This repo is under heavy refactoring: kindly wait to use it as long as you see this notice.
I am currently moving QEMU installation inside a dedicated Docker container in order to not install QEMU locally.
Creating a k(e)rn(e)l for fun.
I use Docker to create the krnl build environment image where I cross-compile the krnl.
I use QEMU to run the krnl on a i686 architecture and GDB to troubleshoot it.
Assuming this is the first time you work with this project.
# Clone this repo
$ git clone ... && cd krnl
# Install Docker, QEMU and GDB
$ sudo apt install ...
# Copy .my-gdbinit in your home and rename it ./gdbinit
# Build the krnl build environment Docker image
$ ./build-lab.sh
[+] Building 17.1s (9/9) FINISHED
=> [internal] load build definition from Dockerfile 0.0s
...
=> => naming to docker.io/library/krnl-development-lab:0.1.0 0.0s
# Compile the krnl
$ ./compile-krnl.sh
# Test the krnl
$ ./emulate-krnl.shThe Docker image will mount this current directory as a volume: this way, if you want to edit the krnl sources, you don't have to re-build the Docker image in order to copy updated sources in lab Docker image; all you have to do is:
- edit krnl sources;
./compile-krnl.sh && ./emulate-krnl.sh
We will troubleshoot our krnl with GDB.
In emulate-krnl.sh, QEMU is started with -s -S command line switches:
-
-S: do not start CPU at startup -
-s: shorthand for -gdb tcp::1234, i.e. open a gdbserver on TCP port 1234
Our custom .gdbinit, .my-gdbinit, has the commands that connects GDB to QEMU.
After running the emulated krnl with emulate-krnl.sh, copy the commands in
.my-gdbinit in your .gdbinit; open another shell and just type gdb:
you should see:
$ gdb -q
0x00100018 in _start ()
(gdb) info functions
All defined functions:
File krnl.c:
61: int main(void);
52: void print_string(char *, unsigned char);
40: void term_init();
36: uint16_t vga_entry(unsigned char, uint8_t);
Non-debugging symbols:
0x0010000c _start
(gdb)