X-Git-Url: https://git.lukelau.me/?p=scheme.git;a=blobdiff_plain;f=codegen.scm;h=dededbec01e0856b19703d8945e096e49b316aa5;hp=4848d4ddfa98731899f6b2ca92413b45eb3086ce;hb=8e106ca13666680051f91ab3f49ce2bd7e19ead7;hpb=dea4c4e4d1be8c0a90bb165bde1e362dc204e061

diff --git a/codegen.scm b/codegen.scm
index 4848d4d..dededbe 100644
--- a/codegen.scm
+++ b/codegen.scm
@@ -1,11 +1,48 @@
 (load "typecheck.scm")
 (load "ast.scm")
+(load "platform.scm")
+
+(define target host-os)
 
 (define (emit . s)
   (begin
     (apply printf s)
     (display "\n")))
 
+(define wordsize 8)
+
+(define (type-size data-layouts type)
+
+  (define (adt-size adt)
+    (let ([sizes
+	   (map (lambda (sum)
+		  (fold-left (lambda (acc x) (+ acc (type-size data-layouts x)))
+			     wordsize ; one word needed to store tag
+			     (cdr sum)))
+		(cdr adt))])
+      (apply max sizes)))
+  
+  (case type
+    ['Int wordsize]
+    ['Bool wordsize]
+    [else
+     (let ([adt (assoc type data-layouts)])
+       (if adt
+	   (adt-size adt)
+	   (error #f "unknown size" type)))]))
+
+(define (on-stack? expr)
+  (case (ast-type expr)
+    ['stack (cadr expr)]
+    [else #f]))
+
+					; an environment consists of adt layouts in scope,
+					; and any bound variables.
+					; bound variables are an assoc list with their stack offset
+(define make-env list)
+(define env-data-layouts car)
+(define env-bindings cadr)
+
 (define (codegen-add xs si env)
   (define (go ys)
     (if (null? ys)
@@ -43,9 +80,11 @@
   (codegen-expr a si env)
   (emit "movq %rax, ~a(%rbp)" si)
   (codegen-expr b (- si wordsize) env)
-  (emit "subq ~a(%rbp), %rax" si)
-  (emit "not %rax")
-  (emit "andq $1, %rax"))
+  (emit "## ~a = ~b" a b)
+  (emit "cmpq ~a(%rbp), %rax" si)
+  (emit "sete %al"))
+
+					; 'write file handle addr-string num-bytes
 
 (define (codegen-print x si env)
   (codegen-expr x si env) ; x should be a static-string, producing a label
@@ -63,109 +102,244 @@
   (emit "not %rcx")      ; -%rcx = strlen + 1
   (emit "dec %rcx")
   
-  (emit "mov %rcx, %rdx") ; number of bytes
-  (emit "mov %rbx, %rsi") ; addr of string
-  (emit "mov $1, %rax") ; file handle 1 (stdout)
-  (emit "mov $1, %rdi") ; syscall 1 (write)
+  (emit "movq %rbx, %rsi") ; string addr
+  (emit "movq %rcx, %rdx") ; num bytes
+  (emit "movq $1, %rdi")   ; file handle (stdout)
+  (case target
+    ('darwin (emit "mov $0x2000004, %rax")) ; syscall 4 (write)
+    ('linux  (emit "mov $1, %rax"))) ; syscall 1 (write)
   (emit "syscall"))
 
-(define (range s n)
-  (if (= 0 n) '()
-      (append (range s (- n 1))
-	      (list (+ s (- n 1))))))
+(define (codegen-let bindings body si env)
 
