diff --git a/boot0.s b/boot0.s index 96284e3..6060e04 100644 --- a/boot0.s +++ b/boot0.s @@ -40,6 +40,7 @@ GPT_SECTORS_LOADED equ 0x16 GPT_CURRENT_LBA equ 0x18 STAGE2_GPT_ENTRY_ADDR equ 0x1a +main: ; Disable interrupts cli @@ -71,7 +72,7 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a mov di, 0x00 mov ah, 0x08 int 0x13 - jc .panic + jc panic ; Load sectors per track into cx & spill and cl, 0x3f xor ch, ch @@ -84,14 +85,14 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a ; Load LBA 1. mov ax, 1 mov bx, 0x7e00 - call .read_lba + call read_lba ; Check the GPT header magic "EFI PART" mov cx, GPT_MAGIC_LEN mov si, gpt_magic mov di, 0x7e00 repe cmpsb - jne .panic + jne panic ; Ensure the 8-byte GPT starting LBA fits in 16 bits mov di, 0x7e00 ; The rep increments di so we need to reset it @@ -99,7 +100,7 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a mov bx, [di + 0x4a] or ax, bx or eax, eax - jnz .panic + jnz panic ; Load and spill the GPT starting LBA mov ax, [di + 0x48] push ax @@ -123,9 +124,9 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a ; - If each entry is larger than a sector (512 bytes), they'll be sector-aligned. ; - If each entry is smaller than a sector, an integer number of them will fit into a sector. or eax, eax ; Test size != 0 because 128 * 2^n != 0 - jz .panic + jz panic and eax, 127 ; Test size is a multiple of 128 - jnz .panic + jnz panic ; Use the (n & (n - 1)) == 0 trick to test if the entry size is a power of 2. Since we already ; know it's a nonzero multiple of 128, if size is a power of 2 then size = 128 * 2^n holds. ; Therefore we don't need to bother dividing by 128 first (shr 7), which saves a couple of bytes. @@ -133,13 +134,13 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a mov ecx, ebx dec ecx and ecx, eax - jnz .panic + jnz panic ; Find the "sector stride", which is the number of sectors we increment by each time we want to ; load a new entry. shr eax, 9 ; Divide by sector size to get sectors per entry cmp eax, 0xffff ; Make sure sectors per entry fits in 16 bits - ja .panic + ja panic or ax, ax jnz .gpt_sector_stride_loaded ; Sector stride must be at least one or we'll load the same sector each time! @@ -175,7 +176,7 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a mov dx, [bp - GPT_CURRENT_ENTRY_IDX] cmp [bp - GPT_N_ENTRIES_16], dx ; Panic if we've run out of partitions and haven't found the second stage yet. - jbe .panic + jbe panic ; If we haven't loaded any sectors yet, load the first one. cmp word [bp - GPT_SECTORS_LOADED], 0 @@ -192,7 +193,7 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a ; Read the current LBA to 0x8000 (just past the end of the GPT header) mov ax, [bp - GPT_CURRENT_LBA] mov bx, 0x8000 - call .read_lba + call read_lba ; Increment number of sectors loaded inc word [bp - GPT_SECTORS_LOADED] @@ -224,9 +225,9 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a mov ebx, [si + 0x24] ; Ensure it fits in 16 bits. or ebx, ebx - jnz .panic + jnz panic cmp ebx, 0xffff - ja .panic + ja panic ; Load partition LBA end. mov ecx, [si + 0x28] mov edx, [si + 0x2c] @@ -235,11 +236,11 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a or edx, edx jnz .stage2_end_lba_ok cmp eax, ecx - ja .panic + ja panic .stage2_end_lba_ok: mov bx, 0x8200 - call .read_lba + call read_lba jmp bx ; Load a single boot disk sector. Panic on failure. @@ -247,7 +248,7 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a ; - ax: LBA to load ; - bx: address to read sector to ; Clobber: ax, cx, dx -.read_lba: +read_lba: ; sector - 1 = LBA % sectors_per_track ; temp = LBA / sectors_per_track ; head = temp % n_heads @@ -270,10 +271,10 @@ STAGE2_GPT_ENTRY_ADDR equ 0x1a mov al, 1 ; Read sector int 0x13 - jc .panic + jc panic ret -.panic: +panic: mov ax, 0x0003 int 0x10 mov word fs:[0x0000], 0x4f21 @@ -287,7 +288,7 @@ guid_stage2 db 0x69, 0xea, 0xff, 0xfd, 0x51, 0x36, 0x2f, 0x44, \ 0xa1, 0x1d, 0x88, 0xa0, 0x9b, 0xf3, 0x72, 0xdd GUID_LEN equ $ - guid_stage2 - ; MBR bootstrap field is 440 bytes long - %if ($ - $$) > 440 - %error "exceeded mbr bootstrap field size" - %endif +; MBR bootstrap field is 440 bytes long +%if ($ - $$) > 440 +%error "exceeded mbr bootstrap field size" +%endif diff --git a/resources.md b/resources.md index 9776601..500c556 100644 --- a/resources.md +++ b/resources.md @@ -6,6 +6,7 @@ - - - +- ## Boot sequence -