Current posix_spawnp implementation wrongly tries to execute invalid
binaries (for instance script without shebang) as a shell script in
non compat mode. It was a regression introduced by
9ff72da471 when __spawni started to use
__execvpe instead of __execve (glibc __execvpe try to execute ENOEXEC
as shell script regardless).
This patch fixes it by using an internal symbol (__execvpex) with the
faulty semantic (since compat mode is handled by spawni.c itself).
It was reported by Daniel Drake on libc-help [1].
Checked on x86_64-linux-gnu and i686-linux-gnu.
[BZ #23264]
* include/unistd.h (__execvpex): New prototype.
* posix/Makefile (tests): Add tst-spawn4.
(tests-internal): Add tst-spawn4-compat.
* posix/execvpe.c (__execvpe_common, __execvpex): New functions.
* posix/tst-spawn4-compat.c: New file.
* posix/tst-spawn4.c: Likewise.
* sysdeps/unix/sysv/linux/spawni.c (__spawni): Do not interpret invalid
binaries as shell scripts.
* sysdeps/posix/spawni.c (__spawni): Likewise.
[1] https://sourceware.org/ml/libc-help/2018-06/msg00012.html
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