Miscellaneous efficiency improvements, and extend read_sectors to
handle multiple sectors.
This commit is contained in:
Michael Brown
parent
bdd1a0f462
commit
839960276d
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@ -20,6 +20,7 @@ find_active_partition:
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movw $STACK_SEG, %ax
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movw %ax, %ss
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movw $STACK_SIZE, %sp
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/* Relocate self to EXEC_SEG */
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pushw $BOOT_SEG
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popw %ds
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@ -34,12 +35,24 @@ find_active_partition:
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popw %es
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pushw %cs
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popw %ds
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/* Check for LBA extensions */
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movb $0x41, %ah
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movw $0x55aa, %bx
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stc
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int $0x13
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jc 1f
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cmpw $0xaa55, %bx
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jne 1f
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movw $read_lba, read_sector
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1:
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/* Read and process root partition table */
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xorb %dh, %dh
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movw $0x0001, %cx
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xorl %esi, %esi
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xorl %edi, %edi
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call process_table
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/* Print failure message */
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movw $10f, %si
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movw $(20f-10f), %cx
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@ -48,6 +61,7 @@ find_active_partition:
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lodsb
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int $0x10
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loop 1b
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/* Boot next device */
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int $0x18
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10: .ascii "Could not locate active partition\r\n"
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@ -69,10 +83,10 @@ find_active_partition:
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*/
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process_table:
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pushal
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movw $446, %bx
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1: call read_sector
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call read_boot_sector
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jc 99f
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call process_partition
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movw $446, %bx
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1: call process_partition
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addw $16, %bx
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cmpw $510, %bx
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jne 1b
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@ -102,7 +116,7 @@ process_partition:
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/* Check active flag */
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testb $0x80, %es:(%bx)
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jz 1f
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call read_sector
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call read_boot_sector
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jc 99f
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jmp *%bp
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1: /* Check for extended partition */
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@ -115,10 +129,12 @@ process_partition:
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jne 99f
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2: call process_table
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99: popal
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/* Reload original partition table */
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call read_boot_sector
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ret
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/*
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* Read single sector to 0000:7c00 and verify 0x55aa signature
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* Read single sector to %es:0000 and verify 0x55aa signature
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*
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* Parameters:
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* %dl : BIOS drive number
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@ -130,32 +146,56 @@ process_partition:
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* Returns:
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* CF set on error
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*/
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read_sector:
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pushal
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/* Check for LBA extensions */
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call check_lba
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jnc read_lba
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read_chs:
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/* Read sector using C/H/S address */
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movw $0x0201, %ax
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xorw %bx, %bx
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stc
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int $0x13
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sti
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jmp 99f
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read_lba:
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/* Read sector using LBA address */
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movb $0x42, %ah
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movl %esi, (lba_desc + 12)
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movl %edi, (lba_desc + 8)
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movw $lba_desc, %si
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int $0x13
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99: /* Check for 55aa signature */
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read_boot_sector:
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pushw %ax
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movw $1, %ax
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call *read_sector
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jc 99f
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cmpw $0xaa55, %es:(510)
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je 99f
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stc
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99: popw %ax
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ret
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/*
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* Read single sector to %es:0000 and verify 0x55aa signature
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*
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* Parameters:
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* %dl : BIOS drive number
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* %dh : Head
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* %cl : Sector (bits 0-5), high two bits of cylinder (bits 6-7)
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* %ch : Low eight bits of cylinder
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* %esi:%edi : LBA address
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* %ax : Number of sectors (max 127)
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*
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* Returns:
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* CF set on error
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*/
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read_sector: .word read_chs
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read_chs:
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/* Read sectors using C/H/S address */
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pushal
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xorw %bx, %bx
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movb $0x02, %ah
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stc
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99: popal
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int $0x13
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sti
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popal
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ret
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read_lba:
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/* Read sectors using LBA address */
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pushal
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movw %ax, (lba_desc + 2)
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pushw %es
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popw (lba_desc + 6)
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movl %edi, (lba_desc + 8)
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movl %esi, (lba_desc + 12)
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movw $lba_desc, %si
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movb $0x42, %ah
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int $0x13
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popal
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ret
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lba_desc:
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@ -163,27 +203,5 @@ lba_desc:
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.byte 0
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.word 1
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.word 0x0000
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.word 0x07c0
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.word 0x0000
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.long 0, 0
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/*
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* Check for LBA extensions
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*
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* Parameters:
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* %dl : BIOS drive number
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*
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* Returns:
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* CF clear if LBA extensions supported
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*/
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check_lba:
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pushal
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movb $0x41, %ah
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movw $0x55aa, %bx
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stc
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int $0x13
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jc 99f
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cmpw $0xaa55, %bx
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je 99f
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stc
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99: popal
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ret
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