To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: GO32 DPMI problem?
Date: Sat, 30 Jul 94 16:56:25 +0300
From: eliz AT is DOT elta DOT co DOT il

Hi, I need help with simulating int 21h from protected mode.

What's wrong with the following program:

-------------- file drv.c ----------------------
#include <dir.h>
#include <dos.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <dpmi.h>

int
is_remote_drive(int drv_no)
{
  _go32_dpmi_registers regs;

  /* INT 21H/AX=4409H returns DX with 12th bit set, if drive is remote. */
  regs.h.ah = 0x44;         /* IOCTL, Subfunction 09h */
  regs.h.al = 9;
  regs.h.bl = drv_no + 1;   /* 0 = default, 1 = 'A', etc.  */
  _go32_dpmi_simulate_int(0x21, &regs);

  if (regs.x.flags & 1)
    {
      errno = ENODEV;
      return -1;
    }
  if (regs.x.dx & 0x1000)
    return 1;
  return 0;
}

void main(void)
{
  int disk = getdisk();

  printf("%d Disk %c: is \n", disk, disk + 'A');
  if (is_remote_drive(disk))
    puts("a REMOTE disk");
  else
    puts("a LOCAL disk");

  exit(0);
}

-------- end of drv.c ------------------------

If the answer is "Nothing wrong", then why does this program crash
my machine?   When invoked under DPMI mode of GO32, it causes Exception 12
to QEMM, which prints:

Exception 12:

   [QEMM apology text deleted]

	Exception #12 at 25DB:06D6, error code: 0000
	AX=4409 BX=0003 CX=40DF DX=0000 SI=1902 DI=189C BP=0001
	DS=213C ES=0000 SS=1759 SP=0001 Flags=3046
	Instruction: 52 06 8A 1E 50 04 32 FF C1 E3 02 8B 97 7F 1D

[end of QEMM message]

The values of CX, DI and SS vary if I include the is_remote_drive() function
in a larger program (this is what I actually am trying to do, not playing
with semi-trivial programs), and BP sometimes comes out as 0000, but the
other registers always have the shown values.  I use QEMM 7.04 and QDPMI 1.05;
go32 is 1.11maint5.

The AX=4409 and BX=0003 shows that the program crashes somewhere in the process
of calling INT 21H with AX=4409, BL=3, which is exactly what I'm trying to do.
But why does it crash?  Am I missing something?  Or is there something wrong
with GO32?
If the program doesn't crash for you, be sure there is no ``nodpmi'' word in
your GO32 environment variable.  When ``nodpmi'' *is* set, this small program
works OK, but I have other very strange effects, and until the smaller program
works under DPMI, I can't continue debugging.  Please help!!!!

Btw, if it doesn't crash under DPMI either, try playing with the printf()
statement: add some more variables to it.  At my place, if I delete the
%d from the format string and the first occurence of `disk', it works OK.

Thanks in advance for any help!

	Eli Zaretskii

For the record, I attach here the contents of my a.bat, c.sys and the output
of SET command:

-------------------- config.sys -------------------
rem
rem ************************************************************************
rem
rem On the following QEMM line:
rem
rem   FB:N UFP:N VHI:N F10:N   for BodyWorks program not to hang
rem
rem ************************************************************************
rem
rem DEVICE=C:\QEMM\QEMM386.SYS ON MA=0
DEVICE=C:\QEMM\DOSDATA.SYS
DEVICE=C:\QEMM\QEMM386.SYS RAM ST:M FB:N UFP:N VHI:N F10:N R:1
DEVICE=C:\QEMM\DOS-UP.SYS @C:\QEMM\DOS-UP.DAT
DEVICE=C:\QEMM\LOADHI.SYS /R:1 /SIZE=8592 C:\QEMM\QDPMI.SYS SWAPFILE=DPMI.SWP SWAPSIZE=40000
rem DEVICE=C:\QEMM\LOADHI.SYS /R:1 /SIZE=6176 C:\DOS\RAMDRIVE.SYS 1536 /E
DEVICE=C:\QEMM\LOADHI.SYS /R:2 /SIZE=2784 C:\BIN\SRDEMSS.SYS
DOS=HIGH
FILES=8
BUFFERS=15
STACKS=9,256
rem LASTDRIVE=M
DEVICE=c:\qemm\loadhi.sys /r:2 /size=2592 c:\usr\hardw\superio\dc2000.sys /t
SHELL=c:\qemm\loadhi.com /r:2 /envhi c:\dos\command.com c:\dos /P /E:1536 /F

