linux-kernel - Re: [PATCH] tools: bpf: Disable stack protector

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Message-ID: <302afd51-07c2-04b3-98a0-ee9d8fc5397c@meta.com>
Date:   Sun, 22 Jan 2023 21:22:28 -0800
From:   Yonghong Song <yhs@...a.com>
To:     Peter Foley <pefoley2@...oley.com>
Cc:     Eduard Zingerman <eddyz87@...il.com>,
        Quentin Monnet <quentin@...valent.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] tools: bpf: Disable stack protector



On 1/22/23 8:28 PM, Peter Foley wrote:
> On Wed, Jan 18, 2023 at 11:34 PM Yonghong Song <yhs@...a.com> wrote:
>> On 1/18/23 11:28 AM, Eduard Zingerman wrote:
>>>
>>> While working on clang patch to disable stack protector
>>> for BPF target I've noticed that there is an option to
>>> disable default configuration file altogether [1]:
>>>
>>>     --no-default-config
>>>
>>> Should we consider it instead of -fno-stack-protector
>>> to shield ourselves from any potential distro-specific
>>> changes?
>>
>> Peter, could you help check whether adding --no-default-config works
>> in your environment or not?
>>
>>>
>>> [1] https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-no-default-config
> 
> I guess I could, but I'm not convinced that's the right thing to do.
> Ideally problems with distro-specific configs would cause loud
> failures (like this one) and result in fixes like the changes being
> made to upstream clang/gcc.
> Simply unconditionally disabling distro configs seems to be the wrong
> way to approach this and makes it less likely that future problems
> will be reported in the first place.

Thanks for confirming. Eduard has implemented a proper fix in clang
(https://reviews.llvm.org/D142046) which will warn if -fstack-protector
is enabled. In gentoo case, since -fno-stack-protector is appended to
compilation flags, no warning will be issued, so we are all good here.