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Fix non-aligned disk reads in bootloader

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vmttmv
2026-01-06 00:39:29 +02:00
parent 9eae2e1005
commit 35ebd5fd72
2 changed files with 115 additions and 119 deletions
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81
bootloader/stage2.asm
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@@ -24,84 +24,3 @@ _start:
call load_kernel
jmp eax
; ----------------------------------------------------------------------------
; ATA read sectors (LBA mode)
;
; sysv32 abi signature:
; void ata_lba_read(uint32_t lba, uint8_t nsect, void *addr);
; ----------------------------------------------------------------------------
ata_lba_read:
push ebp
mov ebp, esp
push ebx
push ecx
push edx
push edi
; Wait BSY=0 before proceeding to write the regs
.wait_rdy:
mov edx, 0x1F7
in al, dx
test al, 0x80
jnz .wait_rdy
mov eax, [ebp+8] ; arg #1 = LBA
mov cl, [ebp+12] ; arg #2 = # of sectors
mov edi, [ebp+16] ; arg #3 = buffer address
and eax, 0x0FFFFFFF
mov ebx, eax ; Save LBA in RBX
mov edx, 0x01F6 ; Port to send drive and bit 24 - 27 of LBA
shr eax, 24 ; Get bit 24 - 27 in al
or al, 11100000b ; Set bit 6 in al for LBA mode
out dx, al
mov edx, 0x01F2 ; Port to send number of sectors
mov al, cl ; Get number of sectors from CL
out dx, al
mov edx, 0x1F3 ; Port to send bit 0 - 7 of LBA
mov eax, ebx ; Get LBA from EBX
out dx, al
mov edx, 0x1F4 ; Port to send bit 8 - 15 of LBA
mov eax, ebx ; Get LBA from EBX
shr eax, 8 ; Get bit 8 - 15 in AL
out dx, al
mov edx, 0x1F5 ; Port to send bit 16 - 23 of LBA
mov eax, ebx ; Get LBA from EBX
shr eax, 16 ; Get bit 16 - 23 in AL
out dx, al
mov edx, 0x1F7 ; Command port
mov al, 0x20 ; Read with retry.
out dx, al
mov bl, cl ; Save # of sectors in BL
.wait_rdy2:
mov edx, 0x1F7
.do_wait_rdy2:
in al, dx
test al, 0x80 ; BSY?
jnz .do_wait_rdy2
test al, 0x8 ; DRQ?
jz .do_wait_rdy2
mov edx, 0x1F0 ; Data port, in and out
mov ecx, 256
rep insw ; in to [RDI]
dec bl ; are we...
jnz .wait_rdy2 ; ...done?
pop edi
pop edx
pop ecx
pop ebx
pop ebp
ret