runtime: convert select implementation to Go.

LGTM=rsc
R=golang-codereviews, bradfitz, iant, khr, rsc
CC=golang-codereviews
https://codereview.appspot.com/139020043

10 files changed, 674 insertions, 672 deletions

diff --git a/src/pkg/reflect/value.go b/src/pkg/reflect/value.go
index 4394ed073..76086c561 100644
--- a/src/pkg/reflect/value.go
+++ b/src/pkg/reflect/value.go
@@ -2073,7 +2073,7 @@ func Copy(dst, src Value) int {
 }
 
 // A runtimeSelect is a single case passed to rselect.
-// This must match ../runtime/chan.c:/runtimeSelect
+// This must match ../runtime/select.go:/runtimeSelect
 type runtimeSelect struct {
 	dir uintptr        // 0, SendDir, or RecvDir
 	typ *rtype         // channel type
@@ -2091,7 +2091,7 @@ func rselect([]runtimeSelect) (chosen int, recvOK bool)
 // A SelectDir describes the communication direction of a select case.
 type SelectDir int
 
-// NOTE: These values must match ../runtime/chan.c:/SelectDir.
+// NOTE: These values must match ../runtime/select.go:/selectDir.
 
 const (
 	_             SelectDir = iota
diff --git a/src/pkg/runtime/chan.go b/src/pkg/runtime/chan.go
index 5e972983c..77df16939 100644
--- a/src/pkg/runtime/chan.go
+++ b/src/pkg/runtime/chan.go
@@ -4,8 +4,7 @@
 
 package runtime
 
-// This file contains the implementation of Go channels
-// and select statements.
+// This file contains the implementation of Go channels.
 
 import "unsafe"
 
diff --git a/src/pkg/runtime/chan.goc b/src/pkg/runtime/chan.goc
deleted file mode 100644
index f14b58d52..000000000
--- a/src/pkg/runtime/chan.goc
+++ /dev/null
@@ -1,664 +0,0 @@
-// Copyright 2009 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package runtime
-#include "runtime.h"
-#include "arch_GOARCH.h"
-#include "type.h"
-#include "race.h"
-#include "malloc.h"
-#include "chan.h"
-#include "mgc0.h"
-#include "typekind.h"
-#include "../../cmd/ld/textflag.h"
-
-static	void	dequeueg(WaitQ*);
-static	SudoG*	dequeue(WaitQ*);
-static	void	enqueue(WaitQ*, SudoG*);
-static	void	racesync(Hchan*, SudoG*);
-
-// TODO(khr): temporary placeholders until the rest of this code is moved to Go.
-extern byte runtime·chansend;
-extern byte runtime·chanrecv;
-
-static int64
-selectsize(int32 size)
-{
-	Select *sel;
-	int64 selsize;
-
-	selsize = sizeof(*sel) +
-		(size-1)*sizeof(sel->scase[0]) +
-		size*sizeof(sel->lockorder[0]) +
-		size*sizeof(sel->pollorder[0]);
-	return ROUND(selsize, Int64Align);
-}
-
-#pragma textflag NOSPLIT
-func newselect(sel *Select, selsize int64, size int32) {
-	if(selsize != selectsize(size)) {
-		runtime·printf("runtime: bad select size %D, want %D\n", selsize, selectsize(size));
-		runtime·throw("bad select size");
-	}
-	sel->tcase = size;
-	sel->ncase = 0;
-	sel->lockorder = (void*)(sel->scase + size);
-	sel->pollorder = (void*)(sel->lockorder + size);
-
-	if(debug)
-		runtime·printf("newselect s=%p size=%d\n", sel, size);
-}
-
-// cut in half to give stack a chance to split
-static void selectsend(Select *sel, Hchan *c, void *pc, void *elem, int32 so);
-
-#pragma textflag NOSPLIT
-func selectsend(sel *Select, c *Hchan, elem *byte) (selected bool) {
-	selected = false;
-
-	// nil cases do not compete
-	if(c != nil)
-		selectsend(sel, c, runtime·getcallerpc(&sel), elem, (byte*)&selected - (byte*)&sel);
-}
-
-static void
-selectsend(Select *sel, Hchan *c, void *pc, void *elem, int32 so)
-{
-	int32 i;
-	Scase *cas;
-
-	i = sel->ncase;
-	if(i >= sel->tcase)
-		runtime·throw("selectsend: too many cases");
-	sel->ncase = i+1;
-	cas = &sel->scase[i];
-
-	cas->pc = pc;
-	cas->chan = c;
-	cas->so = so;
-	cas->kind = CaseSend;
-	cas->sg.elem = elem;
-
-	if(debug)
-		runtime·printf("selectsend s=%p pc=%p chan=%p so=%d\n",
-			sel, cas->pc, cas->chan, cas->so);
-}
-
-// cut in half to give stack a chance to split
-static void selectrecv(Select *sel, Hchan *c, void *pc, void *elem, bool*, int32 so);
-
-#pragma textflag NOSPLIT
-func selectrecv(sel *Select, c *Hchan, elem *byte) (selected bool) {
-	selected = false;
-
-	// nil cases do not compete
-	if(c != nil)
-		selectrecv(sel, c, runtime·getcallerpc(&sel), elem, nil, (byte*)&selected - (byte*)&sel);
-}
-
-#pragma textflag NOSPLIT
-func selectrecv2(sel *Select, c *Hchan, elem *byte, received *bool) (selected bool) {
-	selected = false;
-
-	// nil cases do not compete
-	if(c != nil)
-		selectrecv(sel, c, runtime·getcallerpc(&sel), elem, received, (byte*)&selected - (byte*)&sel);
-}
-
-static void
-selectrecv(Select *sel, Hchan *c, void *pc, void *elem, bool *received, int32 so)
-{
-	int32 i;
-	Scase *cas;
-
-	i = sel->ncase;
-	if(i >= sel->tcase)
-		runtime·throw("selectrecv: too many cases");
-	sel->ncase = i+1;
-	cas = &sel->scase[i];
-	cas->pc = pc;
-	cas->chan = c;
-
-	cas->so = so;
-	cas->kind = CaseRecv;
-	cas->sg.elem = elem;
-	cas->receivedp = received;
-
-	if(debug)
-		runtime·printf("selectrecv s=%p pc=%p chan=%p so=%d\n",
-			sel, cas->pc, cas->chan, cas->so);
-}
-
-// cut in half to give stack a chance to split
-static void selectdefault(Select*, void*, int32);
-
-#pragma textflag NOSPLIT
-func selectdefault(sel *Select) (selected bool) {
-	selected = false;
-	selectdefault(sel, runtime·getcallerpc(&sel), (byte*)&selected - (byte*)&sel);
-}
-
-static void
-selectdefault(Select *sel, void *callerpc, int32 so)
-{
-	int32 i;
-	Scase *cas;
-
-	i = sel->ncase;
-	if(i >= sel->tcase)
-		runtime·throw("selectdefault: too many cases");
-	sel->ncase = i+1;
-	cas = &sel->scase[i];
-	cas->pc = callerpc;
-	cas->chan = nil;
-
-	cas->so = so;
-	cas->kind = CaseDefault;
-
-	if(debug)
-		runtime·printf("selectdefault s=%p pc=%p so=%d\n",
-			sel, cas->pc, cas->so);
-}
-
-static void
-sellock(Select *sel)
-{
-	uint32 i;
-	Hchan *c, *c0;
-
-	c = nil;
-	for(i=0; i<sel->ncase; i++) {
-		c0 = sel->lockorder[i];
-		if(c0 && c0 != c) {
-			c = sel->lockorder[i];
-			runtime·lock(&c->lock);
-		}
-	}
-}
-
-static void
-selunlock(Select *sel)
-{
-	int32 i, n, r;
-	Hchan *c;
-
-	// We must be very careful here to not touch sel after we have unlocked
-	// the last lock, because sel can be freed right after the last unlock.
