diff --git a/ka/command.k b/ka/command.k
index 93d58e7..d2bce5f 100644
--- a/ka/command.k
+++ b/ka/command.k
@@ -11,7 +11,7 @@ FILE_LOADP  := 0x141000     ; 4KB above stack
 start:
     mov rsp, 0x140000
     mov rbp, zero
-    
+
     cls
     cld
     call main
diff --git a/ka/crt/str/strcmp.k b/ka/crt/str/strcmp.k
index cb847a1..e2dfb01 100644
--- a/ka/crt/str/strcmp.k
+++ b/ka/crt/str/strcmp.k
@@ -10,8 +10,14 @@
 ;   <0 if the first character that does not match has a lower value in str1 than in str2
 ;
 strcmp:
-    mov ax2, STRLEN_MAX
-    jmp strncmp
+    mov rcx, STRLEN_MAX
+    cmpzsb.rep.z ax0, ax1
+
+    mov rax, b[ax0-1]
+    mov rcx, b[ax1-1]
+    sub rax, rax, rcx
+
+    ret
 
 ;
 ; int strncmp(const char *str1, const char *str2, int maxn)
diff --git a/ka/sys/intr/trap0.k b/ka/sys/intr/trap0.k
index c4f1d34..f87ea9b 100644
--- a/ka/sys/intr/trap0.k
+++ b/ka/sys/intr/trap0.k
@@ -114,7 +114,7 @@ trap0_handler:
     jmp .fini
 
 .handle_ReadFile:
-    add ax1, ax0, nx0
+    add ax1, ax1, nx0
     call DISK.ReadFile
     jmp .fini
 
diff --git a/ka/usr/cmd/main.k b/ka/usr/cmd/main.k
index ea27139..4846ff9 100644
--- a/ka/usr/cmd/main.k
+++ b/ka/usr/cmd/main.k
@@ -130,6 +130,12 @@ main:
     call strcmp
     b.z rax, 0, .handle_DIR
 
+.builtin_dump = "dump"
+    mov ax0, argv0
+    mov ax1, .builtin_dump
+    call strcmp
+    b.z rax, 0, .handle_DUMP
+
 .builtin_echo = "echo"
     mov ax0, argv0
     mov ax1, .builtin_echo
@@ -198,6 +204,10 @@ main:
     call builtins.dir
     jmp .print_prompt
 
+.handle_DUMP:
+    dump
+    jmp .print_prompt
+
 .handle_ECHO:
     mov rdx, q[argv1pos]
     b.z rdx, 0, .echo.end
@@ -275,6 +285,8 @@ main:
     prns.rep.nz rdx
     mov rdx, .helpmsg.dir
     prns.rep.nz rdx
+    mov rdx, .helpmsg.dump
+    prns.rep.nz rdx
     mov rdx, .helpmsg.echo
     prns.rep.nz rdx
     mov rdx, .helpmsg.exit
@@ -294,6 +306,7 @@ main:
 .helpmsg.cls   = "    CLS        Clear screen\n"
 .helpmsg.date  = "    DATE       Display current date\n"
 .helpmsg.dir   = "    DIR        Print contents of current directory\n"
+.helpmsg.dump  = "    DUMP       Toggles debug instruction dumping\n"
 .helpmsg.echo  = "    ECHO       Write arguments to standard output\n"
 .helpmsg.exit  = "    EXIT       Initiate machine shutdown\n"
 .helpmsg.help  = "    HELP       Display these messages\n"
diff --git a/vm/in/ALU b/vm/in/ALU
index ffc487f..b3d07e9 100644
--- a/vm/in/ALU
+++ b/vm/in/ALU
@@ -23,7 +23,6 @@ not r r
 #
 or r r ri
 # $dest = $src1 OR NOT($src2)
-orn r ri
 orn r r ri
 # $dest = NOT($src1 OR $src2)
 nor r r ri
@@ -149,18 +148,6 @@ add r r ri
 addf r r ri
 addo r r ri
 
-#
-# Atomic exchange and add (XADD)
-#
-#       $tmp = $1
-#       $1 = $1 + $2
-#       $2 = $1
-#
-# Preserves all flags
-#
-xadd r rm
-xadd m r
-
 #
 # Arithmetical SUB operation
 #
diff --git a/vm/in/MISC b/vm/in/MISC
index a056dbc..56d2646 100644
--- a/vm/in/MISC
+++ b/vm/in/MISC
@@ -14,15 +14,11 @@
 break
 
 #
-# Enable/disable instruction dumping (DUMP)
+# Toggles instruction dumping (DUMP)
 #
-#       IF $1 == 0 THEN
-#           (disable instruction dumping)
-#       ELSE
-#           (enable instruction dumping)
-#       FI
+#       (toggles instruction dumping)
 #
-dump ri
+dump
 
 #---------------------------------------------------------------------------#
 # Misc. instructions                                                        #
diff --git a/vm/in/alu.c b/vm/in/alu.c
index 6582c06..e1d2378 100644
--- a/vm/in/alu.c
+++ b/vm/in/alu.c
@@ -39,7 +39,6 @@ IMPL_START_1(dec) { v1--; } IMPL_OUT;
 //----------------------------------------------------------------------------//
 
 IMPL_START_3(add) { v1 = v2 + v3; } IMPL_OUT;
-IMPL_START_2(xadd) { ulong tmp = v1; v1 += v2; v2 = tmp; } IMPL_OUT_2;
 IMPL_START_3(addf) { COMPARE(v2, ~v3+1); v1 = v2 + v3; } IMPL_OUT;
 IMPL_START_3(addo) { COMPARE(v2, ~v3+1); v1 = v2 + v3; INTO(); } IMPL_OUT;
 
diff --git a/vm/in/misc.c b/vm/in/misc.c
index 9065a68..905fd6c 100644
--- a/vm/in/misc.c
+++ b/vm/in/misc.c
@@ -30,20 +30,17 @@ IMPL_START_0(break)
 }
 IMPL_END;
 
-IMPL_START_1(dump)
+IMPL_START_0(dump)
 {
-    (void)v1;
-
 #ifndef NDEBUG
-    if (ctx->dumpsw && !v1)
+    if (ctx->dumpsw)
         trace("0x%lX:\t...\n", rpc);
 
-    else if (!ctx->dumpsw && v1)
+    else if (!ctx->dumpsw)
         dump_instr(ctx, ctx->cur_in, p1, p2, p3, 0, 0);
 
-    ctx->dumpsw = !!v1;
+    ctx->dumpsw = !ctx->dumpsw;
 #endif
-
 }
 IMPL_END;