On Fri, Jan 10, 2020 at 6:54 PM Joe Perches <joe@xxxxxxxxxxx> wrote: > > On Fri, 2020-01-10 at 18:35 +0100, Arnd Bergmann wrote: > > On Fri, Jan 10, 2020 at 5:56 PM Will Deacon <will@xxxxxxxxxx> wrote: > > > Prior to version 4.8, GCC may miscompile READ_ONCE() by erroneously > > > discarding the 'volatile' qualifier: > > > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 > > > > > > We've been working around this using some nasty hacks which make > > > READ_ONCE() both horribly complicated and also prevent us from enforcing > > > that it is only used on scalar types. Since GCC 4.8 is pretty old for > > > kernel builds now, emit a warning if we detect it during the build. > > > > No objection to recommending gcc-4.8, but I think this should either > > just warn once during the kernel build instead of for every file, or > > it should become a hard requirement. > > It might as well be a hard requirement as > gcc 4.8.0 is already nearly 7 years old. > > gcc 4.6.0 released 2011-03-25 > gcc 4.8.0 released 2013-03-22 > > Perhaps there are exceedingly few to zero new > instances using gcc compiler versions < 4.8 The last time we had this discussion, the result was that gcc-4.8 is probably ok as a minimum version, but moving to 5.1+ (from 2015) was not an obvious choice: https://www.spinics.net/lists/linux-kbuild/msg23648.html If nobody complains about the move to 4.8, we can try moving to gcc-5.1 and GNU99/GNU11 next year ;-) Arnd
