Compile procedure headers

Rakefile

@@ -7,8 +7,28 @@ CROSS_GCC = '../riscv32-ilp32d--glibc/bin/riscv32-linux-gcc'
 SYSROOT = '../riscv32-ilp32d--glibc/riscv32-buildroot-linux-gnu/sysroot'
 QEMU = 'qemu-riscv32'
 
+def assemble_stage(output, compiler, source)
+  arguments = [QEMU, '-L', SYSROOT, *compiler]
+
+  puts(arguments * ' ')
+  puts
+  Open3.popen2(*arguments) do |qemu_in, qemu_out|
+    qemu_in.write File.read(*source)
+    qemu_in.close
+
+    IO.copy_stream qemu_out, output
+    qemu_out.close
+  end
+end
+
 desc 'Final stage'
-task default: 'build/stage2'
+task default: ['build/stage2', 'boot/stage2.elna'] do |t|
+  assembler, exe = t.prerequisites.partition { |prerequisite| prerequisite.end_with? '.elna' }
+
+  File.open File::NULL, 'w' do |output|
+    assemble_stage output, exe, assembler
+  end
+end
 
 directory 'build'
 
@@ -21,18 +41,9 @@ 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
+    assemble_stage output, exe, assembler
-    end
-    qemu_out.close
   end
 end
 

boot/echo-boot.s

@@ -188,7 +188,7 @@ _compile_program:
 	sw t0, 8(sp)
 
 	addi a0, sp, 8
-	li a1, 16
+	li a1, 15
 	call write_out
 
 	addi s1, s1, 8 # program\n.
@@ -496,7 +496,160 @@ _compile_procedure:
 	addi s1, s1, 1 # Skip opening argument paren.
 	call _skip_spaces
 	addi s1, s1, 1 # Skip closing argument paren.
+
+	li t0, 0x6e # n
+	sw t0, 12(sp)
+	li t0, 0x69676562 # begi
+	sw t0, 8(sp)
+
+	# Skip all declarations until we find the "begin" keyword, denoting the
+	# beginning of the procedure body.
+.Lcompile_procedure_begin:
 	call _skip_spaces
+	call _read_token
+
+	mv a1, a0
+	mv a0, s1
+	addi a2, sp, 8
+	add s1, s1, a1
+	call _token_compare
+
+	bnez a0, .Lcompile_procedure_begin
+
+	# Generate the procedure prologue with a predefined stack size.
+	li t0, 0x69646461 # addi
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x2c707320 # _sp,
+	sw t0, 12(sp)
+
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x0a36392d # -96\n
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x0a29 # )\n
+	sw t0, 12(sp)
+	li t0, 0x70732832 # 2(sp
+	sw t0, 8(sp)
+	li t0, 0x39202c61 # a, 9
+	sw t0, 4(sp)
+	li t0, 0x72207773 # sw r
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 14
+	call write_out
+
+	li t0, 0x0a29 # )\n
+	sw t0, 12(sp)
+	li t0, 0x70732838 # 2(sp
+	sw t0, 8(sp)
+	li t0, 0x38202c30 # 0, 8
+	sw t0, 4(sp)
+	li t0, 0x73207773 # sw s
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 14
+	call write_out
+
+	li t0, 0x0a363920 # _96\n
+	sw t0, 12(sp)
+	li t0, 0x2c707320 # _sp,
+	sw t0, 8(sp)
+	li t0, 0x2c307320 # _s0,
+	sw t0, 4(sp)
+	li t0, 0x69646461 # addi
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 16
+	call write_out
+
+	# Generate the body of the procedure.
+.Lcompile_procedure_body:
+	call _skip_indentation
+	call _read_line
+	sw a0, 12(sp)
+	li t0, 0x0a646e65 # end\n
+	sw t0, 8(sp)
+	mv a0, s1
+	addi a1, sp, 8
+	li a2, 4
+	call memcmp
+
+	beqz a0, .Lcompile_procedure_end
+
+	lw a0, 12(sp)
+	call _compile_line
+	j .Lcompile_procedure_body
+
+.Lcompile_procedure_end:
+	add s1, s1, 4 # Skip end\n.
+
+	# Generate the procedure epilogue with a predefined stack size.
+	li t0, 0x0a29 # )\n
+	sw t0, 12(sp)
+	li t0, 0x70732832 # 2(sp
+	sw t0, 8(sp)
+	li t0, 0x39202c61 # a, 9
+	sw t0, 4(sp)
+	li t0, 0x7220776c # lw r
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 14
+	call write_out
+
+	li t0, 0x0a29 # )\n
+	sw t0, 12(sp)
+	li t0, 0x70732838 # 2(sp
+	sw t0, 8(sp)
+	li t0, 0x38202c30 # 0, 8
+	sw t0, 4(sp)
+	li t0, 0x7320776c # lw s
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 14
+	call write_out
+
+	li t0, 0x69646461 # addi
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x2c707320 # _sp,
+	sw t0, 12(sp)
+
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x0a3639 # 96\n
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 3
+	call write_out
+
+	li t0, 0x0a746572 # ret\n
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
 
