dosemu 1.2.1.0 hanging during startup

dosemu 1.2.1.0 hanging during startup

[James B. Hiller]

Referencing my post of a few days ago, shown below, I have run dosdebug
with it.  The primary result that I get is that:

a.  When I don't run it with dosdebug, dosemu usually hangs before it
finishes its startup (maybe 1 out of 10 or 15 times it will start and
run correctly).

b.  When I do run it with dosdebug, and simply issue a 'g' and let it
go, dosemu runs fine all the time.

So the presence of the debugger is affecting the hang.  This is making
me think "pointer error" somewhere, but I couldn't even begin to guess
how to proceed.  Any suggestions?

thx,
jbh



> The problem I'm now having is that xdosemu seems to rarely start
> successfully.  I invoke it, and I get:
> 
> Linux DOS emulator 1.2.1.0 $Date: 2004/03/06$
> Last configured at Sun Mar 14 11:49:18 EST 2004 on linux
> This is work in progress.
> Please test against a recent version before reporting bugs and problems.
> Submit Bug Reports, Patches & New Code to linux-msdos@vger.kernel.org or via
> the SourceForge tracking system at http://www.sourceforge.net/projects/dosemu
>  
> DPMI-Server Version 0.9 installed
>  
> Starting Windows 95...
>  
> And then it hangs (this isn't really trying to start Win95 - this is just the
> DOS that I have had around).  Prior to version 1.2.X, it would always start
> fine - after this line, I would get a quick blast of the Win95 splash, and
> then a DOS prompt.
> 
> Once in a very great while, I get it now, but rarely.  Usually it hangs, and
> the CPU is consumed until I kill it.
> 
> If I try to start just regular dosemu (from an xterm still), I get:
> 
>    Note that DOS needs 25 lines. You might want to enlarge your
>    window before continuing.
> 
> 
>    Now type ENTER to start DOSEMU or <Ctrl>C to cancel
> Linux DOS emulator 1.2.1.0 $Date: 2004/03/06$
> Last configured at Sun Mar 14 11:49:18 EST 2004 on linux
> This is work in progress.
> Please test against a recent version before reporting bugs and problems.
> Submit Bug Reports, Patches & New Code to linux-msdos@vger.kernel.org or via
> the SourceForge tracking system at http://www.sourceforge.net/projects/dosemu
> 
> DPMI-Server Version 0.9 installed
> 
> Starting Windows 95...
> 
> [dosemu EMS 4.0 driver installed]
> "Welcome to dosemu 1.2.1!"
> C:\>
> 
> and all is good.
> 
> I don't think I'm doing anything wrong on my side, since I'm using the DOS
> I've been using ever since I put Win95 on my machine, and it has always
> worked fine; and I got rid of the lredirs that had been evidently causing
> problems previously, as well as the attempt to boot directly from the DOS
> partition.  And since regular dosemu seems to work fine, the matter seems
> to be something that only affects xdosemu's startup.
> 
> Thanks!
> 
> jbh
> -
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Re: dosemu 1.2.1.0 hanging during startup

[Stas Sergeev]

Hello.

James B. Hiller wrote:
> So the presence of the debugger is affecting the hang.
You can start dosdebug *after* dosemu
is locked up, not before (not with -H1).

> This is making
> me think "pointer error" somewhere, but I couldn't even begin to guess
> how to proceed.  Any suggestions?
You can use the memory debugger njamd.
It can work with dosemu, but only if
you change every instance of sigaction()
call to dosemu_sigaction() call in emu.h
and recompile the dosemu.
Then you can set LD_PRELOAD to libnjamd.so,
run dosemu, and if it segfaults, then
there is probably a memory corruption
and you'll need to create a stack trace
with gdb at that point.
If this is the case, please open a bug
report on BTS for it.

Re: dosemu 1.2.1.0 hanging during startup

[James B. Hiller]

Hi.

> > So the presence of the debugger is affecting the hang.
> You can start dosdebug *after* dosemu
> is locked up, not before (not with -H1).

My apologies.  I think my use of the word "hang" is imprecise, and other
descriptions I gave got lost in the edits.  The CPU is running forever,
so it's not really a hang, but an infinite loop.  When I do what you
said above, I get:

DOSEMU Debugger V0.6 connected
- type ? to get help on commands -
Reading map file nm /usr/local/bin/dosemu.bin | grep -v '\(compiled\)\|\(\.o$\)\|\( a \)' | sort
3985 symbol(s) processed
highest address 08455898(_end)
system state: running
AX=0101  BX=442b  CX=000a  DX=1c77  SI=40f1  DI=40e6  SP=11d2  BP=0024
DS=0000  ES=8785  FS=0000  GS=0000  FL=02d7
CS:IP=0070:0447       SS:SP=8785:11d2

0070:0447 CA0200           retf    0002
g
already in running state

So I guess I'm going to need to instrument the source code with some printf's
in good places to identify where it's looping forever.  I was hoping from the
output that I had given that someone could give me some idea where to start,
since I'm not at all familiar with the source structure.

Also, as I made my original post, I was hoping that, since this behavior
is happening before dosemu finishes even getting started, and since my
setup for it is trivial, that someone else might be running into the same
issue, or that it might in some way be familiar to someone, so that I
wouldn't have to spend forever knocking it down.

Guess not.

> > how to proceed.  Any suggestions?
> You can use the memory debugger njamd.
> It can work with dosemu, but only if

[snip]

> and you'll need to create a stack trace
> with gdb at that point.
> If this is the case, please open a bug
> report on BTS for it.

If I can get that far with it, yes, certainly.

thx,
jbh