On Tue, Mar 01, 2016 at 01:47:38PM -0800, H. Peter Anvin wrote: > On 03/01/16 13:32, Peter Zijlstra wrote: > > On Tue, Mar 01, 2016 at 08:23:12PM +0000, Mathieu Desnoyers wrote: > >> I think it's important that user-space fast-paths can quickly > >> detect whether the feature is enabled without having to rely on > >> always reading a separate cache-line. I've put together an ABI > >> proposal that take into account the feedback received so far. > > > > Nah, adding detectoring code to fast paths is silly, makes them less > > fast. Doesn't userspace have self modifying code? I know that at least > > glibc does linker trickery to call different functions depending on > > runtime context. > > > > No, userspace does not have self-modifying code. The glibc indirect > function is done at dynamic link time; it is also worth noting that > resolving global symbols through dynamic linking often requires an > indirect call.
Boy that blows. And here I was thinking you could edit the code at dynamic link time because nobody was running it yet :/ And I suppose JITs need an (effective) munmap()+mmap() cycle to ensure the 'old' code is flushed from all caches etc..?
