libgo: delay applying profile stack-frame skip until fixup

    
    When the runtime collects a stack trace to associate it with some
    profiling event (mem alloc, mutex, etc) there is a skip count passed
    to runtime.Callers (or equivalent) to skip some known count of frames
    in order to get to the "interesting" frame corresponding to the
    profile event. Now that the profiling mechanism uses lazy fixup (when
    removing compiler artifacts like thunks, morestack calls etc), we also
    need to move the frame skipping logic after the fixup, so as to insure
    that the skip count isn't thrown off by these artifacts.
    
    Fixes golang/go#32290.
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/179740

From-SVN: r271892

2 files changed, 30 insertions, 14 deletions

diff --git a/libgo/go/runtime/mprof.go b/libgo/go/runtime/mprof.go
index 9238e2bb..132c2ff 100644
--- a/libgo/go/runtime/mprof.go
+++ b/libgo/go/runtime/mprof.go
@@ -56,6 +56,7 @@ type bucket struct {
 	hash    uintptr
 	size    uintptr
 	nstk    uintptr
+	skip    int
 }
 
 // A memRecord is the bucket data for a bucket of type memProfile,
@@ -185,7 +186,7 @@ func max(x, y uintptr) uintptr {
 }
 
 // newBucket allocates a bucket with the given type and number of stack entries.
-func newBucket(typ bucketType, nstk int) *bucket {
+func newBucket(typ bucketType, nstk int, skipCount int) *bucket {
 	size := payloadOffset(typ, uintptr(nstk))
 	switch typ {
 	default:
@@ -203,6 +204,7 @@ func newBucket(typ bucketType, nstk int) *bucket {
 	bucketmem += size
 	b.typ = typ
 	b.nstk = uintptr(nstk)
+	b.skip = skipCount
 	return b
 }
 
@@ -229,7 +231,7 @@ func (b *bucket) bp() *blockRecord {
 }
 
 // Return the bucket for stk[0:nstk], allocating new bucket if needed.
-func stkbucket(typ bucketType, size uintptr, stk []uintptr, alloc bool) *bucket {
+func stkbucket(typ bucketType, size uintptr, skip int, stk []uintptr, alloc bool) *bucket {
 	if buckhash == nil {
 		buckhash = (*[buckHashSize]*bucket)(sysAlloc(unsafe.Sizeof(*buckhash), &memstats.buckhash_sys))
 		if buckhash == nil {
@@ -264,7 +266,7 @@ func stkbucket(typ bucketType, size uintptr, stk []uintptr, alloc bool) *bucket
 	}
 
 	// Create new bucket.
-	b := newBucket(typ, len(stk))
+	b := newBucket(typ, len(stk), skip)
 	copy(b.stk(), stk)
 	b.hash = h
 	b.size = size
@@ -369,9 +371,10 @@ func mProf_PostSweep() {
 // Called by malloc to record a profiled block.
 func mProf_Malloc(p unsafe.Pointer, size uintptr) {
 	var stk [maxStack]uintptr
-	nstk := callersRaw(1, stk[:])
+	nstk := callersRaw(stk[:])
 	lock(&proflock)
-	b := stkbucket(memProfile, size, stk[:nstk], true)
+	skip := 1
+	b := stkbucket(memProfile, size, skip, stk[:nstk], true)
 	c := mProf.cycle
 	mp := b.mp()
 	mpc := &mp.future[(c+2)%uint32(len(mp.future))]
@@ -446,14 +449,14 @@ func saveblockevent(cycles int64, skip int, which bucketType) {
 	var nstk int
 	var stk [maxStack]uintptr
 	if gp.m.curg == nil || gp.m.curg == gp {
-		nstk = callersRaw(skip, stk[:])
+		nstk = callersRaw(stk[:])
 	} else {
 		// FIXME: This should get a traceback of gp.m.curg.
 		// nstk = gcallers(gp.m.curg, skip, stk[:])
-		nstk = callersRaw(skip, stk[:])
+		nstk = callersRaw(stk[:])
 	}
 	lock(&proflock)
-	b := stkbucket(which, 0, stk[:nstk], true)
+	b := stkbucket(which, 0, skip, stk[:nstk], true)
 	b.bp().count++
 	b.bp().cycles += cycles
 	unlock(&proflock)
@@ -605,9 +608,12 @@ func freebucket(tofree *bucket) *bucket {
 // later. Note: there is code in go-callers.c's backtrace_full callback()
 // function that performs very similar fixups; these two code paths
 // should be kept in sync.
-func fixupStack(stk []uintptr, canonStack *[maxStack]uintptr, size uintptr) int {
+func fixupStack(stk []uintptr, skip int, canonStack *[maxStack]uintptr, size uintptr) int {
 	var cidx int
 	var termTrace bool
+	// Increase the skip count to take into account the frames corresponding
+	// to runtime.callersRaw and to the C routine that it invokes.
+	skip += 2
 	for _, pc := range stk {
 		// Subtract 1 from PC to undo the 1 we added in callback in
 		// go-callers.c.
@@ -669,6 +675,16 @@ func fixupStack(stk []uintptr, canonStack *[maxStack]uintptr, size uintptr) int
 			break
 		}
 	}
+
+	// Apply skip count. Needs to be done after expanding inline frames.
+	if skip != 0 {
+		if skip >= cidx {
+			return 0
+		}
+		copy(canonStack[:cidx-skip], canonStack[skip:])
+		return cidx - skip
+	}
+
 	return cidx
 }
 
@@ -680,8 +696,8 @@ func fixupStack(stk []uintptr, canonStack *[maxStack]uintptr, size uintptr) int
 // the new bucket.
 func fixupBucket(b *bucket) {
 	var canonStack [maxStack]uintptr
-	frames := fixupStack(b.stk(), &canonStack, b.size)
-	cb := stkbucket(prunedProfile, b.size, canonStack[:frames], true)
+	frames := fixupStack(b.stk(), b.skip, &canonStack, b.size)
+	cb := stkbucket(prunedProfile, b.size, 0, canonStack[:frames], true)
 	switch b.typ {
 	default:
 		throw("invalid profile bucket type")
diff --git a/libgo/go/runtime/traceback_gccgo.go b/libgo/go/runtime/traceback_gccgo.go
index b0eecf2..4134d28 100644
--- a/libgo/go/runtime/traceback_gccgo.go
+++ b/libgo/go/runtime/traceback_gccgo.go
@@ -63,11 +63,11 @@ func callers(skip int, locbuf []location) int {
 
 //go:noescape
 //extern runtime_callersRaw
-func c_callersRaw(skip int32, pcs *uintptr, max int32) int32
+func c_callersRaw(pcs *uintptr, max int32) int32
 
 // callersRaw returns a raw (PCs only) stack trace of the current goroutine.
-func callersRaw(skip int, pcbuf []uintptr) int {
-	n := c_callersRaw(int32(skip)+1, &pcbuf[0], int32(len(pcbuf)))
+func callersRaw(pcbuf []uintptr) int {
+	n := c_callersRaw(&pcbuf[0], int32(len(pcbuf)))
 	return int(n)
 }