runtime/pprof: set Function.start_line field

Now that we plumb the start line to the runtime, we can include in pprof
files. Since runtime.Frame.startLine is not (currently) exported, we
need a runtime helper to get the value.

For #55022.
Updates #56135.

Change-Id: Ifc5b68a7b7170fd7895e4099deb24df7977b22ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/438255
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Run-TryBot: Michael Pratt <[email protected]>
Reviewed-by: Austin Clements <[email protected]>

src/runtime/pprof/proto.go

@@ -590,6 +590,7 @@ func (b *profileBuilder) emitLocation() uint64 {
  type newFunc struct {
  id uint64
  name, file string
+ startLine int64
  }
  newFuncs := make([]newFunc, 0, 8)
 
@@ -610,7 +611,12 @@ func (b *profileBuilder) emitLocation() uint64 {
  if funcID == 0 {
  funcID = uint64(len(b.funcs)) + 1
  b.funcs[frame.Function] = int(funcID)
- newFuncs = append(newFuncs, newFunc{funcID, frame.Function, frame.File})
+ newFuncs = append(newFuncs, newFunc{
+ id: funcID,
+ name: frame.Function,
+ file: frame.File,
+ startLine: int64(runtime_FrameStartLine(&frame)),
+ })
  }
  b.pbLine(tagLocation_Line, funcID, int64(frame.Line))
  }
@@ -633,6 +639,7 @@ func (b *profileBuilder) emitLocation() uint64 {
  b.pb.int64Opt(tagFunction_Name, b.stringIndex(fn.name))
  b.pb.int64Opt(tagFunction_SystemName, b.stringIndex(fn.name))
  b.pb.int64Opt(tagFunction_Filename, b.stringIndex(fn.file))
+ b.pb.int64Opt(tagFunction_StartLine, fn.startLine)
  b.pb.endMessage(tagProfile_Function, start)
  }
 

src/runtime/pprof/runtime.go

@@ -6,9 +6,13 @@ package pprof
 
 import (
  "context"
+ "runtime"
  "unsafe"
 )
 
+// runtime_FrameStartLine is defined in runtime/symtab.go.
+func runtime_FrameStartLine(f *runtime.Frame) int
+
 // runtime_expandFinalInlineFrame is defined in runtime/symtab.go.
 func runtime_expandFinalInlineFrame(stk []uintptr) []uintptr
 

src/runtime/symtab.go

@@ -170,6 +170,13 @@ func (ci *Frames) Next() (frame Frame, more bool) {
  return
 }
 
+// runtime_FrameStartLine returns the start line of the function in a Frame.
+//
+//go:linkname runtime_FrameStartLine runtime/pprof.runtime_FrameStartLine
+func runtime_FrameStartLine(f *Frame) int {
+ return f.startLine
+}
+
 // runtime_expandFinalInlineFrame expands the final pc in stk to include all
 // "callers" if pc is inline.
 //