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

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Date:   Mon, 5 Jul 2021 10:59:39 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Lecopzer Chen <lecopzer.chen@...iatek.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        yj.chiang@...iatek.com, Michal Marek <michal.lkml@...kovi.net>
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?

Sami