Patching GDB 7.3 for QEMU remote kernel debug

This time I will try to explain how patch GDB 7.3 in order to debug a kernel using QEMU through remote debuging. If we try to debug remotely, we'll find a error message like:

Remote packet too long: 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 ...

I am not sure about problem but I suppose it's about register size. When the virtual machine jumps from real mode to long/protect mode, the register size changes but GDB doesn't know that. Thus, when GDB receives a bigger packet than it expects, it fails. Therefore, The patch just increments the buffer in those cases.

The first step is to download GDB 7.3 from http://www.gnu.org/s/gdb/download/, I've implemented the patch on 7.3 version but I think it works in oldest too.

Once downloaded and uncompressed, edit the file gdb-7.3/gdb/remote.c and go to 5693 line. That's the process_g_packet procedure. Now, look for and replace the original source with the following lines:

/* Further sanity checks, with knowledge of the architecture. */

//if (buf_len > 2 * rsa->sizeof_g_packet)

// error (_("Remote 'g' packet reply is too long: %s"), rs->buf);

if (buf_len > 2 * rsa->sizeof_g_packet)

{

rsa->sizeof_g_packet = buf_len;

for (i = 0; i < gdbarch_num_regs (gdbarch); i++)

{

if (rsa->regs[i].pnum == -1)

continue;

if (rsa->regs[i].offset >= rsa->sizeof_g_packet)

rsa->regs[i].in_g_packet = 0;

else

rsa->regs[i].in_g_packet = 1;

}

}

Finally, it just remains to execute:

$ ./configure

$ make


In some systems may be necessary to install termcap library, simply execute:

$ sudo apt-get install libncurses5-dev

After compilation, the binary could be found in gdb-7.3/gdb/gdb, It must be enough to run GDB correctly.

Matias E. Vara

www.torokernel.org

Toro in Microelectronic Conference (UNLP)

Toro will be shown in the Microelectronic Conference at University of La Plata, Argentina. In the work that I've done I will show the kernel capabilities and a few tests comparing Toro with a general purpose operative system. The conference will be the 8th of September in "Sala A" at 16.20hs.

Matias E. Vara

www.torokernel.org

Toro in Ubuntu 11.04!

Now It is possible to compile and test TORO easy trough Linux Ubuntu 11.04. Actually, I am moving the whole project to Linux environment. In other way, I have started to use GIT in order to simplify the developed. I have updated the WIKI, giving the instructions to compile and TORO in Ubuntu.

Enjoy!

Matias E. Vara

www.torokernel.org

Toro bootloader

How can I start it?. The bootloader is a project itself, if you want to write a hobby OS you do not have to start from the bootloader. First, It will take you a lot of time, second, it is too hard to debug so you will become disappointed fast and you wont finish. I think that the important and interested things happens inside the kernel. Anyway, there are a few crazy guys that they want to make one. For that kind of guys, I have just started to write a few documentation about Toro's bootloader in the wiki. I hope that you find it interesting and appreciate the effort done (Yes, I don't like to write documentation but I know that it is too important ;) ).

Matias E. Vara

www.torokernel.org