706 lines
16 KiB
ArmAsm
706 lines
16 KiB
ArmAsm
;
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; Copyright (c) 2014-2015 Zenith432 All rights reserved.
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;
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; Partition Boot Loader: boot1x
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; This version of boot1x tries to find a stage2 boot file in the root folder.
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;
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; Credits:
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; Portions based on boot1f32.
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; Thanks to Robert Shullich for
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; "Reverse Engineering the Microsoft exFAT File System" dated Dec 1, 2009.
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; T13 Commitee document EDD-4 for information about BIOS int 0x13.
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;
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; This program is designed to reside in blocks 0 - 1 of an exFAT partition.
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; It expects that the MBR has left the drive number in DL.
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;
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; This version requires a BIOS with EBIOS (LBA) support.
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;
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; This code is written for the NASM assembler.
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; nasm -f bin -o boot1x boot1x.s
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;
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; Written by zenith432 during November 2014.
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; Modified by zenith432 January 2015
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; Added Feature: Support digit keypress with two second delay (-DSELECTION_FEATURE)
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;
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bits 16
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%define VERBOSE 1
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%define USESIDL 1
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%define USEBP 1
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kMaxBlockCount equ 127 ; Max block count supported by Int 0x13, function 0x42, old school
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kBootBlockBytes equ 512 ; Bytes in a exFAT Boot block
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kBootSignature equ 0xaa55 ; Boot block signature
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kBoot1StackAddress equ 0xfff0 ; Address of top-of-stack 0:0xfff0
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kBoot1LoadAddr equ 0x7c00 ; Address of loaded boot block 0:0x7c00
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kBoot2Segment equ 0x2000 ; Address for boot2 0x2000:0x200
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kBoot2Address equ 512
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kFATBuf equ 0x6c00 ; Address for FAT block buffer 0:0x6c00 (4K space)
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kRootDirBuf equ 0x5c00 ; Address for Root Directory block buffer 0:0x5c00 (4K space)
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kMaxCluster equ 0xfffffff7 ; exFAT max cluster value + 1 (for FAT32 it's 0x0ffffff8)
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kMaxContigClusters equ 1024 ; Max contiguous clusters returned by getRange
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kBootNameHash equ 0xdc36 ; exFAT name hash for 'BOOT' (in UTF16LE)
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kBoot2MaxBytes equ (512 * 1024 - 512) ; must fit between 0x20200 and 0xa0000
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struc PartitionEntry ; MBR partition entry (truncated)
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times 8 resb 1
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.lba: resd 1 ; starting lba
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endstruc
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struc BootParams ; BOOT file parameters
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.cluster: resd 1 ; 1st cluster of BOOT
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.size: resd 1 ; size of BOOT in bytes
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resw 1
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.flag: resb 1
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endstruc
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struc DirIterator ; exFAT Directory Iterator
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.entries_end: resb 1 ; beyond last 32-byte entry (possible values 16, 32, 64, 128)
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.cluster: resd 1 ; current cluster
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.lba_high: resd 1 ; upper 32 bits of lba
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.lba_end: resd 1 ; beyond last block (lower 32-bits)
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.lba: resd 1 ; current block
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.entry: resb 1 ; current 32-byte entry
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endstruc
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struc FATCache ; Manages cache state for FAT blocks
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.shift: resb 1 ; right shift for converting cluster # to FAT block address
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.mask: resw 1 ; bit mask for finding cluster # in FAT block
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.lba: resd 1 ; lba # cached in FAT block buffer (note that FAT block address is limited to 32 bits)
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endstruc
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%ifdef USEBP
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%define BPR bp - gPartitionOffset +
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%else
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%define BPR
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%endif
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section .text
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org kBoot1LoadAddr
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jmp start
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times (3 - $ + $$) nop
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gOEMName: times 8 db 0 ; 'EXFAT '
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;
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; Scratch Area
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; Used for data structures
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;
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times (64 - BootParams_size - DirIterator_size - FATCache_size - $ + $$) db 0
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gsParams: times BootParams_size db 0
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gsIterator: times DirIterator_size db 0
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gsFATCache: times FATCache_size db 0
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;
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; exFAT BPB
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;
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gPartitionOffset: dd 0, 0
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gVolumeLength: dd 0, 0
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gFATOffset: dd 0
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gFATLength: dd 0
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gClusterHeapOffset: dd 0
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gClusterCount: dd 0
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gRootDirectory1stCluster: dd 0
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gVolumeSerialNubmer: dd 0
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gFileSystemRevision: dw 0 ; 0x100
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gVolumeFlags: dw 0
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gBytesPerBlock: db 0 ; range 9 - 12 (power of 2)
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gBlocksPerCluster: db 0 ; gBytesPerBlock + gBlocksPerCluster <= 25 (power of 2)
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gNumberOfFATs: db 0 ; should be 1
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gDriveSelect: db 0 ; probably 0x80
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gPercentInUse: db 0
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times 7 db 0
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start:
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cli
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xor eax, eax
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mov ss, ax
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mov sp, kBoot1StackAddress
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sti
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mov ds, ax
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mov es, ax
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;
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; Initializing global variables.
