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linux: Use waitid on wait4 if __NR_wait4 is not defined

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If the wait4 syscall is not available (such as y2038 safe 32-bit
systems) waitid should be used instead.  However prior Linux 5.4
waitid is not a full superset of other wait syscalls, since it
does not include support for waiting for the current process group.

It is possible to emulate wait4 by issuing an extra syscall to get
the current process group, but it is inherent racy: after the current
process group is received and before it is passed to waitid a signal
could arrive causing the current process group to change.

So waitid is used if wait4 is not defined iff the build is
enabled with a minimum kernel if 5.4+.  The new assume
__ASSUME_WAITID_PID0_P_PGID is added and an error is issued if waitid
can not be implemented by either __NR_wait4 or
__NR_waitid && __ASSUME_WAITID_PID0_P_PGID.

Checked on x86_64-linux-gnu and i686-linux-gnu.

Co-authored-by: Alistair Francis <alistair.francis@wdc.com>
This commit is contained in:
Adhemerval Zanella 2019-11-13 17:45:13 -03:00
parent c5cbdacb8a
commit 9b2cf9482a
3 changed files with 90 additions and 1 deletions
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6
sysdeps/unix/sysv/linux/kernel-features.h
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@ -208,4 +208,10 @@
# define __ASSUME_TIME64_SYSCALLS 1
#endif
/* Linux waitid prior kernel 5.4 does not support waiting for the current
process group. */
#if __LINUX_KERNEL_VERSION >= 0x050400
# define __ASSUME_WAITID_PID0_P_PGID
#endif
#endif /* kernel-features.h */

1
sysdeps/unix/sysv/linux/syscalls.list
View File

@ -67,7 +67,6 @@ swapoff - swapoff i:s __swapoff swapoff
unshare EXTRA unshare i:i unshare
uselib EXTRA uselib i:s __compat_uselib uselib@GLIBC_2.0:GLIBC_2.23
utime - utime i:sP utime
wait4 - wait4 i:iWiP __wait4 wait4
chown - chown i:sii __libc_chown __chown chown

84
sysdeps/unix/sysv/linux/wait4.c Normal file
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@ -0,0 +1,84 @@
/* Wait for process to change state. Linux version.
Copyright (C) 2019 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <sys/wait.h>
#include <sys/resource.h>
#include <sysdep-cancel.h>
pid_t
__wait4 (pid_t pid, int *stat_loc, int options, struct rusage *usage)
{
#ifdef __NR_wait4
return SYSCALL_CANCEL (wait4, pid, stat_loc, options, usage);
#elif defined (__ASSUME_WAITID_PID0_P_PGID)
idtype_t idtype = P_PID;
if (pid < -1)
{
idtype = P_PGID;
pid *= -1;
}
else if (pid == -1)
idtype = P_ALL;
else if (pid == 0)
idtype = P_PGID;
options |= WEXITED;
siginfo_t infop;
if (SYSCALL_CANCEL (waitid, idtype, pid, &infop, options, usage) < 0)
return -1;
if (stat_loc)
{
switch (infop.si_code)
{
case CLD_EXITED:
*stat_loc = W_EXITCODE (infop.si_status, 0);
break;
case CLD_DUMPED:
*stat_loc = WCOREFLAG | infop.si_status;
break;
case CLD_KILLED:
*stat_loc = infop.si_status;
break;
case CLD_TRAPPED:
case CLD_STOPPED:
*stat_loc = W_STOPCODE (infop.si_status);
break;
case CLD_CONTINUED:
*stat_loc = __W_CONTINUED;
break;
default:
*stat_loc = 0;
break;
}
}
return infop.si_pid;
# else
/* Linux waitid prior kernel 5.4 does not support waiting for the current
process. It is possible to emulate wait4 it by calling getpgid for
PID 0, however, it would require an additional syscall and it is inherent
racy: after the current process group is received and before it is passed
to waitid a signal could arrive causing the current process group to
change. */
# error "The kernel ABI does not provide a way to implement wait4"
#endif
}
weak_alias (__wait4, wait4)