 	# Epilogue.
 	lw ra, 28(sp)
@@ -504,8 +657,52 @@ _compile_procedure:
 	addi sp, sp, 32
 	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
+
 # Parameters:
 # a0 - Line length.
+# Returns 1 in a0 if the parsed line contained a text section element such a
+# procedure or the program entry point. Otherwise sets a0 to 0.
 .type _compile_line, @function
 _compile_line:
 	# Prologue.
@@ -560,14 +757,42 @@ _compile_line:
 	call memcmp
 	beqz a0, .Lcompile_line_procedure
 
+	li t0, 0x0a6e # n\n
+	sw t0, 16(sp)
+	li t0, 0x69676562 # begi
+	sw t0, 12(sp)
+	mv a0, s1
+	addi a1, sp, 12
+	li a2, 6
+	call memcmp
+	beqz a0, .Lcompile_line_begin
+
+	li t0, 0x2e646e65 # end.
+	sw t0, 16(sp)
+	mv a0, s1
+	addi a1, sp, 16
+	li a2, 4
+	call memcmp
+	beqz a0, .Lcompile_line_exit
+
 	j .Lcompile_line_unchanged # Else.
 
+.Lcompile_line_exit:
+	call _compile_exit
+	j .Lcompile_line_section
+
+.Lcompile_line_begin:
+	call _compile_entry_point
+	li a0, 1
+	j .Lcompile_line_end
+
 .Lcompile_line_const:
 	call _compile_constant_section
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_procedure:
 	call _compile_procedure
+	li a0, 1
 	j .Lcompile_line_end
 
 .Lcompile_line_var:
@@ -578,25 +803,28 @@ _compile_line:
 	call write_error */
 
 	call _compile_variable_section
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_program:
 	call _compile_program
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_comment:
 	lw a0, 20(sp)
 	call _skip_comment
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_empty:
 	addi s1, s1, 1
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_unchanged:
 	lw a0, 20(sp)
 	call _compile_assembly
-	j .Lcompile_line_end
+	j .Lcompile_line_section
+
+.Lcompile_line_section:
+	mv a0, zero
 
 .Lcompile_line_end:
 	# Epilogue.
@@ -605,6 +833,109 @@ _compile_line:
 	addi sp, sp, 32
 	ret
 
