wip refactor
pantonshire
9 months ago
parent
ae2720c826
commit
2b1a9f9412
@ -0,0 +1,14 @@
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%ifndef BOOT_FN_H
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%define BOOT_FN_H
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%macro fnstart 0
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push bp
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mov bp, sp
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%endmacro
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%macro fnret 0
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pop bp
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ret
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%endmacro
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%endif
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@ -0,0 +1,18 @@
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%ifndef BOOT_LAYOUT_H
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%define BOOT_LAYOUT_H
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%define S1_ADDR 0x7c00
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%define S2_ADDR 0x8200
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; %define MEMMAP 0x6a00
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; %define MEMMAP_END S2_ADDR
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; %define MEMMAP_ENT_SIZE 32
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; %define MEMMAP_CAP ((MEMMAP_END - MEMMAP) / MEMMAP_ENT_SIZE)
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%define REAL_GLOBALS 0x4000
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%define REAL_GLOBALS_END 0x6a00
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%define REAL_STACK_BASE REAL_GLOBALS
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%define S234_MAGIC 0x544e4150
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%endif
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@ -0,0 +1,28 @@
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%ifndef BOOT_S1_VARS_H
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%define BOOT_S1_VARS_H
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; Stage 1 base stack frame variable offsets / globals
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; (we use the same offsets once we copy the variables to the globals section)
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; -------------------------------------------------------------------------------------------------
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; The boot drive number given to us by the BIOS.
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%define BOOT_DRIVE 0x02
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; Boot drive geometry
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%define SECTORS_PER_TRACK 0x04
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%define N_HEADS 0x06
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; Starting LBA of the GPT partition entries array.
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%define GPT_ENTRIES_START_LBA 0x08
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; Number of GPT entries, saturated to 16 bits.
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%define GPT_N_ENTRIES_16 0x0a
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; Number of sectors to advance by once we've read every GPT entry in the current sector.
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%define GPT_SECTOR_STRIDE 0x0c
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; Number of bytes to advance by in the current sector once we've read a GPT entry.
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%define GPT_BYTE_STRIDE 0x0e
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; Number of GPT entries which can fit in a single sector.
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%define GPT_ENTRIES_PER_SECTOR 0x10
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%define GPT_CURRENT_ENTRY_IDX 0x12
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%define GPT_SECTOR_ENTRY_IDX 0x14
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%define GPT_SECTORS_LOADED 0x16
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%define GPT_CURRENT_LBA 0x18
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%define STAGE_2_GPT_ENTRY_ADDR 0x1a
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%endif
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@ -0,0 +1,8 @@
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%ifndef BOOT_S2_FNS_H
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%define BOOT_S2_FNS_H
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extern addr32_to_addr16
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extern read_sector
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extern panic_simple
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%endif
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@ -0,0 +1,34 @@
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OUTPUT_FORMAT("binary")
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. = 0x8200;
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SECTIONS {
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/* Stage 2 must come first so it's in the single sector loaded by stage 1. */
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.s2_text : {
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KEEP(*(.s2_text))
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*(.s2_text)
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}
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.s3_text : {
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KEEP(*(.s3_text))
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*(.s3_text)
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}
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.s3_data : {
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KEEP(*(.s3_data))
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*(.s3_data)
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}
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.magic : {
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/* Magic bytes stage 2 uses to make sure it's loaded the subsequent sectors correctly. */
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LONG(0x544e4150)
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}
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s234_magic = ADDR(.magic);
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/* Define a symbol for the total length of the binary, so the prelude knows how many blocks to
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* load from disk.
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*/
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s234_bin_len = . - 0x8200;
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s234_bin_sectors = (s234_bin_len + 511) / 512;
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}
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@ -0,0 +1,252 @@
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%include "layout.s"
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%include "s1_vars.s"
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[org S1_ADDR]
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[bits 16]
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main:
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cli
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xor ax, ax
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mov ds, ax
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mov es, ax
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; Put the stack base at 0x4000.
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; Stack grows high->low, so we'll grow away from our globals and program text.
