Subject: Re: [PATCH] powerpc: module: fix TOC symbol CRC

From: Anton Blanchard <[email-masked]>
Date: Thu, 19 Jun 2014 09:44:04 +1000

Hi Laurent,

> 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).

Adding Rusty since he maintains the module loader code.

Anton

> Signed-off-by: Laurent Dufour <[email-masked]>
> Cc: Anton Blanchard <[email-masked]>
> ---
>  arch/powerpc/kernel/module_64.c |    9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/module_64.c
> b/arch/powerpc/kernel/module_64.c index 077d2ce..a80c933 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -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.) */