linux-kernel - Re: [RFC PATCH v2 2/2] kbuild: call check-atomics.sh only if prerequisites change

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Date:   Sat, 14 May 2022 04:01:18 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Rikard Falkeborn <rikard.falkeborn@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH v2 2/2] kbuild: call check-atomics.sh only if
 prerequisites change

On Sat, May 7, 2022 at 10:13 PM Vincent Mailhol
<mailhol.vincent@...adoo.fr> wrote:
>
> check-atomics.sh is executed unconditionally. Most developers will not
> modify the files being checked by this script and thus do not need to
> execute it again for each iterative make.
>
> We first add an additional dependency to include/linux/atomic/* to
> make sure that the script gets executed again if the headers are
> modified. We then use the if_change macro instead of cmd. c.f. [1] and
> create the dot file scripts/atomic/.check-atomics which is used for
> the target timestamp. Finally, the dot file is added to the
> CLEAN_FILES target.
>
> [1] https://www.kernel.org/doc/html/latest/kbuild/makefiles.html#command-change-detection
>
> Signed-off-by: Vincent Mailhol <mailhol.vincent@...adoo.fr>


I do not like this approach.

I wrote a different patch.
https://lore.kernel.org/lkml/20220513185340.239753-1-masahiroy@kernel.org/T/#u

This naturally works by comparing the timestamp
between *_shipped and include/generated/*.







> ---
>  Kbuild   | 7 ++++---
>  Makefile | 3 ++-
>  2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/Kbuild b/Kbuild
> index fa441b98c9f6..c3cb76ebcbaf 100644
> --- a/Kbuild
> +++ b/Kbuild
> @@ -50,10 +50,11 @@ missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE
>  #####
>  # Check atomic headers are up-to-date
>
> -always-y += old-atomics
> +always-y += scripts/atomic/.check-atomics
>
>  quiet_cmd_atomics = CALL    $<
>        cmd_atomics = $(CONFIG_SHELL) $<
>
> -old-atomics: scripts/atomic/check-atomics.sh FORCE
> -       $(call cmd,atomics)
> +scripts/atomic/.check-atomics: scripts/atomic/check-atomics.sh $(wildcard include/linux/atomic/*) FORCE
> +       $(call if_changed,atomics)
> +       @touch $@
> diff --git a/Makefile b/Makefile
> index 9a820c525b86..9e815c8bb0b6 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1483,7 +1483,8 @@ endif # CONFIG_MODULES
>  # Directories & files removed with 'make clean'
>  CLEAN_FILES += include/ksym vmlinux.symvers modules-only.symvers \
>                modules.builtin modules.builtin.modinfo modules.nsdeps \
> -              compile_commands.json .thinlto-cache
> +              compile_commands.json .thinlto-cache \
> +              scripts/atomic/.check-atomics
>
>  # Directories & files removed with 'make mrproper'
>  MRPROPER_FILES += include/config include/generated          \
> --
> 2.35.1
>


-- 
Best Regards
Masahiro Yamada