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mov ss, ax
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mov bp, REAL_STACK_BASE
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mov sp, bp
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; Segment for VGA (0xb800 * 16 = 0xb8000)
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mov ax, 0xb800
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mov fs, ax
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; Set VGA mode
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; https://mendelson.org/wpdos/videomodes.txt
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mov ax, 0x0003
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int 0x10
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; Store boot drive number
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xor dh, dh
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push dx
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; Get drive geometry
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mov di, 0x00
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mov ah, 0x08
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int 0x13
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jc panic
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; Load sectors per track into cx & spill
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and cl, 0x3f
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xor ch, ch
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push cx
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; Load number of heads into bx & spill
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movzx bx, dh
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inc bx
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push bx
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; Load LBA 1.
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mov ax, 1
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mov bx, 0x7e00
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call read_lba
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; Check the GPT header magic "EFI PART"
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mov cx, GPT_MAGIC_LEN
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mov si, gpt_magic
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mov di, 0x7e00
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repe cmpsb
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jne panic
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; Ensure the 8-byte GPT starting LBA fits in 16 bits
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mov di, 0x7e00 ; The rep increments di so we need to reset it
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mov eax, [di + 0x4c]
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mov bx, [di + 0x4a]
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or ax, bx
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or eax, eax
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jnz panic
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; Store the first 16 bits of the GPT starting LBA (we have made sure the remaining bits are 0)
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push word [di + 0x48]
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; Load number of partitions
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mov ax, [di + 0x50]
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mov bx, [di + 0x52]
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or bx, bx
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jz .gpt_n_partitions_loaded
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; Number of partitions overflows 16 bits, so we just concern ourselves with the first 65535.
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; That's an awful lot of partitions anyway.
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mov ax, 0xffff
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.gpt_n_partitions_loaded:
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push ax
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; Load GPT entry size
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mov eax, [di + 0x54] ; Operand size override otherwise this is going to be painful
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mov ebx, eax
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; Assert that the entry size is 128 * 2^n for some integer n>=0. This is required for a valid GPT
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; and has the nice properties that:
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; - If each entry is larger than a sector (512 bytes), they'll be sector-aligned.
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; - If each entry is smaller than a sector, an integer number of them will fit into a sector.
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or eax, eax ; Test size != 0 because 128 * 2^n != 0
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jz panic
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test eax, 127 ; Test size is a multiple of 128
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jnz panic
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; Use the (n & (n - 1)) == 0 trick to test if the entry size is a power of 2. Since we already
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; know it's a nonzero multiple of 128, if size is a power of 2 then size = 128 * 2^n holds.
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; Therefore we don't need to bother dividing by 128 first (shr 7), which saves a couple of bytes.
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mov ecx, ebx
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dec ecx
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and ecx, eax
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jnz panic
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; Find the "sector stride", which is the number of sectors we increment by each time we want to
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; load a new entry.
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shr eax, 9 ; Divide by sector size to get sectors per entry
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cmp eax, 0xffff ; Make sure sectors per entry fits in 16 bits
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ja panic
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or ax, ax
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jnz .gpt_sector_stride_loaded
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; Sector stride must be at least one or we'll load the same sector each time!
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inc ax
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.gpt_sector_stride_loaded:
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push ax
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; Find the "byte stride", which is the number of bytes we increment by each time we want to load
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; the next entry in the same sector.
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cmp ebx, 512
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jb .gpt_find_entries_per_sector
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push word 0 ; Arbitrary byte stride since there's only one entry per sector
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push word 1 ; 1 entry per sector, since an entry is larger than a sector
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jmp .gpt_found_entries_per_sector
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.gpt_find_entries_per_sector:
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push bx ; Store byte stride = entry length in this case
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xor dx, dx
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mov ax, 512
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div bx ; Find entries per sector
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push ax
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.gpt_found_entries_per_sector:
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; Set up stack variables for our second stage search loop.