-	// Consider the following situation.
-	// First M calls runtime·park() in runtime·selectgo() passing the sel.
-	// Once runtime·park() has unlocked the last lock, another M makes
-	// the G that calls select runnable again and schedules it for execution.
-	// When the G runs on another M, it locks all the locks and frees sel.
-	// Now if the first M touches sel, it will access freed memory.
-	n = (int32)sel->ncase;
-	r = 0;
-	// skip the default case
-	if(n>0 && sel->lockorder[0] == nil)
-		r = 1;
-	for(i = n-1; i >= r; i--) {
-		c = sel->lockorder[i];
-		if(i>0 && sel->lockorder[i-1] == c)
-			continue;  // will unlock it on the next iteration
-		runtime·unlock(&c->lock);
-	}
-}
-
-static bool
-selparkcommit(G *gp, void *sel)
-{
-	USED(gp);
-	selunlock(sel);
-	return true;
-}
-
-func block() {
-	runtime·park(nil, nil, runtime·gostringnocopy((byte*)"select (no cases)"));	// forever
-}
-
-static void* selectgo(Select**);
-
-// selectgo(sel *byte);
-//
-// overwrites return pc on stack to signal which case of the select
-// to run, so cannot appear at the top of a split stack.
-#pragma textflag NOSPLIT
-func selectgo(sel *Select) {
-	runtime·setcallerpc(&sel, selectgo(&sel));
-}
-
-static void*
-selectgo(Select **selp)
-{
-	Select *sel;
-	uint32 o, i, j, k, done;
-	int64 t0;
-	Scase *cas, *dfl;
-	Hchan *c;
-	SudoG *sg;
-	G *gp;
-	byte *as;
-	void *pc;
-	extern uint64 runtime·blockprofilerate;
-
-	sel = *selp;
-
-	if(debug)
-		runtime·printf("select: sel=%p\n", sel);
-
-	t0 = 0;
-	if(runtime·blockprofilerate > 0) {
-		t0 = runtime·cputicks();
-		for(i=0; i<sel->ncase; i++)
-			sel->scase[i].sg.releasetime = -1;
-	}
-
-	// The compiler rewrites selects that statically have
-	// only 0 or 1 cases plus default into simpler constructs.
-	// The only way we can end up with such small sel->ncase
-	// values here is for a larger select in which most channels
-	// have been nilled out.  The general code handles those
-	// cases correctly, and they are rare enough not to bother
-	// optimizing (and needing to test).
-
-	// generate permuted order
-	for(i=0; i<sel->ncase; i++)
-		sel->pollorder[i] = i;
-	for(i=1; i<sel->ncase; i++) {
-		o = sel->pollorder[i];
-		j = runtime·fastrand1()%(i+1);
-		sel->pollorder[i] = sel->pollorder[j];
-		sel->pollorder[j] = o;
-	}
-
-	// sort the cases by Hchan address to get the locking order.
-	// simple heap sort, to guarantee n log n time and constant stack footprint.
