c - What's the meaning of the following code? -

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there cas code below can handle int type,i know function of cas don't know details shown below.

inline int cas(unsigned long *mem,unsigned long newval,unsigned long oldval) {     __typeof (*mem) ret;     __asm __volatile ("lock; cmpxchgl %2, %1"     : "=a" (ret), "=m" (*mem)     : "r" (newval), "m" (*mem), "0" (oldval));     return (int) ret; }

i know there should 5 parameters mapped %0,%1,%2,%3,%4 because there 5 parameters in input/output field

i know "=a" means using eax register,"=m" means using memory address,"r" means using register

but don't understand "0" means.

i don't understand why "cmpxchgl" use 2 parameters %2, %1 instead of three?

it should use 3 params cas function.

where can infimation inline c asm?i need complete tutorial.


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