linux-kernel - [PATCH 0/2] Kbuild: lto: add make version checking

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Date:   Wed, 30 Jun 2021 20:14:34 +0800
From:   Lecopzer Chen <lecopzer.chen@...iatek.com>
To:     <keescook@...omium.org>, <samitolvanen@...gle.com>,
        <linux-kbuild@...r.kernel.org>
CC:     <clang-built-linux@...glegroups.com>,
        <linux-kernel@...r.kernel.org>, <yj.chiang@...iatek.com>,
        <masahiroy@...nel.org>, <michal.lkml@...kovi.net>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>
Subject: [PATCH 0/2] Kbuild: lto: add make version checking

LTO with MODVERSION will fail in generating correct CRC because
the makefile rule doesn't work for make with version 3.8X.

Refer to [1]:
> When building modules(CONFIG_...=m), I found some of module versions
> are incorrect and set to 0.
> This can be found in build log for first clean build which shows

> WARNING: EXPORT symbol "XXXX" [drivers/XXX/XXX.ko] version generation failed,
> symbol will not be versioned.

> But in second build(incremental build), the WARNING disappeared and the
> module version becomes valid CRC and make someone who want to change
> modules without updating kernel image can't insert their modules.

> The problematic code is
> + $(foreach n, $(filter-out FORCE,$^),        \
> +   $(if $(wildcard $(n).symversions),      \
> +     ; cat $(n).symversions >> $@...mversions))

The issue fixed when make version upgrading to 4.2.

Thus we need to check make version during selecting on LTO Kconfig.
The MAKE_VERSION_INT means MAKE_VERSION in canonical digits integer and
implemnted by imitating CLANG_VERSION.

[1] https://lore.kernel.org/lkml/20210616080252.32046-1-lecopzer.chen@mediatek.com/
Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>

Lecopzer Chen (2):
  Kbuild: lto: add make-version macros
  Kbuild: lto: add make version checking

 Makefile                |  2 +-
 arch/Kconfig            |  1 +
 init/Kconfig            |  4 ++++
 scripts/Kconfig.include |  3 +++
 scripts/make-version.sh | 13 +++++++++++++
 5 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100755 scripts/make-version.sh

-- 
2.18.0