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glibc/sysdeps/unix/sysv/linux/i386/pthread_cond_wait.S
Nick Alcock 7a25d6a84d 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.
2016-03-23 13:40:14 +01:00

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/* Copyright (C) 2002-2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include <shlib-compat.h>
#include <lowlevellock.h>
#include <lowlevelcond.h>
#include <tcb-offsets.h>
#include <pthread-errnos.h>
#include <pthread-pi-defines.h>
#include <kernel-features.h>
#include <stap-probe.h>
.text
/* int pthread_cond_wait (pthread_cond_t *cond, pthread_mutex_t *mutex) */
.globl __pthread_cond_wait
.type __pthread_cond_wait, @function
.align 16
__pthread_cond_wait:
.LSTARTCODE:
cfi_startproc
#ifdef SHARED
cfi_personality(DW_EH_PE_pcrel | DW_EH_PE_sdata4 | DW_EH_PE_indirect,
DW.ref.__gcc_personality_v0)
cfi_lsda(DW_EH_PE_pcrel | DW_EH_PE_sdata4, .LexceptSTART)
#else
cfi_personality(DW_EH_PE_udata4, __gcc_personality_v0)
cfi_lsda(DW_EH_PE_udata4, .LexceptSTART)
#endif
pushl %ebp
cfi_adjust_cfa_offset(4)
cfi_rel_offset(%ebp, 0)
pushl %edi
cfi_adjust_cfa_offset(4)
cfi_rel_offset(%edi, 0)
pushl %esi
cfi_adjust_cfa_offset(4)
cfi_rel_offset(%esi, 0)
pushl %ebx
cfi_adjust_cfa_offset(4)
cfi_rel_offset(%ebx, 0)
xorl %esi, %esi
movl 20(%esp), %ebx
LIBC_PROBE (cond_wait, 2, 24(%esp), %ebx)
/* Get internal lock. */
movl $1, %edx
xorl %eax, %eax
LOCK
#if cond_lock == 0
cmpxchgl %edx, (%ebx)
#else
cmpxchgl %edx, cond_lock(%ebx)
#endif
jnz 1f
/* Store the reference to the mutex. If there is already a
different value in there this is a bad user bug. */
2: cmpl $-1, dep_mutex(%ebx)
movl 24(%esp), %eax
je 15f
movl %eax, dep_mutex(%ebx)
/* Unlock the mutex. */
15: xorl %edx, %edx
call __pthread_mutex_unlock_usercnt
testl %eax, %eax
jne 12f
addl $1, total_seq(%ebx)
adcl $0, total_seq+4(%ebx)
addl $1, cond_futex(%ebx)
addl $(1 << nwaiters_shift), cond_nwaiters(%ebx)
#define FRAME_SIZE 20
subl $FRAME_SIZE, %esp
cfi_adjust_cfa_offset(FRAME_SIZE)
cfi_remember_state
/* Get and store current wakeup_seq value. */
movl wakeup_seq(%ebx), %edi
movl wakeup_seq+4(%ebx), %edx
movl broadcast_seq(%ebx), %eax
movl %edi, 4(%esp)
movl %edx, 8(%esp)
movl %eax, 12(%esp)
/* Reset the pi-requeued flag. */
8: movl $0, 16(%esp)
movl cond_futex(%ebx), %ebp
/* Unlock. */
LOCK
#if cond_lock == 0
subl $1, (%ebx)
#else
subl $1, cond_lock(%ebx)
#endif
jne 3f
.LcleanupSTART:
4: call __pthread_enable_asynccancel
movl %eax, (%esp)
xorl %ecx, %ecx
cmpl $-1, dep_mutex(%ebx)
sete %cl
je 18f
movl dep_mutex(%ebx), %edi
/* Requeue to a non-robust PI mutex if the PI bit is set and
the robust bit is not set. */
