diff --git a/src/Make.inc b/src/Make.inc
index 3334c2c..f9a3ee2 100644
--- a/src/Make.inc
+++ b/src/Make.inc
@@ -34,9 +34,10 @@
 else ifeq ($(GOOS),linux)
 else ifeq ($(GOOS),nacl)
 else ifeq ($(GOOS),tiny)
+else ifeq ($(GOOS),plan9)
 else ifeq ($(GOOS),windows)
 else
-$(error Invalid $$GOOS '$(GOOS)'; must be darwin, freebsd, linux, nacl, tiny, or windows)
+$(error Invalid $$GOOS '$(GOOS)'; must be darwin, freebsd, linux, nacl, tiny, plan9, or windows)
 endif
 
 ifeq ($(GOHOSTARCH),)
diff --git a/src/cmd/8l/asm.c b/src/cmd/8l/asm.c
index 74b4e9b..b9998b1 100644
--- a/src/cmd/8l/asm.c
+++ b/src/cmd/8l/asm.c
@@ -441,6 +441,7 @@
 			break;
 		case 2:
 			seek(cout, HEADR+textsize+segdata.filelen, 0);
+			symo = HEADR+textsize+segdata.filelen;
 			break;
 		case 3:
 		case 4:
diff --git a/src/cmd/8l/obj.c b/src/cmd/8l/obj.c
index 722857e..b1574fc 100644
--- a/src/cmd/8l/obj.c
+++ b/src/cmd/8l/obj.c
@@ -145,6 +145,9 @@
 		if(strcmp(goos, "tiny") == 0)
 			HEADTYPE = 11;
 		else
+		if(strcmp(goos, "plan9") == 0)
+			HEADTYPE = 2;
+		else
 			print("goos is not known: %s\n", goos);
 	}
 
diff --git a/src/cmd/8l/pass.c b/src/cmd/8l/pass.c
index 329a870..264771f 100644
--- a/src/cmd/8l/pass.c
+++ b/src/cmd/8l/pass.c
@@ -293,6 +293,14 @@
 					p->from.offset = 0;
 				}
 			}
+			if(HEADTYPE == 2) {	// Plan 9
+				if(p->from.type == D_INDIR+D_GS
+				&& p->to.type >= D_AX && p->to.type <= D_DI) {
+					p->as = AMOVL;
+					p->from.type = D_ADDR+D_STATIC;
+					p->from.offset += 0xdfffefc0;
+				}
+			}
 			if(p->as == ACALL || (p->as == AJMP && p->to.type != D_BRANCH)) {
 				s = p->to.sym;
 				if(s) {
@@ -418,7 +426,14 @@
 				p->from.offset = tlsoffset + 0;
 				p->to.type = D_CX;
 				break;
-
+			
+			case 2:	// Plan 9
+				p->as = AMOVL;
+				p->from.type = D_ADDR+D_STATIC;
+				p->from.offset = 0xdfffefc0;
+				p->to.type = D_CX;
+				break;
+			
 			default:
 				p->as = AMOVL;
 				p->from.type = D_INDIR+D_GS;
diff --git a/src/pkg/runtime/386/asm.s b/src/pkg/runtime/386/asm.s
index 614c026..5f0d0ed 100644
--- a/src/pkg/runtime/386/asm.s
+++ b/src/pkg/runtime/386/asm.s
@@ -26,6 +26,8 @@
 	CALL	ldt0setup(SB)
 
 	// store through it, to make sure it works
+	CMPL	isplan9(SB), $1
+	JEQ	ok
 	get_tls(BX)
 	MOVL	$0x123, g(BX)
 	MOVL	tls0(SB), AX
@@ -414,4 +416,4 @@
 GLOBL g0(SB), $1024
 GLOBL tls0(SB), $32
 GLOBL initcgo(SB), $4
-
+GLOBL isplan9(SB), $4
diff --git a/src/pkg/runtime/mkasmh.sh b/src/pkg/runtime/mkasmh.sh
index 8544d15..3ed5f74 100755
--- a/src/pkg/runtime/mkasmh.sh
+++ b/src/pkg/runtime/mkasmh.sh
@@ -24,6 +24,11 @@
 		echo '#define	g(r)	0(r)'
 		echo '#define	m(r)	4(r)'
 		;;
+	plan9)
+		echo '#define	get_tls(r)'
+		echo '#define	g(r)	0xdfffefc0'
+		echo '#define	m(r)	0xdfffefc4'
+		;;
 	linux)
 		# On Linux systems, what we call 0(GS) and 4(GS) for g and m
 		# turn into %gs:-8 and %gs:-4 (using gcc syntax to denote
diff --git a/src/pkg/runtime/plan9/386/defs.h b/src/pkg/runtime/plan9/386/defs.h
new file mode 100644
index 0000000..5df7576
--- /dev/null
+++ b/src/pkg/runtime/plan9/386/defs.h
@@ -0,0 +1 @@
+// nothing to see here
diff --git a/src/pkg/runtime/plan9/386/rt0.s b/src/pkg/runtime/plan9/386/rt0.s
new file mode 100644
index 0000000..e8d65d3
--- /dev/null
+++ b/src/pkg/runtime/plan9/386/rt0.s
@@ -0,0 +1,32 @@
+// Copyright 2010 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.
