Spinlock assembly clarification

From: Frank Coldwell
Date: Mon Jul 18 2011 - 01:33:02 EST

dear friends,

I was looking at spinlock implementation in x86 architecture folder
and this is code i found there:
static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
short inc = 0x0100;

asm volatile (
LOCK_PREFIX "xaddw %w0, %1\n"
"cmpb %h0, %b0\n\t"
"je 2f\n\t"
"rep ; nop\n\t"
"movb %1, %b0\n\t"
/* don't need lfence here, because loads are in-order */
"jmp 1b\n"
: "+Q" (inc), "+m" (lock->slock)
: "memory", "cc");

So to understand this I look at intel manual for these instructions,
and I could not find anything
for instruction xaddw ??

So can anyone can help me understand what this assembly code is doing
and also where are these
assembly instructions converted to real assembly instructions (in gcc maybe) ??

Thanks in advance,
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/