-(define wordsize 8)
+					; is this a closure that captures itself?
+					; e.g. (let ([x 3] [f (closure lambda0 (f x))]) (f))
+  (define (self-captive-closure? name expr)
+    (and (eqv? (ast-type expr) 'closure)
+	 (memv name (caddr expr))))
+
+
+  ;; (define (emit-scc scc env)
+  ;;   ; acc is a pair of the env and list of touchups
+  ;;   (define (emit-binding acc binding)
+  ;;     (let ([binding-name (car binding)]
+  ;; 	    [binding-body (cadr binding)]
+
+  ;; 	    [other-bindings (filter
+  ;; 			     (lambda (x) (not (eqv? binding-name x)))
+  ;; 			     scc)]
+  ;; 	    [mutually-recursives
+  ;; 	     (filter
+  ;; 	      (lambda (other-binding)
+  ;; 		(memv other-binding (references binding-body)))
+  ;; 	      other-bindings)]
+
+  ;; 	    [new-touchups (append touchups (cdr acc))])
+
+  ;; 					; TODO: assert that the only mutually recursives are closures
+  ;; 	(for-each
+  ;; 	 (lambda (binding)
+  ;; 	   (when (not (eqv? (ast-type (cadr binding))
+	
+  ;; 	(emit "asdf")
+  ;; 	(cons new-env new-touchups)
+  ;; 	))
+
+  ;;   (fold-left emit-binding (cons env '()) scc))))
+  
+  (let* ([stack-offsets (map (lambda (name x) ; assoc map of binding name to offset
+			       (cons name (- si (* x wordsize))))
+			     (map car bindings)
+			     (range 0 (length bindings)))]
+	 [inner-si (- si (* (length bindings) wordsize))]
+
+	 [get-offset (lambda (n) (cdr (assoc n stack-offsets)))]
+	 
+	 [inner-env
+	  (fold-left
+	   (lambda (env comps)
+	     (let* ([scc-binding-offsets
+		     (fold-left
+		      (lambda (acc name)
+			(cons (cons name (get-offset name))
+			      acc))
+		      (env-bindings env)
+		      comps)]
+		    [scc-env (make-env (env-data-layouts env) scc-binding-offsets)])
+	       (for-each 
+		(lambda (name)
+		  (let ([expr (cadr (assoc name bindings))])
+		    (emit "## generating ~a with scc-env ~a" name scc-env)
+		    (if (self-captive-closure? name expr)
+					; if self-captive, insert a flag into the environment to let
+					; codegen-closure realise this!
+			(codegen-expr expr
+				      inner-si
+				      (make-env
+				       (env-data-layouts scc-env)
+				       (cons (cons name 'self-captive)
+					     (env-bindings scc-env))))
+			(codegen-expr expr inner-si scc-env))
+		    (emit "movq %rax, ~a(%rbp)" (get-offset name))))
+		comps)
+	       scc-env))
+	   env
+	   (reverse (sccs (graph bindings))))])
     
-(define (codegen-let bindings body si env)
-  (let* ((stack-offsets (map (lambda (x) (- si (* x wordsize)))
-			     (range 0 (length bindings))))
-	 (inner-si (- si (* (length bindings) wordsize)))
-	 (names (map car bindings))
-	 (exprs (map cadr bindings))
-
-	 ; recursive let bindings: build environment as we go
-	 (inner-env (fold-left
-		     (lambda (env name expr offset)
-		       (codegen-expr expr inner-si env)
-		       (emit "movq %rax, ~a(%rbp)" offset)
-		       (cons (cons name offset) env))
-		     env names exprs stack-offsets)))
     (for-each (lambda (form)
 		(codegen-expr form inner-si inner-env))
 	      body)))
 
 (define (codegen-var name si env)
-  (when (not (assoc name env))
-    (error #f (format "Variable ~a is not bound" name)))
-  (let ((offset (cdr (assoc name env))))
-    (emit "movq ~a(%rbp), %rax" offset)))
+  (let ([binding (assoc name (env-bindings env))])
+    (if (not binding)
+	(error #f (format "Variable ~a is not bound" name))
+	(emit "movq ~a(%rbp), %rax" (cdr binding)))))
 
 (define cur-lambda 0)
 (define (fresh-lambda)
   (set! cur-lambda (+ 1 cur-lambda))
   (format "_lambda~a" (- cur-lambda 1)))
 
