From 536443b020d01d0d5372496529086a11b2486621 Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Mon, 21 Apr 2025 22:56:50 +0200
Subject: [PATCH] Add stages and a rakefile

---
 Rakefile           |  41 ++
 boot/asm-boot.s    | 894 +++++++++++++++++++++++++++++++++++++++++++-
 boot/common-boot.s | 906 +--------------------------------------------
 boot/echo-boot.s   |  35 ++
 boot/stage2.elna   |  32 ++
 5 files changed, 1011 insertions(+), 897 deletions(-)
 create mode 100644 Rakefile
 create mode 100644 boot/echo-boot.s
 create mode 100644 boot/stage2.elna

diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..368abfa
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,41 @@
+require 'open3'
+require 'rake/clean'
+
+CLOBBER.include 'build'
+
+CROSS_GCC = '../riscv32-ilp32d--glibc/bin/riscv32-linux-gcc'
+SYSROOT = '../riscv32-ilp32d--glibc/riscv32-buildroot-linux-gnu/sysroot'
+QEMU = 'qemu-riscv32'
+
+desc 'Final stage'
+task default: 'build/stage2'
+
+directory 'build'
+
+desc 'Initial stage'
+file 'build/stage1' => ['boot/echo-boot.s', 'boot/common-boot.s', 'build'] do |t|
+  assembler = t.prerequisites.filter { |prerequisite| prerequisite.end_with? '.s' }
+
+  sh CROSS_GCC, '-nostdlib', '-o', t.name, *assembler
+end
+
+file 'build/stage2.s' => ['build/stage1', 'boot/stage2.elna'] do |t|
+  assembler, exe = t.prerequisites.partition { |prerequisite| prerequisite.end_with? '.elna' }
+  arguments = [QEMU, '-L', SYSROOT, *exe]
+
+  puts(arguments * ' ')
+  puts
+  Open3.popen2(*arguments) do |qemu_in, qemu_out|
+    qemu_in.write File.read(*assembler)
+    qemu_in.close
+
+    File.open t.name, 'w' do |output|
+      IO.copy_stream qemu_out, output
+    end
+    qemu_out.close
+  end
+end
+
+file 'build/stage2' => ['build/stage2.s', 'boot/common-boot.s'] do |t|
+  sh CROSS_GCC, '-nostdlib', '-o', t.name, *t.prerequisites
+end
diff --git a/boot/asm-boot.s b/boot/asm-boot.s
index 594c624..80167a2 100644
--- a/boot/asm-boot.s
+++ b/boot/asm-boot.s
@@ -1,18 +1,897 @@
 # s1 - Contains the current position in the source text.
 
-.data
+.global _start # Program entry point.
+
+.section .rodata
 
-.equ SYS_EXIT, 93
 .equ SOURCE_BUFFER_SIZE, 2048
 
-.bss
+asm_begin: .ascii ".text\n.global _start\n_start:\naddi sp, sp, -64\nsw ra, 60(sp)\nsw s0, 56(sp)\naddi s0, sp, 64\n"
+.equ ASM_BEGIN_SIZE, . - asm_begin
+asm_end: .ascii "addi a0, zero, 0\naddi a7, zero, 93\necall\nlw ra, 60(sp)\nlw s0, 56(sp)\naddi sp, sp, 64\nret\n"
+.equ ASM_END_SIZE, . - asm_end
+asm_program: .ascii ".bss\n"
+.equ ASM_PROGRAM_SIZE, . - asm_program
+asm_type: .ascii ".type "
+.equ ASM_TYPE_SIZE, . - asm_type
+asm_object: .ascii ", @object\n"
+.equ ASM_OBJECT_SIZE, . - asm_object
+asm_size: .ascii ".size "
+.equ ASM_SIZE_SIZE, . - asm_size
+asm_zero: .ascii ".zero "
+.equ ASM_ZERO_SIZE, . - asm_zero
+asm_global: .ascii ".global "
+.equ ASM_GLOBAL_SIZE, . - asm_global
+
+token_begin: .string "begin"
+token_end: .string "end"
+token_import: .string "import"
+token_open_paren: .string "("
+token_close_paren: .string ")"
+token_open_square: .string "["
+token_assign: .string ":="
+token_var: .string "var"
+token_comma: .string ","
+
+space: .ascii " "
+comma: .ascii ","
+new_line: .ascii "\n"
+colon: .ascii ":"
+digit_zero: .ascii "0"
+
+instruction_la: .ascii "la"
+instruction_call: .ascii "call"
+instruction_addi: .ascii "addi"
+instruction_li: .ascii "li"
+instruction_sw: .ascii "sw"
+instruction_lw: .ascii "lw"
+
+register_a0: .ascii "a0"
+register_sp: .ascii "sp"
+register_a: .ascii "a"
+
+.section .bss
 .global source_code
 .type source_code, @object
 .size source_code, SOURCE_BUFFER_SIZE
 source_code: .zero SOURCE_BUFFER_SIZE
 
