linux-kernel - Re: [PATCH v2 3/3] btf: Avoid weak external references

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Message-Id: <fe75de1c-f500-42f3-bef0-8830d9f45ea1@app.fastmail.com>
Date: Tue, 09 Apr 2024 17:05:08 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Ard Biesheuvel" <ardb+git@...gle.com>, linux-kernel@...r.kernel.org
Cc: "Ard Biesheuvel" <ardb@...nel.org>,
 "Masahiro Yamada" <masahiroy@...nel.org>,
 "Martin KaFai Lau" <martin.lau@...ux.dev>,
 Linux-Arch <linux-arch@...r.kernel.org>, linux-kbuild@...r.kernel.org,
 bpf@...r.kernel.org, "Andrii Nakryiko" <andrii@...nel.org>
Subject: Re: [PATCH v2 3/3] btf: Avoid weak external references

On Tue, Apr 9, 2024, at 17:01, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
>
> If the BTF code is enabled in the build configuration, the start/stop
> BTF markers are guaranteed to exist in the final link but not during the
> first linker pass.
>
> Avoid GOT based relocations to these markers in the final executable by
> providing preliminary definitions that will be used by the first linker
> pass, and superseded by the actual definitions in the subsequent ones.
>
> Make the preliminary definitions dependent on CONFIG_DEBUG_INFO_BTF so
> that inadvertent references to this section will trigger a link failure
> if they occur in code that does not honour CONFIG_DEBUG_INFO_BTF.
>
> Note that Clang will notice that taking the address of__start_BTF cannot
> yield NULL any longer, so testing for that condition is no longer
> needed.
>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>

Acked-by: Arnd Bergmann <arnd@...db.de>