- catch trace traps

- disassemble the instructions in a trace trap to see if it's a run-time trap
- if so, print relevant info
- avoid double-printing traceback on panic

R=ken,rsc
DELTA=66  (50 added, 7 deleted, 9 changed)
OCL=15199
CL=15224

src/runtime/rt1_amd64_darwin.c

@@ -130,20 +130,24 @@ typedef struct  sigaction {
 	int32 sa_flags;			/* see signal options below */
 } sigaction;
 
-
 void
 sighandler(int32 sig, siginfo *info, void *context)
 {
-	if(sig < 0 || sig >= NSIG){
-		prints("Signal ");
-		sys·printint(sig);
-	}else{
-		prints(sigtab[sig].name);
-	}
+	if(panicking)	// traceback already printed
+		sys·exit(2);
 
         _STRUCT_MCONTEXT64 *uc_mcontext = get_uc_mcontext(context);
         _STRUCT_X86_THREAD_STATE64 *ss = get___ss(uc_mcontext);
 
+	if(!inlinetrap(sig, (byte *)ss->__rip)) {
+		if(sig < 0 || sig >= NSIG){
+			prints("Signal ");
+			sys·printint(sig);
+		}else{
+			prints(sigtab[sig].name);
+		}
+	}
+
 	prints("\nFaulting address: 0x");  sys·printpointer(info->si_addr);
 	prints("\npc: 0x");  sys·printpointer((void *)ss->__rip);
 	prints("\n\n");

src/runtime/rt1_amd64_linux.c

@@ -138,15 +138,20 @@ typedef struct sigaction {
 void
 sighandler(int32 sig, siginfo* info, void** context)
 {
-	if(sig < 0 || sig >= NSIG){
-		prints("Signal ");
-		sys·printint(sig);
-	}else{
-		prints(sigtab[sig].name);
-	}
+	if(panicking)	// traceback already printed
+		sys·exit(2);
 
         struct sigcontext *sc = &(((struct ucontext *)context)->uc_mcontext);
 
+	if(!inlinetrap(sig, (byte *)sc->rip)) {
+		if(sig < 0 || sig >= NSIG){
+			prints("Signal ");
+			sys·printint(sig);
+		}else{
+			prints(sigtab[sig].name);
+		}
+	}
+
         prints("\nFaulting address: 0x");  sys·printpointer(info->si_addr);
         prints("\npc: 0x");  sys·printpointer((void *)sc->rip);
         prints("\n\n");

src/runtime/rt2_amd64.c

@@ -86,3 +86,33 @@ traceback(uint8 *pc, uint8 *sp, void* r15)
 		prints(", ...)\n");
 	}
 }
+
+/*
+ * For trace traps, disassemble instruction to see if it's INTB of known type.
+ */
+int32
+inlinetrap(int32 sig, byte* pc)
+{
+	extern void etext();
+	extern void _rt0_amd64_darwin();
+
+	if(sig != 5)	/* SIGTRAP */
+		return 0;
+	if(pc-2 < (byte*)_rt0_amd64_darwin || pc >= (byte*)etext)
+		return 0;
+	if(pc[-2] != 0xcd)  /* INTB */
+		return 0;
+	switch(pc[-1]) {
+	case 5:
+		prints("\nTRAP: array out of bounds\n");
+		break;
+	case 6:
+		prints("\nTRAP: leaving function with returning a value\n");
+		break;
+	default:
+		prints("\nTRAP: unknown run-time trap ");
+		sys·printint(pc[-1]);
+		prints("\n");
+	}
+	return 1;
+}

src/runtime/runtime.c

@@ -5,6 +5,7 @@
 #include "runtime.h"
 
 int32	debug	= 0;
+int32	panicking = 0;
 
 void
 sys·panicl(int32 lno)
@@ -19,7 +20,8 @@ sys·panicl(int32 lno)
 	sp = (uint8*)&lno;
 	traceback(sys·getcallerpc(&lno), sp, g);
 	tracebackothers(g);
-	sys·breakpoint();
+	panicking = 1;
+	sys·breakpoint();  // so we can grab it in a debugger
 	sys·exit(2);
 }
 

src/runtime/runtime.h

@@ -207,6 +207,7 @@ M*	allm;
 G*	allg;
 int32	goidgen;
 extern	int32	gomaxprocs;
+extern	int32	panicking;
 
 /*
  * common functions and data
@@ -236,6 +237,7 @@ uint32	cmpstring(string, string);
 void	initsig(void);
 void	traceback(uint8 *pc, uint8 *sp, G* gp);
 void	tracebackothers(G*);
+int32	inlinetrap(int32 sig, byte* pc);
 int32	open(byte*, int32, ...);
 int32	read(int32, void*, int32);
 int32	write(int32, void*, int32);

src/runtime/signals.h

@@ -9,7 +9,7 @@ static struct SigTab sigtab[] = {
 	/* 2 */	0, "SIGINT: interrupt program",
 	/* 3 */	1, "SIGQUIT: quit program",
 	/* 4 */	1, "SIGILL: illegal instruction",
-	/* 5 */	0, "SIGTRAP: trace trap",	/* uncaught; used by panic and signal handler */
+	/* 5 */	1, "SIGTRAP: trace trap",	/* used by panic and array out of bounds, etc. */
 	/* 6 */	1, "SIGABRT: abort program",
 	/* 7 */	1, "SIGEMT: emulate instruction executed",
 	/* 8 */	1, "SIGFPE: floating-point exception",