liblink: remove use of linkmode on ARM

Now that liblink is compiled into the compilers and assemblers,
it must not refer to the "linkmode", since that is not known until
link time. This CL makes the ARM support no longer use linkmode,
which fixes a bug with cgo binaries that contain their own TLS
variables.

The x86 code must also remove linkmode; that is issue 7164.

Fixes #6992.

R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/55160043

src/cmd/ld/data.c

@@ -878,6 +878,14 @@ dodata(void)
 			growdatsize(&datsize, s);
 		}
 		sect->len = datsize;
+	} else {
+		// References to STLSBSS symbols may be in the binary
+		// but should not be used. Give them an invalid address
+		// so that any uses will fault. Using 1 instead of 0 so that
+		// if used as an offset on ARM it will result in an unaligned
+		// address and still cause a fault.
+		for(; s != nil && s->type == STLSBSS; s = s->next)
+			s->value = 1;
 	}
 	
 	if(s != nil) {
@@ -1127,7 +1135,8 @@ address(void)
 
 	for(sym = datap; sym != nil; sym = sym->next) {
 		ctxt->cursym = sym;
-		sym->value += sym->sect->vaddr;
+		if(sym->sect != nil)
+			sym->value += sym->sect->vaddr;
 		for(sub = sym->sub; sub != nil; sub = sub->sub)
 			sub->value += sym->value;
 	}

src/liblink/asm5.c

@@ -368,7 +368,7 @@ static struct {
 static int	checkpool(Link*, Prog*, int);
 static int 	flushpool(Link*, Prog*, int, int);
 static void	addpool(Link*, Prog*, Addr*);
-static void	asmout(Link*, Prog*, Optab*, int32*, LSym*);
+static void	asmout(Link*, Prog*, Optab*, int32*);
 static Optab*	oplook(Link*, Prog*);
 static int32	oprrr(Link*, int, int);
 static int32	olr(Link*, int32, int, int, int);
@@ -394,7 +394,7 @@ static	uchar	repop[ALAST];
 
 static Prog zprg = {
 	.as = AGOK,
-	.scond = 14,
+	.scond = C_SCOND_NONE,
 	.reg = NREG,
 	.from = {
 		.name = D_NONE,
@@ -458,7 +458,6 @@ span5(Link *ctxt, LSym *cursym)
 	int m, bflag, i, v;
 	int32 c, out[6];
 	uchar *bp;
-	LSym *gmsym;
 
 	p = cursym->text;
 	if(p == nil || p->link == nil) // handle external functions and ELF section symbols
@@ -496,11 +495,11 @@ span5(Link *ctxt, LSym *cursym)
 			addpool(ctxt, p, &p->to);
 			break;
 		case LPOOL:
-			if ((p->scond&C_SCOND) == 14)
+			if ((p->scond&C_SCOND) == C_SCOND_NONE)
 				flushpool(ctxt, p, 0, 0);
 			break;
 		}
-		if(p->as==AMOVW && p->to.type==D_REG && p->to.reg==REGPC && (p->scond&C_SCOND) == 14)
+		if(p->as==AMOVW && p->to.type==D_REG && p->to.reg==REGPC && (p->scond&C_SCOND) == C_SCOND_NONE)
 			flushpool(ctxt, p, 0, 0);
 		c += m;
 	}
@@ -570,9 +569,8 @@ span5(Link *ctxt, LSym *cursym)
 	 * code references to be relocated too, and then
 	 * perhaps we'd be able to parallelize the span loop above.
 	 */
-	gmsym = nil;
-	if(ctxt->linkmode == LinkExternal)
-		gmsym = linklookup(ctxt, "runtime.tlsgm", 0);
+	if(ctxt->gmsym == nil)
+		ctxt->gmsym = linklookup(ctxt, "runtime.tlsgm", 0);
 
 	p = cursym->text;
 	ctxt->autosize = p->to.offset + 4;
@@ -583,7 +581,7 @@ span5(Link *ctxt, LSym *cursym)
 		ctxt->pc = p->pc;
 		ctxt->curp = p;
 		o = oplook(ctxt, p);
-		asmout(ctxt, p, o, out, gmsym);
+		asmout(ctxt, p, o, out);
 		for(i=0; i<o->size/4; i++) {
 			v = out[i];
 			*bp++ = v;
@@ -1213,7 +1211,7 @@ buildop(Link *ctxt)
 }
 
