linux-kernel - Re: [PATCH 1/6] POWERPC: use KSYM_NAME

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Message-ID: <20080123190742.GH12877@cvg>
Date:	Wed, 23 Jan 2008 22:07:42 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Paulo Marques <pmarques@...popie.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/6] POWERPC: use KSYM_NAME_LEN

[Paulo Marques - Wed, Jan 23, 2008 at 06:59:09PM +0000]
> Cyrill Gorcunov wrote:
>> [Paulo Marques - Wed, Jan 23, 2008 at 06:26:28PM +0000]
>>> Cyrill Gorcunov wrote:
>>>> [...]
>>>>  	case 's':
>>>> -		getstring(tmp, 64);
>>>> +		getstring(tmp, sizeof(tmp));
>>>>  		if (setjmp(bus_error_jmp) == 0) {
>>>>  			catch_memory_errors = 1;
>>>>  			sync();
>> just after that poin in the original code a call to kallsyms_lookup_name
>> is done - so i think it could be an overflow (of course it depends
>> on what *exactly* the name is being searched, and Paulo - I didn't
>> managed to get *the whole picture* of what is going on in this
>> code - so the thoughs were like: kallsyms_lookup_name could find
>> a quite long name restricted by KSYM_NAME_LEN (dunno how it could
>> happens - due to buggy code or due to memory corruption outside,
>> it does not matter - the only matter - it *could* find that long
>> name).
>
> Ah, now I understand your confusion: kallsyms_lookup_name doesn't fill the 
> name. It searches the name and returns the address. It is the _caller_ that 
> fills the name, not kallsyms_lookup_name.
>
> It is used for stuff like: "give me the address of function foo":
> addr = kallsyms_lookup_name("foo");
>

oh my, how could I oversight that... damn!!! my bad!!!

>> Anyway - it's just an attempt ;) we always could drop it far-far away ;)
>
> I think that using KSYM_NAME_LEN would be a nice cleanup for xmon, but it 
> is for the powerpc guys to decide if they want to do it. I just wanted to 
> point the change in behavior so that it wouldn't go unnoticed.

thanks, it's really important

>
> For all we know, the stack may at that point be close to full and an extra 
> 64 bytes may tip it over the edge.
>

oops, thanks for pointing out

>>> This also introduces a change in behavior. It is still a nice cleanup, 
>>> though. So, if the powerpc people feel they can spare an extra 64 bytes 
>>> of stack here, I guess it's ok.
>> Thanks a lot for review Paulo!
>
> No problem. I always keep an eye out for kallsyms related stuff.

;)

>
> -- 
> Paulo Marques - www.grupopie.com
>
> "There cannot be a crisis today; my schedule is already full."
>
		- Cyrill -
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