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xor ax, ax
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push ax ; Current entry
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push ax ; Current entry within the current sector
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push ax ; Number of sectors loaded
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push word [bp - GPT_ENTRIES_START_LBA] ; Current LBA
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; Search for the partition storing our second stage.
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.loop_find_stage2:
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mov dx, [bp - GPT_CURRENT_ENTRY_IDX]
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cmp [bp - GPT_N_ENTRIES_16], dx
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; Panic if we've run out of partitions and haven't found the second stage yet.
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jbe panic
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; If we haven't loaded any sectors yet, load the first one.
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cmp word [bp - GPT_SECTORS_LOADED], 0
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je .load_first_lba
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; If there's still more entries in the current sector, skip loading a new sector
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mov ax, [bp - GPT_SECTOR_ENTRY_IDX] ; Load current entry index within the current sector
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cmp [bp - GPT_ENTRIES_PER_SECTOR], ax ; Compare to entries per sector
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ja .process_current_entry
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mov ax, [bp - GPT_SECTOR_STRIDE] ; Load sector stride
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add word [bp - GPT_CURRENT_LBA], ax ; Increment current LBA by sector stride
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mov word [bp - GPT_SECTOR_ENTRY_IDX], 0 ; Reset the current entry index within the current sector
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.load_first_lba:
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; Read the current LBA to 0x8000 (just past the end of the GPT header)
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mov ax, [bp - GPT_CURRENT_LBA]
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mov bx, 0x8000
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call read_lba
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; Increment number of sectors loaded
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inc word [bp - GPT_SECTORS_LOADED]
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.process_current_entry:
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; Calculate the address of the current GPT entry.
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mov ax, [bp - GPT_SECTOR_ENTRY_IDX] ; Load current entry index within current sector
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xor dx, dx
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mul word [bp - GPT_BYTE_STRIDE] ; Get the byte offset in the current sector of the current entry
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add ax, 0x8000 ; Convert offset to address (we loaded the sector at 0x8000)
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; Compare entry GUID to our stage 2 partition GUID.
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mov cx, GUID_LEN
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mov si, guid_stage2
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mov di, ax
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repe cmpsb
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je .found_stage2
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; Next iteration
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inc word [bp - GPT_CURRENT_ENTRY_IDX] ; Increment current entry index
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inc word [bp - GPT_SECTOR_ENTRY_IDX] ; Increment current entry index within the current sector
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jmp .loop_find_stage2
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.found_stage2:
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push ax ; Address of the GPT entry for stage 2
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mov si, ax
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; Load partition LBA start.
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mov eax, [si + 0x20]
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mov ebx, [si + 0x24]
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; Ensure it fits in 16 bits.
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or ebx, ebx
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jnz panic
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cmp ebx, 0xffff
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ja panic
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; Load partition LBA end.
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mov ecx, [si + 0x28]
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mov edx, [si + 0x2c]
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; Assert that the end LBA is greater than or equal to the start LBA, so we have at least one
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; sector to load (end LBA is inclusive).
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or edx, edx
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jnz .stage2_end_lba_ok
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cmp eax, ecx
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ja panic
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.stage2_end_lba_ok:
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mov bx, S2_ADDR
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call read_lba
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jmp bx
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; Load a single boot disk sector. Panic on failure.
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; Inputs:
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; - ax: LBA to load
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; - bx: address to read sector to
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; Clobber: ax, cx, dx
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read_lba:
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; sector - 1 = LBA % sectors_per_track
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; temp = LBA / sectors_per_track
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; head = temp % n_heads
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; cylinder = temp / n_heads
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xor dx, dx
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; Divide by sectors per track. dx = mod (sector - 1), ax = div (temp)
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div word [bp - SECTORS_PER_TRACK]
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; Put the sector into cx (the bios call will use cl)
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mov cx, dx
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inc cx
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xor dx, dx
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; Divide by number of heads. dx = mod (head), ax = div (cylinder)
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div word [bp - N_HEADS]
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mov dh, dl
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mov ch, al
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mov dl, byte [bp - BOOT_DRIVE]
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mov ah, 0x02
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mov al, 1
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; Read sector
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int 0x13
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jc panic
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ret
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panic:
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mov ax, 0x0003
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int 0x10
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mov word fs:[0x0000], 0x4f21
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hlt
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gpt_magic db "EFI PART"
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GPT_MAGIC_LEN equ $ - gpt_magic
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; Our stage2 guid: fdffea69-3651-442f-a11d-88a09bf372dd
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guid_stage2 db 0x69, 0xea, 0xff, 0xfd, 0x51, 0x36, 0x2f, 0x44, \
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0xa1, 0x1d, 0x88, 0xa0, 0x9b, 0xf3, 0x72, 0xdd
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GUID_LEN equ $ - guid_stage2
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; MBR bootstrap field is 440 bytes long
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%if ($ - $$) > 440
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%error "exceeded mbr bootstrap field size"
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%endif
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Binary file not shown.
