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688 lines
22 KiB
ArmAsm
688 lines
22 KiB
ArmAsm
// EXT2.ASM
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// EXT2 Boot Sector
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// Copyright (c) 2002, 2003 Brian Palmer
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// [bp-0x04] Here we will store the number of sectors per track
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// [bp-0x08] Here we will store the number of heads
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// [bp-0x0c] Here we will store the size of the disk as the BIOS reports in CHS form
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// [bp-0x10] Here we will store the number of LBA sectors read
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#include <asm.inc>
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.code16
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SECTORS_PER_TRACK = HEX(04)
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NUMBER_OF_HEADS = HEX(08)
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BIOS_CHS_DRIVE_SIZE = HEX(0C)
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LBA_SECTORS_READ = HEX(10)
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EXT2_ROOT_INO = 2
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EXT2_S_IFMT = HEX(0f0)
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EXT2_S_IFREG = HEX(080)
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//org 7c00h
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start:
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jmp short main
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nop
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BootDrive:
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.byte HEX(80)
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//BootPartition db 0 // Moved to end of boot sector to have a standard format across all boot sectors
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//SectorsPerTrack db 63 // Moved to [bp-SECTORS_PER_TRACK]
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//NumberOfHeads dw 16 // Moved to [bp-NUMBER_OF_HEADS]
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//BiosCHSDriveSize dd (1024 * 1024 * 63) // Moved to [bp-BIOS_CHS_DRIVE_SIZE]
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//LBASectorsRead dd 0 // Moved to [bp-LBA_SECTORS_READ]
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Ext2VolumeStartSector:
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.long 263088 // Start sector of the ext2 volume
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Ext2BlockSize:
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.long 2 // Block size in sectors
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Ext2BlockSizeInBytes:
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.long 1024 // Block size in bytes
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Ext2PointersPerBlock:
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.long 256 // Number of block pointers that can be contained in one block
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Ext2GroupDescPerBlock:
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.long 32 // Number of group descriptors per block
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Ext2FirstDataBlock:
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.long 1 // First data block (1 for 1024-byte blocks, 0 for bigger sizes)
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Ext2InodesPerGroup:
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.long 2048 // Number of inodes per group
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Ext2InodesPerBlock:
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.long 8 // Number of inodes per block
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Ext2ReadEntireFileLoadSegment:
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.word 0
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Ext2InodeIndirectPointer:
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.long 0
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Ext2InodeDoubleIndirectPointer:
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.long 0
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Ext2BlocksLeftToRead:
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.long 0
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main:
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xor ax,ax // Setup segment registers
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mov ds,ax // Make DS correct
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mov es,ax // Make ES correct
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mov ss,ax // Make SS correct
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mov bp, HEX(7c00)
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mov sp, HEX(7b00) // Setup a stack
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mov si, offset BootDrive
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cmp byte ptr [si], HEX(0ff) // If they have specified a boot drive then use it
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jne GetDriveParameters
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mov [si],dl // Save the boot drive
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GetDriveParameters:
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mov ah, 8
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mov dl,[si] // Get boot drive in dl
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int HEX(13) // Request drive parameters from the bios
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jnc CalcDriveSize // If the call succeeded then calculate the drive size
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// If we get here then the call to the BIOS failed
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// so just set CHS equal to the maximum addressable
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// size
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mov cx, HEX(0ffff)
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mov dh,cl
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CalcDriveSize:
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// Now that we have the drive geometry
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// lets calculate the drive size
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mov bl,ch // Put the low 8-bits of the cylinder count into BL
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mov bh,cl // Put the high 2-bits in BH
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shr bh,6 // Shift them into position, now BX contains the cylinder count
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and cl, HEX(3f) // Mask off cylinder bits from sector count
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// CL now contains sectors per track and DH contains head count
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movzx eax,dh // Move the heads into EAX
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movzx ebx,bx // Move the cylinders into EBX
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movzx ecx,cl // Move the sectors per track into ECX
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inc eax // Make it one based because the bios returns it zero based
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mov [bp-NUMBER_OF_HEADS],eax // Save number of heads
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mov [bp-SECTORS_PER_TRACK],ecx // Save number of sectors per track
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inc ebx // Make the cylinder count one based also
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mul ecx // Multiply heads with the sectors per track, result in edx:eax
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mul ebx // Multiply the cylinders with (heads * sectors) [stored in edx:eax already]
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// We now have the total number of sectors as reported
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// by the bios in eax, so store it in our variable
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mov [bp-BIOS_CHS_DRIVE_SIZE],eax
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LoadExtraBootCode:
