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5e9a82e898
In order to match reality, allow using these functions with pointers on const objects, and bring us closer to C11. Remove the '+' modifier in the atomic_load_acq_64_i586()'s inline asm statement's constraint for '*p' (the value to load). CMPXCHG8B always writes back some value, even when the value exchange does not happen in which case what was read is written back. atomic_load_acq_64_i586() further takes care of the operation atomically writing back the same value that was read in any case. All in all, this makes the inline asm's write back undetectable by any other code, whether executing on other CPUs or code on the same CPU before and after the call to atomic_load_acq_64_i586(), except for the fact that CMPXCHG8B will trigger a #GP(0) if the memory address is part of a read-only mapping. This unfortunate property is however out of scope of the C abstract machine, and in particular independent of whether the 'uint64_t' pointed to is declared 'const' or not. Approved by: markj (mentor) MFC after: 5 days Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D46887 |
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