2008-02-11 Hans Boehm <Hans.Boehm@hp.com>gc7_1

	   (Really Ian Wienand & Debian maintainers)
	* src/atomic_ops/sysdeps/gcc/x86.h
	(AO_compare_double_and_swap_double_full): Correctly account for
	ebx usage with PIC.

2 files changed, 26 insertions, 7 deletions

diff --git a/ChangeLog b/ChangeLog
index 46039a5..e68ab4c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2008-02-11 Hans Boehm <Hans.Boehm@hp.com>
+	   (Really Ian Wienand & Debian maintainers)
+	* src/atomic_ops/sysdeps/gcc/x86.h
+	(AO_compare_double_and_swap_double_full): Correctly account for
+	ebx usage with PIC.
+
 2008-01-09 Hans Boehm <Hans.Boehm@hp.com>
 	* src/atomic_ops/sysdeps/standard_ao_double_t.h: Let
 	double_ptr_storage default to long long; define everywhere.
diff --git a/src/atomic_ops/sysdeps/gcc/x86.h b/src/atomic_ops/sysdeps/gcc/x86.h
index 0b344a7..96fd2cb 100644
--- a/src/atomic_ops/sysdeps/gcc/x86.h
+++ b/src/atomic_ops/sysdeps/gcc/x86.h
@@ -141,14 +141,27 @@ AO_compare_double_and_swap_double_full(volatile AO_double_t *addr,
 			               AO_t new_val1, AO_t new_val2) 
 {
   char result;
-  register AO_t nv1 asm("%ebx") = new_val1;
-  	/* The above hack seems to avoid a gcc error complaining	*/
-  	/* that ebx is unavailable.					*/
-
-  __asm__ __volatile__("lock; cmpxchg8b %0; setz %1"
+  #if __PIC__
+  /* If PIC is turned on, we can't use %ebx as it is reserved for the
+     GOT poiner.  We can save and restore %ebx because GCC won't be
+     using it for anything else (such as any of the m operands) */
+  __asm__ __volatile__("pushl %%ebx;"   /* save ebx used for PIC GOT ptr */
+		       "movl %6,%%ebx;" /* move new_val2 to %ebx */
+		       "lock; cmpxchg8b %0; setz %1;"
+		       "pop %%ebx;"     /* restore %ebx */
+ 	    	       : "=m"(*addr), "=q"(result)
+		       : "m"(*addr), "d" (old_val2), "a" (old_val1),
+		         "c" (new_val2), "m" (new_val1) : "memory");
+  #else
+  /* We can't just do the same thing in non-PIC mode, because GCC
+   * might be using %ebx as the memory operand.  We could have ifdef'd
+   * in a clobber, but there's no point doing the push/pop if we don't
+   * have to. */
+  __asm__ __volatile__("lock; cmpxchg8b %0; setz %1;"
 	    	       : "=m"(*addr), "=q"(result)
-		       : "m"(*addr), "a" (old_val1), "d" (old_val2),
-		         "b" (nv1), "c" (new_val2) : "memory");
+		       : "m"(*addr), "d" (old_val2), "a" (old_val1),
+		         "c" (new_val2), "b" (new_val1) : "memory");
+  #endif
   return (int) result;
 }