04b initial readme, guessing game, compiler fixes

.gitignore

@@ -1,4 +1,7 @@
 README.html
 out??
 out???
+*.out
+tags
+TAGS
 markdown

04b/Makefile

@@ -1,7 +1,11 @@
-all: out03
+all: out03 guessing_game.out out04b README.html
 out03: in03 ../03/out02
 	../03/out02
 %.html: %.md ../markdown
 	../markdown $<
+out04b: in04b out03
+	./out03
+%.out: % out03
+	./out03 $< $@
 clean:
-	rm -f out* README.html
+	rm -f out* README.html *.out

04b/README.md

@@ -0,0 +1,240 @@
+# stage 04
+
+As usual, the source for this compiler is `in03`, an input to the [previous compiler](../03/README.md).
+`in04b` contains a hello world program written in the stage 4 language.
+Here is the core of the program:
+
+```
+main()
+
+function main
+	puts(.str_hello_world)
+	putc(10) ; newline
+	syscall(0x3c, 0)
+```
+
+As you can see, we can now pass arguments to functions. And let's take a look at `putc`:
+
+```
+function putc
+	argument c
+	local p
+	p = &c
+	syscall(1, 1, p, 1)
+	return
+```
+
+It's so simple compared to previous languages! Rather than mess around with registers, we can now
+declare local (and global) variables, and use them directly. These variables will be placed on the
+stack. Since arguments are also placed on the stack,
+by implementing local variables we get arguments for free. There is no difference
+between the `local` and `argument` keywords in this language other than spelling.
+In fact, the number of agruments to a function call is not checked against
+how many arguments the function has. This does make it easy to screw things up by calling a function
+with the wrong number of arguments, but it also means that we can provide a variable number of arguments
+to the `syscall` function. Speaking of which, if you look at the bottom of `in04b`, you'll see:
+
+```
+function syscall
+	...
+	byte 0x48
+	byte 0x8b
+	byte 0x85
+	byte 0xf0
+	byte 0xff
+	byte 0xff
+	byte 0xff
+	...
+```
+
+Originally I was going to make `syscall` a built-in feature of the language, but then I realized that wasn't
+necessary.
+Instead, `syscall` is a function written manually in machine language.
+We can take a look at its decompilation to make things clearer:
+
+```
+mov    rax,[rbp-0x10]
+mov    rdi,rax
+mov    rax,[rbp-0x18]
+mov    rsi,rax
+mov    rax,[rbp-0x20]
+mov    rdx,rax
+mov    rax,[rbp-0x28]
+mov    r10,rax
+mov    rax,[rbp-0x30]
+mov    r8,rax
+mov    rax,[rbp-0x38]
+mov    r9,rax
+mov    rax,[rbp-0x8]
+syscall
+```
+
+This just sets `rax`, `rdi`, `rsi`, etc. to the arguments the function was called with,
+and then does a syscall.
+
+## functions and local variables
+
+In this language, function arguments are placed onto the stack from left to right
+and all arguments and local variables are 8 bytes.
+As a reminder,
+the stack is just an area of memory which is automatically extended downwards (on x86-64, at least).
+So, how do we keep track of the location of local variables in the stack? We could do something like
+this:
+
+```
+sub rsp, 24      ; make room for 3 variables
+mov [rsp], 10    ; variable1 = 10
+mov [rsp+8], 20  ; variable2 = 20
+mov [rsp+16], 30 ; variable3 = 30
+; ...
+add rsp, 24      ; reset rsp
+```
+
+But now suppose that in the middle of the `; ...` code we want another local variable:
+```
+sub rsp, 8 ; make room for another variable
+```
+well, since we've changed `rsp`, `variable1` is now at `rsp+8` instead of `rsp`,
+`variable2` is at `rsp+16` instead of `rsp+8`, and
+`variable3` is at `rsp+24` instead of `rsp+16`.
+Also, we had better make sure we increment `rsp` by `32` now instead of `24`
+to put it back in the right place.
+It would be annoying (but by no means impossible) to keep track of all this.
+We could just declare all local variables at the start of the function,
+but that makes the language more annoying to use.
+
+Instead, we can use the `rbp` register to keep track of what `rsp` was
+at the start of the function:
+
+```
+; save old value of rbp
+sub rsp, 8
+mov [rsp], rbp
+; set rbp to initial value of rsp
+mov rbp, rsp
+
+lea rsp, [rbp-8]  ; add variable1  (this instruction sets rsp to rbp-8)
+mov [rbp-8], 10 ; variable1 = 10
+lea rsp, [rbp-16] ; add variable2
+mov [rbp-16], 20 ; variable2 = 20
+lea rsp, [rbp-24] ; add variable3
+mov [rbp-24], 30 ; variable3 = 30
+; Note that variable1's address is still rbp-8; adding more variables didn't affect it.
+; ...
+
+; restore old values of rbp and rsp
+mov rsp, rbp
+mov rbp, [rsp]
+add rsp, 8
+```
+
+This is actually the intended use of `rbp` (it *p*oints to the *b*ase of the stack frame).
+Note that setting `rsp` very specifically rather than just doing `sub rsp, 8` is important:
+if we skip over some code with a local variable declaration, or execute a local declaration twice,
+we want `rsp` to be in the right place.
+The first three and last three instructions above are called the function *prologue* and *epilogue*.
+They are all the same for all functions; a prologue is generated at the start of every function,
+and an epilogue is generated for every return statement.
+The return value is placed in `rax`.
+
+## global variables
+
+Global variables are much simpler than local ones. The variable `:static_memory_end` in the compiler
+keeps track of where to put the next global variable in memory. It is initialized at address `0x440000`,
+which gives us 256KB for code (and strings). When a global variable is added, `:static_memory_end` is increased
+by its size.
+
+## language description
+
+Comments begin with `;` and may be put at the end of lines
+with or without code.
+Blank lines are ignored.
+
+To make the compiler simpler, this language doesn't support fancy
+expressions like `2 * (3 + 5) / 6`. There is a limited set of possible
+expressions, specifically there are *terms* and *r-values*.
+
+But first, each program is made up of a series of statements, and
+each statement is one of the following:
+- `global {name}` or `global {size} {name}` - declare a global variable with the given size, or 8 bytes if none is provided.
+- `local {name}` - declare a local variable
+- `argument {name}` - declare a function argument. this is functionally equivalent to `local`, so it just exists for readability.
+- `function {name}` - declare a function
+- `:{name}` - declare a label
+- `goto {label}` - jump to the specified label
+- `if {term} {operator} {term} goto {label}` - 
+conditionally jump to the specified label. `{operator}` should be one of
+`==`, `<`, `>`, `>=`, `<=`, `!=`, `[`, `]`, `[=`, `]=`
+(the last four do unsigned comparisons).
+- `{lvalue} = {rvalue}` - set `lvalue` to `rvalue`
+- `{lvalue} += {rvalue}` - add `rvalue` to `lvalue`
+- `{lvalue} -= {rvalue}` - etc.
+- `{lvalue} *= {rvalue}`
+- `{lvalue} /= {rvalue}`
+- `{lvalue} %= {rvalue}`
+- `{lvalue} &= {rvalue}`
+- `{lvalue} |= {rvalue}`
+- `{lvalue} ^= {rvalue}`
+- `{lvalue} <= {rvalue}` - left shift `lvalue` by `rvalue`
+- `{lvalue} >= {rvalue}` - right shift `lvalue` by `rvalue`
+- `{function}({term}, {term}, ...)` - function call, ignoring the return value
+- `return {rvalue}`
+- `string {str}` - places a literal string in the code
+- `byte {number}` - places a literal byte in the code
+
+Now let's get down into the weeds:
+
+A a *number* is one of:
+- `{decimal number}` - e.g. `108` (note: there's no `d` prefix anymore)
+- `0x{hexadecimal number}` - e.g. `0x2f` for 47
+- `'{character}` - e.g. `'a` for 97 (the character code for `a`)
+
+A *term* is one of:
+- `{variable name}` - the value of a (local or global) variable
+- `.{label name}` - the address of a label
+- `{number}`
+
+An *lvalue* is the left-hand side of an assignment expression,
+and it is one of:
+- `{variable}`
+- `*1{variable}` - dereference 1 byte
+- `*2{variable}` - dereference 2 bytes
+- `*4{variable}` - dereference 4 bytes
+- `*8{variable}` - dereference 8 bytes
+
+An *rvalue* is an expression, which can be more complicated than a term.
+rvalues are one of:
+- `{term}`
+- `&{variable}` - address of variable
+- `*1{variable}` / `*2{variable}` / `*4{variable}` / `*8{variable}` - dereference 1, 2, 4, or 8 bytes
+- `~{term}` - bitwise not
+- `{function}({term}, {term}, ...)`
+- `{term} + {term}`
+- `{term} - {term}`
+- `{term} * {term}`
+- `{term} / {term}`
+- `{term} % {term}`
+- `{term} & {term}`
+- `{term} | {term}`
+- `{term} ^ {term}`
+- `{term} < {term}` - left shift
+- `{term} > {term}` - right shift
+
+That's quite a lot of stuff, and it makes for a pretty powerful
+language, all things considered. To test out the language,
+in addition to the hello world program, I also wrote a little
+guessing game, which you can find in the file `guessing_game`.
+It ended up being quite nice to write!
+
+## limitations
+
+Variables in this language do not have types. This makes it very easy to make mistakes like
+treating numbers as pointers or vice versa.
+
+A big annoyance with this language is the lack of local label names. Due to the limited nature
+of branching in this language (`if ... goto ...` stands in for `if`, `else if`, `while`, etc.),
+you need to use a lot of labels, and that means their names can get quite long. But at least unlike
+the 03 language, you'll get an error if you use the same label name twice!
+
+Overall, though, this language ended up being surprisingly powerful. With any luck, the next stage will
+finally be a C compiler...

