linux-kernel - Re: [PATCH v6 14/25] kbuild: lto: remove duplicate dependencies from .mod files

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Message-ID: <202010141549.412F2BF0@keescook>
Date:   Wed, 14 Oct 2020 15:50:28 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v6 14/25] kbuild: lto: remove duplicate dependencies from
 .mod files

On Mon, Oct 12, 2020 at 05:31:52PM -0700, Sami Tolvanen wrote:
> With LTO, llvm-nm prints out symbols for each archive member
> separately, which results in a lot of duplicate dependencies in the
> .mod file when CONFIG_TRIM_UNUSED_SYMS is enabled. When a module
> consists of several compilation units, the output can exceed the
> default xargs command size limit and split the dependency list to
> multiple lines, which results in used symbols getting trimmed.
> 
> This change removes duplicate dependencies, which will reduce the
> probability of this happening and makes .mod files smaller and
> easier to read.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>

Hi Masahiro,

This appears to be a general improvement as well. This looks like it can
land without depending on the rest of the series.

-Kees

> ---
>  scripts/Makefile.build | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index ab0ddf4884fd..96d6c9e18901 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -266,7 +266,7 @@ endef
>  
>  # List module undefined symbols (or empty line if not enabled)
>  ifdef CONFIG_TRIM_UNUSED_KSYMS
> -cmd_undef_syms = $(NM) $< | sed -n 's/^  *U //p' | xargs echo
> +cmd_undef_syms = $(NM) $< | sed -n 's/^  *U //p' | sort -u | xargs echo
>  else
>  cmd_undef_syms = echo
>  endif
> -- 
> 2.28.0.1011.ga647a8990f-goog
> 

-- 
Kees Cook