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Linux: Use 32-bit vDSO for clock_gettime, gettimeofday, time (BZ# 28071)

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The previous approach defeats the vDSO optimization on older kernels
because a failing clock_gettime64 system call is performed on every
function call.  It also results in a clobbered errno value, exposing
an OpenJDK bug (JDK-8270244).

This patch fixes by open-code INLINE_VSYSCALL macro and replace all
INLINE_SYSCALL_CALL with INTERNAL_SYSCALL_CALLS.  Now for
__clock_gettime64x, the 64-bit vDSO is used and the 32-bit vDSO is
tried before falling back to 64-bit syscalls.

The previous code preferred 64-bit syscall for the case where the kernel
provides 64-bit time_t syscalls *and* also a 32-bit vDSO (in this case
the *64-bit* syscall should be preferable over the vDSO).  All
architectures that provides 32-bit vDSO (i386, mips, powerpc, s390)
modulo sparc; but I am not sure if some kernels versions do provide
only 32-bit vDSO while still providing 64-bit time_t syscall.
Regardless, for such cases the 64-bit time_t syscall is used if the
vDSO returns overflowed 32-bit time_t.

Tested on i686-linux-gnu (with a time64 and non-time64 kernel),
x86_64-linux-gnu.  Built with build-many-glibcs.py.

Co-authored-by: Florian Weimer <fweimer@redhat.com>
This commit is contained in:
Adhemerval Zanella
2021-07-10 17:03:49 -03:00
parent aaacde11f2
commit 72e84d1db2
5 changed files with 175 additions and 12 deletions
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51
sysdeps/unix/sysv/linux/clock_gettime.c
View File

@ -35,27 +35,54 @@ __clock_gettime64 (clockid_t clock_id, struct __timespec64 *tp)
#endif
#ifdef HAVE_CLOCK_GETTIME64_VSYSCALL
r = INLINE_VSYSCALL (clock_gettime64, 2, clock_id, tp);
#else
r = INLINE_SYSCALL_CALL (clock_gettime64, clock_id, tp);
int (*vdso_time64) (clockid_t clock_id, struct __timespec64 *tp)
= GLRO(dl_vdso_clock_gettime64);
if (vdso_time64 != NULL)
{
r = INTERNAL_VSYSCALL_CALL (vdso_time64, 2, clock_id, tp);
if (r == 0)
return 0;
return INLINE_SYSCALL_ERROR_RETURN_VALUE (-r);
}
#endif
if (r == 0 || errno != ENOSYS)
return r;
#ifdef HAVE_CLOCK_GETTIME_VSYSCALL
int (*vdso_time) (clockid_t clock_id, struct timespec *tp)
= GLRO(dl_vdso_clock_gettime);
if (vdso_time != NULL)
{
struct timespec tp32;
r = INTERNAL_VSYSCALL_CALL (vdso_time, 2, clock_id, &tp32);
if (r == 0 && tp32.tv_sec > 0)
{
*tp = valid_timespec_to_timespec64 (tp32);
return 0;
}
else if (r != 0)
return INLINE_SYSCALL_ERROR_RETURN_VALUE (-r);
/* Fallback to syscall if the 32-bit time_t vDSO returns overflows. */
}
#endif
r = INTERNAL_SYSCALL_CALL (clock_gettime64, clock_id, tp);
if (r == 0)
return 0;
if (r != -ENOSYS)
return INLINE_SYSCALL_ERROR_RETURN_VALUE (-r);
#ifndef __ASSUME_TIME64_SYSCALLS
/* Fallback code that uses 32-bit support. */
struct timespec tp32;
# ifdef HAVE_CLOCK_GETTIME_VSYSCALL
r = INLINE_VSYSCALL (clock_gettime, 2, clock_id, &tp32);
# else
r = INLINE_SYSCALL_CALL (clock_gettime, clock_id, &tp32);
# endif
r = INTERNAL_SYSCALL_CALL (clock_gettime, clock_id, &tp32);
if (r == 0)
*tp = valid_timespec_to_timespec64 (tp32);
{
*tp = valid_timespec_to_timespec64 (tp32);
return 0;
}
#endif
return r;
return INLINE_SYSCALL_ERROR_RETURN_VALUE (-r);
}
#if __TIMESIZE != 64