Help wanted with converting 1 line asm i386->x86_64

[Hans de Goede <j w r degoede hhs nl>]

Hi,

The code in question is:
#elif defined(__GNUC__) && defined(__i386__)
/*
 * This is the __linux__ code.
 */
#define P6FENCE \
   asm("xchg %%eax, %0" : : "m" (_GlideRoot.p6Fencer) : "eax");
#else
#  error "P6 Fencing code needs to be added for this compiler"
#endif

Now the questions are:
-what symbol gets defined instead of __i386__ for x86_64
-is the asm code correct for x86_64

Regards,

Hans