[manoweb]

Hello, isn’t part of what you were trying to achieve already taken care of if you use ‘volatile’ or a memory barrier? When writing Linux drivers these patterns are common. In some more exotic cases, even instruction barriers can be used to limit what the out of order or speculative execution is going to be

[smaddox]

Not the OP, and not at all an expert in this area, but I was curious what the answer was, and from a bit of reading it seems like a potential reason that might not work is because volatile also prevents caching the value in a register. So if you want to keep the computation in a register, but you want to explicitly clear the value to zero before writing to it, it seems like C semantics are insufficient (at least without inline assembly).

[manoweb]

Excuse me but what would be the use of zeroing a register before overwriting it?

[p4bl0]

Possibly (I don't know how volatile interact with registers allocation), but the thing is you don't just want this specific example to work, there are a lot of things you want to be able to really ensure, i.e., have rigorous proof of [1]. So maybe if the semantics is adequate and the compiler itself is formally proved like CompCert [2] you can rely on volatile, but that's a lot a assumptions.

[1] See for example the work we did in this paper: Formally Proved Security of Assembly Code Against Power Analysis: A Case Study on Balanced Logic https://eprint.iacr.org/2013/554

[2] https://compcert.org/