-.text
-.global _start # Program entry point.
+.section .text
+
+.type _skip_spaces, @function
+_skip_spaces:
+.Lspace_loop_do:
+	lbu t0, (s1) # t0 = Current character.
+
+	li t1, ' '
+	beq t0, t1, .Lspace_loop_repeat
+	li t1, '\t'
+	beq t0, t1, .Lspace_loop_repeat
+	li t1, '\n'
+	beq t0, t1, .Lspace_loop_repeat
+	li t1, '\r'
+	beq t0, t1, .Lspace_loop_repeat
+
+	j .Lspace_loop_end
+.Lspace_loop_repeat:
+	addi s1, s1, 1
+	j .Lspace_loop_do
+
+.Lspace_loop_end:
+	ret
+
+# Compares two string, which of one has a length, the other one is null-terminated.
+#
+# a0 - The address of the token string.
+# a1 - The length of the string in a0.
+# a2 - The address of the null-terminated string.
+#
+# If the strings match sets a0 to 0, otherwise sets it to 1.
+.type _token_compare, @function
+_token_compare:
+	addi t0, a0, 0
+	addi t1, a1, 0
+	addi t2, a2, 0
+
+.Ltoken_compare_loop:
+	lbu t3, (t2)
+
+	# Will only be 0 if the current character in the null terminated string is \0 and the remaining length of the
+	# another string is 0.
+	or t4, t3, t1
+	beqz t4, .Ltoken_compare_equal
+
+	beqz t1, .Ltoken_compare_not_equal
+	beqz t3, .Ltoken_compare_not_equal
+
+	lbu t4, (t0)
+	bne t3, t4, .Ltoken_compare_not_equal
+
+	addi t0, t0, 1
+	addi t1, t1, -1
+	addi t2, t2, 1
+	j .Ltoken_compare_loop
+
+.Ltoken_compare_not_equal:
+	li a0, 1
+	j .Ltoken_compare_end
+
+.Ltoken_compare_equal:
+	li a0, 0
+
+.Ltoken_compare_end:
+	ret
+
+# Reads a token and returns its length in a0.
+# _read_token doesn't change s1, it finds the length of the token s1 is pointing to.
+.type _read_token, @function
+_read_token:
+	# Prologue.
+	addi sp, sp, -16
+	sw ra, 12(sp)
+	sw s0, 8(sp)
+	addi s0, sp, 16
+
+	lbu t0, (s1) # t0 = Current character.
+	sw zero, 4(sp)
+
+	li t1, '.'
+	beq t0, t1, .Ltoken_character_single
+
+	li t1, ','
+	beq t0, t1, .Ltoken_character_single
+
+	li t1, ':'
+	beq t0, t1, .Ltoken_character_colon
+
+	li t1, ';'
+	beq t0, t1, .Ltoken_character_single
+
+	li t1, '('
+	beq t0, t1, .Ltoken_character_single
+
+	li t1, ')'
+	beq t0, t1, .Ltoken_character_single
+
+	li t1, '['
+	beq t0, t1, .Ltoken_character_single
+
+	li t1, ']'
+	beq t0, t1, .Ltoken_character_single
+
+.Ltoken_character_loop_do: # Expect an identifier or a number.
+	lw t6, 4(sp)
+	add t1, s1, t6
+	lbu a0, (t1) # a0 = Current character.
+
+	call is_alnum
+
+	beqz a0, .Ltoken_character_end
+	lw t6, 4(sp)
+	addi t6, t6, 1
+	sw t6, 4(sp)
+	j .Ltoken_character_loop_do
+
+.Ltoken_character_single:
+	lw t6, 4(sp)
+	addi t6, t6, 1
+	sw t6, 4(sp)
+	j .Ltoken_character_end
+
+.Ltoken_character_colon:
+	lbu t0, 1(s1) # t0 = The character after the colon.
+	lw t6, 4(sp)
+	addi t6, t6, 1
+	sw t6, 4(sp)
+
+	li t1, '='
+	beq t0, t1, .Ltoken_character_single
+	j .Ltoken_character_end
+
+.Ltoken_character_end:
+	lw a0, 4(sp)
+
+	# Epilogue.
+	lw ra, 12(sp)
+	lw s0, 8(sp)
+	addi sp, sp, 16
+	ret
+
+# Generate entry point symbol.
+.type _compile_begin, @function
+_compile_begin:
+	# Prologue.
+	addi sp, sp, -8
+	sw ra, 4(sp)
+	sw s0, 0(sp)
+	addi s0, sp, 8
+
+	# Write initial assembler.
+	la a0, asm_begin
+	addi a1, zero, ASM_BEGIN_SIZE
+	call write_out
+
+	addi s1, s1, 5
+
+	# Epilogue.
+	lw ra, 4(sp)
+	lw s0, 0(sp)
+	addi sp, sp, 8
+	ret
+
+# Generate program termination code.
+.type _compile_end, @function
+_compile_end:
+	# Prologue.
+	addi sp, sp, -8
+	sw ra, 4(sp)
+	sw s0, 0(sp)
+	addi s0, sp, 8
+
+	# Write closing assembler.
+	la a0, asm_end
+	addi a1, zero, ASM_END_SIZE
+	call write_out
+
+	addi s1, s1, 3
+
+	# Epilogue.
+	lw ra, 4(sp)
+	lw s0, 0(sp)
+	addi sp, sp, 8
+	ret
+
+# Ignores the import.
+.type _compile_import, @function
+_compile_import:
+	# Prologue.
+	addi sp, sp, -8
+	sw ra, 4(sp)
+	sw s0, 0(sp)
+	addi s0, sp, 8
+
+	addi s1, s1, 6
+	call _skip_spaces
+	call _read_token
+	add s1, s1, a0 # Skip the imported module name.
+
+	# Epilogue.
+	lw ra, 4(sp)
+	lw s0, 0(sp)
+	addi sp, sp, 8
+	ret
+
+# Compiles a procedure call. Expects s1 to point to the first argument.
+# a0 - Pointer to the procedure name.
+# a1 - Length of the procedure name.
+#
+# Returns the procedure result in a0.
+.type _compile_call, @function
+_compile_call:
+	# Prologue.
+	addi sp, sp, -32
+	sw ra, 28(sp)
+	sw s0, 24(sp)
+	addi s0, sp, 32
+
+	sw a0, 20(sp)
+	sw a1, 16(sp)
+	sw zero, 12(sp) # Argument count for a procedure call.
+
+.Lcompile_call_paren:
+	call _skip_spaces
+	call _read_token
+	addi a1, a0, 0
+	addi a0, s1, 0
+	la a2, token_close_paren
+	call _token_compare
+	beqz a0, .Lcompile_call_complete
+
+.Lcompile_call_argument:
+	call _build_expression
+
+	la a0, instruction_sw
+	li a1, 2
+	call write_out
+
+	la a0, space
+	li a1, 1
+	call write_out
+
+	la a0, register_a0
+	li a1, 2
+	call write_out
+
