runtime/pprof: adjust reported line numbers to show call sites

This is the same logic used in the standard tracebacks.
The caller pc is the pc after the call, so except in the
fake "call" caused by a panic, back up the pc enough
that the lookup will use the previous instruction.

Fixes #4150.
Fixes #4151.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/7317047

diff --git a/src/pkg/runtime/pprof/pprof.go b/src/pkg/runtime/pprof/pprof.go
index ee81c94a25b0049aeb7b3a922feebf2f0e3d26c5..32c1098b9945b0e830ca81ef14a30b328d1ca005 100644 (file)
--- a/src/pkg/runtime/pprof/pprof.go
+++ b/src/pkg/runtime/pprof/pprof.go
@@ -318,21 +318,33 @@ 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
-       for _, pc := range stk {
+       wasPanic := false
+       for i, pc := range stk {
                f := runtime.FuncForPC(pc)
                if f == nil {
                        show = true
                        fmt.Fprintf(w, "#\t%#x\n", pc)
+                       wasPanic = false
                } else {
-                       file, line := f.FileLine(pc)
+                       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.panic"
                        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, f.Name(), pc-f.Entry(), file, line)
+                       fmt.Fprintf(w, "#\t%#x\t%s+%#x\t%s:%d\n", pc, name, pc-f.Entry(), file, line)
                }
        }
        if !show {