Bootloader: Find root partition from GPT header
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d2970b5b8d
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048bbf874a
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@ -186,11 +186,13 @@ stage1_main:
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# setup stack
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movw %ax, %ss
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movw $0x7C00, %sp
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movl $0x7C00, %esp
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# save boot disk number
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movb %dl, (boot_disk_number)
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# FIXME: validate boot disk (needs size optizations)
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# confirm that int 13h extensions are available
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clc
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movb $0x41, %ah
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@ -427,11 +429,35 @@ isprint:
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ret
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# fills memory map data structure
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# doesn't return on error
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get_memory_map:
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# check if drive exists
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# dl: drive number
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# return:
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# al: 1 if disk is usable, 0 otherwise
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drive_exists:
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pusha
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movb $0x48, %ah
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movw $disk_drive_parameters, %si
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movw $0x1A, (disk_drive_parameters) # set buffer size
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clc
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int $0x13
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jc .drive_exists_nope
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popa
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movb $1, %al
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ret
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.drive_exists_nope:
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popa
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movb $0, %al
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ret
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# fills memory map data structure
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# doesn't return on error
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# NO REGISTERS SAVED
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get_memory_map:
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movl $0, (memory_map_entry_count)
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movl $0x0000E820, %eax
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@ -472,7 +498,6 @@ get_memory_map:
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jnc .get_memory_map_rest
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.get_memory_map_done:
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popa
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ret
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.get_memory_map_error:
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@ -481,9 +506,8 @@ get_memory_map:
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# fills command line buffer
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# NO REGISTERS SAVED
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get_command_line:
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pusha
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movw $command_line_enter_msg, %si
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call puts
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@ -532,36 +556,12 @@ get_command_line:
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call print_newline
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popa
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ret
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stage2_main:
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# clear screen and enter 80x25 text mode
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movb $0x03, %al
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movb $0x00, %ah
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int $0x10
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# print hello message
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movw $hello_msg, %si
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call puts
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call print_newline
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call get_memory_map
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call get_command_line
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call print_newline
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movw $start_kernel_load_msg, %si
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call puts
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call print_newline
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movw $command_line_msg, %si
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call puts
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movw $command_line_buffer, %si
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call puts
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call print_newline
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# print memory map from memory_map_entries
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# NO REGISTERS SAVED
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print_memory_map:
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movw $memory_map_msg, %si
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call puts
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call print_newline
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@ -619,10 +619,212 @@ stage2_main:
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decl %edx
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jnz .loop_memory_map
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ret
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# find root disk and populate root_disk_drive_number field
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# NO REGISTERS SAVED
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find_root_disk:
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movb $0x80, %dl
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.find_root_disk_loop:
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call drive_exists
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testb %al, %al
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jz .find_root_disk_not_found
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# read GPT header
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xorw %bx, %bx
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movl $1, %eax
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movw $1, %cx
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movw $gpt_header, %di
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call read_from_disk
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# confirm header (starts with 'EFI PART')
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cmpl $0x20494645, (gpt_header + 0)
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jne .find_root_disk_next_disk
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cmpl $0x54524150, (gpt_header + 4)
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jne .find_root_disk_next_disk
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# compare disk GUID
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movw $root_disk_guid, %si
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movw $(gpt_header + 56), %di
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movw $16, %cx
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call memcmp
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testb %al, %al
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jz .find_root_disk_next_disk
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movb %dl, (root_disk_drive_number)
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ret
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.find_root_disk_next_disk:
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incb %dl
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jmp .find_root_disk_loop
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.find_root_disk_not_found:
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movw $no_root_disk_msg, %si
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jmp print_and_halt
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# finds root partition from root disk
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# fills root_partition_entry data structure
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# NOTE: assumes GPT header is in `gpt_header`
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# NO REGISTERS SAVED
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find_root_partition:
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pushl %ebp
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movl %esp, %ebp
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subl $16, %esp
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# esp + 0: 8 byte entry array lba
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movl (gpt_header + 72), %eax
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movl %eax, 0(%esp)
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movl (gpt_header + 76), %eax
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movl %eax, 4(%esp)
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# FIXME: check that bits 48-63 are zero
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# esp + 8: 4 byte entries per sector
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xorl %edx, %edx
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movl $SECTOR_SIZE, %eax
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divl (gpt_header + 84)
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movl %eax, 8(%esp)
