From: Arnd Bergmann <arnd@arndb.de>
To: Joe Perches <joe@perches.com>
Cc: Will Deacon <will@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
Android Kernel Team <kernel-team@android.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Segher Boessenkool <segher@kernel.crashing.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Subject: Re: [RFC PATCH 1/8] compiler/gcc: Emit build-time warning for GCC prior to version 4.8
Date: Mon, 13 Jan 2020 15:39:45 +0100 [thread overview]
Message-ID: <CAK8P3a1t9757M5CRKNX_X+T9VuLX+5=z5_845rLJGTG50RogXA@mail.gmail.com> (raw)
In-Reply-To: <8fe4f81699517758b44afbe0e1a53bc080f64a62.camel@perches.com>
On Fri, Jan 10, 2020 at 6:54 PM Joe Perches <joe@perches.com> 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@kernel.org> 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
next prev parent reply other threads:[~2020-01-13 14:40 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-10 16:56 [RFC PATCH 0/8] Rework READ_ONCE() to improve codegen Will Deacon
2020-01-10 16:56 ` [RFC PATCH 1/8] compiler/gcc: Emit build-time warning for GCC prior to version 4.8 Will Deacon
2020-01-10 17:35 ` Arnd Bergmann
2020-01-10 17:53 ` Joe Perches
2020-01-13 14:39 ` Arnd Bergmann [this message]
2020-01-13 15:35 ` Masahiro Yamada
2020-01-13 14:27 ` Will Deacon
2020-01-14 21:39 ` Nick Desaulniers
2020-01-15 10:35 ` David Laight
2020-01-15 10:49 ` Arnd Bergmann
2020-01-10 16:56 ` [RFC PATCH 2/8] netfilter: Avoid assigning 'const' pointer to non-const pointer Will Deacon
2020-01-10 16:56 ` [RFC PATCH 3/8] fault_inject: Don't rely on "return value" from WRITE_ONCE() Will Deacon
2020-01-10 16:56 ` [RFC PATCH 4/8] READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE() Will Deacon
2020-01-10 16:56 ` [RFC PATCH 5/8] READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses Will Deacon
2020-01-10 19:24 ` Arnd Bergmann
2020-01-13 16:16 ` Will Deacon
2020-01-10 16:56 ` [RFC PATCH 6/8] READ_ONCE: Drop pointer qualifiers when reading from scalar types Will Deacon
2020-01-10 18:54 ` Linus Torvalds
2020-01-13 14:59 ` Will Deacon
2020-01-13 17:42 ` Luc Van Oostenryck
2020-01-13 19:31 ` Linus Torvalds
2020-01-10 16:56 ` [RFC PATCH 7/8] locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros Will Deacon
2020-01-10 19:42 ` Arnd Bergmann
2020-01-13 15:01 ` Will Deacon
2020-01-10 16:56 ` [RFC PATCH 8/8] arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros Will Deacon
2020-01-10 17:45 ` Mark Rutland
2020-01-10 17:58 ` [RFC PATCH 0/8] Rework READ_ONCE() to improve codegen Arnd Bergmann
2020-01-10 19:46 ` Arnd Bergmann
2020-01-10 20:14 ` Linus Torvalds
2020-01-13 13:03 ` Arnd Bergmann
2020-01-13 11:20 ` David Laight
2020-01-13 12:40 ` Christian Borntraeger
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