I was wondering if there was any way that I could debug a floppy disk emulation in Linux.
The main thing I want to be able to do is to see the values of registers and custom defined bytes and words as the emulation runs.
Another thing I would like to be able to do is to run the emulation one step at a time, and see what line of code my emulation is currently on.
I am currently just running my floppy disk image under qemu-system-x86_64 and letting it run without any feedback besides the emulation.
If anyone can supply me with something along the lines of command line statements that accomplish this sort of thing, and what programs I could either move to or install alongside to help me out, it would be much appreciated.
I don't have enough idea of qemu because I haven't used it much. But from your requirement perspective, I think you should try bochs emulator. It's quite easy to use and comes with a built-in debugger. Only thing is, you need to compile it from source (if on Linux) making sure the --enable-debug and --enable-disasm switches are enabled (alongwith any other options you might want to enable). (On Windows however, the debugger comes as a pre-built (separate) executable in the installation, but that's sort of irrelevant in your case I guess.)
Related
Here is my situation, when I download Gentoo and start to run it and downloaded the stage III Tarball from links and then tried to extract it a stream of white sentences flows down my screen really fast for about a minute just like in the YouTube tutorial I was viewing. However, after that instead of going to the correct stage it says cannot right not enough space on device and I tried repartitioning it but I'm not sure what device it is talkingaboutHowever, after that instead of going to the correct stage it says cannot right not enough space on device and I tried repartitioning it but I'm not sure what device it is talking about. Please help
Sorry you're having this issue, though in general, I truly believe Gentoo Handbook is quite well written and even a newbie can follow it... Here are some advices that I hope I can give you (most important is, digest the handbook and follow it carefully, not that I'm saying "RTFM", it's just that for Gentoo, handbook is essential and without it, we can get lost if you're just starting).
From my experiences, the "stream of white sentences" I'd presume would be from verbose un-tar'ing your stage3. Usually, I only want to see the errors so my suggestions is to remove the "v" (i.e. from "tar xjvpf" to "tar xjpf") so that only errors would appear when un-tar'ing. The caveat to this is that you'll be wondering if it hung or is busy un-tar'ing. Use Alt-F1 and Alt-F2 (if on console/tty mode back-and-forth) to log in on another TTY and do 'ps -auxf' to see if it's still tar'ing. If you're using GUI Terminal, just open another tab and 'ps auxf', you get the picture...
Also, learn the commands "df", it'll come in handy. If you're running out of disk space, perhaps you're trying to install/untar stage3 to your ramdisk (grin) rather than your mounted (i.e. "/mnt/gentoo"). Mount your root '/' device to '/mnt/gentoo' and cd to that mounted path then try it (don't forget to mount your '/boot' as well as your proc, dev, sys, etc before you chroot - again, follow the handbook as carefully as you can - oh also, distro such as Debian hybrids including Ubuntu uses symlink to shm, so read that part about 'rm /dev/shm' and follow it carefully; if you're using Gentoo LiveCD, you can ignore that part).
Other useful commands if you're confused (or new to) mounting devices would be to learn to experiment with commands such as 'lsblk' and 'mount' (by itself) to inspect the sizes of your partition (again, use of 'df' comes in handy as well) as well as what is your device (i.e. /dev/sda1 versus /dev/sdb1). Hint: when you do 'mkfs', use "-L" (or for some file system, it's "-N") to label/name your devices, so that when you use commands such as 'mount' or 'lsblk', you can spot them easier. If you're using GUI/desktop versions of some distro, hopefully there are tools such as "gparted" which can give you visual information in GUI of your devices which can be helpful. One think I'd advise you to stay away from if you're just starting, is to avoid RAID (i.e. mdadm) until you're comfortable with how grub/lilo works. Get your kernel (Gentoo-sources) compiled and MBR written (i.e. grub-install), try booting and have fun first (oh also, if you can avoid GUI like installing Gnome/KDE from the get-go, avoid it as well - you'll get into issues such as "should I use SystemD or OpenRC" and then get hit by the obstacle of some gnome parts needs you to use systemd but you've chosen openrc, and so on).
If I may add my opinions, in my opinion, Gentoo (also Arch and FreeBSD) is an excellent place to start if you want to learn the inside of Linux application workings (library dependencies, why packages are important rather than downloading each libs manually and compile them one by one, etc). I hope this won't discourage you from switching to another distro, but if it does frustrate you on installation and all you want to do is test-drive Linux, there are much easier distro that you'd not have to understand USE and other compilation mechanisms (if you have an old i586, it makes sense to build it with pick-and-chose libraries so that leaner can be faster, but if you have fast machine, why compile binaries when somebody who is expert at it already have done it for you?). SUSE and Fedora/RedHat/CentOS used to be the least frustrating for it was able to find/detect hardwares (legacy and new) but these days, I usually tell people, "if you know how to install Windows, you can install Ubuntu" so that too may be a good way to wet your feet. Good luck!
