runtime, runtime/pprof: add Frames to get file/line for Callers

This indirectly implements a small fix for runtime/pprof: it used to
look for runtime.gopanic when it should have been looking for
runtime.sigpanic.

Update #11432.

Change-Id: I5e3f5203b2ac5463efd85adf6636e64174aacb1d
Reviewed-on: https://go-review.googlesource.com/19869
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/runtime/callers_test.go

@@ -0,0 +1,83 @@
+// Copyright 2016 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 runtime_test
+
+import (
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func f1(pan bool) []uintptr {
+	return f2(pan) // line 14
+}
+
+func f2(pan bool) []uintptr {
+	return f3(pan) // line 18
+}
+
+func f3(pan bool) []uintptr {
+	if pan {
+		panic("f3") // line 23
+	}
+	ret := make([]uintptr, 20)
+	return ret[:runtime.Callers(0, ret)] // line 26
+}
+
+func testCallers(t *testing.T, pcs []uintptr, pan bool) {
+	m := make(map[string]int, len(pcs))
+	frames := runtime.CallersFrames(pcs)
+	for {
+		frame, more := frames.Next()
+		if frame.Function != "" {
+			m[frame.Function] = frame.Line
+		}
+		if !more {
+			break
+		}
+	}
+
+	var seen []string
+	for k := range m {
+		seen = append(seen, k)
+	}
+	t.Logf("functions seen: %s", strings.Join(seen, " "))
+
+	var f3Line int
+	if pan {
+		f3Line = 23
+	} else {
+		f3Line = 26
+	}
+	want := []struct {
+		name string
+		line int
+	}{
+		{"f1", 14},
+		{"f2", 18},
+		{"f3", f3Line},
+	}
+	for _, w := range want {
+		if got := m["runtime_test."+w.name]; got != w.line {
+			t.Errorf("%s is line %d, want %d", w.name, got, w.line)
+		}
+	}
+}
+
+func TestCallers(t *testing.T) {
+	testCallers(t, f1(false), false)
+}
+
+func TestCallersPanic(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Fatal("did not panic")
+		}
+		pcs := make([]uintptr, 20)
+		pcs = pcs[:runtime.Callers(0, pcs)]
+		testCallers(t, pcs, true)
+	}()
+	f1(true)
+}

src/runtime/extern.go

@@ -191,12 +191,9 @@ func Caller(skip int) (pc uintptr, file string, line int, ok bool) {
 //
 // Note that since each slice entry pc[i] is a return program counter,
 // looking up the file and line for pc[i] (for example, using (*Func).FileLine)
-// will return the file and line number of the instruction immediately
+// will normally return the file and line number of the instruction immediately
 // following the call.
-// To look up the file and line number of the call itself, use pc[i]-1.
-// As an exception to this rule, if pc[i-1] corresponds to the function
-// runtime.sigpanic, then pc[i] is the program counter of a faulting
-// instruction and should be used without any subtraction.
+// To easily look up file/line information for the call sequence, use Frames.
 func Callers(skip int, pc []uintptr) int {
 	// runtime.callers uses pc.array==nil as a signal
 	// to print a stack trace.  Pick off 0-length pc here

src/runtime/pprof/pprof.go

@@ -325,33 +325,24 @@ func printCountProfile(w io.Writer, debug int, name string, p countProfile) erro
 // for a single stack trace.
 func printStackRecord(w io.Writer, stk []uintptr, allFrames bool) {
 	show := allFrames
-	wasPanic := false
-	for i, pc := range stk {
-		f := runtime.FuncForPC(pc)
-		if f == nil {
+	frames := runtime.CallersFrames(stk)
+	for {
+		frame, more := frames.Next()
+		name := frame.Function
+		if name == "" {
 			show = true
-			fmt.Fprintf(w, "#\t%#x\n", pc)
-			wasPanic = false
+			fmt.Fprintf(w, "#\t%#x\n", frame.PC)
 		} else {
-			tracepc := pc
-			// Back up to call instruction.
-			if i > 0 && pc > f.Entry() && !wasPanic {
-				if runtime.GOARCH == "386" || runtime.GOARCH == "amd64" {
-					tracepc--
-				} else {
-					tracepc -= 4 // arm, etc
-				}
-			}
-			file, line := f.FileLine(tracepc)
-			name := f.Name()
 			// Hide runtime.goexit and any runtime functions at the beginning.
 			// This is useful mainly for allocation traces.
-			wasPanic = name == "runtime.gopanic"
 			if name == "runtime.goexit" || !show && strings.HasPrefix(name, "runtime.") {
 				continue
 			}
 			show = true
-			fmt.Fprintf(w, "#\t%#x\t%s+%#x\t%s:%d\n", pc, name, pc-f.Entry(), file, line)
+			fmt.Fprintf(w, "#\t%#x\t%s+%#x\t%s:%d\n", frame.PC, name, frame.PC-frame.Entry, frame.File, frame.Line)
+		}
+		if !more {
+			break
 		}
 	}
 	if !show {

src/runtime/symtab.go

@@ -9,6 +9,84 @@ import (
 	"unsafe"
 )
 
+// Frames may be used to get function/file/line information for a
+// slice of PC values returned by Callers.
+type Frames struct {
+	callers []uintptr
+
+	// If previous caller in iteration was a panic, then
+	// ci.callers[0] is the address of the faulting instruction
+	// instead of the return address of the call.
+	wasPanic bool
+}
+
+// Frame is the information returned by Frames for each call frame.
+type Frame struct {
+	// Program counter for this frame; multiple frames may have
+	// the same PC value.
+	PC uintptr
+
+	// Func for this frame; may be nil for non-Go code or fully
+	// inlined functions.
+	Func *Func
+
+	// Function name, file name, and line number for this call frame.
+	// May be the empty string or zero if not known.
+	// If Func is not nil then Function == Func.Name().
+	Function string
+	File     string
+	Line     int
+
+	// Entry point for the function; may be zero if not known.
+	// If Func is not nil then Entry == Func.Entry().
+	Entry uintptr
+}
+
+// CallersFrames takes a slice of PC values returned by Callers and
+// prepares to return function/file/line information.
+// Do not change the slice until you are done with the Frames.
+func CallersFrames(callers []uintptr) *Frames {
+	return &Frames{callers, false}
+}
+
+// Next returns frame information for the next caller.
+// If more is false, there are no more callers (the Frame value is valid).
+func (ci *Frames) Next() (frame Frame, more bool) {
+	if len(ci.callers) == 0 {
+		ci.wasPanic = false
+		return Frame{}, false
+	}
+	pc := ci.callers[0]
+	ci.callers = ci.callers[1:]
+	more = len(ci.callers) > 0
+	f := FuncForPC(pc)
+	if f == nil {
+		ci.wasPanic = false
+		return Frame{}, more
+	}
+
+	entry := f.Entry()
+	xpc := pc
+	if xpc > entry && !ci.wasPanic {
+		xpc--
+	}
+	file, line := f.FileLine(xpc)
+
+	function := f.Name()
+	ci.wasPanic = entry == sigpanicPC
+
+	frame = Frame{
+		PC:       xpc,
+		Func:     f,
+		Function: function,
+		File:     file,
+		Line:     line,
+		Entry:    entry,
+	}
+
+	return frame, more
+}
+
 // NOTE: Func does not expose the actual unexported fields, because we return *Func
 // values to users, and we want to keep them from being able to overwrite the data
 // with (say) *f = Func{}.