+	la a0, comma
+	li a1, 1
+	call write_out
+
+	lw t0, 12(sp) # Argument count for a procedure call.
+
+	# Only 8 arguments are supported with a0-a7.
+	# Save all arguments on the stack so they aren't overriden afterwards.
+	# The offset on the stack always has two digits in this case.
+	li t1, -4
+	mul t1, t0, t1
+	addi t1, t1, 52
+	li t2, 10
+	div t3, t1, t2
+	rem t4, t1, t2
+	addi t3, t3, '0'
+	addi t4, t4, '0'
+
+	sw t3, 8(sp)
+	sw t4, 4(sp)
+
+	addi a0, sp, 8
+	li a1, 1
+	call write_out
+
+	addi a0, sp, 4
+	li a1, 1
+	call write_out
+
+	la a0, token_open_paren
+	li a1, 1
+	call write_out
+
+	la a0, register_sp
+	li a1, 2
+	call write_out
+
+	la a0, token_close_paren
+	li a1, 1
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	call _skip_spaces
+	call _read_token
+	addi a1, a0, 0
+	addi a0, s1, 0
+	la a2, token_comma
+	call  _token_compare
+
+	/* DEBUG. Write the current token to stderr.
+	addi a0, zero, STDERR
+	addi a1, s1, 0
+	li a2, 4 #(sp)
+	addi a7, zero, SYS_WRITE
+	ecall
+	addi a0, zero, STDERR
+	la a1, token_open_square
+	li a2, 1
+	addi a7, zero, SYS_WRITE
+	ecall
+	DEBUG. End */
+
+	bnez a0, .Lcompile_call_paren
+
+	lw t0, 12(sp) # Argument count for a procedure call.
+	addi t0, t0, 1
+	sw t0, 12(sp)
+
+	addi s1, s1, 1 # Skip the comma between the arguments.
+	j .Lcompile_call_argument
+
+.Lcompile_call_complete:
+	sw zero, 12(sp)
+
+.Lcompile_call_restore:
+	# Just go through all a0-a7 registers and read them from stack.
+	# If this stack value contains garbage, the procedure just shouldn't use it.
+	lw t0, 12(sp)
+	li t1, 7
+	bgt t0, t1, .Lcompile_call_perform
+
+	la a0, instruction_lw
+	li a1, 2
+	call write_out
+
+	la a0, space
+	li a1, 1
+	call write_out
+
+	la a0, register_a
+	li a1, 1
+	call write_out
+
+	lw t0, 12(sp)
+	addi t0, t0, '0'
+	sw t0, 8(sp)
+
+	addi a0, sp, 8
+	li a1, 1
+	call write_out
+
+	la a0, comma
+	li a1, 1
+	call write_out
+
+	lw t0, 12(sp) # Argument count for a procedure call.
+
+	li t1, -4
+	mul t1, t0, t1
+	addi t1, t1, 52
+	li t2, 10
+	div t3, t1, t2
+	rem t4, t1, t2
+	addi t3, t3, '0'
+	addi t4, t4, '0'
+
+	sw t3, 8(sp)
+	sw t4, 4(sp)
+
+	addi a0, sp, 8
+	li a1, 1
+	call write_out
+
+	addi a0, sp, 4
+	li a1, 1
+	call write_out
+
+	la a0, token_open_paren
+	li a1, 1
+	call write_out
+
+	la a0, register_sp
+	li a1, 2
+	call write_out
+
+	la a0, token_close_paren
+	li a1, 1
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	lw t0, 12(sp) # Increment.
+	addi t0, t0, 1
+	sw t0, 12(sp)
+
+	j .Lcompile_call_restore
+
+.Lcompile_call_perform:
+	la a0, instruction_call
+	li a1, 4
+	call write_out
+
+	la a0, space
+	li a1, 1
+	call write_out
+
+	lw a0, 20(sp)
+	lw a1, 16(sp)
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	call _skip_spaces
+	addi s1, s1, 1 # Skip the close paren.
+
+	# Epilogue.
+	lw ra, 28(sp)
+	lw s0, 24(sp)
+	addi sp, sp, 32
+	ret
+
+.type _compile, @function
+compile:
+	# Prologue.
+	addi sp, sp, -16
+	sw ra, 12(sp)
+	sw s0, 8(sp)
+	addi s0, sp, 16
+
+	# Write .bss section header for global variables.
+	la a0, asm_program
+	addi a1, zero, ASM_PROGRAM_SIZE
+	call write_out
+
+	call _skip_spaces
+	addi s1, s1, 7 # Skip "program" keyword.
+
+.Lcharacter_loop_do:
+	call _skip_spaces
+
+	lbu t0, (s1) # t0 = Current character.
+	beqz t0, .Lcharacter_loop_end
+
+	call _read_token
+	sw a0, 4(sp) # Save the token length on the stack.
+	beqz a0, .Lcharacter_loop_end # No token read, there is unrecognized input.
+
+	lw a0, 4(sp)
+	call _handle_token
+
+	j .Lcharacter_loop_do
+.Lcharacter_loop_end:
+
+	# Epilogue.
+	lw ra, 12(sp)
+	lw s0, 8(sp)
+	addi sp, sp, 16
+	ret
+
+# Evalutes an expression and saves the result in a0.
+.type _build_expression, @function
+_build_expression:
+	# Prologue.
+	addi sp, sp, -16
+	sw ra, 12(sp)
+	sw s0, 8(sp)
+	addi s0, sp, 16
+
+	call _skip_spaces
+	call _read_token
+	sw s1, 4(sp)
+	sw a0, 0(sp)
+
+	# Integer literal.
+	addi a0, s1, 0
+	lb a0, (a0)
+	call is_digit
+	bnez a0, .Lbuild_expression_number_literal
+
+	# Named identifier.
+	la a0, instruction_la
+	li a1, 2
+	call write_out
+
+	la a0, space
+	li a1, 1
+	call write_out
+
+	la a0, register_a0
+	li a1, 2
+	call write_out
+
+	la a0, comma
+	li a1, 1
+	call write_out
+
+	lw a0, 4(sp)
+	lw a1, 0(sp)
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	j .Lbuild_expression_end
+
+.Lbuild_expression_number_literal:
+	la a0, instruction_li
+	li a1, 2
+	call write_out
+
+	la a0, space
+	li a1, 1
+	call write_out
+
+	la a0, register_a0
+	li a1, 2
+	call write_out
+
+	la a0, comma
+	li a1, 1
+	call write_out
+
+	lw a0, 4(sp)
+	lw a1, 0(sp)
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	j .Lbuild_expression_end
+
+.Lbuild_expression_end:
+	lw a0, 0(sp)
+	add s1, s1, a0
+
+	# Epilogue.
