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

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Message-ID: <20210512160651.GP1336@shell.armlinux.org.uk>
Date:   Wed, 12 May 2021 17:06:51 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] module: check for exit sections in layout_sections()
 instead of module_init_section()

Hi,

On Wed, May 12, 2021 at 04:46:53PM +0200, Jessica Yu wrote:
> diff --git a/kernel/module.c b/kernel/module.c
> index 173a09175511..a5c9842371b1 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2430,6 +2430,9 @@ static void layout_sections(struct module *mod, struct load_info *info)
>  			if ((s->sh_flags & masks[m][0]) != masks[m][0]
>  			    || (s->sh_flags & masks[m][1])
>  			    || s->sh_entsize != ~0UL
> +#ifndef CONFIG_MODULE_UNLOAD
> +			    || module_exit_section(sname)
> +#endif
>  			    || module_init_section(sname))

How about a helper to make this a bit easier in both these places to
make the code more undertsandable? I think the great value comes from
the resulting change in the second hunk.

static bool module_evictable_section(const char *sname)
{
#ifndef CONFIG_MODULE_UNLOAD
	if (module_exit_section(sname))
		return true;
#endif
	return module_init_section(sname);
}

and then just use that above?

>  				continue;
>  			s->sh_entsize = get_offset(mod, &mod->core_layout.size, s, i);
> @@ -2463,7 +2466,11 @@ static void layout_sections(struct module *mod, struct load_info *info)
>  			if ((s->sh_flags & masks[m][0]) != masks[m][0]
>  			    || (s->sh_flags & masks[m][1])
>  			    || s->sh_entsize != ~0UL
> +#ifndef CONFIG_MODULE_UNLOAD
> +			    || (!module_init_section(sname) && !module_exit_section(sname)))
> +#else
>  			    || !module_init_section(sname))
> +#endif

I find this a tad confusing, and this is the reason for my suggestion
above. With that, this becomes:

			    || !module_evictable_section(sname))

which can be clearly seen is the opposite condition from the above
without doing mental logic gymnastics.

Thanks.

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