path: root/bfc.S

.set SYS_READ,  0
.set SYS_WRITE, 1
.set SYS_OPEN,  2
.set SYS_CLOSE, 3
.set SYS_BRK,   12
.set SYS_EXIT,  60

.set F_CREATE_AND_WRITE, 0x41
.set F_MODE_EXECUTABLE, 0744

.section constants, "a"

c_elf_header:
	.byte 0x7f       # Magic Number
	.ascii "ELF"     #
	.byte 0x2        # 64-Bit
	.byte 0x1        # little-endian
	.byte 0x1        # ELFv1
	.byte 0x0        # System V ABI
	.quad 0x0        #
	.hword 0x02      # Executable
	.hword 0x3e      # AMD x86-64
	.int 0x1         # ELFv1
	.quad 0x4005b0   # Entry
	.quad 0x40       # Program Header Offset
	.quad 0xb0       # TODO: Section Header Offset
	.int 0x0         #
	.hword 0x40      # ELF Header Size
	.hword 0x38      # Program Header Table Entry Size
	.hword 0x2       # TODO: Number Of Entries in Program Header Table
	.hword 0x40      # Section Header Table Entry Size
	.hword 0x3       # TODO: Number Of Entries in Section Header Table
	.hword 0x2       # TODO: Index of Section Header Table Entry containing section names

c_elf_data_program_header:
	.int 0x1         # Loadable
	.int 0x6         # Read Write
	.quad 0x1b0      # Offset in ELF
	.quad 0x3001b0   # Virtual Address
	.quad 0x3001b0   # Physical Address
	.quad 0x400      # Virtual Size
	.quad 0x400      # Size in file
	.quad 0x1000     # Aligning

c_elf_data_section_header:
	.int 0x1         # Index of name in SHSTRTAB
	.int 0x1         # Load as Program data
	.quad 0x3        # Is Writable and Readable
	.quad 0x3001b0   # Virtual Address
	.quad 0x1b0      # Offset in ELF
	.quad 0x400      # Size
	.int 0x0         # Index
	.int 0x0         # Info
	.quad 0x1000     # Aligning
	.quad 0x0

c_elf_shstrtab_section_header:
	.int 0xb         # Index of name in SHSTRTAB
	.int 0x3         # Don't load
	.quad 0x0        # No Attributes
	.quad 0x0        # Not mapped to virtual memory
	.quad 0x170      # Offset in ELF
	.quad 0x40       # Size in ELF
	.int 0x0         # Index
	.int 0x0         # No Inof
	.quad 0x1        # Aligning
	.quad 0x0


c_elf_shstrtab:
	.byte 0
	.asciz "data"
	.asciz "code"
	.asciz "shstrtab"

c_elf_data:
	.fill 0x400, 1, 0

c_usage_message:
	.asciz "bfc [input file] [output file]\n"

.section variables, "aw"

c_elf_code_program_header:
	.int 0x1         # Loadable
	.int 0x5         # Read Executable
	.quad 0x5b0      # Offset in ELF
	.quad 0x4005b0   # Virtual Address
	.quad 0x4005b0   # Physical Address
v_elf_code_program_header_file_size:
	.quad 0x0        # File Size
v_elf_code_program_header_memory_size:
	.quad 0x0        # Memory Size
	.quad 0x1000     # Aligning

c_elf_code_section_header:
	.int 0x6         # Index of name in SHSTRTAB
	.int 0x1         # Load as program data
	.quad 0x6        # Is Readable and Executable
	.quad 0x4005b0   # Virtual Address
	.quad 0x5b0      # Offset in ELF
v_elf_code_section_header_size:
	.quad 0x0
	.int 0x0         # Index
	.int 0x0         # Info
	.quad 0x1000     # Aligning
	.quad 0x0

v_input_fd:
	.int 0x0

v_output_fd:
	.int 0x0

v_buffer_start:
	.quad 0x0

v_buffer_end:
	.quad 0x0

v_buffer_cursor:
	.quad 0x0

v_input_char:
	.byte 0x0


.section code, "ax"
.global _start
_start:
	mov %rsp, %rbp
	call f_check_args
	call f_open_files
	call f_init_buffer

l_read_loop:
	call f_read_next_character
	cmp $0, %rax
	je l_read_loop_end

	mov $v_input_char, %rbx
	mov (%rbx), %rax
	cmp $'<', %rax
	je l_compile_move_left
	cmp $'>', %rax
	je l_compile_move_right
	cmp $'+', %rax
	je l_compile_inc
	cmp $'-', %rax
	je l_compile_dec
	cmp $'[', %rax
	je l_compile_loop_start
	cmp $']', %rax
	je l_compile_loop_end
	cmp $'.', %rax
	je l_compile_write
	cmp $',', %rax
	je l_compile_read
	jmp l_read_loop

l_compile_move_left:
	# TODO: fix buffer overflows
	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rsi
	add $3, %rsi
	call f_check_buffer

