linux-kernel - Re: [PATCH v5 21/21] kbuild: implement CONFIG_TRIM_UNUSED

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Message-ID: <CAK7LNASK1kptksxaOh5sKiE=COBusJ2d3F6PE-0vptz91217_g@mail.gmail.com>
Date:   Tue, 16 May 2023 10:41:31 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Pitre <npitre@...libre.com>,
        Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH v5 21/21] kbuild: implement CONFIG_TRIM_UNUSED_KSYMS
 without recursion

On Mon, May 15, 2023 at 12:28 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses
> the directory tree to determine which EXPORT_SYMBOL to trim. If an
> EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the
> second traverse, where some source files are recompiled with their
> EXPORT_SYMBOL() tuned into a no-op.
>
> Linus stated negative opinions about this slowness in commits:
>
>  - 5cf0fd591f2e ("Kbuild: disable TRIM_UNUSED_KSYMS option")
>  - a555bdd0c58c ("Kbuild: enable TRIM_UNUSED_KSYMS again, with some guarding")
>
> We can do this better now. The final data structures of EXPORT_SYMBOL
> are generated by the modpost stage, so modpost can selectively emit
> KSYMTAB entries that are really used by modules.
>
> Commit 2cce989f8461 ("kbuild: unify two modpost invocations") is another

The commit hash is wrong.

Commit f73edc8951b2 ("kbuild: unify two modpost invocations") is correct.






-- 
Best Regards
Masahiro Yamada