-	for(i=0; i<sel->ncase; i++) {
-		j = i;
-		c = sel->scase[j].chan;
-		while(j > 0 && sel->lockorder[k=(j-1)/2] < c) {
-			sel->lockorder[j] = sel->lockorder[k];
-			j = k;
-		}
-		sel->lockorder[j] = c;
-	}
-	for(i=sel->ncase; i-->0; ) {
-		c = sel->lockorder[i];
-		sel->lockorder[i] = sel->lockorder[0];
-		j = 0;
-		for(;;) {
-			k = j*2+1;
-			if(k >= i)
-				break;
-			if(k+1 < i && sel->lockorder[k] < sel->lockorder[k+1])
-				k++;
-			if(c < sel->lockorder[k]) {
-				sel->lockorder[j] = sel->lockorder[k];
-				j = k;
-				continue;
-			}
-			break;
-		}
-		sel->lockorder[j] = c;
-	}
-	/*
-	for(i=0; i+1<sel->ncase; i++)
-		if(sel->lockorder[i] > sel->lockorder[i+1]) {
-			runtime·printf("i=%d %p %p\n", i, sel->lockorder[i], sel->lockorder[i+1]);
-			runtime·throw("select: broken sort");
-		}
-	*/
-	sellock(sel);
-
-loop:
-	// pass 1 - look for something already waiting
-	dfl = nil;
-	for(i=0; i<sel->ncase; i++) {
-		o = sel->pollorder[i];
-		cas = &sel->scase[o];
-		c = cas->chan;
-
-		switch(cas->kind) {
-		case CaseRecv:
-			if(c->dataqsiz > 0) {
-				if(c->qcount > 0)
-					goto asyncrecv;
-			} else {
-				sg = dequeue(&c->sendq);
-				if(sg != nil)
-					goto syncrecv;
-			}
-			if(c->closed)
-				goto rclose;
-			break;
-
-		case CaseSend:
-			if(raceenabled)
-				runtime·racereadpc(c, cas->pc, &runtime·chansend);
-			if(c->closed)
-				goto sclose;
-			if(c->dataqsiz > 0) {
-				if(c->qcount < c->dataqsiz)
-					goto asyncsend;
-			} else {
-				sg = dequeue(&c->recvq);
-				if(sg != nil)
-					goto syncsend;
-			}
-			break;
-
-		case CaseDefault:
-			dfl = cas;
-			break;
-		}
-	}
-
-	if(dfl != nil) {
-		selunlock(sel);
-		cas = dfl;
-		goto retc;
-	}
-
-
-	// pass 2 - enqueue on all chans
-	done = 0;
-	for(i=0; i<sel->ncase; i++) {
-		o = sel->pollorder[i];
-		cas = &sel->scase[o];
-		c = cas->chan;
-		sg = &cas->sg;
-		sg->g = g;
-		sg->selectdone = &done;
-
-		switch(cas->kind) {
-		case CaseRecv:
-			enqueue(&c->recvq, sg);
-			break;
-
-		case CaseSend:
-			enqueue(&c->sendq, sg);
-			break;
-		}
-	}
-
-	g->param = nil;
-	runtime·park(selparkcommit, sel, runtime·gostringnocopy((byte*)"select"));
-
-	sellock(sel);
-	sg = g->param;
-
-	// pass 3 - dequeue from unsuccessful chans
-	// otherwise they stack up on quiet channels
-	for(i=0; i<sel->ncase; i++) {
-		cas = &sel->scase[i];
-		if(cas != (Scase*)sg) {
-			c = cas->chan;
-			if(cas->kind == CaseSend)
-				dequeueg(&c->sendq);
-			else
-				dequeueg(&c->recvq);
-		}
-	}
-
-	if(sg == nil)
-		goto loop;
-
-	cas = (Scase*)sg;
-	c = cas->chan;
-
-	if(c->dataqsiz > 0)
-		runtime·throw("selectgo: shouldn't happen");
-
-	if(debug)
-		runtime·printf("wait-return: sel=%p c=%p cas=%p kind=%d\n",
-			sel, c, cas, cas->kind);
-
-	if(cas->kind == CaseRecv) {
-		if(cas->receivedp != nil)
-			*cas->receivedp = true;
-	}
-
-	if(raceenabled) {
-		if(cas->kind == CaseRecv && cas->sg.elem != nil)
-			runtime·racewriteobjectpc(cas->sg.elem, c->elemtype, cas->pc, &runtime·chanrecv);
-		else if(cas->kind == CaseSend)
-			runtime·racereadobjectpc(cas->sg.elem, c->elemtype, cas->pc, &runtime·chansend);
-	}
-
-	selunlock(sel);
-	goto retc;
-
-asyncrecv:
-	// can receive from buffer
-	if(raceenabled) {
-		if(cas->sg.elem != nil)
-			runtime·racewriteobjectpc(cas->sg.elem, c->elemtype, cas->pc, &runtime·chanrecv);
-		runtime·raceacquire(chanbuf(c, c->recvx));
-		runtime·racerelease(chanbuf(c, c->recvx));
-	}
-	if(cas->receivedp != nil)
-		*cas->receivedp = true;
-	if(cas->sg.elem != nil)
-		runtime·memmove(cas->sg.elem, chanbuf(c, c->recvx), c->elemsize);
-	runtime·memclr(chanbuf(c, c->recvx), c->elemsize);
-	if(++c->recvx == c->dataqsiz)
-		c->recvx = 0;
-	c->qcount--;
-	sg = dequeue(&c->sendq);
-	if(sg != nil) {
-		gp = sg->g;
-		selunlock(sel);
-		if(sg->releasetime)
-			sg->releasetime = runtime·cputicks();
-		runtime·ready(gp);
-	} else {
-		selunlock(sel);
-	}
-	goto retc;
-
-asyncsend:
-	// can send to buffer
-	if(raceenabled) {
-		runtime·raceacquire(chanbuf(c, c->sendx));
-		runtime·racerelease(chanbuf(c, c->sendx));
-		runtime·racereadobjectpc(cas->sg.elem, c->elemtype, cas->pc, &runtime·chansend);
-	}
-	runtime·memmove(chanbuf(c, c->sendx), cas->sg.elem, c->elemsize);
-	if(++c->sendx == c->dataqsiz)
-		c->sendx = 0;
-	c->qcount++;
-	sg = dequeue(&c->recvq);
-	if(sg != nil) {
-		gp = sg->g;
-		selunlock(sel);
-		if(sg->releasetime)
-			sg->releasetime = runtime·cputicks();
-		runtime·ready(gp);
-	} else {
-		selunlock(sel);
-	}
-	goto retc;
-
-syncrecv:
-	// can receive from sleeping sender (sg)
-	if(raceenabled) {
-		if(cas->sg.elem != nil)
-			runtime·racewriteobjectpc(cas->sg.elem, c->elemtype, cas->pc, &runtime·chanrecv);
-		racesync(c, sg);
-	}
-	selunlock(sel);
-	if(debug)
-		runtime·printf("syncrecv: sel=%p c=%p o=%d\n", sel, c, o);
-	if(cas->receivedp != nil)
-		*cas->receivedp = true;
-	if(cas->sg.elem != nil)
-		runtime·memmove(cas->sg.elem, sg->elem, c->elemsize);
-	gp = sg->g;
-	gp->param = sg;
-	if(sg->releasetime)
-		sg->releasetime = runtime·cputicks();
-	runtime·ready(gp);
-	goto retc;
-
-rclose:
-	// read at end of closed channel
-	selunlock(sel);
-	if(cas->receivedp != nil)
-		*cas->receivedp = false;
-	if(cas->sg.elem != nil)
-		runtime·memclr(cas->sg.elem, c->elemsize);
-	if(raceenabled)
-		runtime·raceacquire(c);
-	goto retc;
-
-syncsend:
-	// can send to sleeping receiver (sg)
-	if(raceenabled) {
-		runtime·racereadobjectpc(cas->sg.elem, c->elemtype, cas->pc, &runtime·chansend);
-		racesync(c, sg);
-	}
-	selunlock(sel);
-	if(debug)
-		runtime·printf("syncsend: sel=%p c=%p o=%d\n", sel, c, o);
-	if(sg->elem != nil)
-		runtime·memmove(sg->elem, cas->sg.elem, c->elemsize);
-	gp = sg->g;
-	gp->param = sg;
-	if(sg->releasetime)
-		sg->releasetime = runtime·cputicks();
-	runtime·ready(gp);
-
-retc:
-	// return pc corresponding to chosen case.
