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glibc/sysdeps/unix/sysv/linux/kernel-features.h
Adhemerval Zanella 9b2cf9482a linux: Use waitid on wait4 if __NR_wait4 is not defined 
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>
2019-12-19 16:11:09 -03:00

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/* Set flags signalling availability of kernel features based on given
kernel version number.
Copyright (C) 1999-2019 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/>. */
/* This file must not contain any C code. At least it must be protected
to allow using the file also in assembler files. */
#ifndef _LINUX_KERNEL_FEATURES_H
#define _LINUX_KERNEL_FEATURES_H 1
#include <bits/wordsize.h>
#ifndef __LINUX_KERNEL_VERSION
/* We assume the worst; all kernels should be supported. */
# define __LINUX_KERNEL_VERSION 0
#endif
/* We assume for __LINUX_KERNEL_VERSION the same encoding used in
linux/version.h. I.e., the major, minor, and subminor all get a
byte with the major number being in the highest byte. This means
we can do numeric comparisons.
In the following we will define certain symbols depending on
whether the describes kernel feature is available in the kernel
version given by __LINUX_KERNEL_VERSION. We are not always exactly
recording the correct versions in which the features were
introduced. If somebody cares these values can afterwards be
corrected. */
/* The statfs64 syscalls are available in 2.5.74 (but not for alpha). */
#define __ASSUME_STATFS64 1
/* pselect/ppoll were introduced just after 2.6.16-rc1. On x86_64 and
SH this appeared first in 2.6.19-rc1, on ia64 in 2.6.22-rc1. */
#define __ASSUME_PSELECT 1
/* The *at syscalls were introduced just after 2.6.16-rc1. On PPC
they were introduced in 2.6.17-rc1, on SH in 2.6.19-rc1. */
#define __ASSUME_ATFCTS 1
/* Support for inter-process robust mutexes was added in 2.6.17 (but
some architectures lack futex_atomic_cmpxchg_inatomic in some
configurations). */
#define __ASSUME_SET_ROBUST_LIST 1
/* Support for various CLOEXEC and NONBLOCK flags was added in
2.6.27. */
#define __ASSUME_IN_NONBLOCK 1
/* Support for preadv and pwritev was added in 2.6.30. */
#define __ASSUME_PREADV 1
#define __ASSUME_PWRITEV 1
/* Support for sendmmsg functionality was added in 3.0. */
#define __ASSUME_SENDMMSG 1
/* On most architectures, most socket syscalls are supported for all
supported kernel versions, but on some socketcall architectures
separate syscalls were only added later. */
#define __ASSUME_SENDMSG_SYSCALL 1
#define __ASSUME_RECVMSG_SYSCALL 1
#define __ASSUME_ACCEPT_SYSCALL 1
#define __ASSUME_CONNECT_SYSCALL 1
#define __ASSUME_RECVFROM_SYSCALL 1
#define __ASSUME_SENDTO_SYSCALL 1
#define __ASSUME_ACCEPT4_SYSCALL 1
#define __ASSUME_RECVMMSG_SYSCALL 1
#define __ASSUME_SENDMMSG_SYSCALL 1
/* Support for SysV IPC through wired syscalls. All supported architectures
either support ipc syscall and/or all the ipc correspondent syscalls. */
#define __ASSUME_DIRECT_SYSVIPC_SYSCALLS 1
/* The generic default __IPC_64 value is 0x0, however some architectures
require a different value of 0x100. */
#define __ASSUME_SYSVIPC_DEFAULT_IPC_64 1
/* All supported architectures reserve a 32-bit for MODE field in sysvipc
ipc_perm. However, some kernel ABI interfaces still expect a 16-bit
field. This is only an issue if arch-defined IPC_PERM padding is on a
wrong position regarding endianness. In this case, the IPC control
routines (msgctl, semctl, and semtctl) requires to shift the value to
correct place.
