linux-kernel - Re: [patch] modpost problem when symbols move from one module to another

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Message-ID: <20071018114626.GA19539@uranus.ravnborg.org>
Date:	Thu, 18 Oct 2007 13:46:26 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Trent Piepho <xyzzy@...akeasy.org>
Cc:	Linux Kernel Mailing list <linux-kernel@...r.kernel.org>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	kbuild-devel@...ts.sourceforge.net
Subject: Re: [patch] modpost problem when symbols move from one module to another

On Thu, Oct 11, 2007 at 04:40:10PM -0700, Trent Piepho wrote:
> The v4l-dvb tree recently renamed a module and this caused some problems
> with modpost creating incorrect module dependencies.  This patch fixes that
> problem.  It should be explained thoroughly in the patch description.
> modpost: Fix problem with out of date Module.symvers
> 
> When part of build an external module tree, modpost first reads in the
> kernel's and then the external tree's Module.symvers files.  From these files
> it establishes a symbol => module mapping.  When it later reads in each module
> built and processes the symbols it finds, it discovers the symbol=>module
> mapping from Module.symvers and leaves it as it is.
> 
> The problem comes with a module has been re-named or a symbol has moved from
> one module to another, since the Module.symvers file was generated.  modpost
> does not update the symbol=>module mapping when it finds the new location of
> the symbol when scanning the newly built modules.  This results in the module
> containing incorrect dependency information and the new Module.symvers file
> written by modpost will also contain the incorrect mappings, perpetuating the
> problem to the next build, and so on.
> 
> When building the out of kernel development tree for kernel subsystem, like
> v4l-dvb or ALSA, deleting the external Module.symvers file before building
> (which the kernel build system doesn't do and shouldn't be necessary anyway),
> won't fix the problem.  modpost still reads the kernel's Module.symvers, and
> since we a building a kernel subsystem, it will define the same symbols as the
> external modules.
> 
> Signed-off-by: Trent Piepho <xyzzy@...akeasy.org>

Thanks - applied,

	Sam
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