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

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Message-ID: <20091103132935.GA12841@linux-sh.org>
Date:	Tue, 3 Nov 2009 22:29:36 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Alan Jenkins <alan-jenkins@...fmail.co.uk>, 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 03, 2009 at 07:30:20AM -0500, Mike Frysinger wrote:
> On Tue, Nov 3, 2009 at 07:16, Alan Jenkins wrote:
> > Mike Frysinger wrote:
> >> 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 ...
> >
> > I don't think that's possible.
> >
> > ?? #define VMLINUX_SYMBOL(_sym_) _##_sym_
> >
> > I don't know any "unstringify" operation. ??So I can't convert a string value
> > of CONFIG_SYMBOL_PREFIX to the unquoted underscore we neeed for this macro.
> > ??The same applies for the SYM() macro I use.
> 
> let the build system do the unstringify operation.
> qstrip = $(strip $(subst ",,$(1)))
> CPPFLAGS_vmlinux.lds += -DVMLINUX_SYMBOL_PREFIX=$(call
> qstrip,CONFIG_SYMBOL_PREFIX)
> 
> > If we positively want to keep the generality, I guess I should put
> > MODULE_SYMBOL_PREFIX in a header file of it's own. ??The disadvantage is that
> > it makes it inaccessible to host programs again, like modpost (which
> > currently hardcodes the list of affected architectures in mk_elfconfig.c).
> 
> having it in the arch Kconfig removes any and all possible
> limitations, and it keeps the cruft out of the common init/Kconfig and
> in the arch-specific Kconfig, and avoids a dead symbol
> (HAVE_SYMBOL_PREFIX)

Having it in the Kconfig also makes it a nuisance for platforms that can
use -elf and -linux toolchains for the same tree for different platforms.
It would be nice to have this supported in such a way that we can just
set a flag from the Makefile and have a compiler test that determines
whether it is necessary or not.
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