Complete single file cat

src/args.S

@@ -29,7 +29,7 @@ fetch_argv:
     addi sp, sp, -16
     sd ra, 8(sp)
     sd s0, 0(sp)
-    call fetch_argc
+    call fetch_argc # get argument count
     ld ra, 8(sp)
     ld s0, 0(sp)
     addi sp, sp, 16
@@ -47,14 +47,14 @@ fetch_argv:
     sd ra, 16(sp)
     sd s1, 8(sp)
     sd s0, 0(sp)
-    call _next_argv
+    call _next_argv # grab the next argument
     ld ra, 16(sp)
     ld s1, 8(sp)
     ld s0, 0(sp)
     addi sp, sp, 24
     mv a0, a1
     addi s1, s1, 1
-    bne s1, s0, 1b
+    bne s1, s0, 1b # if we haven't retrieved the requested argument, go again
     
     j 3f
 
@@ -68,7 +68,7 @@ fetch_argv:
     sd s0, 0(sp)
 
     mv a0, a1
-    call _argv_size
+    call _argv_size # grab the size of the retrieved argument
 
     ld ra, 8(sp)
     ld s0, 0(sp)

src/file.S

@@ -0,0 +1,38 @@
+.data
+cat_buf:    .space 4096
+
+.section .text
+.globl cat_file
+
+# Fetch argument count
+# @param[in] a0: ptr to null-terminated file str.
+# @param[out] a0: result code.
+cat_file:
+    mv a1, a0 # since the function takes in a0, move it to a1 for syscall
+    
+    li a0, -100 # relative/absolute path
+    li a2, 0 # readonly
+    li a7, 56 # open
+    ecall
+
+    mv t0, a0 # put fd in t0
+
+    1:
+    mv a0, t0
+    la a1, cat_buf
+    li a2, 4096
+    li a7, 63
+    ecall
+    blez a0, 2f
+    mv a2, a0 # move bytes read into bytes needed to write
+
+    li a0, 1
+    la a1, cat_buf
+    li a7, 64
+    ecall
+    j 1b
+    
+    2:
+    ret
+
+

src/main.S

@@ -12,20 +12,23 @@ _start:
 
     call save_sp
     call fetch_argc
-    mv a0, a1
     li t0, 1
-    sub a0, a0, t0
+    ble a1, t0, 1f # return 1 on no file given
+
+    li a0, 1
     
     call fetch_argv
-    beqz a0, 1f
+    beqz a0, 2f
-    li a0, 1
-    li a7, 93
-    ecall
 
     1:
     li a0, 1
-    li a7, 64
+    li a7, 93
-    ecall
+    ecall # return 1
+
+    2:
+    mv a0, a1
+    call cat_file
+    bnez a0, 1b # error if failed
 
     li a0, 0
     li a7, 93