powerpc: module: fix TOC symbol CRC

The commit 71ec7c55ed91 introduced the magic symbol ".TOC." for ELFv2 ABI. This symbol is built manually and has no CRC value computed. A zero value is put in the CRC section to avoid modpost complaining about a missing CRC. Unfortunately, this breaks the kernel module loading when the kernel is relocated (kdump case for instance) because of the relocation applied to the kcrctab values.

This patch compute a CRC value for the TOC symbol which will match the one compute by the kernel when it is relocated - aka '0 - relocate_start' done in maybe_relocated called by check_version (module.c).

Signed-off-by Laurent Dufour <[email protected]>

Cc Anton Blanchard <[email protected]>

---
 arch/powerpc/kernel/module_64.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

(quoted diff) +0 -0

b/arch/powerpc/kernel/module_64.c index 077d2ce..a80c933 100644

arch/powerpc/kernel/module_64.c +8 -1

@@ -315,8 +315,15 @@ static void dedotify_versions(struct
 modversion_info *vers, struct modversion_info *end;
 
 	for (end = (void *)vers + size; vers < end; vers++)
-		if (vers->name[0] == '.')
+		if (vers->name[0] == '.') {
 			memmove(vers->name, vers->name+1, strlen(vers->name));
+			/* The TOC symbol has no CRC computed. To avoid CRC
+			 * check failing, we must force it to the expected
+			 * value (see CRC check in module.c).
+			 */
+			if (!strcmp(vers->name, "TOC."))
+				vers->crc = -(unsigned long)reloc_start;
+		}
 }
 
 /* Undefined symbols which refer to .funcname, hack to funcname

(or .TOC.) */

Hi Laurent,

Quoted 7 lines

The commit 71ec7c55ed91 introduced the magic symbol ".TOC." for ELFv2 ABI. This symbol is built manually and has no CRC value computed. A zero value is put in the CRC section to avoid modpost complaining about a missing CRC. Unfortunately, this breaks the kernel module loading when the kernel is relocated (kdump case for instance) because of the relocation applied to the kcrctab values.

Quoted 4 lines

This patch compute a CRC value for the TOC symbol which will match the one compute by the kernel when it is relocated - aka '0 - relocate_start' done in maybe_relocated called by check_version (module.c).

Adding Rusty since he maintains the module loader code.

Quoted 14 lines · Anton Blanchard

Hi Laurent,

Quoted 11 lines

The commit 71ec7c55ed91 introduced the magic symbol ".TOC." for ELFv2 ABI. This symbol is built manually and has no CRC value computed. A zero value is put in the CRC section to avoid modpost complaining about a missing CRC. Unfortunately, this breaks the kernel module loading when the kernel is relocated (kdump case for instance) because of the relocation applied to the kcrctab values.

This patch compute a CRC value for the TOC symbol which will match the one compute by the kernel when it is relocated - aka '0 - relocate_start' done in maybe_relocated called by check_version (module.c).

Quoted 1 line

Adding Rusty since he maintains the module loader code.

This patch gives me:

arch/powerpc/kernel/module_64.c: In function 'dedotify_versions':
arch/powerpc/kernel/module_64.c:325:33: error: 'reloc_start' undeclared (first use in this function) arch/powerpc/kernel/module_64.c:325:33: note: each undeclared identifier is reported only once for each function it appears in

Cheers,
Ben.