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Use posix_spawn if possible.

Browse source 
posix_spawn is less error-prone than vfork + execve, and can make
better use of system-specific enhancements like 'clone' on Linux.  Use
it if we don't need to configure a pseudoterminal.

* configure.ac (HAVE_SPAWN_H, HAVE_POSIX_SPAWN)
(HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR)
(HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP)
(HAVE_POSIX_SPAWNATTR_SETFLAGS, HAVE_DECL_POSIX_SPAWN_SETSID): New
configuration variables.
* src/callproc.c (USABLE_POSIX_SPAWN): New configuration macro.
(emacs_posix_spawn_init_actions)
(emacs_posix_spawn_init_attributes, emacs_posix_spawn_init): New
helper functions.
(emacs_spawn): Use posix_spawn if possible.
This commit is contained in:
Philipp Stephani 2020-12-30 14:42:01 +01:00
parent 6c9ac53249
commit a60053f836
2 changed files with 205 additions and 1 deletions
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17
configure.ac
View file

@ -4771,6 +4771,23 @@ dnl AC_CHECK_FUNCS_ONCE wouldn’t be right for snprintf, which needs
dnl the current CFLAGS etc.
AC_CHECK_FUNCS(snprintf)
dnl posix_spawn. The chdir and setsid functionality is relatively
dnl recent, so we check for it specifically.
AC_CHECK_HEADERS([spawn.h])
AC_SUBST([HAVE_SPAWN_H])
AC_CHECK_FUNCS([posix_spawn \
posix_spawn_file_actions_addchdir \
posix_spawn_file_actions_addchdir_np \
posix_spawnattr_setflags])
AC_SUBST([HAVE_POSIX_SPAWN])
AC_SUBST([HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR])
AC_SUBST([HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR_NP])
AC_SUBST([HAVE_POSIX_SPAWNATTR_SETFLAGS])
AC_CHECK_DECLS([POSIX_SPAWN_SETSID], [], [], [[
#include <spawn.h>
]])
AC_SUBST([HAVE_DECL_POSIX_SPAWN_SETSID])
dnl Check for glib. This differs from other library checks in that
dnl Emacs need not link to glib unless some other library is already
dnl linking to glib. Although glib provides no facilities that Emacs