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// First we have to load our extra boot code at
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// sector 1 into memory at [0000:7e00h]
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//mov eax,01h
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xor eax,eax
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inc eax // Read logical sector 1, EAX now = 1
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mov cx,1 // Read one sector
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mov bx, HEX(7e00) // Read sector to [0000:7e00h]
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call ReadSectors
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jmp LoadRootDirectory
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// Reads ext2 group descriptor into [7000:8000]
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// We read it to this arbitrary location so
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// it will not cross a 64k boundary
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// EAX has group descriptor number to read
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Ext2ReadGroupDesc:
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shl eax,5 // Group = (Group * sizeof(GROUP_DESCRIPTOR) /* 32 */)
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xor edx,edx
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div dword ptr [bp+Ext2GroupDescPerBlock] // Group = (Group / Ext2GroupDescPerBlock)
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add eax, dword ptr [bp+Ext2FirstDataBlock] // Group = Group + Ext2FirstDataBlock + 1
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inc eax // EAX now has the group descriptor block number
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// EDX now has the group descriptor offset in the block
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// Adjust the read offset so that the
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// group descriptor is read to 7000:8000
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mov ebx, HEX(78000)
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sub ebx,edx
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shr ebx,4
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mov es,bx
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xor bx,bx
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// Everything is now setup to call Ext2ReadBlock
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// Instead of using the call instruction we will
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// just put Ext2ReadBlock right after this routine
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// Reads ext2 block into ES:[BX]
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// EAX has logical block number to read
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Ext2ReadBlock:
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mov ecx, dword ptr [bp+Ext2BlockSize]
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mul ecx
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jmp ReadSectors
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// Reads ext2 inode into [6000:8000]
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// We read it to this arbitrary location so
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// it will not cross a 64k boundary
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// EAX has inode number to read
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Ext2ReadInode:
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dec eax // Inode = Inode - 1
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xor edx,edx
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div dword ptr [bp+Ext2InodesPerGroup] // Inode = (Inode / Ext2InodesPerGroup)
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mov ebx,eax // EBX now has the inode group number
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mov eax,edx
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xor edx,edx
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div dword ptr [bp+Ext2InodesPerBlock] // Inode = (Inode / Ext2InodesPerBlock)
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shl edx,7 // FIXME: InodeOffset *= 128 (make the array index a byte offset)
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// EAX now has the inode offset block number from inode table
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// EDX now has the inode offset in the block
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// Save the inode values and put the group
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// descriptor number in EAX and read it in
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push edx
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push eax
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mov eax,ebx
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call Ext2ReadGroupDesc
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// Group descriptor has been read, now
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// grab the inode table block number from it
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push HEX(7000)
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pop es
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mov di, HEX(8008)
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pop eax // Restore inode offset block number from stack
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add eax, es:[di] // Add the inode table start block
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// Adjust the read offset so that the
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// inode we want is read to 6000:8000
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pop edx // Restore inode offset in the block from stack
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mov ebx, HEX(68000)
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sub ebx,edx
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shr ebx,4
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mov es,bx
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xor bx,bx
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call Ext2ReadBlock
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ret
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// Reads logical sectors into ES:[BX]
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// EAX has logical sector number to read
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// CX has number of sectors to read
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ReadSectors:
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add eax, dword ptr [bp+Ext2VolumeStartSector] // Add the start of the volume
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cmp eax, [bp-BIOS_CHS_DRIVE_SIZE] // Check if they are reading a sector outside CHS range
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jae ReadSectorsLBA // Yes - go to the LBA routine
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// If at all possible we want to use LBA routines because
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// They are optimized to read more than 1 sector per read
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pushad // Save logical sector number & sector count
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CheckInt13hExtensions: // Now check if this computer supports extended reads
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mov ah, HEX(41) // AH = 41h
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mov bx, HEX(55aa) // BX = 55AAh
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mov dl, byte ptr [bp+BootDrive] // DL = drive (80h-FFh)
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int HEX(13) // IBM/MS INT 13 Extensions - INSTALLATION CHECK
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jc ReadSectorsCHS // CF set on error (extensions not supported)
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cmp bx, HEX(0aa55) // BX = AA55h if installed
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jne ReadSectorsCHS
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test cl,1 // CX = API subset support bitmap
