linux-kernel - Re: [PATCH] module.c: add missing ifdefs for CONFIG_UNUSED

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Message-Id: <20070913160047.159e5e3d.akpm@linux-foundation.org>
Date:	Thu, 13 Sep 2007 16:00:47 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] module.c: add missing ifdefs for CONFIG_UNUSED_SYMBOLS

On Thu, 13 Sep 2007 23:30:33 +0100
Denys Vlasenko <vda.linux@...glemail.com> wrote:

> module.c and module.h conatains code for finding
> exported symbols which are declared with EXPORT_UNUSED_SYMBOL,
> and this code is compiled in even if CONFIG_UNUSED_SYMBOLS is not set
> and thus there can be no EXPORT_UNUSED_SYMBOLs in modules anyway
> (because EXPORT_UNUSED_SYMBOL(x) are compiled out to nothing then).
> 
> This patch adds required #ifdefs.
> 
> This shrinks module.o and each *.ko file.
> 
> Patch also regroups some struct module members so
> that on 64 bit CPUs we are not wasting 32 bits on padding here:
> 
>         const struct kernel_symbol *unused_syms;
>         unsigned int num_unused_syms;
>         const unsigned long *unused_crcs;
> 
> It groups counters and pointers separately.
> 
> Patch makes small edit to help text of CONFIG_MODULE_UNLOAD -
> it explicitly says that without that option, kernel
> will be also faster, not only "smaller and simpler".
> When I realized how much churn is going on under the hood
> in order to make module unloading possible, I felt that
> users are not informed well enough about it in the help text.
> 
> And finally, structure members which hold length of module
> code (four such members there) and count of symbols
> are converted from longs to ints.
> 
> We cannot possibly have a module where 32 bits won't
> be enough to hold such counts.
> 
> For one, module loading checks module size for sanity
> before loading, so such insanely big module will fail
> that test first.
> 
> In short, patch makes trivial changes which are "obviously correct"
> (famous last words).

The intent seems reasonable.  Would have preferred separate patches for the
separate things though..

This:

akpm:/usr/src/25> grep '^+#' patches/modulec-add-missing-ifdefs-for-config_unused_symbols.patch                                                                 +#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif
+#ifdef CONFIG_UNUSED_SYMBOLS
+#endif

is a bit of a maintenance problem though.  Can you think of a way in whcih
we can cut down on that?

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