From: Segher Boessenkool <segher@kernel.crashing.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Borislav Petkov <bp@alien8.de>, Vasily Gorbik <gor@linux.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
x86@kernel.org, llvm@lists.linux.dev,
linux-sparse@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel test robot <lkp@intel.com>,
Nathan Chancellor <nathan@kernel.org>,
linux-toolchains@vger.kernel.org
Subject: Re: [PATCH] objtool: prefer memory clobber & %= to volatile & __COUNTER__
Date: Tue, 25 Jan 2022 17:31:28 -0600 [thread overview]
Message-ID: <20220125233128.GT614@gate.crashing.org> (raw)
In-Reply-To: <CAKwvOdmLzwz=02ypt0_1324_5-7i3Az7HizFaDMqZv__-D99uA@mail.gmail.com>
Hi!
On Mon, Jan 24, 2022 at 03:26:36PM -0800, Nick Desaulniers wrote:
> I noticed in that report and
> https://lore.kernel.org/lkml/202201190702.XNSXrMTK-lkp@intel.com/
> that gcc-9 was used. I wonder if %= has been fixed in gcc-10+? Have
> there been other reports with gcc-10+ for my patch?
None of the %= code (which is trivial) has been changed since 1992.
> If this is fixed in gcc-10, then we can probably add a comment with a
> FIXME link to the issue or commit to replace __COUNTER__ with %= one
> day. If not, then we can probably come up with a reduced test case
> for the GCC devs to take a look at, then add the FIXME comment to
> kernel sources.
Please open a PR?
> I'm more confident that we can remove the `volatile` keyword (I was
> thinking about adding a new diagnostic to clang to warn that volatile
> is redundate+implied for asm goto or inline asm that doesn't have
> outputs) though that's not the problem here and will probably generate
> some kernel wide cleanup before we could enable such a flag.
Its main value is that it would discourage users from thinking volatile
is magic. Seriously worth some pain!
> Perhaps
> there are known compiler versions that still require the keyword for
> those cases for some reason.
It was removed from compiler-gcc.h in 3347acc6fcd4 (which changed the
minimum required GCC version to GCC 5).
Segher
next prev parent reply other threads:[~2022-01-26 0:02 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-14 1:05 [PATCH] objtool: prefer memory clobber & %= to volatile & __COUNTER__ Nick Desaulniers
2022-01-14 21:58 ` Nathan Chancellor
2022-01-16 13:32 ` Borislav Petkov
2022-01-18 19:22 ` Josh Poimboeuf
2022-01-18 23:01 ` Josh Poimboeuf
2022-01-18 23:33 ` Borislav Petkov
2022-01-19 0:03 ` Josh Poimboeuf
2022-01-19 10:01 ` Borislav Petkov
2022-01-24 23:26 ` Nick Desaulniers
2022-01-24 23:38 ` Nick Desaulniers
2022-01-25 18:49 ` Borislav Petkov
2022-01-25 23:31 ` Segher Boessenkool [this message]
2022-01-26 0:59 ` Nick Desaulniers
2022-01-26 2:12 ` Nick Desaulniers
2022-01-26 11:13 ` Segher Boessenkool
2022-01-31 20:45 ` Nick Desaulniers
2022-01-31 22:13 ` Segher Boessenkool
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