bzr commit into mysql-5.5-bugfixing branch (davi:3207) Bug#52419

[Davi Arnaut]

# At a local mysql-5.5-bugfixing repository of davi

 3207 Davi Arnaut	2010-09-17
      Bug#52419: Test "binlog_stm_mix_innodb_myisam" fails, complains about non-transactional
      
      The problem was that the x86 ASM atomic compare and swap
      could copy the wrong value to the ebx register, where the
      cmpxchg8b expects to see part of the "comparand" value.
      Since the original value in the ebx register is saved in
      the stack (that is, the push instruction causes the stack
      pointer to change), a wrong offset could be used if the
      compiler decides to put the source of the comparand value
      in the stack.
      
      The solution is to copy the comparand value directly from
      memory. Since the comparand value is 64-bits wide, it is
      copied in two steps over to the ebx and ecx registers.

    modified:
      include/atomic/x86-gcc.h
=== modified file 'include/atomic/x86-gcc.h'
--- a/include/atomic/x86-gcc.h	2010-07-23 12:37:10 +0000
+++ b/include/atomic/x86-gcc.h	2010-09-17 16:54:44 +0000
@@ -121,11 +121,13 @@
   fine.
 */
 #define make_atomic_cas_body64                                    \
-  int32 ebx=(set & 0xFFFFFFFF), ecx=(set >> 32);                  \
-  asm volatile ("push %%ebx; movl %3, %%ebx;"                     \
-                LOCK_prefix "; cmpxchg8b %0; setz %2; pop %%ebx"  \
-                : "=m" (*a), "+A" (*cmp), "=c" (ret)               \
-                : "m" (ebx), "c" (ecx), "m" (*a)                  \
+  asm volatile ("push %%ebx;"                                     \
+                "movl (%%ecx), %%ebx;"                            \
+                "movl 4(%%ecx), %%ecx;"                           \
+                LOCK_prefix "; cmpxchg8b %0;"                     \
+                "setz %2; pop %%ebx"                              \
+                : "=m" (*a), "+A" (*cmp), "=c" (ret)              \
+                : "c" (&set), "m" (*a)                            \
                 : "memory", "esp")
 #endif
 


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