[PATCH v3 1/2] vdso: clock_gettime: call normal syscall in case of an error

[Hauke Mehrtens <hauke@hauke-m.de>]

When the vdso call returns an error just call the normal syscall and
return its result. clock_gettime() only fails with EFAULT if tp points
to an inaccessible address space or with EINVAL if the clk_id is
unknown. EFAULT is an implementation problem and performance for this
case is not important. When it returns EINVAL a normal syscall could
still work, so try it.

This fixes a bug when an error occurred errno was not set and it was a
value different than -1 returned.
In addition on MIPS the Linux kernel 4.4 only supports some clk_ids and
assumes the libc will call the original function if it gets a -ENOSYS,
so do this for all error codes.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
---
 src/time/clock_gettime.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/time/clock_gettime.c b/src/time/clock_gettime.c
index 1572de0..9d3ff7e 100644
--- a/src/time/clock_gettime.c
+++ b/src/time/clock_gettime.c
@@ -26,16 +26,18 @@ void *__vdsosym(const char *, const char *);
 int __clock_gettime(clockid_t clk, struct timespec *ts)
 {
 #ifdef VDSO_CGT_SYM
+	int r;
 	static int (*volatile cgt)(clockid_t, struct timespec *);
 	if (!cgt) {
 		void *f = __vdsosym(VDSO_CGT_VER, VDSO_CGT_SYM);
 		if (!f) f = (void *)sc_clock_gettime;
 		a_cas_p(&cgt, 0, f);
 	}
-	return cgt(clk, ts);
-#else
-	return sc_clock_gettime(clk, ts);
+	r = cgt(clk, ts);
+	/* In case an error occurred try the normal syscall */
+	if (!r) return r;
 #endif
+	return sc_clock_gettime(clk, ts);
 }
 
 weak_alias(__clock_gettime, clock_gettime);
-- 
2.7.0.rc3