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jz ReadSectorsCHS // Bit 0, extended disk access functions (AH=42h-44h,47h,48h) supported
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popad // Restore sector count & logical sector number
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ReadSectorsLBA:
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pushad // Save logical sector number & sector count
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cmp cx, 64 // Since the LBA calls only support 0x7F sectors at a time we will limit ourselves to 64
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jbe ReadSectorsSetupDiskAddressPacket // If we are reading less than 65 sectors then just do the read
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mov cx,64 // Otherwise read only 64 sectors on this loop iteration
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ReadSectorsSetupDiskAddressPacket:
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mov [bp-LBA_SECTORS_READ],cx
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mov word ptr [bp-LBA_SECTORS_READ+2],0
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data32 push 0
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push eax // Put 64-bit logical block address on stack
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push es // Put transfer segment on stack
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push bx // Put transfer offset on stack
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push cx // Set transfer count
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push 16 // Set size of packet to 10h
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mov si,sp // Setup disk address packet on stack
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mov dl, byte ptr [bp+BootDrive] // Drive number
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mov ah, HEX(42) // Int 13h, AH = 42h - Extended Read
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int HEX(13) // Call BIOS
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jc PrintDiskError // If the read failed then abort
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add sp, 16 // Remove disk address packet from stack
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popad // Restore sector count & logical sector number
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push bx
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mov ebx, [bp-LBA_SECTORS_READ]
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add eax,ebx // Increment sector to read
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shl ebx,5
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mov dx,es
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add dx,bx // Setup read buffer for next sector
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mov es,dx
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pop bx
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sub cx,[bp-LBA_SECTORS_READ]
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jnz ReadSectorsLBA // Read next sector
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ret
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// Reads logical sectors into ES:[BX]
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// EAX has logical sector number to read
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// CX has number of sectors to read
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ReadSectorsCHS:
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popad // Get logical sector number & sector count off stack
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ReadSectorsCHSLoop:
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pushad
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xor edx,edx
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mov ecx, [bp-SECTORS_PER_TRACK]
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div ecx // Divide logical by SectorsPerTrack
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inc dl // Sectors numbering starts at 1 not 0
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mov cl,dl // Sector in CL
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mov edx,eax
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shr edx,16
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div word ptr [bp-NUMBER_OF_HEADS] // Divide logical by number of heads
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mov dh,dl // Head in DH
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mov dl, byte ptr [bp+BootDrive] // Drive number in DL
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mov ch,al // Cylinder in CX
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ror ah,2 // Low 8 bits of cylinder in CH, high 2 bits
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// in CL shifted to bits 6 & 7
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or cl,ah // Or with sector number
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mov ax, HEX(0201)
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int HEX(13) // DISK - READ SECTORS INTO MEMORY
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// AL = number of sectors to read, CH = track, CL = sector
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// DH = head, DL = drive, ES:BX -> buffer to fill
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// Return: CF set on error, AH = status (see AH=01h), AL = number of sectors read
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jc PrintDiskError // If the read failed then abort
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popad
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inc eax // Increment Sector to Read
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mov dx,es
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add dx, HEX(20) // Increment read buffer for next sector
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mov es,dx
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loop ReadSectorsCHSLoop // Read next sector
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ret
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// Displays a disk error message
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// And reboots
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PrintDiskError:
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mov si,msgDiskError // Bad boot disk message
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call PutChars // Display it
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Reboot:
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mov si,msgAnyKey // Press any key message
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call PutChars // Display it
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xor ax,ax
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int HEX(16) // Wait for a keypress
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int HEX(19) // Reboot
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PutChars:
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lodsb
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or al,al
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jz short Done
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call PutCharsCallBios
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jmp short PutChars
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PutCharsCallBios:
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mov ah, HEX(0e)
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mov bx, HEX(07)
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int HEX(10)
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ret
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Done:
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mov al, HEX(0d)
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call PutCharsCallBios
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mov al, HEX(0a)
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call PutCharsCallBios
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ret
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msgDiskError:
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.ascii "Disk error", NUL
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// Sorry, need the space...