0_o wow, well.. how about some 411 like size of your hdd and exactly how you partioned it? Linux will look for specific directorys and if missing will instead start to install into the root dir. How you partion is an importent first step. Once you got a generally good partion setup most linux installs will go fine. Most basic tables include /, /home,/var and a swap.
I am wondering which debugging tool I can use for an assembly program and how to use it.
I have written a simple bootloader in assembly. However, it is not quite working properly as I wished, even though I think the logic is correct. So, I am trying to use a debugger so that I can step through the bootloader, checking the register status and etc.
I tried GDB on Ubuntu, compiling my .asm to .elf and .o (Do I need to do it? If yes, what is the next step?) Also, I read that there is an internal debugger in Bochs simulator, but I can't quite find any document how to use it. I also have Visual Studio 2010, windbg, but I don't know how to use it for .asm file debugging.
If you have done this before, it would be an easy answer. Any help would be really appreciated.
Sincerely
If you want to debug bootloader code, you obviously need to run it in the same environment that the code itself is going to run in. As I'm sure you already know, bootloader code is executed in real mode once the BIOS finishes doing the POST. The bootloader is then loaded into memory at 7c00h and a jump to that address is executed.
Obviously, this kind of environment cannot be reliably emulated once you've got your computer running and a "real" operating system already loaded, since by that time your CPU is in protected mode (or long mode, if it's AMD64). Your only option at this point is to use QEMU or Bochs in order to emulate a real PC inside your operating system. I've used Bochs to debug some bootloader code I've written in the past and it worked quite well. Check the manual pages for more detailed instructions.
I ssh into a linux VM which is setup remotely. I use Vim to write my code. For debugging however, I use netbeans through X11 which can sometimes be painfully slow. I tried using gdb buts its an efficiency killer. I love to hover over my variable and get to now their value rather that doing p variable_name , plus I like see and navigate through the code. Is there something light simple gui based debugging tool I can use. I have tried to use clewn http://clewn.sourceforge.net/ , but that doesnt work because it has a missing netbeans_intg feature. Is there any other similar vim gui based debugging tool ?
You can try ddd
which is a gui for gdb, I think it's lighter than netbeans.
cgdb is an interface to gdb but it is not a graphical one. It does not offer the possibility of hovering over a variable, but it shows you a window with the source code.
Well, I was in sort of your situation sometime ago, and you can have a look at my question about using gdb with remote sources.
First of all, your problem with netbeans_intg feature is related to vim which has been compiled with no support for it. If you can rebuild vim yourself, you can then enable it. Otherwise, as you can see in the answer that I gave myself to my question, you can leverage clewn's remote-vim capabilities.
In a nutshell, you can have a "local" vim (i.e. on a desktop/laptop machine presumably), which must still be built with netbeans_intg support, but now it is a vim under your complete control (i.e. it's on "your" machine), while clewn will run on the linux host where gdb and your debuggee will run.
You can then keep the source files on your desktop/laptop and have the remote clewn sort of "drive" your local vim to the proper source files while debugging.
IOW: clewn will get information out of gdb to know exactly which file/line you're into and connect to remote vim and tell it: "hey, go grab this file and show it around this line", highlighting current line, breakpoints etc.
This is a great solution for when you have far-away deployed systems and you need to debug them with minimum impact on the host where they are running, and presumably no option to transfer there all of your source files.
I don't know if this fits in any way with what you're trying to do, but it did really change things for me.
Hth,
Andrea.
Check out GDB server. Theoretcially, you should be able to start gdb on your linux machine in server mode and connect via GUI of your choice. As long as that GUI supports remote gdb connections, which Netbeans does.
I have compiled my own Kernel module and now I would like to be able to load it
into the GNU Debugger GDB. I did this once, a year ago or so to have a look
at the memory layout. It worked fine then, but of course I was too silly to
write down the single steps I took to accomplish this... Can anyone enlighten
me or point me to a good tutorial?
Thank you so much
For kernels > 2.6.26 (i.e. after May 2008), the preferred way is probably to use "kgdb light" (not to be confused with its ancestor kgdb, available as a set of kernel patches).
"kgdb light" is now part of the kernel (in by default in current Ubuntu kernels, for instance), and it's capabilities are improving fast (Jason Wessel is working on it - possible google key).
Drawback: You need two machines, the one you're debugging and the development machine (host) where gdb runs. Currently, those two machines can only be linked through a serial link.
kgdb runs in the target machine where it handles the breakpoints, stepping, etc. and the remote debugging protocol use to talk with the development machine.
gdb runs in the development machine where it handles the user interface.
An USB-to-serial adapter works OK on the development machine, but currently, you need a real UART on the target machine - and that's not so frequent anymore on recent hardware.
