linux-kernel - Re: [rfc 45/45] Modules: Hack to handle symbols that have a zero value

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Message-ID: <20071120022007.GA16899@Krystal>
Date:	Mon, 19 Nov 2007 21:20:07 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	clameter@....com
Cc:	ak@...e.de, akpm@...ux-foundation.org, travis@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc 45/45] Modules: Hack to handle symbols that have a zero
	value

* clameter@....com (clameter@....com) wrote:
> The module subsystem cannot handle symbols that are zero. It prints out
> a message that these symbols are unresolved. Define a constant
> 
> UNRESOLVED
> 
> that is used to hold the value used for unresolved symbols. Set it to 1
> (its hopefully unlikely that a symbol will have the value 1). This is necessary
> so that the pda variable which is placed at offset 0 of the per cpu
> segment is handled correctly.
> 

Wouldn't it be better to simply return a standard ERR_PTR(-ENO....) ?

> Signed-off-by: Christoph Lameter <clameter@....com>
> 
> ---
>  kernel/module.c |   15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> Index: linux-2.6/kernel/module.c
> ===================================================================
> --- linux-2.6.orig/kernel/module.c	2007-11-19 17:08:40.563625526 -0800
> +++ linux-2.6/kernel/module.c	2007-11-19 17:08:40.855625732 -0800
> @@ -62,6 +62,7 @@ extern int module_sysfs_initialized;
>  /* If this is set, the section belongs in the init part of the module */
>  #define INIT_OFFSET_MASK (1UL << (BITS_PER_LONG-1))
>  
> +#define UNRESOLVED 1
>  /* List of modules, protected by module_mutex or preempt_disable
>   * (add/delete uses stop_machine). */
>  static DEFINE_MUTEX(module_mutex);
> @@ -285,7 +286,7 @@ static unsigned long __find_symbol(const
>  		}
>  	}
>  	DEBUGP("Failed to find symbol %s\n", name);
> -	return 0;
> +	return UNRESOLVED;
>  }
>  
>  /* Search for module by name: must hold module_mutex. */
> @@ -755,7 +756,7 @@ void __symbol_put(const char *symbol)
>  	const unsigned long *crc;
>  
>  	preempt_disable();
> -	if (!__find_symbol(symbol, &owner, &crc, 1))
> +	if (__find_symbol(symbol, &owner, &crc, 1) == UNRESOLVED)
>  		BUG();
>  	module_put(owner);
>  	preempt_enable();
> @@ -899,7 +900,7 @@ static inline int check_modstruct_versio
>  	const unsigned long *crc;
>  	struct module *owner;
>  
> -	if (!__find_symbol("struct_module", &owner, &crc, 1))
> +	if (__find_symbol("struct_module", &owner, &crc, 1) == UNRESOLVED)
>  		BUG();
>  	return check_version(sechdrs, versindex, "struct_module", mod,
>  			     crc);
> @@ -952,7 +953,7 @@ static unsigned long resolve_symbol(Elf_
>  		/* use_module can fail due to OOM, or module unloading */
>  		if (!check_version(sechdrs, versindex, name, mod, crc) ||
>  		    !use_module(mod, owner))
> -			ret = 0;
> +			ret = UNRESOLVED;
>  	}
>  	return ret;
>  }
> @@ -1345,14 +1346,14 @@ static int verify_export_symbols(struct 
>  	const unsigned long *crc;
>  
>  	for (i = 0; i < mod->num_syms; i++)
> -		if (__find_symbol(mod->syms[i].name, &owner, &crc, 1)) {
> +		if (__find_symbol(mod->syms[i].name, &owner, &crc, 1) != UNRESOLVED) {
>  			name = mod->syms[i].name;
>  			ret = -ENOEXEC;
>  			goto dup;
>  		}
>  
>  	for (i = 0; i < mod->num_gpl_syms; i++)
> -		if (__find_symbol(mod->gpl_syms[i].name, &owner, &crc, 1)) {
> +		if (__find_symbol(mod->gpl_syms[i].name, &owner, &crc, 1)!= UNRESOLVED) {
>  			name = mod->gpl_syms[i].name;
>  			ret = -ENOEXEC;
>  			goto dup;
> @@ -1402,7 +1403,7 @@ static int simplify_symbols(Elf_Shdr *se
>  					   strtab + sym[i].st_name, mod);
>  
>  			/* Ok if resolved.  */
> -			if (sym[i].st_value != 0)
> +			if (sym[i].st_value != UNRESOLVED)
>  				break;
>  			/* Ok if weak.  */
>  			if (ELF_ST_BIND(sym[i].st_info) == STB_WEAK)
> 
> -- 

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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