diff options
Diffstat (limited to 'x86-bare-metal')
| -rw-r--r-- | x86-bare-metal/mbr-textmode/.gitignore | 1 | ||||
| -rw-r--r-- | x86-bare-metal/mbr-textmode/Makefile | 28 | ||||
| -rw-r--r-- | x86-bare-metal/mbr-textmode/mbr.S | 98 | ||||
| -rw-r--r-- | x86-bare-metal/mbr-textmode/mbr.ld | 25 | ||||
| -rw-r--r-- | x86-bare-metal/mbr-textmode/zmbr.zig | 39 |
5 files changed, 191 insertions, 0 deletions
diff --git a/x86-bare-metal/mbr-textmode/.gitignore b/x86-bare-metal/mbr-textmode/.gitignore new file mode 100644 index 0000000..a92a67f --- /dev/null +++ b/x86-bare-metal/mbr-textmode/.gitignore @@ -0,0 +1 @@ +BUILD/
\ No newline at end of file diff --git a/x86-bare-metal/mbr-textmode/Makefile b/x86-bare-metal/mbr-textmode/Makefile new file mode 100644 index 0000000..7642791 --- /dev/null +++ b/x86-bare-metal/mbr-textmode/Makefile @@ -0,0 +1,28 @@ +O := BUILD + +$(O)/boot: $(O)/boot.elf | dump_info + objcopy -O binary $< $@ + +$(O)/boot.elf: mbr.ld $(O)/mbr.o $(O)/zmbr.o + ld -o $@ -nostdlib -T $^ + +$(O)/mbr.o: mbr.S | $(O) + gcc -m32 -c -o $@ -ffreestanding mbr.S + +$(O)/zmbr.o: zmbr.zig | $(O) + zig build-obj -femit-bin=$@ -target x86-freestanding-none -O ReleaseSmall $< + +clean: + $(RM) -r $(O) + +$(O): + mkdir -p $(O) + +dump_info: $(O)/boot.elf + objdump -Mintel --disassemble=kmain --visualize-jumps=extended-color $< + readelf -W -l $< + size $< + size $< | awk '/$(notdir $<)/ { print "MBR utilization " $$1/512 "%" }' + +run: $(O)/boot + qemu-system-i386 -hda $< $(QEMU_ARGS) diff --git a/x86-bare-metal/mbr-textmode/mbr.S b/x86-bare-metal/mbr-textmode/mbr.S new file mode 100644 index 0000000..be41bed --- /dev/null +++ b/x86-bare-metal/mbr-textmode/mbr.S @@ -0,0 +1,98 @@ +// -- BOOT TEXT SECTION --------------------------------------------------------- + +.code16 +.intel_syntax noprefix + +.section .boot, "ax", @progbits + // Disable interrupts. + cli + + // Clear segment selectors. + xor ax, ax + mov ds, ax + mov es, ax + mov ss, ax + mov fs, ax + mov gs, ax + + // Set cs to 0x0000, as some BIOSes load the MBR to either 07c0:0000 or 0000:7c000. + jmp 0x0000:entry_rm16 + +entry_rm16: + // Get current video mode [1]. + // Return: + // ah number of columns + // al display mode (see table in [2]) + // + // [1] http://www.ctyme.com/intr/rb-0108.htm + // [2] http://www.ctyme.com/intr/rb-0069.htm + mov ah, 0xf + int 0x10 + + // Execpt that the bios initializes text mode 0x3. + // * 80x25 text mode (cols x rows) + // * 2 byte per character + // [15] blink [14:12] bg color [11:8] fg color [7:0] char + // * 0xB80000 screen address + cmp al, 0x3 + // Else we indicate an error with a blue screen. + je 2f + // Set background color [1]. + // + // [1] http://www.ctyme.com/intr/rb-0101.htm + mov ah, 0xb + mov bx, 1 + int 0x10 +1: + hlt + jmp 1b +2: + + // Enable A20 address line. + in al, 0x92 + or al, 2 + out 0x92, al + + // Load GDT descriptor. + lgdt [gdt_desc] + + // Enable protected mode (set CR0.PE bit). + mov eax, cr0 + or eax, (1 << 0) + mov cr0, eax + + // Far jump which loads segment selector (0x0008) into cs. + // 0x0008 -> RPL=0, TI=0(GDT), I=1 + jmp 0x0008:entry_pm32 + +.code32 +entry_pm32: + // Select data segment selector (0x0010) for ds. + mov ax, gdt_data - gdt + mov ds, ax + + // Initialize stack pointer. + // Real Mode memory (https://wiki.osdev.org/Memory_Map_(x86) + // 0x00000500 - 0x00007BFF | 29.75 KiB | conventional memory + mov esp, 0x7c00 + + // Enter zmbr.zig:kmain. + // Should not return, but for safety we emit a call rather than a jmp. + call kmain + +1: + hlt + jmp 1b + +// -- RODATA SECTION ------------------------------------------------------------ + +.section .rodata, "a", @progbits +.balign 8 +gdt: + .8byte 0x0000000000000000 // 0x00 | null descriptor + .8byte 0x00cf9a000000ffff // 0x08 | 32 bit, code (rx), present, dpl=0, g=4K, base=0, limit=fffff +gdt_data: + .8byte 0x00cf92000000ffff // 0x10 | 32 bit, data (rw), present, dpl=0, g=4K, base=0, limit=fffff +gdt_desc: + .2byte (. - gdt - 1) // size + .4byte gdt // address diff --git a/x86-bare-metal/mbr-textmode/mbr.ld b/x86-bare-metal/mbr-textmode/mbr.ld new file mode 100644 index 0000000..372ea42 --- /dev/null +++ b/x86-bare-metal/mbr-textmode/mbr.ld @@ -0,0 +1,25 @@ +/*OUTPUT_FORMAT(binary)*/ +OUTPUT_FORMAT(elf32-i386) +OUTPUT_ARCH(i386) + +SECTIONS { + . = 0x7c00; + .boot : { + *(.boot) + } + .text : { *(.text) } + .data : { *(.data) } + .rodata : { *(.rodata) } + _boot_end = .; + + . = 0x7c00 + 510; + .mbr.magic : { + BYTE(0x55); + BYTE(0xaa); + } + + /*/DISCARD/ : { *(.*) }*/ + /*rest : { *(.*) }*/ + + ASSERT(_boot_end - 0x7c00 < 510, "boot sector must fit in 510 bytes") +} diff --git a/x86-bare-metal/mbr-textmode/zmbr.zig b/x86-bare-metal/mbr-textmode/zmbr.zig new file mode 100644 index 0000000..2d95249 --- /dev/null +++ b/x86-bare-metal/mbr-textmode/zmbr.zig @@ -0,0 +1,39 @@ +const COLS = 80; +const ROWS = 25; + +/// Clear screen (all black). +fn clear_screen(video: []u16) void { + for (video) |*ch| { + ch.* = 0; + } +} + +/// Draw the color palette. +fn draw_palette(video: []u16) void { + // Each framebuffer entry in text mode is 16bit wide. + // [15] blink + // [14:12] bg color (3 bit) + // [11: 8] fg color (4 bit) + // [ 7: 0] ascii character + // + // https://en.wikipedia.org/wiki/VGA_text_mode + + // Print each bg / fg combination once. + for (video, 0..0x80) |*ch, i| { + ch.* = @as(u16, @truncate(i)) << 8 | 'a'; + } +} + +// kmain should be "callconv(.naked)", once issue is fixed. +// https://github.com/ziglang/zig/issues/18183 +export fn kmain() noreturn { + // Take a slice to VGA video memory (mode 3h text mode 80x25). + const video: []u16 = @as([*]u16, @ptrFromInt(0xB8000))[0 .. COLS * ROWS]; + + clear_screen(video); + draw_palette(video); + + while (true) { + asm volatile ("hlt"); + } +} |