On my system, t9100.1 triggers the following warning:

  ==352== Syscall param write(buf) points to uninitialised byte(s)
  ==352==    at 0x57119C0: __write_nocancel (in /lib64/libc-2.17.so)
  ==352==    by 0x56AC1D2: _IO_file_write@@GLIBC_2.2.5 (in /lib64/libc-2.17.so)
  ==352==    by 0x56AC0B1: new_do_write (in /lib64/libc-2.17.so)
  ==352==    by 0x56AD3B4: _IO_do_write@@GLIBC_2.2.5 (in /lib64/libc-2.17.so)
  ==352==    by 0x56AD6FE: _IO_file_overflow@@GLIBC_2.2.5 (in 
/lib64/libc-2.17.so)
  ==352==    by 0x56AE3D8: _IO_default_xsputn (in /lib64/libc-2.17.so)
  ==352==    by 0x56ACAA2: _IO_file_xsputn@@GLIBC_2.2.5 (in /lib64/libc-2.17.so)
  ==352==    by 0x5682133: buffered_vfprintf (in /lib64/libc-2.17.so)
  ==352==    by 0x567CE9D: vfprintf (in /lib64/libc-2.17.so)
  ==352==    by 0x5687096: fprintf (in /lib64/libc-2.17.so)
  ==352==    by 0x4E7AC5: vreportf (usage.c:15)
  ==352==    by 0x4E7B14: die_builtin (usage.c:38)

The actual complaint appears to be a bug in the underlying
implementation.  What's interesting here is that it is apparently
_triggered_ by closing stderr, which results in (from strace)

  write(2, "fatal: Needed a single revision\n", 32) = -1 EBADF (Bad file 
descriptor)
  write(2, "\0", 1) = -1 EBADF (Bad file descriptor)

Closing stderr is a bad idea anyway: there is a very real chance that
we print fatal error messages to some other file that just happens to
be opened on the now-free FD 2.  So let's not do that.

As pointed out by Eric Wong (thanks), the initial close needs to go:
die() would again write nowhere if we close STDERR beforehand.

Signed-off-by: Thomas Rast <tr...@inf.ethz.ch>
---

> Perhaps we should also do the following:
>
> --- a/perl/Git.pm
> +++ b/perl/Git.pm
> @@ -1489,9 +1489,6 @@ sub _command_common_pipe {
>               if (not defined $pid) {
>                       throw Error::Simple("open failed: $!");
>               } elsif ($pid == 0) {
> -                     if (defined $opts{STDERR}) {
> -                             close STDERR;
> -                     }
>                       if ($opts{STDERR}) {
>                               open (STDERR, '>&', $opts{STDERR})
>                                       or die "dup failed: $!";

Indeed.  Thanks for pointing that out.

 perl/Git.pm | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/perl/Git.pm b/perl/Git.pm
index 96cac39..2cec8cf 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -1489,12 +1489,12 @@ sub _command_common_pipe {
                if (not defined $pid) {
                        throw Error::Simple("open failed: $!");
                } elsif ($pid == 0) {
-                       if (defined $opts{STDERR}) {
-                               close STDERR;
-                       }
                        if ($opts{STDERR}) {
                                open (STDERR, '>&', $opts{STDERR})
                                        or die "dup failed: $!";
+                       } elsif (defined $opts{STDERR}) {
+                               open (STDERR, '>', '/dev/null')
+                                       or die "opening /dev/null failed: $!";
                        }
                        _cmd_exec($self, $cmd, @args);
                }
-- 
1.8.2.607.g19d29d3

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