GNU bug report logs - #61095
possible misuse of posix_spawn API on non-linux OSes

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Ludovic Courtès <ludo <at> gnu.org>
Subject: bug#61079: closed (Re: bug#61095: possible misuse of posix_spawn
 API on non-linux OSes)
Date: Sun, 02 Apr 2023 13:45:02 +0000

[Message part 1 (text/plain, inline)]

Your bug report

#61095: [3.0.9] ‘system*’ broken on GNU/Hurd

which was filed against the guile package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 61079 <at> debbugs.gnu.org.

-- 
61095: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=61095
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Ludovic Courtès <ludo <at> gnu.org>
To: Omar Polo <op <at> omarpolo.com>
Cc: Josselin Poiret <dev <at> jpoiret.xyz>, Andrew Whatson <whatson <at> tailcall.au>,
 61095-done <at> debbugs.gnu.org
Subject: Re: bug#61095: possible misuse of posix_spawn API on non-linux OSes
Date: Sun, 02 Apr 2023 15:44:01 +0200

Hi!

Omar Polo <op <at> omarpolo.com> skribis:

> On 2023/03/30 22:21:28 +0200, Josselin Poiret <dev <at> jpoiret.xyz> wrote:
>> Hi Ludo,
>> 
>> Ludovic Courtès <ludo <at> gnu.org> writes:
>> 
>> > Coming next is an updated patch series addressing this as proposed
>> > above.  Let me know what y’all think!
>> >
>> > I tested the ‘posix_spawn_file_actions_addclosefrom_np’ path by building in:
>> >
>> >   guix time-machine --branch=core-updates -- shell -CP -D -f guix.scm
>> 
>> I didn't test, but this LGTM!  Maybe someone on OpenBSD could test this
>> patchset?
>
>     % gmake check
>     <snip />
>     gmake[5]: Entering directory '/home/op/w/guile/test-suite/standalone'
>     PASS: test-system-cmds
>
> it seems to work on OpenBSD 7.3 :)

Awesome!  Pushed as 9cc85a4f52147fcdaa4c52a62bcc87bdb267d0a9.

> but note that our libc doesn't have posix_spawn_file_actions_addclosefrom_np,
> so this is using the "racy" code path.

Yeah, not great.  :-/  I hope that function will be adopted by other
libcs, especially since ‘closefrom’ is already available.

> Just for curiosity, as it's outside the scope of the bug, what's the
> reason posix_spawn was used instead of a more classic fork() +
> closefrom()?

There’s a long discussion at:

  https://issues.guix.gnu.org/52835

Essentially, ‘fork’ is unusable in multi-threaded context, in addition
to being inefficient.

Thanks,
Ludo’.

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From: Ludovic Courtès <ludo <at> gnu.org>
To: bug-guile <at> gnu.org
Subject: [3.0.9] ‘system*’ broken on GNU/Hurd
Date: Thu, 26 Jan 2023 17:45:38 +0100

This test fails on GNU/Hurd:

--8<---------------cut here---------------start------------->8---
checking for library containing posix_spawn... none required
checking whether posix_spawn is declared... yes
checking for posix_spawn... yes
checking whether posix_spawn is declared... (cached) yes
checking whether posix_spawn works... yes
checking whether posix_spawn rejects scripts without shebang... yes
checking whether posix_spawnp rejects scripts without shebang... yes
checking whether posix_spawnattr_setschedpolicy is supported... yes
checking whether posix_spawnattr_setschedparam is supported... yes
checking for mbstate_t... yes
checking for ssize_t... yes
checking for sched.h... yes
checking for struct sched_param... yes
checking whether <sys/select.h> is self-contained... yes
checking whether setenv is declared... yes
checking for search.h... yes
checking for tsearch... yes
checking for sigset_t... yes
checking for uid_t in sys/types.h... yes
checking for volatile sig_atomic_t... yes
checking for sighandler_t... yes
checking for posix_spawnattr_t... yes
checking for posix_spawn_file_actions_t... yes

[…]

make[5]: Entering directory '/tmp/guix-build-guile-3.0.9rc1.drv-0/guile-3.0.9rc1/test-suite/standalone'
In execvp of guile: Bad file descriptor
test-system-cmds: system* exit status was 127 rather than 42
FAIL: test-system-cmds
--8<---------------cut here---------------end--------------->8---

This looks like a bug in the new ‘posix_spawn’-based ‘system*’, or (more
likely) in the ‘posix_spawn’ implementation for the Hurd in glibc.

Ludo’.

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