movl MUTEX_KIND(%edi), %eax
andl $(ROBUST_BIT|PI_BIT), %eax
cmpl $PI_BIT, %eax
jne 18f
movl $(FUTEX_WAIT_REQUEUE_PI|FUTEX_PRIVATE_FLAG), %ecx
movl %ebp, %edx
xorl %esi, %esi
addl $cond_futex, %ebx
.Ladd_cond_futex_pi:
movl $SYS_futex, %eax
ENTER_KERNEL
subl $cond_futex, %ebx
.Lsub_cond_futex_pi:
/* Set the pi-requeued flag only if the kernel has returned 0. The
kernel does not hold the mutex on error. */
cmpl $0, %eax
sete 16(%esp)
je 19f
/* When a futex syscall with FUTEX_WAIT_REQUEUE_PI returns
successfully, it has already locked the mutex for us and the
pi_flag (16(%esp)) is set to denote that fact. However, if another
thread changed the futex value before we entered the wait, the
syscall may return an EAGAIN and the mutex is not locked. We go
ahead with a success anyway since later we look at the pi_flag to
decide if we got the mutex or not. The sequence numbers then make
sure that only one of the threads actually wake up. We retry using
normal FUTEX_WAIT only if the kernel returned ENOSYS, since normal
and PI futexes don't mix.
Note that we don't check for EAGAIN specifically; we assume that the
only other error the futex function could return is EAGAIN since
anything else would mean an error in our function. It is too
expensive to do that check for every call (which is quite common in
case of a large number of threads), so it has been skipped. */
cmpl $-ENOSYS, %eax
jne 19f
xorl %ecx, %ecx
18: subl $1, %ecx
#ifdef __ASSUME_PRIVATE_FUTEX
andl $FUTEX_PRIVATE_FLAG, %ecx
#else
andl %gs:PRIVATE_FUTEX, %ecx
#endif
#if FUTEX_WAIT != 0
addl $FUTEX_WAIT, %ecx
#endif
movl %ebp, %edx
addl $cond_futex, %ebx
.Ladd_cond_futex:
movl $SYS_futex, %eax
ENTER_KERNEL
subl $cond_futex, %ebx
.Lsub_cond_futex:
19: movl (%esp), %eax
call __pthread_disable_asynccancel
.LcleanupEND:
/* Lock. */
movl $1, %edx
xorl %eax, %eax
LOCK
#if cond_lock == 0
cmpxchgl %edx, (%ebx)
#else
cmpxchgl %edx, cond_lock(%ebx)
#endif
jnz 5f
6: movl broadcast_seq(%ebx), %eax
cmpl 12(%esp), %eax
jne 16f
movl woken_seq(%ebx), %eax
movl woken_seq+4(%ebx), %ecx
movl wakeup_seq(%ebx), %edi
movl wakeup_seq+4(%ebx), %edx
cmpl 8(%esp), %edx
jne 7f
cmpl 4(%esp), %edi
je 22f
7: cmpl %ecx, %edx
jne 9f
cmp %eax, %edi
je 22f
9: addl $1, woken_seq(%ebx)
adcl $0, woken_seq+4(%ebx)
/* Unlock */
16: subl $(1 << nwaiters_shift), cond_nwaiters(%ebx)
/* Wake up a thread which wants to destroy the condvar object. */
movl total_seq(%ebx), %eax
andl total_seq+4(%ebx), %eax
cmpl $0xffffffff, %eax
jne 17f
movl cond_nwaiters(%ebx), %eax
andl $~((1 << nwaiters_shift) - 1), %eax
jne 17f
addl $cond_nwaiters, %ebx
movl $SYS_futex, %eax
