cmd/ld: use TLS relocations on ELF systems in external linking mode

Fixes #7719.

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/87760050

src/cmd/6l/asm.c

@@ -281,6 +281,13 @@ elfreloc1(Reloc *r, vlong sectoff)
 			return -1;
 		break;
 
+	case R_TLS_LE:
+		if(r->siz == 4)
+			VPUT(R_X86_64_TPOFF32 | (uint64)elfsym<<32);
+		else
+			return -1;
+		break;
+		
 	case R_PCREL:
 		if(r->siz == 4) {
 			if(r->xsym->type == SDYNIMPORT)

src/cmd/8l/asm.c

@@ -263,7 +263,8 @@ elfreloc1(Reloc *r, vlong sectoff)
 			return -1;
 		break;
 	
-	case R_TLS:
+	case R_TLS_LE:
+	case R_TLS_IE:
 		if(r->siz == 4)
 			LPUT(R_386_TLS_LE | elfsym<<8);
 		else

src/cmd/ld/data.c

@@ -184,9 +184,30 @@ relocsym(LSym *s)
 				o = r->add;
 			break;
 		case R_TLS_LE:
+			if(linkmode == LinkExternal && iself) {
+				r->done = 0;
+				r->sym = ctxt->gmsym;
+				r->xsym = ctxt->gmsym;
+				r->xadd = r->add;
+				o = 0;
+				if(thechar != '6')
+					o = r->add;
+				break;
+			}
 			o = ctxt->tlsoffset + r->add;
 			break;
+
 		case R_TLS_IE:
+			if(linkmode == LinkExternal && iself) {
+				r->done = 0;
+				r->sym = ctxt->gmsym;
+				r->xsym = ctxt->gmsym;
+				r->xadd = r->add;
+				o = 0;
+				if(thechar != '6')
+					o = r->add;
+				break;
+			}
 			if(iself || ctxt->headtype == Hplan9)
 				o = ctxt->tlsoffset + r->add;
 			else if(ctxt->headtype == Hwindows)

src/cmd/ld/lib.c

@@ -240,6 +240,7 @@ loadlib(void)
 	gmsym->size = 2*PtrSize;
 	gmsym->hide = 1;
 	gmsym->reachable = 1;
+	ctxt->gmsym = gmsym;
 
 	// Now that we know the link mode, trim the dynexp list.
 	x = CgoExportDynamic;

src/liblink/asm6.c

@@ -2427,38 +2427,25 @@ asmandsz(Link *ctxt, Addr *a, int r, int rex, int m64)
 		goto putrelv;
 	}
 	if(t >= D_AX && t <= D_R15) {
-		// TODO: Remove Hwindows condition.
-		if(v == 0 && t != D_BP && t != D_R13 && (a->index != D_TLS || (ctxt->headtype == Hwindows && a->scale == 2))) {
+		if(a->index == D_TLS) {
+			memset(&rel, 0, sizeof rel);
+			rel.type = R_TLS_IE;
+			rel.siz = 4;
+			rel.sym = nil;
+			rel.add = v;
+			v = 0;
+		}
+		if(v == 0 && rel.siz == 0 && t != D_BP && t != D_R13) {
 			*ctxt->andptr++ = (0 << 6) | (reg[t] << 0) | (r << 3);
 			return;
 		}
-		if(v >= -128 && v < 128 && (a->index != D_TLS || a->scale != 1)) {
+		if(v >= -128 && v < 128 && rel.siz == 0) {
 			ctxt->andptr[0] = (1 << 6) | (reg[t] << 0) | (r << 3);
-			if(a->index == D_TLS) {
-				Reloc *r;
-				memset(&rel, 0, sizeof rel);
-				rel.type = R_TLS_IE;
-				rel.siz = 1;
-				rel.sym = nil;
-				rel.add = v;
-				r = addrel(ctxt->cursym);
-				*r = rel;
-				r->off = ctxt->curp->pc + ctxt->andptr + 1 - ctxt->and;
-				v = 0;
-			}
 			ctxt->andptr[1] = v;
 			ctxt->andptr += 2;
 			return;
 		}
 		*ctxt->andptr++ = (2 << 6) | (reg[t] << 0) | (r << 3);
-		if(a->index == D_TLS) {
-			memset(&rel, 0, sizeof rel);
-			rel.type = R_TLS_IE;
-			rel.siz = 4;
-			rel.sym = nil;
-			rel.add = v;
-			v = 0;
-		}
 		goto putrelv;
 	}
 	goto bad;

src/liblink/asm8.c

@@ -1857,43 +1857,25 @@ asmand(Link *ctxt, Addr *a, int r)
 		goto putrelv;
 	}
 	if(t >= D_AX && t <= D_DI) {
-		// TODO(rsc): Remove the Hwindows test.
-		// As written it produces the same byte-identical output as the code it replaced.
-		if(v == 0 && rel.siz == 0 && t != D_BP && (a->index != D_TLS || ctxt->headtype == Hwindows)) {
+		if(a->index == D_TLS) {
+			memset(&rel, 0, sizeof rel);
+			rel.type = R_TLS_IE;
+			rel.siz = 4;
+			rel.sym = nil;
+			rel.add = v;
+			v = 0;
+		}
+		if(v == 0 && rel.siz == 0 && t != D_BP) {
 			*ctxt->andptr++ = (0 << 6) | (reg[t] << 0) | (r << 3);
 			return;
 		}
-		// TODO(rsc): Change a->index tests to check D_TLS.
-		// Then remove the if statement inside the body.
-		// As written the code is clearly incorrect for external linking,
-		// but as written it produces the same byte-identical output as the code it replaced.
-		if(v >= -128 && v < 128 && rel.siz == 0 && (a->index != D_TLS || ctxt->headtype == Hwindows || a->scale != 1))  {
+		if(v >= -128 && v < 128 && rel.siz == 0)  {
 			ctxt->andptr[0] = (1 << 6) | (reg[t] << 0) | (r << 3);
-			if(a->index == D_TLS) {
-				Reloc *r;
-				memset(&rel, 0, sizeof rel);
-				rel.type = R_TLS_IE;
-				rel.siz = 1;
-				rel.sym = nil;
-				rel.add = v;
-				r = addrel(ctxt->cursym);
-				*r = rel;
-				r->off = ctxt->curp->pc + ctxt->andptr + 1 - ctxt->and;
-				v = 0;
-			}
 			ctxt->andptr[1] = v;
 			ctxt->andptr += 2;
 			return;
 		}
 		*ctxt->andptr++ = (2 << 6) | (reg[t] << 0) | (r << 3);
-		if(a->index == D_TLS) {
-			memset(&rel, 0, sizeof rel);
-			rel.type = R_TLS_IE;
-			rel.siz = 4;
-			rel.sym = nil;
-			rel.add = v;
-			v = 0;
-		}
 		goto putrelv;
 	}
 	goto bad;

src/run.bash

@@ -131,6 +131,7 @@ dragonfly-386 | dragonfly-amd64 | freebsd-386 | freebsd-amd64 | linux-386 | linu
 	go test -ldflags '-linkmode=external' || exit 1
 	go test -ldflags '-linkmode=auto' ../testtls || exit 1
 	go test -ldflags '-linkmode=external' ../testtls || exit 1
+	go test -ldflags '-linkmode=external -extldflags "-static -pthread"' ../testtls || exit 1
 esac
 ) || exit $?