+
+TEXT	_rt0_386_plan9(SB),7, $0
+	MOVL	AX, _tos(SB)
+	
+	// move arguments down to make room for
+	// m and g at top of stack, right before Tos.
+	MOVL	SP, SI
+	SUBL	$8, SP
+	MOVL	SP, DI
+		
+	MOVL	AX, CX
+	SUBL	SI, CX
+	CLD
+	REP; MOVSB
+	
+	// adjust argv
+	SUBL	SI, DI
+	MOVL	newargc+0(SP), CX
+	LEAL	newargv+4(SP), BP
+argv_fix:
+	ADDL	DI, 0(BP)
+	ADDL	$4, BP
+	LOOP	argv_fix
+	
+	JMP	_rt0_386(SB)
+
+DATA  isplan9+0(SB)/4, $1
+GLOBL isplan9(SB), $4
+GLOBL _tos(SB), $4
diff --git a/src/pkg/runtime/plan9/386/signal.c b/src/pkg/runtime/plan9/386/signal.c
new file mode 100644
index 0000000..e7c9844
--- /dev/null
+++ b/src/pkg/runtime/plan9/386/signal.c
@@ -0,0 +1,10 @@
+// Copyright 2010 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. 
+
+#include "runtime.h"
+
+void
+gettime(int64*, int32*) 
+{
+}
diff --git a/src/pkg/runtime/plan9/386/sys.s b/src/pkg/runtime/plan9/386/sys.s
new file mode 100644
index 0000000..8dbacc0
--- /dev/null
+++ b/src/pkg/runtime/plan9/386/sys.s
@@ -0,0 +1,76 @@
+// Copyright 2010 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.
+
+#include "defs.h"
+#include "386/asm.h"
+
+// setldt(int entry, int address, int limit)
+TEXT setldt(SB),7,$0
+	RET
+
+TEXT write(SB),7,$0
+	MOVL    $20, AX
+	INT     $64
+	RET
+
+TEXT exits(SB),7,$0
+	MOVL    $8, AX
+	INT     $64
+	RET
+
+TEXT brk_(SB),7,$0
+	MOVL    $24, AX
+	INT     $64
+	RET
+
+TEXT plan9_semacquire(SB),7,$0
+	MOVL	$37, AX
+	INT	$64
+	RET
+	
+TEXT plan9_semrelease(SB),7,$0
+	MOVL	$38, AX
+	INT	$64
+	RET
+	
+TEXT rfork(SB),7,$0
+	MOVL    $19, AX // rfork
+	INT     $64
+
+	// In parent, return.
+	CMPL	AX, $0
+	JEQ	2(PC)
+	RET
+
+	// In child on old stack.
+	MOVL	mm+12(SP), BX	// m
+	MOVL	gg+16(SP), DX	// g
+	MOVL	fn+20(SP), SI	// fn
+
+	// set SP to be on the new child stack
+	MOVL	stack+8(SP), CX
+	MOVL	CX, SP
+
+	// Initialize m, g.