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;
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%ifdef USEBP
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mov bp, gPartitionOffset
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%endif
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%ifdef USESIDL
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;
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; Shouldn't be necessary to use DS:SI because
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; 1) Existing gPartitionOffset must be correct in
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; order for filesystem to work well when mounted.
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; 2) LBA may be 64 bits if booted from GPT.
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; 3) Not all MBR boot records pass DS:SI
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; pointing to MBR partition entry.
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;
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%if 0
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mov ecx, [si + PartitionEntry.lba]
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mov [BPR gPartitionOffset + 4], eax
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mov [BPR gPartitionOffset], ecx
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%endif
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;
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; However, by convention BIOS passes boot
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; drive number in dl, so use that instead
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; of existing gDriveSelect
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;
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mov [BPR gDriveSelect], dl
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%endif
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;
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; Initialize FAT Cache
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;
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dec eax
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mov dword [BPR gsFATCache + FATCache.lba], eax ; alternatively store gFATLength here
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mov cl, [BPR gBytesPerBlock]
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sub cl, 2 ; range 7 - 10
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mov [BPR gsFATCache + FATCache.shift], cl
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neg ax
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shl ax, cl
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dec ax
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mov [BPR gsFATCache + FATCache.mask], ax
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;
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; Initialize Iterator
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;
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mov al, 1
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sub cl, 3 ; range 4 - 7
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shl al, cl
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mov [BPR gsIterator + DirIterator.entries_end], al
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mov [BPR gsIterator + DirIterator.entry], al
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xor eax, eax
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mov ecx, [BPR gRootDirectory1stCluster]
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mov [BPR gsIterator + DirIterator.lba_end], eax
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mov [BPR gsIterator + DirIterator.lba], eax
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mov [BPR gsIterator + DirIterator.cluster], ecx
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%ifdef VERBOSE
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mov di, init_str
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call log_string
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%endif
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%ifdef SELECTION_FEATURE
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call setBootFile
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%endif
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;
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; Search root directory for BOOT
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;
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.loop:
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call nextDirEntry
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jc error
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cld
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lodsb
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.revert:
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test al, al ; end of root directory?
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jz error
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cmp al, 0x85 ; file/subdir entry?
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jnz .loop
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lodsb
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cmp al, 2 ; 2ndary count should be 2
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jb .loop
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add si, 2 ; skip checksum
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lodsb
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test al, 0x10 ; file attributes - check not a directory
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jnz .loop
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call nextDirEntry
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jc error
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cld
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lodsb
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cmp al, 0xc0 ; stream extension entry?
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jnz .revert
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lodsb
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mov dl, al ; General 2ndary flag
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inc si
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lodsb
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.name_length_point:
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cmp al, 4 ; name length
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jnz .loop
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lodsw ; name hash
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.name_hash_point:
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cmp ax, kBootNameHash
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jnz .loop
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add si, 2
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mov eax, [si + 4] ; high 32 bits of valid data length
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test eax, eax
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jz .more
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and dl, 0xfe ; if size too big, mark as no allocation
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.more:
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lodsd ; valid data length
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mov [BPR gsParams + BootParams.size], eax
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add si, 8
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lodsd ; first cluster
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mov [BPR gsParams + BootParams.cluster], eax
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mov [BPR gsParams + BootParams.flag], dl
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call nextDirEntry
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jc error
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cld
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lodsb
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cmp al, 0xc1
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jnz .revert
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inc si ; skip flags
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lodsd ; unicode chars 1 - 2
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or eax, 0x200020 ; tolower
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cmp eax, 0x6f0062 ; 'bo' in UTF16LE
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jnz .loop
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lodsd ; unicode chars 3 - 4
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or eax, 0x200020 ; tolower
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cmp eax, 0x74006f ; 'ot' in UTF16LE
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jnz .loop
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;
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; done - found boot file!
