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 translations, "a"

t_init:
	mov $SYS_BRK, %rax
	mov $0x0, %rdi
	syscall
	add $0x400, %rax
	mov %rax, %rbx
	mov %rax, %rdi
	mov $SYS_BRK, %rax
	syscall
t_init_end:

t_exit:
	mov $60, %rax
	syscall
t_exit_end:

t_move_head_right:
	inc %rbx
t_move_head_right_end:

t_move_head_left:
	dec %rbx
t_move_head_left_end:

t_increase_cell:
	incb (%rbx)
t_increase_cell_end:

t_decrease_cell:
	decb (%rbx)
t_decrease_cell_end:

t_write_cell:
	mov $1, %rax
	mov $1, %rdi
	mov %rbx, %rsi
	mov $1, %rdx
	syscall
t_write_cell_end:

t_read_cell:
	mov $0, %rax
	mov $0, %rdi
	mov %rbx, %rsi
	mov $1, %rdx
	syscall
t_read_cell_end:

t_check_zero:
	mov (%rbx), %rax
	cmp $0, %rax
	.byte 0xf, 0x84  # `je` instruction
	.int 0x0         # relative offset
t_check_zero_end:

t_jump_back:
	.byte 0xe9 # `jmp` instruction
	.int 0x0         # absolute offset
t_jump_back_end:

.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 0x2      # Executable
	.hword 0x3e      # AMD x86-64
	.int 0x1         # ELFv1
	.quad 0x400148   # Entry
	.quad 0x40       # Program Header Offset
	.quad 0x78       # TODO: Section Header Offset
	.int 0x0         #
	.hword 0x40      # ELF Header Size
	.hword 0x38      # Program Header Table Entry Size
	.hword 0x1       # 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_null_section_header:
	.fill 0x40, 1, 0

c_elf_shstrtab_section_header:
	.int 0x6         # Index of name in SHSTRTAB
	.int 0x3         # Don't load
	.quad 0x0        # No Attributes
	.quad 0x0        # Not mapped to virtual memory
	.quad 0x138      # Offset in ELF
	.quad 0xf        # Size in ELF
	.int 0x0         # Index
	.int 0x0         # No Info
	.quad 0x1        # Aligning
	.quad 0x0


c_elf_shstrtab:
	.byte 0
	.asciz "code"
	.asciz "shstrtab"
	.byte 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 0x148      # Offset in ELF
	.quad 0x400148   # Virtual Address
	.quad 0x400148   # 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 0x1         # Index of name in SHSTRTAB
	.int 0x1         # Load as program data
	.quad 0x6        # Is Readable and Executable
	.quad 0x400148   # Virtual Address
	.quad 0x148      # 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

	mov $t_init, %rdi
	mov $t_init_end, %rsi
	call f_write_to_buffer

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

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

l_compile_move_left:
	mov $t_move_head_left, %rdi
	mov $t_move_head_left_end, %rsi
	call f_write_to_buffer
	jmp l_read_loop
l_compile_move_right:
	mov $t_move_head_right, %rdi
	mov $t_move_head_right_end, %rsi
	call f_write_to_buffer
	jmp l_read_loop
l_compile_inc:
	mov $t_increase_cell, %rdi
	mov $t_increase_cell_end, %rsi
	call f_write_to_buffer
	jmp l_read_loop
l_compile_dec:
	mov $t_decrease_cell, %rdi
	mov $t_decrease_cell_end, %rsi
	call f_write_to_buffer
	jmp l_read_loop
l_compile_loop_start:
	mov $v_buffer_cursor, %rbx
	push (%rbx)

	mov $t_check_zero, %rdi
	mov $t_check_zero_end, %rsi
	call f_write_to_buffer
	jmp l_read_loop
l_compile_loop_end:
	pop %r15

	mov $t_jump_back, %rdi
	mov $t_jump_back_end, %rsi
	call f_write_to_buffer

	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rax

	mov %r15, %rbx
	sub %rax, %r15
	mov %r15d, -4(%rax)
	neg %r15
	sub $13, %r15
	mov %r15d, 9(%rbx)

	jmp l_read_loop
l_compile_write:
	mov $t_write_cell, %rdi
	mov $t_write_cell_end, %rsi
	call f_write_to_buffer
	jmp l_read_loop
l_compile_read:
	mov $t_read_cell, %rdi
	mov $t_read_cell_end, %rsi
	call f_write_to_buffer
	jmp l_read_loop
l_read_loop_end:
	mov $t_exit, %rdi
	mov $t_exit_end, %rsi
	call f_write_to_buffer


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

	mov $c_elf_null_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 $0x10, %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
	ret


/* rdi = buffer, %rsi = buffer end */
f_write_to_buffer:
	sub %rdi, %rsi
	mov %rsi, %r12
	mov %rdi, %r13
	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rax
	add %rax, %rsi
	call f_check_buffer

	mov $v_buffer_cursor, %rbx
	mov (%rbx), %rax

l_write_loop_start:
	cmp $0, %r12
	je l_write_loop_end

	mov (%r13), %sil
	mov %sil, (%rax)

	inc %r13
	inc %rax
	dec %r12
	jmp l_write_loop_start
l_write_loop_end:
	mov %rax, (%rbx)
	ret


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)

	mov %eax, %edi
	mov $0, %rsi
	mov $77, %rax
	syscall

	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)
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