Re: vsnprintf broken

[Johannes Hofmann <Johannes.Hofmann@xxxxxx>]

Simon 'corecode' Schubert <corecode@fs.ei.tum.de> wrote:
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> Simon 'corecode' Schubert wrote:
>> Johannes Hofmann wrote:
>>> Hello,
>>>
>>> I see crashes with a string handling library on DragonFly.
>>> The problem can be reduced to the test program below. It crashes on
>>> DragonFly when compiled with "gcc -O2 -o foo foo.c". Without -O2 it 
>>> runs fine. No problems on Linux with or without -O2.
>>> Can anyone spot the problem? I think its related to the use of
>>> va_copy().
>> 
>> No, the problem is that gcc uses %ebx after a function call, which it is
>> not allowed to do:
> [snip]
>> Or does the ABI dictate that %ebx needs to be restored?  Seems that
>> linux/glibc doesn't clobber ebx.
> 
> okay, I am wrong here.  %ebx is supposed to be saved and is also being
> saved by vsnprinf.  gcc is good.
> 
> So this is actually a case of stack smashing.  Have fun finding the bug
> in vsnprintf or in your code :)

Will have :-). On FreeBSD-6.0 it works ok, so I think I will start from
there....

Cheers,
Johannes

> 
>> cheers
>>   simon
> 
> 
> 
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