gc: implement panic and recover

R=ken2, r, ken3
CC=golang-dev
https://golang.org/cl/831042

src/cmd/5g/ggen.c

@@ -190,7 +190,7 @@ ginscall(Node *f, int proc)
 
 		break;
 
-	case 2:	// defered call (defer)
+	case 2:	// deferred call (defer)
 		regalloc(&r, types[tptr], N);
 		p = gins(AMOVW, N, &r);
 		p->from.type = D_OREG;
@@ -222,7 +222,7 @@ ginscall(Node *f, int proc)
 
 		ginscall(deferproc, 0);
 
-		regalloc(&r, types[tptr], N);
+		nodreg(&r, types[tptr], D_R1);
 		p = gins(AMOVW, N, &r);
 		p->from.type = D_OREG;
 		p->from.reg = REGSP;
@@ -233,8 +233,13 @@ ginscall(Node *f, int proc)
 		p->to.reg = REGSP;
 		p->to.offset = 8;
 		p->scond |= C_WBIT;
-		regfree(&r);
 		
+		if(proc == 2) {
+			nodconst(&con, types[TINT32], 0);
+			nodreg(&r, types[tptr], D_R0);
+			gins(ACMP, &con, &r);
+			patch(gbranch(ABNE, T), pret);
+		}
 		break;
 	}
 }

src/cmd/6g/ggen.c

@@ -142,8 +142,8 @@ ginscall(Node *f, int proc)
 		break;
 
 	case 1:	// call in new proc (go)
-	case 2:	// defered call (defer)
-		nodreg(&reg, types[TINT64], D_AX);
+	case 2:	// deferred call (defer)
+		nodreg(&reg, types[TINT64], D_CX);
 		gins(APUSHQ, f, N);
 		nodconst(&con, types[TINT32], argsize(f->type));
 		gins(APUSHQ, &con, N);
@@ -156,6 +156,11 @@ ginscall(Node *f, int proc)
 		}
 		gins(APOPQ, N, &reg);
 		gins(APOPQ, N, &reg);
+		if(proc == 2) {
+			nodreg(&reg, types[TINT64], D_AX);
+			gins(ATESTQ, &reg, &reg);
+			patch(gbranch(AJNE, T), pret);
+		}
 		break;
 	}
 }

src/cmd/8g/ggen.c

@@ -182,8 +182,8 @@ ginscall(Node *f, int proc)
 		break;
 
 	case 1:	// call in new proc (go)
-	case 2:	// defered call (defer)
-		nodreg(&reg, types[TINT32], D_AX);
+	case 2:	// deferred call (defer)
+		nodreg(&reg, types[TINT32], D_CX);
 		gins(APUSHL, f, N);
 		nodconst(&con, types[TINT32], argsize(f->type));
 		gins(APUSHL, &con, N);
@@ -193,6 +193,11 @@ ginscall(Node *f, int proc)
 			ginscall(deferproc, 0);
 		gins(APOPL, N, &reg);
 		gins(APOPL, N, &reg);
+		if(proc == 2) {
+			nodreg(&reg, types[TINT64], D_AX);
+			gins(ATESTL, &reg, &reg);
+			patch(gbranch(AJNE, T), pret);
+		}
 		break;
 	}
 }

src/cmd/gc/builtin.c.boot

@@ -5,7 +5,7 @@ char *runtimeimport =
 	"func \"\".throwreturn ()\n"
 	"func \"\".throwinit ()\n"
 	"func \"\".panic (? interface { })\n"
-	"func \"\".recover () interface { }\n"
+	"func \"\".recover (? *int32) interface { }\n"
 	"func \"\".printbool (? bool)\n"
 	"func \"\".printfloat (? float64)\n"
 	"func \"\".printint (? int64)\n"

src/cmd/gc/dcl.c

@@ -1276,7 +1276,7 @@ addmethod(Sym *sf, Type *t, int local)
 }
 
 void
-funccompile(Node *n)
+funccompile(Node *n, int isclosure)
 {
 	stksize = BADWIDTH;
 	maxarg = 0;
@@ -1290,6 +1290,18 @@ funccompile(Node *n)
 	// assign parameter offsets
 	checkwidth(n->type);
 	
