linux-kernel - Re: .version keeps being updated

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Message-Id: <20070109170550.AFEF460C343@tzec.mtu.ru>
Date:	Tue, 09 Jan 2007 20:05:49 +0300
From:	Andrey Borzenkov <arvidjaar@...l.ru>
To:	Jean Delvare <khali@...ux-fr.org>, linux-kernel@...r.kernel.org
Subject: Re: .version keeps being updated

Jean Delvare wrote:

> Hi all,
> 
> Since 2.6.20-rc1 or so, running "make" always builds a new kernel with
> an incremented version number, whether there has actually been any
> change done to the code or configuration or not. This increases the
> build time quite a bit.
> 
> I've tracked it down to include/linux/compile.h always being updated,
> and this is because .version is updated. I couldn't find what is
> causing .version to be updated each time though. Can anybody help
> there? Was this change made on purpose or is this a bug which we should
> fix? 

I have been bitten by this as well; I have tracked it down to defining
CONFIG_KALLSYMS:

define rule_vmlinux__
        :
        $(if $(CONFIG_KALLSYMS),,+$(call cmd,vmlinux_version))

quiet_cmd_vmlinux_version = GEN     .version
      cmd_vmlinux_version = set -e;                     \
        if [ ! -r .version ]; then                      \
          rm -f .version;                               \
          echo 1 >.version;                             \
        else                                            \
          mv .version .old_version;                     \
          expr 0$$(cat .old_version) + 1 >.version;     \
        fi;                                             \
        $(MAKE) $(build)=init


 Pondering about it, this may be a feature not a bug. Let's assume you have
changed a single function name anywhere - you need to rebuild kallsyms
(ergo vmlinux) for that.

OTOH I do not know if kallsyms include also symbols from modules; if no,
this is indeed a bug.

-andrey

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