wc works really well (as char count)

build.sh

@@ -1,3 +1,5 @@
+# no, I will not use make
+
 QUIET="false"
 CLEAN="false"
 

src/common.asm

@@ -1,5 +1,14 @@
           global     itoa
           global     println_num
+          global     open_file_arg
+
+WRITE_SYSCALL  EQU 1
+OPEN_SYSCALL   EQU 2
+
+STDIN_FD       EQU 0
+STDOUT_FD      EQU 1
+
+
 
           section   .data
 print_num_buf: times 64 db 0
@@ -105,8 +114,36 @@ println_num:
           inc       rbx
 
           mov       rdx, rbx             ; len
-          mov       rax, 1               ; write
+          mov       rax, WRITE_SYSCALL
-          mov       rdi, 1               ; stdout
+          mov       rdi, STDOUT_FD
           mov       rsi, print_num_buf
           syscall
-          ret
+          ret
+
+
+; open_file_arg
+; opens the file, stdin if it's '-'
+; inputs:
+;   rax - filename
+; outputs:
+;   rax - fd, <0 if there was an error
+open_file_arg:
+          ; first, check whether the filename is -
+          cmp       byte [rax], '-'
+          jne       normal_filename
+          cmp       byte [rax + 1], 0
+          jne       normal_filename
+
+          ; filename is just minus
+          mov       rax, STDIN_FD
+          ret
+
+normal_filename:
+          ; we have a normal file that we must open
+
+          mov       rdi, rax
+          mov       rax, OPEN_SYSCALL
+          xor       rsi, rsi            ; no flags
+          xor       rdx, rdx            ; read-only mode
+          syscall
+          ret

src/wc.asm

@@ -1,25 +1,53 @@
           extern     itoa
           extern     println_num
+          extern     open_file_arg
 
           global     _start
 
 IO_BUF_SIZE EQU 1024
 
           section   .data
+file_not_found_msg:
+          db        'File not found', 10, 15
+failed_to_read_msg:
+          db        'Failed to read', 10, 15
 io_buf:   times IO_BUF_SIZE db 0
 
           section   .text
 _start:
+          pop       rax                         ; argc
+
+          cmp       rax, 1
+          je        stdin_init                  ; if we don't have any arguments, read from stdin
+
+          ; we do have at least one argument, open the file
+          pop       rbx                         ; program name
+          pop       rax                         ; filename
+          call      open_file_arg
+          ; test whether there was an error
+          cmp       rax, 0
+          jl        file_not_found
+
+          mov       rdi, rax
+          jmp       init
+
+stdin_init:
+          mov       rdi, 0                      ; stdin
+
+init:
+          ; the input fd is in rdi at this point
           ; r13 is the character counter
           xor       r13, r13
-
 process:
           mov       rax, 0
-          mov       rdi, 0              ; stdin
           mov       rsi, io_buf
           mov       rdx, IO_BUF_SIZE
           syscall
 
+          ; test whether there was an error
+          cmp       rax, 0
+          jl        failed_to_read
+
           add       r13, rax
 
           cmp       rax, 0
@@ -28,7 +56,24 @@ process:
 count_and_print:
           mov       rax, r13
           call      println_num
-
-          mov       rax, 60
           xor       rdi, rdi
+
+exit:
+          mov       rax, 60
           syscall
+
+failed_to_read:
+          mov       rax, 1                      ; write
+          mov       rdi, 2                      ; stderr
+          mov       rsi, failed_to_read_msg     ; buf
+          mov       rdx, 15                     ; len
+          jmp       exit
+
+file_not_found:
+          mov       rax, 1                     ; write
+          mov       rdi, 2                     ; stderr
+          mov       rsi, file_not_found_msg    ; buf
+          mov       rdx, 15                    ; len
+          syscall
+          mov       rdi, 1
+          jmp       exit