------------- autoexec.bat -------------------------
@ECHO OFF
c:\qemm\loadhi /r:2 c:\bin\watch
c:\qemm\loadhi /r:2 c:\dos\smartdrv.exe 2048
c:\qemm\loadhi /r:2 c:\qemm\files=30
c:\qemm\loadhi /r:2 c:\bin\anarkey -a1000 -h3000 -e -iof -x\ -xbak -$$$ <c:\anarkey.inp
C:\QEMM\LOADHI /R:2 C:\WINDOWS\mouse.COM /Y
rem c:\usr\hardw\mouse\mouse.com
c:\qemm\loadhi /r:1 c:\bin\pcspool /i /1 /dc:\tmp
c:\qemm\loadhi /r:2 c:\bin\chi\vegainit -v
set EXPLOSIV=c:\bin\explosiv
c:\qemm\loadhi /r:2 c:\bin\explosiv -
c:\bin\load \anarkey.ini
c:\bin\srdisk /e 512
c:\dos\smartdrv.exe %SRDISK1%- /q
PATH C:\BIN\GCC\BIN;C:\BIN;C:\DOS;C:\BIN\VIRUS;C:\;C:\WINDOWS;C:\USR\DIC\MI
set TMPDIR=%SRDISK1%:/
set GO32=driver c:/bin/gcc/drivers/vga.grd nodpmi
call c:\bin\gcc\bin\setdjgpp c:\bin\gcc c:/bin/gcc
set 387=YES
prompt $p$_) 
set CHIFILES=C:\BIN\CHI
set DSAVER=\BIN\NORTON\fr /SAVE
set DPARKER=\BIN\pcpark
set PAGER=c:\bin\less
set MANPATH=c:\usr\man\
set MANEXT=.hf
set EPSILON=-fsc:\tmp -vl40 -e0 -ef0 -x1536k -xu
set EPSPATH=c:\bin\epsilon;c:\bin\epsilon\info
set EPSDISP=c:\bin\epsilon\oak0x7.b
set USERNAME=EZaretskii
set TEMP=c:\tmp
set INFOPATH=c:/bin/epsilon/info
set WBLIB=c:\usr\eli\undoc
set DIRCMD=/w/l/o
set SCAN=c:\bin\virus\scan.exe
set KILL=c:\bin\virus\clean.exe
set HELP@=c:\usr\man\anarkey.sum
set LESS=-icsqM
set EDITOR=mx -p0
set LESSHELP=c:/lib/less.hlp
VER
cd \hdm
hdm -n
cd\
cls

-------------- output of SET -----------------
COMSPEC=C:\DOS\COMMAND.COM
EXPLOSIV=c:\bin\explosiv
SRDISK1=D
PATH=C:\BIN\GCC\BIN;C:\BIN;C:\DOS;C:\BIN\VIRUS;C:\;C:\WINDOWS;C:\USR\DIC\MI
TMPDIR=D:/
GO32=driver c:/bin/gcc/drivers/vga.grd nodpmi
BISON_HAIRY=c:/bin/gcc/lib/bison.hairy
BISON_SIMPLE=c:/bin/gcc/lib/bison.simple
FLEX_SKELETON=c:/bin/gcc/lib/flex.skeleton
COMPILER_PATH=c:/bin/gcc/bin
C_INCLUDE_PATH=c:/bin/gcc/include
CPLUS_INCLUDE_PATH=c:/bin/gcc/cplusinc;c:/bin/gcc/include
OBJC_INCLUDE_PATH=c:/bin/gcc/include;c:/bin/gcc/include/objc
OBJCPLUS_INCLUDE_PATH=c:/bin/gcc/include;c:/bin/gcc/include/objc
LIBRARY_PATH=c:/bin/gcc/lib
GO32TMP=c:/bin/gcc/tmp
387=YES
PROMPT=$p$_) 
CHIFILES=C:\BIN\CHI
DSAVER=\BIN\NORTON\fr /SAVE
DPARKER=\BIN\pcpark
PAGER=c:\bin\less
MANPATH=c:\usr\man\
MANEXT=.hf
EPSILON=-fsc:\tmp -vl40 -e0 -ef0 -x1536k -xu
EPSPATH=c:\bin\epsilon;c:\bin\epsilon\info
EPSDISP=c:\bin\epsilon\oak0x7.b
USERNAME=EZaretskii
TEMP=c:\tmp
INFOPATH=c:/bin/epsilon/info
WBLIB=c:\usr\eli\undoc
DIRCMD=/w/l/o
SCAN=c:\bin\virus\scan.exe
KILL=c:\bin\virus\clean.exe
HELP@=c:\usr\man\anarkey.sum
LESS=-icsqM
EDITOR=mx -p0
LESSHELP=c:/lib/less.hlp