224 lines
5.4 KiB
ArmAsm
224 lines
5.4 KiB
ArmAsm
.set SECTOR_SIZE, 512
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# file header field offsets
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.set e_type, 16
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.set e_machine, 18
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.set e_version, 20
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.set e_entry, 24
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.set e_phoff, 32
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.set e_shoff, 40
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.set e_flags, 48
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.set e_ehsize, 52
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.set e_phentsize, 54
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.set e_phnum, 56
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.set e_shentsize, 58
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.set e_shnum, 60
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.set e_shstrndx, 62
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# e_ident offsets
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.set EI_CLASS, 4
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.set EI_DATA, 5
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.set EI_VERSION, 6
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# e_ident constants
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.set ELFMAGIC, 0x464C457F
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.set ELFCLASS64, 2
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.set ELFDATA2LSB, 1
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.set EV_CURRENT, 1
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# e_type constants
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.set ET_EXEC, 2
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# program header field offsets
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.set p_type, 0
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.set p_flags, 4
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.set p_offset, 8
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.set p_vaddr, 16
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.set p_paddr, 24
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.set p_filesz, 32
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.set p_memsz, 40
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.set p_align, 48
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# p_type constants
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.set PT_NULL, 0
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.set PT_LOAD, 1
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.code16
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.section .stage2
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# Validate file header stored in elf_file_header
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# returns only on success
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elf_validate_file_header:
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cmpl $ELFMAGIC, (elf_file_header)
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jne .elf_validate_file_header_invalid_magic
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cmpb $ELFCLASS64, (elf_file_header + EI_CLASS)
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jne .elf_validate_file_header_only_64bit_supported
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cmpb $ELFDATA2LSB, (elf_file_header + EI_DATA)
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jne .elf_validate_file_header_only_little_endian_supported
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cmpb $EV_CURRENT, (elf_file_header + EI_VERSION)
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jne .elf_validate_file_header_not_current_version
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cmpl $EV_CURRENT, (elf_file_header + e_version)
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jne .elf_validate_file_header_not_current_version
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cmpw $ET_EXEC, (elf_file_header + e_type)
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jne .elf_validate_file_header_not_executable
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ret
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.elf_validate_file_header_invalid_magic:
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movw $elf_validate_file_header_invalid_magic_msg, %si
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jmp print_and_halt
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.elf_validate_file_header_only_64bit_supported:
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movw $elf_validate_file_header_only_64bit_supported_msg, %si
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jmp print_and_halt
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.elf_validate_file_header_only_little_endian_supported:
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movw $elf_validate_file_header_only_little_endian_supported_msg, %si
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jmp print_and_halt
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.elf_validate_file_header_not_current_version:
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movw $elf_validate_file_header_not_current_version_msg, %si
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jmp print_and_halt
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.elf_validate_file_header_not_executable:
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movw $elf_validate_file_header_not_executable_msg, %si
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jmp print_and_halt
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# read callback format
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# eax: first byte
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# ecx: byte count
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# edi: buffer
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# returns only on success
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# reads kernel to memory
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# esi: callback for reading from kernel image
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# return:
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# eax: kernel entry address
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.global elf_read_kernel_to_memory
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elf_read_kernel_to_memory:
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pushal
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pushl %ebp
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movl %esp, %ebp
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subl $2, %esp
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# read file header
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movl $0, %eax
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movl $64, %ecx
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movl $elf_file_header, %edi
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call *%esi
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call elf_validate_file_header
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cmpl $0, (elf_file_header + e_phoff + 4)
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jnz .elf_read_kernel_to_memory_unsupported_offset
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# current program header
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movw $0, -2(%ebp)
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.elf_read_kernel_to_memory_loop_program_headers:
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movw -2(%ebp), %cx
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cmpw (elf_file_header + e_phnum), %cx
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jae .elf_read_kernel_to_memory_done
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# eax := program_header_index * e_phentsize + e_phoff
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xorl %eax, %eax
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movw %cx, %ax
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xorl %ebx, %ebx
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movw (elf_file_header + e_phentsize), %bx
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mull %ebx
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addl (elf_file_header + e_phoff), %eax
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jc .elf_read_kernel_to_memory_unsupported_offset
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# setup program header size and address
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movl $56, %ecx
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movl $elf_program_header, %edi
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# read the program header
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call *%esi
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# test if program header is empty
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cmpl $PT_NULL, (elf_program_header + p_type)
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je .elf_read_kernel_to_memory_null_program_header
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# confirm that the program header is loadable
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cmpl $PT_LOAD, (elf_program_header + p_type)
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jne .elf_read_kernel_to_memory_not_loadable_header
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# memset p_filesz -> p_memsz to 0
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movl (elf_program_header + p_filesz), %ebx
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movl (elf_program_header + p_vaddr), %edi
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andl $0x7FFFFFFF, %edi
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addl %ebx, %edi
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movl (elf_program_header + p_memsz), %ecx
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subl %ebx, %ecx
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jz .elf_read_kernel_to_memory_memset_done
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.elf_read_kernel_to_memory_memset:
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movb $0, (%edi)
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incl %edi
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decl %ecx
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jnz .elf_read_kernel_to_memory_memset
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.elf_read_kernel_to_memory_memset_done:
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# read file specified in program header to memory
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movl (elf_program_header + p_offset), %eax
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movl (elf_program_header + p_vaddr), %edi
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andl $0x7FFFFFFF, %edi
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movl (elf_program_header + p_filesz), %ecx
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#call print_hex32; call print_newline
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call *%esi
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.elf_read_kernel_to_memory_null_program_header:
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incw -2(%ebp)
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jmp .elf_read_kernel_to_memory_loop_program_headers
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.elf_read_kernel_to_memory_done:
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leavel
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popal
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# set kernel entry address
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movl (elf_file_header + e_entry), %eax
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andl $0x7FFFFF, %eax
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ret
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.elf_read_kernel_to_memory_unsupported_offset:
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movw $elf_read_kernel_to_memory_unsupported_offset_msg, %si
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jmp print_and_halt
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.elf_read_kernel_to_memory_not_loadable_header:
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movw $elf_read_kernel_to_memory_not_loadable_header_msg, %si
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jmp print_and_halt
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.section .data
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elf_validate_file_header_invalid_magic_msg:
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.asciz "ELF: file has invalid ELF magic"
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elf_validate_file_header_only_64bit_supported_msg:
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.asciz "ELF: file is not targettint 64 bit"
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elf_validate_file_header_only_little_endian_supported_msg:
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.asciz "ELF: file is not in little endian format"
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elf_validate_file_header_not_current_version_msg:
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.asciz "ELF: file is not in current ELF version"
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elf_validate_file_header_not_executable_msg:
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.asciz "ELF: file is not an executable"
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elf_read_kernel_to_memory_unsupported_offset_msg:
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.asciz "ELF: unsupported offset (only 32 bit offsets supported)"
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elf_read_kernel_to_memory_not_loadable_header_msg:
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.asciz "ELF: kernel contains non-loadable program header"
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.section .bss
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elf_file_header:
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.skip 64
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elf_program_header:
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.skip 56
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