linux-kernel - Re: [PATCH] allow placing exception table in .rodata (and do so on x86)

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Message-ID: <BANLkTikJN92ogUfxAc+SgzvX1Q8r48ughw@mail.gmail.com>
Date:	Thu, 28 Apr 2011 13:47:33 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>, mingo@...e.hu,
	tglx@...utronix.de, linux-arch@...r.kernel.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	hpa@...or.com
Subject: Re: [PATCH] allow placing exception table in .rodata (and do so on x86)

On Thu, Apr 28, 2011 at 13:40, Jan Beulich <JBeulich@...ell.com> wrote:
>>>> On 28.04.11 at 12:43, Heiko Carstens <heiko.carstens@...ibm.com> wrote:
>> On Wed, Apr 27, 2011 at 04:36:04PM +0100, Jan Beulich wrote:
>>> This is since the table is really a set of pointers, i.e. misplaced in
>>> .text.
>>>
>>> Quite likely other architectures would want to follow.
>>>
>>> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
>>>
>>
>> [...]
>>
>>> --- 2.6.39-rc5/include/asm-generic/vmlinux.lds.h
>>> +++ 2.6.39-rc5-extable-in-rodata/include/asm-generic/vmlinux.lds.h
>>> @@ -226,6 +226,7 @@
>>>              *(.rodata1)                                             \
>>>      }                                                               \
>>>                                                                      \
>>> +    EXCEPTION_TABLE_RO                                              \
>>
>> That's odd. The kernel actually writes to it (sort_main_extable()), so
>> it shouldn't be in the ro data section, but the data section.
>
> This area does get written, but only at boot time, before read-only
> data gets set to r/o (on x86 at least). With this in mind, it's better
> to place it in .rodata, as that way run-time protection will be in place
> (and I think you agree that it was misplaced in .text in any case).

Which means it may be in ROM (which is really read-only) on some embedded
devices, so it cannot be sorted?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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