myOS

This is a hobby operating systems project.

Prerequisites

• gcc: I think any version will do ... maybe.
• qemu: qemu-system-i386 specifically (this is currently the only targeted platform).
• gdb: well, this isn't really needed but is expected by default. If you don't want to install gdb for some reason, you can simply remove the "-s -S" flags from scripts/start.sh

Executing the kernel

To run, simply run the script:

$ ./scripts/run.sh

from the root folder.

Typical Workflow

When you run scripts/run.sh, Qemu will launch a curses window in your terminal. By default, Qemu will not immediately launch the VM but wait for a connection on tcp port 1234 (this is theeffect of the "-s -S" flags in scripts/start.sh). In another terminal, you can cd into the project's root directory and run:

$ gdb kernel.elf

You can then connect to the Qemu instance by running:

$ gdb> target remote :1234

Then let the VM continue execution:

$ gdb> c

After this you can use ctrl+c to pause the VM.

You can then try a couple of things from gdb:

inspect registers

$ gdb> info reg [<register_name>]*

Note: Not supplying a specific register will cause all the registers to be displayed.

step through instructions

$ gdb> stepi

This will cause the VM to execute one instruction: the next instruction.

Print register value

For example, to print the current value in the eax register

$ gdb> print $eax

View content at memory address

To view the content at 0xb8000 for example:

$ gdb> x/x 0xb8000

Add a breakpoint to the kernel

Gdb lets us add breakpoints in multiple ways:

By function name:

To set a breakpoint at main in kernel/kernel.c for example:

$ gdb> b main

By line number:

To set a break point at line 50 in kernel/kernel.c:

$ gdb> b kernel/kernel.c:50

By address:

To set a breakpoint at 0x1000:

b *0x1000

Cheers