From:	Luke Lee <comforth AT ms2 DOT hinet DOT net>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Question about LD.EXE ...
Date:	Fri, 07 Feb 1997 18:10:06 +0800
Organization:	Common Forth Labortory
Lines:	100
Message-ID:	<32FAFF7E.6DBB@ms2.hinet.net>
Reply-To:	comforth AT ms2 DOT hinet DOT net
NNTP-Posting-Host:	@140.109.249.30
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Hi, everyone :

    I'm using ld.exe's facility to allocate an array at a specific 
    location, say 0x140000, but when I try to access that memory
    block , I always got the fatal SIGSEGV. Could someone tell me
    how can I prevent this problem ? I've written a simple testing
    program downthere, please take a look ...

    Thank. Any help will be very appreciated !

    Why am I doing that ? Well, I got some non-relocatable codes which
    need to be loaded at a specific location, I've try some methods :

     1. Put that memory block inside '.bss' section so that it could
        be allocated before 'main()' ... but I am not able to specify
	the precise location by :
		. = 0x140000;
     2. Allocate small blocks of memory before 0x140000, until it is
	about to reach 0x140000, then allocate my memory block. This
	works fine under MSDOS but failed under Win95 DOS box ( even
	if I followed DJGPP's FAQ to adjust DOS box's property ... )
	
     3. The following method, however, I don't know how to prevent 
	that segment violation fault SIGSEGV .

--------- Exmaple code ---------
	System : Cyrix 6x86 P150+ ; 32M RAM , 512K cache
	OS     : DOS 6.22; DOS 7.0+Windows 95
	DJGPP  : version 2.01

----- FILE 1 : TEST.C --------------------------------------------------

#include <stdio.h>

extern int TEST_ARRAY[0x40000] ;  /* total 1M bytes */

void main() {
  int i;
  for (i=0; i<0x40000; i++ ) {
     printf( "i=%5X\t", i ); fflush( stdout );
     TEST_ARRAY[i] = 0x55AA55AA;
  }
}

/* FootNote : this program produce SIGSEGV when 'i=0' */

----- FILE 2 : TEST.LD ------------------------------------------------
----- This file is modified from /djgpp/lib/djgpp.djl 

OUTPUT_FORMAT("coff-go32")
ENTRY(start)
SECTIONS
{
  .text  0x1000+SIZEOF_HEADERS : {
    *(.text)
    etext  =  . ; _etext = .;
    . = ALIGN(0x200);
  }
  .data  ALIGN(0x200) : {
    djgpp_first_ctor = . ;
    *(.ctor)
    djgpp_last_ctor = . ;
    djgpp_first_dtor = . ;
    *(.dtor)
    djgpp_last_dtor = . ;
    *(.data)
     edata  =  . ; _edata = .;
     . = ALIGN(0x200);
  }
  .bss  SIZEOF(.data) + ADDR(.data) :
  { 					
    *(.bss)
    *(COMMON)
     end = . ; _end = .;
     . = 0xCCCCC;
     _Not_CCCCC = . ;
     . = ALIGN(0x200);
  }
  .TEST 0x140000 :
  {
     _TEST_ARRAY = . ;
     . += 0x100000;
     _END_TEST_ARRAY = . ;
  } = 0x0000
}

----- FILE 3 : MAKETEST.BAT --------------------------------------------
gcc -g test.c -o test -Wl,-Map,TEST.MAP,-T,TEST.LD


----- END OF ALL FILES -------------------------------------------------

After MAKETEST, please reference to TEST.MAP, the logical address 
specified at TEST.LD '_Not_CCCCC' is indeed not 0xCCCCC.
Even if 
	. = ABSOLUTE( 0xCCCCC );
Why is that ???

				Sincerely,
					Luke Lee

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