linux-kernel - Re: [PATCH 5/7] kbuild: get rid of duplication in *.mod files

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Message-ID: <CAKwvOdnHneCy6YeanmvDrabYMWysfQ=WMopsT_gRyrruT8=1Dw@mail.gmail.com>
Date:   Thu, 7 Apr 2022 10:55:34 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH 5/7] kbuild: get rid of duplication in *.mod files

On Wed, Apr 6, 2022 at 8:31 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> It is allowed to add the same objects multiple times to obj-y / obj-m:
>
>   obj-y += foo.o foo.o foo.o
>   obj-m += bar.o bar.o bar.o
>
> It is also allowed to add the same objects multiple times to a composite
> module:
>
>   obj-m    += foo.o
>   foo-objs := foo1.o foo2.o foo2.o foo1.o
>
> This flexibility is useful because the same object might be selected by
> different CONFIG options, like this:
>
>   obj-m               += foo.o
>   foo-y               := foo1.o
>   foo-$(CONFIG_FOO_X) += foo2.o
>   foo-$(CONFIG_FOO_Y) += foo2.o
>
> The duplicated objects are omitted at link time. It works naturally in
> Makefiles because GNU Make removes duplication in $^ without changing
> the order.
>
> It is working well, almost...
>
> A small flaw I notice is, *.mod contains duplication in such a case.
>
> This is probably not a big deal. As far as I know, the only small
> problem is scripts/mod/sumversion.c parses the same file multiple
> times.
>
> I am fixing this because I plan to reuse *.mod for other purposes,
> where the duplication can be problematic.
>
> The code change is quite simple. We already use awk to drop duplicated
> lines in modules.order (see cmd_modules_order in the same file).

Why does the top level Makefile reassign cmd_modules_order rather than
use the original value in scripts/Makefile.build?

> I copied the code, but changed RS to use spaces as record separators.
>
> I also changed the file format to list one object per line.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  scripts/Makefile.build   | 3 ++-
>  scripts/mod/sumversion.c | 2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 6ae92d119dfa..f7a30f378e20 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -303,7 +303,8 @@ $(obj)/%.prelink.o: $(obj)/%.o FORCE
>         $(call if_changed,cc_prelink_modules)
>  endif
>
> -cmd_mod = echo $(addprefix $(obj)/, $(call real-search, $*.o, .o, -objs -y -m)) > $@
> +cmd_mod = echo $(addprefix $(obj)/, $(call real-search, $*.o, .o, -objs -y -m)) | \
> +       $(AWK) -v RS='( |\n)' '!x[$$0]++' > $@

God AWK is unreadable. Any reason we can't use GNU make's sort builtin?
https://www.gnu.org/software/make/manual/html_node/Text-Functions.html

>
>  $(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o FORCE
>         $(call if_changed,mod)
> diff --git a/scripts/mod/sumversion.c b/scripts/mod/sumversion.c
> index 0125698f2037..79bb9eaa65ac 100644
> --- a/scripts/mod/sumversion.c
> +++ b/scripts/mod/sumversion.c
> @@ -398,7 +398,7 @@ void get_src_version(const char *modname, char sum[], unsigned sumlen)
>         buf = read_text_file(filelist);
>
>         md4_init(&md);
> -       while ((fname = strsep(&buf, " \n"))) {
> +       while ((fname = strsep(&buf, "\n"))) {
>                 if (!*fname)
>                         continue;
>                 if (!(is_static_library(fname)) &&
> --
> 2.32.0
>


-- 
Thanks,
~Nick Desaulniers