-					; for now we can only call closures
-(define (codegen-call closure args si env)
-  (when (not (eq? (ast-type closure) 'closure))
-    (error #f (format "~a is not a closure" closure)))
-  (let* ((captured (caddr closure))
-	 (label (cadr closure))
-	 (argument-start (length captured)))
-
-					; first move the captured variables into param registers
+					; a closure on the heap looks like:
+					; 0    8         16        24
+					; addr var1....  var2....  var3....
+
+(define (codegen-closure label captured si env)
+  (let* ((heap-offsets (map (lambda (i) (+ 8 (* 8 i)))
+			    (range 0 (length captured))))) ; 4, 12, 20, etc.
+
+    (emit "## creating closure")
+
+    (emit "movq heap_start@GOTPCREL(%rip), %rbx")
+    
+    (emit "movq (%rbx), %rax")          ; %rax = heap addr of closure
+
+
+					; point heap_start to next space
+    (emit "addq $~a, (%rbx)" (+ 8 (* 8 (length captured))))
+
+    (emit "## storing address to lambda")
+					; store the address to the lambda code
+    (emit "movq ~a@GOTPCREL(%rip), %rbx" label)
+    (emit "movq %rbx, 0(%rax)")
+
+    (emit "## storing captives")
+					; store the captured vars
     (for-each
-     (lambda (e i)
-       (emit "movq ~a(%rbp), ~a"
-	     (cdr (assoc e env)) ; offset of the var
-	     (param-register i)))
-     captured (range 0 (length captured)))
+     (lambda (var-name heap-offset)
+       (let ([stack-offset (cdr (assoc var-name (env-bindings env)))])
+	 (emit "### captive ~a" var-name)
+	 (if (eqv? stack-offset 'self-captive)
+					; captive refers to this closure:
+					; move heap addr of this closure to stack! 
+	     (emit "movq %rax, ~a(%rax)" heap-offset)
+	     (begin
+	       (emit "movq ~a(%rbp), %rbx" stack-offset)
+	       (emit "movq %rbx, ~a(%rax)" heap-offset)))))
+     captured
+     heap-offsets)))
 
+					; for now we can only call closures
+(define (codegen-call f args si env)
+  (codegen-expr f si env)
 
-					; then codegen the arguments and move them into the next param registers
+  (emit "## starting call")
+  
+  (emit "movq %rax, ~a(%rbp)" si) ; store address of closure first on stack
+  
+					; codegen the arguments, store them intermediately
   (for-each
    (lambda (e i)
      (begin
-	 (codegen-expr e si env)
-					; move result to correct param register
-	 (emit "movq %rax, ~a" (param-register i))))
-     args (range argument-start (length args)))
+       (emit "## arg no. ~a" (- i 1))
+       (codegen-expr e (- si (* wordsize i)) env)
+					; store intermediate result on stack
+       (emit "movq %rax, ~a(%rbp)" (- si (* wordsize i)))))
+
+   args (range 1 (length args)))
+
+					; now that we have everything we need on the stack,
+					; move them into the param registers
+
+  (emit "## moving args into place")
+  (for-each
+   (lambda (i) (emit "movq ~a(%rbp), ~a"
+		     (- si (* wordsize i))
+		     (param-register i)))
+   (range 1 (length args)))
+
+					; todo: can this be made more efficient
+  (emit "movq ~a(%rbp), %rax" si)       ; load back pointer to closure
+
+  (emit "## moving captives into place")
+  
+					; move captives into first argument
+  (emit "movq %rax, %rbx")
+  (emit "addq $8, %rbx")
+  (emit "movq %rbx, ~a" (param-register 0))
+
+  (emit "## performing call")
 
   (emit "addq $~a, %rsp" si) ; adjust the stack pointer to account all the stuff we put in the env
-    (emit "callq ~a" label)
-    (emit "subq $~a, %rsp" si)))
+  (emit "callq *(%rax)")                ; call closure function
+  (emit "subq $~a, %rsp" si))
+
+					; LAMBDAS:
+					; 1st param: pointer to captured args
+					; 2nd param: 1st arg
+					; 3rd param: 2nd arg, etc.
 
