linux-kernel - Re: [PATCH] arm64: fix clang warning about TRAMP

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Date:   Tue, 22 Mar 2022 10:02:23 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        James Morse <james.morse@....com>,
        Arnd Bergmann <arnd@...db.de>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] arm64: fix clang warning about TRAMP_VALIAS

On Fri, Mar 18, 2022 at 12:52 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Fri, Mar 18, 2022 at 12:11 PM Robin Murphy <robin.murphy@....com> wrote:
> >
> > On 2022-03-16 18:38, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@...db.de>
> > >
> > > The newly introduced TRAMP_VALIAS definition causes a build warning
> > > with clang-14:
> > >
> > > arch/arm64/include/asm/vectors.h:66:31: error: arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension [-Werror,-Wnull-pointer-arithmetic]
> >
> > Tangentially, all the other GNU extensions we depend on throughout Linux
> > are also GNU extensions. Do we know what's special about this one?
>
> My first thought is that -Wnull-pointer-arithmetic should be in the
> -Wgnu flag group, such that -Wno-gnu (as set by Kbuild) implies
> -Wno-null-pointer-arithmetic.
>
> One issue seems to be that -Wnull-pointer-arithmetic seems to control
> at least 2 different checks in clang.
>
> https://godbolt.org/z/hdYYejj3d
>
> So it's likely these two checks should have 2 distinct flags, such
> that the warning we're observing can be grouped under -Wgnu.
>
> Filed: https://github.com/llvm/llvm-project/issues/54444

Fix should be landing shortly:
https://reviews.llvm.org/D122224

-- 
Thanks,
~Nick Desaulniers