@ -0,0 +1,217 @@
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[bits 16]
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%include "fn.s"
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%include "layout.s"
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%include "s1_vars.s"
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extern s234_bin_len
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extern s234_bin_sectors
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extern s234_magic
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extern s3_main
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extern s234_bin_len
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extern s234_bin_sectors
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extern s234_magic
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section .s2_text
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%macro copy_stack_var_to_globals 2
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mov %1, [bp - %2]
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mov [REAL_GLOBALS + %2], %1
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%endmacro
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; Load stages 3 and 4 into memory.
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load_s234:
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; Now that we're not doing instruction byte golf like we were in stage 1, we can afford to move
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; the various stage 1 stack variables to the globals section.
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copy_stack_var_to_globals ax, BOOT_DRIVE
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copy_stack_var_to_globals ax, SECTORS_PER_TRACK
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copy_stack_var_to_globals ax, N_HEADS
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copy_stack_var_to_globals ax, GPT_ENTRIES_START_LBA
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copy_stack_var_to_globals ax, GPT_N_ENTRIES_16
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copy_stack_var_to_globals ax, GPT_SECTOR_STRIDE
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copy_stack_var_to_globals ax, GPT_BYTE_STRIDE
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copy_stack_var_to_globals ax, GPT_ENTRIES_PER_SECTOR
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copy_stack_var_to_globals ax, GPT_CURRENT_ENTRY_IDX
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copy_stack_var_to_globals ax, GPT_SECTOR_ENTRY_IDX
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copy_stack_var_to_globals ax, GPT_SECTORS_LOADED
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copy_stack_var_to_globals ax, GPT_CURRENT_LBA
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copy_stack_var_to_globals ax, STAGE_2_GPT_ENTRY_ADDR
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; Reset the stack, now we've got everything we need from it.
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mov sp, bp
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mov si, [REAL_GLOBALS + STAGE_2_GPT_ENTRY_ADDR]
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mov eax, [si + 0x20] ; Partition / boot1 start LBA lower
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mov ebx, [si + 0x24] ; Partition / boot1 start LBA upper
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mov ecx, [si + 0x28] ; Partition end LBA lower
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mov edx, [si + 0x32] ; Partition LBA upper
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; Panic if the partition / boot1 starting LBA overflows 16 bits.
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or ebx, ebx
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jnz panic_simple
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ror eax, 16
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or ax, ax
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jnz panic_simple
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ror eax, 16
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; Calculate the s234 end LBA and panic if it overflows 16 bits.
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; n.b. ebx is zero before this so both bx and ebx can be used as the s234 end LBA.
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mov bx, ax
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add bx, s234_bin_sectors
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jc panic_simple
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; Panic if the s234 end LBA is after the partition end LBA.
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; If the upper 32 bits of the partition end LBA are nonzero, then it must be greater than our
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; 16-bit s234 end LBA.
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or edx, edx
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jnz .end_lba_ok
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; Compare the s234 end LBA to the lower 32 bits of the partition end LBA.
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cmp ebx, ecx
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ja panic_simple
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.end_lba_ok:
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; The first sector has already been loaded (we're running it right now!) so increment the
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; current LBA.