 (define (codegen-lambda l)
   (let* ((label (car l))
-	 (args (cadr l))
-	 (captured (caddr l))
-	 (body (cadddr l))
+	 (stuff (cdr l))
+	 (captives (car stuff))
+	 (args (cadr stuff))
+	 (body (caddr stuff))
 					; params = what actually gets passed
-	 (params (append captured args))
+	 (params (append captives args))
 
-	 (param-registers (map param-register
-			       (range 0 (length params))))
 	 (stack-offsets (map (lambda (i)
-			       (* (- wordsize) i))
-			     (range 1 (length params))))
-
-	 (copy-insts (map (lambda (r o)
-			    (format "movq ~a, ~a(%rbp)" r o))
-			  param-registers stack-offsets))
+			       (* (- wordsize) (+ 1 i)))
+			     (range 0 (length params))))
 
-	 (env (map cons params stack-offsets)))
+	 [bindings (map cons params stack-offsets)]
+	 [env (make-env '() bindings)])
     (emit "~a:" label)
+
+    (display "## lambda captives: ")
+    (display captives)
+    (newline)
+    (display "## lambda args: ")
+    (display args)
+    (newline)
     (display "## lambda body: ")
     (display body)
     (newline)
-    (display "## environment: ")
-    (display env)
-    (newline)
     
     (emit "push %rbp") ; preserve caller's base pointer
+    
     (emit "movq %rsp, %rbp") ; set up our own base pointer
 
-    (for-each emit copy-insts)
+					; load the captured vars onto the stack
+    (for-each
+     (lambda (i)
+       (begin
+	 (emit "# loading captive ~a" (list-ref captives i))
+	 (emit "movq ~a(~a), %rbx" (* wordsize i) (param-register 0))
+	 (emit "movq %rbx, ~a(%rbp)" (* (- wordsize) (+ 1 i)))))
+     (range 0 (length captives)))
+
+					; load the args onto the stack
+    (for-each
+     (lambda (i)
+       (begin
+	 (emit "movq ~a, %rbx" (param-register (+ 1 i)))
+	 (emit "movq %rbx, ~a(%rbp)"
+	       (* (- wordsize)
+		  (+ 1 (length captives) i)))))
+     (range 0 (length args)))
+    
     (codegen-expr body (* (- wordsize) (+ 1 (length params))) env)
 
     (emit "pop %rbp") ; restore caller's base pointer
@@ -188,13 +362,88 @@
     (codegen-expr else si env)
     (emit "~a:" exit-label)))
 
+(define (data-tor env e)
+  (if (not (list? e)) #f    
+      (assoc (car e) (flat-map data-tors (env-data-layouts env)))))
+
+					; returns the internal offset in bytes of a product within an ADT
+					; given the constructor layout
+					; constructor-layout: (foo (Int Bool))
+(define (data-product-offset data-layouts type sum index)
+  (let* ([products (cdr (assoc sum (cdr (assoc type data-layouts))))]
+	 [to-traverse (list-head products index)])
+    (fold-left
+     (lambda (acc t) (+ acc (type-size data-layouts t)))
+     wordsize ; skip the tag in the first word
+     to-traverse)))
+
+(define (data-sum-tag data-layouts type sum)
+
+  (define (go acc sums)
+    (when (null? sums) (error #f "data-sum-tag no sum for type" sum type))
+    (if (eqv? sum (car sums))
+	acc
+	(go (+ 1 acc) (cdr sums))))
+  (let* ([type-sums (cdr (assoc type data-layouts))])
+    (go 0 (map car type-sums))))
+
+(define (codegen-data-tor e si env)
+
+  (define (codegen-destructor tor)
+    (let* ([res (codegen-expr (cadr e) si env)]
+	   [info (cadr tor)]
+	   [index (caddr info)]
+	   [type (car info)]
+	   [sum (cadr info)])
+      (when (not (stack-expr? res))
+	(error #f "codegened something that wasn't a stack expression"))
+					;TODO handle stack types
+      (emit "movq ~a(%rbp), %rax"
+	    (- si (data-product-offset (env-data-layouts env) type sum index)))))				      
+
+  (define (codegen-constructor tor)
+    (let* ([info (cadr tor)]
+	   [type (car info)]
+	   [sum (cadr info)]
+	   [constructor (car e)]
+
+	   [args (cdr e)]
+
+	   [tag (data-sum-tag (env-data-layouts env)
+			      type
+			      sum)]
+	   
+	   [insert-product
+	    (lambda (expr i)
+	      (let ([res (codegen-expr expr si env)]
+		    [stack-offset (- si (data-product-offset (env-data-layouts env)
+							     type sum
+							     i))])
+		(if (stack-expr? res)
+		    (error #f "todo: handle stack-exprs in stack exprs")
+		    (emit "movq %rax, ~a(%rbp)" stack-offset))))])
+
+					; emit the tag
+      (emit "movq $~a, ~a(%rbp)" tag si)
+      
+      (for-each insert-product args (range 0 (length args)))
+      (type-size (env-data-layouts env) type)))
+  
+  (let* ([tor (data-tor env e)]
+	 [constructor (eqv? 'constructor (caddr (cadr tor)))])
+    (if constructor
+	(codegen-constructor tor)
+	(codegen-destructor tor))))
+
+(define stack-expr? number?)
+
+					; returns a number if result was stored on stack 
 (define (codegen-expr e si env)
+  (emit "# ~a" e)
   (case (ast-type e)
-    ('builtin e)
-    ('closure e)
+    ('closure (codegen-closure (cadr e) (caddr e) si env))
     ('app
-     (let ((callee (codegen-expr (car e) si env)))
-       (case callee
+     (case (car e)
        ('+ (codegen-add (cdr e) si env))
        ('- (codegen-sub (cadr e) (caddr e) si env))
        ('* (codegen-mul (cadr e) (caddr e) si env))
@@ -202,7 +451,14 @@
        ('= (codegen-eq  (cadr e) (caddr e) si env))
        ('bool->int (codegen-expr (cadr e) si env))
        ('print (codegen-print (cadr e) si env))
-	 (else (codegen-call callee (cdr e) si env)))))
+       (else
+	(if (data-tor env e)
+	    (codegen-data-tor e si env)
+	    (codegen-call (car e) (cdr e) si env)))))
+
+					; this is a builtin being passed around as a variable
+					; this should have been converted to a closure!
+    ('builtin (error #f "passing about a builtin!" e))
 
