runtime: deferproc/deferreturn in Go

LGTM=rsc
R=golang-codereviews, rsc, khr
CC=golang-codereviews
https://codereview.appspot.com/139900043

13 files changed, 259 insertions, 217 deletions

diff --git a/src/cmd/api/goapi.go b/src/cmd/api/goapi.go
index 7f7b389be..ce806fc95 100644
--- a/src/cmd/api/goapi.go
+++ b/src/cmd/api/goapi.go
@@ -379,7 +379,9 @@ func (w *Walker) parseFile(dir, file string) (*ast.File, error) {
 	if w.context != nil && file == fmt.Sprintf("zruntime_defs_%s_%s.go", w.context.GOOS, w.context.GOARCH) {
 		// Just enough to keep the api checker happy.
 		src := "package runtime; type (" +
+			" _defer struct{};" +
 			" _func struct{};" +
+			" _select struct{}; " +
 			" _type struct{};" +
 			" alg struct{};" +
 			" chantype struct{};" +
@@ -403,7 +405,6 @@ func (w *Walker) parseFile(dir, file string) (*ast.File, error) {
 			" sudog struct{};" +
 			" waitq struct{};" +
 			" wincallbackcontext struct{};" +
-			" _select struct{}; " +
 			"); " +
 			"const (" +
 			" cb_max = 2000;" +
diff --git a/src/pkg/runtime/asm_386.s b/src/pkg/runtime/asm_386.s
index 8a5fd3fb0..2477726f5 100644
--- a/src/pkg/runtime/asm_386.s
+++ b/src/pkg/runtime/asm_386.s
@@ -2310,3 +2310,7 @@ TEXT runtime·fastrand1(SB), NOSPLIT, $0-4
 	MOVL	DX, m_fastrand(AX)
 	MOVL	DX, ret+0(FP)
 	RET
+
+TEXT runtime·return0(SB), NOSPLIT, $0
+	MOVL	$0, AX
+	RET
diff --git a/src/pkg/runtime/asm_amd64.s b/src/pkg/runtime/asm_amd64.s
index 0846966f1..d7e30de7b 100644
--- a/src/pkg/runtime/asm_amd64.s
+++ b/src/pkg/runtime/asm_amd64.s
@@ -2362,3 +2362,7 @@ TEXT runtime·fastrand1(SB), NOSPLIT, $0-4
 	MOVL	DX, m_fastrand(AX)
 	MOVL	DX, ret+0(FP)
 	RET
+
+TEXT runtime·return0(SB), NOSPLIT, $0
+	MOVL	$0, AX
+	RET
diff --git a/src/pkg/runtime/asm_amd64p32.s b/src/pkg/runtime/asm_amd64p32.s
index 7886861eb..5ff89cf06 100644
--- a/src/pkg/runtime/asm_amd64p32.s
+++ b/src/pkg/runtime/asm_amd64p32.s
@@ -1232,3 +1232,7 @@ TEXT runtime·fastrand1(SB), NOSPLIT, $0-4
 	MOVL	DX, m_fastrand(AX)
 	MOVL	DX, ret+0(FP)
 	RET
+
+TEXT runtime·return0(SB), NOSPLIT, $0
+	MOVL	$0, AX
+	RET
diff --git a/src/pkg/runtime/asm_arm.s b/src/pkg/runtime/asm_arm.s
index 67763e1b2..26b58cfb1 100644
--- a/src/pkg/runtime/asm_arm.s
+++ b/src/pkg/runtime/asm_arm.s
@@ -1286,3 +1286,6 @@ TEXT runtime·fastrand1(SB), NOSPLIT, $-4-4
 TEXT runtime·gocputicks(SB), NOSPLIT, $0
 	B runtime·cputicks(SB)
 
