runtime: make onM and mcall take Go func values

This gives them correct types in Go and also makes it
possible to use them to run Go code on an m stack.

LGTM=iant
R=golang-codereviews, dave, iant
CC=dvyukov, golang-codereviews, khr, r
https://codereview.appspot.com/137970044

18 files changed, 141 insertions, 92 deletions

diff --git a/src/pkg/runtime/asm_386.s b/src/pkg/runtime/asm_386.s
index e99c114ad..07158ef0f 100644
--- a/src/pkg/runtime/asm_386.s
+++ b/src/pkg/runtime/asm_386.s
@@ -162,7 +162,7 @@ TEXT runtime·gogo(SB), NOSPLIT, $0-4
 	MOVL	gobuf_pc(BX), BX
 	JMP	BX
 
-// void mcall(void (*fn)(G*))
+// func mcall(fn func(*g))
 // Switch to m->g0's stack, call fn(g).
 // Fn must never return.  It should gogo(&g->sched)
 // to keep running g.
@@ -188,6 +188,8 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-4
 	MOVL	SI, g(CX)	// g = m->g0
 	MOVL	(g_sched+gobuf_sp)(SI), SP	// sp = m->g0->sched.sp
 	PUSHL	AX
+	MOVL	DI, DX
+	MOVL	0(DI), DI
 	CALL	DI
 	POPL	AX
 	MOVL	$runtime·badmcall2(SB), AX
@@ -202,7 +204,7 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-4
 TEXT runtime·switchtoM(SB), NOSPLIT, $0-4
 	RET
 
-// void onM(void (*fn)())
+// func onM(fn func())
 // calls fn() on the M stack.
 // switches to the M stack if not already on it, and
 // switches back when fn() returns.
@@ -227,6 +229,8 @@ TEXT runtime·onM(SB), NOSPLIT, $0-4
 
 	// call target function
 	ARGSIZE(0)
+	MOVL	DI, DX
+	MOVL	0(DI), DI
 	CALL	DI
 
 	// switch back to g
@@ -241,6 +245,8 @@ TEXT runtime·onM(SB), NOSPLIT, $0-4
 
 onm:
 	// already on m stack, just call directly
+	MOVL	DI, DX
+	MOVL	0(DI), DI
 	CALL	DI
 	RET
 
diff --git a/src/pkg/runtime/asm_amd64.s b/src/pkg/runtime/asm_amd64.s
index 0933fa92c..1d98fc265 100644
--- a/src/pkg/runtime/asm_amd64.s
+++ b/src/pkg/runtime/asm_amd64.s
@@ -153,7 +153,7 @@ TEXT runtime·gogo(SB), NOSPLIT, $0-8
 	MOVQ	gobuf_pc(BX), BX
 	JMP	BX
 
-// void mcall(void (*fn)(G*))
+// func mcall(fn func(*g))
 // Switch to m->g0's stack, call fn(g).
 // Fn must never return.  It should gogo(&g->sched)
 // to keep running g.
@@ -180,6 +180,8 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-8
 	MOVQ	(g_sched+gobuf_sp)(SI), SP	// sp = m->g0->sched.sp
 	PUSHQ	AX
 	ARGSIZE(8)
+	MOVQ	DI, DX
+	MOVQ	0(DI), DI
 	CALL	DI
 	POPQ	AX
 	MOVQ	$runtime·badmcall2(SB), AX
@@ -194,7 +196,7 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-8
 TEXT runtime·switchtoM(SB), NOSPLIT, $0-8
 	RET
 
-// void onM(void (*fn)())
+// func onM(fn func())
 // calls fn() on the M stack.
 // switches to the M stack if not already on it, and
 // switches back when fn() returns.
@@ -220,6 +222,8 @@ TEXT runtime·onM(SB), NOSPLIT, $0-8
 
 	// call target function
 	ARGSIZE(0)
+	MOVQ	DI, DX
+	MOVQ	0(DI), DI
 	CALL	DI
 
 	// switch back to g
@@ -234,6 +238,8 @@ TEXT runtime·onM(SB), NOSPLIT, $0-8
 
 onm:
 	// already on m stack, just call directly
+	MOVQ	DI, DX
+	MOVQ	0(DI), DI
 	CALL	DI
 	RET
 
diff --git a/src/pkg/runtime/asm_amd64p32.s b/src/pkg/runtime/asm_amd64p32.s
index 4a391033d..20069a6c7 100644
--- a/src/pkg/runtime/asm_amd64p32.s
+++ b/src/pkg/runtime/asm_amd64p32.s
@@ -131,7 +131,7 @@ TEXT runtime·gogo(SB), NOSPLIT, $0-4
 	MOVL	gobuf_pc(BX), BX
 	JMP	BX
 