	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rax
	movl $0xc0ff48, (%rax)
	add $3, %rax
	mov %rax, (%rbx)

	jmp l_read_loop

l_compile_move_right:
	# TODO: fix buffer overflows
	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rsi
	add $3, %rsi
	call f_check_buffer

	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rax
	movl $0xc8ff48, (%rax)
	add $3, %rax
	mov %rax, (%rbx)
	jmp l_read_loop

l_compile_inc:
	jmp l_read_loop

l_compile_dec:
	jmp l_read_loop

l_compile_loop_start:
	jmp l_read_loop

l_compile_loop_end:
	jmp l_read_loop

l_compile_write:
	jmp l_read_loop

l_compile_read:
	jmp l_read_loop

l_read_loop_end:
	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rax
	movl $0x3cc0c748, (%rax)
	add $7, %rax
	movl $0x050f, (%rax)
	add $2, %rax
	mov %rax, (%rbx)


	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rax
	mov $v_buffer_start, %rbx
	mov (%rbx), %rbx
	sub %rbx, %rax
	mov %rax, %r12
	
	mov $v_elf_code_program_header_file_size, %rbx
	mov %rax, (%rbx)
	mov $v_elf_code_program_header_memory_size, %rbx
	mov %rax, (%rbx)
	mov $v_elf_code_section_header_size, %rbx
	mov %rax, (%rbx)


	mov $c_elf_header, %rsi
	mov $0x40, %rdx
	call f_write_to_output

	mov $c_elf_data_program_header, %rsi
	mov $0x38, %rdx
	call f_write_to_output

	mov $c_elf_code_program_header, %rsi
	mov $0x38, %rdx
	call f_write_to_output

	mov $c_elf_data_section_header, %rsi
	mov $0x40, %rdx
	call f_write_to_output

	mov $c_elf_code_section_header, %rsi
	mov $0x40, %rdx
	call f_write_to_output

	mov $c_elf_shstrtab_section_header, %rsi
	mov $0x40, %rdx
	call f_write_to_output

	mov $c_elf_shstrtab, %rsi
	mov $0x40, %rdx
	call f_write_to_output

	mov $c_elf_data, %rsi
	mov $0x400, %rdx
	call f_write_to_output

	mov $v_buffer_start, %rbx
	mov (%rbx), %rsi
	mov %r12, %rdx
	call f_write_to_output

	call f_close_files
	mov $0, %rdi
	jmp f_exit


f_exit:
	mov $SYS_EXIT, %rax
	syscall

/* rsi = buffer, %rdx = len */
f_write_to_output:
	mov $SYS_WRITE, %rax
	mov $v_output_fd, %rbx
	mov (%rbx), %rdi
	syscall


f_check_args:
	mov (%rbp), %rax
	cmp $3, %rax
	je l_check_args_success

	mov $SYS_WRITE, %rax
	mov $2, %rdi
	mov $c_usage_message, %rsi
	mov $32, %rdx
	syscall

	mov $-1, %rdi
	jmp f_exit

l_check_args_success:
	ret


f_open_files:
	mov $SYS_OPEN, %rax
	mov 16(%rbp), %rdi
	mov $0, %rsi
	mov $0, %rdx
	syscall
	mov $v_input_fd, %rbx
	mov %eax, (%rbx)

	mov $SYS_OPEN, %rax
	mov 24(%rbp), %rdi
	mov $F_CREATE_AND_WRITE, %rsi
	mov $F_MODE_EXECUTABLE, %rdx
	syscall
	mov $v_output_fd, %rbx
	mov %eax, (%rbx)
	ret


f_close_files:
	mov $SYS_CLOSE, %rax
	mov %rbx, %rsi
	syscall

	mov $SYS_CLOSE, %rax
	mov %rcx, %rsi
	syscall
	ret


f_init_buffer:
	mov $SYS_BRK, %rax
	mov $0, %rdi
	syscall
	mov $v_buffer_start, %rbx
	mov %rax, (%rbx)
	mov $v_buffer_end, %rbx
	mov %rax, (%rbx)
	mov $v_buffer_cursor, %rbx
	mov %rax, (%rbx)
	/*
	 * We directly skip to f_resize_buffer
	 * since we want to resize it to a usable amount
	 */
f_resize_buffer:
	mov $SYS_BRK, %rax
	mov $v_buffer_end, %rbx
	mov (%rbx), %rdi
	add $0x400, %rdi
	syscall
	mov %rax, (%rbx)
	ret

/* %rsi = needed end */
f_check_buffer:
	mov $v_buffer_end, %rbx
	mov (%rbx), %rax
	cmp %rax, %rsi
	jl l_check_buffer_large_enough
	call f_resize_buffer
l_check_buffer_large_enough:
	ret


f_read_next_character:
	mov $SYS_READ, %rax
	mov $v_input_fd, %rbx
	mov (%rbx), %rdi
	mov $v_input_char, %rsi
	mov $1, %rdx
	syscall
	ret