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posix: Use posix_spawn on system

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This patch uses posix_spawn on system implementation.  On Linux this has
the advantage of much lower memory consumption (usually 32 Kb minimum for
the mmap stack area).

Although POSIX does not require, glibc system implementation aims to be
thread and cancellation safe.  The cancellation code is moved to generic
implementation and enabled iff SIGCANCEL is defined (similar on how the
cancellation handler is enabled on nptl-init.c).

Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
arm-linux-gnueabihf, and powerpc64le-linux-gnu.

	* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Use
	__sigismember instead of sigismember.
	* sysdeps/posix/system.c [SIGCANCEL] (cancel_handler_args,
	cancel_handler): New definitions.
	(CLEANUP_HANDLER, CLEANUP_RESET): Likewise.
	(DO_LOCK, DO_UNLOCK, INIT_LOCK, ADD_REF, SUB_REF): Remove.
	(do_system): Use posix_spawn instead of fork and execl and remove
	reentracy code.
	* sysdeps/generic/not-errno.h (__kill_noerrno): New prototype.
	* sysdeps/unix/sysv/linux/not-errno.h (__kill_noerrno): Likewise.
	* sysdeps/unix/sysv/linux/ia64/system.c: Remove file.
	* sysdeps/unix/sysv/linux/s390/system.c: Likewise.
	* sysdeps/unix/sysv/linux/sparc/system.c: Likewise.
	* sysdeps/unix/sysv/linux/system.c: Likewise.
This commit is contained in:
Adhemerval Zanella
2018-10-24 16:29:38 -03:00
parent 14d0e87d9b
commit 5fb7fc9635
9 changed files with 131 additions and 255 deletions
Download Patch File Download Diff File Expand all files Collapse all files

