x86, pthread_cond_*wait: Do not depend on %eax not being clobbered

The x86-specific versions of both pthread_cond_wait and
pthread_cond_timedwait have (in their fall-back-to-futex-wait slow
paths) calls to __pthread_mutex_cond_lock_adjust followed by
__pthread_mutex_unlock_usercnt, which load the parameters before the
first call but then assume that the first parameter, in %eax, will
survive unaffected.  This happens to have been true before now, but %eax
is a call-clobbered register, and this assumption is not safe: it could
change at any time, at GCC's whim, and indeed the stack-protector canary
checking code clobbers %eax while checking that the canary is
uncorrupted.

So reload %eax before calling __pthread_mutex_unlock_usercnt.  (Do this
unconditionally, even when stack-protection is not in use, because it's
the right thing to do, it's a slow path, and anything else is dicing
with death.)

	* sysdeps/unix/sysv/linux/i386/pthread_cond_timedwait.S: Reload
	call-clobbered %eax on retry path.
	* sysdeps/unix/sysv/linux/i386/pthread_cond_wait.S: Likewise.

diff --git a/ChangeLog b/ChangeLog
index 54454a5..b7574b0 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2016-03-23  Nick Alcock  <nick.alcock@oracle.com>
+
+       * sysdeps/unix/sysv/linux/i386/pthread_cond_timedwait.S: Reload
+        call-clobbered %eax on retry path.
+        * sysdeps/unix/sysv/linux/i386/pthread_cond_wait.S: Likewise.
+
 2016-03-22  H.J. Lu  <hongjiu.lu@intel.com>
 
        * sysdeps/x86_64/multiarch/memcpy-avx-unaligned.S (MEMCPY):

diff --git a/sysdeps/unix/sysv/linux/i386/pthread_cond_timedwait.S b/sysdeps/unix/sysv/linux/i386/pthread_cond_timedwait.S
index 96f8a8d..6256376 100644 (file)
--- a/sysdeps/unix/sysv/linux/i386/pthread_cond_timedwait.S
+++ b/sysdeps/unix/sysv/linux/i386/pthread_cond_timedwait.S
@@ -297,6 +297,7 @@ __pthread_cond_timedwait:
           correctly.  */
        movl    dep_mutex(%ebx), %eax
        call    __pthread_mutex_cond_lock_adjust
+       movl    dep_mutex(%ebx), %eax
        xorl    %edx, %edx
        call    __pthread_mutex_unlock_usercnt
        jmp     8b

diff --git a/sysdeps/unix/sysv/linux/i386/pthread_cond_wait.S b/sysdeps/unix/sysv/linux/i386/pthread_cond_wait.S
index 94302b0..5016718 100644 (file)
--- a/sysdeps/unix/sysv/linux/i386/pthread_cond_wait.S
+++ b/sysdeps/unix/sysv/linux/i386/pthread_cond_wait.S
@@ -309,6 +309,7 @@ __pthread_cond_wait:
           correctly.  */
        movl    dep_mutex(%ebx), %eax
        call    __pthread_mutex_cond_lock_adjust
+       movl    dep_mutex(%ebx), %eax
        xorl    %edx, %edx
        call    __pthread_mutex_unlock_usercnt
        jmp     8b