+	// record offset to actual frame pointer.
+	// for closure, have to skip over leading pointers and PC slot.
+	nodfp->xoffset = 0;
+	if(isclosure) {
+		NodeList *l;
+		for(l=n->nname->ntype->list; l; l=l->next) {
+			nodfp->xoffset += widthptr;
+			if(l->n->left == N)	// found slot for PC
+				break;
+		}
+	}
+
 	if(curfn)
 		fatal("funccompile %S inside %S", n->nname->sym, curfn->nname->sym);
 	curfn = n;

src/cmd/gc/go.h

@@ -1004,7 +1004,7 @@ NodeList*	constiter(NodeList*, Node*, NodeList*);
 
 Node*	unsafenmagic(Node*, NodeList*);
 void	dclchecks(void);
-void	funccompile(Node*);
+void	funccompile(Node*, int);
 
 Node*	typedcl0(Sym*);
 Node*	typedcl1(Node*, Node*, int);
@@ -1169,6 +1169,8 @@ EXTERN	Prog*	breakpc;
 EXTERN	Prog*	pc;
 EXTERN	Prog*	firstpc;
 
+EXTERN	Node*	nodfp;
+
 void	allocparams(void);
 void	cgen_as(Node *nl, Node *nr);
 void	cgen_callmeth(Node *n, int proc);

src/cmd/gc/init.c

@@ -197,5 +197,5 @@ fninit(NodeList *n)
 	fn->nbody = r;
 	funcbody(fn);
 	typecheck(&fn, Etop);
-	funccompile(fn);
+	funccompile(fn, 0);
 }

src/cmd/gc/lex.c

@@ -138,14 +138,14 @@ main(int argc, char *argv[])
 	resumecheckwidth();
 	for(l=xtop; l; l=l->next)
 		if(l->n->op == ODCLFUNC)
-			funccompile(l->n);
+			funccompile(l->n, 0);
 	if(nerrors == 0)
 		fninit(xtop);
 	while(closures) {
 		l = closures;
 		closures = nil;
 		for(; l; l=l->next)
-			funccompile(l->n);
+			funccompile(l->n, 1);
 	}
 	dclchecks();
 
@@ -1443,6 +1443,13 @@ lexfini(void)
 		*s->def = *nodbool(0);
 		s->def->sym = s;
 	}
+	
+	nodfp = nod(ONAME, N, N);
+	nodfp->noescape = 1;
+	nodfp->type = types[TINT32];
+	nodfp->xoffset = 0;
+	nodfp->class = PPARAM;
+	nodfp->sym = lookup(".fp");
 }
 
 struct

src/cmd/gc/runtime.go

@@ -16,7 +16,7 @@ func throwreturn()
 func throwinit()
 
 func panic(interface{})
-func recover() interface{}
+func recover(*int32) interface{}
 
 func printbool(bool)
 func printfloat(float64)

src/cmd/gc/subr.c

@@ -2923,7 +2923,7 @@ genwrapper(Type *rcvr, Type *method, Sym *newnam)
 
 	funcbody(fn);
 	typecheck(&fn, Etop);
-	funccompile(fn);
+	funccompile(fn, 0);
 }
 
 /*

src/cmd/gc/walk.c

@@ -391,6 +391,7 @@ walkstmt(Node **np)
 	case OPRINTN:
 	case OPANIC:
 	case OEMPTY:
+	case ORECOVER:
 		if(n->typecheck == 0)
 			fatal("missing typecheck");
 		init = n->ninit;
@@ -631,7 +632,7 @@ walkexpr(Node **np, NodeList **init)
 		goto ret;
 
 	case ORECOVER:
-		n = mkcall("recover", n->type, init);
+		n = mkcall("recover", n->type, init, nod(OADDR, nodfp, N));
 		goto ret;
 
 	case OLITERAL:

src/libmach/8db.c

@@ -147,8 +147,6 @@ i386trace(Map *map, uvlong pc, uvlong sp, uvlong link, Tracer trace)
 	// G is
 	//	byte* stackguard
 	//	byte* stackbase (= Stktop*)
-	//	Defer* defer
-	//	Gobuf sched
 	// TODO(rsc): Need some way to get at the g for other threads.
 	// Probably need to pass it into the trace function.
 	g = 0;

src/pkg/runtime/proc.c

@@ -447,6 +447,32 @@ scheduler(void)
 	lock(&sched);
 	if(gosave(&m->sched) != 0){
 		gp = m->curg;
+		if(gp->status == Grecovery) {
+			// switched to scheduler to get stack unwound.
+			// don't go through the full scheduling logic.
+			Defer *d;
+
+			d = gp->defer;
+			gp->defer = d->link;
+			
+			// unwind to the stack frame with d->sp in it.
+			unwindstack(gp, d->sp);
+			if(d->sp < gp->stackguard || gp->stackbase < d->sp)
+				throw("bad stack in recovery");
+			
+			// make the deferproc for this d return again,
+			// this time returning 1.  function will jump to
+			// standard return epilogue.
+			// the -2*sizeof(uintptr) makes up for the
+			// two extra words that are on the stack at
+			// each call to deferproc.
+			// (the pc we're returning to does pop pop
+			// before it tests the return value.)
+			gp->sched.sp = d->sp - 2*sizeof(uintptr);
+			gp->sched.pc = d->pc;
+			free(d);
+			gogo(&gp->sched, 1);
+		}
 
