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From: countingtoten AT gmail DOT com
Newsgroups: comp.os.msdos.djgpp
Subject: Accessing absolute address above 1MB
Date: 7 Nov 2006 07:58:18 -0800
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I am trying to access the memory address 0x3FFF0000 in DOS using dpmi.
When executed, I receive the following seg fault:

Exiting due to signal SIGSEGV
General Protection Fault at eip=00003af6
eax=000001cf ebx=00000299 ecx=00000000 edx=3fff0000 esi=00000054
edi=0000ff70
ebp=0008ff08 esp=0008ff08
program=C:\DOCUME~1\WEINERT\DESKTOP\TEST\DPMITEST.EXE
cs: sel=01a7  base=02990000  limit=0009ffff
ds: sel=01af  base=02990000  limit=0009ffff
es: sel=01af  base=02990000  limit=0009ffff
fs: sel=01cf  base=3fff0000  limit=00000fff
gs: sel=01bf  base=00000000  limit=0010ffff
ss: sel=01af  base=02990000  limit=0009ffff
App stack: [0008ff70..0000ff70]  Exceptn stack: [0000fed0..0000df90]

Call frame traceback EIPs:
  0x00003af6
  0x00001e8a
  0x000036c8

from this code:

#include <go32.h>
#include <sys/farptr.h>
#include <dpmi.h>
#include <stdio.h>

int selector;

int main(int argc, char** argv)
{
  __dpmi_meminfo mi;
 int selector;
 char buffer[4];

 /* Map the physical device address to linear memory.  */
 mi.address = 0x3FFF0000;
 mi.size    = 0x1000;

 if(mi.address < 0x100000)
 {
	buffer[0] = _farpeekb(_dos_ds, mi.address);
 }
 else
 {
	 __dpmi_physical_address_mapping (&mi);
 	selector = __dpmi_allocate_ldt_descriptors (1);
 	__dpmi_set_segment_base_address (selector, mi.address);
 	__dpmi_set_segment_limit (selector, mi.size - 1);
 
 	buffer[0] = _farpeekb(selector, mi.address);
 }
}