+	lw ra, 12(sp)
+	lw s0, 8(sp)
+	addi sp, sp, 16
+	ret
+
+# Compiles a statement beginning with an identifier.
+.type _compile_identifier, @function
+_compile_identifier:
+	# Prologue.
+	addi sp, sp, -32
+	sw ra, 28(sp)
+	sw s0, 24(sp)
+	addi s0, sp, 32
+
+	# Save the pointer to the identifier and its length on the stack.
+	sw a0, 20(sp)
+	sw a1, 16(sp)
+
+	add s1, s1, a1
+	call _skip_spaces
+	call _read_token
+
+	# Save the pointer and the length of the token following the identifier.
+	sw s1, 12(sp)
+	sw a0, 8(sp)
+
+	add s1, s1, a0 # Skip that token.
+	call _skip_spaces
+
+	lw a0, 12(sp)
+	lw a1, 8(sp)
+	la a2, token_assign
+	call _token_compare
+	beqz a0, .Lcompile_identifier_assign
+
+	lw a0, 12(sp)
+	lw a1, 8(sp)
+	la a2, token_open_paren
+	call _token_compare
+	beqz a0, .Lcompile_identifier_call
+
+	j .Lcompile_identifier_end
+
+.Lcompile_identifier_call:
+	lw a0, 20(sp)
+	lw a1, 16(sp)
+	call _compile_call
+
+	j .Lcompile_identifier_end
+
+.Lcompile_identifier_assign:
+	call _build_expression
+
+	la a0, instruction_addi
+	li a1, 4
+	call write_out
+
+	la a0, space
+	li a1, 1
+	call write_out
+
+	lw a0, 20(sp)
+	lw a1, 16(sp)
+	call write_out
+
+	la a0, comma
+	li a1, 1
+	call write_out
+
+	la a0, register_a0
+	li a1, 2
+	call write_out
+
+	la a0, comma
+	li a1, 1
+	call write_out
+
+	la a0, digit_zero
+	li a1, 1
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	j .Lcompile_identifier_end
+
+.Lcompile_identifier_end:
+	# Epilogue.
+	lw ra, 28(sp)
+	lw s0, 24(sp)
+	addi sp, sp, 32
+	ret
+
+.type _compile_var, @function
+_compile_var:
+	# Prologue.
+	addi sp, sp, -32
+	sw ra, 28(sp)
+	sw s0, 24(sp)
+	addi s0, sp, 32
+
+	# Variable name.
+	addi s1, s1, 3
+	call _skip_spaces
+	call _read_token
+	sw s1, 20(sp)
+	sw a0, 16(sp)
+	add s1, s1, a0
+
+	# Skip the colon.
+	call _skip_spaces
+	call _read_token
+	add s1, s1, a0
+
+	call _skip_spaces
+	call _read_token
+	sw a0, 12(sp)
+
+	addi a0, s1, 0
+	lw a1, 12(sp)
+	la a2, token_open_square
+	call _token_compare
+	beqz a0, .Lcompile_var_array
+
+	j .Lcompile_var_end
+
+.Lcompile_var_array:
+	call _skip_spaces
+	add s1, s1, 1 # Skip the opening square bracket.
+
+	call _skip_spaces
+	call _read_token
+	sw a0, 8(sp)
+
+	la a0, asm_type
+	li a1, ASM_TYPE_SIZE
+	call write_out
+
+	lw a0, 20(sp)
+	lw a1, 16(sp)
+	call write_out
+
+	la a0, asm_object
+	li a1, ASM_OBJECT_SIZE
+	call write_out
+
+	la a0, asm_size
+	li a1, ASM_SIZE_SIZE
+	call write_out
+
+	lw a0, 20(sp)
+	lw a1, 16(sp)
+	call write_out
+
+	la a0, comma
+	li a1, 1
+	call write_out
+
+	addi a0, s1, 0
+	lw a1, 8(sp)
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	lw a0, 20(sp)
+	lw a1, 16(sp)
+	call write_out
+
+	la a0, colon
+	li a1, 1
+	call write_out
+
+	la a0, asm_zero
+	li a1, ASM_ZERO_SIZE
+	call write_out
+
+	addi a0, s1, 0
+	lw a1, 8(sp)
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	la a0, asm_global
+	li a1, ASM_GLOBAL_SIZE
+	call write_out
+
+	lw a0, 20(sp)
+	lw a1, 16(sp)
+	call write_out
+
+	la a0, new_line
+	li a1, 1
+	call write_out
+
+	lw a0, 8(sp)
+	add s1, s1, a0
+
+	call _skip_spaces
+	add s1, s1, 1 # Skip the closing square bracket.
+
+	call _skip_spaces
+	call _read_token
+
+	sw a0, 12(sp)
+	j .Lcompile_var_end
+
+.Lcompile_var_end:
+	lw a0, 12(sp)
+	add s1, s1, a0
+
+	# Epilogue.
+	lw ra, 28(sp)
+	lw s0, 24(sp)
+	addi sp, sp, 32
+	ret
+
+.type _handle_token, @function
+_handle_token:
+	# Prologue.
+	addi sp, sp, -32
+	sw ra, 28(sp)
+	sw s0, 24(sp)
+	addi s0, sp, 32
+
+	sw a0, 20(sp)
+
+	# Detect what token has been read.
+	addi a0, s1, 0
+	lw a1, 20(sp)
+	la a2, token_begin
+	call _token_compare
+	beqz a0, .Lhandle_token_begin
+
+	addi a0, s1, 0
+	lw a1, 20(sp)
+	la a2, token_end
+	call _token_compare
+	beqz a0, .Lhandle_token_end
+
+	addi a0, s1, 0
+	lw a1, 20(sp)
+	la a2, token_import
+	call _token_compare
+	beqz a0, .Lhandle_token_import
+
+	addi a0, s1, 0
+	lw a1, 20(sp)
+	la a2, token_var
+	call _token_compare
+	beqz a0, .Lhandle_token_var
+
+	# If the first symbol in the token is a character, assume an identifier.
+	addi a0, s1, 0
+	lb a0, (a0)
+	call is_alpha
+	bnez a0, .Lhandle_token_identifier
+
+	# Ignore the unknown token.
+	lw t0, 20(sp)
+	add s1, s1, t0
+	j .Lhandle_token_return
+
+.Lhandle_token_begin:
+	call _compile_begin
+	j .Lhandle_token_return
+
+.Lhandle_token_end:
+	call _compile_end
+	j .Lhandle_token_return
+
+.Lhandle_token_import:
+	call _compile_import
+	j .Lhandle_token_return
+
+.Lhandle_token_var:
+	call _compile_var
+	j .Lhandle_token_return
+
+.Lhandle_token_identifier:
+	addi a0, s1, 0
+	lw a1, 20(sp)
+	call _compile_identifier
+	j .Lhandle_token_return
+
+.Lhandle_token_return:
+	# Epilogue.
+	lw ra, 28(sp)
+	lw s0, 24(sp)
+	addi sp, sp, 32
+	ret
 
