Browse Source

Added BPB and minor changes

master
Mattia Giambirtone 2 months ago
parent
commit
946f7e72c3
  1. 3
      .gitignore
  2. 3
      .vscode/c_cpp_properties.json
  3. 1
      Makefile
  4. 108
      src/boot/mbr.s
  5. 2
      src/kernel/drivers/vga/screen.c
  6. 5
      src/kernel/main.c
  7. 2
      src/kernel/util.c

3
.gitignore

@ -69,5 +69,6 @@ _deps
*.bin
*.img
dist/
obj/
build/

3
.vscode/c_cpp_properties.json

@ -10,7 +10,8 @@
"compilerPath": "/usr/bin/gcc",
"cStandard": "gnu17",
"cppStandard": "gnu++17",
"intelliSenseMode": "linux-gcc-x64"
"intelliSenseMode": "linux-gcc-x64",
"configurationProvider": "ms-vscode.makefile-tools"
}
],
"version": 4

1
Makefile

@ -67,6 +67,7 @@ $(OBJDIR)/%.o: prepare $(SRCDIR)/%.c
# Compile kernel drivers
drivers: $(DRIVERS_OBJS)
# Compile and link the kernel
$(BUILDDIR)/kernel.bin: $(OBJDIR)/entrypoint.o $(KERNEL_OBJS) $(DRIVERS_OBJS)
$(LD) -o $@ -Ttext 0x1000 $^ --oformat binary

108
src/boot/mbr.s

@ -12,43 +12,82 @@
; See the License for the specific language governing permissions and
; limitations under the License.
; Definition of the MBR (Master Boot Record). This is basically our bootloader and
; is located in the first 512 bytes of the drive we're booting from. From here, we
; do some basic setup and then call into the kernel
; Welcome to TSBL: The Simple Bootloader
[org 0x7c00] ; Address where the code expects to be loaded in. The BIOS always loads us here
[bits 16] ; All x86 CPUs start in 16 bit (aka "real") mode, so we tell nasm to emit 16-bit code
kernel_offset: equ 0x1000
reserved_sectors: equ 4
; This isn't needed inside the qemu emulator, but
; real hardware is unlikely to start up with the
; segment registers zeroed, so we do it here
mov ax, 0
mov ds, ax
mov ss, ax
mov es, ax
xor ax, ax
; We save the value of the current boot drive
mov [boot_drive], dl
; Now we setup the stack by setting the
; base pointer to a location that's far
; enough from where the code for the BIOS
; is located
mov sp, 0x9000
mov bp, sp
call bios_cls
mov si, loading_stage2_msg
call bios_println
mov bx, stage2
mov cl, 2
mov dh, reserved_sectors
mov dl, [boot_drive]
call load_disk
jmp stage2
; Code copied from the limine bootloader
jmp skip_bpb ; Workaround for some BIOSes that require this stub
nop
; Some BIOSes will do a funny and decide to overwrite bytes of code in
; the section where a FAT BPB would be, potentially overwriting
; bootsector code.
; Avoid that by filling the BPB area with dummy values.
; Some of the values have to be set to certain values in order
; to boot on even quirkier machines.
; Source: https://github.com/freebsd/freebsd-src/blob/82a21151cf1d7a3e9e95b9edbbf74ac10f386d6a/stand/i386/boot2/boot1.S
bpb:
times 3-($-$$) db 0
bpb_oem_id: db "TSBL "
bpb_sector_size: dw 512
bpb_sects_per_cluster: db 0
bpb_reserved_sects: dw 0
bpb_fat_count: db 0
bpb_root_dir_entries: dw 0
bpb_sector_count: dw 0
bpb_media_type: db 0
bpb_sects_per_fat: dw 0
bpb_sects_per_track: dw 18
bpb_heads_count: dw 2
bpb_hidden_sects: dd 0
bpb_sector_count_big: dd 0
bpb_drive_num: db 0
bpb_reserved: db 0
bpb_signature: db 0
bpb_volume_id: dd 0
bpb_volume_label: db "TSBL "
bpb_filesystem_type: times 8 db 0
kernel_offset: equ 0x1000 ; Address in memory where kernel will be loaded
reserved_sectors: equ 4 ; How many disk sectors we reserve for our second stage
skip_bpb:
cli
cld
; This isn't needed inside the qemu emulator, but
; real hardware is unlikely to start up with the
; segment registers zeroed, so we do it here
xor si, si
mov ds, si
mov ss, si
mov es, si
; We save the value of the current boot drive
mov [boot_drive], dl
; Now we setup the stack by setting the
; base pointer to a location that's far
; enough from where the code for the BIOS
; is located
mov sp, 0x7c00
mov bp, sp
sti
call bios_cls
mov si, loading_stage2_msg
call bios_println
mov bx, stage2
mov cl, 2
mov dh, reserved_sectors
mov dl, [boot_drive]
call load_disk
jmp stage2
; Variables needed in the boot
@ -66,6 +105,7 @@ times 510 - ($ - $$) db 0
dw 0xaa55
[bits 16]
stage2:
; Here we're no longer limited by the size of the
; boot sector, so we can perform the more complex
@ -76,7 +116,7 @@ stage2:
call switch_to_protected_mode
load_kernel:
load_kernel:
; Loads the kernel into memory
mov bx, kernel_offset
mov cl, reserved_sectors + 1

2
src/kernel/drivers/vga/screen.c

@ -59,7 +59,7 @@ void kprintAt(char* message, i32 col, i32 row) {
}
void kprint(char* message) {
void inline kprint(char* message) {
/*
Prints a null-terminated string to the
VGA text buffer

5
src/kernel/main.c

@ -21,7 +21,8 @@ limitations under the License.
i32 kmain(void) {
/*
The kernel entry point of TSOS
The kernel entry point of TSKL: The
Simple Kernel
*/
@ -29,5 +30,5 @@ i32 kmain(void) {
// log messages like this is just awful
kprintln("\n\n\nTSKL - INFO: Kernel booted successfully");
// TODO...
return 0x022172; // :D
return 0x202172; // :D
}

2
src/kernel/util.c

@ -82,6 +82,4 @@ void itoa(i32 n, char* a) {
if (sign < 0) a[--i] = '-';
a[--i] = '\0';
/* TODO: implement "reverse" */
}
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