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This section written on 7/10/96.
Send comments to Max Parke
<mhp@light.lightlink.com> and to Hans Lermen
<lermen@fgan.de>
This is release v0.4 of the DOSEMU debugger, with the
following features:
- interactive
- DPMI-support
- display/disassembly/modify of registers and memory (DOS and DPMI)
- display/disassembly memory (dosemu code and data)
- read-only access to DOSEMU kernel via memory dump and disassembly
- uses /usr/src/dosemu/dosemu.map for above
- breakpoints (int3-style, breakpoint on INT xx and DPMI-INT xx)
- DPMI-INT breakpoints can have an AX value for matching.
(e.g. 'bpintd 31 0203' will stop _before_ DPMI function 0x203)
- symbolic debugging via microsoft linker .MAP file support
- access is via the 'dosdebug' client from another virtual console.
So, you have a "debug window" and the DOS window/keyboard, etc. are
undisturbed. VM86 execution can be started, stopped, etc.
- If dosemu 'hangs' you can use the 'kill' command from dosbugger to
recover.
- code base is on dosemu-0.63.1.50
All changes are #ifdef'ed with USE_MHPDBG
modules
- ./scr/arch/linux/debugger/mhpdbg.c
- ./scr/arch/linux/debugger/mhpdbgc.c
- ./scr/arch/linux/debugger/dis8086.c
- ./src/arch/linux/debugger/dosdebug.c
- ./src/include/mhpdbg.h
executable
In order to use DOSEMU debugger you must also use EMUMODULE.
During ./configure be sure you have NOT set --enable-noemumod
To run, start up DOSEMU. Then switch to another virtual console
(or remote login) and do:
dosdebug
If there are more then one dosemu process running, you will need
to pass the pid to dosdebug, e.g:
dosdebug 2134
NOTE: You must be the owner of the running dosemu to 'debug-login'.
You should get connected and a banner message.
If you type 'q', only the terminal client will terminate,
if you type 'kill', both dosemu and the terminal client will be
terminated.
See mhpdbgc.c for code and cmd table.
(all numeric args in hex)
- ?
Print a help page
- q
Quit the debug session
- kill
Kill the dosemu process
(this may take a while, so be patient)
See also
Recovering the display
- console n
Switch to console n
- r
list regs
- r reg val
change contents of 'reg' to 'val'
(e.g: r AX 1234)
- e ADDR HEXSTR
modify memory (0-1Mb)
- d ADDR SIZE
dump memory (no limit)
- u ADDR SIZE
unassemble memory (no limit)
- g
go (if stopped)
- stop
stop (if running)
- mode 0|1|+d|-d
set mode (0=SEG16, 1=LIN32) for u and d commands
+d enables DPMI mode (default on startup),
-d disables DPMI mode.
- t
single step (not fully debugged!!!)
- tf
single step, force over IRET and POPF
NOTE: the scope of 't' 'tf' or a 'come back for break'
is either 'in DPMI' or realmode, depending on
wether a DPMI-client is active (in_dpmi).
- r32
dump regs in 32 bit format
- bp addr
set int3 style breakpoint
NOTE: the scope is defined wether a DPMI-client is active
(in_dpmi). The resulting 'come back' will force
the mode that was when you defined the breakpoint.
- bc breakp.No.
Clear a breakpoint.
- bpint xx
set breakpoint on INT xx
- bcint xx
clr breakpoint on INT xx
- bpintd xx ax
set breakpoint on DPMI INT xx optionaly matching ax.
- bcintd xx ax
clear breakpoint on DPMI INT xx.
- bpload
set one shot breakpoint at entry point
of the next loaded DOS-program.
- bl
list active breakpoints
- ldt sel lines
dump ldt starting at selector 'sel' for 'lines'
'sel' may be a symbolic register name.
- (rmapfile)
(internal command to read /usr/src/dosemu/dosemu.map
at startup time)
- rusermap org fn
read microsoft linker format .MAP file "fn"
code origin = "org".
for example if your code is at 1234:0, org would
be 12340.
Addresses may be specified as:
- a linear address. Allows 'd' and 'u' commands to look at both
DOSEMU kernel and DOS box memory (0-1Mb).
- a seg:off address (0-1Mb)
seg as well as off can be a symbolic registers name (e.g cs:eip)
'seg' under DPMI is resolved via LDT, if so a numeric 'seg' value
is prefixed by # (e.g. #00af:0000.
You may force a seg to treaten as LDT selector by prefixing the '#'.
Accordingly to the default address mode 'off' under DPMI is 16 or
32 bit.
When in DPMI mode, and you want to address/display realmode
stuff, then you must switch off DPMI mode ('mode -d')
- a symbolic address. usermap is searched first, then dosemu map.
( not for DPMI programms )
- an asterisk(*): CS:IP (cs:eip)
- a dollar sign($): SS:SP (ss:esp)
If you have dosemu compiled with the debugger support, but the
debugger is not active and/or the process is not stopped, you
will not see any great performance penalty.
Main wish is to add support for hardware debug registers (if someone
would point me in the direction, what syscalls to use, etc.)
Then you could breakpoint on memory reads/writes, etc!
There must be some.
Known bugs
- Though you may set breakpoints and do singlestep in Windows31,
this is a 'one shot': It will bomb after you type 'g' again.
( I suspect this is a timer problem, we really should freeze
the timer and all hardware/mouse IRQs while the program is in 'stop').
Debugging and singlestepping through DJGPP code doesn't have any
problems.
- INT3 type breakpoints in DPMI code are very tricky, because you
never know when the client has remapped/freed the piece of code
that is patched with 0xCC ( the one byte INT3 instruction ).
Use that with caution !!
- Single stepping doesn't work correctly on call's. May be the
trap-flag is lost.
However, when in DPMI the problems are minor.
- popf sometime clears the trap-flag, so single stepping
results in a 'go' command.
'tf' works around, but we should do it better.
- When stopped for a long period, the BIOS-timer will be updated to
fast and may result in stack overflow. We need to also stop the timer
for dosemu.
- When not stopped, setting break points doesn't work properly.
So, as a work around: Only set breakpoints while in stop.
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