-	// Set boolean passed during select creation
-	// (at offset selp + cas->so) to true.
-	// If cas->so == 0, this is a reflect-driven select and we
-	// don't need to update the boolean.
-	pc = cas->pc;
-	if(cas->so > 0) {
-		as = (byte*)selp + cas->so;
-		*as = true;
-	}
-	if(cas->sg.releasetime > 0)
-		runtime·blockevent(cas->sg.releasetime - t0, 2);
-	return pc;
-
-sclose:
-	// send on closed channel
-	selunlock(sel);
-	runtime·panicstring("send on closed channel");
-	return nil;  // not reached
-}
-
-// This struct must match ../reflect/value.go:/runtimeSelect.
-typedef struct runtimeSelect runtimeSelect;
-struct runtimeSelect
-{
-	uintptr dir;
-	ChanType *typ;
-	Hchan *ch;
-	byte *val;
-};
-
-// This enum must match ../reflect/value.go:/SelectDir.
-enum SelectDir {
-	SelectSend = 1,
-	SelectRecv,
-	SelectDefault,
-};
-
-func reflect·rselect(cases Slice) (chosen int, recvOK bool) {
-	int32 i;
-	Select *sel;
-	runtimeSelect* rcase, *rc;
-
-	chosen = -1;
-	recvOK = false;
-
-	rcase = (runtimeSelect*)cases.array;
-
-	// FlagNoScan is safe here, because all objects are also referenced from cases.
-	sel = runtime·mallocgc(selectsize(cases.len), 0, FlagNoScan);
-	runtime·newselect(sel, selectsize(cases.len), cases.len);
-	for(i=0; i<cases.len; i++) {
-		rc = &rcase[i];
-		switch(rc->dir) {
-		case SelectDefault:
-			selectdefault(sel, (void*)i, 0);
-			break;
-		case SelectSend:
-			if(rc->ch == nil)
-				break;
-			selectsend(sel, rc->ch, (void*)i, rc->val, 0);
-			break;
-		case SelectRecv:
-			if(rc->ch == nil)
-				break;
-			selectrecv(sel, rc->ch, (void*)i, rc->val, &recvOK, 0);
-			break;
-		}
-	}
-
-	chosen = (intgo)(uintptr)selectgo(&sel);
-}
-
-static SudoG*
-dequeue(WaitQ *q)
-{
-	SudoG *sgp;
-
-loop:
-	sgp = q->first;
-	if(sgp == nil)
-		return nil;
-	q->first = sgp->next;
-	if(q->last == sgp)
-		q->last = nil;
-
-	// if sgp participates in a select and is already signaled, ignore it
-	if(sgp->selectdone != nil) {
-		// claim the right to signal
-		if(*sgp->selectdone != 0 || !runtime·cas(sgp->selectdone, 0, 1))
-			goto loop;
-	}
-
-	return sgp;
-}
-
-static void
-dequeueg(WaitQ *q)
-{
-	SudoG **l, *sgp, *prevsgp;
-
-	prevsgp = nil;
-	for(l=&q->first; (sgp=*l) != nil; l=&sgp->next, prevsgp=sgp) {
-		if(sgp->g == g) {
-			*l = sgp->next;
-			if(q->last == sgp)
-				q->last = prevsgp;
-			break;
-		}
-	}
-}
-
-static void
-enqueue(WaitQ *q, SudoG *sgp)
-{
-	sgp->next = nil;
-	if(q->first == nil) {
-		q->first = sgp;
-		q->last = sgp;
-		return;
-	}
-	q->last->next = sgp;
-	q->last = sgp;
-}
-
-static void
-racesync(Hchan *c, SudoG *sg)
-{
-	runtime·racerelease(chanbuf(c, 0));
-	runtime·raceacquireg(sg->g, chanbuf(c, 0));
-	runtime·racereleaseg(sg->g, chanbuf(c, 0));
-	runtime·raceacquire(chanbuf(c, 0));
-}
diff --git a/src/pkg/runtime/chan.h b/src/pkg/runtime/chan.h
index a439fa7c9..c34ff1533 100644
--- a/src/pkg/runtime/chan.h
+++ b/src/pkg/runtime/chan.h
@@ -47,12 +47,13 @@ enum
 // Changes here must also be made in src/cmd/gc/select.c's selecttype.
 struct	Scase
 {
-	SudoG	sg;			// must be first member (cast to Scase)
+	void*	elem;			// data element
 	Hchan*	chan;			// chan
-	byte*	pc;			// return pc
+	uintptr	pc;			// return pc
 	uint16	kind;
 	uint16	so;			// vararg of selected bool
 	bool*	receivedp;		// pointer to received bool (recv2)
+	int64	releasetime;
 };
 
 // Known to compiler.
