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[PATCH v7] y2038: Introduce __ASSUME_TIME64_SYSCALLS define
- From: Lukasz Majewski <lukma at denx dot de>
- To: libc-alpha at sourceware dot org, Joseph Myers <joseph at codesourcery dot com>
- Cc: Stepan Golosunov <stepan at golosunov dot pp dot ru>, Arnd Bergmann <arnd at arndb dot de>, Paul Eggert <eggert at cs dot ucla dot edu>, Lukasz Majewski <lukma at denx dot de>
- Date: Tue, 11 Jun 2019 18:02:43 +0200
- Subject: [PATCH v7] y2038: Introduce __ASSUME_TIME64_SYSCALLS define
This define indicates if the Linux kernel provides interfaces (syscalls)
to support 64 bit time.
* sysdeps/unix/sysv/linux/kernel-features.h:
(__ASSUME_TIME64_SYSCALLS): Define.
---
Changes for v7:
- Move the flag description from commit message to in-code comment.
- Check if relevant syscalls were defined in v3.2 (oldest glibc supported
kernel).
- New syscalls, added to v5.1, like semtimedop_time64, which need extra
code for handling, shall be excluded from __ASSUME_TIME64_SYSCALLS and
would receive new flag - e.g. __ASSUME_SEMTIMEDOP_TIME64
Changes for v6:
- Change the logical meaning of __ASSUME_TIME64_SYSCALLS - now it
indicates if the system supports the 64 bit time ABI (if for both
__WORDSIZE==64 and __WORDSIZE==32 systems equally functional syscalls
are provided).
- Update commit description
Changes for v5:
- Rewrite the in-code comment (x32 description more precise)
- Change patch description (for x32)
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
Syscall's ABI compatibility checking:
1. Code to check if syscalls are defined since v3.2 kernel on the
intersection of archs supported by v3.2 kernel and contemporary glibc
(SHA1: e6e24243905957c36596f50a22af0acfd83793e2):
(Assumption: syscall ABI change require changing the name - like __NR_epoll_create
and __NR_epoll_create1)
export syscalls_table="\
clock_gettime clock_settime clock_adjtime \
clock_getres clock_nanosleep timer_gettime \
timer_settime timerfd_gettime timerfd_settime \
utimensat pselect6 ppoll io_pgetevents recvmmsg \
mq_timedsend mq_timedreceive rt_sigtimedwait futex \
sched_rr_get_interval"
for syscall in ${syscalls_table} ; do echo -n "syscall: ${syscall} -> "; \
grep -rnIw "__NR_${syscall}" | grep ^arch/ | \
grep -vE "mn10300|avr32|cris|m32r|frv|blackfin|xtensa|h8300|vdso" | \
wc -l; done
Excluded syscalls (needs to be re-checked when syscall is converted to
64 bit):
- recvmmsg - is not defined for s390 (64 bit) and m68k (32 bit)
- io_pgetevents - is not defined at all for 3.2 kernel
2. Architectures (ports) supported by current glibc, but added to Linux
after v3.2:
find sysdeps/unix/sysv/linux/ -type d | grep linux | \
grep -vE "x86|sparc|m68k|powerpc|microblaze|arm|sh|ia64|s390|alpha|mips|i386" | \
grep -vE "generic|net|bits|include|scsi|nfs|sys$"
Ports:
- 32 bit: nios2, csky, hppa (is the same as parisc?) - no need to
check as they will either use syscalls with 32 bit time support
or new ones from v5.1 kernel
- aarch64, riscv - 64 bit (the __ASSUME_TIME64_SYSCALLS set of
syscalls is defined)
For linux 5.0 - syscalls are available in: include/uapi/asm-generic/unistd.h
for syscall in ${syscalls_table} ; do echo -n "syscall: ${syscall} -> "; \
grep -rnIw "__NR_${syscall}" | grep ^include/ | \
grep -vE "mn10300|avr32|cris|m32r|frv|blackfin|xtensa|h8300|vdso" | \
wc -l; done
The __ASSUME_TIME64_SYSCALLS set of syscalls is also defined in this case.
Considering the above - it shall be safe to 'add' above set of syscalls to
__ASSUME_TIME64_SYSCALLS flag.
---
sysdeps/unix/sysv/linux/kernel-features.h | 70 +++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)
diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
index bc5c959f58..cf99cfac17 100644
--- a/sysdeps/unix/sysv/linux/kernel-features.h
+++ b/sysdeps/unix/sysv/linux/kernel-features.h
@@ -143,3 +143,73 @@
*/
#define __ASSUME_CLONE_DEFAULT 1
+
+/* This flag indicates support for Linux kernel syscalls, which are able
+ to handle 64 bit time ABI. It is defined for architectures with both
+ present 64 bit time support (__WORDSIZE == 64 and __SYSCALL_WORDSIZE
+ == 64) as well as ones gaining it with new syscalls added to Linux
+ kernel version 5.1 (listed below).
+
+ To be more specific - this flag focuses on higer level of abstraction,
+ which indicates the system's ability to support 64 bit time.
+
+ In the other words this flag indicates availability of specific 64 bit
+ time supporting interfaces (syscalls in this case) from Linux kernel.
+
+ As an example - the syscall to set clock (clock_settime) - if the
+ __ASSUME_TIME64_SYSCALLS is defined, it indicates that 64 bit time can
+ be set in the system.
+
+ On systems with __WORDSIZE == 64 the __NR_clock_settime syscall is used
+ to achieve this goal. Contrary, systems with __WORDSIZE == 32 do use
+ new __NR_clock_settime64 syscall available from Linux version 5.1.
+
+ The __ASSUME_TIME64_SYSCALLS is defined for:
+
+ 1. Systems which currently provide 64 bit time support (__WORDSIZE == 64).
+
+ 2. For 'x32' architecture, which is a special case in respect to 64 bit
+ time support (it has __WORDSIZE==32 but __TIMESIZE==64)
+
+ For point 1 and 2, defined __ASSUME_TIME64_SYSCALL means, that the
+ syscall semantics are identical for both the old syscall (on systems
+ where __WORDSIZE or _SYSCALL_WORDSIZE is 64) and for the new one (if
+ ever defined from listed below v5.1 subset), so that no code will
+ ever have to handle the two syscalls differently.
+
+ 3. Systems with __WORDSIZE==32, which gain 64 bit time support with new
+ set of syscalls added to Linux kernel 5.1.
+
+ List of new syscalls added to v5.1. kernel (they accept data based on
+ struct timespec and timeval with 64 bit tv_sec) consistent with
+ __ASSUME_TIME64_SYSCALLS flag definition:
+
+ 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
+ mq_timedsend_time64
+ mq_timedreceive_time64
+ rt_sigtimedwait_time64
+ futex_time64
+ sched_rr_get_interval_time64
+
+ Listed above syscalls have counterparts already providing 64 bit time support
+ on systems with __WORDSIZE == 64 or __SYSCALL_WORDSIZE == 64 since the oldest
+ supported by glibc Linux kernel (v3.2). */
+
+#include <bits/wordsize.h>
+#if (__WORDSIZE == 64 \
+ || (__WORDSIZE == 32 \
+ && (__LINUX_KERNEL_VERSION >= 0x050100 \
+ || (defined __SYSCALL_WORDSIZE && __SYSCALL_WORDSIZE == 64))))
+# define __ASSUME_TIME64_SYSCALLS 1
+#endif
--
2.11.0