Fix stack on FreeBSD / add stack check across the board

FreeBSD was passing stk as the new thread's stack base, while
stk is the top of the stack in go. The added check should cause
a trap if this ever comes up in any new ports, or regresses
in current ones.

R=rsc
CC=golang-dev
https://golang.org/cl/167055

src/pkg/runtime/386/asm.s

@@ -323,6 +323,17 @@ TEXT	runcgo(SB),7,$16
 	MOVL	4(SP), SP
 	RET
 
+// check that SP is in range [g->stackbase, g->stackguard)
+TEXT stackcheck(SB), 7, $0
+	MOVL g, AX
+	CMPL g_stackbase(AX), SP
+	JHI 2(PC)
+	INT $3
+	CMPL SP, g_stackguard(AX)
+	JHI 2(PC)
+	INT $3
+	RET
+
 
 GLOBL m0(SB), $1024
 GLOBL g0(SB), $1024

src/pkg/runtime/amd64/asm.s

@@ -301,3 +301,13 @@ TEXT runcgo(SB),7,$32
 	MOVQ	8(SP), SP
 	RET
 
+// check that SP is in range [g->stackbase, g->stackguard)
+TEXT stackcheck(SB), 7, $0
+	CMPQ g_stackbase(g), SP
+	JHI 2(PC)
+	INT $3
+	CMPQ SP, g_stackguard(g)
+	JHI 2(PC)
+	INT $3
+	RET
+

src/pkg/runtime/darwin/386/sys.s

@@ -153,6 +153,7 @@ TEXT bsdthread_start(SB),7,$0
 	MOVL	AX, g
 	MOVL	DX, m
 	MOVL	BX, m_procid(DX)	// m->procid = thread port (for debuggers)
+	CALL	stackcheck(SB)		// smashes AX
 	CALL	CX	// fn()
 	CALL	exit1(SB)
 	RET

src/pkg/runtime/freebsd/386/sys.s

@@ -9,13 +9,13 @@
 #include "386/asm.h"
 	
 TEXT sys_umtx_op(SB),7,$-4
-	MOVL $454, AX
-	INT $0x80
+	MOVL	$454, AX
+	INT	$0x80
 	RET
 
 TEXT thr_new(SB),7,$-4
-	MOVL $455, AX
-	INT $0x80
+	MOVL	$455, AX
+	INT	$0x80
 	RET
 
 TEXT thr_start(SB),7,$0
@@ -33,10 +33,11 @@ TEXT thr_start(SB),7,$0
 	POPL	AX
 	POPL	AX
 	POPAL
-	MOVL BX, g
-	MOVL AX, m
-	CALL mstart(SB)
-	MOVL 0, AX			// crash (not reached)
+	MOVL	BX, g
+	MOVL	AX, m
+	CALL	stackcheck(SB)		// smashes AX
+	CALL	mstart(SB)
+	MOVL	0, AX			// crash (not reached)
 
 // Exit the entire program (like C exit)
 TEXT exit(SB),7,$-4

src/pkg/runtime/freebsd/amd64/sys.s

@@ -28,6 +28,7 @@ TEXT thr_new(SB),7,$0
 TEXT thr_start(SB),7,$0
 	MOVQ DI, m
 	MOVQ m_g0(m), g
+	CALL stackcheck(SB)
 	CALL mstart(SB)
 	MOVQ 0, AX			// crash (not reached)
 

src/pkg/runtime/freebsd/thread.c

@@ -139,8 +139,8 @@ newosproc(M *m, G *g, void *stk, void (*fn)(void))
 
 	param.start_func = thr_start;
 	param.arg = m;
-	param.stack_base = stk;
-	param.stack_size = g->stackbase - g->stackguard + 256;
+	param.stack_base = (int8*)g->stackbase;
+	param.stack_size = (byte*)stk - (byte*)g->stackbase;
 	param.child_tid = (intptr*)&m->procid;
 	param.parent_tid = nil;
 	param.tls_base = (int8*)&m->tls[0];

src/pkg/runtime/linux/386/sys.s

@@ -152,6 +152,7 @@ TEXT clone(SB),7,$0
 	MOVL	DX, g
 	MOVL	BX, m
 
+	CALL	stackcheck(SB)	// smashes AX
 	MOVL	0(DX), DX	// paranoia; check they are not nil
 	MOVL	0(BX), BX
 

src/pkg/runtime/linux/amd64/sys.s

@@ -149,6 +149,7 @@ TEXT clone(SB),7,$0
 	MOVQ	SI, SP
 	MOVQ	R8, m
 	MOVQ	R9, g
+	CALL	stackcheck(SB)
 
 	// Initialize m->procid to Linux tid
 	MOVL	$186, AX	// gettid