+.type _compile_text_section, @function
+_compile_text_section:
+	# Prologue.
+	addi sp, sp, -24
+	sw ra, 20(sp)
+	sw s0, 16(sp)
+	addi s0, sp, 24
+
+	# .section .text
+	li t0, 0x0a7478 # xt\n
+	sw t0, 12(sp)
+	li t0, 0x65742e20 # _.te
+	sw t0, 8(sp)
+	li t0, 0x6e6f6974 # tion
+	sw t0, 4(sp)
+	li t0, 0x6365732e # .sec
+	sw t0, 0(sp)
+
+	addi a0, sp, 0
+	li a1, 15
+	call write_out
+
+	# Epilogue.
+	lw ra, 20(sp)
+	lw s0, 16(sp)
+	addi sp, sp, 24
+	ret
+
+.type _compile_entry_point, @function
+_compile_entry_point:
+	# Prologue.
+	addi sp, sp, -64
+	sw ra, 60(sp)
+	sw s0, 56(sp)
+	addi s0, sp, 64
+
+	# .type _start, @function
+	li t0, 0x0a3a7472 # rt:\n
+	sw t0, 52(sp)
+	li t0, 0x6174735f # _sta
+	sw t0, 48(sp)
+	li t0, 0x0a6e6f69 # ion\n
+	sw t0, 44(sp)
+	li t0, 0x74636e75 # unct
+	sw t0, 40(sp)
+	li t0, 0x6640202c # , @f
+	sw t0, 36(sp)
+	li t0, 0x74726174 # tart
+	sw t0, 32(sp)
+	li t0, 0x735f2065 # e _s
+	sw t0, 28(sp)
+	li t0, 0x7079742e # .typ
+	sw t0, 24(sp)
+	addi a0, sp, 24
+	li a1, 32
+	call write_out
+
+	addi s1, s1, 6 # Skip begin\n.
+
+	# Epilogue.
+	lw ra, 60(sp)
+	lw s0, 56(sp)
+	addi sp, sp, 64
+	ret
+
+.type _compile_exit, @function
+_compile_exit:
+	# Prologue.
+	addi sp, sp, -64
+	sw ra, 60(sp)
+	sw s0, 56(sp)
+	addi s0, sp, 64
+
+	# li a0, 0
+	# li a7, SYS_EXIT
+	# ecall
+	li t0, 0x0a # \n
+	sw t0, 52(sp)
+	li t0, 0x6c6c6163 # call
+	sw t0, 48(sp)
+	li t0, 0x650a3339 # 93\ne
+	sw t0, 44(sp)
+	li t0, 0x202c3761 # a7,_
+	sw t0, 40(sp)
+	li t0, 0x20696c0a # \nli_
+	sw t0, 36(sp)
+	li t0, 0x30202c30 # 0, 0
+	sw t0, 32(sp)
+	li t0, 0x6120696c # li a
+	sw t0, 28(sp)
+	addi a0, sp, 28
+	li a1, 25
+	call write_out
+
+	addi s1, s1, 4 # Skip end.
+	call _skip_spaces # Read the possible new line at the end of the file.
+
+	# Epilogue.
+	lw ra, 60(sp)
+	lw s0, 56(sp)
+	addi sp, sp, 64
+	ret
+
 # Finds the end of the line and returns its length in a0.
 .type _read_line, @function
 _read_line:
@@ -626,10 +957,10 @@ _read_line:
 .type _compile, @function
 _compile:
 	# Prologue.
-	addi sp, sp, -8
+	addi sp, sp, -16
-	sw ra, 4(sp)
+	sw ra, 12(sp)
-	sw s0, 0(sp)
+	sw s0, 8(sp)
-	addi s0, sp, 8
+	addi s0, sp, 16
 
 .Lcompile_do:
 	lbu t0, (s1) # t0 = Current character.
@@ -643,9 +974,9 @@ _compile:
 .Lcompile_end:
 
 	# Epilogue.
-	lw ra, 4(sp)
+	lw ra, 12(sp)
-	lw s0, 0(sp)
+	lw s0, 8(sp)
-	addi sp, sp, 8
+	addi sp, sp, 16
 	ret
 
 # Entry point.

boot/stage2.elna

@@ -12,12 +12,7 @@ var
 # 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.
 proc _read_token()
-	# Prologue.
+begin
-	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)
 
@@ -76,16 +71,11 @@ proc _read_token()
 
 .Ltoken_character_end:
 	lw a0, 4(sp)
-
+end
-	# Epilogue.
-	lw ra, 12(sp)
-	lw s0, 8(sp)
-	addi sp, sp, 16
-	ret
 
 # Skips the spaces till the next non space character.
-.type _skip_spaces, @function
+proc _skip_spaces()
-_skip_spaces:
+begin
 .Lspace_loop_do:
 	lbu t0, (s1) # t0 = Current character.
 