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//msgAnyKey db 'Press any key to restart',0
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msgAnyKey:
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.ascii "Press key", NUL
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// times 509-($-$$) db 0 // Pad to 509 bytes
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.org 509
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BootPartition:
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.byte 0
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.word HEX(0aa55) // BootSector signature
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// End of bootsector
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//
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// Now starts the extra boot code that we will store
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// at sector 1 on a EXT2 volume
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LoadRootDirectory:
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mov eax,EXT2_ROOT_INO // Put the root directory inode number in EAX
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call Ext2ReadInode // Read in the inode
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// Point ES:DI to the inode structure at 6000:8000
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push HEX(6000)
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pop es
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mov di, HEX(8000)
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push di
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push es // Save these for later
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// Get root directory size from inode structure
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mov eax, es:[di+4]
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push eax
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// Now that the inode has been read in load
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// the root directory file data to 0000:8000
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call Ext2ReadEntireFile
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// Since the root directory was loaded to 0000:8000
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// then add 8000h to the root directory's size
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pop eax
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mov edx, HEX(8000) // Set EDX to the current offset in the root directory
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add eax,edx // Initially add 8000h to the size of the root directory
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SearchRootDirectory:
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push edx // Save current offset in root directory
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push eax // Save the size of the root directory
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// Now we have to convert the current offset
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// in the root directory to a SEGMENT:OFFSET pair
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mov eax,edx
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xor edx,edx
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mov ecx,16
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div ecx // Now AX:DX has segment & offset
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mov es,ax
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mov di,dx
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push di // Save the start of the directory entry
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add di, 8 // Add the offset to the filename
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mov si,filename
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mov cl,11
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repe cmpsb // Compare the file names
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pop di
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pop eax
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pop edx
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jz FoundFile
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// Nope, didn't find it in this entry, keep looking
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movzx ecx,word ptr es:[di+4]
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add edx,ecx
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// Check to see if we have reached the
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// end of the root directory
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cmp edx,eax
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jb SearchRootDirectory
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jmp PrintFileNotFound
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FoundFile:
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mov eax,es:[di] // Get inode number from directory entry
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call Ext2ReadInode // Read in the inode
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// Point ES:DI to the inode structure at 6000:8000
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pop es
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pop di // These were saved earlier
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mov cx, es:[di] // Get the file mode so we can make sure it's a regular file
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and ch,EXT2_S_IFMT // Mask off everything but the file type
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cmp ch,EXT2_S_IFREG // Make sure it's a regular file
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je LoadFreeLoader
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jmp PrintRegFileError
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LoadFreeLoader:
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mov si,msgLoading // "Loading FreeLoader..." message
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call PutChars // Display it
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call Ext2ReadEntireFile // Read freeldr.sys to 0000:8000
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mov dl, byte ptr [bp+BootDrive]
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mov dh, byte ptr [bp+BootPartition]
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push 0 // push segment (0x0000)
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mov eax, [HEX(8000) + HEX(0A8)] // load the RVA of the EntryPoint into eax
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add eax, HEX(8000) // RVA -> VA
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push ax // push offset
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retf // Transfer control to FreeLoader
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// Reads ext2 file data into [0000:8000]
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// This function assumes that the file's
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// inode has been read in to 6000:8000 *and*
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// ES:DI points to 6000:8000
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// This will load all the blocks up to
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// and including the double-indirect pointers.
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// This should be sufficient because it
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// allows for ~64MB which is much bigger
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// than we need for a boot loader.
