banan-os/bootloader/bios/elf.S

321 lines
7.8 KiB
ArmAsm

.set SECTOR_SIZE, 512
# file header field offsets
.set e_type, 16
.set e_machine, 18
.set e_version, 20
.set e_entry, 24
.set e32_phoff, 28
.set e32_shoff, 32
.set e32_flags, 36
.set e32_ehsize, 40
.set e32_phentsize, 42
.set e32_phnum, 44
.set e32_shentsize, 46
.set e32_shnum, 48
.set e32_shstrndx, 50
.set e64_phoff, 32
.set e64_shoff, 40
.set e64_flags, 48
.set e64_ehsize, 52
.set e64_phentsize, 54
.set e64_phnum, 56
.set e64_shentsize, 58
.set e64_shnum, 60
.set e64_shstrndx, 62
# e_ident offsets
.set EI_CLASS, 4
.set EI_DATA, 5
.set EI_VERSION, 6
# e_ident constants
.set ELFMAGIC, 0x464C457F
.set ELFCLASS32, 1
.set ELFCLASS64, 2
.set ELFDATA2LSB, 1
.set EV_CURRENT, 1
# e_type constants
.set ET_EXEC, 2
# program header field offsets
.set p_type, 0
.set p32_offset, 4
.set p32_vaddr, 8
.set p32_paddr, 12
.set p32_filesz, 16
.set p32_memsz, 20
.set p32_flags, 24
.set p32_align, 28
.set p64_flags, 4
.set p64_offset, 8
.set p64_vaddr, 16
.set p64_paddr, 24
.set p64_filesz, 32
.set p64_memsz, 40
.set p64_align, 48
# p_type constants
.set PT_NULL, 0
.set PT_LOAD, 1
# mask for entry point and segment loading
.set LOAD_MASK, 0x07FFFFFF
.code16
.section .stage2
# Validate file header stored in elf_file_header
# returns only on success
elf_validate_file_header:
cmpl $ELFMAGIC, (elf_file_header)
jne .elf_validate_file_header_invalid_magic
cmpb $ELFCLASS32, (elf_file_header + EI_CLASS)
je .elf_validate_file_header_class_valid
cmpb $ELFCLASS64, (elf_file_header + EI_CLASS)
je .elf_validate_file_header_class_valid
jmp .elf_validate_file_header_invalid_class
.elf_validate_file_header_class_valid:
cmpb $ELFDATA2LSB, (elf_file_header + EI_DATA)
jne .elf_validate_file_header_only_little_endian_supported
cmpb $EV_CURRENT, (elf_file_header + EI_VERSION)
jne .elf_validate_file_header_not_current_version
cmpl $EV_CURRENT, (elf_file_header + e_version)
jne .elf_validate_file_header_not_current_version
cmpw $ET_EXEC, (elf_file_header + e_type)
jne .elf_validate_file_header_not_executable
ret
.elf_validate_file_header_invalid_magic:
movw $elf_validate_file_header_invalid_magic_msg, %si
jmp print_and_halt
.elf_validate_file_header_invalid_class:
movw $elf_validate_file_header_invalid_class_msg, %si
jmp print_and_halt
.elf_validate_file_header_only_little_endian_supported:
movw $elf_validate_file_header_only_little_endian_supported_msg, %si
jmp print_and_halt
.elf_validate_file_header_not_current_version:
movw $elf_validate_file_header_not_current_version_msg, %si
jmp print_and_halt
.elf_validate_file_header_not_executable:
movw $elf_validate_file_header_not_executable_msg, %si
jmp print_and_halt
# reads memory specified by 32 bit elf_program_header to memory
elf_read_program_header32_to_memory:
pushal
pushl %ebp
movl %esp, %ebp
# memset p_filesz -> p_memsz to 0
movl (elf_program_header + p32_filesz), %ebx
movl (elf_program_header + p32_vaddr), %edi
andl $LOAD_MASK, %edi
addl %ebx, %edi
movl (elf_program_header + p32_memsz), %ecx
subl %ebx, %ecx
xorb %al, %al; call memset32
# read file specified in program header to memory
movl (elf_program_header + p32_offset), %eax
movl (elf_program_header + p32_vaddr), %edi
andl $LOAD_MASK, %edi
movl (elf_program_header + p32_filesz), %ecx
call *%esi
leavel
popal
ret
# reads memory specified by 64 bit elf_program_header to memory
elf_read_program_header64_to_memory:
pushal
pushl %ebp
movl %esp, %ebp
# memset p_filesz -> p_memsz to 0
movl (elf_program_header + p64_filesz), %ebx
movl (elf_program_header + p64_vaddr), %edi
andl $LOAD_MASK, %edi
addl %ebx, %edi
movl (elf_program_header + p64_memsz), %ecx
subl %ebx, %ecx
xorb %al, %al; call memset32
# read file specified in program header to memory
movl (elf_program_header + p64_offset), %eax
movl (elf_program_header + p64_vaddr), %edi
andl $LOAD_MASK, %edi
movl (elf_program_header + p64_filesz), %ecx
call *%esi
