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https://github.com/golang/go
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os: depend on Readlink only when necessary
Currently Readlink gets linked into the binary even when Executable is not needed. This reduces a simple "os.Stdout.Write([]byte("hello"))" by ~10KiB. Previously the executable path was read during init time, because deleting the executable would make "Readlink" return "(deleted)" suffix. There's probably a slight chance that the init time reading would return it anyways. Updates #6853 Change-Id: Ic76190c5b64d9320ceb489cd6a553108614653d1 Reviewed-on: https://go-review.googlesource.com/c/go/+/311790 Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org> Trust: Tobias Klauser <tobias.klauser@gmail.com>
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parent
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commit
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@ -12,10 +12,7 @@ import (
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"runtime"
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)
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// We query the executable path at init time to avoid the problem of
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// readlink returns a path appended with " (deleted)" when the original
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// binary gets deleted.
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var executablePath, executablePathErr = func() (string, error) {
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func executable() (string, error) {
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var procfn string
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switch runtime.GOOS {
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default:
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@ -25,9 +22,17 @@ var executablePath, executablePathErr = func() (string, error) {
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case "netbsd":
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procfn = "/proc/curproc/exe"
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}
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return Readlink(procfn)
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}()
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path, err := Readlink(procfn)
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func executable() (string, error) {
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return executablePath, executablePathErr
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// When the executable has been deleted then Readlink returns a
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// path appended with " (deleted)".
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return stringsTrimSuffix(path, " (deleted)"), err
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}
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// stringsTrimSuffix is the same as strings.TrimSuffix.
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func stringsTrimSuffix(s, suffix string) string {
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if len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix {
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return s[:len(s)-len(suffix)]
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}
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return s
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}
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@ -86,3 +86,68 @@ func init() {
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os.Exit(0)
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}
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}
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func TestExecutableDeleted(t *testing.T) {
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testenv.MustHaveExec(t)
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switch runtime.GOOS {
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case "windows":
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t.Skip("windows does not support deleting running binary")
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case "openbsd", "freebsd":
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t.Skipf("%v does not support reading deleted binary name", runtime.GOOS)
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}
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dir := t.TempDir()
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src := filepath.Join(dir, "testdel.go")
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exe := filepath.Join(dir, "testdel.exe")
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err := os.WriteFile(src, []byte(testExecutableDeletion), 0666)
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if err != nil {
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t.Fatal(err)
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}
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out, err := osexec.Command(testenv.GoToolPath(t), "build", "-o", exe, src).CombinedOutput()
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t.Logf("build output:\n%s", out)
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if err != nil {
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t.Fatal(err)
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}
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out, err = osexec.Command(exe).CombinedOutput()
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t.Logf("exec output:\n%s", out)
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if err != nil {
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t.Fatal(err)
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}
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}
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const testExecutableDeletion = `package main
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import (
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"fmt"
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"os"
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)
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func main() {
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before, err := os.Executable()
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if err != nil {
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fmt.Fprintf(os.Stderr, "failed to read executable name before deletion: %v\n", err)
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os.Exit(1)
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}
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err = os.Remove(before)
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if err != nil {
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fmt.Fprintf(os.Stderr, "failed to remove executable: %v\n", err)
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os.Exit(1)
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}
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after, err := os.Executable()
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if err != nil {
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fmt.Fprintf(os.Stderr, "failed to read executable name after deletion: %v\n", err)
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os.Exit(1)
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}
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if before != after {
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fmt.Fprintf(os.Stderr, "before and after do not match: %v != %v\n", before, after)
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os.Exit(1)
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}
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}
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`
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