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

[Kees Cook]

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