-// void mcall(void (*fn)(G*))
+// func mcall(fn func(*g))
 // Switch to m->g0's stack, call fn(g).
 // Fn must never return.  It should gogo(&g->sched)
 // to keep running g.
@@ -158,6 +158,8 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-4
 	MOVL	(g_sched+gobuf_sp)(SI), SP	// sp = m->g0->sched.sp
 	PUSHQ	AX
 	ARGSIZE(8)
+	MOVL	DI, DX
+	MOVL	0(DI), DI
 	CALL	DI
 	POPQ	AX
 	MOVL	$runtime·badmcall2(SB), AX
@@ -172,7 +174,7 @@ TEXT runtime·mcall(SB), NOSPLIT, $0-4
 TEXT runtime·switchtoM(SB), NOSPLIT, $0-4
 	RET
 
-// void onM(void (*fn)())
+// func onM(fn func())
 // calls fn() on the M stack.
 // switches to the M stack if not already on it, and
 // switches back when fn() returns.
@@ -198,6 +200,8 @@ TEXT runtime·onM(SB), NOSPLIT, $0-4
 
 	// call target function
 	ARGSIZE(0)
+	MOVL	DI, DX
+	MOVL	0(DI), DI
 	CALL	DI
 
 	// switch back to g
@@ -212,6 +216,8 @@ TEXT runtime·onM(SB), NOSPLIT, $0-4
 
 onm:
 	// already on m stack, just call directly
+	MOVL	DI, DX
+	MOVL	0(DI), DI
 	CALL	DI
 	RET
 
diff --git a/src/pkg/runtime/asm_arm.s b/src/pkg/runtime/asm_arm.s
index 6954bb7c0..6e12cf60f 100644
--- a/src/pkg/runtime/asm_arm.s
+++ b/src/pkg/runtime/asm_arm.s
@@ -147,7 +147,7 @@ TEXT runtime·gogo(SB), NOSPLIT, $-4-4
 	MOVW	gobuf_pc(R1), R11
 	B	(R11)
 
-// void mcall(void (*fn)(G*))
+// func mcall(fn func(*g))
 // Switch to m->g0's stack, call fn(g).
 // Fn must never return.  It should gogo(&g->sched)
 // to keep running g.
@@ -173,6 +173,8 @@ TEXT runtime·mcall(SB), NOSPLIT, $-4-4
 	MOVW	(g_sched+gobuf_sp)(g), SP
 	SUB	$8, SP
 	MOVW	R1, 4(SP)
+	MOVW	R0, R7
+	MOVW	0(R0), R0
 	BL	(R0)
 	B	runtime·badmcall2(SB)
 	RET
@@ -187,7 +189,7 @@ TEXT runtime·switchtoM(SB), NOSPLIT, $0-4
 	BL	(R0) // clobber lr to ensure push {lr} is kept
 	RET
 
-// void onM(void (*fn)())
+// func onM(fn func())
 // calls fn() on the M stack.
 // switches to the M stack if not already on it, and
 // switches back when fn() returns.
@@ -213,6 +215,8 @@ TEXT runtime·onM(SB), NOSPLIT, $0-4
 
 	// call target function
 	ARGSIZE(0)
+	MOVW	R0, R7
+	MOVW	0(R0), R0
 	BL	(R0)
 
 	// switch back to g
@@ -224,6 +228,8 @@ TEXT runtime·onM(SB), NOSPLIT, $0-4
 	RET
 
 onm:
+	MOVW	R0, R7
+	MOVW	0(R0), R0
 	BL	(R0)
 	RET
 
diff --git a/src/pkg/runtime/export_test.go b/src/pkg/runtime/export_test.go
index cce9afbef..35a4130ee 100644
--- a/src/pkg/runtime/export_test.go
+++ b/src/pkg/runtime/export_test.go
@@ -31,23 +31,21 @@ type LFNode struct {
 	Pushcnt uintptr
 }
 