04b/guessing_game

@@ -0,0 +1,238 @@
+global 0x1000 exit_code
+global y
+y = 4
+exit_code = main()
+exit(exit_code)
+
+function main
+	local secret_number
+	local guess
+	global 32 input_line
+	local p_line
+	p_line = &input_line
+	secret_number = getrand(100)
+	fputs(1, .str_intro)
+	
+	:guess_loop
+		fputs(1, .str_guess)
+		syscall(0, 0, p_line, 30)
+		guess = stoi(p_line)
+		if guess < secret_number goto too_low
+		if guess > secret_number goto too_high
+		fputs(1, .str_got_it)
+		return 0
+		:too_low
+			fputs(1, .str_too_low)
+			goto guess_loop
+		:too_high
+			fputs(1, .str_too_high)
+			goto guess_loop
+
+:str_intro
+	string I'm thinking of a number.
+	byte 10
+	byte 0
+
+:str_guess
+	string Guess what it is:
+	byte 32
+	byte 0
+
+:str_got_it
+	string You got it!
+	byte 10
+	byte 0
+
+:str_too_low
+	string Too low!
+	byte 10
+	byte 0
+
+:str_too_high
+	string Too high!
+	byte 10
+	byte 0
+
+; get a "random" number from 0 to x using the system clock
+function getrand
+	argument x
+	global 16 getrand_time
+	local ptime
+	local n
+	
+	ptime = &getrand_time
+	syscall(228, 1, ptime)
+	ptime += 8 ; nanoseconds at offset 8 in struct timespec
+	n = *4ptime
+	n %= x
+	return n
+
+; returns a pointer to a null-terminated string containing the number given
+function itos
+	global 32 itos_string
+	argument x
+	local c
+	local p
+	p = &itos_string
+	p += 30
+	:itos_loop
+		c = x % 10
+		c += '0
+		*1p = c
+		x /= 10
+		if x == 0 goto itos_loop_end
+		p -= 1
+		goto itos_loop
+	:itos_loop_end
+	return p
+
+
+; returns the number at the start of the given string
+function stoi
+	argument s
+	local p
+	local n
+	local c
+	n = 0
+	p = s
+	:stoi_loop
+		c = *1p
+		if c < '0 goto stoi_loop_end
+		if c > '9 goto stoi_loop_end
+		n *= 10
+		n += c - '0
+		p += 1
+		goto stoi_loop
+	:stoi_loop_end
+	return n
+
+
+function strlen
+	argument s
+	local c
+	local p
+	p = s
+	:strlen_loop
+		c = *1p
+		if c == 0 goto strlen_loop_end
+		p += 1
+		goto strlen_loop
+	:strlen_loop_end
+	return p - s
+
+function fputs
+	argument fd
+	argument s
+	local length
+	length = strlen(s)
+	syscall(1, fd, s, length)
+	return
+	
+
+function fputn
+	argument fd
+	argument n
+	local s
+	s = itos(n)
+	fputs(fd, s)
+	return
+
+function exit
+	argument status_code
+	syscall(0x3c, status_code)
+
+function syscall
+	; I've done some testing, and this should be okay even if
+	; rbp-56 goes beyond the end of the stack.
+	; mov rax, [rbp-16]
+	byte 0x48
+	byte 0x8b
+	byte 0x85
+	byte 0xf0
+	byte 0xff
+	byte 0xff
+	byte 0xff
+	; mov rdi, rax
+	byte 0x48
+	byte 0x89
+	byte 0xc7
+	
+	; mov rax, [rbp-24]
+	byte 0x48
+	byte 0x8b
+	byte 0x85
+	byte 0xe8
+	byte 0xff
+	byte 0xff
+	byte 0xff
+	; mov rsi, rax
+	byte 0x48
+	byte 0x89
+	byte 0xc6
+	
+	; mov rax, [rbp-32]
+	byte 0x48
+	byte 0x8b
+	byte 0x85
+	byte 0xe0
+	byte 0xff
+	byte 0xff
+	byte 0xff
+	; mov rdx, rax
+	byte 0x48
+	byte 0x89
+	byte 0xc2
+	
+	; mov rax, [rbp-40]
+	byte 0x48
+	byte 0x8b
+	byte 0x85
+	byte 0xd8
+	byte 0xff
+	byte 0xff
+	byte 0xff
+	; mov r10, rax
+	byte 0x49
+	byte 0x89
+	byte 0xc2
+	
+	; mov rax, [rbp-48]
+	byte 0x48
+	byte 0x8b
+	byte 0x85
+	byte 0xd0
+	byte 0xff
+	byte 0xff
+	byte 0xff
+	; mov r8, rax
+	byte 0x49
+	byte 0x89
+	byte 0xc0
+	
+	; mov rax, [rbp-56]
+	byte 0x48
+	byte 0x8b
+	byte 0x85
+	byte 0xc8
+	byte 0xff
+	byte 0xff
+	byte 0xff
+	; mov r9, rax
+	byte 0x49
+	byte 0x89
+	byte 0xc1
+	
+	; mov rax, [rbp-8]
+	byte 0x48
+	byte 0x8b
+	byte 0x85
+	byte 0xf8
+	byte 0xff
+	byte 0xff
+	byte 0xff
+	
+	; syscall
+	byte 0x0f
+	byte 0x05
+	
+	return

