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linux: Add clone3 CLONE_CLEAR_SIGHAND optimization to posix_spawn

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The clone3 flag resets all signal handlers of the child not set to
SIG_IGN to SIG_DFL.  It allows to skip most of the sigaction calls
to setup child signal handling, where previously a posix_spawn
had to issue 2 times NSIG sigaction calls (one to obtain the current
disposition and another to set either SIG_DFL or SIG_IGN).

With POSIX_SPAWN_SETSIGDEF the child will setup the signal for the case
where the disposition is SIG_IGN.

The code must handle the fallback where clone3 is not available. This is
done by splitting __clone_internal_fallback from __clone_internal.

Checked on x86_64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Adhemerval Zanella Netto
2023-01-12 10:58:51 -03:00
committed by Adhemerval Zanella
parent 2290cf73cc
commit 2053c11331
7 changed files with 238 additions and 27 deletions
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31
sysdeps/unix/sysv/linux/spawni.c
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@@ -66,6 +66,7 @@ struct posix_spawn_args
ptrdiff_t argc;
char *const *envp;
int xflags;
bool use_clone3;
int err;
};
@@ -104,12 +105,11 @@ __spawni_child (void *arguments)
const posix_spawnattr_t *restrict attr = args->attr;
const posix_spawn_file_actions_t *file_actions = args->fa;
/* The child must ensure that no signal handler are enabled because it shared
memory with parent, so the signal disposition must be either SIG_DFL or
SIG_IGN. It does by iterating over all signals and although it could
possibly be more optimized (by tracking which signal potentially have a
signal handler), it might requires system specific solutions (since the
sigset_t data type can be very different on different architectures). */
/* The child must ensure that no signal handler is enabled because it
shares memory with parent, so all signal dispositions must be either
SIG_DFL or SIG_IGN. If clone3/CLONE_CLEAR_SIGHAND is used, there is
only the need to set the defined signals POSIX_SPAWN_SETSIGDEF to
SIG_DFL; otherwise, the code iterates over all signals. */
struct sigaction sa;
memset (&sa, '\0', sizeof (sa));
@@ -122,7 +122,7 @@ __spawni_child (void *arguments)
{
sa.sa_handler = SIG_DFL;
}
else if (__sigismember (&hset, sig))
else if (!args->use_clone3 && __sigismember (&hset, sig))
{
if (is_internal_signal (sig))
sa.sa_handler = SIG_IGN;
@@ -382,12 +382,25 @@ __spawnix (pid_t * pid, const char *file,
for instance). */
struct clone_args clone_args =
{
.flags = CLONE_VM | CLONE_VFORK,
/* Unsupported flags like CLONE_CLEAR_SIGHAND will be cleared up by
__clone_internal_fallback. */
.flags = CLONE_CLEAR_SIGHAND | CLONE_VM | CLONE_VFORK,
.exit_signal = SIGCHLD,
.stack = (uintptr_t) stack,
.stack_size = stack_size,
};
new_pid = __clone_internal (&clone_args, __spawni_child, &args);
#ifdef HAVE_CLONE3_WRAPPER
args.use_clone3 = true;
new_pid = __clone3 (&clone_args, sizeof (clone_args), __spawni_child,
&args);
/* clone3 was added in 5.3 and CLONE_CLEAR_SIGHAND in 5.5. */
if (new_pid == -1 && (errno == ENOSYS || errno == EINVAL))
#endif
{
args.use_clone3 = false;
new_pid = __clone_internal_fallback (&clone_args, __spawni_child,
&args);
}
/* It needs to collect the case where the auxiliary process was created
but failed to execute the file (due either any preparation step or