189
src/callproc.c
View file

@ -28,6 +28,20 @@ along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>. */
#include <sys/file.h>
#include <fcntl.h>
/* 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
#include "lisp.h"
#ifdef SETUP_SLAVE_PTY
@ -1247,6 +1261,130 @@ child_setup (int in, int out, int err, char **new_argv, char **env,
#endif /* not WINDOWSNT */
}
#if USABLE_POSIX_SPAWN
/* Set up ACTIONS and ATTRIBUTES for `posix_spawn'. Return an error
number. */
static int
emacs_posix_spawn_init_actions (posix_spawn_file_actions_t *actions,
int std_in, int std_out, int std_err,
const char *cwd)
{
int error = posix_spawn_file_actions_init (actions);
if (error != 0)
return error;
error = posix_spawn_file_actions_adddup2 (actions, std_in,
STDIN_FILENO);
if (error != 0)
goto out;
error = posix_spawn_file_actions_adddup2 (actions, std_out,
STDOUT_FILENO);
if (error != 0)
goto out;
error = posix_spawn_file_actions_adddup2 (actions,
std_err < 0 ? std_out
: std_err,
STDERR_FILENO);
if (error != 0)
goto out;
error =
#ifdef HAVE_POSIX_SPAWN_FILE_ACTIONS_ADDCHDIR
posix_spawn_file_actions_addchdir
#else
posix_spawn_file_actions_addchdir_np
#endif
(actions, cwd);
if (error != 0)
goto out;
out:
if (error != 0)
posix_spawn_file_actions_destroy (actions);
return error;
}
static int
emacs_posix_spawn_init_attributes (posix_spawnattr_t *attributes)
{
int error = posix_spawnattr_init (attributes);
if (error != 0)
return error;
error = posix_spawnattr_setflags (attributes,
POSIX_SPAWN_SETSID
| POSIX_SPAWN_SETSIGDEF
| POSIX_SPAWN_SETSIGMASK);
if (error != 0)
goto out;
sigset_t sigdefault;
sigemptyset (&sigdefault);
#ifdef DARWIN_OS
/* Work around a macOS bug, where SIGCHLD is apparently
delivered to a vforked child instead of to its parent. See:
https://lists.gnu.org/r/emacs-devel/2017-05/msg00342.html
*/
sigaddset (&sigdefault, SIGCHLD);
#endif
sigaddset (&sigdefault, SIGINT);
sigaddset (&sigdefault, SIGQUIT);
#ifdef SIGPROF
sigaddset (&sigdefault, SIGPROF);
#endif
/* Emacs ignores SIGPIPE, but the child should not. */
sigaddset (&sigdefault, SIGPIPE);
/* Likewise for SIGPROF. */
#ifdef SIGPROF
sigaddset (&sigdefault, SIGPROF);
#endif
error = posix_spawnattr_setsigdefault (attributes, &sigdefault);
if (error != 0)
goto out;
/* Stop blocking SIGCHLD in the child. */
sigset_t oldset;
error = pthread_sigmask (SIG_SETMASK, NULL, &oldset);
if (error != 0)
goto out;
error = posix_spawnattr_setsigmask (attributes, &oldset);
if (error != 0)
goto out;
out:
if (error != 0)
posix_spawnattr_destroy (attributes);
return error;
}
static int
emacs_posix_spawn_init (posix_spawn_file_actions_t *actions,
posix_spawnattr_t *attributes, int std_in,
int std_out, int std_err, const char *cwd)
{
int error = emacs_posix_spawn_init_actions (actions, std_in,
std_out, std_err, cwd);
if (error != 0)
return error;
error = emacs_posix_spawn_init_attributes (attributes);
if (error != 0)
return error;
return 0;
}
#endif
/* Start a new asynchronous subprocess. If successful, return zero
and store the process identifier of the new process in *NEWPID.
Use STDIN, STDOUT, and STDERR as standard streams for the new
@ -1266,10 +1404,58 @@ emacs_spawn (pid_t *newpid, int std_in, int std_out, int std_err,
char **argv, char **envp, const char *cwd,
const char *pty, const sigset_t *oldset)
{
#if USABLE_POSIX_SPAWN
/* Prefer the simpler `posix_spawn' if available. `posix_spawn'
doesn't yet support setting up pseudoterminals, so we fall back
to `vfork' if we're supposed to use a pseudoterminal. */
bool use_posix_spawn = pty == NULL;
posix_spawn_file_actions_t actions;
posix_spawnattr_t attributes;
if (use_posix_spawn)
{
/* Initialize optional attributes before blocking. */
int error
= emacs_posix_spawn_init (&actions, &attributes, std_in,
std_out, std_err, cwd);
if (error != 0)
return error;
}
#endif
int pid;
int vfork_error;
eassert (input_blocked_p ());
#if USABLE_POSIX_SPAWN
if (use_posix_spawn)
{
vfork_error = posix_spawn (&pid, argv[0], &actions, &attributes,
argv, envp);
if (vfork_error != 0)
pid = -1;
int error = posix_spawn_file_actions_destroy (&actions);
if (error != 0)
{
errno = error;
emacs_perror ("posix_spawn_file_actions_destroy");
}
error = posix_spawnattr_destroy (&attributes);
if (error != 0)
{
errno = error;
emacs_perror ("posix_spawnattr_destroy");
}
goto fork_done;
}
#endif
#ifndef WINDOWSNT
/* vfork, and prevent local vars from being clobbered by the vfork. */
pid_t *volatile newpid_volatile = newpid;
@ -1413,8 +1599,9 @@ emacs_spawn (pid_t *newpid, int std_in, int std_out, int std_err,
/* Back in the parent process. */
int vfork_error = pid < 0 ? errno : 0;
vfork_error = pid < 0 ? errno : 0;
fork_done:
if (pid < 0)
{
eassert (0 < vfork_error);