-var (
-	lfstackpush_m,
-	lfstackpop_m mFunction
-)
+func lfstackpush_m()
+func lfstackpop_m()
 
 func LFStackPush(head *uint64, node *LFNode) {
 	mp := acquirem()
 	mp.ptrarg[0] = unsafe.Pointer(head)
 	mp.ptrarg[1] = unsafe.Pointer(node)
-	onM(&lfstackpush_m)
+	onM(lfstackpush_m)
 	releasem(mp)
 }
 
 func LFStackPop(head *uint64) *LFNode {
 	mp := acquirem()
 	mp.ptrarg[0] = unsafe.Pointer(head)
-	onM(&lfstackpop_m)
+	onM(lfstackpop_m)
 	node := (*LFNode)(unsafe.Pointer(mp.ptrarg[0]))
 	mp.ptrarg[0] = nil
 	releasem(mp)
@@ -65,17 +63,15 @@ type ParFor struct {
 	wait    bool
 }
 
-var (
-	newparfor_m,
-	parforsetup_m,
-	parfordo_m,
-	parforiters_m mFunction
-)
+func newparfor_m()
+func parforsetup_m()
+func parfordo_m()
+func parforiters_m()
 
 func NewParFor(nthrmax uint32) *ParFor {
 	mp := acquirem()
 	mp.scalararg[0] = uintptr(nthrmax)
-	onM(&newparfor_m)
+	onM(newparfor_m)
 	desc := (*ParFor)(mp.ptrarg[0])
 	mp.ptrarg[0] = nil
 	releasem(mp)
@@ -93,14 +89,14 @@ func ParForSetup(desc *ParFor, nthr, n uint32, ctx *byte, wait bool, body func(*
 	if wait {
 		mp.scalararg[2] = 1
 	}
-	onM(&parforsetup_m)
+	onM(parforsetup_m)
 	releasem(mp)
 }
 
 func ParForDo(desc *ParFor) {
 	mp := acquirem()
 	mp.ptrarg[0] = unsafe.Pointer(desc)
-	onM(&parfordo_m)
+	onM(parfordo_m)
 	releasem(mp)
 }
 
@@ -108,7 +104,7 @@ func ParForIters(desc *ParFor, tid uint32) (uint32, uint32) {
 	mp := acquirem()
 	mp.ptrarg[0] = unsafe.Pointer(desc)
 	mp.scalararg[0] = uintptr(tid)
-	onM(&parforiters_m)
+	onM(parforiters_m)
 	begin := uint32(mp.scalararg[0])
 	end := uint32(mp.scalararg[1])
 	releasem(mp)
diff --git a/src/pkg/runtime/heapdump.c b/src/pkg/runtime/heapdump.c
index 63ffe6806..83c2be2ac 100644
--- a/src/pkg/runtime/heapdump.c
+++ b/src/pkg/runtime/heapdump.c
@@ -746,6 +746,8 @@ mdump(G *gp)
 void
 runtime∕debug·WriteHeapDump(uintptr fd)
 {
+	void (*fn)(G*);
+
 	// Stop the world.
 	runtime·semacquire(&runtime·worldsema, false);
 	g->m->gcing = 1;
@@ -762,7 +764,8 @@ runtime∕debug·WriteHeapDump(uintptr fd)
 	// Call dump routine on M stack.
 	runtime·casgstatus(g, Grunning, Gwaiting);
 	g->waitreason = runtime·gostringnocopy((byte*)"dumping heap");
-	runtime·mcall(mdump);
+	fn = mdump;
+	runtime·mcall(&fn);
 