diff --git a/src/pkg/runtime/pprof/pprof_test.go b/src/pkg/runtime/pprof/pprof_test.go
index dd8f2d052..df271273c 100644
--- a/src/pkg/runtime/pprof/pprof_test.go
+++ b/src/pkg/runtime/pprof/pprof_test.go
@@ -328,13 +328,13 @@ func TestBlockProfile(t *testing.T) {
 `},
 		{"select recv async", blockSelectRecvAsync, `
 [0-9]+ [0-9]+ @ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+
-#	0x[0-9,a-f]+	runtime\.selectgo\+0x[0-9,a-f]+	.*/src/pkg/runtime/chan.goc:[0-9]+
+#	0x[0-9,a-f]+	runtime\.selectgo\+0x[0-9,a-f]+	.*/src/pkg/runtime/select.go:[0-9]+
 #	0x[0-9,a-f]+	runtime/pprof_test\.blockSelectRecvAsync\+0x[0-9,a-f]+	.*/src/pkg/runtime/pprof/pprof_test.go:[0-9]+
 #	0x[0-9,a-f]+	runtime/pprof_test\.TestBlockProfile\+0x[0-9,a-f]+	.*/src/pkg/runtime/pprof/pprof_test.go:[0-9]+
 `},
 		{"select send sync", blockSelectSendSync, `
 [0-9]+ [0-9]+ @ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+ 0x[0-9,a-f]+
-#	0x[0-9,a-f]+	runtime\.selectgo\+0x[0-9,a-f]+	.*/src/pkg/runtime/chan.goc:[0-9]+
+#	0x[0-9,a-f]+	runtime\.selectgo\+0x[0-9,a-f]+	.*/src/pkg/runtime/select.go:[0-9]+
 #	0x[0-9,a-f]+	runtime/pprof_test\.blockSelectSendSync\+0x[0-9,a-f]+	.*/src/pkg/runtime/pprof/pprof_test.go:[0-9]+
 #	0x[0-9,a-f]+	runtime/pprof_test\.TestBlockProfile\+0x[0-9,a-f]+	.*/src/pkg/runtime/pprof/pprof_test.go:[0-9]+
 `},
diff --git a/src/pkg/runtime/race.go b/src/pkg/runtime/race.go
index 3707549a3..df8493e35 100644
--- a/src/pkg/runtime/race.go
+++ b/src/pkg/runtime/race.go
@@ -45,3 +45,16 @@ func raceReadObjectPC(t *_type, addr unsafe.Pointer, callerpc, pc uintptr) {
 		racereadpc(addr, callerpc, pc)
 	}
 }
+
+func raceWriteObjectPC(t *_type, addr unsafe.Pointer, callerpc, pc uintptr) {
+	kind := t.kind & kindMask
+	if kind == kindArray || kind == kindStruct {
+		// for composite objects we have to write every address
+		// because a write might happen to any subobject.
+		racewriterangepc(addr, int(t.size), callerpc, pc)
+	} else {
+		// for non-composite objects we can write just the start
+		// address, as any write must write the first byte.
+		racewritepc(addr, callerpc, pc)
+	}
+}
diff --git a/src/pkg/runtime/race0.go b/src/pkg/runtime/race0.go
index f228c6d7b..2e67ae6a5 100644
--- a/src/pkg/runtime/race0.go
+++ b/src/pkg/runtime/race0.go
@@ -16,3 +16,5 @@ const raceenabled = false
 
 func raceReadObjectPC(t *_type, addr unsafe.Pointer, callerpc, pc uintptr) {
 }
+func raceWriteObjectPC(t *_type, addr unsafe.Pointer, callerpc, pc uintptr) {
+}
diff --git a/src/pkg/runtime/select.go b/src/pkg/runtime/select.go
new file mode 100644
index 000000000..31976cd6f
--- /dev/null
+++ b/src/pkg/runtime/select.go
@@ -0,0 +1,645 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+// This file contains the implementation of Go select statements.
+
+import "unsafe"
+
+const (
+	debugSelect = false
+)
+
+var (
+	chansendpc uintptr
+	chanrecvpc uintptr
+)
+
+func init() {
+	f := chansend
+	chansendpc = **(**uintptr)(unsafe.Pointer(&f))
+	g := chanrecv
+	chanrecvpc = **(**uintptr)(unsafe.Pointer(&g))
+}
+
+func selectsize(size uintptr) uintptr {
+	selsize := unsafe.Sizeof(_select{}) +
+		(size-1)*unsafe.Sizeof(_select{}.scase[0]) +
+		size*unsafe.Sizeof(*_select{}.lockorder) +
+		size*unsafe.Sizeof(*_select{}.pollorder)
+	return round(selsize, _Int64Align)
+}
+
+func newselect(sel *_select, selsize int64, size int32) {
+	if selsize != int64(selectsize(uintptr(size))) {
+		print("runtime: bad select size ", selsize, ", want ", selectsize(uintptr(size)), "\n")
+		gothrow("bad select size")
+	}
+	sel.tcase = uint16(size)
+	sel.ncase = 0
+	sel.lockorder = (**hchan)(add(unsafe.Pointer(&sel.scase), uintptr(size)*unsafe.Sizeof(_select{}.scase[0])))
+	sel.pollorder = (*uint16)(add(unsafe.Pointer(sel.lockorder), uintptr(size)*unsafe.Sizeof(*_select{}.lockorder)))
+
+	if debugSelect {
+		print("newselect s=", sel, " size=", size, "\n")
+	}
+}
+
+//go:nosplit
+func selectsend(sel *_select, c *hchan, elem unsafe.Pointer) (selected bool) {
+	// nil cases do not compete
+	if c != nil {
+		selectsendImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
+	}
+	return
+}
+
+// cut in half to give stack a chance to split
+func selectsendImpl(sel *_select, c *hchan, pc uintptr, elem unsafe.Pointer, so uintptr) {
+	i := sel.ncase
+	if i >= sel.tcase {
+		gothrow("selectsend: too many cases")
+	}
+	sel.ncase = i + 1
+	cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
+
+	cas.pc = pc
+	cas._chan = c
+	cas.so = uint16(so)
+	cas.kind = _CaseSend
+	cas.elem = elem
+
+	if debugSelect {
+		print("selectsend s=", sel, " pc=", hex(cas.pc), " chan=", cas._chan, " so=", cas.so, "\n")
+	}
+}
+
+//go:nosplit
+func selectrecv(sel *_select, c *hchan, elem unsafe.Pointer) (selected bool) {
+	// nil cases do not compete
+	if c != nil {