@@ -104,11 +94,11 @@ _skip_spaces:
 	j .Lspace_loop_do
 
 .Lspace_loop_end:
-	ret
+end
 
 # Skips tabs at the line beginning.
-.type _skip_indentation, @function
+proc _skip_indentation()
-_skip_indentation:
+begin
 .Lskip_indentation_do:
 	lbu t0, (s1)
 
@@ -122,26 +112,20 @@ _skip_indentation:
 	j .Lskip_indentation_do
 
 .Lskip_indentation_end:
-	ret
+end
 
 # Parameters:
 # a0 - Line length.
-.type _skip_comment, @function
+proc _skip_comment()
-_skip_comment:
+begin
 	add s1, s1, a0
 	addi s1, s1, 1 # Skip the new line.
-	ret
+end
 
 # Parameters:
 # a0 - Line length.
-.type _compile_assembly, @function
+proc _compile_assembly()
-_compile_assembly:
+begin
-	# Prologue.
-	addi sp, sp, -16
-	sw ra, 12(sp)
-	sw s0, 8(sp)
-	addi s0, sp, 16
-
 	sw a0, 4(sp) # a0 - Line length.
 
 	# Write the source to the standard output.
@@ -159,21 +143,10 @@ _compile_assembly:
 	call write_out
 
 	addi s1, s1, 1 # Skip the new line.
+end
 
-	# Epilogue.
+proc _compile_program()
-	lw ra, 12(sp)
+begin
-	lw s0, 8(sp)
-	addi sp, sp, 16
-	ret
-
-.type _compile_program, @function
-_compile_program:
-	# Prologue.
-	addi sp, sp, -32
-	sw ra, 28(sp)
-	sw s0, 24(sp)
-	addi s0, sp, 32
-
 	# .global _start
 	li t0, 0x0a7472 # rt\n
 	sw t0, 20(sp)
@@ -185,25 +158,14 @@ _compile_program:
 	sw t0, 8(sp)
 
 	addi a0, sp, 8
-	li a1, 16
+	li a1, 15
 	call write_out
 
 	addi s1, s1, 8 # program\n.
+end
 
-	# Epilogue.
+proc _compile_constant_section()
-	lw ra, 28(sp)
+begin
-	lw s0, 24(sp)
-	addi sp, sp, 32
-	ret
-
-.type _compile_constant_section, @function
-_compile_constant_section:
-	# Prologue.
-	addi sp, sp, -32
-	sw ra, 28(sp)
-	sw s0, 24(sp)
-	addi s0, sp, 32
-
 	# .section .rodata
 	li t0, 0x0a # \n
 	sw t0, 20(sp)
@@ -232,20 +194,10 @@ _compile_constant_section:
 	j .Lcompile_constant_section_item
 
 .Lcompile_constant_section_end:
-	# Epilogue.
+end
-	lw ra, 28(sp)
-	lw s0, 24(sp)
-	addi sp, sp, 32
-	ret
-
-.type _compile_constant, @function
-_compile_constant:
-	# Prologue.
-	addi sp, sp, -16
-	sw ra, 12(sp)
-	sw s0, 8(sp)
-	addi s0, sp, 16
 
+proc _compile_constant()
+begin
 	call _read_token
 
 	mv a1, a0 # The identifier length from _read_token should be in a1.
@@ -279,21 +231,10 @@ _compile_constant:
 	addi a0, sp, 4
 	li a1, 1
 	call write_out
+end
 
