On Tue, Jan 14, 2020 at 10:39 PM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > On Fri, Jan 10, 2020 at 06:35:02PM +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. > > Yeah, hard requirement sounds good to me. Arnd, do you have stats on which > distros have which versions of GCC (IIRC, you had some stats for the GCC 4.6 > upgrade)? This allows us to clean up more cruft in the kernel (grep for > GCC_VERSION). This is the list that Kirill and I came up with in the thread I linked to > - Debian 8.0 Jessie has 4.9.2, EOL 2020-05 > - Ubuntu 14.04 LTS Trusty has 4.8.2, EOL 2019-04; > - Fedora 21 has 4.9.2, EOL 2015-12; > - OpenSUSE 42.3 has 4.8.5, EOL 2019-06; > - RHEL 7.7 has 4.8.5, EOL 2024-06; > - RHEL 6.9 has 4.4.7, EOL 2020-11; > - SUSE 12-SP4 has 4.8.6, EOL 2024, extended support 2027 > - Oracle 7.6 has 4.8.5, EOL ?; > - Slackware 14.1 (no EOL announced): gcc-4.8 In an older thread about moving to gcc-4.3 or 4.6 as a minimum, this were the even older distros: > - RHEL 5.x has 4.1; extended support EOL 2020 > - SLES11 had gcc-4.3; extended support EOL 2022 > - Debian Wheezy (oldoldstable) had gcc-4.6, EOL 2018. > - OpenWRT 12.07 Attitude Adjustment had gcc-4.6 > and is still used with devices that have only 4MB flash / 32 MB RAM Arnd