189
sysdeps/posix/system.c
View File

@@ -17,20 +17,36 @@
#include <errno.h>
#include <signal.h>
#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include <sigsetops.h>
#include <spawn.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <libc-lock.h>
#include <sysdep-cancel.h>
#include <sigsetops.h>
#include <stdio.h>
#include <libc-lock.h>
#include <not-errno.h>
#include <not-cancel.h>
#include <internal-signals.h>
#define SHELL_PATH "/bin/sh" /* Path of the shell. */
#define SHELL_NAME "sh" /* Name to give it. */
/* This system implementation aims to be thread-safe, which requires to
restore the signal dispositions for SIGINT and SIGQUIT correctly and to
deal with cancellation by terminating the child process.
The signal disposition restoration on the single-thread case is
straighfoward. For multithreaded case, a reference-counter with a lock
is used, so the first thread will set the SIGINT/SIGQUIT dispositions and
last thread will restore them.
Cancellation handling is done with thread cancellation clean-up handlers
on waitpid call. */
#ifdef _LIBC_REENTRANT
static struct sigaction intr, quit;
static int sa_refcntr;
@@ -50,17 +66,45 @@ __libc_lock_define_initialized (static, lock);
#endif
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
struct cancel_handler_args
{
struct sigaction *quit;
struct sigaction *intr;
pid_t pid;
};
static void
cancel_handler (void *arg)
{
struct cancel_handler_args *args = (struct cancel_handler_args *) (arg);
__kill_noerrno (args->pid, SIGKILL);
TEMP_FAILURE_RETRY (__waitpid_nocancel (args->pid, NULL, 0));
DO_LOCK ();
if (SUB_REF () == 0)
{
__sigaction (SIGQUIT, args->quit, NULL);
__sigaction (SIGINT, args->intr, NULL);
}
DO_UNLOCK ();
}
#endif
/* Execute LINE as a shell command, returning its status. */
static int
do_system (const char *line)
{
int status, save;
int status;
pid_t pid;
struct sigaction sa;
#ifndef _LIBC_REENTRANT
struct sigaction intr, quit;
#endif
sigset_t omask;
sigset_t reset;
sa.sa_handler = SIG_IGN;
sa.sa_flags = 0;
@@ -69,105 +113,72 @@ do_system (const char *line)
DO_LOCK ();
if (ADD_REF () == 0)
{
if (__sigaction (SIGINT, &sa, &intr) < 0)
{
(void) SUB_REF ();
goto out;
}
if (__sigaction (SIGQUIT, &sa, &quit) < 0)
{
save = errno;
(void) SUB_REF ();
goto out_restore_sigint;
}
/* sigaction can not fail with SIGINT/SIGQUIT used with SIG_IGN. */
__sigaction (SIGINT, &sa, &intr);
__sigaction (SIGQUIT, &sa, &quit);
}
DO_UNLOCK ();
/* We reuse the bitmap in the 'sa' structure. */
__sigaddset (&sa.sa_mask, SIGCHLD);
save = errno;
if (__sigprocmask (SIG_BLOCK, &sa.sa_mask, &omask) < 0)
/* sigprocmask can not fail with SIG_BLOCK used with valid input
arguments. */
__sigprocmask (SIG_BLOCK, &sa.sa_mask, &omask);
__sigemptyset (&reset);
if (intr.sa_handler != SIG_IGN)
__sigaddset(&reset, SIGINT);
if (quit.sa_handler != SIG_IGN)
__sigaddset(&reset, SIGQUIT);
posix_spawnattr_t spawn_attr;
/* None of the posix_spawnattr_* function returns an error, including
posix_spawnattr_setflags for the follow specific usage (using valid
flags). */
__posix_spawnattr_init (&spawn_attr);
__posix_spawnattr_setsigmask (&spawn_attr, &omask);
__posix_spawnattr_setsigdefault (&spawn_attr, &reset);
__posix_spawnattr_setflags (&spawn_attr,
POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK);
status = __posix_spawn (&pid, SHELL_PATH, 0, &spawn_attr,
(char *const[]){ (char*) SHELL_NAME,
(char*) "-c",
(char *) line, NULL },
__environ);
__posix_spawnattr_destroy (&spawn_attr);
if (status == 0)
{
#ifndef _LIBC
if (errno == ENOSYS)
__set_errno (save);
else
/* Cancellation results in cleanup handlers running as exceptions in
the block where they were installed, so it is safe to reference
stack variable allocate in the broader scope. */
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
struct cancel_handler_args cancel_args =
{
.quit = &quit,
.intr = &intr,
.pid = pid
};
__libc_cleanup_region_start (1, cancel_handler, &cancel_args);
#endif
{
DO_LOCK ();
if (SUB_REF () == 0)
{
save = errno;
(void) __sigaction (SIGQUIT, &quit, (struct sigaction *) NULL);
out_restore_sigint:
(void) __sigaction (SIGINT, &intr, (struct sigaction *) NULL);
__set_errno (save);
}
out:
DO_UNLOCK ();
return -1;
}
}
#ifdef CLEANUP_HANDLER
CLEANUP_HANDLER;
#endif
#ifdef FORK
pid = FORK ();
#else
pid = __fork ();
#endif
if (pid == (pid_t) 0)
{
/* Child side. */
const char *new_argv[4];
new_argv[0] = SHELL_NAME;
new_argv[1] = "-c";
new_argv[2] = line;
new_argv[3] = NULL;
/* Restore the signals. */
(void) __sigaction (SIGINT, &intr, (struct sigaction *) NULL);
(void) __sigaction (SIGQUIT, &quit, (struct sigaction *) NULL);
(void) __sigprocmask (SIG_SETMASK, &omask, (sigset_t *) NULL);
INIT_LOCK ();
/* Exec the shell. */
(void) __execve (SHELL_PATH, (char *const *) new_argv, __environ);
_exit (127);
}
else if (pid < (pid_t) 0)
/* The fork failed. */
status = -1;
else
/* Parent side. */
{
/* Note the system() is a cancellation point. But since we call
waitpid() which itself is a cancellation point we do not
have to do anything here. */
if (TEMP_FAILURE_RETRY (__waitpid (pid, &status, 0)) != pid)
status = -1;
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
__libc_cleanup_region_end (0);
#endif
}
#ifdef CLEANUP_HANDLER
CLEANUP_RESET;
#endif
save = errno;
DO_LOCK ();
if ((SUB_REF () == 0
&& (__sigaction (SIGINT, &intr, (struct sigaction *) NULL)
| __sigaction (SIGQUIT, &quit, (struct sigaction *) NULL)) != 0)
|| __sigprocmask (SIG_SETMASK, &omask, (sigset_t *) NULL) != 0)
if (SUB_REF () == 0)
{
#ifndef _LIBC
/* glibc cannot be used on systems without waitpid. */
if (errno == ENOSYS)
__set_errno (save);
else
#endif
status = -1;
/* sigaction can not fail with SIGINT/SIGQUIT used with old
disposition. Same applies for sigprocmask. */
__sigaction (SIGINT, &intr, NULL);
__sigaction (SIGQUIT, &quit, NULL);
__sigprocmask (SIG_SETMASK, &omask, NULL);
}
DO_UNLOCK ();