y2038: Introduce __ASSUME_TIME64_SYSCALLS define
Commit Message
This define indicates if the Linux kernel (5.1+) provides syscalls supporting
64 bit versions of struct timespec and timeval.
For architectures with __WORDSIZE==64 && __TIMESIZE==64 (e.g. x86_64, aarch64
this flag is never defined (as those already use 64 bit versions of struct
timespec and timeval).
The __ASSUME_TIME64_SYSCALLS shall be only defined on systems with
__WORDSIZE==32.
For x32 this flag is explicitly undefined as this architecture has
64 bit registers but only 32 bit longs and pointers. Moreover, it uses
syscalls from x86_64.
* sysdeps/unix/sysv/linux/kernel-features.h: (__ASSUME_TIME64_SYSCALLS):
[__LINUX_KERNEL_VERSION >= 0x050100]: Define.
* sysdeps/unix/sysv/linux/x86_64/kernel-features.h (__ASSUME_TIME64_SYSCALLS):
#undef the __ASSUME_TIME64_SYSCALLS for x32 architecture
---
Changes for v4:
- Exclude this patch from the clock_settime64 patch series
- Rewrite the in-code comment
- Change patch description
Changes for v3:
- Provide more detailed and verbose description
- Change name to __ASSUME_TIME64_SYSCALLS
- Undefine __ASSUME_TIME64_SYSCALLS on x32
Changes for v2:
- New patch
---
sysdeps/unix/sysv/linux/kernel-features.h | 38 ++++++++++++++++++++++++
sysdeps/unix/sysv/linux/x86_64/kernel-features.h | 9 ++++++
2 files changed, 47 insertions(+)
Comments
On Wed, 8 May 2019, Lukasz Majewski wrote:
> For x32 this flag is explicitly undefined as this architecture has
> 64 bit registers but only 32 bit longs and pointers. Moreover, it uses
> syscalls from x86_64.
The first sentence there is not an accurate description of the reason for
undefining this for x32; other ILP32 configurations with 64-bit registers
don't have this peculiarity. "Moreover, it uses syscalls from x86_64."
isn't a good description either; x86_64 has three syscall tables (for
32-bit compat, x32 and the normal LP64 syscall interface).
> + Linux kernel, as of version 5.1, provides following set of syscalls,
> + which accept data based on struct timespec and timeval with 64 bit
> + tv_sec:
Do any of these actually use timeval? I thought the idea was that the new
syscalls for 64-bit time would all use timespec, with it being the
responsibility of libc to handle conversions to and from timeval as needed
(e.g. for gettimeofday with _TIME_BITS=64).
09.05.2019 в 15:58:38 +0000 Joseph Myers написал:
> On Wed, 8 May 2019, Lukasz Majewski wrote:
> > + Linux kernel, as of version 5.1, provides following set of syscalls,
> > + which accept data based on struct timespec and timeval with 64 bit
> > + tv_sec:
>
> Do any of these actually use timeval? I thought the idea was that the new
> syscalls for 64-bit time would all use timespec, with it being the
> responsibility of libc to handle conversions to and from timeval as needed
> (e.g. for gettimeofday with _TIME_BITS=64).
clock_adjtime uses __kernel_timex_timeval, as is explained in
https://lore.kernel.org/lkml/CAK8P3a0OBBEwU044jbe-YK2CmCnpNpUSiCA9uRo-8EwtcUva6g@mail.gmail.com/
@@ -143,3 +143,41 @@
*/
#define __ASSUME_CLONE_DEFAULT 1
+
+#include <bits/wordsize.h>
+#if __WORDSIZE != 64
+/* Support for Linux kernel syscalls, which are able to handle 64 bit
+ time on 32 bit systems (with 'long' and __WORDSIZE equal to 32 bits).
+
+ Linux kernel, as of version 5.1, provides following set of syscalls,
+ which accept data based on struct timespec and timeval with 64 bit
+ tv_sec:
+
+ clock_gettime64
+ clock_settime64
+ clock_adjtime64
+ clock_getres_time64
+ clock_nanosleep_time64
+ timer_gettime64
+ timer_settime64
+ timerfd_gettime64
+ timerfd_settime64
+ utimensat_time64
+ pselect6_time64
+ ppoll_time64
+ io_pgetevents_time64
+ recvmmsg_time64
+ mq_timedsend_time64
+ mq_timedreceive_time64
+ semtimedop_time64
+ rt_sigtimedwait_time64
+ futex_time64
+ sched_rr_get_interval_time64
+
+ Above syscalls are supposed to replace legacy ones, which handle 32
+ bit version of struct timespec and timeval (i.e. without the '64'
+ suffix). */
+# if __LINUX_KERNEL_VERSION >= 0x050100
+# define __ASSUME_TIME64_SYSCALLS 1
+# endif
+#endif
@@ -24,3 +24,12 @@
#endif
#include_next <kernel-features.h>
+
+/* For x32, which is a special case in respect to 64 bit time support,
+ the __ASSUME_TIME64_SYSCALLS define needs to be explicitly undefined.
+
+ It uses Linux time related syscalls for x86_64 (in compatibility
+ mode). */
+#ifdef __ILP32__
+# undef __ASSUME_TIME64_SYSCALLS
+#endif