linux-kernel - Re: [PATCH] module: set ksymtab/kcrctab* section addresses to 0x0

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Date:	Tue, 27 Jan 2015 10:20:32 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Rabin Vincent <rabin.vincent@...s.com>
Cc:	linux-kernel@...r.kernel.org, Rabin Vincent <rabinv@...s.com>
Subject: Re: [PATCH] module: set ksymtab/kcrctab* section addresses to 0x0

Rabin Vincent <rabin.vincent@...s.com> writes:
> These __ksymtab*/__kcrctab* sections currently have non-zero addresses.
> Non-zero section addresses in a relocatable ELF confuse GDB and it ends
> up not relocating all symbols when add-symbol-file is used on modules
> which have exports.  The kernel's module loader does not care about
> these addresses, so let's just set them to zero.

Hi Rabin,

        You're right, we don't use sh_addr.  This should be safe, I've
applied it for the next merge window.

AFAICT this would have always been a problem; wonder if it should be
CC:stable?  I don't use gdb on modules so haven't got a good feel for
how many people this would be hurting.

Thanks,
Rusty.

>  Before:
>
>   $ readelf -S lib/notifier-error-inject.ko   | grep 'Name\| __ksymtab_gpl'
>     [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
>     [ 8] __ksymtab_gpl     PROGBITS        0000000c 0001b4 000010 00   A  0   0  4
>
>   (gdb) add-symbol-file lib/notifier-error-inject.ko 0x500000 -s .bss 0x700000
>   add symbol table from file "lib/notifier-error-inject.ko" at
>      .text_addr = 0x500000
>      .bss_addr = 0x700000
>   (gdb) p &notifier_err_inject_dir
>   $3 = (struct dentry **) 0x0
>
>  After:
>
>   $ readelf -S lib/notifier-error-inject.ko   | grep 'Name\| __ksymtab_gpl'
>     [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
>     [ 8] __ksymtab_gpl     PROGBITS        00000000 0001b4 000010 00   A  0   0  4
>
>   (gdb) add-symbol-file lib/notifier-error-inject.ko 0x500000 -s .bss 0x700000
>   add symbol table from file "lib/notifier-error-inject.ko" at
>      .text_addr = 0x500000
>      .bss_addr = 0x700000
>   (gdb) p &notifier_err_inject_dir
>   $3 = (struct dentry **) 0x700000
>
> Signed-off-by: Rabin Vincent <rabin.vincent@...s.com>
> ---
>  scripts/module-common.lds |   20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/scripts/module-common.lds b/scripts/module-common.lds
> index 0865b3e..bec15f9 100644
> --- a/scripts/module-common.lds
> +++ b/scripts/module-common.lds
> @@ -6,14 +6,14 @@
>  SECTIONS {
>  	/DISCARD/ : { *(.discard) }
>  
> -	__ksymtab		: { *(SORT(___ksymtab+*)) }
> -	__ksymtab_gpl		: { *(SORT(___ksymtab_gpl+*)) }
> -	__ksymtab_unused	: { *(SORT(___ksymtab_unused+*)) }
> -	__ksymtab_unused_gpl	: { *(SORT(___ksymtab_unused_gpl+*)) }
> -	__ksymtab_gpl_future	: { *(SORT(___ksymtab_gpl_future+*)) }
> -	__kcrctab		: { *(SORT(___kcrctab+*)) }
> -	__kcrctab_gpl		: { *(SORT(___kcrctab_gpl+*)) }
> -	__kcrctab_unused	: { *(SORT(___kcrctab_unused+*)) }
> -	__kcrctab_unused_gpl	: { *(SORT(___kcrctab_unused_gpl+*)) }
> -	__kcrctab_gpl_future	: { *(SORT(___kcrctab_gpl_future+*)) }
> +	__ksymtab		0 : { *(SORT(___ksymtab+*)) }
> +	__ksymtab_gpl		0 : { *(SORT(___ksymtab_gpl+*)) }
> +	__ksymtab_unused	0 : { *(SORT(___ksymtab_unused+*)) }
> +	__ksymtab_unused_gpl	0 : { *(SORT(___ksymtab_unused_gpl+*)) }
> +	__ksymtab_gpl_future	0 : { *(SORT(___ksymtab_gpl_future+*)) }
> +	__kcrctab		0 : { *(SORT(___kcrctab+*)) }
> +	__kcrctab_gpl		0 : { *(SORT(___kcrctab_gpl+*)) }
> +	__kcrctab_unused	0 : { *(SORT(___kcrctab_unused+*)) }
> +	__kcrctab_unused_gpl	0 : { *(SORT(___kcrctab_unused_gpl+*)) }
> +	__kcrctab_gpl_future	0 : { *(SORT(___kcrctab_gpl_future+*)) }
>  }
> -- 
> 1.7.10.4
>
> --
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