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

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>

1 files changed, 39 insertions, 12 deletions

diff --git a/sysdeps/unix/sysv/linux/clock_gettime.c b/sysdeps/unix/sysv/linux/clock_gettime.c
index cfe9370455..91df6b3d96 100644
--- a/sysdeps/unix/sysv/linux/clock_gettime.c
+++ b/sysdeps/unix/sysv/linux/clock_gettime.c
@@ -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