 _start:
 	# Read the source from the standard input.
@@ -24,6 +903,5 @@ _start:
 	call compile
 
 	# Call exit.
-	addi a0, zero, 0   # Use 0 return code.
-	addi a7, zero, SYS_EXIT
-	ecall
+	li a0, 0   # Use 0 return code.
+	call exit
diff --git a/boot/common-boot.s b/boot/common-boot.s
index 1ad60a4..bfd1dbb 100644
--- a/boot/common-boot.s
+++ b/boot/common-boot.s
@@ -1,57 +1,15 @@
-.data
+.global is_alpha, is_digit, is_alnum, write_out, read_file, exit
+
+.section .rodata
 
 .equ SYS_READ, 63
 .equ SYS_WRITE, 64
+.equ SYS_EXIT, 93
 .equ STDIN, 0
 .equ STDOUT, 1
 .equ STDERR, 2
 
-token_begin: .string "begin"
-token_end: .string "end"
-token_import: .string "import"
-token_open_paren: .string "("
-token_close_paren: .string ")"
-token_open_square: .string "["
-token_assign: .string ":="
-token_var: .string "var"
-token_comma: .string ","
-
-space: .ascii " "
-comma: .ascii ","
-new_line: .ascii "\n"
-colon: .ascii ":"
-digit_zero: .ascii "0"
-
-instruction_la: .ascii "la"
-instruction_call: .ascii "call"
-instruction_addi: .ascii "addi"
-instruction_li: .ascii "li"
-instruction_sw: .ascii "sw"
-instruction_lw: .ascii "lw"
-
-register_a0: .ascii "a0"
-register_sp: .ascii "sp"
-register_a: .ascii "a"
-
-asm_program: .ascii ".bss\n"
-.equ ASM_PROGRAM_SIZE, . - asm_program
-asm_begin: .ascii ".text\n.global _start\n_start:\naddi sp, sp, -64\nsw ra, 60(sp)\nsw s0, 56(sp)\naddi s0, sp, 64\n"
-.equ ASM_BEGIN_SIZE, . - asm_begin
-asm_end: .ascii "addi a0, zero, 0\naddi a7, zero, 93\necall\nlw ra, 60(sp)\nlw s0, 56(sp)\naddi sp, sp, 64\nret\n"
-.equ ASM_END_SIZE, . - asm_end
-asm_type: .ascii ".type "
-.equ ASM_TYPE_SIZE, . - asm_type
-asm_object: .ascii ", @object\n"
-.equ ASM_OBJECT_SIZE, . - asm_object
-asm_size: .ascii ".size "
-.equ ASM_SIZE_SIZE, . - asm_size
-asm_zero: .ascii ".zero "
-.equ ASM_ZERO_SIZE, . - asm_zero
-asm_global: .ascii ".global "
-.equ ASM_GLOBAL_SIZE, . - asm_global
-
-.text
-.global is_alpha, is_digit, is_alnum, compile, write_out, read_file
+.section .text
 
 # Detects if the passed character is a 7-bit alpha character or an underscore.
 # The character is passed in a0.
@@ -113,803 +71,6 @@ is_alnum:
 	addi sp, sp, 16
 	ret
 