+		selectrecvImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, nil, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
+	}
+	return
+}
+
+//go:nosplit
+func selectrecv2(sel *_select, c *hchan, elem unsafe.Pointer, received *bool) (selected bool) {
+	// nil cases do not compete
+	if c != nil {
+		selectrecvImpl(sel, c, getcallerpc(unsafe.Pointer(&sel)), elem, received, uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
+	}
+	return
+}
+
+func selectrecvImpl(sel *_select, c *hchan, pc uintptr, elem unsafe.Pointer, received *bool, so uintptr) {
+	i := sel.ncase
+	if i >= sel.tcase {
+		gothrow("selectrecv: too many cases")
+	}
+	sel.ncase = i + 1
+	cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
+	cas.pc = pc
+	cas._chan = c
+	cas.so = uint16(so)
+	cas.kind = _CaseRecv
+	cas.elem = elem
+	cas.receivedp = received
+
+	if debugSelect {
+		print("selectrecv s=", sel, " pc=", hex(cas.pc), " chan=", cas._chan, " so=", cas.so, "\n")
+	}
+}
+
+//go:nosplit
+func selectdefault(sel *_select) (selected bool) {
+	selectdefaultImpl(sel, getcallerpc(unsafe.Pointer(&sel)), uintptr(unsafe.Pointer(&selected))-uintptr(unsafe.Pointer(&sel)))
+	return
+}
+
+func selectdefaultImpl(sel *_select, callerpc uintptr, so uintptr) {
+	i := sel.ncase
+	if i >= sel.tcase {
+		gothrow("selectdefault: too many cases")
+	}
+	sel.ncase = i + 1
+	cas := (*scase)(add(unsafe.Pointer(&sel.scase), uintptr(i)*unsafe.Sizeof(sel.scase[0])))
+	cas.pc = callerpc
+	cas._chan = nil
+	cas.so = uint16(so)
+	cas.kind = _CaseDefault
+
+	if debugSelect {
+		print("selectdefault s=", sel, " pc=", hex(cas.pc), " so=", cas.so, "\n")
+	}
+}
+
+func sellock(sel *_select) {
+	lockslice := sliceStruct{unsafe.Pointer(sel.lockorder), int(sel.ncase), int(sel.ncase)}
+	lockorder := *(*[]*hchan)(unsafe.Pointer(&lockslice))
+	var c *hchan
+	for _, c0 := range lockorder {
+		if c0 != nil && c0 != c {
+			c = c0
+			lock(&c.lock)
+		}
+	}
+}
+
+func selunlock(sel *_select) {
+	// We must be very careful here to not touch sel after we have unlocked
+	// the last lock, because sel can be freed right after the last unlock.
+	// Consider the following situation.
+	// First M calls runtime·park() in runtime·selectgo() passing the sel.
+	// Once runtime·park() has unlocked the last lock, another M makes
+	// the G that calls select runnable again and schedules it for execution.
+	// When the G runs on another M, it locks all the locks and frees sel.
+	// Now if the first M touches sel, it will access freed memory.
+	n := int(sel.ncase)
+	r := 0
+	lockslice := sliceStruct{unsafe.Pointer(sel.lockorder), n, n}
+	lockorder := *(*[]*hchan)(unsafe.Pointer(&lockslice))
+	// skip the default case
+	if n > 0 && lockorder[0] == nil {
+		r = 1
+	}
+	for i := n - 1; i >= r; i-- {
+		c := lockorder[i]
+		if i > 0 && c == lockorder[i-1] {
+			continue // will unlock it on the next iteration
+		}
+		unlock(&c.lock)
+	}
+}
+
+func selparkcommit(gp *g, sel *_select) bool {
+	selunlock(sel)
+	return true
+}
+
+func block() {
+	gopark(nil, nil, "select (no cases)") // forever
+}
+
+// overwrites return pc on stack to signal which case of the select
+// to run, so cannot appear at the top of a split stack.
+//go:nosplit
+func selectgo(sel *_select) {
+	pc, offset := selectgoImpl(sel)
+	*(*bool)(add(unsafe.Pointer(&sel), uintptr(offset))) = true
+	setcallerpc(unsafe.Pointer(&sel), pc)
+}
+
+// selectgoImpl returns scase.pc and scase.so for the select
+// case which fired.
+func selectgoImpl(sel *_select) (uintptr, uint16) {
+	if debugSelect {
+		print("select: sel=", sel, "\n")
+	}
+
+	scaseslice := sliceStruct{unsafe.Pointer(&sel.scase), int(sel.ncase), int(sel.ncase)}
+	scases := *(*[]scase)(unsafe.Pointer(&scaseslice))
+
+	var t0 int64
+	if blockprofilerate > 0 {
+		t0 = cputicks()
+		for i := 0; i < int(sel.ncase); i++ {
+			scases[i].releasetime = -1
+		}
+	}
+
+	// The compiler rewrites selects that statically have
+	// only 0 or 1 cases plus default into simpler constructs.
+	// The only way we can end up with such small sel.ncase
+	// values here is for a larger select in which most channels
+	// have been nilled out.  The general code handles those
+	// cases correctly, and they are rare enough not to bother
+	// optimizing (and needing to test).
+
+	// generate permuted order
+	pollslice := sliceStruct{unsafe.Pointer(sel.pollorder), int(sel.ncase), int(sel.ncase)}
+	pollorder := *(*[]uint16)(unsafe.Pointer(&pollslice))
+	for i := 0; i < int(sel.ncase); i++ {
+		pollorder[i] = uint16(i)
+	}
+	for i := 1; i < int(sel.ncase); i++ {
+		o := pollorder[i]
+		j := int(fastrand2()) % (i + 1)
+		pollorder[i] = pollorder[j]
+		pollorder[j] = o
+	}
+
+	// sort the cases by Hchan address to get the locking order.
+	// simple heap sort, to guarantee n log n time and constant stack footprint.