04b/in03

@@ -4,28 +4,54 @@ D=:global_variables
 8C=D
 ; initialize static_memory_end
 C=:static_memory_end
-; 0x40000 = 256KB for code
+; 0x80000 = 512KB for code
-D=x440000
+D=x480000
 8C=D
 ; initialize labels_end
 C=:labels_end
 D=:labels
 8C=D
 
-; open input file
+I=8S
-	J=:input_filename
+A=d2
+?I>A:argv_file_names
+	; use default input/output filenames
+	; open input file
+		J=:input_filename
+		I=d0
+		syscall x2
+		J=A
+		?J<0:input_file_error
+	; open output file
+		J=:output_filename
+		I=x241
+		D=x1ed
+		syscall x2
+		J=A
+		?J<0:output_file_error
+	!:second_pass_starting_point
+:argv_file_names
+	; open input file
+	J=S
+	; argv[1] is at *(rsp+16)
+	J+=d16
+	J=8J
 	I=d0
 	syscall x2
 	J=A
 	?J<0:input_file_error
-; open output file
+	; open output file
-	J=:output_filename
+	J=S
+	; argv[2] is at *(rsp+24)
+	J+=d24
+	J=8J
 	I=x241
 	D=x1ed
 	syscall x2
 	J=A
 	?J<0:output_file_error
 
+
 :second_pass_starting_point
 ; write ELF header
 J=d4
@@ -161,15 +187,16 @@ call :string=
 D=A
 ?D!0:handle_if
 
-; set delimiter to newline
-C=xa
-
 I=:line
 J=:"function"
 call :string=
 D=A
 ?D!0:handle_function
 