+TEXT runtime·return0(SB), NOSPLIT, $0
+	MOVW	$0, R0
+	RET
diff --git a/src/pkg/runtime/extern.go b/src/pkg/runtime/extern.go
index d75d2b4e5..2ca22d923 100644
--- a/src/pkg/runtime/extern.go
+++ b/src/pkg/runtime/extern.go
@@ -77,15 +77,6 @@ package runtime
 
 import "unsafe"
 
-// Goexit terminates the goroutine that calls it.  No other goroutine is affected.
-// Goexit runs all deferred calls before terminating the goroutine.
-//
-// Calling Goexit from the main goroutine terminates that goroutine
-// without func main returning. Since func main has not returned,
-// the program continues execution of other goroutines.
-// If all other goroutines exit, the program crashes.
-func Goexit()
-
 // sigpanic is the C function sigpanic.
 // That is, unsafe.Pointer(&sigpanic) is the C function pointer for sigpanic.
 var sigpanic struct{}
diff --git a/src/pkg/runtime/malloc.c b/src/pkg/runtime/malloc.c
index 821008155..311cc442c 100644
--- a/src/pkg/runtime/malloc.c
+++ b/src/pkg/runtime/malloc.c
@@ -21,7 +21,7 @@ MHeap runtime·mheap;
 #pragma dataflag NOPTR
 MStats runtime·memstats;
 
-static Type* notype;
+Type* runtime·conservative;
 
 void runtime·cmallocgc(uintptr size, Type *typ, uint32 flag, void **ret);
 void runtime·gc_notype_ptr(Eface*);
@@ -35,7 +35,7 @@ runtime·mallocgc(uintptr size, Type *typ, uint32 flag)
 	// TODO: maybe someday we can get rid of this.  It is
 	// probably the only location where we run Go code on the M stack.
 	if((flag&FlagNoScan) == 0 && typ == nil)
-		typ = notype;
+		typ = runtime·conservative;
 	runtime·cmallocgc(size, typ, flag, &ret);
 	return ret;
 }
@@ -259,7 +259,7 @@ runtime·mallocinit(void)
 	g->m->mcache = runtime·allocmcache();
 
 	runtime·gc_notype_ptr(&notype_eface);
-	notype = notype_eface.type;
+	runtime·conservative = notype_eface.type;
 }
 
 void*
diff --git a/src/pkg/runtime/malloc.h b/src/pkg/runtime/malloc.h
index f328feb17..d9a2bf84b 100644
--- a/src/pkg/runtime/malloc.h
+++ b/src/pkg/runtime/malloc.h
@@ -528,6 +528,7 @@ void*	runtime·cnewarray(Type*, intgo);
 void	runtime·tracealloc(void*, uintptr, Type*);
 void	runtime·tracefree(void*, uintptr);
 void	runtime·tracegc(void);
+extern Type*	runtime·conservative;
 
 int32	runtime·gcpercent;
 int32	runtime·readgogc(void);
diff --git a/src/pkg/runtime/panic.c b/src/pkg/runtime/panic.c
index 4b6829e01..72078f434 100644
--- a/src/pkg/runtime/panic.c
+++ b/src/pkg/runtime/panic.c
@@ -10,182 +10,32 @@
 
 // Code related to defer, panic and recover.
 
+// TODO: remove once code is moved to Go
+extern Defer* runtime·newdefer(int32 siz);
+extern runtime·freedefer(Defer *d);
+
 uint32 runtime·panicking;
 static Mutex paniclk;
 
