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clock_gettime: add time64 syscall support, decouple 32-bit time_t

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the time64 syscall has to be used if time_t is 64-bit, since there's
no way of knowing before making a syscall whether the result will fit
in 32 bits, and the 32-bit syscalls do not report overflow as an
error.

on 64-bit archs, there is no change to the code after preprocessing.
on current 32-bit archs, the result is now read from the kernel
through long[2] array, then copied into the timespec, to remove the
assumption that time_t is the same as long.

vdso clock_gettime is still used in place of a syscall if available.
32-bit archs with 64-bit time_t must use the time64 version of the
vdso function; if it's not available, performance will significantly
suffer. support for both vdso functions could be added, but would
break the ability to move a long-lived process from a pre-time64
kernel to one that can outlast Y2038 with checkpoint/resume, at least
without added hacks to identify that the 32-bit function is no longer
usable and stop using it (e.g. by seeing negative tv_sec). this
possibility may be explored in future work on the function.
This commit is contained in:
Rich Felker 2019-07-31 00:26:16 -04:00
parent 2b4fd6f75b
commit 72f50245d0
1 changed files with 19 additions and 0 deletions
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19
src/time/clock_gettime.c
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@ -40,6 +40,24 @@ int __clock_gettime(clockid_t clk, struct timespec *ts)
}
#endif
#ifdef SYS_clock_gettime64
if (sizeof(time_t) > 4)
r = __syscall(SYS_clock_gettime64, clk, ts);
if (SYS_clock_gettime == SYS_clock_gettime64 || r!=-ENOSYS)
return __syscall_ret(r);
long ts32[2];
r = __syscall(SYS_clock_gettime, clk, ts32);
if (r==-ENOSYS && clk==CLOCK_REALTIME) {
r = __syscall(SYS_gettimeofday, ts32, 0);
ts32[1] *= 1000;
}
if (!r) {
ts->tv_sec = ts32[0];
ts->tv_nsec = ts32[1];
return r;
}
return __syscall_ret(r);
#else
r = __syscall(SYS_clock_gettime, clk, ts);
if (r == -ENOSYS) {
if (clk == CLOCK_REALTIME) {
@ -50,6 +68,7 @@ int __clock_gettime(clockid_t clk, struct timespec *ts)
r = -EINVAL;
}
return __syscall_ret(r);
#endif
}
weak_alias(__clock_gettime, clock_gettime);