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Message-ID:	<416646E3.1090000@eik.bme.hu>
Date:	Fri, 08 Oct 2004 09:50:59 +0200
From:	solyom <solyom AT eik DOT bme DOT hu>
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To:	djgpp AT delorie DOT com
Subject:	Re: Free() crash my program!
References:	<D7Kdnfji89etsfvcRVn-qA AT comcast DOT com> <41663c2c$0$179$cc7c7865 AT news DOT luth DOT se>
In-Reply-To:	<41663c2c$0$179$cc7c7865@news.luth.se>
Reply-To:	djgpp AT delorie DOT com

Martin Str|mberg wrote:

>JC <jessechao AT comcast DOT net> wrote:
>  
>
>>I used djgpp to develop a simple program, using dosmemget(),
>>to dump some DOS memory. The code is like following:
>>    
>>
>
>  
>
>>    p = (UINT8 *)malloc(len+1);
>>    if (p == NULL)
>>    {
>>        ...
>>    }
>>    dosmemget(addr, len, p);
>>    /* Code to printf the contents in *p */
>> ...
>> free(p);
>>    
>>
>
>  
>
>>The code compiled & ran fine. But when the code execute
>>the free(). The code crashed and got SIGSEG error:
>>    
>>
>
>  
>
>>    Exiting due to signal SIGSEGV
>>    General Protection Fault at eip=00006ac4
>>    
>>
>
>  
>
>>Anyone can help me on this?
>>    
>>
>
>1. Remove that UINT8 * cast.
>
>2. If that doesn't help you need to give more information, because
>malloc() and free() work fine so it must be something else.
>
>
>Right,
>
>						MartinS
>
>  
>
Removing the cast doesn't make any difference for free(). The cast 
simply says that p should be considered as a pointer to UINT8 instead of 
o void. Free may crash if there is a memory overwrite somewhere after 
the comment

Code to printf the contents in *p

When the memory gets corrupted free() may fail.

Andras

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