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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Fri, 25 Sep 2020 02:27:45 +0900
Message-ID: <CAK7LNAQauxa+R+hxuKrVk8g4o1GDdrdxY1dyJ58AMcoGMoByZg@mail.gmail.com>
Subject: Re: [PATCH v2] scripts/setlocalversion: make git describe output more reliable
To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc:     Randy Dunlap <rdunlap@infradead.org>,
        Brian Norris <briannorris@chromium.org>,
        Bhaskar Chowdhury <unixbhaskar@gmail.com>,
        Nico Schottelius <nico-linuxsetlocalversion@schottelius.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, Sep 17, 2020 at 3:56 PM Rasmus Villemoes
<linux@rasmusvillemoes.dk> wrote:
>
> When building for an embedded target using Yocto, we're sometimes
> observing that the version string that gets built into vmlinux (and
> thus what uname -a reports) differs from the path under /lib/modules/
> where modules get installed in the rootfs, but only in the length of
> the -gabc123def suffix. Hence modprobe always fails.
>
> The problem is that Yocto has the concept of "sstate" (shared state),
> which allows different developers/buildbots/etc. to share build
> artifacts, based on a hash of all the metadata that went into building
> that artifact - and that metadata includes all dependencies (e.g. the
> compiler used etc.). That normally works quite well; usually a clean
> build (without using any sstate cache) done by one developer ends up
> being binary identical to a build done on another host. However, one
> thing that can cause two developers to end up with different builds
> [and thus make one's vmlinux package incompatible with the other's
> kernel-dev package], which is not captured by the metadata hashing, is
> this `git describe`: The output of that can be affected by
>
> (1) git version: before 2.11 git defaulted to a minimum of 7, since
> 2.11 (git.git commit e6c587) the default is dynamic based on the
> number of objects in the repo
> (2) hence even if both run the same git version, the output can differ
> based on how many remotes are being tracked (or just lots of local
> development branches or plain old garbage)
> (3) and of course somebody could have a core.abbrev config setting in
> ~/.gitconfig
>
> So in order to avoid `uname -a` output relying on such random details
> of the build environment which are rather hard to ensure are
> consistent between developers and buildbots, make sure the abbreviated
> sha1 always consists of exactly 12 hex characters. That is consistent
> with the current rule for -stable patches, and is almost always enough
> to identify the head commit unambigously - in the few cases where it
> does not, the v5.4.3-00021- prefix would certainly nail it down.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
> v2: use 12 instead of 15, and ensure that the result does have exactly
> 12 hex chars.
>
>  scripts/setlocalversion | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)


Applied to linux-kbuild.
Thanks.

-- 
Best Regards
Masahiro Yamada