+	get_tls(AX)
+	MOVL	DX, g(AX)
+	MOVL	BX, m(AX)
+
+	// Initialize AX from _tos->pid
+	MOVL	0xdfffeff8, AX
+	MOVL	AX, m_procid(BX)	// save pid as m->procid
+
+	CALL	stackcheck(SB)	// smashes AX, CX
+	
+	MOVL	0(DX), DX	// paranoia; check they are not nil
+	MOVL	0(BX), BX
+	
+	// more paranoia; check that stack splitting code works
+	PUSHAL
+	CALL	emptyfunc(SB)
+	POPAL
+	
+	CALL	SI	// fn()
+	CALL	exit(SB)
+	RET
diff --git a/src/pkg/runtime/plan9/mem.c b/src/pkg/runtime/plan9/mem.c
new file mode 100644
index 0000000..7d214c3
--- /dev/null
+++ b/src/pkg/runtime/plan9/mem.c
@@ -0,0 +1,49 @@
+// Copyright 2010 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.
+
+#include "runtime.h"
+#include "malloc.h"
+
+extern byte end[];
+static byte *bloc = { end };
+
+enum
+{
+	Round = 7
+};
+
+void*
+SysAlloc(uintptr ask)
+{
+	uintptr bl;
+	
+	// Plan 9 sbrk from /sys/src/libc/9sys/sbrk.c
+	bl = ((uintptr)bloc + Round) & ~Round;
+	if(brk_((void*)(bl + ask)) < 0)
+		return (void*)-1;
+	bloc = (byte*)bl + ask;
+	return (void*)bl;
+}
+
+void
+SysFree(void *v, uintptr n)
+{
+	// from tiny/mem.c
+	// Push pointer back if this is a free
+	// of the most recent SysAlloc.
+	n += (n + Round) & ~Round;
+	if(bloc == (byte*)v+n)
+		bloc -= n;	
+}
+
+void
+SysUnused(void *v, uintptr n)
+{
+	USED(v, n);
+}
+
+void
+SysMemInit(void)
+{
+}
diff --git a/src/pkg/runtime/plan9/os.h b/src/pkg/runtime/plan9/os.h
new file mode 100644
index 0000000..748cf7a
--- /dev/null
+++ b/src/pkg/runtime/plan9/os.h
@@ -0,0 +1,27 @@
+// Copyright 2010 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.
+
+extern int32 write(int32 fd, void* buffer, int32 nbytes);
+extern void exits(int8* msg);
+extern int32 brk_(void*);
+
+/* rfork */
+enum
+{
+	RFNAMEG         = (1<<0),
+	RFENVG          = (1<<1),
+	RFFDG           = (1<<2),
+	RFNOTEG         = (1<<3),
+	RFPROC          = (1<<4),
+	RFMEM           = (1<<5),
+	RFNOWAIT        = (1<<6),
+	RFCNAMEG        = (1<<10),
+	RFCENVG         = (1<<11),
+	RFCFDG          = (1<<12),
+	RFREND          = (1<<13),
+	RFNOMNT         = (1<<14)
+};
+extern int32 rfork(int32 flags, void *stk, M *m, G *g, void (*fn)(void));
+extern int32 plan9_semacquire(uint32 *addr, int32 block);
+extern int32 plan9_semrelease(uint32 *addr, int32 count);
diff --git a/src/pkg/runtime/plan9/signals.h b/src/pkg/runtime/plan9/signals.h
new file mode 100644
index 0000000..5df7576
--- /dev/null
+++ b/src/pkg/runtime/plan9/signals.h
@@ -0,0 +1 @@
+// nothing to see here
diff --git a/src/pkg/runtime/plan9/thread.c b/src/pkg/runtime/plan9/thread.c
new file mode 100644
index 0000000..96e83fc
--- /dev/null
+++ b/src/pkg/runtime/plan9/thread.c
@@ -0,0 +1,135 @@
+// Copyright 2010 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.