-.type _skip_spaces, @function
-_skip_spaces:
-.Lspace_loop_do:
-	lbu t0, (s1) # t0 = Current character.
-
-	li t1, ' '
-	beq t0, t1, .Lspace_loop_repeat
-	li t1, '\t'
-	beq t0, t1, .Lspace_loop_repeat
-	li t1, '\n'
-	beq t0, t1, .Lspace_loop_repeat
-	li t1, '\r'
-	beq t0, t1, .Lspace_loop_repeat
-
-	j .Lspace_loop_end
-.Lspace_loop_repeat:
-	addi s1, s1, 1
-	j .Lspace_loop_do
-
-.Lspace_loop_end:
-	ret
-
-# Compares two string, which of one has a length, the other one is null-terminated.
-#
-# a0 - The address of the token string.
-# a1 - The length of the string in a0.
-# a2 - The address of the null-terminated string.
-#
-# If the strings match sets a0 to 0, otherwise sets it to 1.
-.type _token_compare, @function
-_token_compare:
-	addi t0, a0, 0
-	addi t1, a1, 0
-	addi t2, a2, 0
-
-.Ltoken_compare_loop:
-	lbu t3, (t2)
-
-	# Will only be 0 if the current character in the null terminated string is \0 and the remaining length of the
-	# another string is 0.
-	or t4, t3, t1
-	beqz t4, .Ltoken_compare_equal
-
-	beqz t1, .Ltoken_compare_not_equal
-	beqz t3, .Ltoken_compare_not_equal
-
-	lbu t4, (t0)
-	bne t3, t4, .Ltoken_compare_not_equal
-
-	addi t0, t0, 1
-	addi t1, t1, -1
-	addi t2, t2, 1
-	j .Ltoken_compare_loop
-
-.Ltoken_compare_not_equal:
-	li a0, 1
-	j .Ltoken_compare_end
-
-.Ltoken_compare_equal:
-	li a0, 0
-
-.Ltoken_compare_end:
-	ret
-
-# Reads a token and returns its length in a0.
-# _read_token doesn't change s1, it finds the length of the token s1 is pointing to.
-.type _read_token, @function
-_read_token:
-	# Prologue.
-	addi sp, sp, -16
-	sw ra, 12(sp)
-	sw s0, 8(sp)
-	addi s0, sp, 16
-
-	lbu t0, (s1) # t0 = Current character.
-	sw zero, 4(sp)
-
-	li t1, '.'
-	beq t0, t1, .Ltoken_character_single
-
-	li t1, ','
-	beq t0, t1, .Ltoken_character_single
-
-	li t1, ':'
-	beq t0, t1, .Ltoken_character_colon
-
-	li t1, ';'
-	beq t0, t1, .Ltoken_character_single
-
-	li t1, '('
-	beq t0, t1, .Ltoken_character_single
-
-	li t1, ')'
-	beq t0, t1, .Ltoken_character_single
-
-	li t1, '['
-	beq t0, t1, .Ltoken_character_single
-
-	li t1, ']'
-	beq t0, t1, .Ltoken_character_single
-
-.Ltoken_character_loop_do: # Expect an identifier or a number.
-	lw t6, 4(sp)
-	add t1, s1, t6
-	lbu a0, (t1) # a0 = Current character.
-
-	call is_alnum
-
-	beqz a0, .Ltoken_character_end
-	lw t6, 4(sp)
-	addi t6, t6, 1
-	sw t6, 4(sp)
-	j .Ltoken_character_loop_do
-
-.Ltoken_character_single:
-	lw t6, 4(sp)
-	addi t6, t6, 1
-	sw t6, 4(sp)
-	j .Ltoken_character_end
-
-.Ltoken_character_colon:
-	lbu t0, 1(s1) # t0 = The character after the colon.
-	lw t6, 4(sp)
-	addi t6, t6, 1
-	sw t6, 4(sp)
-
-	li t1, '='
-	beq t0, t1, .Ltoken_character_single
-	j .Ltoken_character_end
-
-.Ltoken_character_end:
-	lw a0, 4(sp)
-
-	# Epilogue.
-	lw ra, 12(sp)
-	lw s0, 8(sp)
-	addi sp, sp, 16
-	ret
-
-# Generate entry point symbol.
-.type _compile_begin, @function
-_compile_begin:
-	# Prologue.
-	addi sp, sp, -8
-	sw ra, 4(sp)
-	sw s0, 0(sp)
-	addi s0, sp, 8
-
-	# Write initial assembler.
-	la a0, asm_begin
-	addi a1, zero, ASM_BEGIN_SIZE
-	call write_out
-
-	addi s1, s1, 5
-
-	# Epilogue.
-	lw ra, 4(sp)
-	lw s0, 0(sp)
-	addi sp, sp, 8
-	ret
-
-# Generate program termination code.
-.type _compile_end, @function
-_compile_end:
-	# Prologue.
-	addi sp, sp, -8
-	sw ra, 4(sp)
-	sw s0, 0(sp)
-	addi s0, sp, 8
-
-	# Write closing assembler.
-	la a0, asm_end
-	addi a1, zero, ASM_END_SIZE
-	call write_out
-
-	addi s1, s1, 3
-
-	# Epilogue.
-	lw ra, 4(sp)
-	lw s0, 0(sp)
-	addi sp, sp, 8
-	ret
-
-# Ignores the import.
-.type _compile_import, @function
-_compile_import:
-	# Prologue.
-	addi sp, sp, -8
-	sw ra, 4(sp)
-	sw s0, 0(sp)
-	addi s0, sp, 8
-
-	addi s1, s1, 6
-	call _skip_spaces
-	call _read_token
-	add s1, s1, a0 # Skip the imported module name.
-
-	# Epilogue.
-	lw ra, 4(sp)
-	lw s0, 0(sp)
-	addi sp, sp, 8
-	ret
-
-# Compiles a procedure call. Expects s1 to point to the first argument.
-# a0 - Pointer to the procedure name.
-# a1 - Length of the procedure name.
-#
-# Returns the procedure result in a0.
-.type _compile_call, @function
-_compile_call:
-	# Prologue.
-	addi sp, sp, -32
-	sw ra, 28(sp)
-	sw s0, 24(sp)
-	addi s0, sp, 32
-
-	sw a0, 20(sp)
-	sw a1, 16(sp)
-	sw zero, 12(sp) # Argument count for a procedure call.
-
-.Lcompile_call_paren:
-	call _skip_spaces
-	call _read_token
-	addi a1, a0, 0
-	addi a0, s1, 0
-	la a2, token_close_paren
-	call _token_compare
-	beqz a0, .Lcompile_call_complete
-
-.Lcompile_call_argument:
-	call _build_expression
-
-	la a0, instruction_sw
-	li a1, 2
-	call write_out
-
-	la a0, space
-	li a1, 1
-	call write_out
-
-	la a0, register_a0
-	li a1, 2
-	call write_out
-
-	la a0, comma
-	li a1, 1
-	call write_out
-
-	lw t0, 12(sp) # Argument count for a procedure call.
-
-	# Only 8 arguments are supported with a0-a7.
-	# Save all arguments on the stack so they aren't overriden afterwards.
-	# The offset on the stack always has two digits in this case.
-	li t1, -4
-	mul t1, t0, t1
-	addi t1, t1, 52
-	li t2, 10
-	div t3, t1, t2
-	rem t4, t1, t2
-	addi t3, t3, '0'
-	addi t4, t4, '0'
-
-	sw t3, 8(sp)
-	sw t4, 4(sp)
-
-	addi a0, sp, 8
-	li a1, 1
-	call write_out
-
-	addi a0, sp, 4
-	li a1, 1
-	call write_out
-
-	la a0, token_open_paren
-	li a1, 1
-	call write_out
-
-	la a0, register_sp
-	li a1, 2
-	call write_out
-
-	la a0, token_close_paren
-	li a1, 1
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	call _skip_spaces
-	call _read_token
-	addi a1, a0, 0
-	addi a0, s1, 0
-	la a2, token_comma
-	call  _token_compare
-
-	/* DEBUG. Write the current token to stderr.
-	addi a0, zero, STDERR
-	addi a1, s1, 0
-	li a2, 4 #(sp)
-	addi a7, zero, SYS_WRITE
-	ecall
-	addi a0, zero, STDERR
-	la a1, token_open_square
-	li a2, 1
-	addi a7, zero, SYS_WRITE
-	ecall
-	DEBUG. End */
-
-	bnez a0, .Lcompile_call_paren
-
-	lw t0, 12(sp) # Argument count for a procedure call.
-	addi t0, t0, 1
-	sw t0, 12(sp)
-
-	addi s1, s1, 1 # Skip the comma between the arguments.
-	j .Lcompile_call_argument
-
-.Lcompile_call_complete:
-	sw zero, 12(sp)
-
-.Lcompile_call_restore:
-	# Just go through all a0-a7 registers and read them from stack.
-	# If this stack value contains garbage, the procedure just shouldn't use it.
-	lw t0, 12(sp)
-	li t1, 7
-	bgt t0, t1, .Lcompile_call_perform
-
-	la a0, instruction_lw
-	li a1, 2
-	call write_out
-
-	la a0, space
-	li a1, 1
-	call write_out
-
-	la a0, register_a
-	li a1, 1
-	call write_out
-
-	lw t0, 12(sp)
-	addi t0, t0, '0'
-	sw t0, 8(sp)
-
-	addi a0, sp, 8
-	li a1, 1
-	call write_out
-
-	la a0, comma
-	li a1, 1
-	call write_out
-
-	lw t0, 12(sp) # Argument count for a procedure call.
-
-	li t1, -4
-	mul t1, t0, t1
-	addi t1, t1, 52
-	li t2, 10
-	div t3, t1, t2
-	rem t4, t1, t2
-	addi t3, t3, '0'