#if FUTEX_PRIVATE_FLAG > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex-cond_nwaiters(%ebx)
sete %cl
subl $1, %ecx
#ifdef __ASSUME_PRIVATE_FUTEX
andl $FUTEX_PRIVATE_FLAG, %ecx
#else
andl %gs:PRIVATE_FUTEX, %ecx
#endif
addl $FUTEX_WAKE, %ecx
movl $1, %edx
ENTER_KERNEL
subl $cond_nwaiters, %ebx
17: LOCK
#if cond_lock == 0
subl $1, (%ebx)
#else
subl $1, cond_lock(%ebx)
#endif
jne 10f
/* With requeue_pi, the mutex lock is held in the kernel. */
11: movl 24+FRAME_SIZE(%esp), %eax
movl 16(%esp), %ecx
testl %ecx, %ecx
jnz 21f
call __pthread_mutex_cond_lock
20: addl $FRAME_SIZE, %esp
cfi_adjust_cfa_offset(-FRAME_SIZE);
14: popl %ebx
cfi_adjust_cfa_offset(-4)
cfi_restore(%ebx)
popl %esi
cfi_adjust_cfa_offset(-4)
cfi_restore(%esi)
popl %edi
cfi_adjust_cfa_offset(-4)
cfi_restore(%edi)
popl %ebp
cfi_adjust_cfa_offset(-4)
cfi_restore(%ebp)
/* We return the result of the mutex_lock operation. */
ret
cfi_restore_state
21: call __pthread_mutex_cond_lock_adjust
xorl %eax, %eax
jmp 20b
cfi_adjust_cfa_offset(-FRAME_SIZE);
/* We need to go back to futex_wait. If we're using requeue_pi, then
release the mutex we had acquired and go back. */
22: movl 16(%esp), %edx
test %edx, %edx
jz 8b
/* Adjust the mutex values first and then unlock it. The unlock
should always succeed or else the kernel did not lock the mutex
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
/* Initial locking failed. */
1:
#if cond_lock == 0
movl %ebx, %edx
#else
leal cond_lock(%ebx), %edx
#endif
#if (LLL_SHARED-LLL_PRIVATE) > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex(%ebx)
setne %cl
subl $1, %ecx
andl $(LLL_SHARED-LLL_PRIVATE), %ecx
#if LLL_PRIVATE != 0
addl $LLL_PRIVATE, %ecx
#endif
call __lll_lock_wait
jmp 2b
/* The initial unlocking of the mutex failed. */
12:
LOCK
#if cond_lock == 0
subl $1, (%ebx)
#else
subl $1, cond_lock(%ebx)
#endif
jne 14b
movl %eax, %esi
#if cond_lock == 0
movl %ebx, %eax
#else
leal cond_lock(%ebx), %eax
#endif
#if (LLL_SHARED-LLL_PRIVATE) > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex(%ebx)
setne %cl
subl $1, %ecx
andl $(LLL_SHARED-LLL_PRIVATE), %ecx
#if LLL_PRIVATE != 0
addl $LLL_PRIVATE, %ecx
#endif
call __lll_unlock_wake
movl %esi, %eax
jmp 14b
cfi_adjust_cfa_offset(FRAME_SIZE)
/* Unlock in loop requires wakeup. */
3:
#if cond_lock == 0
movl %ebx, %eax
#else
leal cond_lock(%ebx), %eax
#endif
#if (LLL_SHARED-LLL_PRIVATE) > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex(%ebx)
setne %cl
subl $1, %ecx
andl $(LLL_SHARED-LLL_PRIVATE), %ecx
#if LLL_PRIVATE != 0
addl $LLL_PRIVATE, %ecx
#endif
call __lll_unlock_wake
jmp 4b
/* Locking in loop failed. */
5:
#if cond_lock == 0
movl %ebx, %edx
#else
leal cond_lock(%ebx), %edx
#endif