-	# Epilogue.
+proc _compile_variable_section()
-	lw ra, 12(sp)
+begin
-	lw s0, 8(sp)
-	addi sp, sp, 16
-	ret
-
-.type _compile_variable_section, @function
-_compile_variable_section:
-	# Prologue.
-	addi sp, sp, -24
-	sw ra, 20(sp)
-	sw s0, 16(sp)
-	addi s0, sp, 24
-
 	# .section .bss
 	li t0, 0x0a73 # s\n
 	sw t0, 12(sp)
@@ -320,20 +261,10 @@ _compile_variable_section:
 	j .Lcompile_variable_section_item
 
 .Lcompile_variable_section_end:
-	# Epilogue.
+end
-	lw ra, 20(sp)
-	lw s0, 16(sp)
-	addi sp, sp, 24
-	ret
-
-.type _compile_variable, @function
-_compile_variable:
-	# Prologue.
-	addi sp, sp, -40
-	sw ra, 36(sp)
-	sw s0, 32(sp)
-	addi s0, sp, 40
 
+proc _compile_variable()
+begin
 	call _read_token
 
 	# Save the identifier on the stack since it should emitted multiple times.
@@ -435,21 +366,10 @@ _compile_variable:
 	addi a0, sp, 12
 	li a1, 1
 	call write_out
+end
 
-	# Epilogue.
+proc _compile_procedure()
-	lw ra, 36(sp)
+begin
-	lw s0, 32(sp)
-	addi sp, sp, 40
-	ret
-
-.type _compile_procedure, @function
-_compile_procedure:
-	# Prologue.
-	addi sp, sp, -32
-	sw ra, 28(sp)
-	sw s0, 24(sp)
-	addi s0, sp, 32
-
 	addi s1, s1, 5 # Skip proc_
 	call _read_token
 	sw s1, 20(sp)
@@ -493,24 +413,210 @@ _compile_procedure:
 	addi s1, s1, 1 # Skip opening argument paren.
 	call _skip_spaces
 	addi s1, s1, 1 # Skip closing argument paren.
-	call _skip_spaces
 
-	# Epilogue.
+	li t0, 0x6e # n
-	lw ra, 28(sp)
+	sw t0, 12(sp)
-	lw s0, 24(sp)
+	li t0, 0x69676562 # begi
-	addi sp, sp, 32
+	sw t0, 8(sp)
-	ret
+
+	# Skip all declarations until we find the "begin" keyword, denoting the
+	# beginning of the procedure body.
+.Lcompile_procedure_begin:
+	call _skip_spaces
+	call _read_token
+
+	mv a1, a0
+	mv a0, s1
+	addi a2, sp, 8
+	add s1, s1, a1
+	call _token_compare
+
+	bnez a0, .Lcompile_procedure_begin
+
+	# Generate the procedure prologue with a predefined stack size.
+	li t0, 0x69646461 # addi
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x2c707320 # _sp,
+	sw t0, 12(sp)
+
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x0a36392d # -96\n
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x0a29 # )\n
+	sw t0, 12(sp)
+	li t0, 0x70732832 # 2(sp
+	sw t0, 8(sp)
+	li t0, 0x39202c61 # a, 9
+	sw t0, 4(sp)
+	li t0, 0x72207773 # sw r
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 14
+	call write_out
+
+	li t0, 0x0a29 # )\n
+	sw t0, 12(sp)
+	li t0, 0x70732838 # 2(sp
+	sw t0, 8(sp)
+	li t0, 0x38202c30 # 0, 8
+	sw t0, 4(sp)
+	li t0, 0x73207773 # sw s
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 14
+	call write_out
+
+	li t0, 0x0a363920 # _96\n
+	sw t0, 12(sp)
+	li t0, 0x2c707320 # _sp,
+	sw t0, 8(sp)
+	li t0, 0x2c307320 # _s0,
+	sw t0, 4(sp)
+	li t0, 0x69646461 # addi
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 16
+	call write_out
+
+	# Generate the body of the procedure.
+.Lcompile_procedure_body:
+	call _skip_indentation
+	call _read_line
+	sw a0, 12(sp)
+	li t0, 0x0a646e65 # end\n
+	sw t0, 8(sp)
+	mv a0, s1
+	addi a1, sp, 8
+	li a2, 4
+	call memcmp
+
+	beqz a0, .Lcompile_procedure_end
+
+	lw a0, 12(sp)
+	call _compile_line
+	j .Lcompile_procedure_body
+
+.Lcompile_procedure_end:
+	add s1, s1, 4 # Skip end\n.
+
+	# Generate the procedure epilogue with a predefined stack size.
+	li t0, 0x0a29 # )\n
+	sw t0, 12(sp)
+	li t0, 0x70732832 # 2(sp
+	sw t0, 8(sp)
+	li t0, 0x39202c61 # a, 9
+	sw t0, 4(sp)
+	li t0, 0x7220776c # lw r
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 14
+	call write_out
+
+	li t0, 0x0a29 # )\n
+	sw t0, 12(sp)
+	li t0, 0x70732838 # 2(sp
+	sw t0, 8(sp)
+	li t0, 0x38202c30 # 0, 8
+	sw t0, 4(sp)
+	li t0, 0x7320776c # lw s
+	sw t0, 0(sp)
+	addi a0, sp, 0
+	li a1, 14
+	call write_out
+
+	li t0, 0x69646461 # addi
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x2c707320 # _sp,
+	sw t0, 12(sp)
+
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+
+	li t0, 0x0a3639 # 96\n
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 3
+	call write_out
+
+	li t0, 0x0a746572 # ret\n
+	sw t0, 12(sp)
+	addi a0, sp, 12
+	li a1, 4
+	call write_out
+end
+
+# 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.
+proc _token_compare()
+begin
+	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:
+end
 
