minor boot0 cleanup

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

resources.md

@@ -6,6 +6,7 @@
 - <https://www.eecg.utoronto.ca/~amza/www.mindsec.com/files/x86regs.html>
 - <https://en.wikibooks.org/wiki/X86_Assembly/16,_32,_and_64_Bits>
 - <https://www.plantation-productions.com/Webster/www.artofasm.com/DOS/ch04/CH04-2.html>
+- <https://www.tortall.net/projects/yasm/manual/html/nasm-local-label.html>
 
 ## Boot sequence
 - <https://wiki.osdev.org/Boot_Sequence>