 		// Jumped here via gosave/gogo, so didn't
 		// execute lock(&sched) above.
@@ -720,6 +746,10 @@ newstack(void)
 	top->args = args;
 	top->free = free;
 	
+	// copy flag from panic
+	top->panic = g1->ispanic;
+	g1->ispanic = false;
+
 	g1->stackbase = (byte*)top;
 	g1->stackguard = stk + StackGuard;
 
@@ -819,7 +849,7 @@ newproc1(byte *fn, byte *argp, int32 narg, int32 nret)
 }
 
 #pragma textflag 7
-void
+uintptr
 ·deferproc(int32 siz, byte* fn, ...)
 {
 	Defer *d;
@@ -828,10 +858,19 @@ void
 	d->fn = fn;
 	d->sp = (byte*)(&fn+1);
 	d->siz = siz;
+	d->pc = ·getcallerpc(&siz);
 	mcpy(d->args, d->sp, d->siz);
 
 	d->link = g->defer;
 	g->defer = d;
+	
+	// deferproc returns 0 normally.
+	// a deferred func that stops a panic
+	// makes the deferproc return 1.
+	// the code the compiler generates always
+	// checks the return value and jumps to the
+	// end of the function if deferproc returns != 0.
+	return 0;
 }
 
 #pragma textflag 7
@@ -888,6 +927,131 @@ unwindstack(G *gp, byte *sp)
 	}
 }
 
+static void
+printpanics(Panic *p)
+{
+	if(p->link) {
+		printpanics(p->link);
+		printf("\t");
+	}
+	printf("panic: ");
+	printany(p->arg);
+	if(p->recovered)
+		printf(" [recovered]");
+	printf("\n");
+}
+	
+void
+·panic(Eface e)
+{
+	Defer *d;
+	Panic *p;
+
+	p = mal(sizeof *p);
+	p->arg = e;
+	p->link = g->panic;
+	p->stackbase = g->stackbase;
+	g->panic = p;
+
+	for(;;) {
+		d = g->defer;
+		if(d == nil)
+			break;
+		// take defer off list in case of recursive panic
+		g->defer = d->link;
+		g->ispanic = true;	// rock for newstack, where reflect.call ends up
+		reflect·call(d->fn, d->args, d->siz);
+		if(p->recovered) {
+			g->panic = p->link;
+			free(p);
+			// put recovering defer back on list
+			// for scheduler to find.
+			d->link = g->defer;
+			g->defer = d;
+			g->status = Grecovery;
+			gosched();
+			throw("recovery failed"); // gosched should not return
+		}
+		free(d);
+	}
+
+	// ran out of deferred calls - old-school panic now
+	fd = 2;
+	printpanics(g->panic);
+	panic(0);
+}
+
+#pragma textflag 7	/* no split, or else g->stackguard is not the stack for fp */
+void
+·recover(byte *fp, Eface ret)
+{
+	Stktop *top, *oldtop;
+	Panic *p;
+
+	// Must be a panic going on.
+	if((p = g->panic) == nil || p->recovered)
+		goto nomatch;
+
+	// Frame must be at the top of the stack segment,
+	// because each deferred call starts a new stack
+	// segment as a side effect of using reflect.call.
+	// (There has to be some way to remember the
+	// variable argument frame size, and the segment
+	// code already takes care of that for us, so we
+	// reuse it.)
+	//
+	// As usual closures complicate things: the fp that
+	// the closure implementation function claims to have
+	// is where the explicit arguments start, after the
+	// implicit pointer arguments and PC slot.
+	// If we're on the first new segment for a closure,
+	// then fp == top - top->args is correct, but if
+	// the closure has its own big argument frame and
+	// allocated a second segment (see below),
+	// the fp is slightly above top - top->args.
+	// That condition can't happen normally though
+	// (stack pointer go down, not up), so we can accept
+	// any fp between top and top - top->args as
+	// indicating the top of the segment.
+	top = (Stktop*)g->stackbase;
+	if(fp < (byte*)top - top->args || (byte*)top < fp)
+		goto nomatch;
+
+	// The deferred call makes a new segment big enough
+	// for the argument frame but not necessarily big
+	// enough for the function's local frame (size unknown
+	// at the time of the call), so the function might have
+	// made its own segment immediately.  If that's the
+	// case, back top up to the older one, the one that
+	// reflect.call would have made for the panic.
+	//
+	// The fp comparison here checks that the argument
+	// frame that was copied during the split (the top->args
+	// bytes above top->fp) abuts the old top of stack.
+	// This is a correct test for both closure and non-closure code.
+	oldtop = (Stktop*)top->stackbase;
+	if(oldtop != nil && top->fp == (byte*)oldtop - top->args)
+		top = oldtop;
+
+	// Now we have the segment that was created to
+	// run this call.  It must have been marked as a panic segment.
+	if(!top->panic)
+		goto nomatch;
+
+	// Okay, this is the top frame of a deferred call
+	// in response to a panic.  It can see the panic argument.
+	p->recovered = 1;
+	ret = p->arg;
+	FLUSH(&ret);
+	return;
+
+nomatch:
+	ret.type = nil;
+	ret.data = nil;
+	FLUSH(&ret);
+}
+
+
 // Put on gfree list.  Sched must be locked.
 static void
 gfput(G *g)