-// Each P holds pool for defers with arg sizes 8, 24, 40, 56 and 72 bytes.
-// Memory block is 40 (24 for 32 bits) bytes larger due to Defer header.
-// This maps exactly to malloc size classes.
-
-// defer size class for arg size sz
-#define DEFERCLASS(sz) (((sz)+7)>>4)
-// total size of memory block for defer with arg size sz
-#define TOTALSIZE(sz) (sizeof(Defer) - sizeof(((Defer*)nil)->args) + ROUND(sz, sizeof(uintptr)))
-
-// Allocate a Defer, usually using per-P pool.
-// Each defer must be released with freedefer.
-static Defer*
-newdefer(int32 siz)
-{
-	int32 total, sc;
-	Defer *d;
-	P *p;
-
-	d = nil;
-	sc = DEFERCLASS(siz);
-	if(sc < nelem(p->deferpool)) {
-		p = g->m->p;
-		d = p->deferpool[sc];
-		if(d)
-			p->deferpool[sc] = d->link;
-	}
-	if(d == nil) {
-		// deferpool is empty or just a big defer
-		total = runtime·roundupsize(TOTALSIZE(siz));
-		d = runtime·mallocgc(total, nil, 0);
-	}
-	d->siz = siz;
-	d->special = 0;
-	d->link = g->defer;
-	g->defer = d;
-	return d;
-}
-
-// Free the given defer.
-// The defer cannot be used after this call.
-static void
-freedefer(Defer *d)
-{
-	int32 sc;
-	P *p;
-
-	if(d->special)
-		return;
-	sc = DEFERCLASS(d->siz);
-	if(sc < nelem(p->deferpool)) {
-		p = g->m->p;
-		d->link = p->deferpool[sc];
-		p->deferpool[sc] = d;
-		// No need to wipe out pointers in argp/pc/fn/args,
-		// because we empty the pool before GC.
-	}
-}
-
-// Create a new deferred function fn with siz bytes of arguments.
-// The compiler turns a defer statement into a call to this.
-// Cannot split the stack because it assumes that the arguments
-// are available sequentially after &fn; they would not be
-// copied if a stack split occurred.  It's OK for this to call
-// functions that split the stack.
-#pragma textflag NOSPLIT
-uintptr
-runtime·deferproc(int32 siz, FuncVal *fn, ...)
-{
-	Defer *d;
-
-	d = newdefer(siz);
-	d->fn = fn;
-	d->pc = (uintptr)runtime·getcallerpc(&siz);
-	if(thechar == '5')
-		d->argp = (uintptr)(&fn+2);  // skip caller's saved link register
-	else
-		d->argp = (uintptr)(&fn+1);
-	runtime·memmove(d->args, (byte*)d->argp, d->siz);
-
-	// 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;
-}
-
-// Run a deferred function if there is one.
-// The compiler inserts a call to this at the end of any
-// function which calls defer.
-// If there is a deferred function, this will call runtime·jmpdefer,
-// which will jump to the deferred function such that it appears
-// to have been called by the caller of deferreturn at the point
-// just before deferreturn was called.  The effect is that deferreturn
-// is called again and again until there are no more deferred functions.
-// Cannot split the stack because we reuse the caller's frame to
-// call the deferred function.
-
-// The single argument isn't actually used - it just has its address
-// taken so it can be matched against pending defers.
-#pragma textflag NOSPLIT
 void
-runtime·deferreturn(uintptr arg0)
-{
-	Defer *d;
-	uintptr argp;
+runtime·deferproc_m(void) {
+	int32 siz;
 	FuncVal *fn;
-
-	d = g->defer;
-	if(d == nil)
-		return;
-	argp = (uintptr)&arg0;
-	if(d->argp != argp)
-		return;
-
-	// Moving arguments around.
-	// Do not allow preemption here, because the garbage collector
-	// won't know the form of the arguments until the jmpdefer can
-	// flip the PC over to fn.
-	g->m->locks++;
-	runtime·memmove((byte*)argp, d->args, d->siz);
-	fn = d->fn;
-	g->defer = d->link;
-	freedefer(d);
-	g->m->locks--;
-	if(g->m->locks == 0 && g->preempt)
-		g->stackguard0 = StackPreempt;
-	runtime·jmpdefer(fn, argp);
-}
-
-// Ensure that defer arg sizes that map to the same defer size class
-// also map to the same malloc size class.
-void
-runtime·testdefersizes(void)
-{
-	P *p;
-	int32 i, siz, defersc, mallocsc;
-	int32 map[nelem(p->deferpool)];
-
-	for(i=0; i<nelem(p->deferpool); i++)
-		map[i] = -1;
-	for(i=0;; i++) {
-		defersc = DEFERCLASS(i);
-		if(defersc >= nelem(p->deferpool))
-			break;
-		siz = TOTALSIZE(i);
-		mallocsc = runtime·SizeToClass(siz);
-		siz = runtime·class_to_size[mallocsc];
-		// runtime·printf("defer class %d: arg size %d, block size %d(%d)\n", defersc, i, siz, mallocsc);
-		if(map[defersc] < 0) {
-			map[defersc] = mallocsc;
-			continue;
-		}
-		if(map[defersc] != mallocsc) {
-			runtime·printf("bad defer size class: i=%d siz=%d mallocsc=%d/%d\n",
-				i, siz, map[defersc], mallocsc);
-			runtime·throw("bad defer size class");
-		}
-	}
-}
-
-// Run all deferred functions for the current goroutine.
-static void
-rundefer(void)
-{
+	uintptr argp;
+	uintptr callerpc;
 	Defer *d;
 
