linux-kernel - Re: [PATCH v6 06/15] x86/module: Deal with GOT based stack cookie load on Clang

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Message-ID: <B085D893-C3CE-4D6D-8BB5-834328819E68@zytor.com>
Date: Tue, 18 Feb 2025 13:52:59 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Brian Gerst <brgerst@...il.com>, Ingo Molnar <mingo@...nel.org>
CC: linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
        Ard Biesheuvel <ardb@...nel.org>, Uros Bizjak <ubizjak@...il.com>
Subject: Re: [PATCH v6 06/15] x86/module: Deal with GOT based stack cookie load on Clang < 17

On February 18, 2025 6:05:37 AM PST, Brian Gerst <brgerst@...il.com> wrote:
>On Tue, Feb 18, 2025 at 4:07 AM Ingo Molnar <mingo@...nel.org> wrote:
>>
>>
>> * Brian Gerst <brgerst@...il.com> wrote:
>>
>> >  #define R_X86_64_GOTPCREL    9       /* 32 bit signed pc relative
>> > -                                        offset to GOT */
>> > +#define R_X86_64_GOTPCRELX   41         offset to GOT */
>>                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> > +#define R_X86_64_REX_GOTPCRELX       42
>>
>> Uhm, I'm pretty sure this won't even build, should any code use
>> R_X86_64_GOTPCRELX - which it doesn't currently...
>>
>> Also, each entry here has a comment explaining it - except these two
>> new GOTPCREL variants.
>
>Should we remove the non-REX version that isn't used by the kernel?
>This header is not exported to userspace.
>
>
>Brian Gerst
>

I would personally like to see them in there for the sake of documentation at least. If something runs into this in the future then at least it will be a little quicker to debug. This is an ABI constant, after all.