cat start

src/cat.asm

@@ -0,0 +1,93 @@
+          extern     open_file_arg
+
+          global     _start
+
+IO_BUF_SIZE  EQU 1024
+STDIN_FD     EQU 0
+STDOUT_FD    EQU 1
+
+          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
+newline:  db        10, 1
+
+          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, STDIN_FD
+
+init:
+          ; the input fd is in rdi at this point
+          xor       r13, r13
+process:
+          ; read in from the file
+          mov       rax, 0
+          mov       rsi, io_buf
+          mov       rdx, IO_BUF_SIZE
+          syscall
+
+          ; test whether it is finished
+          cmp       rax, 0
+          jz        finish
+
+          ; test whether there was an error
+          cmp       rax, 0
+          jl        failed_to_read
+
+          ; write to the file
+          mov       rdx, rax
+          mov       rax, 1
+          mov       rsi, io_buf
+          mov       rdi, STDOUT_FD
+          syscall
+
+          jmp       process
+
+finish:
+          ; write a trailing newline
+          mov       rax, 1
+          mov       rdx, 1
+          mov       rsi, newline
+          mov       rdi, STDOUT_FD
+          syscall
+
+exit_success:
+          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