-	while((d = g->defer) != nil) {
-		g->defer = d->link;
-		reflect·call(d->fn, (byte*)d->args, d->siz, d->siz);
-		freedefer(d);
-	}
+	siz = g->m->scalararg[0];
+	fn = g->m->ptrarg[0];
+	argp = g->m->scalararg[1];
+	callerpc = g->m->scalararg[2];
+	g->m->ptrarg[0] = nil;
+
+	d = runtime·newdefer(siz);
+	d->fn = fn;
+	d->pc = callerpc;
+	d->argp = argp;
+	runtime·memmove(d->args, (void*)argp, siz);
 }
 
 // Print all currently active panics.  Used when crashing.
@@ -252,14 +102,14 @@ runtime·panic(Eface e)
 			runtime·throw("bad defer entry in panic");
 		g->defer = dabort.link;
 
-		freedefer(d);
+		runtime·freedefer(d);
 		if(p.recovered) {
 			g->panic = p.link;
 			// Aborted panics are marked but remain on the g->panic list.
 			// Recovery will unwind the stack frames containing their Panic structs.
 			// Remove them from the list and free the associated defers.
 			while(g->panic && g->panic->aborted) {
-				freedefer(g->panic->defer);
+				runtime·freedefer(g->panic->defer);
 				g->panic = g->panic->link;
 			}
 			if(g->panic == nil)	// must be done with signal
@@ -464,20 +314,6 @@ runtime·dopanic(int32 unused)
 	runtime·exit(2);
 }
 
-void
-runtime·throwreturn(void)
-{
-	// can only happen if compiler is broken
-	runtime·throw("no return at end of a typed function - compiler is broken");
-}
-
-void
-runtime·throwinit(void)
-{
-	// can only happen with linker skew
-	runtime·throw("recursive call during initialization - linker skew");
-}
-
 bool
 runtime·canpanic(G *gp)
 {
@@ -560,16 +396,3 @@ runtime·panicstring(int8 *s)
 	runtime·newErrorCString(s, &err);
 	runtime·panic(err);
 }
-
-void
-runtime·Goexit(void)
-{
-	rundefer();
-	runtime·goexit();
-}
-
-void
-runtime·panicdivide(void)
-{
-	runtime·panicstring("integer divide by zero");
-}
diff --git a/src/pkg/runtime/panic.go b/src/pkg/runtime/panic.go
index 9b95f4967..1e35561d1 100644
--- a/src/pkg/runtime/panic.go
+++ b/src/pkg/runtime/panic.go
@@ -4,6 +4,8 @@
 
 package runtime
 
+import "unsafe"
+
 var indexError = error(errorString("index out of range"))
 
