diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 8ae96a031e..8834c3db5a 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -15,6 +15,7 @@ import (
 	"go/token"
 	"io"
 	"os"
+	"path/filepath"
 	"sort"
 	"strings"
 )
@@ -526,7 +527,7 @@ func (p *Package) writeOutput(f *File, srcfile string) {
 	if strings.HasSuffix(base, ".go") {
 		base = base[0 : len(base)-3]
 	}
-	base = strings.Map(slashToUnderscore, base)
+	base = filepath.Base(base)
 	fgo1 := creat(*objDir + base + ".cgo1.go")
 	fgcc := creat(*objDir + base + ".cgo2.c")
 
diff --git a/src/cmd/go/go_test.go b/src/cmd/go/go_test.go
index 9dd5f8347c..075f430778 100644
--- a/src/cmd/go/go_test.go
+++ b/src/cmd/go/go_test.go
@@ -2439,16 +2439,16 @@ func TestCoverageErrorLine(t *testing.T) {
 	tg.setenv("GOTMPDIR", tg.tempdir)
 
 	tg.runFail("test", "coverbad")
-	tg.grepStderr(`coverbad[\\/]p.go:4`, "did not find correct line number for error")
+	tg.grepStderr(`coverbad[\\/]p\.go:4`, "did not find coverbad/p.go:4")
+	tg.grepStderr(`coverbad[\\/]p1\.go:6`, "did not find coverbad/p1.go:6")
 	tg.grepStderrNot(regexp.QuoteMeta(tg.tempdir), "found temporary directory in error")
 	stderr := tg.getStderr()
 
 	tg.runFail("test", "-cover", "coverbad")
-	tg.grepStderr(`coverbad[\\/]p.go:4`, "did not find correct line number for error")
 	stderr2 := tg.getStderr()
 
 	// It's OK that stderr2 drops the character position in the error,
-	// because of the //line directive.
+	// because of the //line directive (see golang.org/issue/22662).
 	stderr = strings.Replace(stderr, "p.go:4:2:", "p.go:4:", -1)
 	if stderr != stderr2 {
 		t.Logf("test -cover changed error messages:\nbefore:\n%s\n\nafter:\n%s", stderr, stderr2)
@@ -4707,10 +4707,11 @@ func TestExecBuildX(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	out, err = exec.Command("/bin/sh", sh).CombinedOutput()
+	out, err = exec.Command("/usr/bin/env", "bash", "-x", sh).CombinedOutput()
 	if err != nil {
 		t.Fatalf("/bin/sh %s: %v\n%s", sh, err, out)
 	}
+	t.Logf("shell output:\n%s", out)
 
 	out, err = exec.Command(obj).CombinedOutput()
 	if err != nil {
diff --git a/src/cmd/go/internal/work/exec.go b/src/cmd/go/internal/work/exec.go
index 08f7d00da1..60e6cedda1 100644
--- a/src/cmd/go/internal/work/exec.go
+++ b/src/cmd/go/internal/work/exec.go
@@ -426,7 +426,7 @@ func (b *Builder) build(a *Action) (err error) {
 			sfiles = nil
 		}
 
-		outGo, outObj, err := b.cgo(a, base.Tool("cgo"), objdir, pcCFLAGS, pcLDFLAGS, cgofiles, objdirCgofiles, gccfiles, cxxfiles, a.Package.MFiles, a.Package.FFiles)
+		outGo, outObj, err := b.cgo(a, base.Tool("cgo"), objdir, pcCFLAGS, pcLDFLAGS, mkAbsFiles(a.Package.Dir, cgofiles), objdirCgofiles, gccfiles, cxxfiles, a.Package.MFiles, a.Package.FFiles)
 		if err != nil {
 			return err
 		}
@@ -481,17 +481,10 @@ func (b *Builder) build(a *Action) (err error) {
 		// so that vet's error messages will use absolute paths,
 		// so that we can reformat them relative to the directory
 		// in which the go command is invoked.
-		absfiles := make([]string, len(gofiles))
-		for i, f := range gofiles {
-			if !filepath.IsAbs(f) {
-				f = filepath.Join(a.Package.Dir, f)
-			}
-			absfiles[i] = f
-		}
 		vcfg = &vetConfig{
 			Compiler:    cfg.BuildToolchainName,
 			Dir:         a.Package.Dir,
-			GoFiles:     absfiles,
+			GoFiles:     mkAbsFiles(a.Package.Dir, gofiles),
 			ImportMap:   make(map[string]string),
 			PackageFile: make(map[string]string),
 		}
@@ -1351,8 +1344,8 @@ func (b *Builder) showOutput(a *Action, dir, desc, out string) {
 // print this error.
 var errPrintedOutput = errors.New("already printed output - no need to show error")
 
-var cgoLine = regexp.MustCompile(`\[[^\[\]]+\.cgo1\.go:[0-9]+(:[0-9]+)?\]`)
-var cgoTypeSigRe = regexp.MustCompile(`\b_Ctype_\B`)
+var cgoLine = regexp.MustCompile(`\[[^\[\]]+\.(cgo1|cover)\.go:[0-9]+(:[0-9]+)?\]`)
+var cgoTypeSigRe = regexp.MustCompile(`\b_C2?(type|func|var|macro)_\B`)
 
 // run runs the command given by cmdline in the directory dir.
 // If the command fails, run prints information about the failure
@@ -1895,9 +1888,9 @@ func (b *Builder) cgo(a *Action, cgoExe, objdir string, pcCFLAGS, pcLDFLAGS, cgo
 	gofiles := []string{objdir + "_cgo_gotypes.go"}
 	cfiles := []string{"_cgo_export.c"}
 	for _, fn := range cgofiles {
-		f := cgoRe.ReplaceAllString(fn[:len(fn)-2], "_")
-		gofiles = append(gofiles, objdir+f+"cgo1.go")
-		cfiles = append(cfiles, f+"cgo2.c")
+		f := strings.TrimSuffix(filepath.Base(fn), ".go")
+		gofiles = append(gofiles, objdir+f+".cgo1.go")
+		cfiles = append(cfiles, f+".cgo2.c")
 	}
 
 	// TODO: make cgo not depend on $GOARCH?
@@ -2286,3 +2279,17 @@ func (b *Builder) disableBuildID(ldflags []string) []string {
 	}
 	return ldflags
 }
+
+// mkAbsFiles converts files into a list of absolute files,
+// assuming they were originally relative to dir,
+// and returns that new list.
+func mkAbsFiles(dir string, files []string) []string {
+	abs := make([]string, len(files))
+	for i, f := range files {
+		if !filepath.IsAbs(f) {
+			f = filepath.Join(dir, f)
+		}
+		abs[i] = f
+	}
+	return abs
+}
diff --git a/src/cmd/go/testdata/src/coverbad/p1.go b/src/cmd/go/testdata/src/coverbad/p1.go
new file mode 100644
index 0000000000..2d25c8e190
--- /dev/null
+++ b/src/cmd/go/testdata/src/coverbad/p1.go
@@ -0,0 +1,7 @@
+package p
+
+import "C"
+
+func h() {
+	j()
+}