-	addi t4, t4, '0'
-
-	sw t3, 8(sp)
-	sw t4, 4(sp)
-
-	addi a0, sp, 8
-	li a1, 1
-	call write_out
-
-	addi a0, sp, 4
-	li a1, 1
-	call write_out
-
-	la a0, token_open_paren
-	li a1, 1
-	call write_out
-
-	la a0, register_sp
-	li a1, 2
-	call write_out
-
-	la a0, token_close_paren
-	li a1, 1
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	lw t0, 12(sp) # Increment.
-	addi t0, t0, 1
-	sw t0, 12(sp)
-
-	j .Lcompile_call_restore
-
-.Lcompile_call_perform:
-	la a0, instruction_call
-	li a1, 4
-	call write_out
-
-	la a0, space
-	li a1, 1
-	call write_out
-
-	lw a0, 20(sp)
-	lw a1, 16(sp)
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	call _skip_spaces
-	addi s1, s1, 1 # Skip the close paren.
-
-	# Epilogue.
-	lw ra, 28(sp)
-	lw s0, 24(sp)
-	addi sp, sp, 32
-	ret
-
-# Evalutes an expression and saves the result in a0.
-.type _build_expression, @function
-_build_expression:
-	# Prologue.
-	addi sp, sp, -16
-	sw ra, 12(sp)
-	sw s0, 8(sp)
-	addi s0, sp, 16
-
-	call _skip_spaces
-	call _read_token
-	sw s1, 4(sp)
-	sw a0, 0(sp)
-
-	# Integer literal.
-	addi a0, s1, 0
-	lb a0, (a0)
-	call is_digit
-	bnez a0, .Lbuild_expression_number_literal
-
-	# Named identifier.
-	la a0, instruction_la
-	li a1, 2
-	call write_out
-
-	la a0, space
-	li a1, 1
-	call write_out
-
-	la a0, register_a0
-	li a1, 2
-	call write_out
-
-	la a0, comma
-	li a1, 1
-	call write_out
-
-	lw a0, 4(sp)
-	lw a1, 0(sp)
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	j .Lbuild_expression_end
-
-.Lbuild_expression_number_literal:
-	la a0, instruction_li
-	li a1, 2
-	call write_out
-
-	la a0, space
-	li a1, 1
-	call write_out
-
-	la a0, register_a0
-	li a1, 2
-	call write_out
-
-	la a0, comma
-	li a1, 1
-	call write_out
-
-	lw a0, 4(sp)
-	lw a1, 0(sp)
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	j .Lbuild_expression_end
-
-.Lbuild_expression_end:
-	lw a0, 0(sp)
-	add s1, s1, a0
-
-	# Epilogue.
-	lw ra, 12(sp)
-	lw s0, 8(sp)
-	addi sp, sp, 16
-	ret
-
-# Compiles a statement beginning with an identifier.
-.type _compile_identifier, @function
-_compile_identifier:
-	# Prologue.
-	addi sp, sp, -32
-	sw ra, 28(sp)
-	sw s0, 24(sp)
-	addi s0, sp, 32
-
-	# Save the pointer to the identifier and its length on the stack.
-	sw a0, 20(sp)
-	sw a1, 16(sp)
-
-	add s1, s1, a1
-	call _skip_spaces
-	call _read_token
-
-	# Save the pointer and the length of the token following the identifier.
-	sw s1, 12(sp)
-	sw a0, 8(sp)
-
-	add s1, s1, a0 # Skip that token.
-	call _skip_spaces
-
-	lw a0, 12(sp)
-	lw a1, 8(sp)
-	la a2, token_assign
-	call _token_compare
-	beqz a0, .Lcompile_identifier_assign
-
-	lw a0, 12(sp)
-	lw a1, 8(sp)
-	la a2, token_open_paren
-	call _token_compare
-	beqz a0, .Lcompile_identifier_call
-
-	j .Lcompile_identifier_end
-
-.Lcompile_identifier_call:
-	lw a0, 20(sp)
-	lw a1, 16(sp)
-	call _compile_call
-
-	j .Lcompile_identifier_end
-
-.Lcompile_identifier_assign:
-	call _build_expression
-
-	la a0, instruction_addi
-	li a1, 4
-	call write_out
-
-	la a0, space
-	li a1, 1
-	call write_out
-
-	lw a0, 20(sp)
-	lw a1, 16(sp)
-	call write_out
-
-	la a0, comma
-	li a1, 1
-	call write_out
-
-	la a0, register_a0
-	li a1, 2
-	call write_out
-
-	la a0, comma
-	li a1, 1
-	call write_out
-
-	la a0, digit_zero
-	li a1, 1
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	j .Lcompile_identifier_end
-
-.Lcompile_identifier_end:
-	# Epilogue.
-	lw ra, 28(sp)
-	lw s0, 24(sp)
-	addi sp, sp, 32
-	ret
-
-.type _compile_var, @function
-_compile_var:
-	# Prologue.
-	addi sp, sp, -32
-	sw ra, 28(sp)
-	sw s0, 24(sp)
-	addi s0, sp, 32
-
-	# Variable name.
-	addi s1, s1, 3
-	call _skip_spaces
-	call _read_token
-	sw s1, 20(sp)
-	sw a0, 16(sp)
-	add s1, s1, a0
-
-	# Skip the colon.
-	call _skip_spaces
-	call _read_token
-	add s1, s1, a0
-
-	call _skip_spaces
-	call _read_token
-	sw a0, 12(sp)
-
-	addi a0, s1, 0
-	lw a1, 12(sp)
-	la a2, token_open_square
-	call _token_compare
-	beqz a0, .Lcompile_var_array
-
-	j .Lcompile_var_end
-
-.Lcompile_var_array:
-	call _skip_spaces
-	add s1, s1, 1 # Skip the opening square bracket.
-
-	call _skip_spaces
-	call _read_token
-	sw a0, 8(sp)
-
-	la a0, asm_type
-	li a1, ASM_TYPE_SIZE
-	call write_out
-
-	lw a0, 20(sp)
-	lw a1, 16(sp)
-	call write_out
-
-	la a0, asm_object
-	li a1, ASM_OBJECT_SIZE
-	call write_out
-
-	la a0, asm_size
-	li a1, ASM_SIZE_SIZE
-	call write_out
-
-	lw a0, 20(sp)
-	lw a1, 16(sp)
-	call write_out
-
-	la a0, comma
-	li a1, 1
-	call write_out
-
-	addi a0, s1, 0
-	lw a1, 8(sp)
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	lw a0, 20(sp)
-	lw a1, 16(sp)
-	call write_out
-
-	la a0, colon
-	li a1, 1
-	call write_out
-
-	la a0, asm_zero
-	li a1, ASM_ZERO_SIZE
-	call write_out
-
-	addi a0, s1, 0
-	lw a1, 8(sp)
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	la a0, asm_global
-	li a1, ASM_GLOBAL_SIZE
-	call write_out
-
-	lw a0, 20(sp)
-	lw a1, 16(sp)
-	call write_out
-
-	la a0, new_line
-	li a1, 1
-	call write_out
-
-	lw a0, 8(sp)
-	add s1, s1, a0
-
-	call _skip_spaces
-	add s1, s1, 1 # Skip the closing square bracket.
-
-	call _skip_spaces
-	call _read_token
-
-	sw a0, 12(sp)
-	j .Lcompile_var_end
-
-.Lcompile_var_end:
-	lw a0, 12(sp)
-	add s1, s1, a0
-
-	# Epilogue.
-	lw ra, 28(sp)
-	lw s0, 24(sp)
-	addi sp, sp, 32
-	ret
-
-.type _handle_token, @function
-_handle_token:
-	# Prologue.
-	addi sp, sp, -32
-	sw ra, 28(sp)
-	sw s0, 24(sp)
-	addi s0, sp, 32
-
-	sw a0, 20(sp)
-
-	# Detect what token has been read.
-	addi a0, s1, 0
-	lw a1, 20(sp)
-	la a2, token_begin
-	call _token_compare
-	beqz a0, .Lhandle_token_begin
-
-	addi a0, s1, 0
-	lw a1, 20(sp)
-	la a2, token_end
-	call _token_compare
-	beqz a0, .Lhandle_token_end
-
-	addi a0, s1, 0
-	lw a1, 20(sp)
-	la a2, token_import
-	call _token_compare
-	beqz a0, .Lhandle_token_import
-
-	addi a0, s1, 0
-	lw a1, 20(sp)
-	la a2, token_var
-	call _token_compare
-	beqz a0, .Lhandle_token_var
-
-	# If the first symbol in the token is a character, assume an identifier.
-	addi a0, s1, 0
-	lb a0, (a0)
-	call is_alpha
-	bnez a0, .Lhandle_token_identifier
-
-	# Ignore the unknown token.
-	lw t0, 20(sp)
-	add s1, s1, t0
-	j .Lhandle_token_return
-
-.Lhandle_token_begin:
-	call _compile_begin
-	j .Lhandle_token_return
-
-.Lhandle_token_end:
-	call _compile_end
-	j .Lhandle_token_return
-
-.Lhandle_token_import:
-	call _compile_import
-	j .Lhandle_token_return
-
-.Lhandle_token_var:
-	call _compile_var
-	j .Lhandle_token_return
-
-.Lhandle_token_identifier:
-	addi a0, s1, 0
-	lw a1, 20(sp)
-	call _compile_identifier
-	j .Lhandle_token_return
-
-.Lhandle_token_return:
-	# Epilogue.
-	lw ra, 28(sp)
-	lw s0, 24(sp)
-	addi sp, sp, 32
-	ret
-
 .type write, @function
 write_out:
 	# Prologue.
@@ -918,10 +79,10 @@ write_out:
 	sw s0, 0(sp)
 	addi s0, sp, 8
 