 func panicindex() {
@@ -15,3 +17,200 @@ var sliceError = error(errorString("slice bounds out of range"))
 func panicslice() {
 	panic(sliceError)
 }
+
+var divideError = error(errorString("integer divide by zero"))
+
+func panicdivide() {
+	panic(divideError)
+}
+
+func throwreturn() {
+	gothrow("no return at end of a typed function - compiler is broken")
+}
+
+func throwinit() {
+	gothrow("recursive call during initialization - linker skew")
+}
+
+// Create a new deferred function fn with siz bytes of arguments.
+// The compiler turns a defer statement into a call to this.
+//go:nosplit
+func deferproc(siz int32, fn *funcval) { // arguments of fn follow fn
+	// the arguments of fn are in a perilous state.  The stack map
+	// for deferproc does not describe them.  So we can't let garbage
+	// collection or stack copying trigger until we've copied them out
+	// to somewhere safe.  deferproc_m does that.  Until deferproc_m,
+	// we can only call nosplit routines.
+	argp := uintptr(unsafe.Pointer(&fn))
+	argp += unsafe.Sizeof(fn)
+	if GOARCH == "arm" {
+		argp += ptrSize // skip caller's saved link register
+	}
+	mp := acquirem()
+	mp.scalararg[0] = uintptr(siz)
+	mp.ptrarg[0] = unsafe.Pointer(fn)
+	mp.scalararg[1] = argp
+	mp.scalararg[2] = getcallerpc(unsafe.Pointer(&siz))
+
+	if mp.curg != getg() {
+		// go code on the m stack can't defer
+		gothrow("defer on m")
+	}
+
+	onM(deferproc_m)
+
+	releasem(mp)
+
+	// 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.
+	return0()
+	// No code can go here - the C return register has
+	// been set and must not be clobbered.
+}
+
+// Each P holds pool for defers with arg sizes 8, 24, 40, 56 and 72 bytes.
+// Memory block is 40 (24 for 32 bits) bytes larger due to Defer header.
+// This maps exactly to malloc size classes.
+
+// defer size class for arg size sz
+func deferclass(siz uintptr) uintptr {
+	return (siz + 7) >> 4
+}
+
+// total size of memory block for defer with arg size sz
+func totaldefersize(siz uintptr) uintptr {
+	return (unsafe.Sizeof(_defer{}) - unsafe.Sizeof(_defer{}.args)) + round(siz, ptrSize)
+}
+
+// Ensure that defer arg sizes that map to the same defer size class
+// also map to the same malloc size class.
+func testdefersizes() {
+	var m [len(p{}.deferpool)]int32
+
+	for i := range m {
+		m[i] = -1
+	}
+	for i := uintptr(0); ; i++ {
+		defersc := deferclass(i)
+		if defersc >= uintptr(len(m)) {
+			break
+		}
+		siz := goroundupsize(totaldefersize(i))
+		if m[defersc] < 0 {
+			m[defersc] = int32(siz)
+			continue
+		}
+		if m[defersc] != int32(siz) {
+			print("bad defer size class: i=", i, " siz=", siz, " defersc=", defersc, "\n")
+			gothrow("bad defer size class")
+		}
+	}
+}
+
+// Allocate a Defer, usually using per-P pool.
+// Each defer must be released with freedefer.
+// Note: runs on M stack
+func newdefer(siz int32) *_defer {
+	var d *_defer
+	sc := deferclass(uintptr(siz))
+	mp := acquirem()
+	if sc < uintptr(len(p{}.deferpool)) {
+		pp := mp.p
+		d = pp.deferpool[sc]
+		if d != nil {