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inc ax
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push ax ; Current LBA
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push bx ; s234 end LBA
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mov ebx, S2_ADDR + 512 ; Current sector load address
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.load_loop:
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mov ax, [bp - 0x02] ; Load current LBA
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cmp word [bp - 0x04], ax ; Compare to s234 end LBA
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jb .load_done
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mov ecx, ebx
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call read_sector
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jc panic_simple
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add ebx, 512
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inc word [bp - 0x02]
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jmp .load_loop
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.load_done:
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; Check the magic bytes at the end of s234.
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push es
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mov ebx, s234_magic
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call addr32_to_addr16
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cmp dword es:[bx], S234_MAGIC
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pop es
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jne panic_simple
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jmp s3_main
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; Converts a 32-bit address to a 16-bit sector and offset.
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; Arguments:
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; - ebx: 32-bit address
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; Return:
|
||||
; - es: 16-bit address segment (unchanged on failure)
|
||||
; - ebx: 16-bit address offset
|
||||
; - cf: unset on success, set on failure
|
||||
; Clobber: none
|
||||
addr32_to_addr16:
|
||||
fnstart
|
||||
push es
|
||||
push eax
|
||||
|
||||
mov eax, ebx
|
||||
; Divide addr by 16 and saturate to 16 bits to get the segment.
|
||||
shr eax, 4
|
||||
ror eax, 16
|
||||
or ax, ax
|
||||
jz .segment_ok
|
||||
mov eax, 0xffff0000
|
||||
.segment_ok:
|
||||
ror eax, 16
|
||||
mov es, ax
|
||||
|
||||
; Calculate offset = addr - (16 * segment), failing if the offset doesn't fit in 16 bits.
|
||||
shl eax, 4
|
||||
sub ebx, eax
|
||||
ror ebx, 16
|
||||
or bx, bx
|
||||
jnz .fail
|
||||
ror ebx, 16
|
||||
|
||||
pop eax
|
||||
add sp, 2 ; Discard the original es from the stack
|
||||
pop bp
|
||||
clc
|
||||
ret
|
||||
|
||||
.fail:
|
||||
pop eax
|
||||
pop es
|
||||
stc
|
||||
fnret
|
||||
|
||||
global addr32_to_addr16
|
||||
|
||||
|
||||
; Reads a single sector at the given LBA into memory.
|
||||
; Arguments:
|
||||
; - ax: start LBA
|
||||
; - ecx: address to read sector to
|
||||
; Return:
|
||||
; - cf: unset on success, set on failure
|
||||
; Clobber: eax, ecx, edx
|
||||
read_sector:
|
||||
; sector - 1 = LBA % sectors_per_track
|
||||
; temp = LBA / sectors_per_track
|
||||
; head = temp % n_heads
|
||||
; cylinder = temp / n_heads
|
||||
|
||||
fnstart
|
||||
push es
|
||||
push ebx
|
||||
|
||||
mov ebx, ecx
|
||||
call addr32_to_addr16
|
||||
jc .return
|
||||
|
||||
; Calculate sector and temp
|
||||
xor dx, dx
|
||||
; Divide by sectors per track. dx = mod (sector - 1), ax = div (temp)
|
||||
div word [REAL_GLOBALS + SECTORS_PER_TRACK]
|
||||
; Put the sector into cx (the bios call will use cl)
|
||||
mov cx, dx
|
||||
inc cx
|
||||
|
||||
; Calculate head and cylinder
|
||||
xor dx, dx
|
||||
; Divide by number of heads. dx = mod (head), ax = div (cylinder)
|
||||
div word [REAL_GLOBALS + N_HEADS]
|
||||
mov dh, dl
|
||||
mov ch, al
|
||||
|
||||
mov dl, byte [REAL_GLOBALS + BOOT_DRIVE]
|
||||
mov ah, 0x02
|
||||
mov al, 1
|
||||
; Read sector
|
||||
int 0x13
|
||||
|
||||
.return:
|
||||
pop ebx
|
||||
pop es
|
||||
fnret
|
||||
|
||||
global read_sector
|
||||
|
||||
|
||||
panic_simple:
|
||||
mov ax, 0x0003
|
||||
int 0x10
|
||||
mov word fs:[0x0000], 0x4f21
|
||||
.halt:
|
||||
hlt
|
||||
jmp .halt
|
||||
|
||||
global panic_simple
|
||||
|
||||
|
||||
%if ($ - $$) > 512
|
||||
%error "stage 2 exceeded sector size"
|
||||
%endif
|
||||
Binary file not shown.
