makes stack traces work for segmented stacks

SVN=125371

src/runtime/rt0_amd64.s

@@ -175,7 +175,16 @@ easy:
 	ADDQ	$8, SP
 	RET
 
+// marker.  must be here; used by traceback() to discover calls to _morestack
+TEXT _endmorestack(SB), 7, $-8
+	RET
+
 TEXT	FLUSH(SB),7,$-8
 	RET
 
+TEXT	getu(SB),7,$-8
+	MOVQ	R15, AX
+	RET
+
+
 GLOBL	peruser<>(SB),$64

src/runtime/rt1_amd64_darwin.c

@@ -145,11 +145,11 @@ sighandler(int32 sig, siginfo *info, void *context)
         _STRUCT_X86_THREAD_STATE64 *ss = get___ss(uc_mcontext);
 
 	prints("\nFaulting address: 0x");  sys·printpointer(info->si_addr);
-        prints("\npc: 0x");  sys·printpointer((void *)ss->__rip);
-        prints("\n\n");
+	prints("\npc: 0x");  sys·printpointer((void *)ss->__rip);
+	prints("\n\n");
         
-	traceback((void *)ss->__rip, (void *)ss->__rsp);
-        print_thread_state(ss);
+	traceback((void *)ss->__rip, (void *)ss->__rsp, (void*)ss->__r15);
+	print_thread_state(ss);
         
 	sys·exit(2);
 }

src/runtime/rt1_amd64_linux.c

@@ -152,7 +152,7 @@ sighandler(int32 sig, siginfo* info, void** context)
         prints("\npc: 0x");  sys·printpointer((void *)sc->rip);
         prints("\n\n");
         
-	traceback((void *)sc->rip, (void *)sc->rsp);
+	traceback((void *)sc->rip, (void *)sc->rsp, (void *)sc->r15);
         print_sigcontext(sc);
 
 	sys·breakpoint();

src/runtime/rt2_amd64.c

@@ -8,22 +8,54 @@ extern int32	debug;
 
 static int8 spmark[] = "\xa7\xf1\xd9\x2a\x82\xc8\xd8\xfe";
 
+typedef struct U U;
+struct U {
+	uint8*	stackguard;
+	uint8*	stackbase;
+	uint8*	istackguard;
+	uint8*	istackbase;
+};
+
+typedef struct Stktop Stktop;
+struct Stktop {
+	uint8*	oldbase;
+	uint8*	oldsp;
+	uint8*	magic;
+	uint8*	oldguard;
+};
+
+extern void _morestack();
+extern void _endmorestack();
+
 void
-traceback(uint8 *pc, uint8 *sp)
+traceback(uint8 *pc, uint8 *sp, void* r15)
 {
 	int32 spoff;
 	int8* spp;
+	uint8* callpc;
 	int32 counter;
 	int32 i;
 	int8* name;
+	U u;
+	Stktop *stktop;
 
+	// store local copy of per-process data block that we can write as we unwind
+	mcpy((byte*)&u, (byte*)r15, sizeof(U));
 
 	counter = 0;
 	name = "panic";
 	for(;;){
-		prints("0x");
-		sys·printpointer(pc);
-		prints("?zi\n");
+		callpc = pc;
+		if((uint8*)_morestack < pc && pc < (uint8*)_endmorestack) {
+			// call site in _morestack(); pop to earlier stack block to get true caller
+			stktop = (Stktop*)u.stackbase;
+			u.stackbase = stktop->oldbase;
+			u.stackguard = stktop->oldguard;
+			sp = stktop->oldsp;
+			pc = ((uint8**)sp)[1];
+			sp += 16;  // two irrelevant calls on stack - morestack, plus the call morestack made
+			continue;
+		}
 		/* find SP offset by stepping back through instructions to SP offset marker */
 		while(pc > (uint8*)0x1000+sizeof spmark-1) {
 			for(spp = spmark; *spp != '\0' && *pc++ == (uint8)*spp++; )
@@ -43,7 +75,11 @@ traceback(uint8 *pc, uint8 *sp)
 		}
 		if((pc = ((uint8**)sp)[-1]) <= (uint8*)0x1000)
 			break;
-		/* print args for this frame */
+
+		/* print this frame */
+		prints("0x");
+		sys·printpointer(callpc);
+		prints("?zi\n");
 		prints("\t");
 		prints(name);
 		prints("(");

src/runtime/runtime.c

@@ -18,7 +18,7 @@ sys·panicl(int32 lno)
 	sys·printpc(&lno);
 	prints("\n");
 	sp = (uint8*)&lno;
-	traceback(sys·getcallerpc(&lno), sp);
+	traceback(sys·getcallerpc(&lno), sp, getu());
 	sys·breakpoint();
 	sys·exit(2);
 }

src/runtime/runtime.h

@@ -93,13 +93,14 @@ extern int32 debug;
  * very low level c-called
  */
 void	FLUSH(void*);
+void*	getu(void);
 void	throw(int8*);
 void	prints(int8*);
 void	mcpy(byte*, byte*, uint32);
 void*	mal(uint32);
 uint32	cmpstring(string, string);
 void	initsig(void);
-void	traceback(uint8 *pc, uint8 *sp);
+void	traceback(uint8 *pc, uint8 *sp, void* up);
 int32	open(byte*, int32);
 int32	read(int32, void*, int32);
 void	close(int32);