diff --git a/14-checkpoint/Makefile b/14-checkpoint/Makefile new file mode 100644 index 0000000..61497ea --- /dev/null +++ b/14-checkpoint/Makefile @@ -0,0 +1,43 @@ +C_SOURCES = $(wildcard kernel/*.c drivers/*.c) +HEADERS = $(wildcard kernel/*.h drivers/*.h) +OBJ = ${C_SOURCES:.c=.o} + +# Change this if your cross-compiler is somewhere else +CC = /usr/local/i386elfgcc/bin/i386-elf-gcc +GDB = /usr/local/i386elfgcc/bin/i386-elf-gdb +# -g: Use debugging symbols +CFLAGS = -g + +# First rule is run by default +os-image.bin: boot/bootsect.bin kernel.bin + cat $^ > os-image.bin + +kernel.bin: kernel.elf + i386-elf-ld -o $@ -Ttext 0x1000 $^ --oformat binary + +run: os-image.bin + qemu-system-i386 -fda os-image.bin + +debug: os-image.bin kernel.elf + qemu-system-i386 -s -fda os-image.bin & + ${GDB} -ex "target remote localhost:1234" -ex "symbol-file kernel.elf" + +# To build the kernel: make all objects first +kernel.elf: boot/kernel_entry.o ${OBJ} + i386-elf-ld -o $@ -Ttext 0x1000 $^ + +# To make an object, always compile from its .c +%.o: %.c ${HEADERS} + ${CC} ${CFLAGS} -ffreestanding -c $< -o $@ + +# Object files from asm files +%.o: %.asm + nasm $< -f elf -o $@ + +%.bin: %.asm + nasm $< -f bin -o $@ + + +clean: + rm -rf *.bin *.dis *.o os-image.bin *.elf + rm -rf kernel/*.o boot/*.bin drivers/*.o diff --git a/14-checkpoint/README.md b/14-checkpoint/README.md index 16f415b..cf31211 100644 --- a/14-checkpoint/README.md +++ b/14-checkpoint/README.md @@ -1,4 +1,4 @@ -*Concepts you may want to Google beforehand: monolithic kernel, microkernel* +*Concepts you may want to Google beforehand: monolithic kernel, microkernel, debugger, gdb* **Goal: Pause and organize our code a little bit** @@ -13,6 +13,39 @@ Take a look at the new folder structure. Most of the files have been symlinked from previous lessons, so if we have to change them at some point, it will be a better idea to remove the symlink and create a new file. +Furthermore, since from now on we will use mostly C to code, we'll take advantage of qemu's +ability to open a connection to gdb. First, let's install a cross-compiled `gdb` since +OSX uses `lldb` which is not compatible with the ELF file format (neither is the `gdb` available +on Homebrew's repos) + +```sh +cd /tmp/src +curl -O http://ftp.rediris.es/mirror/GNU/gnu/gdb/gdb-7.8.tar.gz +tar xf gdb-7.8.tar.gz +mkdir gdb-build +cd gdb-build +export PREFIX="/usr/local/i386elfgcc" +export TARGET=i386-elf +../gdb-7.8/configure --target="$TARGET" --prefix="$PREFIX" --program-prefix=i386-elf- +make +make install +``` + +Check out the Makefile target `make debug`. We can take +advantage of this cool qemu feature. Type `make debug` and, on the gdb shell: + +- Set up a breakpoint in `kernel.c:main()`: `b main` +- Run the OS: `continue` +- Run two steps into the code: `next` then `next`. You will see that we are just about to set + the 'X' on the screen, but it isn't there yet (chech out the qemu screen) +- Let's see what's in the video memory: `print *video_memory`. There is the 'L' from "Landed in + 32-bit Protected Mode" +- Hmmm, let's make sure that `video_memory` points to the correct address: `print video_memory` +- `next` to put there our 'X' +- Let's make sure: `print *video_memory` and look at the qemu screen. It's definitely there. + +Now is a good time to read some tutorial on `gdb`! + Strategy -------- diff --git a/14-checkpoint/boot/32bit_print.asm b/14-checkpoint/boot/32bit_print.asm new file mode 120000 index 0000000..b249c3a --- /dev/null +++ b/14-checkpoint/boot/32bit_print.asm @@ -0,0 +1 @@ +../../08-32bit-print/32bit-print.asm \ No newline at end of file diff --git a/14-checkpoint/boot/bootsect.asm b/14-checkpoint/boot/bootsect.asm new file mode 100644 index 0000000..361d7ef --- /dev/null +++ b/14-checkpoint/boot/bootsect.asm @@ -0,0 +1,51 @@ +; Identical to lesson 13's boot sector, but the %included files have new paths +[org 0x7c00] +KERNEL_OFFSET equ 0x1000 ; The same one we used when linking the kernel + + mov [BOOT_DRIVE], dl ; Remember that the BIOS sets us the boot drive in 'dl' on boot + mov bp, 0x9000 + mov sp, bp + + mov bx, MSG_REAL_MODE + call print + call print_nl + + call load_kernel ; read the kernel from disk + call switch_to_pm ; disable interrupts, load GDT, etc. Finally jumps to 'BEGIN_PM' + jmp $ ; Never executed + +%include "boot/print.asm" +%include "boot/print_hex.asm" +%include "boot/disk.asm" +%include "boot/gdt.asm" +%include "boot/32bit_print.asm" +%include "boot/switch_pm.asm" + +[bits 16] +load_kernel: + mov bx, MSG_LOAD_KERNEL + call print + call print_nl + + mov bx, KERNEL_OFFSET ; Read from disk and store in 0x1000 + mov dh, 2 + mov dl, [BOOT_DRIVE] + call disk_load + ret + +[bits 32] +BEGIN_PM: + mov ebx, MSG_PROT_MODE + call print_string_pm + call KERNEL_OFFSET ; Give control to the kernel + jmp $ ; Stay here when the kernel returns control to us (if ever) + + +BOOT_DRIVE db 0 ; It is a good idea to store it in memory because 'dl' may get overwritten +MSG_REAL_MODE db "Started in 16-bit Real Mode", 0 +MSG_PROT_MODE db "Landed in 32-bit Protected Mode", 0 +MSG_LOAD_KERNEL db "Loading kernel into memory", 0 + +; padding +times 510 - ($-$$) db 0 +dw 0xaa55 diff --git a/14-checkpoint/boot/bootsect.bin b/14-checkpoint/boot/bootsect.bin new file mode 100644 index 0000000..e8d27fb Binary files /dev/null and b/14-checkpoint/boot/bootsect.bin differ diff --git a/14-checkpoint/boot/disk.asm b/14-checkpoint/boot/disk.asm new file mode 120000 index 0000000..b01433e --- /dev/null +++ b/14-checkpoint/boot/disk.asm @@ -0,0 +1 @@ +../../07-bootsector-disk/boot_sect_disk.asm \ No newline at end of file diff --git a/14-checkpoint/boot/gdt.asm b/14-checkpoint/boot/gdt.asm new file mode 120000 index 0000000..3ebae1a --- /dev/null +++ b/14-checkpoint/boot/gdt.asm @@ -0,0 +1 @@ +../../09-32bit-gdt/32bit-gdt.asm \ No newline at end of file diff --git a/14-checkpoint/boot/kernel_entry.asm b/14-checkpoint/boot/kernel_entry.asm new file mode 120000 index 0000000..387cb0d --- /dev/null +++ b/14-checkpoint/boot/kernel_entry.asm @@ -0,0 +1 @@ +../../13-kernel-barebones/kernel_entry.asm \ No newline at end of file diff --git a/14-checkpoint/boot/kernel_entry.o b/14-checkpoint/boot/kernel_entry.o new file mode 100644 index 0000000..d421a6a Binary files /dev/null and b/14-checkpoint/boot/kernel_entry.o differ diff --git a/14-checkpoint/boot/switch_pm.asm b/14-checkpoint/boot/switch_pm.asm new file mode 120000 index 0000000..3eac90c --- /dev/null +++ b/14-checkpoint/boot/switch_pm.asm @@ -0,0 +1 @@ +../../10-32bit-enter/32bit-switch.asm \ No newline at end of file diff --git a/14-checkpoint/kernel.elf b/14-checkpoint/kernel.elf new file mode 100755 index 0000000..8b000fb Binary files /dev/null and b/14-checkpoint/kernel.elf differ diff --git a/14-checkpoint/kernel.sym b/14-checkpoint/kernel.sym new file mode 100755 index 0000000..c165349 Binary files /dev/null and b/14-checkpoint/kernel.sym differ diff --git a/14-checkpoint/kernel/kernel.c b/14-checkpoint/kernel/kernel.c new file mode 100644 index 0000000..ea8fd38 --- /dev/null +++ b/14-checkpoint/kernel/kernel.c @@ -0,0 +1,8 @@ +/* This will force us to create a kernel entry function instead of jumping to kernel.c:0x00 */ +void dummy_test_entrypoint() { +} + +void main() { + char* video_memory = (char*) 0xb8000; + *video_memory = 'X'; +} diff --git a/14-checkpoint/kernel/kernel.o b/14-checkpoint/kernel/kernel.o new file mode 100644 index 0000000..c7cfa2e Binary files /dev/null and b/14-checkpoint/kernel/kernel.o differ