linux-kernel - Re: [PATCH v5 06/16] x86/relocs: Handle R_X86_64_REX

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Message-ID: <CAFULd4b9RqWD5uaZEzejQfzJ4cH85sCgbTaHJdg-qJ-OaLJiWA@mail.gmail.com>
Date: Thu, 7 Nov 2024 12:20:43 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, 
	Ingo Molnar <mingo@...nel.org>, "H . Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Borislav Petkov <bp@...en8.de>, Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH v5 06/16] x86/relocs: Handle R_X86_64_REX_GOTPCRELX relocations

On Tue, Nov 5, 2024 at 4:58 PM Brian Gerst <brgerst@...il.com> wrote:
>
> Clang may produce R_X86_64_REX_GOTPCRELX relocations when redefining the
> stack protector location.  Treat them as another type of PC-relative
> relocation.
>
> Signed-off-by: Brian Gerst <brgerst@...il.com>
> ---
>  arch/x86/tools/relocs.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
> index 6afe2e5e9102..7d7fc7f0a250 100644
> --- a/arch/x86/tools/relocs.c
> +++ b/arch/x86/tools/relocs.c
> @@ -32,6 +32,11 @@ static struct relocs         relocs32;
>  static struct relocs           relocs32neg;
>  static struct relocs           relocs64;
>  # define FMT PRIu64
> +
> +#ifndef R_X86_64_REX_GOTPCRELX
> +#define R_X86_64_REX_GOTPCRELX 42
> +#endif

The next patch (7/16) introduces the above definition to
arch/x86/include/asm/elf.h. If you swap patches 6 and 7 in the series,
you won't have to introduce the above conditional definition.

Uros.

> +
>  #else
>  # define FMT PRIu32
>  #endif
> @@ -226,6 +231,7 @@ static const char *rel_type(unsigned type)
>                 REL_TYPE(R_X86_64_PC16),
>                 REL_TYPE(R_X86_64_8),
>                 REL_TYPE(R_X86_64_PC8),
> +               REL_TYPE(R_X86_64_REX_GOTPCRELX),
>  #else
>                 REL_TYPE(R_386_NONE),
>                 REL_TYPE(R_386_32),
> @@ -860,6 +866,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
>
>         case R_X86_64_PC32:
>         case R_X86_64_PLT32:
> +       case R_X86_64_REX_GOTPCRELX:
>                 /*
>                  * PC relative relocations don't need to be adjusted unless
>                  * referencing a percpu symbol.
> --
> 2.47.0
>