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<article>

<artheader>

<title>Known dosemu problems</title>

<abstract>

<para>
This file lists programs and groups of programs not running or running
only partially under dosemu. The most up-to-date version of this file
may be found on: 
<emphasis remap="bf"><ulink
url="http://www.dosemu.org/"
>http://www.dosemu.org/</ulink
></emphasis>.
Please report about possible additions to
<emphasis remap="bf"><ulink
url="mailto:linux-msdos@vger.kernel.org"
>linux-msdos@vger.kernel.org</ulink
></emphasis> 
or the SourceForge BTS at 
<emphasis remap="bf"><ulink
url="http://www.dosemu.org/"
>http://www.dosemu.org/</ulink
></emphasis>.
Perhaps your program can be made going
with the help of others. Have a look at the dosemu-howto how to do so.
</para>

</abstract>

</artheader>

<sect1>
<title>Fundamental problems</title>

<para>
Programs that don't work under the MSDOS Emulator and probably won't
ever work, because of fundamental problems. Some of these fundamental
problems result in these programs not being runnable on
Win3.x/Win95/WinNT and under OS/2 DOS box either. These programs
are characterized by using any of these features:
</para>

<sect2>
<title>Virtual Control Program Interface (VCPI)</title>

<para>
VCPI allows programs to run in ring 0. This is kernel mode in Linux
and not sensible.
</para>

<para>
Example: sim2181.exe from Analog Devices DSP Kit
</para>

</sect2>

<sect2>
<title>Programs using older versions of the Pharlap Extender </title>

<para>
Older versions of the Pharlap Extender (run286) need ring-0 access
under DOSEMU to install their own DPMI server. The use of proprietary
undocumented extensions to the DPMI protocol makes DOSEMU's DPMI server
unsuitable for this extender.
</para>

<para>
Example: Autocad Version 12c1 For DOS
</para>

<para>
Example: the game BioForge by Origin Systems.
</para>

</sect2>

<sect2>
<title>Programs using the JEMM memory manager</title>

<para>
The JEMM memory manager provides proprietary extensions to the EMS
protocol. These are not supported by DOSEMU.
</para>

<para>
Example: Wing Commander Privateer by Origin Systems
</para>

</sect2>

<sect2>
<title>Does my failing program belong to these groups?</title>

<para>
Check with "strings &lt;program.exe&gt; | less" if the program
contains some of these keywords: <emphasis remap="bf"> vcpi, RUN286</emphasis>.
</para>

</sect2>

<sect2>
<title>
Fundamental problem with the Linux kernel
</title>
<para>
The Programmable Interval Timer (PIT) can be programmed to produce
interrupts with frequencies up to almost 2MHz. Linux sets this to
only 100Hz (2.6 kernels can set it to 1KHz) and doesn't allow the
software to change that. This limits the minimal interval between subsequent
SIGALRM notifications for software that uses the setitimer(2) syscall.
To emulate the PIT frequencies that are higher than the frequency Linux
sets the PIT to, dosemu uses "interrupt bursts": on every SIGALRM
reception dosemu triggers the timer interrupt as many times as necessary
to compensate the gap since the previous SIGALRM reception. This allows
to keep a precise timing but causes problems for some programs. When
the timer interrupt handler is invoked more than once without letting
the main thread to execute, some programs can lock up. The game "Cosmo" is
one of those.
</para>
<para>
Another problem is that due to the aforementioned low timer frequency
dosemu is not able to properly emulate the timings for different
emulated hardware. That also causes problems for some programs.
Scream Tracker 3, for example, can lock up at startup because the
interrupt from an emulated SB card can be triggered earlier than it
should be in a real system.
</para>
<para>
Possibly a workaround may be found in future DOSEMU versions.
</para>
<para>
Linux kernels prior to 3.16 may have various problems on x86-64.
Make sure to not use 3.14 and 3.15 as they
<ulink url="https://www.codeweavers.com/support/wiki/Diag/BrokenLDT16">
lack 16bit segments support
</ulink>
</para>
<para>
3.16 adds support for espfix64 feature.
</para>
</sect2>

<sect2>
<title>
Fundamental problems with the CPU
</title>
<para>
There are several defects in Intel's x86 CPUs that are causing
problems for some software. Below is a description of the defects
that are known to cause problems for software running under dosemu.
</para>

<sect3>
<title>
Problem with the virtualization of the IF flag
</title>

<para>
<ulink url="http://www.intel.com/design/intarch/techinfo/pentium/inout.htm">
Intel's manual
</ulink>
says:
</para>
<para>
" A procedure may use the POPF instruction to change the setting of the IF
 flag only if the CPL is less than or equal to the current IOPL. An attempt
 by a less privileged procedure to change the IF flag does not result in
 an exception; the IF flag simply remains unchanged. "
</para>
<para>
The fact that the exception is not being generated, prevents dosemu from
catching and properly simulating the POPF instruction executed in protected
mode. That, in particular, means that the following code, executed in
protected mode (not in v86 mode) under dosemu, will end up with interrupts
disabled (IF cleared):
</para>