 static void
-asmout(Link *ctxt, Prog *p, Optab *o, int32 *out, LSym *gmsym)
+asmout(Link *ctxt, Prog *p, Optab *o, int32 *out)
 {
 	int32 o1, o2, o3, o4, o5, o6, v;
 	int r, rf, rt, rt2;
@@ -1366,7 +1364,7 @@ if(0 /*debug['G']*/) print("%ux: %s: arm %d\n", (uint32)(p->pc), p->from.sym->na
 			rel->siz = 4;
 			rel->sym = p->to.sym;
 			rel->add = p->to.offset;
-			if(rel->sym == gmsym) {
+			if(rel->sym == ctxt->gmsym) {
 				rel->type = D_TLS;
 				if(ctxt->flag_shared)
 					rel->add += ctxt->pc - p->pcrel->pc - 8 - rel->siz;

src/liblink/obj5.c

@@ -37,7 +37,7 @@
 
 static Prog zprg = {
 	.as = AGOK,
-	.scond = 14,
+	.scond = C_SCOND_NONE,
 	.reg = NREG,
 	.from = {
 		.name = D_NONE,
@@ -207,8 +207,7 @@ addstacksplit(Link *ctxt, LSym *cursym)
 		ctxt->symmorestack[0] = linklookup(ctxt, "runtime.morestack", 0);
 	
 	tlsfallback = linklookup(ctxt, "runtime.read_tls_fallback", 0);
-	ctxt->gmsym = nil;
-	if(ctxt->linkmode == LinkExternal)
+	if(ctxt->gmsym == nil)
 		ctxt->gmsym = linklookup(ctxt, "runtime.tlsgm", 0);
 	q = nil;
 	
@@ -355,7 +354,9 @@ addstacksplit(Link *ctxt, LSym *cursym)
 			if((p->to.offset & 0xffff0fff) == 0xee1d0f70) {
 				if(ctxt->headtype == Hopenbsd) {
 					p->as = ARET;
-				} else if(ctxt->goarm < 7) {
+					break;
+				}
+				if(ctxt->goarm < 7) {
 					// BL runtime.read_tls_fallback(SB)
 					p->as = ABL;
 					p->to.type = D_BRANCH;
@@ -363,63 +364,62 @@ addstacksplit(Link *ctxt, LSym *cursym)
 					p->to.offset = 0;
 					cursym->text->mark &= ~LEAF;
 				}
-				if(ctxt->linkmode == LinkExternal) {
-					// runtime.tlsgm is relocated with R_ARM_TLS_LE32
-					// and $runtime.tlsgm will contain the TLS offset.
-					//
-					// MOV $runtime.tlsgm+ctxt->tlsoffset(SB), REGTMP
-					// ADD REGTMP, <reg>
-					//
-					// In shared mode, runtime.tlsgm is relocated with
-					// R_ARM_TLS_IE32 and runtime.tlsgm(SB) will point
-					// to the GOT entry containing the TLS offset.
-					//
-					// MOV runtime.tlsgm(SB), REGTMP
-					// ADD REGTMP, <reg>
-					// SUB -ctxt->tlsoffset, <reg>
-					//
-					// The SUB compensates for ctxt->tlsoffset
-					// used in runtime.save_gm and runtime.load_gm.
-					q = p;
-					p = appendp(ctxt, p);
-					p->as = AMOVW;
-					p->scond = 14;
-					p->reg = NREG;
-					if(ctxt->flag_shared) {
-						p->from.type = D_OREG;
-						p->from.offset = 0;
-					} else {
-						p->from.type = D_CONST;
-						p->from.offset = ctxt->tlsoffset;
-					}
-					p->from.sym = ctxt->gmsym;
-					p->from.name = D_EXTERN;
-					p->to.type = D_REG;
-					p->to.reg = REGTMP;
-					p->to.offset = 0;
+				// runtime.tlsgm is relocated with R_ARM_TLS_LE32
+				// and $runtime.tlsgm will contain the TLS offset.
+				//
+				// MOV $runtime.tlsgm+ctxt->tlsoffset(SB), REGTMP
+				// ADD REGTMP, <reg>
+				//
+				// In shared mode, runtime.tlsgm is relocated with
+				// R_ARM_TLS_IE32 and runtime.tlsgm(SB) will point
+				// to the GOT entry containing the TLS offset.
+				//
+				// MOV runtime.tlsgm(SB), REGTMP
+				// ADD REGTMP, <reg>
+				// SUB -ctxt->tlsoffset, <reg>
+				//
+				// The SUB compensates for ctxt->tlsoffset
+				// used in runtime.save_gm and runtime.load_gm.
+				q = p;
+				p = appendp(ctxt, p);
+				p->as = AMOVW;
+				p->scond = C_SCOND_NONE;
+				p->reg = NREG;
+				if(ctxt->flag_shared) {
+					p->from.type = D_OREG;
+					p->from.offset = 0;
+				} else {
+					p->from.type = D_CONST;
+					p->from.offset = ctxt->tlsoffset;
+				}
+				p->from.sym = ctxt->gmsym;
+				p->from.name = D_EXTERN;
+				p->to.type = D_REG;
+				p->to.reg = REGTMP;
+				p->to.offset = 0;
 