 	// Reset dump file.
 	dumpfd = 0;
diff --git a/src/pkg/runtime/malloc.go b/src/pkg/runtime/malloc.go
index 84587a36d..dbe37c810 100644
--- a/src/pkg/runtime/malloc.go
+++ b/src/pkg/runtime/malloc.go
@@ -144,7 +144,7 @@ func gomallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
 			if v == nil {
 				mp := acquirem()
 				mp.scalararg[0] = tinySizeClass
-				onM(&mcacheRefill_m)
+				onM(mcacheRefill_m)
 				releasem(mp)
 				s = c.alloc[tinySizeClass]
 				v = s.freelist
@@ -175,7 +175,7 @@ func gomallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
 			if v == nil {
 				mp := acquirem()
 				mp.scalararg[0] = uintptr(sizeclass)
-				onM(&mcacheRefill_m)
+				onM(mcacheRefill_m)
 				releasem(mp)
 				s = c.alloc[sizeclass]
 				v = s.freelist
@@ -196,7 +196,7 @@ func gomallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
 		mp := acquirem()
 		mp.scalararg[0] = uintptr(size)
 		mp.scalararg[1] = uintptr(flags)
-		onM(&largeAlloc_m)
+		onM(largeAlloc_m)
 		s = (*mspan)(mp.ptrarg[0])
 		mp.ptrarg[0] = nil
 		releasem(mp)
@@ -246,7 +246,7 @@ func gomallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
 				mp.ptrarg[1] = unsafe.Pointer(typ)
 				mp.scalararg[0] = uintptr(size)
 				mp.scalararg[1] = uintptr(size0)
-				onM(&unrollgcproginplace_m)
+				onM(unrollgcproginplace_m)
 				releasem(mp)
 				goto marked
 			}
@@ -255,7 +255,7 @@ func gomallocgc(size uintptr, typ *_type, flags int) unsafe.Pointer {
 			if uintptr(atomicloadp(unsafe.Pointer(ptrmask)))&0xff == 0 {
 				mp := acquirem()
 				mp.ptrarg[0] = unsafe.Pointer(typ)
-				onM(&unrollgcprog_m)
+				onM(unrollgcprog_m)
 				releasem(mp)
 			}
 			ptrmask = (*uint8)(add(unsafe.Pointer(ptrmask), 1)) // skip the unroll flag byte
@@ -459,7 +459,7 @@ func gogc(force int32) {
 		} else {
 			mp.scalararg[2] = 0
 		}
-		onM(&gc_m)
+		onM(gc_m)
 	}
 
 	// all done
@@ -571,7 +571,7 @@ func SetFinalizer(obj interface{}, finalizer interface{}) {
 		// switch to M stack and remove finalizer
 		mp := acquirem()
 		mp.ptrarg[0] = e.data
-		onM(&removeFinalizer_m)
+		onM(removeFinalizer_m)
 		releasem(mp)
 		return
 	}
@@ -624,7 +624,7 @@ okarg:
 	mp.scalararg[0] = nret
 	mp.ptrarg[2] = unsafe.Pointer(fint)
 	mp.ptrarg[3] = unsafe.Pointer(ot)
-	onM(&setFinalizer_m)
+	onM(setFinalizer_m)
 	if mp.scalararg[0] != 1 {
 		gothrow("runtime.SetFinalizer: finalizer already set")
 	}
diff --git a/src/pkg/runtime/mcache.c b/src/pkg/runtime/mcache.c
index e17bd2144..8e98890e8 100644
--- a/src/pkg/runtime/mcache.c
+++ b/src/pkg/runtime/mcache.c
@@ -65,8 +65,11 @@ freemcache_m(G *gp)
 void
 runtime·freemcache(MCache *c)
 {
+	void (*fn)(G*);
+
 	g->m->ptrarg[0] = c;
-	runtime·mcall(freemcache_m);
+	fn = freemcache_m;
+	runtime·mcall(&fn);
 }
 
 // Gets a span that has a free object in it and assigns it
diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index 3e22acc52..2ae23e8bf 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -1141,6 +1141,7 @@ runtime·updatememstats(GCStats *stats)
 	int32 i;
 	uint64 smallfree;
 	uint64 *src, *dst;
+	void (*fn)(G*);
 
 	if(stats)
 		runtime·memclr((byte*)stats, sizeof(*stats));
@@ -1177,8 +1178,10 @@ runtime·updatememstats(GCStats *stats)
 	// Flush MCache's to MCentral.
 	if(g == g->m->g0)
 		flushallmcaches();
-	else
-		runtime·mcall(flushallmcaches_m);
+	else {
+		fn = flushallmcaches_m;
+		runtime·mcall(&fn);
+	}
 
