Date: Wed, 20 May 2015 13:05:19 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: trouble spots for atomic access * Jens Gustedt <jens.gustedt@...ia.fr> [2015-05-20 00:47:44 +0200]: > Am Dienstag, den 19.05.2015, 18:07 -0400 schrieb Rich Felker: > > On Tue, May 19, 2015 at 03:57:00PM +0200, Jens Gustedt wrote: > > > - pthread_once_t should always be volatile > > > - pthread_spinlock_t should always be volatile > > > > These are C++ ABI changes. I'd like to make the change but I'm > > concerned it might break things. > > Both are broken as they are now, if you fall into a compiler that > "knows" that the object itself isn't volatile qualified, and by that > excuse takes the liberty to optimize out loads. For both types there > is one point where there is a cast to (volatile int*) followed by a > load, that might not do what we want. > > (For pthread_once_t, this on line 43 in pthread_once.c) > > I think the safest would be to make the data types volatile. If that > is not possible, do the load with some new function "a_load_rel" that > is guaranteed to be volatile, atomic and with memory_order relaxed. > fwiw i scanned a significant portion of debian packages with nm -CD for volatile int* usage and didnt find any case that was related to posix types (a few libraries dealing with atomics had their own volatile int*) (found 6553 packages with c++ dependencies in stable, scanned them all) so changing the types wouldnt break too many musl binaries i think
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