linux-kernel - Re: [PATCH 04/10] module: make MODULE_SYMBOL

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Message-ID: <8bd0f97a0911030219y685a1dafy2a8e066d7132ac45@mail.gmail.com>
Date:	Tue, 3 Nov 2009 05:19:19 -0500
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
Cc:	greg@...ah.com, linux-kbuild@...r.kernel.org, carmelo73@...il.com,
	linux-kernel@...r.kernel.org, rusty@...tcorp.com.au
Subject: Re: [PATCH 04/10] module: make MODULE_SYMBOL_PREFIX into a CONFIG 
	option

On Tue, Nov 3, 2009 at 05:06, Alan Jenkins wrote:
> The next commit will require the use of MODULE_SYMBOL_PREFIX in
> .tmp_exports-asm.S.  Currently it is mixed in with C structure
> definitions in "asm/module.h".  Move the definition of this arch option
> into Kconfig, so it can be easily accessed by any code.
>
> This also lets modpost.c use the same definition.  Previously modpost
> relied on a hardcoded list of architectures in mk_elfconfig.c.

this should also let us push VMLINUX_SYMBOL() out of
arch/*/kernel/vmlinux.lds.S and into asm-generic/vmlinux.lds.h ...

> A build test for blackfin, one of the two MODULE_SYMBOL_PREFIX archs,
> showed the generated code was unchanged.  vmlinux was identical save
> for build ids, and an apparently randomized suffix on a single "__key"
> symbol in the kallsyms data).

when you get localized (static) namespace collisions, the linker
automatically does that

> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1171,6 +1171,17 @@ config MODULE_SRCVERSION_ALL
>
>  endif # MODULES
>
> +config HAVE_SYMBOL_PREFIX
> +       bool
> +       help
> +         Some arch toolchains use a `_' prefix for all user symbols.
> +         This option will be taken into account when loading modules.
> +
> +config SYMBOL_PREFIX
> +       string
> +       default "_" if HAVE_SYMBOL_PREFIX
> +       default ""

in practice, the symbol prefix is an underscore.  but there is no
technical limitation here -- the toolchain could use whatever prefix
they wanted

so if the Kconfig option was pushed to arch/*/Kconfig, we could drop
HAVE_SYMBOL_PREFIX and let the arch declare the exact SYMBOL_PREFIX
value itself
-mike
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