From: Ben Peddell <killer DOT lightspeed AT bigpond DOT com>
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Subject: Re: Bug 00314 -- div() still broken
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Date: Fri, 25 Apr 2003 22:00:22 +1000
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To: djgpp AT delorie DOT com
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Eric Rudd wrote:
> Ben Peddell wrote:
> 
>> Eric Rudd wrote:
>>
>>> I think I had some problem with -fomit-frame-pointer, but I'm still 
>>> investigating.
>>
>>
>> Things are being pushed wrong.
>> edi is supposed to hold the address of the div_t structure, yet is has 
>> 0x28 (40) in it. eax and ebx are supposed to have 40 in them, yet they 
>> have -3 in them.
>> div() wants the stack to look like:
>>     16(%ebp): divisor
>>     12(%ebp): numerator
>>      8(%ebp): &return
>> But it appears to look like:
>>     16(%ebp): something between -2 and +2
>>     12(%ebp): divisor
>>      8(%ebp): numerator
>>
>> There in lies the problem.
> 
> 
> This confirms my suspicion that there is a problem with 
> -fomit-frame-pointer.  I thought that routines in libc.a could be called 
> from a program compiled either with or without -fomit-frame-pointer, but 
> I found that I could call the existing div.o in libc.a only if I didn't 
> use -fomit-frame-pointer.  Hmm...
> 
> -Eric Rudd
> rudd AT cyberoptics DOT com
> 

Obviously, some sort of optimization puts the div_t structure in 
%edx:%eax instead of 16(%ebp). It would be a good optimization if it 
didn't break the libraries.