     ('let (codegen-let (let-bindings e)
 		       (let-body e)
@@ -216,35 +472,57 @@
     ('bool-literal (emit "movq $~a, %rax" (if e 1 0)))
     ('int-literal (emit "movq $~a, %rax" e))
     
-    ('static-string (emit "lea ~a, %rax" (cadr e))) ; move label
+    ('static-string (emit "movq ~a@GOTPCREL(%rip), %rax"
+			  (cadr e)))
 
-    (else (error #f "don't know how to codegen this"))))
+    ('stack (codegen-expr (caddr e) si env))
 
+    (else (error #f "don't know how to codegen this"))))
 
-(define (fold-map f x) (fold-left append '() (map f x)))
+					; takes in a expr annotated with types and returns a type-less AST
+					; with stack values wrapped
+(define (annotate-stack-values data-layout ann-e)
+  (define (stack-type? type)
+    (assoc type data-layout))
+  (define (strip e)
+    (ast-traverse strip (ann-expr e)))
+  (let* ([e (ann-expr ann-e)]
+	 [type (ann-type ann-e)])
+    (if (stack-type? type)
+	`(stack ,type ,(ast-traverse strip e))
+	(ast-traverse (lambda (x)
+			(annotate-stack-values data-layout x))
+		      e))))
 
 (define (free-vars prog)
   (define bound '())
   (define (collect e)
     (case (ast-type e)
       ('builtin '()) ; do nothing
-      ('var (if (memq e bound) '() (list e)))
+      ('var (if (memv e bound) '() (list e)))
       ('lambda
+	  (begin
 	    (set! bound (append (lambda-args e) bound))
-	(collect (lambda-body e)))
+	    (collect (lambda-body e))))
 
-      ('app (fold-map collect e))
+      ('app (flat-map collect e))
+      ('if (flat-map collect (cdr e)))
       ('let
-	  (let ((bind-fvs (fold-map (lambda (a)
-				      ((set! bound (cons (car a) bound))
+	  (let ([bind-fvs (flat-map (lambda (a)
+				      (begin
+					(set! bound (cons (car a) bound))
 					(collect (cdr a))))
-				    (let-bindings cadr)))
-		(body-fvs (fold-map collect (let-body e))))
-	    (append bind-fvs body-fvs)))
+				    (let-bindings e))])
+	    (append bind-fvs (flat-map collect (let-body e)))))
       (else '())))
   (collect prog))
 
