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cmd/go: fix spurious rebuild of binaries using cgo on OS X

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The text segment starts farther into the binary when using
external linking on the mac. Test and fix.

Fixes #12173.

Change-Id: I1f0c81814bf70cd9decfceac3022784f4608eeef
Reviewed-on: https://go-review.googlesource.com/13672
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Russ Cox 2015-08-17 20:47:29 -04:00
parent 3f016215a8
commit d2cf46dedf
2 changed files with 21 additions and 4 deletions
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17
src/cmd/go/note_test.go
View File

@ -6,6 +6,7 @@ package main_test
import (
"cmd/go"
"runtime"
"testing"
)
@ -22,4 +23,20 @@ func TestNoteReading(t *testing.T) {
if id != buildID {
t.Fatalf("buildID in hello binary = %q, want %q", id, buildID)
}
switch runtime.GOOS {
case "plan9":
// no external linking
t.Logf("no external linking - skipping linkmode=external test")
default:
tg.run("build", "-ldflags", "-buildid="+buildID+" -linkmode=external", "-o", tg.path("hello.exe"), tg.path("hello.go"))
id, err := main.ReadBuildIDFromBinary(tg.path("hello.exe"))
if err != nil {
t.Fatalf("reading build ID from hello binary (linkmode=external): %v", err)
}
if id != buildID {
t.Fatalf("buildID in hello binary = %q, want %q (linkmode=external)", id, buildID)
}
}
}

8
src/cmd/go/pkg.go
View File

@ -1796,10 +1796,10 @@ func ReadBuildIDFromBinary(filename string) (id string, err error) {
return "", &os.PathError{Op: "parse", Path: filename, Err: errBuildIDUnknown}
}
// Read the first 8 kB of the binary file.
// Read the first 16 kB of the binary file.
// That should be enough to find the build ID.
// In ELF files, the build ID is in the leading headers,
// which are typically less than 4 kB, not to mention 8 kB.
// which are typically less than 4 kB, not to mention 16 kB.
// On other systems, we're trying to read enough that
// we get the beginning of the text segment in the read.
// The offset where the text segment begins in a hello
@ -1807,7 +1807,7 @@ func ReadBuildIDFromBinary(filename string) (id string, err error) {
//
// Plan 9: 0x20
// Windows: 0x600
// Mach-O: 0x1000
// Mach-O: 0x2000
//
f, err := os.Open(filename)
if err != nil {
@ -1815,7 +1815,7 @@ func ReadBuildIDFromBinary(filename string) (id string, err error) {
}
defer f.Close()
data := make([]byte, 8192)
data := make([]byte, 16*1024)
_, err = io.ReadFull(f, data)
if err == io.ErrUnexpectedEOF {
err = nil