+				p = appendp(ctxt, p);
+				p->as = AADD;
+				p->scond = C_SCOND_NONE;
+				p->reg = NREG;
+				p->from.type = D_REG;
+				p->from.reg = REGTMP;
+				p->to.type = D_REG;
+				p->to.reg = (q->to.offset & 0xf000) >> 12;
+				p->to.offset = 0;
+
+				if(ctxt->flag_shared) {
 					p = appendp(ctxt, p);
-					p->as = AADD;
-					p->scond = 14;
+					p->as = ASUB;
+					p->scond = C_SCOND_NONE;
 					p->reg = NREG;
-					p->from.type = D_REG;
-					p->from.reg = REGTMP;
+					p->from.type = D_CONST;
+					p->from.offset = -ctxt->tlsoffset;
 					p->to.type = D_REG;
 					p->to.reg = (q->to.offset & 0xf000) >> 12;
 					p->to.offset = 0;
-
-					if(ctxt->flag_shared) {
-						p = appendp(ctxt, p);
-						p->as = ASUB;
-						p->scond = 14;
-						p->reg = NREG;
-						p->from.type = D_CONST;
-						p->from.offset = -ctxt->tlsoffset;
-						p->to.type = D_REG;
-						p->to.reg = (q->to.offset & 0xf000) >> 12;
-						p->to.offset = 0;
-					}
 				}
+				break;
 			}
 		}
 		q = p;
@@ -984,7 +984,7 @@ loop:
 				i--;
 				continue;
 			}
-			if(a == AB || (a == ARET && q->scond == 14) || a == ARFE || a == AUNDEF)
+			if(a == AB || (a == ARET && q->scond == C_SCOND_NONE) || a == ARFE || a == AUNDEF)
 				goto copy;
 			if(q->pcond == nil || (q->pcond->mark&FOLL))
 				continue;
@@ -1005,7 +1005,7 @@ loop:
 				}
 				(*last)->link = r;
 				*last = r;
-				if(a == AB || (a == ARET && q->scond == 14) || a == ARFE || a == AUNDEF)
+				if(a == AB || (a == ARET && q->scond == C_SCOND_NONE) || a == ARFE || a == AUNDEF)
 					return;
 				r->as = ABNE;
 				if(a == ABNE)
@@ -1031,7 +1031,7 @@ loop:
 	p->mark |= FOLL;
 	(*last)->link = p;
 	*last = p;
-	if(a == AB || (a == ARET && p->scond == 14) || a == ARFE || a == AUNDEF){
+	if(a == AB || (a == ARET && p->scond == C_SCOND_NONE) || a == ARFE || a == AUNDEF){
 		return;
 	}
 	if(p->pcond != nil)

src/pkg/runtime/asm_arm.s

@@ -627,14 +627,19 @@ _next:
 // Note: all three functions will clobber R0, and the last
 // two can be called from 5c ABI code.
 
-// g (R10) at 8(TP), m (R9) at 12(TP)
 TEXT runtime·save_gm(SB),NOSPLIT,$0
+	// NOTE: Liblink adds some instructions following the MRC
+	// to adjust R0 so that 8(R0) and 12(R0) are the TLS copies of
+	// the g and m registers. It's a bit too magical for its own good.
 	MRC		15, 0, R0, C13, C0, 3 // Fetch TLS register
 	MOVW	g, 8(R0)
 	MOVW	m, 12(R0)
 	RET
 
 TEXT runtime·load_gm(SB),NOSPLIT,$0
+	// NOTE: Liblink adds some instructions following the MRC
+	// to adjust R0 so that 8(R0) and 12(R0) are the TLS copies of
+	// the g and m registers. It's a bit too magical for its own good.
 	MRC		15, 0, R0, C13, C0, 3 // Fetch TLS register
 	MOVW	8(R0), g
 	MOVW	12(R0), m
@@ -646,7 +651,6 @@ TEXT setmg_gcc<>(SB),NOSPLIT,$0
 	MOVW	R1, g
 	B		runtime·save_gm(SB)
 
-
 // TODO: share code with memeq?
 TEXT bytes·Equal(SB),NOSPLIT,$0
 	MOVW	a_len+4(FP), R1