CSCE611 OS Project01 Note

Hanzhong

2024-01-25

In this document, I describe the steps I took to add gdb debug support to the kernel in MacBook M2.

1) Environment preparation

Set up Bochs with GDB support on MacBook M2:

Step01, download source code from bochs’s GitHub releases: https://github.com/bochs-emu/Bochs/releases/tag/REL_2_7_FINAL

Step02, set the configure to enable GDB stub:

$ cd [Bochs' dir]
$ ./configure --enable-ne2000 \
            --enable-all-optimizations \
            --enable-cpu-level=6 \
            --enable-x86-64 \
            --enable-vmx=2 \
            --enable-pci \
            --enable-usb \
            --enable-usb-ohci \
            --enable-e1000 \
            --enable-disasm \
            --disable-debugger-gui \
            --with-sdl \
            --prefix=$HOME/opt/bochs \
            --enable-gdb-stub  # important, --enable-debugger is not work

Step03, prepare and make Bochs:

1 2	$ brew install sdl $ make

Step04, install GDB:

Now, no native gdb is supposed in MacBook M2. So I installed another one : i386-elf-gdb

1	$ brew install i386-elf-gdb

2) Add debug support to the kernel

Step05, modify MP’s makefile:

Add -g flag in makefile:

AS=nasm

GCC=/opt/homebrew/Cellar/x86_64-elf-gcc/13.2.0/bin/x86_64-elf-gcc
LD=/opt/homebrew/Cellar/x86_64-elf-binutils/2.41_1/bin/x86_64-elf-ld

GCC_OPTIONS = -m32 -nostdlib -fno-builtin -nostartfiles -nodefaultlibs -fno-exceptions -fno-rtti -fno-stack-protector -fleading-underscore -fno-asynchronous-unwind-tables

all: kernel.bin

clean:
	rm -f *.o *.bin

# ==== KERNEL ENTRY POINT ====
start.o: start.asm
	$(AS) -f elf -o start.o start.asm

# ==== UTILITIES ====
utils.o: utils.H utils.C
	$(GCC) $(GCC_OPTIONS) -g -c -o utils.o utils.C

# ==== DEVICES ====
console.o: console.H console.C
	$(GCC) $(GCC_OPTIONS) -g -c -o console.o console.C

# ==== KERNEL MAIN FILE ====
kernel.o: kernel.C
	$(GCC) $(GCC_OPTIONS) -g -c -o kernel.o kernel.C


kernel.bin: start.o kernel.o console.o utils.o linker.ld
	$(LD) -melf_i386 -T linker.ld -o kernel.bin start.o kernel.o console.o utils.o

Modify linker.ld, delete the first line OUTPUT_FOTMAT(‘binary’).

Debug

Step06, start Bochs:

I did not install bochs. So I use the path to call its runnable file directly

1	$ /Users/lhz/bochs/bochs -f bochsrc.bxrc

Step07, start GDB and connect to Bochs:

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$ i386-elf-gdb kernel.bin # start GDB
$ set architecture i386:x86-64:intel
$ target remote localhost:1234 # connect to bochs

Step08, set breakpoint and debug in kernel:

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$ b main() # set breakpoint
$ continue # stop at main(), the breakpoint
$ continue # enter main(), start console