linux-kernel - Re: [PATCH v2] module: check for exit sections in layout_sections() instead of module_init

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Date:   Fri, 14 May 2021 18:09:30 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] module: check for exit sections in layout_sections()
 instead of module_init_section()

On Fri, May 14, 2021 at 06:09:04PM +0200, Jessica Yu wrote:
> Previously, when CONFIG_MODULE_UNLOAD=n, the module loader just does not
> attempt to load exit sections since it never expects that any code in those
> sections will ever execute. However, dynamic code patching (alternatives,
> jump_label and static_call) can have sites in __exit code, even if __exit is
> never executed. Therefore __exit must be present at runtime, at least for as
> long as __init code is.
> 
> Commit 33121347fb1c ("module: treat exit sections the same as init
> sections when !CONFIG_MODULE_UNLOAD") solves the requirements of
> jump_labels and static_calls by putting the exit sections in the init
> region of the module so that they are at least present at init, and
> discarded afterwards. It does this by including a check for exit
> sections in module_init_section(), so that it also returns true for exit
> sections, and the module loader will automatically sort them in the init
> region of the module.
> 
> However, the solution there was not completely arch-independent. ARM is
> a special case where it supplies its own module_{init, exit}_section()
> functions. Instead of pushing the exit section checks into
> module_init_section(), just implement the exit section check in
> layout_sections(), so that we don't have to touch arch-dependent code.
> 
> Fixes: 33121347fb1c ("module: treat exit sections the same as init sections when !CONFIG_MODULE_UNLOAD")
> Signed-off-by: Jessica Yu <jeyu@...nel.org>

Looks good!

Reviewed-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

Thanks!

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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