linux-kernel - Re: [PATCH] modpost: Skip .llvm.call-graph-profile section check

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Message-ID: <CAFP8O3J2pUddEfL+W2j=tpjdj1ufsQMJqjcARbYvY3+khtBPig@mail.gmail.com>
Date:   Tue, 22 Aug 2023 00:05:56 -0700
From:   Fangrui Song <maskray@...gle.com>
To:     Denis Nikitin <denik@...omium.org>
Cc:     linux-kbuild@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] modpost: Skip .llvm.call-graph-profile section check

On Mon, Aug 21, 2023 at 11:54 PM Denis Nikitin <denik@...omium.org> wrote:
>
> .llvm.call-graph-profile section is added when the kernel is built with
> profiles (e.g. -fprofile-sample-use=<llvm.profile>).

Right. .llvm.call-graph-profile may also be added when the kernel is
built with clang -fprofile-use= (though instrumentation-based PGO
support is not upstreamed yet).

> The section holds
> metadata for symbols beloning to other sections and hence doesn't need
> modpost checks.

Typo: belonging.

.llvm.call-graph-profile contains edge information derived from text
sections, so .llvm.call-graph-profile itself doesn't need more
analysis as the text sections have been analyzed.

> This change fixes the kernel build with sample profiles which fails
> with:
> "FATAL: modpost: Please add code to calculate addend for this architecture"
>
> Signed-off-by: Denis Nikitin <denik@...omium.org>
> ---
>  scripts/mod/modpost.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index b29b29707f10..64bd13f7199c 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -761,6 +761,7 @@ static const char *const section_white_list[] =
>         ".fmt_slot*",                   /* EZchip */
>         ".gnu.lto*",
>         ".discard.*",
> +       ".llvm.call-graph-profile",     /* call graph */
>         NULL
>  };
>
> --
> 2.42.0.rc1.204.g551eb34607-goog
>
>

Otherwise the change looks good to me.


-- 
宋方睿