+	lockslice := sliceStruct{unsafe.Pointer(sel.lockorder), int(sel.ncase), int(sel.ncase)}
+	lockorder := *(*[]*hchan)(unsafe.Pointer(&lockslice))
+	for i := 0; i < int(sel.ncase); i++ {
+		j := i
+		c := scases[j]._chan
+		for j > 0 && lockorder[(j-1)/2].sortkey() < c.sortkey() {
+			k := (j - 1) / 2
+			lockorder[j] = lockorder[k]
+			j = k
+		}
+		lockorder[j] = c
+	}
+	for i := int(sel.ncase) - 1; i >= 0; i-- {
+		c := lockorder[i]
+		lockorder[i] = lockorder[0]
+		j := 0
+		for {
+			k := j*2 + 1
+			if k >= i {
+				break
+			}
+			if k+1 < i && lockorder[k].sortkey() < lockorder[k+1].sortkey() {
+				k++
+			}
+			if c.sortkey() < lockorder[k].sortkey() {
+				lockorder[j] = lockorder[k]
+				j = k
+				continue
+			}
+			break
+		}
+		lockorder[j] = c
+	}
+	/*
+		for i := 0; i+1 < int(sel.ncase); i++ {
+			if lockorder[i].sortkey() > lockorder[i+1].sortkey() {
+				print("i=", i, " x=", lockorder[i], " y=", lockorder[i+1], "\n")
+				gothrow("select: broken sort")
+			}
+		}
+	*/
+
+	// lock all the channels involved in the select
+	sellock(sel)
+
+	var (
+		gp     *g
+		done   uint32
+		sg     *sudog
+		c      *hchan
+		k      *scase
+		sglist *sudog
+		sgnext *sudog
+		fn     func(*g, *_select) bool
+	)
+
+loop:
+	// pass 1 - look for something already waiting
+	var dfl *scase
+	var cas *scase
+	for i := 0; i < int(sel.ncase); i++ {
+		cas = &scases[pollorder[i]]
+		c = cas._chan
+
+		switch cas.kind {
+		case _CaseRecv:
+			if c.dataqsiz > 0 {
+				if c.qcount > 0 {
+					goto asyncrecv
+				}
+			} else {
+				sg = c.sendq.dequeue()
+				if sg != nil {
+					goto syncrecv
+				}
+			}
+			if c.closed != 0 {
+				goto rclose
+			}
+
+		case _CaseSend:
+			if raceenabled {
+				racereadpc(unsafe.Pointer(c), cas.pc, chansendpc)
+			}
+			if c.closed != 0 {
+				goto sclose
+			}
+			if c.dataqsiz > 0 {
+				if c.qcount < c.dataqsiz {
+					goto asyncsend
+				}
+			} else {
+				sg = c.recvq.dequeue()
+				if sg != nil {
+					goto syncsend
+				}
+			}
+
+		case _CaseDefault:
+			dfl = cas
+		}
+	}
+
+	if dfl != nil {
+		selunlock(sel)
+		cas = dfl
+		goto retc
+	}
+
+	// pass 2 - enqueue on all chans
+	gp = getg()
+	done = 0
+	for i := 0; i < int(sel.ncase); i++ {
+		cas = &scases[pollorder[i]]
+		c = cas._chan
+		sg := acquireSudog()
+		sg.g = gp
+		// Note: selectdone is adjusted for stack copies in stack.c:adjustsudogs
+		sg.selectdone = (*uint32)(noescape(unsafe.Pointer(&done)))
+		sg.elem = cas.elem
+		sg.releasetime = 0
+		if t0 != 0 {
+			sg.releasetime = -1
+		}
+		sg.waitlink = gp.waiting
+		gp.waiting = sg
+
+		switch cas.kind {
+		case _CaseRecv:
+			c.recvq.enqueue(sg)
+
+		case _CaseSend:
+			c.sendq.enqueue(sg)
+		}
+	}
+
+	// wait for someone to wake us up
+	gp.param = nil
+	fn = selparkcommit
+	gopark(**(**unsafe.Pointer)(unsafe.Pointer(&fn)), unsafe.Pointer(sel), "select")
+
+	// someone woke us up
+	sellock(sel)
+	sg = (*sudog)(gp.param)
+
+	// pass 3 - dequeue from unsuccessful chans
+	// otherwise they stack up on quiet channels
+	// record the successful case, if any.
+	// We singly-linked up the SudoGs in case order, so when
+	// iterating through the linked list they are in reverse order.
+	cas = nil
+	sglist = gp.waiting
+	gp.waiting = nil
+	for i := int(sel.ncase) - 1; i >= 0; i-- {
+		k = &scases[pollorder[i]]
+		if sglist.releasetime > 0 {
+			k.releasetime = sglist.releasetime
+		}
+		if sg == sglist {
+			cas = k
+		} else {
+			c = k._chan
+			if k.kind == _CaseSend {
+				c.sendq.dequeueg(gp)
+			} else {
+				c.recvq.dequeueg(gp)
+			}
+		}
+		sgnext = sglist.waitlink
+		releaseSudog(sglist)
+		sglist = sgnext
+	}
+
+	if cas == nil {
+		goto loop
+	}
+
+	c = cas._chan
+
+	if c.dataqsiz > 0 {
+		gothrow("selectgo: shouldn't happen")
+	}
+
+	if debugSelect {
+		print("wait-return: sel=", sel, " c=", c, " cas=", cas, " kind=", cas.kind, "\n")
+	}
+
+	if cas.kind == _CaseRecv {
+		if cas.receivedp != nil {
+			*cas.receivedp = true
+		}
+	}
+
+	if raceenabled {
+		if cas.kind == _CaseRecv && cas.elem != nil {
+			raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
+		} else if cas.kind == _CaseSend {
+			raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
+		}
+	}
+
+	selunlock(sel)
+	goto retc
+
+asyncrecv:
+	// can receive from buffer
+	if raceenabled {
+		if cas.elem != nil {
+			raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
+		}
+		raceacquire(chanbuf(c, c.recvx))
+		racerelease(chanbuf(c, c.recvx))
+	}
+	if cas.receivedp != nil {
+		*cas.receivedp = true
+	}
+	if cas.elem != nil {
+		memmove(cas.elem, chanbuf(c, c.recvx), uintptr(c.elemsize))
+	}
+	memclr(chanbuf(c, c.recvx), uintptr(c.elemsize))
+	c.recvx++
+	if c.recvx == c.dataqsiz {
+		c.recvx = 0
+	}
+	c.qcount--
+	sg = c.sendq.dequeue()
+	if sg != nil {
