Complete argc argv

src/args.S

@@ -10,13 +10,102 @@ save_sp:
 
 # Fetch argument count
 # @param[in] a0: unused.
-# @param[out] a0: number of arguments.
+# @param[out] a0: result code.
+# @param[out] a1: number of arguments.
 fetch_argc:
-    ld t0, sp_start # dereference the buffer
-    ld a0, 0(t0) # dereference the address
+    ld t0, sp_start
+    ld a1, 0(t0) # dereference the buffer
+    li a0, 0 # success
     ret
 
 # Fetch argument value
 # @param[in] a0: argv[a0].
-# @param[out] a0: address of arg.
+# @param[out] a0: result code.
+# @param[out] a1: address of argv[a0].
+# @param[out] a2: sizeof(argv[a0]).
 fetch_argv:
+    mv s0, a0
+
+    addi sp, sp, -16
+    sd ra, 8(sp)
+    sd s0, 0(sp)
+    call fetch_argc
+    ld ra, 8(sp)
+    ld s0, 0(sp)
+    addi sp, sp, 16
+
+    bge s0, a1, 2f # fail if a0 larger than argc
+    bltz a1, 2f # fail if a0 less than zero
+    ld t0, sp_start
+    addi t0, t0, 8
+    li s1, 0
+
+    ld a0, 0(t0)
+
+    1:
+    addi sp, sp, -24
+    sd ra, 16(sp)
+    sd s1, 8(sp)
+    sd s0, 0(sp)
+    call _next_argv
+    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
+    
+    j 3f
+
+    2:    
+    li a0, 1 # fail
+    j 4f
+    3:
+    mv s0, a1
+    addi sp, sp, -16
+    sd ra, 8(sp)
+    sd s0, 0(sp)
+
+    mv a0, a1
+    call _argv_size
+
+    ld ra, 8(sp)
+    ld s0, 0(sp)
+    addi sp, sp, 16
+
+    li a0, 0
+    mv a2, a1
+    mv a1, s0
+
+    4:
+    ret
+
+
+# Fetch argument value
+# @param[in] a0: address of current argv.
+# @param[out] a0: result code.
+# @param[out] a1: address of next argv.
+_next_argv:
+    lb t2, 0(a0) # deref val at reg
+    addi a0, a0, 1 # inc reg
+    bnez t2, _next_argv # deref val != 0
+    mv a1, a0
+    li a0, 0 # success
+    ret
+
+# Fetch argument value
+# @param[in] a0: address of argv.
+# @param[out] a0: result code.
+# @param[out] a1: address of next argv.
+_argv_size:
+    li t0, 0
+    1:
+    lb t1, 0(a0) # deref val at reg
+    addi a0, a0, 1 # inc reg
+    addi t0, t0, 1
+    bnez t1, 1b # deref val != 0
+
+    mv a1, t0
+    li a0, 0 # success
+    ret

src/main.S

@@ -12,17 +12,18 @@ _start:
 
     call save_sp
     call fetch_argc
+    mv a0, a1
+    li t0, 1
+    sub a0, a0, t0
     
-    li t0, 48
-    add a0, a0, t0
-    sd a0, argc, t0
+    call fetch_argv
+    beqz a0, 1f
+    li a0, 1
+    li a7, 93
+    ecall
 
-    # li a0, 1
-    # call fetch_argv
-
+    1:
     li a0, 1
-    la a1, argc
-    li a2, 1
     li a7, 64
     ecall