Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread

On Tue, Mar 01, 2016 at 10:32:02PM +0100, Peter Zijlstra wrote:

quoted

        /*
         * Thread-local ABI rseq_seqnum field.
         * Updated by the kernel, and read by user-space with
         * single-copy atomicity semantics. Aligned on 32-bit.
         * Values:
         * >= 0: current seqnum for this thread (feature is active).
         * -1 (initial value): means the rseq feature is inactive.
         * -2: rseq feature is not available.
         */
        int32_t rseq_seqnum;

So I really hate that, that makes we have to check for these special
values whenever we increment the seq count and cannot have it wrap
naturally.

Also, since it will wrap, uint32_t is more natural, since the whole
signed overflow thing is somewhat undefined in C.