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# esp + 12: 4 byte entries remaining
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movl (gpt_header + 80), %eax
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testl %eax, %eax
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jz .find_root_partition_not_found
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movl %eax, 12(%esp)
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.find_root_partition_read_entry_section:
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movl 0(%esp), %eax
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movl 4(%esp), %ebx
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movw $1, %cx
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movb (root_disk_drive_number), %dl
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movw $sector_buffer, %di
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call read_from_disk
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# ecx: min(entries per section, entries remaining)
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movl 8(%esp), %ecx
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cmpl 12(%esp), %ecx
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jae .find_root_partition_got_entry_count
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movl 12(%esp), %ecx
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.find_root_partition_got_entry_count:
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# update entries remaining
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subl %ecx, 12(%esp)
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# si: entry pointer
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movw $sector_buffer, %si
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.find_root_partition_loop_entries:
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# temporarily save cx in dx
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movw %cx, %dx
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# check that entry is used
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movw $16, %cx
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movw $zero_guid, %di
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call memcmp
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test %al, %al
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jnz .find_root_partition_next_entry
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# compare entry guid to root guid
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movw $16, %cx
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addw $16, %si
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movw $root_partition_guid, %di
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call memcmp
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subw $16, %si
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testb %al, %al
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jnz .find_root_partition_found
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.find_root_partition_next_entry:
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# restore cx
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movw %dx, %cx
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# entry pointer += entry size
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addw (gpt_header + 84), %si
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loop .find_root_partition_loop_entries
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# entry not found in this sector
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# increment 8 byte entry array lba
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incl 0(%esp)
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jno .find_root_partition_no_overflow
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incl 4(%esp)
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.find_root_partition_no_overflow:
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# loop to read next section if entries remaining
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cmpl $0, 12(%esp)
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jnz .find_root_partition_read_entry_section
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.find_root_partition_not_found:
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movw $no_root_partition_msg, %si
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jmp print_and_halt
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.find_root_partition_found:
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# copy entry to buffer
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movw $root_partition_entry, %di
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movw $128, %cx
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rep movsb
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leavel
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ret
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stage2_main:
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# clear screen and enter 80x25 text mode
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movb $0x03, %al
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movb $0x00, %ah
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int $0x10
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# print hello message
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movw $hello_msg, %si
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call puts; call print_newline
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call get_memory_map
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call get_command_line
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call print_newline
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movw $start_kernel_load_msg, %si
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call puts; call print_newline
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call print_memory_map
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call find_root_disk
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movw $root_disk_found_msg, %si
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call puts; call print_newline
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call find_root_partition
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movw $root_partition_found_msg, %si
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call puts; call print_newline
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movw $16, %bx
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movw $2, %cx
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movw (root_partition_entry + 38), %ax; call printnum
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movw (root_partition_entry + 36), %ax; call printnum
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movw (root_partition_entry + 34), %ax; call printnum
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movw (root_partition_entry + 32), %ax; call printnum
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movb $'-', %al; call putc
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movb $'>', %al; call putc
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movw (root_partition_entry + 46), %ax; call printnum
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movw (root_partition_entry + 44), %ax; call printnum
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movw (root_partition_entry + 42), %ax; call printnum
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movw (root_partition_entry + 40), %ax; call printnum
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jmp halt
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# These will be patched during bootloader installation
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root_disk_guid:
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.ascii "root disk guid "
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root_partition_guid:
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.ascii "root part guid "
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zero_guid:
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.quad 0
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.quad 0
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hello_msg:
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.asciz "This is banan-os bootloader"
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@ -639,6 +841,16 @@ memory_map_error_msg:
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start_kernel_load_msg:
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.asciz "Starting to load kernel"
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root_disk_found_msg:
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.asciz "Root disk found!"
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no_root_disk_msg:
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.asciz "Root disk not found"
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root_partition_found_msg:
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.asciz "Root partition found!"
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no_root_partition_msg:
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.asciz "Root partition not found"
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stage2_end:
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@ -650,12 +862,24 @@ gpt_header:
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gpt_entry_data:
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.skip SECTOR_SIZE
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sector_buffer:
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.skip SECTOR_SIZE
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disk_drive_parameters:
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.skip 0x1A
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disk_address_packet:
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.skip 16
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printnum_buffer:
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.skip 10
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root_disk_drive_number:
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.skip 1
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root_partition_entry:
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.skip 128
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memory_map_entry_count:
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.skip 4
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# 100 entries should be enough...
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