In studying the kernel I find many gcc inline 'asm' statements,
like so.
asm ( assembler template
: output operands (optional)
: input operands (optional)
: list of clobbered registers (optional)
);
I have read all the docs and I still can't clearly understand when it is
required to specify a clobberlist - a register or memory that will be modified
and must be preserved by gcc.
In searching the kernel source there were very few clobbers given
and most of those were for memory.
For example in arch/i386/lib/delay.c:
71 __asm__("mull %0"
72 :"=d" (xloops), "=&a" (d0)
73 :"1" (xloops),"" (current_cpu_data.loops_per_jiffy));
74 __delay(xloops * HZ);
It's pretty obvious that eax gets clobbered. Why is it unlisted?
Does the answer to this question apply in all cases? What about memory
clobbers - how do they happen?
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