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Re: atomic accesses
I'm really wondering why this is being considered.
A documented property of the form "GCC will use a single instruction
to do X when possible" means exactly nothing. In particular, to call
such a statement a "guarantee" is seriously misleading.
If Linux needs the single-instruction property for atomicity, and it
thinks it can rely on this supposed property, then Linux has a bug.
To do atomic operations, you have to use primitives that are
guaranteed always to have the necessary atomicity properties.
Typically those would be found in asm statements.
I suspect it would be valuable to have standardized primitives for
atomic actions (semaphores, spinlocks, test-and-set primitives,
circular buffers, pick one). But GCC's load/store semantics are not
those primitives, with or without a documented "single instruction
when possible" property.