![]() This problem used to persist for quite a long time, so it may or may not be fixed in the meantime. Special version of bochs compiled with a gdb stub so that the software running inside the emulator can be debugged with gdb. Unfortunately it has some problems with switching between 32 and 64 bit mode and crashes when I try to debug my 64 bit kernel, so for me it's rather usesless for kernel debugging. GDB is certainly a great debugger and it's usable with both QEMU and Bochs (with GDB stub). (Most of the time I just do things like "set a breakpoint at x, run, dump register contents (and some other relevant information), quit".) Displaying of this information together with other commands can be automated, so I can write automated tests and dump the results into a log file. Most important for me is that it shows lots of CPU internal information (descriptor tables, page tables, segment registers (including their shadowed parts), TLBs) and also information on several devices using the Bochs param tree. After creating a virtual serial port, one port in the pair should be used for the emulator the other one should specified in gdb for remote debugging.Ĭom0com can be used in Windows and a pseudo terminal might be used in Linux to create virtual serial port pairs.I'm mainly using Bochs and its internal debugger for debugging my OS, so I can mainly comment on this one. If you have gdbstub inside your kernel and run your kernel inside an emulator, you can use a COM Port redirector to create a virtual serial port. This will allow Emacs to follow along as you place breakpoints and single-step through your kernel. Try using M-x gdb and when it asks you for command-line arguments to GDB, use -annotate=3. This will connect to GDB-stub whenever you start GDB and will load symbols from kernel.bin.Įmacs is well integrated with GDB. If you are using a 64-bit kernel, you may need to set up the address size using set command. ![]() If it prompts you after the " target remote" line asking whether to kill a program that is already being debugged answer " n". If you are debugging a kernel running on a real machine then use target remote /dev/tty2 instead of the network port. GDB on the host machine can be started like this: ![]() Thats because GDB stub is not active in standard Bochs binary package. The bochssrc (or whatever configuration script is being used) will need to have the gdbstub line set to something like gdbstub: enabled=1, port=1234, text_base=0, data_base=0, bss_base=0.Īfter an emulator/kernel is configured it will then wait for a connection from GDB. To use GDB tools with Bochs, first we need to rebuild Bochs with gdb-stub enabled. Note that, since there are several slightly different ways to integrate gdb with Bochs, the TA and instructor won't be able to be helpful in debugging your installation. QEMU - GDB can be connected to QEMU by simply starting qemu with the -s -S command line switches.īochs - For GDB to be able to interface with Bochs, Bochs will need to be configured with the -enable-gdb-stub argument. Another document describing the integration of Bochs with gdb is Integrating Bochs Environment with GDB A third document on integrating Bochs with gdb is this one. Now start your test machine and your kernel will wait for a GDB host connection. _asm_ ( "int3" ) /*break point exception to sync with GDB host*/ Kprintf ( "Waiting for GDB(0x%X) : ", sys_gdb_port ) Set_debug_traps ( ) /*setup exception handlers*/ InitSerialPort (sys_gdb_port, 9600, UART_DATA_BIT_8, UART_PARITY_NONE, UART_STOP_BIT_1 ) /*set up the serial port*/ virtual, which virtualizer did you use (Bochs, VMWare, etc.) Another, how do you debug and/or whitebox-test the kernel Is there something along the lines of. It requires the following three functions from the kernel to read/write from a serial port and to set up the exception handlers. For the i386 platform, GDB source includes a reference implementation of gdb-stub.c. To debug (using GDB) a kernel running on a real machine, the kernel needs to contain a GDB stub. If you are using an emulator (Bochs or QEMU), you can use the GDB stub compiled into the emulator. This requires a kernel source change and it is a must if you are running your kernel on a test(real) machine and debugging from another machine. That means the kernel should contain the remote stub to talk to the host GDB during the debug session. For example, you might use remote debugging on an operating system kernel, or on a small system which does not have a general purpose operating system powerful enough to run a full-featured debugger.”įor remote debugging, a remote stub should be implemented in the remote program that needs to be debugged. From the GDB manual, “If you are trying to debug a program running on a machine that cannot run GDB in the usual way, it is often useful to use remote debugging. We are interested in the remote debugging facility of GDB.
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