linux-kernel - Re: [PATCH v2 05/13] kbuild: detect objtool update without using .SECONDEXPANSION

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Message-ID: <202108311032.F503B07@keescook>
Date:   Tue, 31 Aug 2021 10:32:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 05/13] kbuild: detect objtool update without using
 .SECONDEXPANSION

On Tue, Aug 31, 2021 at 04:39:56PM +0900, Masahiro Yamada wrote:
> Redo commit 8852c5524029 ("kbuild: Fix objtool dependency for
> 'OBJECT_FILES_NON_STANDARD_<obj> := n'") to add the objtool
> dependency in a cleaner way.
> 
> Using .SECONDEXPANSION ends up with unreadable code due to escaped
> dollars. Also, it is not efficient because the second half of
> Makefile.build is parsed twice every time.
> 
> Append the objtool dependency to the *.cmd files at the build time.
> 
> This is what fixdep and gen_ksymdeps.sh already do. So, following the
> same pattern seems a natural solution.
> 
> This allows us to drop $$(objtool_deps) entirely.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Okay, so IIUC, this means objtool (and args) now ends up in the .cmd
file instead of in the Makefile dep rules? That seems reasonable.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook