From 946f7e72c332efd56feb5ef056480dfe1e772e42 Mon Sep 17 00:00:00 2001 From: Mattia Giambirtone Date: Sat, 19 Nov 2022 18:20:25 +0100 Subject: [PATCH] Added BPB and minor changes --- .gitignore | 3 +- .vscode/c_cpp_properties.json | 3 +- Makefile | 1 + src/boot/mbr.s | 102 ++++++++++++++++++++++---------- src/kernel/drivers/vga/screen.c | 2 +- src/kernel/main.c | 5 +- src/kernel/util.c | 2 - 7 files changed, 80 insertions(+), 38 deletions(-) diff --git a/.gitignore b/.gitignore index 419a80e..11f5653 100644 --- a/.gitignore +++ b/.gitignore @@ -69,5 +69,6 @@ _deps *.bin *.img dist/ - +obj/ +build/ diff --git a/.vscode/c_cpp_properties.json b/.vscode/c_cpp_properties.json index 900f09f..22fb36f 100644 --- a/.vscode/c_cpp_properties.json +++ b/.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 diff --git a/Makefile b/Makefile index 9dc16e9..15c286e 100644 --- a/Makefile +++ b/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 $^ --oformat binary diff --git a/src/boot/mbr.s b/src/boot/mbr.s index 46d04b0..f68caa5 100644 --- a/src/boot/mbr.s +++ b/src/boot/mbr.s @@ -12,43 +12,82 @@ ; See the License for the specific language governing permissions and ; limitations under the License. -; Definition of the MBR (Master Boot Record). This is basically our bootloader and -; is located in the first 512 bytes of the drive we're booting from. From here, we -; do some basic setup and then call into the kernel +; Welcome to TSBL: The Simple Bootloader [org 0x7c00] ; Address where the code expects to be loaded in. The BIOS always loads us here [bits 16] ; All x86 CPUs start in 16 bit (aka "real") mode, so we tell nasm to emit 16-bit code -kernel_offset: equ 0x1000 -reserved_sectors: equ 4 +; Code copied from the limine bootloader -; This isn't needed inside the qemu emulator, but -; real hardware is unlikely to start up with the -; segment registers zeroed, so we do it here -mov ax, 0 -mov ds, ax -mov ss, ax -mov es, ax -xor ax, ax +jmp skip_bpb ; Workaround for some BIOSes that require this stub +nop -; We save the value of the current boot drive -mov [boot_drive], dl +; Some BIOSes will do a funny and decide to overwrite bytes of code in +; the section where a FAT BPB would be, potentially overwriting +; bootsector code. +; Avoid that by filling the BPB area with dummy values. +; Some of the values have to be set to certain values in order +; to boot on even quirkier machines. +; Source: https://github.com/freebsd/freebsd-src/blob/82a21151cf1d7a3e9e95b9edbbf74ac10f386d6a/stand/i386/boot2/boot1.S -; Now we setup the stack by setting the -; base pointer to a location that's far -; enough from where the code for the BIOS -; is located -mov sp, 0x9000 -mov bp, sp -call bios_cls -mov si, loading_stage2_msg -call bios_println -mov bx, stage2 -mov cl, 2 -mov dh, reserved_sectors -mov dl, [boot_drive] -call load_disk -jmp stage2 +bpb: + times 3-($-$$) db 0 + bpb_oem_id: db "TSBL " + bpb_sector_size: dw 512 + bpb_sects_per_cluster: db 0 + bpb_reserved_sects: dw 0 + bpb_fat_count: db 0 + bpb_root_dir_entries: dw 0 + bpb_sector_count: dw 0 + bpb_media_type: db 0 + bpb_sects_per_fat: dw 0 + bpb_sects_per_track: dw 18 + bpb_heads_count: dw 2 + bpb_hidden_sects: dd 0 + bpb_sector_count_big: dd 0 + bpb_drive_num: db 0 + bpb_reserved: db 0 + bpb_signature: db 0 + bpb_volume_id: dd 0 + bpb_volume_label: db "TSBL " + bpb_filesystem_type: times 8 db 0 + + +kernel_offset: equ 0x1000 ; Address in memory where kernel will be loaded +reserved_sectors: equ 4 ; How many disk sectors we reserve for our second stage + + +skip_bpb: + cli + cld + ; This isn't needed inside the qemu emulator, but + ; real hardware is unlikely to start up with the + ; segment registers zeroed, so we do it here + xor si, si + mov ds, si + mov ss, si + mov es, si + + + ; We save the value of the current boot drive + mov [boot_drive], dl + + ; Now we setup the stack by setting the + ; base pointer to a location that's far + ; enough from where the code for the BIOS + ; is located + mov sp, 0x7c00 + mov bp, sp + sti + call bios_cls + mov si, loading_stage2_msg + call bios_println + mov bx, stage2 + mov cl, 2 + mov dh, reserved_sectors + mov dl, [boot_drive] + call load_disk + jmp stage2 ; Variables needed in the boot @@ -66,6 +105,7 @@ times 510 - ($ - $$) 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 diff --git a/src/kernel/drivers/vga/screen.c b/src/kernel/drivers/vga/screen.c index b4295a4..10e6613 100644 --- a/src/kernel/drivers/vga/screen.c +++ b/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 diff --git a/src/kernel/main.c b/src/kernel/main.c index ff84861..b0ebc0c 100644 --- a/src/kernel/main.c +++ b/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 } \ No newline at end of file diff --git a/src/kernel/util.c b/src/kernel/util.c index 8b0cb3a..27d802b 100644 --- a/src/kernel/util.c +++ b/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" */ } \ No newline at end of file