From: Shenghou Ma <minux.ma@gmail.com>
Date: Tue, 5 Feb 2013 17:18:37 +0000 (+0800)
Subject: runtime: save LR to stack when panicking to handle leaf function traceback
X-Git-Tag: go1.1rc2~1130
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=7de3d71797a0e6f25975fa5c3c69c7b0e27d23d2;p=gostls13.git

runtime: save LR to stack when panicking to handle leaf function traceback

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7289047
---

diff --git a/src/pkg/runtime/signal_linux_arm.c b/src/pkg/runtime/signal_linux_arm.c
index 31444a7243..c425696d56 100644
--- a/src/pkg/runtime/signal_linux_arm.c
+++ b/src/pkg/runtime/signal_linux_arm.c
@@ -68,11 +68,17 @@ runtime·sighandler(int32 sig, Siginfo *info, void *context, G *gp)
 		gp->sigcode1 = r->fault_address;
 		gp->sigpc = r->arm_pc;
 
-		// If this is a leaf function, we do smash LR,
-		// but we're not going back there anyway.
-		// Don't bother smashing if r->arm_pc is 0,
-		// which is probably a call to a nil func: the
-		// old link register is more useful in the stack trace.
+		// We arrange lr, and pc to pretend the panicking
+		// function calls sigpanic directly.
+		// Always save LR to stack so that panics in leaf
+		// functions are correctly handled. This smashes
+		// the stack frame but we're not going back there
+		// anyway.
+		r->arm_sp -= 4;
+		*(uint32 *)r->arm_sp = r->arm_lr;
+		// Don't bother saving PC if it's zero, which is
+		// probably a call to a nil func: the old link register
+		// is more useful in the stack trace.
 		if(r->arm_pc != 0)
 			r->arm_lr = r->arm_pc;
 		// In case we are panicking from external C code
diff --git a/src/pkg/runtime/traceback_arm.c b/src/pkg/runtime/traceback_arm.c
index fd60490ae4..39dc6fd22c 100644
--- a/src/pkg/runtime/traceback_arm.c
+++ b/src/pkg/runtime/traceback_arm.c
@@ -182,6 +182,12 @@ runtime·gentraceback(byte *pc0, byte *sp, byte *lr0, G *gp, int32 skip, uintptr
 		// If this was deferproc or newproc, the caller had an extra 12.
 		if(f->entry == (uintptr)runtime·deferproc || f->entry == (uintptr)runtime·newproc)
 			sp += 12;
+
+		// sighandler saves the lr on stack before fake a call to sigpanic
+		if(waspanic) {
+			pc = *(uintptr *)sp;
+			sp += 4;
+		}
 	}
 	
 	if(pcbuf == nil && (pc = gp->gopc) != 0 && (f = runtime·findfunc(pc)) != nil