Re: [PATCH 04/10] module: make MODULE_SYMBOL_PREFIX into a CONFIGoption

From: Alan Jenkins
Date: Tue Nov 03 2009 - 07:16:34 EST

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/ and into asm-generic/ ...

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

+ bool
+ help
+ Some arch toolchains use a `_' prefix for all user symbols.
+ This option will be taken into account when loading modules.
+ 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

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. Currently it assumes the prefix is a single underscore:

#define __SYM(sym) _##sym
#define __SYM(sym) sym

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).

Personally I favour "look, a small cleanup!" against "who knows what crazy things the next toolchain will do". Of course I'm open to being outvoted by experience :).

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