cmd/link: merge note sections into one segment

The ld from binutils merges note sections into one PT_NOTE
segment.
We should do that for consistency with binutils.

Change-Id: I45703525c720972d49c36c4f10ac47d1628b5698
Reviewed-on: https://go-review.googlesource.com/c/go/+/265957
Trust: Meng Zhuo <mzh@golangcn.org>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Meng Zhuo <mzh@golangcn.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

2 files changed, 71 insertions, 23 deletions

diff --git a/src/cmd/link/elf_test.go b/src/cmd/link/elf_test.go
index 012c0b5169..760d9ea60d 100644
--- a/src/cmd/link/elf_test.go
+++ b/src/cmd/link/elf_test.go
@@ -201,6 +201,61 @@ func TestMinusRSymsWithSameName(t *testing.T) {
 	}
 }
 
+func TestMergeNoteSections(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+	expected := 1
+
+	switch runtime.GOOS {
+	case "linux", "freebsd", "dragonfly":
+	case "openbsd", "netbsd":
+		// These OSes require independent segment
+		expected = 2
+	default:
+		t.Skip("We should only test on elf output.")
+	}
+	t.Parallel()
+
+	goFile := filepath.Join(t.TempDir(), "notes.go")
+	if err := ioutil.WriteFile(goFile, []byte(goSource), 0444); err != nil {
+		t.Fatal(err)
+	}
+	outFile := filepath.Join(t.TempDir(), "notes.exe")
+	goTool := testenv.GoToolPath(t)
+	// sha1sum of "gopher"
+	id := "0xf4e8cd51ce8bae2996dc3b74639cdeaa1f7fee5f"
+	cmd := exec.Command(goTool, "build", "-o", outFile, "-ldflags",
+		"-B "+id, goFile)
+	cmd.Dir = t.TempDir()
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Logf("%s", out)
+		t.Fatal(err)
+	}
+
+	ef, err := elf.Open(outFile)
+	if err != nil {
+		t.Fatalf("open elf file failed:%v", err)
+	}
+	defer ef.Close()
+	sec := ef.Section(".note.gnu.build-id")
+	if sec == nil {
+		t.Fatalf("can't find gnu build id")
+	}
+
+	sec = ef.Section(".note.go.buildid")
+	if sec == nil {
+		t.Fatalf("can't find go build id")
+	}
+	cnt := 0
+	for _, ph := range ef.Progs {
+		if ph.Type == elf.PT_NOTE {
+			cnt += 1
+		}
+	}
+	if cnt != expected {
+		t.Fatalf("want %d PT_NOTE segment, got %d", expected, cnt)
+	}
+}
+
 const pieSourceTemplate = `
 package main
 
diff --git a/src/cmd/link/internal/ld/elf.go b/src/cmd/link/internal/ld/elf.go
index fb75c761a1..4a143dfcaa 100644
--- a/src/cmd/link/internal/ld/elf.go
+++ b/src/cmd/link/internal/ld/elf.go
@@ -1682,13 +1682,18 @@ func asmbElf(ctxt *Link) {
 
 	var pph *ElfPhdr
 	var pnote *ElfPhdr
+	getpnote := func() *ElfPhdr {
+		if pnote == nil {
+			pnote = newElfPhdr()
+			pnote.Type = elf.PT_NOTE
+			pnote.Flags = elf.PF_R
+		}
+		return pnote
+	}
 	if *flagRace && ctxt.IsNetbsd() {
 		sh := elfshname(".note.netbsd.pax")
 		resoff -= int64(elfnetbsdpax(sh, uint64(startva), uint64(resoff)))
-		pnote = newElfPhdr()
-		pnote.Type = elf.PT_NOTE
-		pnote.Flags = elf.PF_R
-		phsh(pnote, sh)
+		phsh(getpnote(), sh)
 	}
 	if ctxt.LinkMode == LinkExternal {
 		/* skip program headers */
@@ -1787,7 +1792,6 @@ func asmbElf(ctxt *Link) {
 		phsh(ph, sh)
 	}
 
-	pnote = nil
 	if ctxt.HeadType == objabi.Hnetbsd || ctxt.HeadType == objabi.Hopenbsd {
 		var sh *ElfShdr
 		switch ctxt.HeadType {
@@ -1799,34 +1803,23 @@ func asmbElf(ctxt *Link) {
 			sh = elfshname(".note.openbsd.ident")
 			resoff -= int64(elfopenbsdsig(sh, uint64(startva), uint64(resoff)))
 		}
-
-		pnote = newElfPhdr()
-		pnote.Type = elf.PT_NOTE
-		pnote.Flags = elf.PF_R
-		phsh(pnote, sh)
+		// netbsd and openbsd require ident in an independent segment.
+		pnotei := newElfPhdr()
+		pnotei.Type = elf.PT_NOTE
+		pnotei.Flags = elf.PF_R
+		phsh(pnotei, sh)
 	}
 
 	if len(buildinfo) > 0 {
 		sh := elfshname(".note.gnu.build-id")
 		resoff -= int64(elfbuildinfo(sh, uint64(startva), uint64(resoff)))
-
-		if pnote == nil {
-			pnote = newElfPhdr()
-			pnote.Type = elf.PT_NOTE
-			pnote.Flags = elf.PF_R
-		}
-
-		phsh(pnote, sh)
+		phsh(getpnote(), sh)
 	}
 
 	if *flagBuildid != "" {
 		sh := elfshname(".note.go.buildid")
 		resoff -= int64(elfgobuildid(sh, uint64(startva), uint64(resoff)))
-
-		pnote := newElfPhdr()
-		pnote.Type = elf.PT_NOTE
-		pnote.Flags = elf.PF_R
-		phsh(pnote, sh)
+		phsh(getpnote(), sh)
 	}
 
 	// Additions to the reserved area must be above this line.