linux-kernel - Re: [RFC] improve_stack: make stack dump output useful again

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Date:	Thu, 13 Mar 2014 18:20:10 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] improve_stack: make stack dump output useful again

On 03/13/2014 06:03 PM, Linus Torvalds wrote:
> On Thu, Mar 13, 2014 at 8:16 AM, Sasha Levin <sasha.levin@...cle.com> wrote:
>>
>> I've looked into doing it in the kernel, but it seems that it would require
>> a rather
>> large code addition just to deal with getting pretty line numbers.
>
> No no no. The *kernel* will never do line numbers, especially since
> only people who don't care about build performance compile with debug
> info, and even if you do do that, the kernel won't load it anyway.
>
> You missed the point.
>
> The kernel is going to *remove* all the hex numbers that your script
> relies on, because those hex numbers are completely worthless. They
> are worthless and annoying now, but they are *doubly* worthless if the
> kernel is compiled with base address randomization, since nobody will
> know what the hex numbers mean.
>
>> Unless I'm missing something big, is it really worth it?
>
> You're missing something big. The patch I sent earlier *is* going to
> happen one of these days, possible for 3.15. So your script that looks
> at hex numbers is broken.
>
> You need to look at the *symbol* number. In this output:
>
>       [<ffffffff810020c2>] do_one_initcall+0xc2/0x1e0
>
> that "ffffffff810020c2" is crap, and is going away. The address that
> is meaningful and valid is the "do_one_initcall+0xc2" part.
>
> *That* is the part you'd use to parse in user space.
>
> Try it today with the CONFIG_RANDOMIZE_BASE option to see. Using the
> hex number doesn't *work*.

Oh. doh. that was stupid of me.

I'll fix it up and re-send this patch.


Thanks,
Sasha

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