Allocate heap at the start

diff --git a/codegen.scm b/codegen.scm
index 4848d4ddfa98731899f6b2ca92413b45eb3086ce..9b3878a2e947f3d3314c8c9c4bc96bca38a83a7f 100644 (file)
--- a/codegen.scm
+++ b/codegen.scm
@@ -121,7 +121,6 @@
             (param-register i)))
      captured (range 0 (length captured)))
 
-
                                        ; then codegen the arguments and move them into the next param registers
     (for-each
      (lambda (e i)
@@ -343,6 +342,21 @@
     (for-each codegen-lambda lambdas)
 
     (emit "_start:")
+
+    ; allocate some heap memory
+    (emit "mov $9, %rax") ; mmap
+    (emit "xor %rdi, %rdi")  ; addr = null
+    (emit "movq $1024, %rsi")   ; length = 1kb
+    (emit "movq $0x3, %rdx") ; prot = read | write = 0x2 | 0x1
+    (emit "movq $0x22, %r10") ; flags = anonymous | private = 0x20 | 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 %rax, (heap_start)")
+    
     (emit "movq %rsp, %rbp")            ; set up the base pointer
     (codegen-expr xform-prog 0 '())
 
@@ -351,7 +365,10 @@
     (emit "mov $60, %rax")
     (emit "syscall")
 
-    (emit "\t.data")
+    (emit ".data")
+
+    (emit "heap_start:")
+    (emit "\t.quad 0")
 
     (for-each emit-string-data strings)))
 
@@ -362,3 +379,13 @@
     (with-output-to-file tmp-path
       (lambda () (codegen program)))
     (system (format "clang -nostdlib /tmp/a.s -o ~a" output))))
+
+; NOTES
+; syscalls in linux 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