@ -0,0 +1,112 @@
|
||||
%include "fn.s"
|
||||
%include "ps2.s"
|
||||
|
||||
|
||||
%macro mov_out 3
|
||||
mov %1, %3
|
||||
out %2, %1
|
||||
%endmacro
|
||||
|
||||
|
||||
; Check whether the A20 line is enabled. Writes to the boot sector identifier.
|
||||
; Arguments: none
|
||||
; Return:
|
||||
; - ax: 0 if A20 disabled, nonzero if A20 enabled
|
||||
; Clobber: none
|
||||
test_a20:
|
||||
push bp
|
||||
mov bp, sp
|
||||
push gs
|
||||
|
||||
; Restore the boot sector identifier in case it was overwritten by anything.
|
||||
mov word [0x7dfe], 0xaa55
|
||||
|
||||
mov ax, 0xffff
|
||||
mov gs, ax
|
||||
xor ax, ax
|
||||
|
||||
; If the word at 0x107dfe (1 MiB after the boot sector identifier) is different to the boot
|
||||
; sector identifier, than A20 must be enabled.
|
||||
cmp word gs:[0x7e0e], 0xaa55
|
||||
setne al
|
||||
jne .return
|
||||
|
||||
; Even if A20 was enabled, the two words may have been equal by chance, so we temporarily swap
|
||||
; the boot sector identifier bytes and test again.
|
||||
ror word [0x7dfe], 8
|
||||
cmp word gs:[0x7e0e], 0x55aa
|
||||
setne al
|
||||
ror word [0x7dfe], 8
|
||||
jmp .return
|
||||
|
||||
.return:
|
||||
pop gs
|
||||
pop bp
|
||||
ret
|
||||
|
||||
global test_a20
|
||||
|
||||
|
||||
; Try to enable A20 using the Intel 8042 PS/2 keyboard controller.
|
||||
; Arguments: none
|
||||
; Return: none
|
||||
; Clobber: ax, cx, dx
|
||||
enable_a20_intel_8042:
|
||||
; Temporarily disable the keyboard.
|
||||
call intel_8042_wait_write
|
||||
mov_out al, INTEL_8042_OUT_CMD, INTEL_8042_CMD_PS2_1_DISABLE
|
||||
|
||||
; Read the controller output port.
|
||||
call intel_8042_wait_write
|
||||
mov_out al, INTEL_8042_OUT_CMD, INTEL_8042_CMD_CONTROLLER_OUT_PORT_READ
|
||||
call intel_8042_wait_read
|
||||
in al, INTEL_8042_IO_DATA
|
||||
|
||||
; The second bit is "A20 enabled", so set it.
|
||||
mov cl, al
|
||||
or cl, 2
|
||||
|
||||
; Write the modified byte back to the controller output port.
|
||||
call intel_8042_wait_write
|
||||
mov_out al, INTEL_8042_OUT_CMD, INTEL_8042_CMD_CONTROLLER_OUT_PORT_WRITE
|
||||
call intel_8042_wait_write
|
||||
mov_out al, INTEL_8042_IO_DATA, cl
|
||||
|
||||
; Re-enable the keyboard.
|
||||
call intel_8042_wait_write
|
||||
mov_out al, INTEL_8042_OUT_CMD, INTEL_8042_CMD_PS2_1_ENABLE
|
||||
|
||||
; Wait for writes to finish.
|
||||
call intel_8042_wait_write
|
||||
|
||||
ret
|
||||
|
||||
global enable_a20_intel_8042
|
||||
|
||||
|
||||
; Wait for the Intel 8042 input buffer to become empty, so we can write.