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Ext2ReadEntireFile:
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// Reset the load segment
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mov word ptr [bp+Ext2ReadEntireFileLoadSegment], HEX(800)
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// Now we must calculate how
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// many blocks to read in
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// We will do this by rounding the
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// file size up to the next block
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// size and then dividing by the block size
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mov eax, dword ptr [bp+Ext2BlockSizeInBytes] // Get the block size in bytes
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push eax
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dec eax // Ext2BlockSizeInBytes -= 1
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add eax, es:[di+4] // Add the file size
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xor edx,edx
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pop ecx // Divide by the block size in bytes
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div ecx // EAX now contains the number of blocks to load
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push eax
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// Make sure the file size isn't zero
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cmp eax, 0
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jnz Ext2ReadEntireFile2
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jmp PrintFileSizeError
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Ext2ReadEntireFile2:
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// Save the indirect & double indirect pointers
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mov edx, es:[di+ HEX(58)] // Get indirect pointer
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mov dword ptr [bp+Ext2InodeIndirectPointer], edx // Save indirect pointer
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mov edx, es:[di+ HEX(5c)] // Get double indirect pointer
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mov dword ptr [bp+Ext2InodeDoubleIndirectPointer],edx // Save double indirect pointer
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// Now copy the direct pointers to 7000:0000
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// so that we can call Ext2ReadDirectBlocks
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push ds // Save DS
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push es
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push HEX(7000)
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pop es
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pop ds
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mov si, HEX(8028)
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xor di,di // DS:SI = 6000:8028 ES:DI = 7000:0000
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mov cx,24 // Moving 24 words of data
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rep movsw
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pop ds // Restore DS
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// Now we have all the block pointers in the
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// right location so read them in
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pop eax // Restore the total number of blocks in this file
|
|
xor ecx,ecx // Set the max count of blocks to read to 12
|
|
mov cl,12 // which is the number of direct block pointers in the inode
|
|
call Ext2ReadDirectBlockList
|
|
|
|
// Check to see if we actually have
|
|
// blocks left to read
|
|
cmp eax, 0
|
|
jz Ext2ReadEntireFileDone
|
|
|
|
// Now we have read all the direct blocks in
|
|
// the inode. So now we have to read the indirect
|
|
// block and read all it's direct blocks
|
|
push eax // Save the total block count
|
|
mov eax, dword ptr [bp+Ext2InodeIndirectPointer] // Get the indirect block pointer
|
|
push HEX(7000)
|
|
pop es
|
|
xor bx,bx // Set the load address to 7000:0000
|
|
call Ext2ReadBlock // Read the block
|
|
|
|
// Now we have all the block pointers from the
|
|
// indirect block in the right location so read them in
|
|
pop eax // Restore the total block count
|
|
mov ecx, dword ptr [bp+Ext2PointersPerBlock] // Get the number of block pointers that one block contains
|
|