+
+; set delimiter to newline
+C=xa
+
 I=:line
 J=:"return\n"
 call :string=
@@ -203,6 +230,7 @@ I=:line
 	!:call_check_loop
 :call_check_loop_end
 
+!:bad_statement
 
 !:read_line
 
@@ -217,6 +245,7 @@ I=:line
 	J=d4
 	I=:static_memory_end
 	I=8I
+	I-=x400000
 	syscall x4d
 	; seek both files back to start
 	J=d3
@@ -292,15 +321,6 @@ align
 	!:read_line
 	
 :handle_local
-	R=I
-	
-	; emit sub rsp, 8
-	J=d4
-	I=:sub_rsp_8
-	D=d7
-	syscall x1
-	
-	I=R
 	; skip ' '
 	I+=d1
 	
@@ -333,23 +353,36 @@ align
 	; update :local_variables_end
 	I=:local_variables_end
 	8I=J
+	
+	; set rsp appropriately
+	C=:rbp_offset
+	J=d0
+	J-=D
+	4C=J
+
+	J=d4
+	I=:lea_rsp_[rbp_offset]
+	D=d7
+	syscall x1
+	
+	
 	; read the next line
 	!:read_line
 
-:sub_rsp_8
+:lea_rsp_[rbp_offset]
 	x48
-	x81
+	x8d
-	xec
+	xa5
-	x08
+:rbp_offset
-	x00
+	reserve d4
-	x00
-	x00
 
 align
 :global_start
 	reserve d8
 :global_variable_name
 	reserve d8
+:global_variable_size
+	reserve d8
 :handle_global
 	; ignore if this is the second pass
 	C=:second_pass
@@ -359,6 +392,27 @@ align
 	; skip ' '
 	I+=d1
 	
+	C=1I
+	D='9
+	?C>D:global_default_size
+		; read specific size of global
+		call :read_number
+		D=A
+		C=:global_variable_size
+		8C=D
+		; check and skip space after number
+		C=1I
+		D=x20
+		?C!D:bad_number
+		I+=d1
+		!:global_cont
+	:global_default_size
+		; default size = 8
+		C=:global_variable_size
+		D=d8
+		8C=D
+	:global_cont
+		
 	; store away pointer to variable name
 	C=:global_variable_name
 	8C=I
@@ -380,8 +434,11 @@ align
 	C=4D
 	4J=C
 	J+=d4
-	; increase static_memory_end
+	; increase static_memory_end by size
-	C+=d8
+	D=:global_variable_size
+	D=8D
+	C+=D
+	D=:static_memory_end
 	4D=C
 	; store null terminator
 	1J=0
@@ -392,6 +449,12 @@ align
 	!:read_line
 
 :handle_function
+	I=:line
+	; length of "function "
+	I+=d9
+	; make function name a label
+	call :add_label
+	
 	; emit prologue
 	J=d4
 	I=:function_prologue
@@ -450,14 +513,25 @@ align
 	; total length = 15 bytes
 
 :handle_label_definition
+	I=:line
+	I+=d1
+	call :add_label
+	!:read_line
+
+align
+:label_name
+	reserve d8
+; add the label in rsi to the label list (with the current pc address)
+:add_label
 	; ignore if this is the second pass
 	C=:second_pass
 	C=1C
-	?C!0:read_line
+	?C!0:return_0
+	
+	C=:label_name
+	8C=I
 	
 	; make sure label only has identifier characters
-	I=:line
-	I+=d1
 	:label_checking_loop
 		C=1I
 		D=xa
@@ -470,8 +544,8 @@ align
 		!:bad_label
 	:label_checking_loop_end
 	
-	I=:line
+	C=:label_name
-	I+=d1
+	I=8C
 	J=:labels
 	call :ident_lookup
 	C=A
@@ -479,8 +553,8 @@ align
 	
 	J=:labels_end
 	J=8J
-	I=:line
+	C=:label_name
-	I+=d1
+	I=8C
 	call :ident_copy
 	R=J
 	