#if (LLL_SHARED-LLL_PRIVATE) > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex(%ebx)
setne %cl
subl $1, %ecx
andl $(LLL_SHARED-LLL_PRIVATE), %ecx
#if LLL_PRIVATE != 0
addl $LLL_PRIVATE, %ecx
#endif
call __lll_lock_wait
jmp 6b
/* Unlock after loop requires wakeup. */
10:
#if cond_lock == 0
movl %ebx, %eax
#else
leal cond_lock(%ebx), %eax
#endif
#if (LLL_SHARED-LLL_PRIVATE) > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex(%ebx)
setne %cl
subl $1, %ecx
andl $(LLL_SHARED-LLL_PRIVATE), %ecx
#if LLL_PRIVATE != 0
addl $LLL_PRIVATE, %ecx
#endif
call __lll_unlock_wake
jmp 11b
.size __pthread_cond_wait, .-__pthread_cond_wait
versioned_symbol (libpthread, __pthread_cond_wait, pthread_cond_wait,
GLIBC_2_3_2)
.type __condvar_w_cleanup2, @function
__condvar_w_cleanup2:
subl $cond_futex, %ebx
.size __condvar_w_cleanup2, .-__condvar_w_cleanup2
.LSbl4:
.type __condvar_w_cleanup, @function
__condvar_w_cleanup:
movl %eax, %esi
/* Get internal lock. */
movl $1, %edx
xorl %eax, %eax
LOCK
#if cond_lock == 0
cmpxchgl %edx, (%ebx)
#else
cmpxchgl %edx, cond_lock(%ebx)
#endif
jz 1f
#if cond_lock == 0
movl %ebx, %edx
#else
leal cond_lock(%ebx), %edx
#endif
#if (LLL_SHARED-LLL_PRIVATE) > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex(%ebx)
setne %cl
subl $1, %ecx
andl $(LLL_SHARED-LLL_PRIVATE), %ecx
#if LLL_PRIVATE != 0
addl $LLL_PRIVATE, %ecx
#endif
call __lll_lock_wait
1: movl broadcast_seq(%ebx), %eax
cmpl 12(%esp), %eax
jne 3f
/* We increment the wakeup_seq counter only if it is lower than
total_seq. If this is not the case the thread was woken and
then canceled. In this case we ignore the signal. */
movl total_seq(%ebx), %eax
movl total_seq+4(%ebx), %edi
cmpl wakeup_seq+4(%ebx), %edi
jb 6f
ja 7f
cmpl wakeup_seq(%ebx), %eax
jbe 7f
6: addl $1, wakeup_seq(%ebx)
adcl $0, wakeup_seq+4(%ebx)
addl $1, cond_futex(%ebx)
7: addl $1, woken_seq(%ebx)
adcl $0, woken_seq+4(%ebx)
3: subl $(1 << nwaiters_shift), cond_nwaiters(%ebx)
/* Wake up a thread which wants to destroy the condvar object. */
xorl %edi, %edi
movl total_seq(%ebx), %eax
andl total_seq+4(%ebx), %eax
cmpl $0xffffffff, %eax
jne 4f
movl cond_nwaiters(%ebx), %eax
andl $~((1 << nwaiters_shift) - 1), %eax
jne 4f
addl $cond_nwaiters, %ebx
movl $SYS_futex, %eax
#if FUTEX_PRIVATE_FLAG > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex-cond_nwaiters(%ebx)
sete %cl
subl $1, %ecx
#ifdef __ASSUME_PRIVATE_FUTEX
andl $FUTEX_PRIVATE_FLAG, %ecx
#else
andl %gs:PRIVATE_FUTEX, %ecx
#endif
addl $FUTEX_WAKE, %ecx
movl $1, %edx
ENTER_KERNEL
subl $cond_nwaiters, %ebx
movl $1, %edi
4: LOCK
#if cond_lock == 0
subl $1, (%ebx)
#else
subl $1, cond_lock(%ebx)
#endif
je 2f
#if cond_lock == 0