 # Parameters:
 # a0 - Line length.
-.type _compile_line, @function
+# Returns 1 in a0 if the parsed line contained a text section element such a
-_compile_line:
+# procedure or the program entry point. Otherwise sets a0 to 0.
-	# Prologue.
+proc _compile_line()
-	addi sp, sp, -32
+begin
-	sw ra, 28(sp)
-	sw s0, 24(sp)
-	addi s0, sp, 32
-
 	sw a0, 20(sp) # a0 - Line length.
 
 	beqz a0, .Lcompile_line_empty # Skip an empty line.
@@ -557,14 +663,42 @@ _compile_line:
 	call memcmp
 	beqz a0, .Lcompile_line_procedure
 
+	li t0, 0x0a6e # n\n
+	sw t0, 16(sp)
+	li t0, 0x69676562 # begi
+	sw t0, 12(sp)
+	mv a0, s1
+	addi a1, sp, 12
+	li a2, 6
+	call memcmp
+	beqz a0, .Lcompile_line_begin
+
+	li t0, 0x2e646e65 # end.
+	sw t0, 16(sp)
+	mv a0, s1
+	addi a1, sp, 16
+	li a2, 4
+	call memcmp
+	beqz a0, .Lcompile_line_exit
+
 	j .Lcompile_line_unchanged # Else.
 
+.Lcompile_line_exit:
+	call _compile_exit
+	j .Lcompile_line_section
+
+.Lcompile_line_begin:
+	call _compile_entry_point
+	li a0, 1
+	j .Lcompile_line_end
+
 .Lcompile_line_const:
 	call _compile_constant_section
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_procedure:
 	call _compile_procedure
+	li a0, 1
 	j .Lcompile_line_end
 
 .Lcompile_line_var:
@@ -575,36 +709,105 @@ _compile_line:
 	call write_error */
 
 	call _compile_variable_section
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_program:
 	call _compile_program
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_comment:
 	lw a0, 20(sp)
 	call _skip_comment
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_empty:
 	addi s1, s1, 1
-	j .Lcompile_line_end
+	j .Lcompile_line_section
 
 .Lcompile_line_unchanged:
 	lw a0, 20(sp)
 	call _compile_assembly
-	j .Lcompile_line_end
+	j .Lcompile_line_section
+
+.Lcompile_line_section:
+	mv a0, zero
 
