[glibc/google/grte/v5-2.27/master] Add workaround for infinite looping in ppc vsyscalls

[glibc/google/grte/v5-2.27/master] Add workaround for infinite looping in ppc vsyscalls

[Fangrui Song]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b2d69ea7ac4b918e5325bf477bf06a3ad6685f4d

commit b2d69ea7ac4b918e5325bf477bf06a3ad6685f4d
Author: Stan Shebs <stanshebs@google.com>
Date:   Tue Sep 25 10:52:37 2018 -0700

    Add workaround for infinite looping in ppc vsyscalls

Diff:
---
 sysdeps/posix/clock_getres.c | 17 +++++++++++++++++
 sysdeps/unix/clock_gettime.c | 17 +++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/sysdeps/posix/clock_getres.c b/sysdeps/posix/clock_getres.c
index 8bc7e813e6..3f6fdcf9aa 100644
--- a/sysdeps/posix/clock_getres.c
+++ b/sysdeps/posix/clock_getres.c
@@ -73,6 +73,19 @@ realtime_getres (struct timespec *res)
   return -1;
 }
 
+#if defined __clang__ && defined __powerpc64__
+/* On ppc, __clock_getres's body eventually expands into asm code
+   that does a bctrl, but clang does not recognize the need to save
+   the link register, so calls loop infinitely instead of returning.
+   As workaround, make a dummy function call that forces a link
+   register save.  */
+volatile int clock_getres_dummy_glob;
+
+void __attribute__((noinline)) clock_getres_dummy ()
+{
+  clock_getres_dummy_glob = 45;
+}
+#endif
 
 /* Get resolution of clock.  */
 int
@@ -80,6 +93,10 @@ __clock_getres (clockid_t clock_id, struct timespec *res)
 {
   int retval = -1;
 
+#if defined __clang__ && defined __powerpc64__
+  clock_getres_dummy ();
+#endif
+
   switch (clock_id)
     {
 #ifdef SYSDEP_GETRES
diff --git a/sysdeps/unix/clock_gettime.c b/sysdeps/unix/clock_gettime.c
index 96df78ab1e..7ef43307b5 100644
--- a/sysdeps/unix/clock_gettime.c
+++ b/sysdeps/unix/clock_gettime.c
@@ -86,6 +86,19 @@ realtime_gettime (struct timespec *tp)
   return retval;
 }
 
+#if defined __clang__ && defined __powerpc64__
+/* On ppc, __clock_gettime's body eventually expands into asm code
+   that does a bctrl, but clang does not recognize the need to save
+   the link register, so calls loop infinitely instead of returning.
+   As workaround, make a dummy function call that forces a link
+   register save.  */
+volatile int clock_gettime_dummy_glob;
+
+void __attribute__((noinline)) clock_gettime_dummy ()
+{
+  clock_gettime_dummy_glob = 45;
+}
+#endif
 
 /* Get current value of CLOCK and store it in TP.  */
 int
@@ -93,6 +106,10 @@ __clock_gettime (clockid_t clock_id, struct timespec *tp)
 {
   int retval = -1;
 
+#if defined __clang__ && defined __powerpc64__
+  clock_gettime_dummy ();
+#endif
+
   switch (clock_id)
     {
 #ifdef SYSDEP_GETTIME