+		gp = sg.g
+		selunlock(sel)
+		if sg.releasetime != 0 {
+			sg.releasetime = cputicks()
+		}
+		goready(gp)
+	} else {
+		selunlock(sel)
+	}
+	goto retc
+
+asyncsend:
+	// can send to buffer
+	if raceenabled {
+		raceacquire(chanbuf(c, c.sendx))
+		racerelease(chanbuf(c, c.sendx))
+		raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
+	}
+	memmove(chanbuf(c, c.sendx), cas.elem, uintptr(c.elemsize))
+	c.sendx++
+	if c.sendx == c.dataqsiz {
+		c.sendx = 0
+	}
+	c.qcount++
+	sg = c.recvq.dequeue()
+	if sg != nil {
+		gp = sg.g
+		selunlock(sel)
+		if sg.releasetime != 0 {
+			sg.releasetime = cputicks()
+		}
+		goready(gp)
+	} else {
+		selunlock(sel)
+	}
+	goto retc
+
+syncrecv:
+	// can receive from sleeping sender (sg)
+	if raceenabled {
+		if cas.elem != nil {
+			raceWriteObjectPC(c.elemtype, cas.elem, cas.pc, chanrecvpc)
+		}
+		racesync(c, sg)
+	}
+	selunlock(sel)
+	if debugSelect {
+		print("syncrecv: sel=", sel, " c=", c, "\n")
+	}
+	if cas.receivedp != nil {
+		*cas.receivedp = true
+	}
+	if cas.elem != nil {
+		memmove(cas.elem, sg.elem, uintptr(c.elemsize))
+	}
+	gp = sg.g
+	gp.param = unsafe.Pointer(sg)
+	if sg.releasetime != 0 {
+		sg.releasetime = cputicks()
+	}
+	goready(gp)
+	goto retc
+
+rclose:
+	// read at end of closed channel
+	selunlock(sel)
+	if cas.receivedp != nil {
+		*cas.receivedp = false
+	}
+	if cas.elem != nil {
+		memclr(cas.elem, uintptr(c.elemsize))
+	}
+	if raceenabled {
+		raceacquire(unsafe.Pointer(c))
+	}
+	goto retc
+
+syncsend:
+	// can send to sleeping receiver (sg)
+	if raceenabled {
+		raceReadObjectPC(c.elemtype, cas.elem, cas.pc, chansendpc)
+		racesync(c, sg)
+	}
+	selunlock(sel)
+	if debugSelect {
+		print("syncsend: sel=", sel, " c=", c, "\n")
+	}
+	if sg.elem != nil {
+		memmove(sg.elem, cas.elem, uintptr(c.elemsize))
+	}
+	gp = sg.g
+	gp.param = unsafe.Pointer(sg)
+	if sg.releasetime != 0 {
+		sg.releasetime = cputicks()
+	}
+	goready(gp)
+
+retc:
+	if cas.releasetime > 0 {
+		blockevent(cas.releasetime-t0, 2)
+	}
+	return cas.pc, cas.so
+
+sclose:
+	// send on closed channel
+	selunlock(sel)
+	panic("send on closed channel")
+}
+
+func (c *hchan) sortkey() uintptr {
+	// TODO(khr): if we have a moving garbage collector, we'll need to
+	// change this function.
+	return uintptr(unsafe.Pointer(c))
+}
+
+// A runtimeSelect is a single case passed to rselect.
+// This must match ../reflect/value.go:/runtimeSelect
+type runtimeSelect struct {
+	dir selectDir
+	typ unsafe.Pointer // channel type (not used here)
+	ch  *hchan         // channel
+	val unsafe.Pointer // ptr to data (SendDir) or ptr to receive buffer (RecvDir)
+}
+
+// These values must match ../reflect/value.go:/SelectDir.
+type selectDir int
+
+const (
+	_             selectDir = iota
+	selectSend              // case Chan <- Send
+	selectRecv              // case <-Chan:
+	selectDefault           // default
+)
+
+func reflect_rselect(cases []runtimeSelect) (chosen int, recvOK bool) {
+	// flagNoScan is safe here, because all objects are also referenced from cases.
+	size := selectsize(uintptr(len(cases)))
+	sel := (*_select)(gomallocgc(size, nil, flagNoScan))
+	newselect(sel, int64(size), int32(len(cases)))
+	r := new(bool)
+	for i := range cases {
+		rc := &cases[i]
+		switch rc.dir {
+		case selectDefault:
+			selectdefaultImpl(sel, uintptr(i), 0)
+		case selectSend:
+			if rc.ch == nil {
+				break
+			}
+			selectsendImpl(sel, rc.ch, uintptr(i), rc.val, 0)
+		case selectRecv:
+			if rc.ch == nil {
+				break
+			}
+			selectrecvImpl(sel, rc.ch, uintptr(i), rc.val, r, 0)
+		}
+	}
+
+	pc, _ := selectgoImpl(sel)
+	chosen = int(pc)
+	recvOK = *r
+	return
+}
+
+func (q *waitq) dequeueg(gp *g) {
+	var prevsgp *sudog
+	l := &q.first
+	for {
+		sgp := *l
+		if sgp == nil {
+			return
+		}
+		if sgp.g == gp {
+			*l = sgp.next
+			if q.last == sgp {
+				q.last = prevsgp
+			}
+			return
+		}
+		l = &sgp.next
+		prevsgp = sgp
+	}
+}
diff --git a/src/pkg/runtime/stack.c b/src/pkg/runtime/stack.c
index 1f51e667f..62ec5993a 100644
--- a/src/pkg/runtime/stack.c
+++ b/src/pkg/runtime/stack.c
@@ -764,6 +764,9 @@ adjustsudogs(G *gp, AdjustInfo *adjinfo)
 		e = s->elem;
 		if(adjinfo->oldstk <= e && e < adjinfo->oldbase)
 			s->elem = e + adjinfo->delta;
+		e = (byte*)s->selectdone;
+		if(adjinfo->oldstk <= e && e < adjinfo->oldbase)
+			s->selectdone = (uint32*)(e + adjinfo->delta);
 	}
 }
 
diff --git a/src/pkg/runtime/thunk.s b/src/pkg/runtime/thunk.s
index eaba5e148..048b7a723 100644
--- a/src/pkg/runtime/thunk.s
+++ b/src/pkg/runtime/thunk.s
@@ -115,3 +115,6 @@ TEXT reflect·unsafe_NewArray(SB),NOSPLIT,$0-0
 
 TEXT reflect·makechan(SB),NOSPLIT,$0-0
 	JMP	runtime·makechan(SB)
+
+TEXT reflect·rselect(SB), NOSPLIT, $0-0
+	JMP	runtime·reflect_rselect(SB)