Messages in this thread | | | Date | Wed, 21 Dec 2005 21:01:01 +0100 | From | Ingo Molnar <> | Subject | Re: [patch 3/8] mutex subsystem, add atomic_*_call_if_*() to i386 |
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* Linus Torvalds <torvalds@osdl.org> wrote:
> > Umm. This asm is broken. It doesn't mark %eax as changed, so this is only > > reliable if the function you call is > > > > - a "fastcall" one > > - always returns as its return value the pointer to the atomic count > > > > which is not true (you verify that it's a fastcall, but it's of type > > "void"). > > Actually (and re-reading the email I sent that wasn't obvious at all), > my _preferred_ fix is to literally force the use of the above kind of > function: not save/restore %eax at all, but just say that any function > that is called by the magic "atomic_*_call_if()" needs to always > return the argument it gets as its return value too. > > That allows the caller to not even have to care. And the callee > obviously already _has_ that value, so it might as well return it (and > in the best case it's not going to add any cost at all, either to the > caller or the callee). > > So you might opt to keep the asm the same, just change the calling > conventions.
ok, i've added this fix, thanks. Right now we dont do anything after those functions (that's probably how the bug never showed up), but at least one interim stage i tried to use the call_if functions at other places too, so the potential is there.
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