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Linus Torvalds <torvalds@linux-foundation.org> 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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