The (terse) kgdb documentation is in the kernel sources, in
Documentation/DocBook
I suggest you google around for "kgdb light" for the complete story.
Again, don't confuse kgdb and kgdb light, they come together in google searches but are mostly different animals. In particular, info from linsyssoft.com relate to the "ancestor" kgdb, so try queries like:
kgdb module debugging -"linsyssoft.com" -site:linsyssoft.com
and discard articles prior to May 2008 / 2.6.26 kernel.
Finally, for module debugging, you need to manually load the module symbols in the dev machine for all the code and sections you are interested in. That's a bit too long to address here, but some clues there, there and there.
Bottom line is, kgdb is a very welcome improvement but don't expect this trip to be as easy as running gdb in user mode. Yet. :)
It has been a while since I was actively developing drivers for Linux, so maybe my answer is a bit out of date. I would say you cannot use GDB. If at all, only to debug post mortem on dump files. To debug you should rather use a kernel debugger. Build the kernel with a kernel debugger enabled (there is one out-of-the box debugger for 2.6, which was lacking at the time I was active). I used the kernel patches for KDB from Sun ftp://oss.sgi.com/www/projects/kdb/download/, which I was quite happy with. A user space tool won't be of much use unless new gdb communicate somehow with the internal kernel debugger (which anyway you would have to activate)
I hope this gives you at least some hints, while not being a detailled answer. Better than no answer at all. Regards.
I suspect what you did was
gdb /boot/vmlinux /proc/kcore
Of course you can't actually do any debugging, but it's certainly good enough to have a poke around the kernel.
I have big system that make my system crash hard. When I boot up, I don't even have
a coredump. If I log every line that
get executed until my system goes down. I will find that evil code.
Can I log every source code line in GDB to a file?
UPDATE:
ok, I found the bug. It was nasty. The application I started did not
take the system down. After learning about coredump inspection with mdb, and some gdb stepping I found out that the systemcall causing the dump, was not implemented. Updating the system to latest kernel will fix my problem. Thanks to all of you.
MY LESSON:
make sure you know what process causes the coredump. It's not always the one you started.
Sounds like a tricky little problem.
I often try to eliminate as many possible suspects as I can by commenting out large chunks of code, configuring the system to not run certain pieces (if it allows you to do that) etc. This amounts to doing an ad-hoc binary search on the problem, and is a surprisingly effective way of zooming in on offending code relatively quickly.
A potential problem with logging is that the log might not hit the disk before the system locks up - if you don't get a core dump, you might not get the log.
Speaking of core dumps, make sure you don't have a limit on your core dump size (man ulimit.)
You could try to obtain a list of all the functions in your code using objdump, process it a little bit and create a bunch of GDB trace statements on those functions - basically creating a GDB script automatically. If that turns out to be overkill, then a binary search on the code using tracepoints can also help you zoom in on the problem.
And don't panic. You're smarter than the bug - you'll find it.
You can not reasonably track every line of your source using GDB (too slow). Besides, a system crash is most likely a result of a system call, and libc is probably doing the system call on your behalf. Even if you find the line of the application that caused OS crash, you still don't really know anything.
You should start by clarifying which OS is crashing. For Linux, you can try the following approaches:
strace -fo trace.out /path/to/app
After reboot, trace.out will contain syscalls the application was doing just before the crash. If you are lucky, you'll see the last syscall-of-death, but I wouldn't count on it.
Alternatively, try to reproduce the crash on the user-mode Linux, or on kernel with KGDB compiled in.
These will tell you where the problem in the kernel is. Finding the matching system call in your application will likely be trivial.
Please clarify your problem: What part of the system is crashing?
Is it an application?
If so, which application? Is this an application which you have written yourself? Is this an application you have obtained from elsewhere? Can you obtain a clean interrupt if you use a debugger? Can you obtain a backtrace showing which functions are calling the section of code which crashes?
Is it a new hardware driver?
Is it based on an older driver? If so, what has changed? Is it based on a manufacturer's data sheet? Is that data sheet the latest and most correct?
Is it somewhere in the kernel? Which kernel?
What is the OS? I assume it is linux, seeing that you are using the GNU debugger. But of course, that is not necessarily so.
You say you have no coredump. Have you enabled coredumps on your machine? Most systems these days do not have coredumps enabled by default.
Regarding logging GDB output, you may have some success, but it depends where the problem is whether or not you will have the right output logged before the system crashes. There is plenty of delay in writing to disk. You may not catch it in time.
I'm not familiar with the gdb way of doing this, but with windbg the way to go is to have a debugger attached to the kernel and control the debugger remotely over a serial cable (or firewire) from a second debugger. I'm pretty sure gdb has similar capabilities, I could quickly find some hints here: http://www.digipedia.pl/man/gdb.4.html