Re: bug#54667: 29.0.50; posix_spawn breaks emacs-gdb

[Robert Pluim]

>>>>> On Wed, 06 Apr 2022 15:21:16 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Robert Pluim <rpluim@gmail.com>
    >> Cc: emacs-devel@gnu.org
    >> Date: Wed, 06 Apr 2022 14:04:39 +0200
    >> 
    >> >>>>> On Wed, 06 Apr 2022 14:09:04 +0300, Eli Zaretskii <eliz@gnu.org> 
said:
    >> 
    >> >> From: Robert Pluim <rpluim@gmail.com>
    >> >> Date: Wed, 06 Apr 2022 11:02:12 +0200
    >> >> 
    >> >> >>>>> On Mon, 04 Apr 2022 16:11:51 +0200, Robert Pluim 
<rpluim@gmail.com> said:
    Robert> In emacs-28 we only use posix_spawn on macOS because its vork is
    Robert> sub-optimal. I donʼt remember the rationale for switching to using 
it
    Robert> everywhere, itʼs undoubtedly in the archives somewhere.
    >> >> 
    Robert> Closing.
    Robert> Committed as 8103b060d8
    >> >> 
    >> >> Actually, do we want this in emacs-28 as well?
    >> 
    Eli> The fix installed on master isn't macOS-specific, AFAICT.  Can it be
    Eli> reasonably installed on emacs-28 as macOS-specific?  If yes, I think
    Eli> we should indeed backport it.
    >> 
    >> USABLE_POSIX_SPAWN is 0 on emacs-28 for every platform except macOS,
    >> so applying the same patch as on master is all thatʼs needed.

    Eli> I didn't see USABLE_POSIX_SPAWN in the patch.  Maybe I was looking at
    Eli> the wrong patch.  Can you show it?

USABLE_POSIX_SPAWN is 0 on emacs-28 for all platforms except macOS,
and 1 on master for all platforms (modulo availability of some other
required features) => posix_spawn can only be used by macOS on
emacs-28.

emacs-28 callproc.c:

/* In order to be able to use `posix_spawn', it needs to support some
   variant of `chdir' as well as `setsid'.  */
#if defined DARWIN_OS                                       \
  && defined HAVE_SPAWN_H && defined HAVE_POSIX_SPAWN       \
  && defined HAVE_POSIX_SPAWNATTR_SETFLAGS                  \
  && (defined HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR        \
      || defined HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP) \
  && defined HAVE_DECL_POSIX_SPAWN_SETSID                   \
  && HAVE_DECL_POSIX_SPAWN_SETSID == 1
# include <spawn.h>
# define USABLE_POSIX_SPAWN 1
#else
# define USABLE_POSIX_SPAWN 0
#endif

master callproc.c:

/* In order to be able to use `posix_spawn', it needs to support some
   variant of `chdir' as well as `setsid'.  */
#if defined HAVE_SPAWN_H && defined HAVE_POSIX_SPAWN        \
  && defined HAVE_POSIX_SPAWNATTR_SETFLAGS                  \
  && (defined HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR        \
      || defined HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP) \
  && defined HAVE_DECL_POSIX_SPAWN_SETSID                   \
  && HAVE_DECL_POSIX_SPAWN_SETSID == 1
# include <spawn.h>
# define USABLE_POSIX_SPAWN 1
#else
# define USABLE_POSIX_SPAWN 0
#endif

and all uses of posix_spawn are protected by USABLE_POSIX_SPAWN

Robert
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