linux-kernel - Re: [PATCH v3 1/2] Kbuild: lto: add CONFIG_MAKE

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Date:   Tue, 6 Jul 2021 17:06:07 +0800
From:   Lecopzer Chen <lecopzer.chen@...iatek.com>
To:     <samitolvanen@...gle.com>
CC:     <clang-built-linux@...glegroups.com>, <keescook@...omium.org>,
        <lecopzer.chen@...iatek.com>, <linux-kbuild@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <masahiroy@...nel.org>,
        <michal.lkml@...kovi.net>, <nathan@...nel.org>,
        <ndesaulniers@...gle.com>, <yj.chiang@...iatek.com>
Subject: Re: [PATCH v3 1/2] Kbuild: lto: add CONFIG_MAKE_VERSION

> On Sun, Jul 4, 2021 at 7:03 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > On Fri, Jul 2, 2021 at 12:29 PM Lecopzer Chen
> > <lecopzer.chen@...iatek.com> wrote:
> > >
> > > To check the GNU make version. Used by the LTO Kconfig.
> > >
> > > LTO with MODVERSIONS will fail in generating correct CRC because
> > > the makefile rule doesn't work for make with version 3.8X.[1]
> > >
> > > Thus we need to check make version during selecting on LTO Kconfig.
> > > Add CONFIG_MAKE_VERSION which means MAKE_VERSION in canonical digits
> > > for arithmetic comparisons.
> > >
> > > [1] https://lore.kernel.org/lkml/20210616080252.32046-1-lecopzer.chen@mediatek.com/
> > > Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
> > > ---
> >
> >
> > NACK.
> >
> > "Let's add MAKE_VERSION >= 40200 restriction
> > just because I cannot write correct code that
> > works for older Make" is a horrible idea.
> >
> > Also, Kconfig is supposed to check the compiler
> > (or toolchains) capability, not host tool versions.
> 
> I feel like requiring a Make that's half a decade old for a feature
> that also requires a toolchain released last October ago isn't
> entirely unreasonable.
> 
> That being said, if Masahiro prefers not to rely on the wildcard
> function's behavior here, which is a reasonable request, we could
> simply use the shell to test for the file's existence:
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 34d257653fb4..c6bd62f518ff 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -388,7 +388,7 @@ ifeq ($(CONFIG_LTO_CLANG) $(CONFIG_MODVERSIONS),y y)
>        cmd_update_lto_symversions =                                     \
>         rm -f $@...mversions                                            \
>         $(foreach n, $(filter-out FORCE,$^),                            \
> -               $(if $(wildcard $(n).symversions),                      \
> +               $(if $(shell test -s $(n).symversions && echo y),       \
>                         ; cat $(n).symversions >> $@...mversions))
>  else
>        cmd_update_lto_symversions = echo >/dev/null
> 
> This is not quite as efficient as using wildcard, but should work with
> older Make versions too. Thoughts?
> 


I've tested this in both make-4.3 and 3.81, and the CRC is correct.
But I'm not sure if anyone would have the "arg list too long" issue.

Tested-by: Lecopzer Chen <lecopzer.chen@...iatek.com>