Linus Torvalds wrote:
> "volatile" should be equivalent to clobbering memory, although the gcc
> manual pages are certainly not very verbose on the issue.
It isn't. Try the following with/without the memory clobber:
x = *p;
__asm__ __volatile__ ("" : : : "memory");
x = *p;
With or without, the program reads *p only once. However, with the
clobber it reads _after_ the asm; without, it reads _before_ the asm.
It's ok for the compiler to do that (given we don't know what "volatile"
means anyway :-). But it does have implications for spin_lock:
spin_lock must say that it clobbers memory.
spin_unlock should also say it clobbers memory but I have no test case
to demonstrate the compiler moving reads down past an asm.
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This archive was generated by hypermail 2b29 : Thu Sep 07 2000 - 21:00:30 EST