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;
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mov dl, [BPR gsParams + BootParams.flag]
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test dl, 1 ; no allocation or length too big?
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jz error
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mov ebx, [BPR gsParams + BootParams.size]
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cmp ebx, kBoot2MaxBytes + 1
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jnb error
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call BytesToBlocks ; convert size to blocks
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; boot2 file size in blocks is in bx
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load_boot2: ; anchor for localizing next labels
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xor esi, esi ; no blocks after 1st range
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test dl, 2 ; FAT Chain?
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cmovnz edx, [BPR gsParams + BootParams.cluster] ; if not
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jnz .oneshot ; load contiguous file
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;
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; load via FAT
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;
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mov si, bx ; total blocks to si
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.loop:
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mov eax, [BPR gsParams + BootParams.cluster]
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mov edx, eax
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call getRange
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test ebx, ebx
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jnz .nonempty
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test si, si
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jnz error
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jmp boot2
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.nonempty:
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cmp ebx, esi
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cmovnb bx, si
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sub si, bx
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mov [BPR gsParams + BootParams.cluster], eax
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.oneshot:
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call ClusterToLBA
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mov ax, bx
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mov ecx, edx
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mov edx, (kBoot2Segment << 4) | kBoot2Address
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call readBlocks
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; TODO: error
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test si, si
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jnz .loop
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; fall through to boot2
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boot2:
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mov dl, [BPR gDriveSelect] ; load BIOS drive number
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jmp kBoot2Segment:kBoot2Address
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error:
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%ifdef VERBOSE
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mov di, error_str
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call log_string
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%endif
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hang:
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hlt
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jmp hang
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;--------------------------------------------------------------------------
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; ClusterToLBA - Converts cluster number to 64-bit LBA
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;
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; Arguments:
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; EDX = cluster number
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;
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; Returns
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; EDI:EDX = corresponding block address
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;
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; Assumes input cluster number is valid
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;
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ClusterToLBA:
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push cx
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xor edi, edi
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sub edx, 2
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mov cl, [BPR gBlocksPerCluster]
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shld edi, edx, cl
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shl edx, cl
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add edx, [BPR gClusterHeapOffset]
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adc edi, 0
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pop cx
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ret
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;--------------------------------------------------------------------------
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; BytesToBlocks - Converts byte size to blocks (rounding up to next block)
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;
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; Arguments:
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; EBX = size in bytes
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;
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; Returns:
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; EBX = size in blocks (rounded up)
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;
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; Clobbers eax, cl
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;
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BytesToBlocks:
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xor eax, eax
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inc ax
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mov cl, [BPR gBytesPerBlock]
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shl ax, cl
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dec ax
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add ebx, eax
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shr ebx, cl
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ret
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times (kBootBlockBytes - 2 - $ + $$) nop
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dw kBootSignature
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block1_end:
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;--------------------------------------------------------------------------
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; nextDirEntry - Locates the next 32-byte entry in Root Directory,
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; loading block if necessary.
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;
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; Returns:
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; CF set if end of Root Directory
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; CF clear, and DS:SI points to next entry if exists
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;
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; Clobbers eax, ebx, ecx, edx, edi
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;
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nextDirEntry:
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movzx ax, [BPR gsIterator + DirIterator.entry]
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cmp al, [BPR gsIterator + DirIterator.entries_end]
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jb .addressentry
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mov ecx, [BPR gsIterator + DirIterator.lba]
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mov edi, [BPR gsIterator + DirIterator.lba_high]
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cmp ecx, [BPR gsIterator + DirIterator.lba_end]
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jnz .readblock
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mov eax, [BPR gsIterator + DirIterator.cluster]
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mov edx, eax
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call getRange
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test ebx, ebx
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jnz .nonempty
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stc
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ret
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.nonempty:
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mov [BPR gsIterator + DirIterator.cluster], eax
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call ClusterToLBA
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mov ecx, edx
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add edx, ebx
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mov [BPR gsIterator + DirIterator.lba_high], edi
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mov [BPR gsIterator + DirIterator.lba_end], edx
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.readblock:
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mov al, 1
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%if 0
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mov edx, kRootDirBuf
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%else
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xor edx, edx
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mov dh, kRootDirBuf >> 8
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%endif
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call readLBA
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; TODO error
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inc ecx
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jnz .skip
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inc edi
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mov [BPR gsIterator + DirIterator.lba_high], edi
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.skip:
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mov [BPR gsIterator + DirIterator.lba], ecx
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xor ax, ax