|
||||
; Arguments: none
|
||||
; Return: none
|
||||
; Clobber: al
|
||||
intel_8042_wait_write:
|
||||
.loop:
|
||||
; Read the 8042 status register.
|
||||
in al, INTEL_8042_IN_STATUS
|
||||
; Input buffer status flag set means the input buffer is full, so loop in this case.
|
||||
test al, INTEL_8042_STATUS_MASK_IBUF
|
||||
jnz .loop
|
||||
ret
|
||||
|
||||
|
||||
; Wait for the Intel 8042 output buffer to become filled, so we can read.
|
||||
; Arguments: none
|
||||
; Return: none
|
||||
; Clobber: al
|
||||
intel_8042_wait_read:
|
||||
.loop:
|
||||
; Read the 8042 status register.
|
||||
in al, INTEL_8042_IN_STATUS
|
||||
; Output buffer status flag unset means output buffer is empty, so loop in this case.
|
||||
test al, INTEL_8042_STATUS_MASK_OBUF
|
||||
jz .loop
|
||||
ret
|
||||
Binary file not shown.
@ -0,0 +1,180 @@
|
||||
[bits 16]
|
||||
|
||||
%include "fn.s"
|
||||
%include "layout.s"
|
||||
%include "s2_fns.s"
|
||||
|
||||
extern test_a20
|
||||
extern enable_a20_intel_8042
|
||||
|
||||
section .s3_text
|
||||
|
||||
s3_main:
|
||||
call test_a20
|
||||
test al, al
|
||||
jnz .a20_enabled
|
||||
|
||||
; Try to enable A20 using the Intel 8042 PS/2 keyboard controller.
|
||||
call enable_a20_intel_8042
|
||||
call test_a20
|
||||
test al, al
|
||||
jnz .a20_enabled
|
||||
|
||||
; TODO: try other methods first before we panic:
|
||||
; - [ ] BIOS interrupt
|
||||
; - [ ] Fast A20 enable
|
||||
jmp panic_simple
|
||||
|
||||
.a20_enabled:
|
||||
mov ax, 0x0003
|
||||
int 0x10
|
||||
|
||||
; Disable cursor
|
||||
mov ax, 0x0100
|
||||
mov cx, 0x3f00
|
||||
int 0x10
|
||||
|
||||
; Ensure interrupts are definitely disabled.
|
||||
cli
|
||||
|
||||
; Load our flat-address-space GDT.
|
||||
lgdt [gdt_flat_slice]
|
||||
|
||||
; Set the protected-mode bit in cr0.
|
||||
mov eax, cr0
|
||||
or al, 0x01
|
||||
mov cr0, eax
|
||||
|
||||
; Long jump to set the code segment to gdt_flat.segment_code, and to clear the instruction
|
||||
; pipeline.
|
||||
jmp GDT_FLAT_IDX_CODE_32:.protected_mode_32
|
||||
|
||||
[bits 32]
|
||||
.protected_mode_32:
|
||||
|
||||
; Set the data segments to gdt_flat.segment_data.
|
||||
mov eax, GDT_FLAT_IDX_DATA
|
||||
mov ds, eax
|
||||
mov es, eax
|
||||
mov fs, eax
|
||||
mov gs, eax
|
||||
mov ss, eax
|
||||
|
||||
; Reset the stack.
|
||||
; TODO: put the 32-bit stack somewhere else.
