linux-kernel - Re: [PATCH] kbuild: make clean rule robust against too long argument error

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Date:   Mon, 19 Jun 2023 00:50:48 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Eugeniu Rosca <erosca@...adit-jv.com>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Eugeniu Rosca <roscaeugeniu@...il.com>
Subject: Re: [PATCH] kbuild: make clean rule robust against too long argument error

On Sun, Jun 18, 2023 at 5:07 AM Eugeniu Rosca <erosca@...adit-jv.com> wrote:
>
> Hello Yamada-san,
>
> Many thanks for your feedback and for your patch.
> It indeed addresses the issue I have reported in [1].
>
> On Sun, Jun 18, 2023 at 12:30:25AM +0900, Masahiro Yamada wrote:
> > Commit cd968b97c492 ("kbuild: make built-in.a rule robust against too
> > long argument error") made a build rule robust against "Argument list
> > too long" error.
> >
> > Eugeniu Rosca reported the same error occurred when cleaning an external
> > module.
> >
> > The $(obj)/ prefix can be a very long path for external modules.
>
> Confirmed. I am seeing an instance of $(obj) being 150 characters long,
> due to an out-of-tree module deeply buried in a specific Yocto build.
>
> In the current vanilla version of 'make clean' (w/o this patch), the
> $(obj) prefix is applied to each and every file being removed,
> dramatically increasing the strlen of arguments passed to 'rm -rf'.
>
> >
> > Apply a similar solution to 'make clean'.
> >
> > Reported-by: Eugeniu Rosca <erosca@...adit-jv.com>
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  scripts/Makefile.clean | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
> > index 3649900696dd..235408a44f90 100644
> > --- a/scripts/Makefile.clean
> > +++ b/scripts/Makefile.clean
> > @@ -37,8 +37,9 @@ __clean-files   := $(wildcard $(addprefix $(obj)/, $(__clean-files)))
> >
> >  # ==========================================================================
> >
> > +# Use xargs to make this robust against "Argument list too long" error
>
> Please, correct me if I am wrong, but it looks like the magic/brilliance
> is in the 'patsubst' function, since below version also fails for me:
>
> NOK: cmd_clean = printf '%s ' $(__clean-files) | xargs rm -rf

Right.
Now, 'printf' (instead of 'rm') failed with the too long argument list.

GNU Make does not have the length limit, but shell does.
So, the full-path list must be passed via stdout
instead of the command line.


The comment might be confusing.

I will repeat the same comment written in scripts/Makefile.build:

  # To make this rule robust against "Argument list too long" error,
  # remove $(obj)/ prefix, and restore it by a shell command.




-- 
Best Regards
Masahiro Yamada