From d4c2da409b8a5491b6f5e69bcff93e2c01577b7a Mon Sep 17 00:00:00 2001
From: Rob Pike <r@golang.org>
Date: Mon, 23 Jun 2008 20:12:39 -0700
Subject: [PATCH] safety checks, waiting for gri's real tracking of PC and SP
 extant code is too fragile

SVN=124223
---
 src/runtime/rt0_amd64_darwin.s |  2 +-
 src/runtime/rt1_amd64_darwin.c | 11 ++++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/runtime/rt0_amd64_darwin.s b/src/runtime/rt0_amd64_darwin.s
index 16592b90ae2..fcd86b9879c 100644
--- a/src/runtime/rt0_amd64_darwin.s
+++ b/src/runtime/rt0_amd64_darwin.s
@@ -64,7 +64,7 @@ TEXT	sys_sigaction(SB),1,$-8
 	CALL	notok(SB)
 	RET
 
-TEXT sigtramp(SB),1,$-24
+TEXT sigtramp(SB),1,$24
 	MOVL	DX,0(SP)
 	MOVQ	CX,8(SP)
 	MOVQ	R8,16(SP)
diff --git a/src/runtime/rt1_amd64_darwin.c b/src/runtime/rt1_amd64_darwin.c
index c24b40fae5b..94d27ee70e1 100644
--- a/src/runtime/rt1_amd64_darwin.c
+++ b/src/runtime/rt1_amd64_darwin.c
@@ -39,6 +39,7 @@ typedef struct  sigaction {
 void
 sighandler(int32 sig, siginfo* info, void** context) {
 	int32 i;
+	void *pc, *sp;
 
 	if(sig < 0 || sig >= NSIG){
 		prints("Signal ");
@@ -46,14 +47,18 @@ sighandler(int32 sig, siginfo* info, void** context) {
 	}else{
 		prints(sigtab[sig].name);
 	}
+
 	prints("\nFaulting address: 0x");
 	sys_printpointer(info->si_addr);
 	prints("\nPC: 0x");
-	sys_printpointer(((void**)((&sig)+1))[22]);
+	pc = ((void**)((&sig)+1))[22];
+	sys_printpointer(pc);
 	prints("\nSP: 0x");
-	sys_printpointer(((void**)((&sig)+1))[13]);
+	sp = ((void**)((&sig)+1))[13];
+	sys_printpointer(sp);
 	prints("\n");
-	traceback(((void**)((&sig)+1))[22], ((void**)((&sig)+1))[13]);	/* empirically discovered locations */
+	if (pc != 0 && sp != 0)
+		traceback(pc, sp);	/* empirically discovered locations */
 	sys_exit(2);
 }