-	addi a2, a1, 0
-	addi a1, a0, 0
-	addi a0, zero, STDOUT
-	addi a7, zero, SYS_WRITE
+	mv a2, a1
+	mv a1, a0
+	li a0, STDOUT
+	li a7, SYS_WRITE
 	ecall
 
 	# Epilogue.
@@ -943,10 +104,10 @@ read_file:
 	sw s0, 0(sp)
 	addi s0, sp, 8
 
-	addi a2, a1, 0
-	addi a1, a0, 0
-	addi a0, zero, STDIN
-	addi a7, zero, SYS_READ
+	mv a2, a1
+	mv a1, a0
+	li a0, STDIN
+	li a7, SYS_READ
 	ecall
 
 	# Epilogue.
@@ -955,40 +116,7 @@ read_file:
 	addi sp, sp, 8
 	ret
 
-.type _compile, @function
-compile:
-	# Prologue.
-	addi sp, sp, -16
-	sw ra, 12(sp)
-	sw s0, 8(sp)
-	addi s0, sp, 16
-
-	# Write .bss section header for global variables.
-	la a0, asm_program
-	addi a1, zero, ASM_PROGRAM_SIZE
-	call write_out
-
-	call _skip_spaces
-	addi s1, s1, 7 # Skip "program" keyword.
-
-.Lcharacter_loop_do:
-	call _skip_spaces
-
-	lbu t0, (s1) # t0 = Current character.
-	beqz t0, .Lcharacter_loop_end
-
-	call _read_token
-	sw a0, 4(sp) # Save the token length on the stack.
-	beqz a0, .Lcharacter_loop_end # No token read, there is unrecognized input.
-
-	lw a0, 4(sp)
-	call _handle_token
-
-	j .Lcharacter_loop_do
-.Lcharacter_loop_end:
-
-	# Epilogue.
-	lw ra, 12(sp)
-	lw s0, 8(sp)
-	addi sp, sp, 16
-	ret
+# Terminates the program. a0 contains the return code.
+exit:
+	li a7, SYS_EXIT
+	ecall
diff --git a/boot/echo-boot.s b/boot/echo-boot.s
new file mode 100644
index 0000000..b6e65f7
--- /dev/null
+++ b/boot/echo-boot.s
@@ -0,0 +1,35 @@
+.global _start, source_code
+
+.section .rodata
+.type SOURCE_BUFFER_SIZE, @object
+.size SOURCE_BUFFER_SIZE, 4
+SOURCE_BUFFER_SIZE: .long 4096
+
+.section .bss
+.type source_code, @object
+.size source_code, 4096
+source_code: .zero 4096
+
+.section .text
+
+_compile:
+	ret
+
+_start:
+	# Read the source from the standard input.
+	la a0, source_code
+	la a1, SOURCE_BUFFER_SIZE # Buffer size.
+	lw a1, (a1)
+	call read_file
+	mv s1, a0
+
+	call _compile
+
+	# Write the source to the standard output.
+	la a0, source_code
+	mv a1, s1
+	call write_out
+
+	# Call exit.
+	li a0, 0   # Use 0 return code.
+	call exit
diff --git a/boot/stage2.elna b/boot/stage2.elna
new file mode 100644
index 0000000..a119f4a
--- /dev/null
+++ b/boot/stage2.elna
@@ -0,0 +1,32 @@
+.global _start, source_code
+
+.equ SYS_READ, 63
+.equ SYS_WRITE, 64
+.equ SYS_EXIT, 93
+.equ STDIN, 0
+.equ STDOUT, 1
+.equ STDERR, 2
+
+.equ SOURCE_BUFFER_SIZE, 2048
+
+.section .bss
+.type source_code, @object
+.size source_code, SOURCE_BUFFER_SIZE
+source_code: .zero SOURCE_BUFFER_SIZE
+
+.section .text
+
+_start:
+	# Read the source from the standard input.
+	la a0, source_code
+	li a1, SOURCE_BUFFER_SIZE # Buffer size.
+	call read_file
+
+	# Write the source to the standard output.
+	mv a1, a0
+	la a0, source_code
+	call write_out
+
+	# Call exit.
+	li a0, 0   # Use 0 return code.
+	call exit