 	// Aggregate local stats.
 	cachestats();
diff --git a/src/pkg/runtime/mgc0.go b/src/pkg/runtime/mgc0.go
index 93af63e63..2d9d76a47 100644
--- a/src/pkg/runtime/mgc0.go
+++ b/src/pkg/runtime/mgc0.go
@@ -37,7 +37,7 @@ func gc_unixnanotime(now *int64) {
 
 func freeOSMemory() {
 	gogc(2) // force GC and do eager sweep
-	onM(&scavenge_m)
+	onM(scavenge_m)
 }
 
 var poolcleanup func()
diff --git a/src/pkg/runtime/mheap.c b/src/pkg/runtime/mheap.c
index 93f33f21c..0050e9655 100644
--- a/src/pkg/runtime/mheap.c
+++ b/src/pkg/runtime/mheap.c
@@ -229,6 +229,7 @@ MSpan*
 runtime·MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass, bool large, bool needzero)
 {
 	MSpan *s;
+	void (*fn)(G*);
 
 	// Don't do any operations that lock the heap on the G stack.
 	// It might trigger stack growth, and the stack growth code needs
@@ -240,7 +241,8 @@ runtime·MHeap_Alloc(MHeap *h, uintptr npage, int32 sizeclass, bool large, bool
 		g->m->scalararg[0] = npage;
 		g->m->scalararg[1] = sizeclass;
 		g->m->scalararg[2] = large;
-		runtime·mcall(mheap_alloc_m);
+		fn = mheap_alloc_m;
+		runtime·mcall(&fn);
 		s = g->m->ptrarg[0];
 		g->m->ptrarg[0] = nil;
 	}
@@ -488,13 +490,16 @@ mheap_free_m(G *gp)
 void
 runtime·MHeap_Free(MHeap *h, MSpan *s, int32 acct)
 {
+	void (*fn)(G*);
+
 	if(g == g->m->g0) {
 		mheap_free(h, s, acct);
 	} else {
 		g->m->ptrarg[0] = h;
 		g->m->ptrarg[1] = s;
 		g->m->scalararg[0] = acct;
-		runtime·mcall(mheap_free_m);
+		fn = mheap_free_m;
+		runtime·mcall(&fn);
 	}
 }
 
diff --git a/src/pkg/runtime/panic.c b/src/pkg/runtime/panic.c
index ecf411133..4b6829e01 100644
--- a/src/pkg/runtime/panic.c
+++ b/src/pkg/runtime/panic.c
@@ -214,6 +214,7 @@ runtime·panic(Eface e)
 	Defer *d, dabort;
 	Panic p;
 	uintptr pc, argp;
+	void (*fn)(G*);
 
 	runtime·memclr((byte*)&p, sizeof p);
 	p.arg = e;
@@ -266,7 +267,8 @@ runtime·panic(Eface e)
 			// Pass information about recovering frame to recovery.
 			g->sigcode0 = (uintptr)argp;
 			g->sigcode1 = (uintptr)pc;
-			runtime·mcall(recovery);
+			fn = recovery;
+			runtime·mcall(&fn);
 			runtime·throw("recovery failed"); // mcall should not return
 		}
 	}
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index b85baca14..bc15d822c 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -1439,10 +1439,13 @@ dropg(void)
 void
 runtime·park(bool(*unlockf)(G*, void*), void *lock, String reason)
 {
+	void (*fn)(G*);
+
 	g->m->waitlock = lock;
 	g->m->waitunlockf = unlockf;
 	g->waitreason = reason;
-	runtime·mcall(runtime·park_m);
+	fn = runtime·park_m;
+	runtime·mcall(&fn);
 }
 
 bool
@@ -1487,7 +1490,10 @@ runtime·park_m(G *gp)
 void
 runtime·gosched(void)
 {
-	runtime·mcall(runtime·gosched_m);
+	void (*fn)(G*);
+	
+	fn = runtime·gosched_m;
+	runtime·mcall(&fn);
 }
 
 // runtime·gosched continuation on g0.
@@ -1518,9 +1524,12 @@ runtime·gosched_m(G *gp)
 void
 runtime·goexit(void)
 {
+	void (*fn)(G*);
+
 	if(raceenabled)
 		runtime·racegoend();
-	runtime·mcall(goexit0);
+	fn = goexit0;
+	runtime·mcall(&fn);
 }
 
 // runtime·goexit continuation on g0.
@@ -1689,6 +1698,8 @@ runtime·entersyscallblock_m(void)
 void
 runtime·exitsyscall(void)
 {
+	void (*fn)(G*);
+
 	g->m->locks++;  // see comment in entersyscall
 
 	g->waitsince = 0;
@@ -1716,7 +1727,8 @@ runtime·exitsyscall(void)
 	g->m->locks--;
 
