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y2038: Introduce the __ASSUME_TIME64_SYSCALLS define

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Add a macro to linux/kernel-features.h, __ASSUME_TIME64_SYSCALLS, to
indicate whether the kernel can be assumed to provide a set of system
calls that process 64-bit time_t.

__ASSUME_TIME64_SYSCALLS does not indicate whether time_t is actually
64 bits (that's __TIMEBITS) and also does not indicate whether the
64-bit time_t system calls have "time64" suffixes on their names.

Code that uses __ASSUME_TIME64_SYSCALLS will be added in subsequent
patches.

	* sysdeps/unix/sysv/linux/kernel-features.h
	(__ASSUME_TIME64_SYSCALLS): New macro.

Reviewed-by: Alistair Francis <alistair23@gmail.com>
Reviewed-by: Joseph Myers <joseph@codesourcery.com>
Reviewed-by: Zack Weinberg <zackw@panix.com>
This commit is contained in:
Lukasz Majewski 2019-08-28 14:27:03 -04:00 committed by Zack Weinberg
parent 7b5af2d8f2
commit a26918cfda
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ChangeLog
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@ -1,3 +1,8 @@
2019-09-04 Lukasz Majewski <lukma@denx.de>
* sysdeps/unix/sysv/linux/kernel-features.h
(__ASSUME_TIME64_SYSCALLS): New macro.
2019-09-04 Zack Weinberg <zackw@panix.com>
[BZ #24959]

59
sysdeps/unix/sysv/linux/kernel-features.h
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@ -20,6 +20,11 @@
/* 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
@ -139,3 +144,57 @@
*/
#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
#endif /* kernel-features.h */