From patchwork Tue Feb  1 20:15:23 2011
Content-Type: text/plain; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Subject: libgo patch committed: Add __sync_bool_compare_and_swap_4
Date: Tue, 01 Feb 2011 10:15:23 -0000
From: Ian Taylor <iant@google.com>
X-Patchwork-Id: 81370
Message-Id: <mcrd3nbldes.fsf@google.com>
To: gcc-patches@gcc.gnu.org, gofrontend-dev@googlegroups.com

The libgo library uses __sync_bool_compare_and_swap_4 (i.e., uses
__sync_bool_compare_and_swap on uint32 types).  That function is not
available for all gcc targets.  This patch adds the function to the
library for those cases.  Ideally this would be handled by libgcc, but
that does not currently happen.  This function should be harmless if
libgcc does get an implementation.

This implementation is rather slow but it is better than having the
build fail.

Bootstrapped and ran Go testsuite on x86_64-unknown-linux-gnu.
Committed to mainline.

Ian


diff -r 948edbf8367c libgo/runtime/thread.c
--- a/libgo/runtime/thread.c	Mon Jan 31 15:32:52 2011 -0800
+++ b/libgo/runtime/thread.c	Tue Feb 01 12:11:10 2011 -0800
@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 #include "runtime.h"
+#include "go-assert.h"
 
 void
 runtime_initlock(Lock *l)
@@ -75,3 +76,38 @@
 {
 	sem_destroy(&l->sem);
 }
+
+#ifndef __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
+
+// For targets which don't have the required sync support.  Really
+// this should be provided by gcc itself.  FIXME.
+
+static pthread_mutex_t sync_lock = PTHREAD_MUTEX_INITIALIZER;
+
+_Bool
+__sync_bool_compare_and_swap_4(uint32*, uint32, uint32)
+  __attribute__((visibility("hidden")));
+
+_Bool
+__sync_bool_compare_and_swap_4(uint32* ptr, uint32 old, uint32 new)
+{
+  int i;
+  _Bool ret;
+
+  i = pthread_mutex_lock(&sync_lock);
+  __go_assert(i == 0);
+
+  if(*ptr != old) {
+    ret = 0;
+  } else {
+    *ptr = new;
+    ret = 1;
+  }
+
+  i = pthread_mutex_unlock(&sync_lock);
+  __go_assert(i == 0);
+
+  return ret;
+}
+
+#endif