The ABIs that requires it define __ASSUME_SYSVIPC_BROKEN_MODE_T. */
/* Support for p{read,write}v2 was added in 4.6. However Linux default
implementation does not assume the __ASSUME_* and instead use a fallback
implementation based on p{read,write}v and returning an error for
non supported flags. */
/* Support for the renameat2 system call was added in kernel 3.15. */
#if __LINUX_KERNEL_VERSION >= 0x030F00
# define __ASSUME_RENAMEAT2
#endif
/* Support for the execveat syscall was added in 3.19. */
#if __LINUX_KERNEL_VERSION >= 0x031300
# define __ASSUME_EXECVEAT 1
#endif
#if __LINUX_KERNEL_VERSION >= 0x040400
# define __ASSUME_MLOCK2 1
#endif
/* Support for statx was added in kernel 4.11. */
#if __LINUX_KERNEL_VERSION >= 0x040B00
# define __ASSUME_STATX 1
#endif
/* Support for clone call used on fork. The signature varies across the
architectures with current 4 different variants:
1. long int clone (unsigned long flags, unsigned long newsp,
int *parent_tidptr, unsigned long tls,
int *child_tidptr)
2. long int clone (unsigned long newsp, unsigned long clone_flags,
int *parent_tidptr, int * child_tidptr,
unsigned long tls)
3. long int clone (unsigned long flags, unsigned long newsp,
int stack_size, int *parent_tidptr,
int *child_tidptr, unsigned long tls)
4. long int clone (unsigned long flags, unsigned long newsp,
int *parent_tidptr, int *child_tidptr,
unsigned long tls)
The fourth variant is intended to be used as the default for newer ports,
Also IA64 uses the third variant but with __NR_clone2 instead of
__NR_clone.
The macros names to define the variant used for the architecture is
similar to kernel:
- __ASSUME_CLONE_BACKWARDS: for variant 1.
- __ASSUME_CLONE_BACKWARDS2: for variant 2 (s390).
- __ASSUME_CLONE_BACKWARDS3: for variant 3 (microblaze).
- __ASSUME_CLONE_DEFAULT: for variant 4.
- __ASSUME_CLONE2: for clone2 with variant 3 (ia64).
*/
#define __ASSUME_CLONE_DEFAULT 1
/* Support for 64-bit time_t in the system call interface. When this
flag is set, the kernel provides a version of each of these system
calls that accepts 64-bit time_t:
clock_adjtime(64)
clock_gettime(64)
clock_settime(64)
clock_getres(_time64)
clock_nanosleep(_time64)
futex(_time64)
mq_timedreceive(_time64)
mq_timedsend(_time64)
ppoll(_time64)
pselect6(_time64)
rt_sigtimedwait(_time64)
sched_rr_get_interval(_time64)
timer_gettime(64)
timer_settime(64)
timerfd_gettime(64)
timerfd_settime(64)
utimensat(_time64)
On architectures where time_t has historically been 64 bits,
only the 64-bit version of each system call exists, and there
are no suffixes on the __NR_ constants.
On architectures where time_t has historically been 32 bits,
both 32-bit and 64-bit versions of each system call may exist,
depending on the kernel version. When the 64-bit version exists,
there is a '64' or '_time64' suffix on the name of its __NR_
constant, as shown above.
This flag is always set for Linux 5.1 and later. Prior to that
version, it is set only for some CPU architectures and ABIs:
- __WORDSIZE == 64 - all supported architectures where pointers
are 64 bits also have always had 64-bit time_t.
- __WORDSIZE == 32 && __SYSCALL_WORDSIZE == 64 - this describes
only one supported configuration, x86's 'x32' subarchitecture,
where pointers are 32 bits but time_t has always been 64 bits.
__ASSUME_TIME64_SYSCALLS being set does not mean __TIMESIZE is 64,
and __TIMESIZE equal to 64 does not mean __ASSUME_TIME64_SYSCALLS
is set. All four cases are possible. */
#if __LINUX_KERNEL_VERSION >= 0x050100 \
|| __WORDSIZE == 64 \
|| (defined __SYSCALL_WORDSIZE && __SYSCALL_WORDSIZE == 64)
# 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 */
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