Linus Torvalds <[email protected]> wrote:
> > So, using the "+" constraint modifier for memory, like "+m" is bogus.
> > We must simply specify "=m" which handles the case correctly.
>
> No. This is wrong.
Agreed.
> "=m" means that the new value of the memory location is *set*.
>
> Which means that gcc will potentially optimize away any previous stores to
> that memory location.
>
> And yes, it happens, and yes, we've seen it.
I had a lot of "fun" with this when mucking around with the asm-optimised R/W
semaphores.
David
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