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authorWaldemar Brodkorb <wbx@openadk.org>2016-05-31 20:51:29 +0200
committerWaldemar Brodkorb <wbx@openadk.org>2016-05-31 20:51:29 +0200
commit3ac3d4e61a1de0c2d0e0d2bebf0d1b111f153f12 (patch)
tree1f4937d22617218f5ebd2a0e26441fcd3a44db49 /libpthread
parent95174cb69c523a1544e5f6f20e47f7d60007e569 (diff)
arm: add non-assembly versions of pthread_spin_lock/pthread_spin_trylock
Sync pthread_spin_lock/pthread_spin_trylock with GNU libc as it avoids any usage of deprecated SWP instruction. This allows to build uClibc-ng for ARMv8 Cortex-A53 CPU in 32 Bit mode.
Diffstat (limited to 'libpthread')
-rw-r--r--libpthread/nptl/sysdeps/arm/pthread_spin_lock.c66
-rw-r--r--libpthread/nptl/sysdeps/arm/pthread_spin_trylock.S33
-rw-r--r--libpthread/nptl/sysdeps/arm/pthread_spin_trylock.c (renamed from libpthread/nptl/sysdeps/arm/pthread_spin_lock.S)23
3 files changed, 76 insertions, 46 deletions
diff --git a/libpthread/nptl/sysdeps/arm/pthread_spin_lock.c b/libpthread/nptl/sysdeps/arm/pthread_spin_lock.c
new file mode 100644
index 000000000..77f5f502e
--- /dev/null
+++ b/libpthread/nptl/sysdeps/arm/pthread_spin_lock.c
@@ -0,0 +1,66 @@
+/* pthread_spin_lock -- lock a spin lock. Generic version.
+ Copyright (C) 2012-2016 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ 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 <atomic.h>
+#include "pthreadP.h"
+
+/* A machine-specific version can define SPIN_LOCK_READS_BETWEEN_CMPXCHG
+ to the number of plain reads that it's optimal to spin on between uses
+ of atomic_compare_and_exchange_val_acq. If spinning forever is optimal
+ then use -1. If no plain reads here would ever be optimal, use 0. */
+#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
+
+int
+pthread_spin_lock (pthread_spinlock_t *lock)
+{
+ /* atomic_exchange usually takes less instructions than
+ atomic_compare_and_exchange. On the other hand,
+ atomic_compare_and_exchange potentially generates less bus traffic
+ when the lock is locked.
+ We assume that the first try mostly will be successful, and we use
+ atomic_exchange. For the subsequent tries we use
+ atomic_compare_and_exchange. */
+ if (atomic_exchange_acq (lock, 1) == 0)
+ return 0;
+
+ do
+ {
+ /* The lock is contended and we need to wait. Going straight back
+ to cmpxchg is not a good idea on many targets as that will force
+ expensive memory synchronizations among processors and penalize other
+ running threads.
+ On the other hand, we do want to update memory state on the local core
+ once in a while to avoid spinning indefinitely until some event that
+ will happen to update local memory as a side-effect. */
+ if (SPIN_LOCK_READS_BETWEEN_CMPXCHG >= 0)
+ {
+ int wait = SPIN_LOCK_READS_BETWEEN_CMPXCHG;
+
+ while (*lock != 0 && wait > 0)
+ --wait;
+ }
+ else
+ {
+ while (*lock != 0)
+ ;
+ }
+ }
+ while (atomic_compare_and_exchange_val_acq (lock, 1, 0) != 0);
+
+ return 0;
+}
diff --git a/libpthread/nptl/sysdeps/arm/pthread_spin_trylock.S b/libpthread/nptl/sysdeps/arm/pthread_spin_trylock.S
deleted file mode 100644
index 8ccaffd75..000000000
--- a/libpthread/nptl/sysdeps/arm/pthread_spin_trylock.S
+++ /dev/null
@@ -1,33 +0,0 @@
-/* Copyright (C) 2005 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- 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/>. */
-
-#define _ERRNO_H 1
-#include <bits/errno.h>
-
-#include <sysdep.h>
-
- .text
- .align 4
-
-ENTRY (pthread_spin_trylock)
- mov r1, #1
- swp r2, r1, [r0]
- teq r2, #0
- moveq r0, #0
- movne r0, #EBUSY
- PSEUDO_RET_NOERRNO
-END (pthread_spin_trylock)
diff --git a/libpthread/nptl/sysdeps/arm/pthread_spin_lock.S b/libpthread/nptl/sysdeps/arm/pthread_spin_trylock.c
index a9c07c87d..4e1a96c03 100644
--- a/libpthread/nptl/sysdeps/arm/pthread_spin_lock.S
+++ b/libpthread/nptl/sysdeps/arm/pthread_spin_trylock.c
@@ -1,4 +1,5 @@
-/* Copyright (C) 2005 Free Software Foundation, Inc.
+/* pthread_spin_trylock -- trylock a spin lock. Generic version.
+ Copyright (C) 2012-2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
@@ -15,16 +16,12 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
-#include <sysdep.h>
+#include <errno.h>
+#include <atomic.h>
+#include "pthreadP.h"
- .text
- .align 4
-
-ENTRY (pthread_spin_lock)
- mov r1, #1
-1: swp r2, r1, [r0]
- teq r2, #0
- bne 1b
- mov r0, #0
- PSEUDO_RET_NOERRNO
-END (pthread_spin_lock)
+int
+pthread_spin_trylock (pthread_spinlock_t *lock)
+{
+ return atomic_exchange_acq (lock, 1) ? EBUSY : 0;
+}