diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/entry.asm | 122 |
1 files changed, 102 insertions, 20 deletions
diff --git a/src/entry.asm b/src/entry.asm index c13cf8e..11c3f71 100644 --- a/src/entry.asm +++ b/src/entry.asm @@ -3,23 +3,31 @@ ; MIT License, Copyright (c) 2020 Marvin Borner ; Definitions + %define LOCATION 0x7c00 ; Bootloader location +; Interrupts +%define VIDEO_INT 0x10 ; Video BIOS Interrupt +%define DISK_INT 0x13 ; Disk BIOS Interrupt +%define MISC_INT 0x15 ; Miscellaneous services BIOS Interrupt + +; Characters %define NEWLINE 0x0A ; Newline character (\n) %define RETURN 0x0D ; Return character (\r) %define NULL 0x00 ; NULL character (\0) -%define VIDEO_INT 0x10 ; Video BIOS Interrupt +; Video commands %define VIDEO_CLEAR 0x03 ; Clear screen command %define VIDEO_OUT 0x0e ; Teletype output command -%define DISK_INT 0x13 ; Disk BIOS Interrupt +; Disk commands %define DISK_EXT_CHECK 0x41 ; Disk extension check command %define DISK_EXT_CHECK_SIG1 0x55aa ; First extension check signature %define DISK_EXT_CHECK_SIG2 0xaa55 ; Second extension check signature %define DISK_ZERO 0x80 ; First disk - TODO: Disk detection %define DISK_READ 0x42 ; Disk extended read command +; EXT2 constants %define EXT2_SB_SIZE 0x400 ; Superblock size %define EXT2_SIG_OFFSET 0x38 ; Signature offset in superblock %define EXT2_TABLE_OFFSET 0x08 ; Inode table offset after superblock @@ -31,12 +39,21 @@ %define EXT2_POINTER_OFFSET 0x28 ; Inode offset of first data pointer %define EXT2_SIG 0xef53 ; Signature -%define STACK_POINTER 0x00900000 ; The initial stack pointer in kernel mode -%define KERNEL_POSITION 0x00050000 ; Loaded kernel position in protected mode (* 0x10) +; MMAP constants +%define MMAP_START 0x400 ; Starts at 0x400, ends at 0x500 +%define MMAP_SIZE 0x18 ; Struct size +%define MMAP_SIG 0x0534d4150 ; Signature ("SMAP") +%define MMAP_BIOS_MAGIC 0xe820 ; BIOS int 15h code to get address map +; A20 constants %define A20_GATE 0x92 ; Fast A20 gate %define A20_ENABLED 0b10 ; Bit 1 defines whether A20 is enabled %define A20_EXCLUDE_BIT 0xfe ; Bit 0 may be write-only, causing a crash + +; Kernel constants +%define STACK_POINTER 0x00900000 ; The initial stack pointer in kernel mode +%define KERNEL_POSITION 0x00050000 ; Loaded kernel position in protected mode (* 0x10) + ; ENOUGH, let's go! bits 16 @@ -174,6 +191,14 @@ stage_two: mov [dest], bx call kernel_load + ; Load mmap + xor eax, eax + mov es, eax + mov edi, MMAP_START + push edi + call memory_map + push edi + jmp protected_mode_enter kernel_load: @@ -193,6 +218,49 @@ kernel_load: jnz kernel_load ret +; Tries to load a memory map using BIOS INT 15h and e820h +memory_map: + xor ebx, ebx ; Must be 0 by spec + mov edx, MMAP_SIG ; "SMAP" in hex + mov eax, MMAP_BIOS_MAGIC ; Specify MMAP information + mov [es:di + 20], dword 1 ; Force a valid ACPI entry + mov ecx, MMAP_SIZE ; Request struct size + int MISC_INT ; BIOS interrupt + jc short .fail ; Carry means "unsupported function" + mov edx, MMAP_SIG ; Mov for verification + cmp eax, edx ; Verification: Must be "SMAP" + jne short .fail ; Result wasn't correct signature + test ebx, ebx ; Is size >1 + je short .fail ; Nope, worthless :( + jmp short .loop +.next: + mov eax, MMAP_BIOS_MAGIC ; Re-move because 0x15 clears or sth + mov [es:di + 20], dword 1 ; Force a valid ACPI entry + mov ecx, MMAP_SIZE ; Request struct size + int MISC_INT ; BIOS interrupt + jc short .done ; Carry means "end of list already reached" + mov edx, MMAP_SIG ; Repair register (safety first!) +.loop: + jcxz .skip ; Skip 0-length entries + cmp cl, 20 ; Is the response correct ACPI spec (24 byte)? + jbe short .notext ; Nope? Jump! + test byte [es:di + 20], 1 ; Is the "ignore this data" bit clear? + je short .skip ; Yep? Skip! +.notext: + mov ecx, [es:di + 8] ; Get lower 32 bits of region + or ecx, [es:di + 12] ; "Or" with upper 32 bits to test for zero + jz .skip ; It's zero, skip! + add di, MMAP_SIZE ; Else, next! +.skip: + test ebx, ebx ; If ebx is 0, list is complete + jne short .next ; Else, next! +.done: + clc ; Clear carry + ret ; Finished! +.fail: + stc ; Set "unsupported function" + ret ; Finished! + protected_mode_enter: cli ; Turn off interrupts mov si, protected_msg @@ -226,6 +294,11 @@ protected_mode_enter: bits 32 ; Woah, so big! protected_mode: + pop ecx ; End of memory map + mov [mem_info + 4], ecx ; Ending boundary of struct + pop ecx ; Start of memory map + mov [mem_info], ecx ; Starting boundary of struct + mov ax, 10h ; Set data segement indentifier mov ds, ax mov es, ax @@ -235,30 +308,39 @@ protected_mode: mov esp, STACK_POINTER ; Move stack pointer + mov eax, mem_info ; Pass meminfo to kernel + push eax ; Push as first kernel parameter + mov edx, KERNEL_POSITION lea eax, [edx] call eax +; Memory map +align 16 +mem_info: + dd 0 ; Start address + dd 0 ; End address + ; GDT align 32 -gdt: -gdt_null: +gdt: ; GDTs start +gdt_null: ; Must be null dd 0 dd 0 -gdt_code: - dw 0xFFFF - dw 0 - db 0 - db 0x9A - db 0xCF - db 0 -gdt_data: - dw 0xFFFF - dw 0 - db 0 - db 0x92 - db 0xCF - db 0 +gdt_code: ; Code section + dw 0xFFFF ; Limit + dw 0 ; First base + db 0 ; Second base + db 0x9A ; Configuration + db 0xCF ; Granularity + db 0 ; Third base +gdt_data: ; Data section + dw 0xFFFF ; Limit + dw 0 ; First base + db 0 ; Second base + db 0x92 ; Configuration + db 0xCF ; Granularity + db 0 ; Third base gdt_end: gdt_desc: dw gdt_end - gdt - 1 |