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.addressentry:
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mov si, ax
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inc al
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mov [BPR gsIterator + DirIterator.entry], al
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shl si, 5
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add si, kRootDirBuf
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clc
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ret
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;--------------------------------------------------------------------------
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; getRange - Calculates contiguous range of clusters from FAT
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;
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; Arguments:
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; EAX = start cluster
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;
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; Returns:
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; EAX = next cluster after range
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; EBX = number of contiguous blocks in range
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;
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; Range calculated is at most kMaxContigClusters clusters long
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;
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getRange:
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push ecx
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push edx
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push edi
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push si
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xor edi, edi
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%if 0
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mov edx, kFATBuf
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%else
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mov edx, edi
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mov dh, kFATBuf >> 8
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%endif
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mov ebx, edi
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.loop:
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cmp eax, 2
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jb .finishup
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cmp eax, -9 ;kMaxCluster
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jnb .finishup
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cmp bx, kMaxContigClusters
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jnb .finishup
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inc bx
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mov si, ax
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and si, [BPR gsFATCache + FATCache.mask]
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shl si, 2
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mov ecx, eax
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inc ecx
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push ecx
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mov cl, [BPR gsFATCache + FATCache.shift]
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shr eax, cl
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cmp eax, [BPR gsFATCache + FATCache.lba]
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jz .iscached
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mov ecx, [BPR gFATOffset]
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add ecx, eax
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mov [BPR gsFATCache + FATCache.lba], eax
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mov al, 1
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call readLBA
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; TODO: error?
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.iscached:
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pop ecx
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mov eax, [kFATBuf + si]
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cmp eax, ecx
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jz .loop
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.finishup:
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mov cl, [BPR gBlocksPerCluster]
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shl ebx, cl
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pop si
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pop edi
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pop edx
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pop ecx
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ret
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%ifdef SELECTION_FEATURE
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;--------------------------------------------------------------------------
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; setBootFile - Waits two seconds for a keypress.
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; If keypress is digit '0' - '9' alters boot file from /boot to /boot<digit>
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; If keypress anything else or no keypress - uses /boot.
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;
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; Arguments:
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; None
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;
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; Returns:
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; None
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;
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; Clobbers ax, cx, dx
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;
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setBootFile:
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mov cx, 2000 ; loop counter = max 2000 miliseconds in total
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.loop:
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mov ah, 1 ; int 0x16, Func 0x01 - get keyboard status/preview key
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int 0x16
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jnz .keypress ; got keypress
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; wait for 1 ms: int 0x15, Func 0x86 (wait for cx:dx microseconds)
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push cx ; save loop counter
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xor cx, cx
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mov dx, 1000
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mov ah, 0x86
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int 0x15
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pop cx ; restore loop counter
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loop .loop
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.done:
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ret
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.keypress:
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xor ah, ah ; read the char from buffer to spend it
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int 0x16
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; have a key - ASCII is in al
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cmp al, '0'
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jb .done
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cmp al, '9' + 1
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jae .done
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;
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; Alter code so name length tested is 5 instead of 4
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; Compute new hash value with digit and alter code
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; to check for modified hash value.
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; Note: code continues to compare 4 characters 'boot'.
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; For any other ascii character in 5th position,
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; the hash value does not collide. There are
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; non-ascii unicode characters in 5th position that
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; collide with hash-value, but ignore those for simplicity.
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;
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xor ah, ah
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inc byte [start.name_length_point + 1]
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add ax, (kBootNameHash >> 1) | ((kBootNameHash & 1) << 15)
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ror ax, 1
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mov [start.name_hash_point + 1], ax
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ret
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%endif
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;--------------------------------------------------------------------------
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; readBlocks - Reads more than kMaxBlockCount blocks using LBA addressing.
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;
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; Arguments:
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; AX = number of blocks to read (valid from 1-1280).
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; EDX = pointer to where the blocks should be stored.
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; EDI:ECX = block offset in partition (64 bits)
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;
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; Returns:
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; CF = 0 success
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; 1 error
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;
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readBlocks:
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pushad
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mov bx, ax
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|
.loop:
|
|
xor eax, eax
|
|
mov al, kMaxBlockCount
|
|
cmp bx, ax
|
|
cmovb ax, bx
|
|
call readLBA
|
|
; TODO: error?
|
|
sub bx, ax
|
|
jz .exit
|
|
add ecx, eax
|
|
adc edi, 0
|
|
push cx
|
|
mov cl, [BPR gBytesPerBlock]
|
|
shl eax, cl
|
|
pop cx
|
|
add edx, eax
|
|
jmp .loop
|
|
|
|
.exit:
|
|
popad
|
|
ret
|
|
|
|
;--------------------------------------------------------------------------
|
|
; readLBA - Read blocks from a partition using LBA addressing.