leavel
popal
ret
# read callback format
# eax: first byte
# ecx: byte count
# edi: buffer
# returns only on success
# reads kernel to memory
# esi: callback for reading from kernel image
# return:
# eax: kernel entry address
.global elf_read_kernel_to_memory
elf_read_kernel_to_memory:
pushal
pushl %ebp
movl %esp, %ebp
subl $2, %esp
# read start of file header
movl $0, %eax
movl $24, %ecx
movl $elf_file_header, %edi
call *%esi
call elf_validate_file_header
# determine file header size
movl $52, %ecx
movl $64, %edx
cmpb $ELFCLASS64, (elf_file_header + EI_CLASS)
cmovel %edx, %ecx
# read full file header
movl $0, %eax
movl $elf_file_header, %edi
call *%esi
# verify that e_phoff fits in 32 bits
cmpb $ELFCLASS64, (elf_file_header + EI_CLASS)
jne .elf_read_kernel_to_memory_valid_offset
cmpl $0, (elf_file_header + e64_phoff + 4)
jnz .elf_read_kernel_to_memory_unsupported_offset
.elf_read_kernel_to_memory_valid_offset:
# read architecture phentsize and phnum to fixed locations
movw (elf_file_header + e32_phentsize), %ax
movw (elf_file_header + e32_phnum), %bx
movl (elf_file_header + e32_phoff), %ecx
cmpb $ELFCLASS64, (elf_file_header + EI_CLASS)
cmovew (elf_file_header + e64_phentsize), %ax
cmovew (elf_file_header + e64_phnum), %bx
cmovel (elf_file_header + e64_phoff), %ecx
movw %ax, (elf_file_header_phentsize)
movw %bx, (elf_file_header_phnum)
movl %ecx, (elf_file_header_phoff)
# current program header
movw $0, -2(%ebp)
.elf_read_kernel_to_memory_loop_program_headers:
movw -2(%ebp), %cx
cmpw (elf_file_header_phnum), %cx
jae .elf_read_kernel_to_memory_done
# eax := program_header_index * e_phentsize + e_phoff
xorl %eax, %eax
movw %cx, %ax
xorl %ebx, %ebx
movw (elf_file_header_phentsize), %bx
mull %ebx
addl (elf_file_header_phoff), %eax
jc .elf_read_kernel_to_memory_unsupported_offset
# determine program header size
movl $32, %ecx
movl $56, %edx
cmpb $ELFCLASS64, (elf_file_header + EI_CLASS)
cmovel %edx, %ecx
# read program header
movl $elf_program_header, %edi
call *%esi
# test if program header is NULL header
cmpl $PT_NULL, (elf_program_header + p_type)
je .elf_read_kernel_to_memory_null_program_header
# confirm that the program header is loadable
cmpl $PT_LOAD, (elf_program_header + p_type)
jne .elf_read_kernel_to_memory_not_loadable_header
# read program header to memory
movl $elf_read_program_header32_to_memory, %eax
movl $elf_read_program_header64_to_memory, %ebx
cmpb $ELFCLASS64, (elf_file_header + EI_CLASS)
cmovel %ebx, %eax
call *%eax
.elf_read_kernel_to_memory_null_program_header:
incw -2(%ebp)
jmp .elf_read_kernel_to_memory_loop_program_headers
.elf_read_kernel_to_memory_done:
leavel
popal
# set kernel entry address
movl (elf_file_header + e_entry), %eax
andl $LOAD_MASK, %eax
ret
.elf_read_kernel_to_memory_unsupported_offset:
movw $elf_read_kernel_to_memory_unsupported_offset_msg, %si
jmp print_and_halt
.elf_read_kernel_to_memory_not_loadable_header:
movw $elf_read_kernel_to_memory_not_loadable_header_msg, %si
jmp print_and_halt
.section .data
elf_validate_file_header_invalid_magic_msg:
.asciz "ELF: file has invalid ELF magic"
elf_validate_file_header_invalid_class_msg:
.asciz "ELF: file has invalid ELF class"
elf_validate_file_header_only_little_endian_supported_msg:
.asciz "ELF: file is not in little endian format"
elf_validate_file_header_not_current_version_msg:
.asciz "ELF: file is not in current ELF version"
elf_validate_file_header_not_executable_msg:
.asciz "ELF: file is not an executable"
elf_read_kernel_to_memory_unsupported_offset_msg:
.asciz "ELF: unsupported offset (only 32 bit offsets supported)"
elf_read_kernel_to_memory_not_loadable_header_msg:
.asciz "ELF: kernel contains non-loadable program header"
.section .bss
elf_file_header:
.skip 64
elf_file_header_phentsize:
.skip 2
elf_file_header_phnum:
.skip 2
elf_file_header_phoff:
.skip 4 # NOTE: only 32 bit offsets are supported
elf_program_header:
.skip 56