cmd/ld: handle a special case of scattered relocation 2/1 on Darwin/386

        Fixes #1635.

R=golang-dev, dave, r
CC=golang-dev
https://golang.org/cl/6496043

misc/cgo/test/cgo_test.go

@@ -28,5 +28,6 @@ func TestParallelSleep(t *testing.T)       { testParallelSleep(t) }
 func TestSetEnv(t *testing.T)              { testSetEnv(t) }
 func TestHelpers(t *testing.T)             { testHelpers(t) }
 func TestLibgcc(t *testing.T)              { testLibgcc(t) }
+func Test1635(t *testing.T)                { test1635(t) }
 
 func BenchmarkCgoCall(b *testing.B) { benchCgoCall(b) }

misc/cgo/test/issue1635.go

+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cgotest
+
+/*
+// Mac OS X's gcc will generate scattered relocation 2/1 for
+// this function on Darwin/386, and 8l couldn't handle it.
+// this example is in issue 1635
+#include <stdio.h>
+void scatter() {
+	void *p = scatter;
+	printf("scatter = %p\n", p);
+}
+
+// this example is in issue 3253
+int hola = 0;
+int testHola() { return hola; }
+*/
+import "C"
+
+import "testing"
+
+func test1635(t *testing.T) {
+	C.scatter()
+	if v := C.hola; v != 0 {
+		t.Fatalf("C.hola is %d, should be 0", v)
+	}
+	if v := C.testHola(); v != 0 {
+		t.Fatalf("C.testHola() is %d, should be 0", v)
+	}
+}

src/cmd/ld/ldmacho.c

@@ -680,19 +680,28 @@ ldmacho(Biobuf *f, char *pkg, int64 len, char *pn)
 				int k;
 				MachoSect *ks;
 
-				if(thechar != '8')
+				if(thechar != '8') {
+					// mach-o only uses scattered relocation on 32-bit platforms
 					diag("unexpected scattered relocation");
+					continue;
+				}
 
-				// on 386, rewrite scattered 4/1 relocation into
-				// the pseudo-pc-relative reference that it is.
+				// on 386, rewrite scattered 4/1 relocation and some
+				// scattered 2/1 relocation into the pseudo-pc-relative
+				// reference that it is.
 				// assume that the second in the pair is in this section
 				// and use that as the pc-relative base.
-				if(thechar != '8' || rel->type != 4 || j+1 >= sect->nreloc ||
-						!(rel+1)->scattered || (rel+1)->type != 1 ||
-						(rel+1)->value < sect->addr || (rel+1)->value >= sect->addr+sect->size) {
+				if(j+1 >= sect->nreloc) {
+					werrstr("unsupported scattered relocation %d", (int)rel->type);
+					goto bad;
+				}
+				if(!(rel+1)->scattered || (rel+1)->type != 1 ||
+				   (rel->type != 4 && rel->type != 2) ||
+				   (rel+1)->value < sect->addr || (rel+1)->value >= sect->addr+sect->size) {
 					werrstr("unsupported scattered relocation %d/%d", (int)rel->type, (int)(rel+1)->type);
 					goto bad;
 				}
+
 				rp->siz = rel->length;
 				rp->off = rel->addr;