 	// Call the scheduler.
-	runtime·mcall(exitsyscall0);
+	fn = exitsyscall0;
+	runtime·mcall(&fn);
 
 	// Scheduler returned, so we're allowed to run now.
 	// Delete the gcstack information that we left for
@@ -1858,6 +1870,7 @@ runtime·malg(int32 stacksize)
 {
 	G *newg;
 	byte *stk;
+	void (*fn)(G*);
 
 	if(StackTop < sizeof(Stktop)) {
 		runtime·printf("runtime: SizeofStktop=%d, should be >=%d\n", (int32)StackTop, (int32)sizeof(Stktop));
@@ -1874,7 +1887,8 @@ runtime·malg(int32 stacksize)
 			// have to call stackalloc on scheduler stack.
 			newg->stacksize = stacksize;
 			g->param = newg;
-			runtime·mcall(mstackalloc);
+			fn = mstackalloc;
+			runtime·mcall(&fn);
 			stk = g->param;
 			g->param = nil;
 		}
@@ -1915,6 +1929,7 @@ void
 runtime·newproc(int32 siz, FuncVal* fn, ...)
 {
 	byte *argp;
+	void (*mfn)(void);
 
 	if(thechar == '5')
 		argp = (byte*)(&fn+2);  // skip caller's saved LR
@@ -1926,7 +1941,8 @@ runtime·newproc(int32 siz, FuncVal* fn, ...)
 	g->m->scalararg[1] = (uintptr)runtime·getcallerpc(&siz);
 	g->m->ptrarg[0] = argp;
 	g->m->ptrarg[1] = fn;
-	runtime·onM(newproc_m);
+	mfn = newproc_m;
+	runtime·onM(&mfn);
 	g->m->locks--;
 }
 
@@ -2090,6 +2106,7 @@ gfget(P *p)
 {
 	G *gp;
 	byte *stk;
+	void (*fn)(G*);
 
 retry:
 	gp = p->gfree;
@@ -2117,7 +2134,8 @@ retry:
 			} else {
 				gp->stacksize = FixedStack;
 				g->param = gp;
-				runtime·mcall(mstackalloc);
+				fn = mstackalloc;
+				runtime·mcall(&fn);
 				stk = g->param;
 				g->param = nil;
 			}
diff --git a/src/pkg/runtime/proc.go b/src/pkg/runtime/proc.go
index a36b931b8..f060640a2 100644
--- a/src/pkg/runtime/proc.go
+++ b/src/pkg/runtime/proc.go
@@ -55,7 +55,7 @@ func forcegchelper() {
 // Gosched yields the processor, allowing other goroutines to run.  It does not
 // suspend the current goroutine, so execution resumes automatically.
 func Gosched() {
-	mcall(&gosched_m)
+	mcall(gosched_m)
 }
 
 func readgStatus(gp *g) uint32 {
@@ -77,7 +77,7 @@ func gopark(unlockf unsafe.Pointer, lock unsafe.Pointer, reason string) {
 	gp.waitreason = reason
 	releasem(mp)
 	// can't do anything that might move the G between Ms here.
-	mcall(&park_m)
+	mcall(park_m)
 }
 
 // Puts the current goroutine into a waiting state and unlocks the lock.
@@ -89,7 +89,7 @@ func goparkunlock(lock *mutex, reason string) {
 func goready(gp *g) {
 	mp := acquirem()
 	mp.ptrarg[0] = unsafe.Pointer(gp)
-	onM(&ready_m)
+	onM(ready_m)
 	releasem(mp)
 }
 