@@ -500,8 +574,7 @@ align
 	C=:labels_end
 	8C=J
 	
-	; read the next line
+	return
-	!:read_line
 
 :handle_goto
 	J=d4
@@ -2004,6 +2077,15 @@ align
 	xa
 	x0
 
+:bad_statement
+	B=:bad_statement_error_message
+	!:program_error
+
+:bad_statement_error_message
+	str Bad statement.
+	xa
+	x0
+
 :bad_jump
 	B=:bad_jump_error_message
 	!:program_error
@@ -2205,6 +2287,7 @@ align
 		1J=D
 		J-=d1
 		?I!0:eputn_loop
+	J+=d1
 	D=S
 	D-=J
 	I=J
@@ -2271,7 +2354,7 @@ align
 	x20
 :"function"
 	str function
-	xa
+	x20
 :"=="
 	str ==
 	x20

04b/in04b

@@ -1,93 +1,42 @@
-; declaration:
-;     global <name>
-;     local <name>
-;     argument <name>
-;     :<label>
-; statement:
-;     <declaration>
-;     if <term> <==/</>/>=/<=/!=/[/]/[=/]=> <term> goto <label>   NOTE: this uses signed comparisons
-;     goto <label>
-;     <lvalue> = <rvalue>
-;     <lvalue> += <rvalue>
-;     <lvalue> -= <rvalue>
-;     <function>(<term>, <term>, ...)
-;     return <rvalue>
-;     string <str>
-;     byte <number>
-; term:
-;     <var>
-;     .<label>
-;     <number>
-; number:
-;     'c
-;     12345
-;     0xabc
-; lvalue:
-;     <var>
-;     *1<var> / *2<var> / *4<var> / *8<var>
-; rvalue:
-;     <term>
-;     &<var>
-;     *1<var> / *2<var> / *4<var> / *8<var>
-;     ~<term>
-;     <function>(<term>, <term>, ...)
-;     <term> + <term>
-;     <term> - <term>
-;    NOTE: *, /, % are signed (imul and idiv)
-;     <term> * <term>
-;     <term> / <term>
-;     <term> % <term>
-;     <term> & <term>
-;     <term> | <term>
-;     <term> ^ <term>
-;     <term> < <term>  (left shift)
-;     <term> > <term>  (unsigned right shift)
-
 main()
 
-:main
+function main
-function
 	puts(.str_hello_world)
 	putc(10) ; newline
 	syscall(0x3c, 0)
-:str_hello_world
-string Hello, world!
-byte 0
 
-:strlen
+:str_hello_world
-function
+	string Hello, world!
+	byte 0
+
+function strlen
 	argument s
-	local len
 	local c
 	local p
-	len = 0
+	p = s
 	:strlen_loop
-		p = s + len
 		c = *1p
 		if c == 0 goto strlen_loop_end
-		len += 1
+		p += 1
 		goto strlen_loop
 	:strlen_loop_end
-	return len
+	return p - s
 
-:putc
+function putc
-function
 	argument c
 	local p
 	p = &c
 	syscall(1, 1, p, 1)
 	return
 
-:puts
+function puts
-function
 	argument s
 	local len
 	len = strlen(s)
 	syscall(1, 1, s, len)
 	return
 
-:syscall
+function syscall
-function
 	; I've done some testing, and this should be okay even if
 	; rbp-56 goes beyond the end of the stack.
 	; mov rax, [rbp-16]

README.md

@@ -26,6 +26,8 @@ command codes.
 - [stage 02](02/README.md) - a language with labels
 - [stage 03](03/README.md) - a language with longer labels, better error messages, and less register manipulation
 - more coming soon (hopefully)
+- [stage 04a](04a/README.md) - (interlude) a very simple preprocessor
+- [stage 04b](04b/README.md) - a language with nice functions and local variables
 
 ## prerequisite knowledge
 
@@ -46,6 +48,7 @@ decimal.
 - what a CPU is
 - what a CPU architecture is
 - what a CPU register is
+- what the (call) stack is
 - bits, bytes, kilobytes, etc.
 - bitwise operations (not, or, and, xor, left shift, right shift)
 - 2's complement

instructions.txt

@@ -43,6 +43,8 @@ mov rax, qword [rbp+imm32]
 >48 8b 85 IMM32    (note: imm may be negative)
 lea rax, [rbp+imm32]
 >48 8d 85 IMM32    (note: imm may be negative)
+lea rsp, [rbp+imm32]
+>48 8d a5 IMM32    (note: imm may be negative)
 mov qword [rbp+imm32], rax
 >48 89 85 IMM32    (note: imm may be negative)
 mov qword [rsp+imm32], rax