Date: Thu, 18 Mar 93 10:28:55 JST
From: Makoto Kobayashi <na70103 AT cc DOT mie-u DOT ac DOT jp>
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Re: DPMI & new GO32
References: <9303171317 DOT AA00683 AT delorie DOT ctron>
	<9303171535 DOT AA04672 AT DG1 DOT CHEMIE DOT UNI-KONSTANZ DOT DE>

"go32.com" in ftp.sigmath.osaka-u.ac.jp can work with various 
restrictions and some modifications under DPMI.   It does 
not supports graphics, emu387, stack is limited to 1 mega bytes, etc.
 
    DPMI 0.9 does *NOT* support demand-loading mechanism.
For i386 demand-paged executable the SEGMENT_SIZE is fixed to 
0x400000 bytes, and then DATA must be started after 0x400000. 
This is because a.out requires incomprehensibly large memory size
running in windows environment.
    Of cource the stack must be located in another segment and 
you must not use -foimit-frame-pointer optimizing option because the 
default segment of BP is SS. 
 
    I found that go32 supports COFF header (0x14c) and this header has 
an information of SEGMENT_SIZE in it.  I added the two line in ld.c :
    #define COFF_ENCAPSULATE
    #define SEGMENT_SIZE page_size
and recompiled it.   This time the linker creates a nice a.out which requires
less memory than before.  ( e.g. 10 mega bytes to 2 mega bytes for same
source file)
 
 Other points to run a.out in windows:
 
1. New fashion read/write cannot be used.  Only old style read.s and 
write.s can do.
 
2. sbrk() returens uninitialized memory and malloc occurs trouble.
 
A patch to solve this problem is follows.
 
 
*** paging.c	Tue Nov 10 01:57:36 1992
--- c:paging.c	Wed Mar 10 16:36:34 1993
***************
*** 813,819 ****
--- 813,822 ----
  int
  changeBreak(word32 breakPoint)
  {
+ 	word32 oldbytes;
    word32 newBytes = (breakPoint + 0xfff) & ~0xfff;
+ 	oldbytes=myMemory.bytes;
+ 	if (oldbytes < areas[3].first_addr) oldbytes=areas[3].first_addr;
    if (myMemory.bytes != newBytes) {
      DPMIprotectedMode();
      if (! DPMIrealloc(&myMemory, newBytes)) {
***************
*** 826,831 ****
--- 829,838 ----
  		       (areas[A_stack].first_addr - 1) >> 12);
      DPMIrealMode();
    }
+ 
+     if(newBytes > oldbytes) 
+ 		Pmemset(mySelector, oldbytes, 0, newBytes - oldbytes );
+ 
    areas[3].last_addr = breakPoint - 1;
    return 1;
  }
 
 
 
/* read.s */
	.text
	.globl _read
_read:
	pushl	%ebx
	pushl	%esi
	pushl	%edi
	movl	16(%esp),%ebx
	movl	20(%esp),%edx
	movl	24(%esp),%ecx
	movb	$0x3f,%ah
	int	$0x21
error:
	popl	%edi
	popl	%esi
	popl	%ebx
	jb	syscall_error
	ret
 
 
/* write.s */
	.text
	.globl _write
_write:
	pushl	%ebx
	pushl	%esi
	pushl	%edi
	movl	16(%esp),%ebx
	movl	20(%esp),%edx
	movl	24(%esp),%ecx
	cmpl	$4096,%ecx
	movb	$0x40,%ah
	int	$0x21
	popl	%edi
	popl	%esi
	popl	%ebx
	jb	syscall_error
	ret
 

                     Faculty of Eng., Mi'e Univ., Tsu, Japan.
                     na70103 AT cc DOT mie-u DOT ac DOT jp    Makoto Kobayashi