cmd/link: if -B option was used, pass it to the external linker

Fixes #10607.

Change-Id: Ib294cf65b07103b60f62b86b21ff2d07b25136fe
Reviewed-on: https://go-review.googlesource.com/12242Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/link/internal/ld/lib.go

@@ -980,6 +980,10 @@ func hostlink() {
 		argv = append(argv, "-Wl,-znow")
 	}
 
+	if Iself && len(buildinfo) > 0 {
+		argv = append(argv, fmt.Sprintf("-Wl,--build-id=0x%x", buildinfo))
+	}
+
 	argv = append(argv, "-o")
 	argv = append(argv, outfile)
 

test/fixedbugs/issue10607.go

+// +build linux
+// run
+
+// Copyright 2015 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.
+
+// Test that a -B option is passed through when using both internal
+// and external linking mode.
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+)
+
+func main() {
+	test("internal")
+	test("external")
+}
+
+func test(linkmode string) {
+	out, err := exec.Command("go", "run", "-ldflags", "-B=0x12345678 -linkmode="+linkmode, filepath.Join("fixedbugs", "issue10607a.go")).CombinedOutput()
+	if err != nil {
+		fmt.Printf("BUG: linkmode=%s %v\n%s\n", linkmode, err, out)
+		os.Exit(1)
+	}
+}

test/fixedbugs/issue10607a.go

+// skip
+
+// Copyright 2015 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.
+
+// This is built by issue10607.go with a -B option.
+// Verify that we have one build-id note with the expected value.
+
+package main
+
+import (
+	"bytes"
+	"debug/elf"
+	"fmt"
+	"os"
+)
+
+func main() {
+	f, err := elf.Open("/proc/self/exe")
+	if err != nil {
+		if os.IsNotExist(err) {
+			return
+		}
+		fmt.Fprintln(os.Stderr, "opening /proc/self/exe:", err)
+		os.Exit(1)
+	}
+
+	c := 0
+	fail := false
+	for i, s := range f.Sections {
+		if s.Type != elf.SHT_NOTE {
+			continue
+		}
+
+		d, err := s.Data()
+		if err != nil {
+			fmt.Fprintln(os.Stderr, "reading data of note section %d: %v", i, err)
+			continue
+		}
+
+		for len(d) > 0 {
+			namesz := f.ByteOrder.Uint32(d)
+			descsz := f.ByteOrder.Uint32(d[4:])
+			typ := f.ByteOrder.Uint32(d[8:])
+
+			an := (namesz + 3) &^ 3
+			ad := (descsz + 3) &^ 3
+
+			if int(12+an+ad) > len(d) {
+				fmt.Fprintf(os.Stderr, "note section %d too short for header (%d < 12 + align(%d,4) + align(%d,4))\n", i, len(d), namesz, descsz)
+				break
+			}
+
+			// 3 == NT_GNU_BUILD_ID
+			if typ == 3 && namesz == 4 && bytes.Equal(d[12:16], []byte("GNU\000")) {
+				id := string(d[12+an:12+an+descsz])
+				if id == "\x12\x34\x56\x78" {
+					c++
+				} else {
+					fmt.Fprintf(os.Stderr, "wrong build ID data: %q\n", id)
+					fail = true
+				}
+			}
+
+			d = d[12+an+ad:]
+		}
+	}
+
+	if c == 0 {
+		fmt.Fprintln(os.Stderr, "no build-id note")
+		fail = true
+	} else if c > 1 {
+		fmt.Fprintln(os.Stderr, c, "build-id notes")
+		fail = true
+	}
+
+	if fail {
+		os.Exit(1)
+	}
+}