cmd/ld: support 2 byte relocations

ppc64 has a bunch of these.

Change-Id: I3b93ed2bae378322a8dec036b1681e520b56ff53
Reviewed-on: https://go-review.googlesource.com/2003Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/ld/data.c

@@ -132,6 +132,7 @@ relocsym(LSym *s)
 {
 	Reloc *r;
 	LSym *rs;
+	int16 i16;
 	int32 i, off, siz, fl;
 	vlong o;
 	uchar *cast;
@@ -317,6 +318,14 @@ relocsym(LSym *s)
 			// TODO(rsc): Remove.
 			s->p[off] = (int8)o;
 			break;
+		case 2:
+			if(o != (int16)o)
+				diag("relocation address is too big: %#llx", o);
+			i16 = o;
+			cast = (uchar*)&i16;
+			for(i=0; i<2; i++)
+				s->p[off+i] = cast[inuxi2[i]];
+			break;
 		case 4:
 			if(r->type == R_PCREL || r->type == R_CALL) {
 				if(o != (int32)o)

src/cmd/ld/ldelf.c

@@ -721,6 +721,8 @@ ldelf(Biobuf *f, char *pkg, int64 len, char *pn)
 				else
 					diag("invalid rela size %d", rp->siz);
 			}
+			if(rp->siz == 2)
+				rp->add = (int16)rp->add;
 			if(rp->siz == 4)
 				rp->add = (int32)rp->add;
 			//print("rel %s %d %d %s %#llx\n", sect->sym->name, rp->type, rp->siz, rp->sym->name, rp->add);