convert 386 to use %gs instead of %fs for extern register.

required for nacl and may be nicer for ffi,
because %gs is the standard register for thread-local storage.

R=ken
OCL=34861
CL=34866

src/cmd/8c/txt.c

@@ -450,7 +450,7 @@ naddr(Node *n, Adr *a)
 		break;
 
 	case OEXREG:
-		a->type = D_INDIR + D_FS;
+		a->type = D_INDIR + D_GS;
 		a->offset = n->reg - 1;
 		break;
 

src/cmd/8l/pass.c

@@ -464,6 +464,7 @@ dostkoff(void)
 	int a, f, curframe, curbecome, maxbecome;
 	Prog *pmorestack;
 	Sym *symmorestack;
+	static int fsreg;
 
 	pmorestack = P;
 	symmorestack = lookup("sys·morestack", 0);
@@ -565,7 +566,7 @@ dostkoff(void)
 			if(!(p->from.scale & NOSPLIT)) {
 				p = appendp(p);	// load g into CX
 				p->as = AMOVL;
-				p->from.type = D_INDIR+D_FS;
+				p->from.type = D_INDIR+D_GS;
 				p->from.offset = 0;
 				p->to.type = D_CX;
 

src/pkg/runtime/386/asm.s

@@ -15,12 +15,12 @@ TEXT _rt0_386(SB),7,$0
 
 	CALL	ldt0setup(SB)
 
-	// set up %fs to refer to that ldt entry
+	// set up %gs to refer to that ldt entry
 	MOVL	$(7*8+7), AX
-	MOVW	AX, FS
+	MOVW	AX, GS
 
 	// store through it, to make sure it works
-	MOVL	$0x123, 0(FS)
+	MOVL	$0x123, 0(GS)
 	MOVL	tls0(SB), AX
 	CMPL	AX, $0x123
 	JEQ	ok

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

@@ -139,7 +139,7 @@ TEXT bsdthread_start(SB),7,$0
 	POPAL
 	SHLL	$3, DI	// segment# is ldt*8 + 7.
 	ADDL	$7, DI
-	MOVW	DI, FS
+	MOVW	DI, GS
 
 	// Now segment is established.  Initialize m, g.
 	MOVL	AX, g

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

@@ -8,20 +8,6 @@
 
 #include "386/asm.h"
 
-TEXT syscall(SB),7,$0
-	MOVL 4(SP), AX	// syscall number
-	MOVL 8(SP), BX	// arg1
-	MOVL 12(SP), CX	// arg2
-	MOVL 16(SP), DX	// arg3
-	MOVL 20(SP), SI	// arg4
-	MOVL 24(SP), DI	// arg5
-	MOVL 28(SP), BP	// arg6
-	INT $0x80
-	CMPL AX, $0xfffff001
-	JLS 2(PC)
-	INT $3	// not reached
-	RET
-
 TEXT exit(SB),7,$0
 	MOVL	$252, AX	// syscall number
 	MOVL	4(SP), BX
@@ -159,7 +145,7 @@ TEXT clone(SB),7,$0
 	POPAL
 	SHLL	$3, DI	// segment# is ldt*8 + 7 (different 7 than above)
 	ADDL	$7, DI
-	MOVW	DI, FS
+	MOVW	DI, GS
 
 	// Now segment is established.  Initialize m, g.
 	MOVL	DX, g
@@ -223,10 +209,15 @@ TEXT setldt(SB),7,$32
 	MOVL	$(SEG_32BIT|USEABLE|CONTENTS_DATA), 12(AX)	// flag bits
 
 	// call modify_ldt
-	MOVL	$123, 0(SP)	// syscall - modify_ldt
-	MOVL	$1, 4(SP)	// func = 1 (write)
-	MOVL	AX, 8(SP)	// user_desc
-	MOVL	$16, 12(SP)	// sizeof(user_desc)
-	CALL	syscall(SB)
+	MOVL	$1, BX	// func = 1 (write)
+	MOVL	AX, CX	// user_desc
+	MOVL	$16, DX	// sizeof(user_desc)
+	MOVL	$123, AX	// syscall - modify_ldt
+	INT	$0x80
+
+	// breakpoint on error
+	CMPL AX, $0xfffff001
+	JLS 2(PC)
+	INT $3
 	RET
 

src/pkg/runtime/mkasmh.sh

@@ -13,8 +13,8 @@ EOF
 
 case "$GOARCH" in
 386)
-	echo '#define	g	0(FS)'
-	echo '#define	m	4(FS)'
+	echo '#define	g	0(GS)'
+	echo '#define	m	4(GS)'
 	;;
 amd64)
 	echo '#define	g	R15'