|
||||
mov ebp, REAL_STACK_BASE
|
||||
mov esp, ebp
|
||||
|
||||
; TODO
|
||||
; jmp _start
|
||||
|
||||
.halt:
|
||||
hlt
|
||||
jmp .halt
|
||||
|
||||
; panic_simple_32:
|
||||
; mov word [0xb8000], 0x4f21
|
||||
; .halt:
|
||||
; hlt
|
||||
; jmp .halt
|
||||
|
||||
global s3_main
|
||||
|
||||
|
||||
section .s3_data
|
||||
|
||||
gdt_flat_slice:
|
||||
dw GDT_FLAT_LEN
|
||||
dd gdt_flat
|
||||
|
||||
global gdt_flat_slice
|
||||
|
||||
; Segment descriptor layout
|
||||
; | Range (bits) | Field |
|
||||
; |--------------|---------------|
|
||||
; | 0-16 | limit |
|
||||
; | 16-32 | base |
|
||||
; | 32-40 | base cont. |
|
||||
; | 40-48 | access |
|
||||
; | 48-52 | limit cont. |
|
||||
; | 52-56 | flags |
|
||||
; | 56-64 | base cont. |
|
||||
;
|
||||
; Flags
|
||||
; - 0: reserved
|
||||
; - 1: long-mode code segment
|
||||
; - 2: size
|
||||
; - unset: 16-bit
|
||||
; - set: 32-bit
|
||||
; - 3: granularity
|
||||
; - unset: limit is measured in bytes
|
||||
; - set: limit is measured in 4KiB pages
|
||||
;
|
||||
; Access
|
||||
; - 0: accessed
|
||||
; - unset: CPU will set it when the segment is accessed
|
||||
; - 1: readable / writable
|
||||
; - data segments: is segment writable (data segments are always readable)
|
||||
; - code segments: is segment readable (code segments are never writable)
|
||||
; - 2: direction / conforming
|
||||
; - data segments: whether segment grows down
|
||||
; - code segments: whether this can be executed from a lower-privilege ring
|
||||
; - 3: executable
|
||||
; - unset: this is a data segment
|
||||
; - set: this is a code segment
|
||||
; - 4: descriptor type
|
||||
; - unset: this is a task state segment
|
||||
; - set: this is a data or code segment
|
||||
; - 5-6: privilege level (ring number)
|
||||
; - 7: present (must be set)
|
||||
;
|
||||
|
||||
; FIXME: copy this to a fixed memory location
|
||||
align 8
|
||||
gdt_flat:
|
||||
; First GDT entry must be 0.
|
||||
dq 0
|
||||
|
||||
; 32-bit code segment.
|
||||
; Bytes 0x0000 - 0xffff.
|
||||
.segment_code_32:
|
||||
db 0xff, 0xff, \
|
||||
0x00, 0x00, \
|
||||
0x00, \
|
||||
10011011b, \
|
||||
01000000b, \
|
||||
0x00
|
||||
|
||||
; 16-bit code segment, to use if we want to switch back to real mode.
|
||||
; Bytes 0x0000 - 0xffff.
|
||||
.segment_code_16:
|
||||
db 0xff, 0xff, \
|
||||
0x00, 0x00, \
|
||||
0x00, \
|
||||
10011011b, \
|
||||
00000000b, \
|
||||
0x00
|
||||
|
||||
; Data segment.
|
||||
; Pages 0x000000 - 0x0fffff, which covers the entire 32-bit address space (start of 0xfffff-th page
|
||||
; is 0xfffff * 4096 = 0xfffff000, end of page exclusive is 0xfffff000 + 4096 = 0x100000000).
|
||||
.segment_data:
|
||||
db 0xff, 0xff, \
|
||||
0x00, 0x00, \
|
||||
0x00, \
|
||||
10010011b, \
|
||||
11001111b, \
|
||||
0x00
|
||||
|
||||
global gdt_flat
|
||||
|
||||
GDT_FLAT_LEN equ ($ - gdt_flat)
|
||||
|
||||
GDT_FLAT_IDX_CODE_32 equ (gdt_flat.segment_code_32 - gdt_flat)
|
||||
global GDT_FLAT_IDX_CODE_32
|
||||
|
||||
GDT_FLAT_IDX_CODE_16 equ (gdt_flat.segment_code_16 - gdt_flat)
|
||||
global GDT_FLAT_IDX_CODE_16
|
||||
|
||||
GDT_FLAT_IDX_DATA equ (gdt_flat.segment_data - gdt_flat)
|
||||
global GDT_FLAT_IDX_DATA
|
||||
Loading…
Reference in New Issue