call Ext2ReadDirectBlockList
|
|
|
|
// Check to see if we actually have
|
|
// blocks left to read
|
|
cmp eax, 0
|
|
jz Ext2ReadEntireFileDone
|
|
|
|
// Now we have read all the direct blocks from
|
|
// the inode's indirect block pointer. So now
|
|
// we have to read the double indirect block
|
|
// and read all it's indirect blocks
|
|
// (whew, it's a good thing I don't support triple indirect blocks)
|
|
mov dword ptr [bp+Ext2BlocksLeftToRead],eax // Save the total block count
|
|
mov eax, dword ptr [bp+Ext2InodeDoubleIndirectPointer] // Get the double indirect block pointer
|
|
push HEX(7800)
|
|
pop es
|
|
push es // Save an extra copy of this value on the stack
|
|
xor bx,bx // Set the load address to 7000:8000
|
|
call Ext2ReadBlock // Read the block
|
|
|
|
pop es // Put 7800h into ES (saved on the stack already)
|
|
xor di,di
|
|
|
|
Ext2ReadIndirectBlock:
|
|
mov eax, es:[di] // Get indirect block pointer
|
|
add di, 4 // Update DI for next array index
|
|
push es
|
|
push di
|
|
|
|
push HEX(7000)
|
|
pop es
|
|
xor bx,bx // Set the load address to 7000:0000
|
|
call Ext2ReadBlock // Read the indirect block
|
|
|
|
// Now we have all the block pointers from the
|
|
// indirect block in the right location so read them in
|
|
mov eax, dword ptr [bp+Ext2BlocksLeftToRead] // Restore the total block count
|
|
mov ecx, dword ptr [bp+Ext2PointersPerBlock] // Get the number of block pointers that one block contains
|
|
call Ext2ReadDirectBlockList
|
|
mov dword ptr [bp+Ext2BlocksLeftToRead],eax // Save the total block count
|
|
pop di
|
|
pop es
|
|
|
|
// Check to see if we actually have
|
|
// blocks left to read
|
|
cmp eax, 0
|
|
jnz Ext2ReadIndirectBlock
|
|
|
|
Ext2ReadEntireFileDone:
|
|
ret
|
|
|
|
// Reads a maximum number of blocks
|
|
// from an array at 7000:0000
|
|
// and updates the total count
|
|
// ECX contains the max number of blocks to read
|
|
// EAX contains the number of blocks left to read
|
|
// On return:
|
|
// EAX contains the new number of blocks left to read
|
|
Ext2ReadDirectBlockList:
|
|
cmp eax,ecx // Compare it to the maximum number of blocks to read
|
|
ja CallExt2ReadDirectBlocks // If it will take more blocks then just read all of the blocks
|
|
mov cx,ax // Otherwise adjust the block count accordingly
|
|
|
|
CallExt2ReadDirectBlocks:
|
|
sub eax,ecx // Subtract the number of blocks being read from the total count
|
|
push eax // Save the new total count
|
|
call Ext2ReadDirectBlocks
|
|
pop eax // Restore the total count
|
|
ret
|
|
|
|
|
|
// Reads a specified number of blocks
|
|
// from an array at 7000:0000
|
|
// CX contains the number of blocks to read
|
|
Ext2ReadDirectBlocks:
|
|
|
|
push HEX(7000)
|
|
pop es
|
|
xor di,di // Set ES:DI = 7000:0000
|
|
|
|
Ext2ReadDirectBlocksLoop:
|
|
mov eax,es:[di] // Get direct block pointer from array
|
|
add di, 4 // Update DI for next array index
|
|
|
|
push cx // Save number of direct blocks left
|
|
push es // Save array segment
|
|
push di // Save array offset
|
|
mov es,[bp+Ext2ReadEntireFileLoadSegment]
|
|
xor bx,bx // Setup load address for next read
|
|
|
|
call Ext2ReadBlock // Read the block (this updates ES for the next read)
|
|
|
|
mov [bp+Ext2ReadEntireFileLoadSegment],es // Save updated ES
|
|
|
|
pop di // Restore the array offset
|
|
pop es // Restore the array segment
|
|
pop cx // Restore the number of blocks left
|
|
|
|
loop Ext2ReadDirectBlocksLoop
|
|
|
|
// At this point all the direct blocks should
|
|
// be loaded and ES (Ext2ReadEntireFileLoadSegment)
|
|
// should be ready for the next read.
|
|
ret
|
|
|
|
|
|
|
|
// Displays a file not found error message
|
|
// And reboots
|
|
PrintFileNotFound:
|
|
mov si,msgFreeLdr // FreeLdr not found message
|
|
jmp short DisplayItAndReboot
|
|
|
|
// Displays a file size is 0 error
|
|
// And reboots
|
|
PrintFileSizeError:
|
|
mov si,msgFileSize // Error message
|
|
jmp short DisplayItAndReboot
|
|
|
|
// Displays a file is not a regular file error
|
|
// And reboots
|
|
PrintRegFileError:
|
|
mov si,msgRegFile // Error message
|
|
DisplayItAndReboot:
|
|
call PutChars // Display it
|
|
jmp Reboot
|
|
|
|
msgFreeLdr:
|
|
.ascii "freeldr.sys not found", NUL
|
|
msgFileSize:
|
|
.ascii "File size 0", NUL
|
|
msgRegFile:
|
|
.ascii "freeldr.sys isnt a regular file", NUL
|
|
filename:
|
|
.ascii "freeldr.sys"
|
|
msgLoading:
|
|
.ascii "Loading...", NUL
|
|
|
|
// times 1022-($-$$) db 0 // Pad to 1022 bytes
|
|
.org 1022
|
|
|
|
.word HEX(0aa55) // BootSector signature
|
|
|
|
.endcode16
|
|
|
|
END
|