+			pp.deferpool[sc] = d.link
+		}
+	}
+	if d == nil {
+		// deferpool is empty or just a big defer
+		total := goroundupsize(totaldefersize(uintptr(siz)))
+		d = (*_defer)(gomallocgc(total, conservative, 0))
+	}
+	d.siz = siz
+	d.special = false
+	gp := mp.curg
+	d.link = gp._defer
+	gp._defer = d
+	releasem(mp)
+	return d
+}
+
+// Free the given defer.
+// The defer cannot be used after this call.
+func freedefer(d *_defer) {
+	if d.special {
+		return
+	}
+	sc := deferclass(uintptr(d.siz))
+	if sc < uintptr(len(p{}.deferpool)) {
+		mp := acquirem()
+		pp := mp.p
+		d.link = pp.deferpool[sc]
+		pp.deferpool[sc] = d
+		releasem(mp)
+		// No need to wipe out pointers in argp/pc/fn/args,
+		// because we empty the pool before GC.
+	}
+}
+
+// Run a deferred function if there is one.
+// The compiler inserts a call to this at the end of any
+// function which calls defer.
+// If there is a deferred function, this will call runtime·jmpdefer,
+// which will jump to the deferred function such that it appears
+// to have been called by the caller of deferreturn at the point
+// just before deferreturn was called.  The effect is that deferreturn
+// is called again and again until there are no more deferred functions.
+// Cannot split the stack because we reuse the caller's frame to
+// call the deferred function.
+
+// The single argument isn't actually used - it just has its address
+// taken so it can be matched against pending defers.
+//go:nosplit
+func deferreturn(arg0 uintptr) {
+	gp := getg()
+	d := gp._defer
+	if d == nil {
+		return
+	}
+	argp := uintptr(unsafe.Pointer(&arg0))
+	if d.argp != argp {
+		return
+	}
+
+	// Moving arguments around.
+	// Do not allow preemption here, because the garbage collector
+	// won't know the form of the arguments until the jmpdefer can
+	// flip the PC over to fn.
+	mp := acquirem()
+	memmove(unsafe.Pointer(argp), unsafe.Pointer(&d.args), uintptr(d.siz))
+	fn := d.fn
+	gp._defer = d.link
+	freedefer(d)
+	releasem(mp)
+	jmpdefer(fn, argp)
+}
+
+// Goexit terminates the goroutine that calls it.  No other goroutine is affected.
+// Goexit runs all deferred calls before terminating the goroutine.
+//
+// Calling Goexit from the main goroutine terminates that goroutine
+// without func main returning. Since func main has not returned,
+// the program continues execution of other goroutines.
+// If all other goroutines exit, the program crashes.
+func Goexit() {
+	// Run all deferred functions for the current goroutine.
+	gp := getg()
+	for gp._defer != nil {
+		d := gp._defer
+		gp._defer = d.link
+		reflectcall(unsafe.Pointer(d.fn), unsafe.Pointer(&d.args), uint32(d.siz), uint32(d.siz))
+		freedefer(d)
+		// Note: we ignore recovers here because Goexit isn't a panic
+	}
+	goexit()
+}
diff --git a/src/pkg/runtime/stubs.go b/src/pkg/runtime/stubs.go
index b002da98b..bf83500b5 100644
--- a/src/pkg/runtime/stubs.go
+++ b/src/pkg/runtime/stubs.go
@@ -41,6 +41,7 @@ func racereleaseg(gp *g, addr unsafe.Pointer)
 func racefingo()
 