movl %ebx, %eax
#else
leal cond_lock(%ebx), %eax
#endif
#if (LLL_SHARED-LLL_PRIVATE) > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex(%ebx)
setne %cl
subl $1, %ecx
andl $(LLL_SHARED-LLL_PRIVATE), %ecx
#if LLL_PRIVATE != 0
addl $LLL_PRIVATE, %ecx
#endif
call __lll_unlock_wake
/* Wake up all waiters to make sure no signal gets lost. */
2: testl %edi, %edi
jnz 5f
addl $cond_futex, %ebx
#if FUTEX_PRIVATE_FLAG > 255
xorl %ecx, %ecx
#endif
cmpl $-1, dep_mutex-cond_futex(%ebx)
sete %cl
subl $1, %ecx
#ifdef __ASSUME_PRIVATE_FUTEX
andl $FUTEX_PRIVATE_FLAG, %ecx
#else
andl %gs:PRIVATE_FUTEX, %ecx
#endif
addl $FUTEX_WAKE, %ecx
movl $SYS_futex, %eax
movl $0x7fffffff, %edx
ENTER_KERNEL
/* Lock the mutex only if we don't own it already. This only happens
in case of PI mutexes, if we got cancelled after a successful
return of the futex syscall and before disabling async
cancellation. */
5: movl 24+FRAME_SIZE(%esp), %eax
movl MUTEX_KIND(%eax), %ebx
andl $(ROBUST_BIT|PI_BIT), %ebx
cmpl $PI_BIT, %ebx
jne 8f
movl (%eax), %ebx
andl $TID_MASK, %ebx
cmpl %ebx, %gs:TID
jne 8f
/* We managed to get the lock. Fix it up before returning. */
call __pthread_mutex_cond_lock_adjust
jmp 9f
8: call __pthread_mutex_cond_lock
9: movl %esi, (%esp)
.LcallUR:
call _Unwind_Resume
hlt
.LENDCODE:
cfi_endproc
.size __condvar_w_cleanup, .-__condvar_w_cleanup
.section .gcc_except_table,"a",@progbits
.LexceptSTART:
.byte DW_EH_PE_omit # @LPStart format (omit)
.byte DW_EH_PE_omit # @TType format (omit)
.byte DW_EH_PE_sdata4 # call-site format
# DW_EH_PE_sdata4
.uleb128 .Lcstend-.Lcstbegin
.Lcstbegin:
.long .LcleanupSTART-.LSTARTCODE
.long .Ladd_cond_futex_pi-.LcleanupSTART
.long __condvar_w_cleanup-.LSTARTCODE
.uleb128 0
.long .Ladd_cond_futex_pi-.LSTARTCODE
.long .Lsub_cond_futex_pi-.Ladd_cond_futex_pi
.long __condvar_w_cleanup2-.LSTARTCODE
.uleb128 0
.long .Lsub_cond_futex_pi-.LSTARTCODE
.long .Ladd_cond_futex-.Lsub_cond_futex_pi
.long __condvar_w_cleanup-.LSTARTCODE
.uleb128 0
.long .Ladd_cond_futex-.LSTARTCODE
.long .Lsub_cond_futex-.Ladd_cond_futex
.long __condvar_w_cleanup2-.LSTARTCODE
.uleb128 0
.long .Lsub_cond_futex-.LSTARTCODE
.long .LcleanupEND-.Lsub_cond_futex
.long __condvar_w_cleanup-.LSTARTCODE
.uleb128 0
.long .LcallUR-.LSTARTCODE
.long .LENDCODE-.LcallUR
.long 0
.uleb128 0
.Lcstend:
#ifdef SHARED
.hidden DW.ref.__gcc_personality_v0
.weak DW.ref.__gcc_personality_v0
.section .gnu.linkonce.d.DW.ref.__gcc_personality_v0,"aw",@progbits
.align 4
.type DW.ref.__gcc_personality_v0, @object
.size DW.ref.__gcc_personality_v0, 4
DW.ref.__gcc_personality_v0:
.long __gcc_personality_v0
#endif
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