linux-kernel - Re: Modules: Handle symbols that have a zero value

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Message-ID: <Pine.LNX.4.64.0711211300590.3625@schroedinger.engr.sgi.com>
Date:	Wed, 21 Nov 2007 13:02:09 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: Modules: Handle symbols that have a zero value

On Wed, 21 Nov 2007, Mathieu Desnoyers wrote:

> return -ENOENT;
> 
> directly ?
> 
> (ERR_PTR() in linux/err.h is a simple cast from long to void*).

Right and there is also IS_ERR_VALUE. Thanks for the feedback. New 
version:


Modules: Handle symbols that have a zero value

The module subsystem cannot handle symbols that are zero. If symbols are
present that have a zero value then the module resolver prints out
a message that these symbols are unresolved.

Use ERR_PTR to return an error code instead of 0. This is a bit awkward
since the addresses are handled as unsigned longs. So we need to convert
them everywhere.

Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc: Kay Sievers <kay.sievers@...y.org
Signed-off-by: Christoph Lameter <clameter@....com>

---
 kernel/module.c |   17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

Index: linux-2.6/kernel/module.c
===================================================================
--- linux-2.6.orig/kernel/module.c	2007-11-21 12:58:33.095608448 -0800
+++ linux-2.6/kernel/module.c	2007-11-21 13:00:30.199108674 -0800
@@ -285,7 +285,7 @@ static unsigned long __find_symbol(const
 		}
 	}
 	DEBUGP("Failed to find symbol %s\n", name);
-	return 0;
+	return -ENOENT;
 }
 
 /* Search for module by name: must hold module_mutex. */
@@ -756,7 +756,7 @@ void __symbol_put(const char *symbol)
 	const unsigned long *crc;
 
 	preempt_disable();
-	if (!__find_symbol(symbol, &owner, &crc, 1))
+	if (IS_ERR_VALUE(__find_symbol(symbol, &owner, &crc, 1)))
 		BUG();
 	module_put(owner);
 	preempt_enable();
@@ -902,7 +902,8 @@ static inline int check_modstruct_versio
 	const unsigned long *crc;
 	struct module *owner;
 
-	if (!__find_symbol("struct_module", &owner, &crc, 1))
+	if (IS_ERR_VALUE(__find_symbol("struct_module",
+						&owner, &crc, 1)))
 		BUG();
 	return check_version(sechdrs, versindex, "struct_module", mod,
 			     crc);
@@ -955,7 +956,7 @@ 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 = -EINVAL;
 	}
 	return ret;
 }
@@ -1348,14 +1349,16 @@ 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 (!IS_ERR_VALUE(__find_symbol(mod->syms[i].name,
+							&owner, &crc, 1))) {
 			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 (!IS_ERR_VALUE(__find_symbol(mod->gpl_syms[i].name,
+							&owner, &crc, 1))) {
 			name = mod->gpl_syms[i].name;
 			ret = -ENOEXEC;
 			goto dup;
@@ -1405,7 +1408,7 @@ static int simplify_symbols(Elf_Shdr *se
 					   strtab + sym[i].st_name, mod);
 
 			/* Ok if resolved.  */
-			if (sym[i].st_value != 0)
+			if (!IS_ERR_VALUE(sym[i].st_value))
 				break;
 			/* Ok if weak.  */
 			if (ELF_ST_BIND(sym[i].st_info) == STB_WEAK)
-
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