-					; ((lambda (x) (+ x 1)) 42) => {lambda0: (x) (+ x 1)}, (@lambda0 42)
+					; ((lambda (x) (+ x y)) 42) => ((closure lambda1 (y)) 42)
+                                        ;                              [(lambda1 . ((y), (x), (+ x y))]
+					; for builtins, this generates a closure if it is used
+					; outside of an immediate app
+					; but only one closure for each builtin
+
 (define (extract-lambdas program)
   (define lambdas '())
   (define (add-lambda e)
@@ -252,16 +530,62 @@
 	   (args (lambda-args e))
 	   (captured (free-vars e))
 	   (body (extract (lambda-body e)))
-	   (new-lambda (list label args captured body)))
+	   (new-lambda (cons label (list captured args body))))
       (set! lambdas (cons new-lambda lambdas))
       `(closure ,label ,captured))) ; todo: should we string->symbol?
+
+  (define (find-builtin-lambda e)
+    (let [(l (assq (builtin-name e) lambdas))]
+      (if l `(closure ,(car l) ,(caadr l)) #f)))
+
+  (define (builtin-name e)
+    (case e
+      ('+ "_add")
+      ('- "_sub")
+      ('* "_mul")
+      ('! "_not")
+      ('= "_eq")
+      ('bool->int "_bool2int")
+      ('print "_print")
+      (else (error #f "don't know this builtin"))))
+  (define (builtin-args e)
+    (case e
+      ('+ '(x y))
+      ('- '(x y))
+      ('* '(x y))
+      ('! '(x))
+      ('= '(x y))
+      ('bool->int '(x))
+      ('print '(x))
+      (else (error #f "don't know this builtin"))))
+
+  (define (add-builtin-lambda e)
+    (let* [(label (builtin-name e))
+	   (captured '())
+	   (args (builtin-args e))
+	   (body `(,e ,@args))
+	   (new-lambda (cons label (list captured args body)))]
+      (set! lambdas (cons new-lambda lambdas))
+      `(closure ,label ,captured)))
+  
   (define (extract e)
     (case (ast-type e)
       ('lambda (add-lambda e))
-      ('let `(let ,(map extract (let-bindings e))
+      ('let `(let ,(map (lambda (b) `(,(car b) ,@(extract (cdr b)))) (let-bindings e))
 	       ,@(map extract (let-body e))))
-      ('app (append (list (extract (car e)))
+      ('app (append
+					; if a builtin is used as a function, don't generate lambda
+	     (if (eqv? 'builtin (ast-type (car e)))
+		 (list (car e))
+		 (list (extract (car e))))
 	     (map extract (cdr e))))
+      
+      ('builtin
+       (if (find-builtin-lambda e)
+	   (find-builtin-lambda e)
+	   (add-builtin-lambda e)))
+
+      
       (else (ast-traverse extract e))))
   (let ((transformed (extract program)))
     (cons lambdas transformed)))
@@ -286,29 +610,6 @@
   (emit "~a:" (car s))
   (emit "\t.string \"~a\"" (cdr s)))
 
-;; (define (amd64-abi f)
-;; 					; preserve registers
-;;   (emit "push %rbp")
-;;   ;; (emit "push %rbx")
-;;   ;; (for-each (lambda (i)
-;;   ;; 	      (emit (string-append
-;;   ;; 		     "push %r"
-;;   ;; 		     (number->string i))))
-;;   ;; 	    '(12 13 14 15))
-
-;;   (emit "movq %rsp, %rbp")              ; set up the base pointer
-
-;;   (f) ; call stuff
-;; 					; restore preserved registers
-;;   ;; (for-each (lambda (i)
-;;   ;; 	      (emit (string-append
-;;   ;; 		     "pop %r"
-;;   ;; 		     (number->string i))))
-;;   ;; 	    '(15 14 13 12))
-;;   ;; (emit "pop %rbx")
-;;   (emit "pop %rbp")
-;;   (emit "ret"))
-
 					; 24(%rbp) mem arg 1
 					; 16(%rbp) mem arg 0          prev frame
 					; -----------------------
@@ -329,12 +630,44 @@
     (else (error #f "need to test out the below"))
     (else (format "~a(%rsp)" (- n 6)))))
 
