linux-kernel - Re: [RFC -next] linux/linkage.h: fix symbol prefix handling

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Message-ID: <514044FD.2040502@imgtec.com>
Date:	Wed, 13 Mar 2013 09:21:01 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Sam Ravnborg <sam@...nborg.org>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Al Viro <viro@...iv.linux.org.uk>,
	Michal Marek <mmarek@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Jean Delvare <khali@...ux-fr.org>,
	<linux-kbuild@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	"Mike Frysinger" <vapier@...too.org>,
	<uclinux-dist-devel@...ckfin.uclinux.org>,
	<linux-next@...r.kernel.org>
Subject: Re: [RFC -next] linux/linkage.h: fix symbol prefix handling

Hi Sam,

On 13/03/13 06:31, Sam Ravnborg wrote:
>>  /* Some toolchains use a `_' prefix for all user symbols. */
>> -#ifdef CONFIG_SYMBOL_PREFIX
>> -#define MODULE_SYMBOL_PREFIX CONFIG_SYMBOL_PREFIX
>> +#ifdef CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX
>> +#define __VMLINUX_SYMBOL(x) _##x
>> +#define __VMLINUX_SYMBOL_STR(x) "_" #x
>> +#define VMLINUX_SYMBOL_PREFIX_STR "_"
>>  #else
>> -#define MODULE_SYMBOL_PREFIX ""
>> +#define __VMLINUX_SYMBOL(x) x
>> +#define __VMLINUX_SYMBOL_STR(x) #x
>> +#define VMLINUX_SYMBOL_PREFIX_STR ""
>>  #endif
> 
> We know the prefix is an underscore. No benefits from defining
> VMLINUX_SYMBOL_PREFIX_STR.

scripts/modpost.c uses the actual prefix string though:

>	if (memcmp(symname, MODULE_SYMBOL_PREFIX,
>		   strlen(MODULE_SYMBOL_PREFIX)) == 0) {
>		mod->unres =
>		  alloc_symbol(symname +
>		               strlen(MODULE_SYMBOL_PREFIX),
> 		               ELF_ST_BIND(sym->st_info) == STB_WEAK,
> 		               mod->unres);

See also my "module: fix symbol versioning with symbol prefixes" patch
for an additional use in modpost.

Having a MODULE_SYMBOL_PREFIX/VMLINUX_SYMBOL_PREFIX_STR seems like the
simplest way to keep this code clean and readable without special cases.

Cheers
James

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