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* [PATCH] module: set ksymtab/kcrctab* section addresses to 0x0
@ 2015-01-26 20:45 Rabin Vincent
  2015-01-26 23:50 ` Rusty Russell
  0 siblings, 1 reply; 3+ messages in thread
From: Rabin Vincent @ 2015-01-26 20:45 UTC (permalink / raw)
  To: Rusty Russell; +Cc: linux-kernel, Rabin Vincent

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.

 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@axis.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


^ permalink raw reply related	[flat|nested] 3+ messages in thread
* Re: [PATCH] module: set ksymtab/kcrctab* section addresses to 0x0
  2015-01-26 20:45 [PATCH] module: set ksymtab/kcrctab* section addresses to 0x0 Rabin Vincent
@ 2015-01-26 23:50 ` Rusty Russell
  2015-01-27 19:52   ` Rabin Vincent
  0 siblings, 1 reply; 3+ messages in thread
From: Rusty Russell @ 2015-01-26 23:50 UTC (permalink / raw)
  To: Rabin Vincent; +Cc: linux-kernel, Rabin Vincent

Rabin Vincent <rabin.vincent@axis.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@axis.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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^ permalink raw reply	[flat|nested] 3+ messages in thread
* Re: [PATCH] module: set ksymtab/kcrctab* section addresses to 0x0
  2015-01-26 23:50 ` Rusty Russell
@ 2015-01-27 19:52   ` Rabin Vincent
  0 siblings, 0 replies; 3+ messages in thread
From: Rabin Vincent @ 2015-01-27 19:52 UTC (permalink / raw)
  To: Rusty Russell; +Cc: linux-kernel

On Tue, Jan 27, 2015 at 10:20:32AM +1030, Rusty Russell wrote:
> Rabin Vincent <rabin.vincent@axis.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.
> 
>         You're right, we don't use sh_addr.  This should be safe, I've
> applied it for the next merge window.

Thanks.

> 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.

I've no opinion on -stable.  This method of debugging kernel modules is
described in for example LDD3, so it would be nice if it worked in all
cases, but I guess most people won't be affected even if they use it
since it only affects modules with exported symbols.

^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2015-01-27 19:52 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2015-01-26 20:45 [PATCH] module: set ksymtab/kcrctab* section addresses to 0x0 Rabin Vincent
2015-01-26 23:50 ` Rusty Russell
2015-01-27 19:52   ` Rabin Vincent

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