Hi,
For the following function, I have two questions:
static inline int test_and_set_bit(int nr, volatile unsigned long * addr)
{
int oldbit;
__asm__ __volatile__( LOCK_PREFIX
"btsl %2,%1\n\tsbbl %0,%0"
:"=r" (oldbit),"+m" (ADDR)
:"Ir" (nr) : "memory");
return oldbit;
}
1. There are two instructions in the inline assemably, namely btsl and
sbbl. But, can the only one LOCK_PREFIX ensure that the operation is
atomic?
2. The clobber list of the inline assembly contains a string of
"memory". What is the meaning of this declaration and why does the
operation need it ? After all, some other operations such as
clear_bit() dose not need "memory" indeed. The declaration of "memory"
appears in source code of kernel here and there, and bothers me for a
long time. So any details about it will be appreciated.
static inline void clear_bit(int nr, volatile unsigned long * addr)
{
__asm__ __volatile__( LOCK_PREFIX
"btrl %1,%0"
:"+m" (ADDR)
:"Ir" (nr));
}
Thanks!
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