 .Lcompile_line_end:
-	# Epilogue.
+end
-	lw ra, 28(sp)
+
-	lw s0, 24(sp)
+proc _compile_text_section()
-	addi sp, sp, 32
+begin
-	ret
+	# .section .text
+	li t0, 0x0a7478 # xt\n
+	sw t0, 12(sp)
+	li t0, 0x65742e20 # _.te
+	sw t0, 8(sp)
+	li t0, 0x6e6f6974 # tion
+	sw t0, 4(sp)
+	li t0, 0x6365732e # .sec
+	sw t0, 0(sp)
+
+	addi a0, sp, 0
+	li a1, 15
+	call write_out
+end
+
+proc _compile_entry_point()
+begin
+	# .type _start, @function
+	li t0, 0x0a3a7472 # rt:\n
+	sw t0, 52(sp)
+	li t0, 0x6174735f # _sta
+	sw t0, 48(sp)
+	li t0, 0x0a6e6f69 # ion\n
+	sw t0, 44(sp)
+	li t0, 0x74636e75 # unct
+	sw t0, 40(sp)
+	li t0, 0x6640202c # , @f
+	sw t0, 36(sp)
+	li t0, 0x74726174 # tart
+	sw t0, 32(sp)
+	li t0, 0x735f2065 # e _s
+	sw t0, 28(sp)
+	li t0, 0x7079742e # .typ
+	sw t0, 24(sp)
+	addi a0, sp, 24
+	li a1, 32
+	call write_out
+
+	addi s1, s1, 6 # Skip begin\n.
+end
+
+proc _compile_exit()
+begin
+	# li a0, 0
+	# li a7, SYS_EXIT
+	# ecall
+	li t0, 0x0a # \n
+	sw t0, 52(sp)
+	li t0, 0x6c6c6163 # call
+	sw t0, 48(sp)
+	li t0, 0x650a3339 # 93\ne
+	sw t0, 44(sp)
+	li t0, 0x202c3761 # a7,_
+	sw t0, 40(sp)
+	li t0, 0x20696c0a # \nli_
+	sw t0, 36(sp)
+	li t0, 0x30202c30 # 0, 0
+	sw t0, 32(sp)
+	li t0, 0x6120696c # li a
+	sw t0, 28(sp)
+	addi a0, sp, 28
+	li a1, 25
+	call write_out
+
+	addi s1, s1, 4 # Skip end.
+	call _skip_spaces # Read the possible new line at the end of the file.
+end
 
 # Finds the end of the line and returns its length in a0.
-.type _read_line, @function
+proc _read_line()
-_read_line:
+begin
 	mv t0, s1 # Local position in the source text.
 
 .Lread_line_do:
@@ -618,16 +821,10 @@ _read_line:
 
 .Lread_line_end:
 	sub a0, t0, s1 # Return the line length.
-	ret
+end
-
-.type _compile, @function
-_compile:
-	# Prologue.
-	addi sp, sp, -8
-	sw ra, 4(sp)
-	sw s0, 0(sp)
-	addi s0, sp, 8
 
+proc _compile()
+begin
 .Lcompile_do:
 	lbu t0, (s1) # t0 = Current character.
 	beqz t0, .Lcompile_end # Exit the loop on the NUL character.
@@ -638,16 +835,10 @@ _compile:
 
 	j .Lcompile_do
 .Lcompile_end:
-
+end
-	# Epilogue.
-	lw ra, 4(sp)
-	lw s0, 0(sp)
-	addi sp, sp, 8
-	ret
 
 # Entry point.
-.type _start, @function
+begin
-_start:
 	# Read the source from the standard input.
 	la a0, source_code
 	la a1, SOURCE_BUFFER_SIZE # Buffer size.
@@ -656,7 +847,4 @@ _start:
 
 	la s1, source_code # s1 = Source code position.
 	call _compile
-
+end.
-	# Call exit.
-	li a0, 0   # Use 0 return code.
-	call exit