+(define (initialize-heap)
+  (let ((mmap
+	 (case target
+	   ('darwin "0x20000c5")
+	   ('linux "9"))))
+					; allocate some heap memory
+    (emit "mov $~a, %rax" mmap) ; mmap
+    (emit "xor %rdi, %rdi")  ; addr = null
+    (emit "movq $1024, %rsi")   ; length = 1kb
+    (emit "movq $0x3, %rdx") ; prot = read | write = 0x2 | 0x1
+					;    flags = anonymous | private
+    (case target
+      ('darwin (emit "movq $0x1002, %r10")) ; anon = 0x1000, priv = 0x02
+      ('linux (emit "movq $0x22, %r10")))   ; anon = 0x20,   priv = 0x02
+    (emit "movq $-1, %r8") ; fd = -1
+    (emit "xor %r9, %r9") ; offset = 0
+    (emit "syscall")
+					; %rax now contains pointer to the start of the heap
+					; keep track of it
+
+    (emit "movq heap_start@GOTPCREL(%rip), %rsi")
+    (emit "movq %rax, (%rsi)")))
+
 (define (codegen program)
-  (let* ((extract-res-0 (extract-strings program))
-	 (strings (car extract-res-0))
-	 (extract-res-1 (extract-lambdas (cdr extract-res-0)))
-	 (lambdas (car extract-res-1))
-	 (xform-prog (cdr extract-res-1)))
+  (set! cur-label 0)
+  (set! cur-lambda 0)
+  (let* ([data-layouts (program-data-layouts program)]
+
+	 [pattern-matched (expand-pattern-matches program)]
+	 [type-annotated (annotate-types pattern-matched)]
+	 [stack-annotated (annotate-stack-values data-layouts
+						 type-annotated)]
+	 
+	 (strings-res (extract-strings stack-annotated))
+	 (strings (car strings-res))
+	 (lambdas-res (extract-lambdas (cdr strings-res)))
+	 (lambdas (car lambdas-res))
+	 (xform-prog (cdr lambdas-res)))
 
     (emit "\t.global _start")
     (emit "\t.text")
@@ -343,22 +676,53 @@
     (for-each codegen-lambda lambdas)
 
     (emit "_start:")
+
+    (initialize-heap)
+
     (emit "movq %rsp, %rbp")            ; set up the base pointer
-    (codegen-expr xform-prog 0 '())
+    
+    (codegen-expr xform-prog (- wordsize) (make-env data-layouts '()))
 
 					; exit syscall
     (emit "mov %rax, %rdi")
-    (emit "mov $60, %rax")
+    (case target
+      ('darwin (emit "movq $0x2000001, %rax"))
+      ('linux (emit "mov $60, %rax")))
     (emit "syscall")
 
-    (emit "\t.data")
+    (emit ".data")
+
+    (emit "heap_start:")
+    (emit "\t.quad 0")
 
     (for-each emit-string-data strings)))
 
-(define (compile-to-binary program output)
-  (when (not (eq? (typecheck program) 'int)) (error #f "not an int"))
+(define (compile-to-binary program output t)
+  (set! target t)
+  (when (not (eq? (typecheck program) 'Int)) (error #f "not an Int"))
   (let ([tmp-path "/tmp/a.s"])
     (when (file-exists? tmp-path) (delete-file tmp-path))
     (with-output-to-file tmp-path
       (lambda () (codegen program)))
-    (system (format "clang -nostdlib /tmp/a.s -o ~a" output))))
+
+    (case target
+      ('darwin
+       (system "as /tmp/a.s -o /tmp/a.o")
+       (system (format "ld /tmp/a.o -e _start -macosx_version_min 10.14 -static -o ~a" output)))
+      ('linux
+       (system "as /tmp/a.s -o /tmp/a.o")
+       (system (format "ld /tmp/a.o -o ~a" output))))))
+
+; NOTES
+; syscalls in linux and darwin use the following arguments for syscall instruction:
+; %rax = syscall #
+; %rdi = 1st arg
+; %rsi = 2nd arg
+; %rdx = 3rd arg
+; %r10 = 4th arg
+; %r8  = 5th arg
+; %r9  = 6th arg
+
+; on darwin, unix/posix syscalls are offset by 0x2000000 (syscall classes)
+; https://opensource.apple.com/source/xnu/xnu-2782.20.48/bsd/kern/syscalls.master
+; documentation for most syscalls: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys