Uintptr)(u)
 
-	// Prevent preemption. We want to make sure that another GC cycle can't start.
+	// Prevent preemption. We want to make sure that another GC cycle can't start
+	// and that work.strongFromWeak.block can't change out from under us.
 	mp := acquirem()
+
+	// Yield to the GC if necessary.
+	if work.strongFromWeak.block {
+		releasem(mp)
+
+		// Try to park and wait for mark termination.
+		// N.B. gcParkStrongFromWeak calls acquirem before returning.
+		mp = gcParkStrongFromWeak()
+	}
+
 	p := handle.Load()
 	if p == 0 {
 		releasem(mp)
@@ -2073,14 +2084,67 @@ func internal_weak_runtime_makeStrongFromWeak(u unsafe.Pointer) unsafe.Pointer {
 	// Even if we just swept some random span that doesn't contain this object, because
 	// this object is long dead and its memory has since been reused, we'll just observe nil.
 	ptr := unsafe.Pointer(handle.Load())
+
+	// This is responsible for maintaining the same GC-related
+	// invariants as the Yuasa part of the write barrier. During
+	// the mark phase, it's possible that we just created the only
+	// valid pointer to the object pointed to by ptr. If it's only
+	// ever referenced from our stack, and our stack is blackened
+	// already, we could fail to mark it. So, mark it now.
+	if gcphase != _GCoff {
+		shade(uintptr(ptr))
+	}
 	releasem(mp)
+
+	// Explicitly keep ptr alive. This seems unnecessary since we return ptr,
+	// but let's be explicit since it's important we keep ptr alive across the
+	// call to shade.
+	KeepAlive(ptr)
 	return ptr
 }
 
+// gcParkStrongFromWeak puts the current goroutine on the weak->strong queue and parks.
+func gcParkStrongFromWeak() *m {
+	// Prevent preemption as we check strongFromWeak, so it can't change out from under us.
+	mp := acquirem()
+
+	for work.strongFromWeak.block {
+		lock(&work.strongFromWeak.lock)
+		releasem(mp) // N.B. Holding the lock prevents preemption.
+
+		// Queue ourselves up.
+		work.strongFromWeak.q.pushBack(getg())
+
+		// Park.
+		goparkunlock(&work.strongFromWeak.lock, waitReasonGCWeakToStrongWait, traceBlockGCWeakToStrongWait, 2)
+
+		// Re-acquire the current M since we're going to check the condition again.
+		mp = acquirem()
+
+		// Re-check condition. We may have awoken in the next GC's mark termination phase.
+	}
+	return mp
+}
+
+// gcWakeAllStrongFromWeak wakes all currently blocked weak->strong
+// conversions. This is used at the end of a GC cycle.
+//
+// work.strongFromWeak.block must be false to prevent woken goroutines
+// from immediately going back to sleep.
+func gcWakeAllStrongFromWeak() {
+	lock(&work.strongFromWeak.lock)
+	list := work.strongFromWeak.q.popList()
+	injectglist(&list)
+	unlock(&work.strongFromWeak.lock)
+}
+
 // Retrieves or creates a weak pointer handle for the object p.
 func getOrAddWeakHandle(p unsafe.Pointer) *atomic.Uintptr {
 	// First try to retrieve without allocating.
 	if handle := getWeakHandle(p); handle != nil {
+		// Keep p alive for the duration of the function to ensure
+		// that it cannot die while we're trying to do this.
+		KeepAlive(p)
 		return handle
 	}
 
@@ -2105,7 +2169,17 @@ func getOrAddWeakHandle(p unsafe.Pointer) *atomic.Uintptr {
 			scanblock(uintptr(unsafe.Pointer(&s.handle)), goarch.PtrSize, &oneptrmask[0], gcw, nil)
 			releasem(mp)
 		}
-		return s.handle
+
+		// Keep p alive for the duration of the function to ensure
+		// that it cannot die while we're trying to do this.
+		//
+		// Same for handle, which is only stored in the special.
+		// There's a window where it might die if we don't keep it
+		// alive explicitly. Returning it here is probably good enough,
+		// but let's be defensive and explicit. See #70455.
+		KeepAlive(p)
+		KeepAlive(handle)
+		return handle
 	}
 
