liblink: use pc-relative addressing for all memory references in amd64 code

LGTM=rminnich, iant
R=golang-codereviews, rminnich, iant
CC=golang-codereviews, r
https://golang.org/cl/125140043

src/cmd/6l/asm.c

@@ -290,7 +290,6 @@ elfreloc1(Reloc *r, vlong sectoff)
 		break;
 		
 	case R_CALL:
-	case R_PCREL:
 		if(r->siz == 4) {
 			if(r->xsym->type == SDYNIMPORT)
 				VPUT(R_X86_64_GOTPCREL | (uint64)elfsym<<32);
@@ -300,6 +299,13 @@ elfreloc1(Reloc *r, vlong sectoff)
 			return -1;
 		break;
 
+	case R_PCREL:
+		if(r->siz == 4) {
+			VPUT(R_X86_64_PC32 | (uint64)elfsym<<32);
+		} else
+			return -1;
+		break;
+
 	case R_TLS:
 		if(r->siz == 4) {
 			if(flag_shared)
@@ -323,7 +329,7 @@ machoreloc1(Reloc *r, vlong sectoff)
 	
 	rs = r->xsym;
 
-	if(rs->type == SHOSTOBJ) {
+	if(rs->type == SHOSTOBJ || r->type == R_PCREL) {
 		if(rs->dynid < 0) {
 			diag("reloc %d to non-macho symbol %s type=%d", r->type, rs->name, rs->type);
 			return -1;
@@ -345,10 +351,13 @@ machoreloc1(Reloc *r, vlong sectoff)
 		v |= MACHO_X86_64_RELOC_UNSIGNED<<28;
 		break;
 	case R_CALL:
-	case R_PCREL:
 		v |= 1<<24; // pc-relative bit
 		v |= MACHO_X86_64_RELOC_BRANCH<<28;
 		break;
+	case R_PCREL:
+		// NOTE: Only works with 'external' relocation. Forced above.
+		v |= 1<<24; // pc-relative bit
+		v |= MACHO_X86_64_RELOC_SIGNED<<28;
 	}
 	
 	switch(r->siz) {

src/cmd/ld/data.c

@@ -281,9 +281,13 @@ relocsym(LSym *s)
 					if(thechar == '6')
 						o = 0;
 				} else if(HEADTYPE == Hdarwin) {
+					if(r->type == R_CALL) {
 						if(rs->type != SHOSTOBJ)
 							o += symaddr(rs) - rs->sect->vaddr;
-					o -= r->off; // WTF?
+						o -= r->off; // relative to section offset, not symbol
+					} else {
+						o += r->siz;
+					}
 				} else {
 					diag("unhandled pcrel relocation for %s", headstring);
 				}

src/liblink/asm6.c

@@ -1932,10 +1932,7 @@ oclass(Link *ctxt, Addr *a)
 				switch(a->index) {
 				case D_EXTERN:
 				case D_STATIC:
-					if(ctxt->flag_shared || ctxt->headtype == Hnacl)
-						return Yiauto;
-					else
-						return Yi32;	/* TO DO: Yi64 */
+					return Yiauto; // use pc-relative addressing
 				case D_AUTO:
 				case D_PARAM:
 					return Yiauto;
@@ -2290,15 +2287,12 @@ vaddr(Link *ctxt, Addr *a, Reloc *r)
 		r->sym = s;
 		r->add = v;
 		v = 0;
-		if(ctxt->flag_shared || ctxt->headtype == Hnacl) {
+		r->type = R_PCREL;
 		if(s->type == STLSBSS) {
 			r->xadd = r->add - r->siz;
 			r->type = R_TLS;
 			r->xsym = s;
-			} else
-				r->type = R_PCREL;
-		} else
-			r->type = R_ADDR;
+		}
 		break;
 	
 	case D_INDIR+D_TLS:
@@ -2333,13 +2327,6 @@ asmandsz(Link *ctxt, Addr *a, int r, int rex, int m64)
 			switch(t) {
 			default:
 				goto bad;
-			case D_STATIC:
-			case D_EXTERN:
-				if(ctxt->flag_shared || ctxt->headtype == Hnacl)
-					goto bad;
-				t = D_NONE;
-				v = vaddr(ctxt, a, &rel);
-				break;
 			case D_AUTO:
 			case D_PARAM:
 				t = D_SP;
@@ -2399,7 +2386,7 @@ asmandsz(Link *ctxt, Addr *a, int r, int rex, int m64)
 
 	ctxt->rexflag |= (regrex[t] & Rxb) | rex;
 	if(t == D_NONE || (D_CS <= t && t <= D_GS) || t == D_TLS) {
-		if((ctxt->flag_shared || ctxt->headtype == Hnacl) && t == D_NONE && (a->type == D_STATIC || a->type == D_EXTERN) || ctxt->asmode != 64) {
+		if(t == D_NONE && (a->type == D_STATIC || a->type == D_EXTERN) || ctxt->asmode != 64) {
 			*ctxt->andptr++ = (0 << 6) | (5 << 0) | (r << 3);
 			goto putrelv;
 		}