read-print file

lang/src/main.asm

@@ -10,6 +10,8 @@ section .data
     file_error_msg_len equ $ - file_error_msg
     error_msg db "Error: "
     error_msg_len equ $ - error_msg
+    buffer_size equ 1024
+    buffer times buffer_size db 0
 
 section .text
 global _start
@@ -30,14 +32,37 @@ _start:
     ; open file for reading
     mov rdx, rax          ; filename pointer
     call fopen_read
-    mov rax, 42
-    ; exit with success
-    mov rdx, 0
-    call exit
+
+.read_loop:
+    mov r9, rax          ; file descriptor
+    mov rax, 0           ; syscall: read
+    mov rdi, r9          ; fd
+    lea rsi, [buffer]    ; buffer
+    mov rdx, buffer_size ; size
+    syscall
+    cmp rax, 0           ; check for EOF
+    jle .exit            ; if rax <= 0, exit loop
+    mov rcx, rax         ; number of bytes read
+
+    ; write to stdout for now
+    mov rax, 1           ; syscall: write
+    mov rdi, 1           ; fd: stdout
+    lea rsi, [buffer]    ; buffer
+    mov rdx, rcx         ; len: bytes read
+    syscall
+    jmp .read_loop
 
 .no_filename:
     call panic
+.exit:
+    call exit
 
+
+;; ==============================
+;; Helper functions
+;; ==============================
+
+;; Abort the program with a default panic message
 panic:
     mov rdx, panic_msg
     mov rcx, panic_msg_len
@@ -54,10 +79,6 @@ exit:
     mov rdi, rdx
     syscall
 
-;; ==============================
-;; Helper functions
-;; ==============================
-
 ;; Writes a string to stderr:
 ;; rdx: pointer to string
 ;; rcx: length of string
@@ -147,4 +168,4 @@ fopen_read:
 
     pop rsi
     add rsp, rsi                ; dealloc
-    ret
+    call panic