 	// There was an existing handle. Free the special
@@ -2124,8 +2198,11 @@ func getOrAddWeakHandle(p unsafe.Pointer) *atomic.Uintptr {
 	}
 
 	// Keep p alive for the duration of the function to ensure
-	// that it cannot die while we're trying to this.
+	// that it cannot die while we're trying to do this.
+	//
+	// Same for handle, just to be defensive.
 	KeepAlive(p)
+	KeepAlive(handle)
 	return handle
 }
 
@@ -2154,6 +2231,9 @@ func getWeakHandle(p unsafe.Pointer) *atomic.Uintptr {
 	unlock(&span.speciallock)
 	releasem(mp)
 
+	// Keep p alive for the duration of the function to ensure
+	// that it cannot die while we're trying to do this.
+	KeepAlive(p)
 	return handle
 }
 

src/runtime/mklockrank.go

@@ -50,6 +50,7 @@ NONE < defer;
 NONE <
   sweepWaiters,
   assistQueue,
+  strongFromWeakQueue,
   sweep;
 
 # Test only
@@ -66,6 +67,7 @@ assistQueue,
   hchan,
   pollDesc, # pollDesc can interact with timers, which can lock sched.
   scavenge,
+  strongFromWeakQueue,
   sweep,
   sweepWaiters,
   testR,

src/runtime/mprof.go

@@ -1136,11 +1136,12 @@ func expandFrames(p []BlockProfileRecord) {
 	for i := range p {
 		cf := CallersFrames(p[i].Stack())
 		j := 0
-		for ; j < len(expandedStack); j++ {
+		for j < len(expandedStack) {
 			f, more := cf.Next()
 			// f.PC is a "call PC", but later consumers will expect
 			// "return PCs"
 			expandedStack[j] = f.PC + 1
+			j++
 			if !more {
 				break
 			}
@@ -1270,7 +1271,8 @@ func pprof_mutexProfileInternal(p []profilerecord.BlockProfileRecord) (n int, ok
 // of calling ThreadCreateProfile directly.
 func ThreadCreateProfile(p []StackRecord) (n int, ok bool) {
 	return threadCreateProfileInternal(len(p), func(r profilerecord.StackRecord) {
-		copy(p[0].Stack0[:], r.Stack)
+		i := copy(p[0].Stack0[:], r.Stack)
+		clear(p[0].Stack0[i:])
 		p = p[1:]
 	})
 }
@@ -1649,7 +1651,8 @@ func GoroutineProfile(p []StackRecord) (n int, ok bool) {
 		return
 	}
 	for i, mr := range records[0:n] {
-		copy(p[i].Stack0[:], mr.Stack)
+		l := copy(p[i].Stack0[:], mr.Stack)
+		clear(p[i].Stack0[l:])
 	}
 	return
 }

src/runtime/os_linux.go

@@ -881,6 +881,7 @@ func runPerThreadSyscall() {
 const (
 	_SI_USER     = 0
 	_SI_TKILL    = -6
+	_SYS_SECCOMP = 1
 )
 
 // sigFromUser reports whether the signal was sent because of a call
@@ -892,6 +893,14 @@ func (c *sigctxt) sigFromUser() bool {
 	return code == _SI_USER || code == _SI_TKILL
 }
 
+// sigFromSeccomp reports whether the signal was sent from seccomp.
+//
+//go:nosplit
+func (c *sigctxt) sigFromSeccomp() bool {
+	code := int32(c.sigcode())
+	return code == _SYS_SECCOMP
+}
+
 //go:nosplit
 func mprotect(addr unsafe.Pointer, n uintptr, prot int32) (ret int32, errno int32) {
 	r, _, err := syscall.Syscall6(syscall.SYS_MPROTECT, uintptr(addr), n, uintptr(prot), 0, 0, 0)

src/runtime/os_unix_nonlinux.go

@@ -13,3 +13,10 @@ package runtime
 func (c *sigctxt) sigFromUser() bool {
 	return c.sigcode() == _SI_USER
 }
+
+// sigFromSeccomp reports whether the signal was sent from seccomp.
+//
+//go:nosplit
+func (c *sigctxt) sigFromSeccomp() bool {
+	return false
+}