Debugging ponchoOS kernel

instructions.sh

# INSIDE WSL, install gdb (one-time instruction)
sudo apt install gdb

# Add the following to your kernel Makefile CFLAGS, so that gcc will generate 
# debug symbols that the debugger can use
# Note: The thing being added is -g, so as of lesson 12 it should look like this.  
# Delete all the contents of the lib folder to force a recompile
CFLAGS = -ffreestanding -fshort-wchar -g

# Add the following to your qemu invocation and start QEmu:
#    -s (Starts a gdb debug server on port 1234)
#    -S (Pauses the virtual machine after  power on to wait for a debugger connection)
qemu-system-x86_64 -drive file=%BUILDDIR%/%OSNAME%.img -m 256M -cpu qemu64 \
-drive if=pflash,format=raw,unit=0,file=%OVMFDIR%/OVMF_CODE-pure-efi.fd,readonly=on \
-drive if=pflash,format=raw,unit=1,file=%OVMFDIR%/OVMF_VARS-pure-efi.fd -net none -s -S

# Start gdb using your built kernel file, this will read the kernel 
# information into gdb.  If your kernel name is different, then replace it, 
# it's NOT the image, but the kernel binary
gdb bin/kernel.elf 

# Your shell will look different now, as you are inside the gdb command prompt.  
# Connect it to the kernel running in QEmu
target remote :1234

# You will see some output similar to '0x000000000000fff0 in ?? ()'.  
# This is correct, it means that the machine is halted almost immediately after power on 
# and is waiting for the signal to continue.  First, add a hardware assisted breakpoint 
# at your kernel start function
hbreak _start

# You should see output like 
# 'Hardware assisted breakpoint 1 at 0x134: file src/kernel.cpp, line 3.'  
# Now you can ask the program to continue, and it will stop at your start method
continue # or 'c' for short

# 'Continuing' is written, and qemu will continue into the uefi shell and eventually 
# into your kernel and then pause again displaying something like 
#    'Breakpoint 1, _start (bootInfo=0xff14f28) at src/kernel.cpp:3
#     3       extern "C" void _start(BootInfo* bootInfo){

# Common debugging commands include "step" (which will go forward one line and enter 
# any function on that line, similar to step into in most IDE), "next" 
# (analogous to "step over") and "finish" (step out).  These can be abbreviated as "s", "n",
# and "fin".  You can print out varibles using the "print" command (p for short):
p bootInfo

# $1 = (BootInfo *) 0xff14f28

# Tab autocomplete is available, as well as command history via the up key.  Happy debugging!