diff --git a/src/pkg/runtime/rdebug.go b/src/pkg/runtime/rdebug.go
index eef0f281f..e5e691122 100644
--- a/src/pkg/runtime/rdebug.go
+++ b/src/pkg/runtime/rdebug.go
@@ -13,7 +13,7 @@ func setMaxStack(in int) (out int) {
 func setGCPercent(in int32) (out int32) {
 	mp := acquirem()
 	mp.scalararg[0] = uintptr(int(in))
-	onM(&setgcpercent_m)
+	onM(setgcpercent_m)
 	out = int32(int(mp.scalararg[0]))
 	releasem(mp)
 	return out
@@ -30,7 +30,7 @@ func setPanicOnFault(new bool) (old bool) {
 func setMaxThreads(in int) (out int) {
 	mp := acquirem()
 	mp.scalararg[0] = uintptr(in)
-	onM(&setmaxthreads_m)
+	onM(setmaxthreads_m)
 	out = int(mp.scalararg[0])
 	releasem(mp)
 	return out
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index 3cc6f9a81..d67d7a007 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -809,8 +809,8 @@ void	runtime·runpanic(Panic*);
 uintptr	runtime·getcallersp(void*);
 int32	runtime·mcount(void);
 int32	runtime·gcount(void);
-void	runtime·mcall(void(*)(G*));
-void	runtime·onM(void(*)(void));
+void	runtime·mcall(void(**)(G*));
+void	runtime·onM(void(**)(void));
 uint32	runtime·fastrand1(void);
 void	runtime·rewindmorestack(Gobuf*);
 int32	runtime·timediv(int64, int32, int32*);
diff --git a/src/pkg/runtime/sigqueue.go b/src/pkg/runtime/sigqueue.go
index c51ede026..464355970 100644
--- a/src/pkg/runtime/sigqueue.go
+++ b/src/pkg/runtime/sigqueue.go
@@ -9,7 +9,7 @@ package runtime
 func signal_recv() (m uint32) {
 	for {
 		mp := acquirem()
-		onM(&signal_recv_m)
+		onM(signal_recv_m)
 		ok := mp.scalararg[0] != 0
 		m = uint32(mp.scalararg[1])
 		releasem(mp)
@@ -24,19 +24,17 @@ func signal_recv() (m uint32) {
 func signal_enable(s uint32) {
 	mp := acquirem()
 	mp.scalararg[0] = uintptr(s)
-	onM(&signal_enable_m)
+	onM(signal_enable_m)
 	releasem(mp)
 }
 
 func signal_disable(s uint32) {
 	mp := acquirem()
 	mp.scalararg[0] = uintptr(s)
-	onM(&signal_disable_m)
+	onM(signal_disable_m)
 	releasem(mp)
 }
 
-var (
-	signal_recv_m,
-	signal_enable_m,
-	signal_disable_m mFunction
-)
+func signal_recv_m()
+func signal_enable_m()
+func signal_disable_m()
diff --git a/src/pkg/runtime/stubs.go b/src/pkg/runtime/stubs.go
index 86dc47f4a..b002da98b 100644
--- a/src/pkg/runtime/stubs.go
+++ b/src/pkg/runtime/stubs.go
@@ -57,37 +57,34 @@ func acquirem() *m
 func releasem(mp *m)
 func gomcache() *mcache
 
-// An mFunction represents a C function that runs on the M stack.  It
-// can be called from Go using mcall or onM.  Through the magic of
-// linking, an mFunction variable and the corresponding C code entry
-// point live at the same address.
-type mFunction byte
-
 // in asm_*.s
-func mcall(fn *mFunction)
-func onM(fn *mFunction)
-
-// C functions that run on the M stack.  Call these like
-//   mcall(&mcacheRefill_m)
-// Arguments should be passed in m->scalararg[x] and
-// m->ptrarg[x].  Return values can be passed in those
-// same slots.
-var (
-	mcacheRefill_m,
-	largeAlloc_m,
-	gc_m,
-	scavenge_m,
-	setFinalizer_m,
-	removeFinalizer_m,
-	markallocated_m,
-	unrollgcprog_m,
-	unrollgcproginplace_m,
-	gosched_m,
-	setgcpercent_m,
-	setmaxthreads_m,
-	ready_m,
-	park_m mFunction
-)
+func mcall(func(*g))
+func onM(fn func())
+
+// C functions that run on the M stack.
+// Call using mcall.
+// These functions need to be written to arrange explicitly
+// for the goroutine to continue execution.
+func gosched_m(*g)
+func park_m(*g)
+
+// More C functions that run on the M stack.
+// Call using onM.
+// Arguments should be passed in m->scalararg[x] and m->ptrarg[x].
+// Return values can be passed in those same slots.
+// These functions return to the goroutine when they return.
+func mcacheRefill_m()
+func largeAlloc_m()
+func gc_m()
+func scavenge_m()
+func setFinalizer_m()
+func removeFinalizer_m()
+func markallocated_m()
+func unrollgcprog_m()
+func unrollgcproginplace_m()
+func setgcpercent_m()
+func setmaxthreads_m()
+func ready_m()
 
 // memclr clears n bytes starting at ptr.
 // in memclr_*.s