Example

Compiling this function:

static inline __attribute__((always_inline))
void cpu_reg_disable_bits(volatile uint32_t *reg, uint32_t mask)
{
    __atomic_fetch_and(reg, ~mask, __ATOMIC_RELAXED);
}

produces this Rust code:

#[inline(always)]
unsafe extern "C" fn cpu_reg_disable_bits(mut reg: *mut uint32_t,
                                          mut mask: uint32_t) {
    ::core::intrinsics::atomic_and_relaxed(reg, !mask);
}

This is correct, but requires the core_intrinsics on the produced code (which is otherwise usable on stable Rust).

Code orientation

The relevant code is produced in c2rust-transpile/src/translator/builtins.rs around line 530; note that one doesn't find precisely "atomic_and_relaxed" because the name is assembled from the operation and the ordering.

Replacement

The AtomicXX family of types has a fetch_and, which are suitable replacements -- at least if the type that is being operated on is part of the family.

I'm holding off on fixing this while #364 is hot; I plan to come back to this later and can probably come up with a PR then.