 // Should be a built-in for unsafe.Pointer?
+//go:nosplit
 func add(p unsafe.Pointer, x uintptr) unsafe.Pointer {
 	return unsafe.Pointer(uintptr(p) + x)
 }
@@ -85,6 +86,8 @@ func unrollgcproginplace_m()
 func setgcpercent_m()
 func setmaxthreads_m()
 func ready_m()
+func deferproc_m()
+func goexit_m()
 
 // memclr clears n bytes starting at ptr.
 // in memclr_*.s
@@ -126,6 +129,7 @@ func gothrow(s string)
 // output depends on the input.  noescape is inlined and currently
 // compiles down to a single xor instruction.
 // USE CAREFULLY!
+//go:nosplit
 func noescape(p unsafe.Pointer) unsafe.Pointer {
 	x := uintptr(p)
 	return unsafe.Pointer(x ^ 0)
@@ -141,7 +145,9 @@ func gosave(buf *gobuf)
 func read(fd int32, p unsafe.Pointer, n int32) int32
 func close(fd int32) int32
 func mincore(addr unsafe.Pointer, n uintptr, dst *byte) int32
-func jmpdefer(fv *funcval, argp unsafe.Pointer)
+
+//go:noescape
+func jmpdefer(fv *funcval, argp uintptr)
 func exit1(code int32)
 func asminit()
 func setg(gg *g)
@@ -162,6 +168,7 @@ func persistentalloc(size, align uintptr, stat *uint64) unsafe.Pointer
 func readgogc() int32
 func purgecachedstats(c *mcache)
 func gostringnocopy(b *byte) string
+func goexit()
 
 //go:noescape
 func write(fd uintptr, p unsafe.Pointer, n int32) int32
@@ -249,8 +256,15 @@ func gofuncname(f *_func) string {
 
 const _NoArgs = ^uintptr(0)
 
-var newproc, deferproc, lessstack struct{} // C/assembly functions
+var newproc, lessstack struct{} // C/assembly functions
 
 func funcspdelta(*_func, uintptr) int32 // symtab.c
 func funcarglen(*_func, uintptr) int32  // symtab.c
 const _ArgsSizeUnknown = -0x80000000    // funcdata.h
+
+// return0 is a stub used to return 0 from deferproc.
+// It is called at the very end of deferproc to signal
+// the calling Go function that it should not jump
+// to deferreturn.
+// in asm_*.s
+func return0()
diff --git a/src/pkg/runtime/traceback.go b/src/pkg/runtime/traceback.go
index 26d0f5fc9..6286c9dac 100644
--- a/src/pkg/runtime/traceback.go
+++ b/src/pkg/runtime/traceback.go
@@ -33,6 +33,7 @@ const usesLR = GOARCH != "amd64" && GOARCH != "amd64p32" && GOARCH != "386"
 // jmpdeferPC is the PC at the beginning of the jmpdefer assembly function.
 // The traceback needs to recognize it on link register architectures.
 var jmpdeferPC = funcPC(jmpdefer)
+var deferprocPC = funcPC(deferproc)
 
 // System-specific hook. See traceback_windows.go
 var systraceback func(*_func, *stkframe, *g, bool, func(*stkframe, unsafe.Pointer) bool, unsafe.Pointer) (changed, aborted bool)
@@ -342,7 +343,7 @@ func gentraceback(pc0 uintptr, sp0 uintptr, lr0 uintptr, gp *g, skip int, pcbuf
 
 	skipped:
 		waspanic = f.entry == uintptr(unsafe.Pointer(&sigpanic))
-		wasnewproc = f.entry == uintptr(unsafe.Pointer(&newproc)) || f.entry == uintptr(unsafe.Pointer(&deferproc))
+		wasnewproc = f.entry == uintptr(unsafe.Pointer(&newproc)) || f.entry == deferprocPC
 
 		// Do not unwind past the bottom of the stack.
 		if flr == nil {
@@ -582,7 +583,6 @@ func tracebackothers(me *g) {
 	unlock(&allglock)
 }
 
-func goexit()
 func mstart()
 func morestack()
 func rt0_go()
diff --git a/src/pkg/runtime/vlrt.go b/src/pkg/runtime/vlrt.go
index 50097edde..6370732ca 100644
--- a/src/pkg/runtime/vlrt.go
+++ b/src/pkg/runtime/vlrt.go
@@ -256,5 +256,3 @@ func slowdodiv(n, d uint64) (q, r uint64) {
 	}
 	return q, n
 }
-
-func panicdivide()