runtime/pprof: plumb labels for goroutine profiles

Goroutines are directly associated with labels. It's relatively easy to
plumb those through without creating goroutine-locals in the wild.

This is accomplished by splitting out most of the code from the public
`runtime.GoroutineProfile` into a new unexported
`runtime.goroutineProfileWithLabels`, which then has a thin wrapper
linked into the `runtime/pprof` package as
`runtime_goroutineProfileWithLabels`. (mirroring the way labels get
associated with the `g` for a goroutine in the first place)

Per-#6104, OS-thread creation profiles are a bit useless, as `M`s tend
to be created be created by a background goroutine. As such, I decided
not to add support for capturing the labels at `M`-creation-time, since
the stack-traces seem to always come out `nil` for my simple test
binaries.

This change currently provides labels for debug=0 and debug=1, as
debug=2 is currently entirely generated by the runtime package and I
don't see a clean way of getting the `labelMap` type handled properly
within the `runtime` package.

Update the comment added in cl/131275 to mention goroutine support for
labels.

Updates #23458

Change-Id: Ia4b558893d7d10156b77121cd9b70c4ccd9e1889
Reviewed-on: https://go-review.googlesource.com/c/go/+/189318
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

1 files changed, 32 insertions, 9 deletions

diff --git a/src/runtime/mprof.go b/src/runtime/mprof.go
index 2bd41b650f..128498d69b 100644
--- a/src/runtime/mprof.go
+++ b/src/runtime/mprof.go
@@ -711,13 +711,16 @@ func ThreadCreateProfile(p []StackRecord) (n int, ok bool) {
 	return
 }
 
-// GoroutineProfile returns n, the number of records in the active goroutine stack profile.
-// If len(p) >= n, GoroutineProfile copies the profile into p and returns n, true.
-// If len(p) < n, GoroutineProfile does not change p and returns n, false.
-//
-// Most clients should use the runtime/pprof package instead
-// of calling GoroutineProfile directly.
-func GoroutineProfile(p []StackRecord) (n int, ok bool) {
+//go:linkname runtime_goroutineProfileWithLabels runtime/pprof.runtime_goroutineProfileWithLabels
+func runtime_goroutineProfileWithLabels(p []StackRecord, labels []unsafe.Pointer) (n int, ok bool) {
+	return goroutineProfileWithLabels(p, labels)
+}
+
+// labels may be nil. If labels is non-nil, it must have the same length as p.
+func goroutineProfileWithLabels(p []StackRecord, labels []unsafe.Pointer) (n int, ok bool) {
+	if labels != nil && len(labels) != len(p) {
+		labels = nil
+	}
 	gp := getg()
 
 	isOK := func(gp1 *g) bool {
@@ -737,7 +740,7 @@ func GoroutineProfile(p []StackRecord) (n int, ok bool) {
 
 	if n <= len(p) {
 		ok = true
-		r := p
+		r, lbl := p, labels
 
 		// Save current goroutine.
 		sp := getcallersp()
@@ -747,6 +750,12 @@ func GoroutineProfile(p []StackRecord) (n int, ok bool) {
 		})
 		r = r[1:]
 
+		// If we have a place to put our goroutine labelmap, insert it there.
+		if labels != nil {
+			lbl[0] = gp.labels
+			lbl = lbl[1:]
+		}
+
 		// Save other goroutines.
 		for _, gp1 := range allgs {
 			if isOK(gp1) {
@@ -756,16 +765,30 @@ func GoroutineProfile(p []StackRecord) (n int, ok bool) {
 					break
 				}
 				saveg(^uintptr(0), ^uintptr(0), gp1, &r[0])
+				if labels != nil {
+					lbl[0] = gp1.labels
+					lbl = lbl[1:]
+				}
 				r = r[1:]
 			}
 		}
 	}
 
 	startTheWorld()
-
 	return n, ok
 }
 
+// GoroutineProfile returns n, the number of records in the active goroutine stack profile.
+// If len(p) >= n, GoroutineProfile copies the profile into p and returns n, true.
+// If len(p) < n, GoroutineProfile does not change p and returns n, false.
+//
+// Most clients should use the runtime/pprof package instead
+// of calling GoroutineProfile directly.
+func GoroutineProfile(p []StackRecord) (n int, ok bool) {
+
+	return goroutineProfileWithLabels(p, nil)
+}
+
 func saveg(pc, sp uintptr, gp *g, r *StackRecord) {
 	n := gentraceback(pc, sp, 0, gp, 0, &r.Stack0[0], len(r.Stack0), nil, nil, 0)
 	if n < len(r.Stack0) {