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

Kees Cook
2020-10-15T01:19:53Z

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@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.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