Messages in this thread | | | Date | Mon, 8 Apr 2002 08:59:55 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH] rw-semaphore asm constraints patch fix |
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On Mon, 8 Apr 2002, David Howells wrote: > > The attached patch should fix the compile error that asm-i386/rwsem.h causes > with old gcc's whilst maintaining the asm constraints correctly.
Doesn't work.
> + : "=m"(sem->count), "=d"(tmp) > + : "0"(sem->count), "1"(tmp), "a"(sem)
A "m" constraint cannot be used together with a subsequent number (ie the "=m" -> "0" thing is illegal - the numbering traditionally only works on hard registers). It may work with some compilers and with the right register pressure, but it absolutely _will_ cause problems on other setups.
I should know, I tried to work around gcc stupidities in this area enough times, and cursed how various things didn't work with various compilers.
The best thing to do is probably to mark "sem->count" a memory input only, which together with the memory clobber should be ok.
Linus
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