+
+#include "runtime.h"
+#include "os.h"
+
+int8 *goos = "plan9";
+
+void
+minit(void)
+{
+}
+
+void
+osinit(void)
+{
+}
+
+void
+initsig(int32 queue)
+{
+}
+
+void
+exit(int32)
+{
+	exits(nil);
+}
+
+void
+newosproc(M *m, G *g, void *stk, void (*fn)(void))
+{
+	USED(m, g, stk, fn);
+	
+	m->tls[0] = m->id;	// so 386 asm can find it
+	if(0){
+		printf("newosproc stk=%p m=%p g=%p fn=%p rfork=%p id=%d/%d ostk=%p\n",
+			stk, m, g, fn, rfork, m->id, m->tls[0], &m);
+	}        
+	
+	if (rfork(RFPROC | RFMEM, stk, m, g, fn) < 0 )
+		throw("newosproc: rfork failed");
+}
+
+// Blocking locks.
+
+// Implement Locks, using semaphores.
+// l->key is the number of threads who want the lock.
+// In a race, one thread increments l->key from 0 to 1
+// and the others increment it from >0 to >1.  The thread
+// who does the 0->1 increment gets the lock, and the
+// others wait on the semaphore.  When the 0->1 thread
+// releases the lock by decrementing l->key, l->key will
+// be >0, so it will increment the semaphore to wake up
+// one of the others.  This is the same algorithm used
+// in Plan 9's user-level locks.
+
+void
+lock(Lock *l)
+{
+	if(m->locks < 0)
+		throw("lock count");
+	m->locks++;
+	
+	if(xadd(&l->key, 1) == 1)
+		return; // changed from 0 -> 1; we hold lock
+	// otherwise wait in kernel
+	while(plan9_semacquire(&l->sema, 1) < 0) {
+		/* interrupted; try again */
+	}
+}
+
+void
+unlock(Lock *l)
+{
+	m->locks--;
+	if(m->locks < 0)
+		throw("lock count");
+
+	if(xadd(&l->key, -1) == 0)
+		return; // changed from 1 -> 0: no contention
+	
+	plan9_semrelease(&l->sema, 1);
+}
+
+
+void 
+destroylock(Lock *l)
+{
+	// nothing
+}
+
+// User-level semaphore implementation:
+// try to do the operations in user space on u,
+// but when it's time to block, fall back on the kernel semaphore k.
+// This is the same algorithm used in Plan 9.
+void
+usemacquire(Usema *s)
+{
+	if((int32)xadd(&s->u, -1) < 0)
+		while(plan9_semacquire(&s->k, 1) < 0) {
+			/* interrupted; try again */
+		}
+}
+
+void
+usemrelease(Usema *s)
+{
+	if((int32)xadd(&s->u, 1) <= 0)
+		plan9_semrelease(&s->k, 1);
+}
+
+
+// Event notifications.
+void
+noteclear(Note *n)
+{
+	n->wakeup = 0;
+}
+
+void
+notesleep(Note *n)
+{
+	while(!n->wakeup)
+		usemacquire(&n->sema);
+}
+
+void
+notewakeup(Note *n)
+{
+	n->wakeup = 1;
+	usemrelease(&n->sema);
+}
+
diff --git a/src/pkg/runtime/runtime.c b/src/pkg/runtime/runtime.c
index 4b09f7b..a8f8177 100644
--- a/src/pkg/runtime/runtime.c
+++ b/src/pkg/runtime/runtime.c
@@ -147,15 +147,20 @@
 	argv = v;
 }
 
+extern int32 isplan9;
+
 void
 goargs(void)
 {
 	String *gargv;
 	String *genvv;
 	int32 i, envc;
-
-	for(envc=0; argv[argc+1+envc] != 0; envc++)
-		;
+	
+	if(isplan9)
+		envc=0;
+	else
+		for(envc=0; argv[argc+1+envc] != 0; envc++)
+			;
 
 	gargv = malloc(argc*sizeof gargv[0]);
 	genvv = malloc(envc*sizeof genvv[0]);
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index 88f53e2..92da669 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -76,7 +76,7 @@
  * segment register.
  *
  * amd64: allocated downwards from R15
- * x86: allocated upwards from 0(FS)
+ * x86: allocated upwards from 0(GS)
  * arm: allocated downwards from R10
  *
  * every C file linked into a Go program must include runtime.h