Date: Thu, 9 Sep 1999 13:28:34 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
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To: aperes <ajps AT mail DOT telepac DOT pt>
cc: djgpp AT delorie DOT com
Subject: Re: SIGSEGV
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On Thu, 9 Sep 1999, aperes wrote:

> Why this program receives SIGSEGV?
[snip]
>   size_of_file = filelength(sound_handle);
> tmp_ptr = s_ptr = 
> (unsigned char*)__dpmi_allocate_dos_memory((size_of_file+15) >> 4,
> selector);     OK
> 
>  
>   do {          OK
>      _dos_read(sound_handle, temp_ptr, 0x4000, &bytes_read);

You cannot read a file into a buffer (here tmp_ptr) that is allocated in 
conventional memory.  _dos_read (and most other DJGPP library functions) 
only operate on buffers in extended memory.

In fact, your cast of the value returned by __dpmi_allocate_dos_memory to 
a pointer is something that will never work: __dpmi_allocate_dos_memory
returns a real-mode segment of an allocated conventional memory buffer.  
In contrast, C pointers are offsets relative to a protected-mode 
selector.  You cannot mix them.

What you need to do is to read the sound data into a normal buffer, e.g. 
allocated by a call to malloc, and then move it into the conventional 
memory using dosmemput.  See section 18.4 of the FAQ for more details.