[release-branch.go1.2] runtime: fix crash in runtime.GoroutineProfile

This CL is not exactly a copy of the original quoted below.
This CL omits the changes made to mgc0.c in the original.
Those changes do not apply cleanly to the Go 1.2 tree,
and they were cosmetic, simplifying code that was already
doing the right thing.

To double-check that omitting the mgc0.c change has not
invalidated the fix, I have verified by hand that the test program
in issue 6946 fails without this CL and passes with this CL.

««« CL 41640043 / e4c381446b48
runtime: fix crash in runtime.GoroutineProfile

This is a possible Go 1.2.1 candidate.

Fixes #6946.

R=iant, r
CC=golang-dev
https://golang.org/cl/41640043
»»»

LGTM=adg
R=adg
CC=golang-codereviews, golang-dev, iant, r
https://golang.org/cl/68820045

4 files changed, 26 insertions, 4 deletions

diff --git a/src/pkg/runtime/mprof.goc b/src/pkg/runtime/mprof.goc
index 5b92cec95c..4ae74f0c28 100644
--- a/src/pkg/runtime/mprof.goc
+++ b/src/pkg/runtime/mprof.goc
@@ -477,7 +477,7 @@ saveg(uintptr pc, uintptr sp, G *gp, TRecord *r)
 {
 	int32 n;
 	
-	n = runtime·gentraceback((uintptr)pc, (uintptr)sp, 0, gp, 0, r->stk, nelem(r->stk), nil, nil, false);
+	n = runtime·gentraceback(pc, sp, 0, gp, 0, r->stk, nelem(r->stk), nil, nil, false);
 	if(n < nelem(r->stk))
 		r->stk[n] = 0;
 }
@@ -505,7 +505,7 @@ func GoroutineProfile(b Slice) (n int, ok bool) {
 			for(gp = runtime·allg; gp != nil; gp = gp->alllink) {
 				if(gp == g || gp->status == Gdead)
 					continue;
-				saveg(gp->sched.pc, gp->sched.sp, gp, r++);
+				saveg(~(uintptr)0, ~(uintptr)0, gp, r++);
 			}
 		}
 	
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index de26c72d3d..ed3e1e73ee 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -276,7 +276,7 @@ runtime·tracebackothers(G *me)
 	if((gp = m->curg) != nil && gp != me) {
 		runtime·printf("\n");
 		runtime·goroutineheader(gp);
-		runtime·traceback(gp->sched.pc, gp->sched.sp, gp->sched.lr, gp);
+		runtime·traceback(~(uintptr)0, ~(uintptr)0, 0, gp);
 	}
 
 	for(gp = runtime·allg; gp != nil; gp = gp->alllink) {
@@ -290,7 +290,7 @@ runtime·tracebackothers(G *me)
 			runtime·printf("\tgoroutine running on other thread; stack unavailable\n");
 			runtime·printcreatedby(gp);
 		} else
-			runtime·traceback(gp->sched.pc, gp->sched.sp, gp->sched.lr, gp);
+			runtime·traceback(~(uintptr)0, ~(uintptr)0, 0, gp);
 	}
 }
 
diff --git a/src/pkg/runtime/traceback_arm.c b/src/pkg/runtime/traceback_arm.c
index 341aa20588..8a3685e76c 100644
--- a/src/pkg/runtime/traceback_arm.c
+++ b/src/pkg/runtime/traceback_arm.c
@@ -20,6 +20,18 @@ runtime·gentraceback(uintptr pc0, uintptr sp0, uintptr lr0, G *gp, int32 skip,
 	Stktop *stk;
 	String file;
 
+	if(pc0 == ~(uintptr)0 && sp0 == ~(uintptr)0) { // Signal to fetch saved values from gp.
+		if(gp->syscallstack != (uintptr)nil) {
+			pc0 = gp->syscallpc;
+			sp0 = gp->syscallsp;
+			lr0 = 0;
+		} else {
+			pc0 = gp->sched.pc;
+			sp0 = gp->sched.sp;
+			lr0 = gp->sched.lr;
+		}
+	}
+
 	nprint = 0;
 	runtime·memclr((byte*)&frame, sizeof frame);
 	frame.pc = pc0;
diff --git a/src/pkg/runtime/traceback_x86.c b/src/pkg/runtime/traceback_x86.c
index d658e8f11a..8e3063f43a 100644
--- a/src/pkg/runtime/traceback_x86.c
+++ b/src/pkg/runtime/traceback_x86.c
@@ -30,6 +30,16 @@ runtime·gentraceback(uintptr pc0, uintptr sp0, uintptr lr0, G *gp, int32 skip,
 	String file;
 
 	USED(lr0);
+	
+	if(pc0 == ~(uintptr)0 && sp0 == ~(uintptr)0) { // Signal to fetch saved values from gp.
+		if(gp->syscallstack != (uintptr)nil) {
+			pc0 = gp->syscallpc;
+			sp0 = gp->syscallsp;
+		} else {
+			pc0 = gp->sched.pc;
+			sp0 = gp->sched.sp;
+		}
+	}
 
 	nprint = 0;
 	runtime·memclr((byte*)&frame, sizeof frame);