Messages in this thread | | | Date | Mon, 27 Sep 2004 06:30:25 +1000 | From | Paul Mackerras <> | Subject | Re: ptep_establish/establish_pte needs set_pte_atomic and all set_pte must be written in asm |
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Benjamin Herrenschmidt writes:
> On Sun, 2004-09-26 at 10:46, Andrea Arcangeli wrote: > > > As far as the C language is concerned that *ptep = something can be > > implemented with 8 writes of 1 byte each (or alternatively with an > > assembler instruction that may make the written data visible not > > atomically to other cpus, despite it was written with a single opcode, > > similarly to what happens if you use incl without the lock prefix). I'm > > not saying such instruction exists in ppc64, but the compiler is > > definitely allowed to break the above. You can blame on the compiler to > > be inefficient, but you can't blame on the compiler for the security > > hazard it would generate. Only the kernel would be to blame if for > > whatever reason a gcc version would be underoptimized. > > BTW, for your reading pleasure :) > > #define atomic_set(v,i) (((v)->counter) = (i))
FWIW, we also rely on several other things that are not guaranteed by the C standard, for instance that integer arithmetic is 2's complement, that bytes are individually addressable, and that pointers are represented by an address that is no bigger than a long.
Paul.
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