src/pkg/runtime/runtime.c

@@ -41,15 +41,6 @@ panic(int32 unused)
 	exit(2);
 }
 
-void
-·panic(Eface e)
-{
-	fd = 2;
-	printf("panic: ");
-	printany(e);
-	panic(0);
-}
-
 void
 ·throwindex(void)
 {

src/pkg/runtime/runtime.h

@@ -62,6 +62,7 @@ typedef	struct	Itab		Itab;
 typedef	struct	Eface		Eface;
 typedef	struct	Type		Type;
 typedef	struct	Defer		Defer;
+typedef	struct	Panic		Panic;
 typedef	struct	hash		Hmap;
 typedef	struct	Hchan		Hchan;
 typedef	struct	Complex64	Complex64;
@@ -98,6 +99,7 @@ enum
 	Gwaiting,
 	Gmoribund,
 	Gdead,
+	Grecovery,
 };
 enum
 {
@@ -176,7 +178,8 @@ struct	G
 	byte*	stackguard;	// cannot move - also known to linker, libmach, libcgo
 	byte*	stackbase;	// cannot move - also known to libmach, libcgo
 	Defer*	defer;
-	Gobuf	sched;		// cannot move - also known to libmach
+	Panic*	panic;
+	Gobuf	sched;
 	byte*	stack0;
 	byte*	entry;		// initial function
 	G*	alllink;	// on allg
@@ -186,6 +189,7 @@ struct	G
 	uint32	selgen;		// valid sudog pointer
 	G*	schedlink;
 	bool	readyonstop;
+	bool	ispanic;
 	M*	m;		// for debuggers, but offset not hard-coded
 	M*	lockedm;
 	void	(*cgofn)(void*);	// for cgo/ffi
@@ -240,6 +244,7 @@ struct	Stktop
 	// function call, which uses an off-stack argument frame.
 	uint8*	fp;
 	bool	free;	// call stackfree for this frame?
+	bool	panic;	// is this frame the top of a panic?
 };
 struct	Alg
 {
@@ -311,11 +316,23 @@ struct Defer
 {
 	int32	siz;
 	byte*	sp;
+	byte*	pc;
 	byte*	fn;
 	Defer*	link;
 	byte	args[8];	// padded to actual size
 };
 
+/*
+ * panics
+ */
+struct Panic
+{
+	Eface	arg;		// argument to panic
+	byte*	stackbase;	// g->stackbase in panic
+	Panic*	link;		// link to earlier panic
+	bool	recovered;	// whether this panic is over
+};
+
 /*
  * external data
  */
@@ -400,6 +417,7 @@ void*	malloc(uintptr size);
 void	free(void *v);
 void	addfinalizer(void*, void(*fn)(void*), int32);
 void	walkfintab(void (*fn)(void*));
+void	runpanic(Panic*);
 
 void	exit(int32);
 void	breakpoint(void);

test/golden.out

@@ -190,5 +190,6 @@ bar
 bal
 bal
 panic: barCount != 1
+
 panic PC=xxx
 BUG