string instrs doc

vm/in/INSTRS

@@ -380,6 +380,62 @@ leave
 # String manipulation instructions                                          #
 #---------------------------------------------------------------------------#
 
+#
+# Store value into string (STOSx)
+#
+#       [%str] = $val
+#       IF (DF == 0) THEN
+#           %str = %str + sizeof(x)
+#       ELSE
+#           %str = %str - sizeof(x)
+#       FI
+#
+# When no parameters are given, %str = RDI and $val = RAX
+# When one parameter is given, %str = RDI and $val = $1
+# When two parameters are given, %str = $1 and $val = $2
+#
+stosb
+stosb rim
+stosb r rim
+
+#
+# Load value from string (LODSx)
+#
+#       %dest = [%str]
+#       IF (DF == 0) THEN
+#           %str = %str + sizeof(x)
+#       ELSE
+#           %str = %str - sizeof(x)
+#       FI
+#
+# When no parameters are given, %str = RDI and %dest = RAX
+# When one parameter is given, %str = RDI and %dest = $1
+# When two parameters are given, %str = $2 and %dest = $1
+#
+lodsb
+lodsb r
+lodsb rm r
+
+#
+# Move value from string to string (MOVSx)
+#
+#       [%str1] = [%str2]
+#       IF (DF == 0) THEN
+#           %str1 = %str1 + sizeof(x)
+#           %str2 = %str2 + sizeof(x)
+#       ELSE
+#           %str1 = %str1 - sizeof(x)
+#           %str2 = %str2 - sizeof(x)
+#       FI
+#
+# When no parameters are given, %str1 = RDI and %str2 = RSI
+# When one parameter is given, %str1 = RDI and %str2 = $1
+# When two parameters are given, %str1 = $1 and %str2 = $2
+#
+movsb
+movsb r
+movsb r r
+
 #---------------------------------------------------------------------------#
 # Supervisor only instructions                                              #
 #---------------------------------------------------------------------------#

vm/in/string.c

@@ -0,0 +1,24 @@
+// The OS/K Team licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#include <in/instrs.h>
+
+//----------------------------------------------------------------------------//
+
+IMPL_START_0(stosb)
+{
+}
+IMPL_END;
+
+IMPL_START_0(lodsb)
+{
+}
+IMPL_END;
+
+IMPL_START_0(movsb)
+{
+}
+IMPL_END;
+
+//----------------------------------------------------------------------------//
+

vm/pc/decd.c

@@ -304,11 +304,15 @@ void exec_instr(ctx_t *ctx,
     // Debugging
     dump_instr(ctx, in, p1, p2, lock, rep, cond, pc);
 
-do_rep:
-
-    if (!eval_cond(ctx, cond))
+    //
+    // For REPs we evaluate the condition AFTER running the instruction,
+    // in a do ... while(cond) fashion
+    //
+    if (!rep && !eval_cond(ctx, cond))
         return;
 
+do_rep:
+
     out = in->func(ctx, p1, p2, &r1, &r2);
 
     if (out)
@@ -343,6 +347,13 @@ do_rep:
 
     if (rep && rcx > 0)
     {
+        // RCX remains untouched when condition fails
+        if (!eval_cond(ctx, cond))
+            return;
+
+        // Show that we're REP'ing
+        dump_instr(ctx, in, p1, p2, lock, rep, cond, pc);
+
         rcx--;
         goto do_rep;
     }