<para>
<screen>
sti
pushf
cli
popf
</screen>
[ the interrupts are still disabled here ]
</para>
<para>
This bug can only affect DPMI programs, as using DPMI is the only way
to execute protected mode code under dosemu.
Known programs that are affected are the games from ID software, namely
Doom2 and Duke Nukem 3D, but only when configured with sound.
An optional work-around was added to dosemu, which just re-enables the
interrupts if they were disabled for too long in protected mode.
Additionally the address of the instruction that disabled the interrupts,
is added to a black-list and this instruction is ignored for subsequent
passes so that it can't disable the interrupts any more.
This is potentially unsafe, but if the timeout is long enough, no harm
was observed so far.
The timeout is configured via the $_cli_timeout option, which is measured
in a 10ms timer ticks. Setting that option to 0 disables the workaround
completely, making Doom2 unplayable with sound enabled.
</para>

</sect3>
<sect3>
<title>ESP register corruption</title>

<para>
Intel's x86 CPUs have a defect
<ulink url="http://www.intel.com/design/intarch/specupdt/27287402.PDF">
described here
</ulink>,
chapter "Specification Clarifications"
section 4: "Use Of ESP In 16-Bit Code With 32-Bit Interrupt Handlers",
which reads as follows:
</para>
<para>
"ISSUE: When a 32-bit IRET is used to return to another privilege level,
and the old level uses a 4G stack (D/B bit in the segment register = 1),
while the new level uses a 64k stack (D/B bit = 0), then only the
lower word of ESP is updated. The upper word remains unchanged. This is
fine for pure 16-bit code, as well as pure 32-bit code. However, when
32-bit interrupt handlers are present, 16-bit code should avoid any
dependence on the upper word of ESP. No changes are necessary in existing
16-bit code, since the only way to access ESP in USE16 segments is
through the 32-bit address size prefix."
</para>
<para>
Unfortunately, the above quote from Intel is silent about the 32-bit
programs that use 16-bit stack segment - this is where the problem pops us.
The corruption happens when the Linux kernel returns control to the dosemu
process, while a 32-bit DPMI client that uses a 16-bit data segment for
the stack is active. This is not the usual case, but unfortunately some
32-bit DPMI clients are actually using a 16-bit segment for the stack,
and even the dos4gw extender behaves that way sometimes.
</para>
<para>
Programs that are known to be affected by this issue are:
<itemizedlist>
<listitem>
<para>
Need For Speed 1 (demo version at least, when configured with sound)
</para>
</listitem>
<listitem>
<para>
Syndicate Wars (when used with dos4gw 0.8)
</para>
</listitem>
<listitem>
<para>
Open Cubic Player
</para>
</listitem>
</itemizedlist>
</para>

<para>
These programs are crashing shortly after startup, but this problem
is difficult to detect reliably, so there may be many more programs
that experience a random crashes due to this CPU bug.
</para>

<para>
The reliable work-around was developed and added into linux-2.6.12
for 32-bit systems, and into linux-3.16 for 64-bit systems.
</para>
<para>
Note: linux kernels prior to 3.16 may have various problems on x86-64.
</para>

</sect3>

</sect2>

</sect1>

<sect1>
<title>Known bugs</title>

<sect2>
<title>Things YOU may help changing</title>

<sect3>
<title>
List of currently known bugs in dosemu2
</title>
<itemizedlist>

<listitem>
<para>
Some documentation is known to be well out of date. 
</para>
</listitem>

<listitem>
<para>
Some database programs (Clipper, FoxPro) have problems with
locking in certain configurations. smbfs doesn't support
locking. $_full_file_locks=(on) may or may not help.
</para>
</listitem>

<listitem>
<para>
Mortal Kombat 1 and 2 are not producing any sound for unknown reasons.
</para>
</listitem>

<listitem>
<para>
X-COM Apocalypse (DEMO version) locks up at startup if configured with sound.
</para>
</listitem>
</itemizedlist>

</sect3>
</sect2>

</sect1>

<sect1>
<title>Programs exhibiting graphical problems in xdosemu</title>
<para>
The following programs work perfectly on the Linux console
(suid/sudo/root) with graphics enabled but exhibit minor or
major glitches in xdosemu.
</para>

<sect2>
<title>
Games with graphical problems
</title>
<para>
The following games exhibit glitches or don't work at all in
xdosemu. Please let us know when any problems are solved or
even better, help us solving!
</para>
<itemizedlist>
<listitem>
<para>
Commander Keen 1 wobbles like jelly and the window shakes 
every time it scrolls.
</para>
</listitem>
<listitem>
<para>
Pinball Dreams 2 takes a long time to start. Once it's past
the startup screen it runs fine though.
</para>
</listitem>
</itemizedlist>
</sect2>
</sect1>

<sect1>
<title>Differences in behaviour between Dosemu and Dosemu2</title>
<para>
The following differences may be apparent if you have previously been
using Dosemu.
</para>
<sect2>
<title>
Filesystems
</title>

<sect3>
<title>
MFS
</title>
<para>
Network device DOS filesystem that provides read write access to the host filesystem.
</para>
<itemizedlist>
<listitem>
<para>
Dosemu2 does not redirect a drive to arbitrary host paths on the command
line of the emufs.sys driver when it is loaded in config.sys. Use the lredir2
command to accomplish this in autoexec.bat instead.
</para>
</listitem>
<listitem>
<para>
Dosemu2 does not support LFN on the SUBST / JOIN drives.
</para>
</listitem>
<listitem>
<para>
Dosemu2 now provides enhanced FAT32 disk functions only as a fallback
to the native DOS in the event that the DOS does not implement them itself.
A consequence of being a fallback is that if the DOS has a bug in its
implementation it is not overriden by Dosemu2. Examples of this are
MS-DOS 7.0 and PC-DOS 7.10.
</para>
</listitem>
</itemizedlist>
</sect3>
</sect2>
</sect1>

</article>