|
|
;
|
|
; Arguments:
|
|
; AL = number of blocks to read (valid from 1-kMaxBlockCount).
|
|
; EDX = pointer to where the blocks should be stored.
|
|
; EDI:ECX = block offset in partition (64 bits)
|
|
; [gDriveSelect] = drive number (0x80 + unit number)
|
|
; [gPartitionOffset] = partition location on drive
|
|
;
|
|
; Returns:
|
|
; CF = 0 success
|
|
; 1 error
|
|
; Presently, jumps to error on BIOS-reported failure
|
|
;
|
|
readLBA:
|
|
pushad ; save all registers
|
|
push es ; save ES
|
|
mov bp, sp ; save current SP
|
|
|
|
;
|
|
; Adjust to 16 bit segment:offset address
|
|
; to allow for reading up to 64K
|
|
;
|
|
mov bl, dl
|
|
and bx, 0xf
|
|
shr edx, 4
|
|
mov es, dx
|
|
|
|
;
|
|
; Create the Disk Address Packet structure for the
|
|
; INT13/F42 (Extended Read Sectors) on the stack.
|
|
;
|
|
|
|
add ecx, [gPartitionOffset]
|
|
adc edi, [gPartitionOffset + 4]
|
|
push edi
|
|
push ecx
|
|
push es
|
|
push bx
|
|
xor ah, ah
|
|
push ax
|
|
push word 16
|
|
|
|
;
|
|
; INT13 Func 42 - Extended Read Sectors
|
|
;
|
|
; Arguments:
|
|
; AH = 0x42
|
|
; DL = drive number (0x80 + unit number)
|
|
; DS:SI = pointer to Disk Address Packet
|
|
;
|
|
; Returns:
|
|
; AH = return status (sucess is 0)
|
|
; carry = 0 success
|
|
; 1 error
|
|
;
|
|
; Packet offset 2 indicates the number of sectors read
|
|
; successfully.
|
|
;
|
|
mov dl, [gDriveSelect] ; load BIOS drive number
|
|
mov si, sp
|
|
mov ah, 0x42
|
|
int 0x13
|
|
|
|
jc error
|
|
|
|
;
|
|
; Issue a disk reset on error.
|
|
; Should this be changed to Func 0xD to skip the diskette controller
|
|
; reset?
|
|
;
|
|
; xor ax, ax ; Func 0
|
|
; int 0x13 ; INT 13
|
|
; stc ; set carry to indicate error
|
|
|
|
;.exit
|
|
mov sp, bp
|
|
pop es
|
|
popad
|
|
ret
|
|
|
|
%ifdef VERBOSE
|
|
|
|
;--------------------------------------------------------------------------
|
|
; Write a string with log_title_str prefix to the console.
|
|
;
|
|
; Arguments:
|
|
; DS:DI pointer to a NULL terminated string.
|
|
;
|
|
log_string:
|
|
pushad
|
|
push di
|
|
mov si, log_title_str
|
|
call print_string
|
|
pop si
|
|
call print_string
|
|
popad
|
|
ret
|
|
|
|
;-------------------------------------------------------------------------
|
|
; Write a string to the console.
|
|
;
|
|
; Arguments:
|
|
; DS:SI pointer to a NULL terminated string.
|
|
;
|
|
; Clobber list:
|
|
; AX, BX, SI
|
|
;
|
|
print_string:
|
|
mov bx, 1 ; BH=0, BL=1 (blue)
|
|
|
|
.loop:
|
|
lodsb ; load a byte from DS:SI into AL
|
|
test al, al ; Is it a NULL?
|
|
jz .exit ; yes, all done
|
|
mov ah, 0xE ; INT10 Func 0xE
|
|
int 0x10 ; display byte in tty mode
|
|
jmp .loop
|
|
|
|
.exit:
|
|
ret
|
|
|
|
%endif ; VERBOSE
|
|
|
|
;--------------------------------------------------------------------------
|
|
; Static data.
|
|
;
|
|
|
|
%ifdef VERBOSE
|
|
log_title_str: db 13, 10, 'boot1x: ', 0
|
|
init_str: db 'init', 0
|
|
error_str: db 'error', 0
|
|
%endif
|
|
|
|
times (kBootBlockBytes - 4 - $ + block1_end) db 0
|
|
dw 0, kBootSignature
|