oasm: Introduce encoding for the NOP instruction

The NOP (no operation) instruction simply tells the processor to do nothing.
This can be useful for various things such as padding, timing, etc.

--
nop
nop
nop
...
--

Signed-off-by: Ian Moffett <ian@osmora.org>

5 files changed, 39 insertions, 1 deletions

diff --git a/etc/oemu/test-00.s b/etc/oemu/test-00.s
index ca0094d..ccd7da1 100644
--- a/etc/oemu/test-00.s
+++ b/etc/oemu/test-00.s
@@ -12,4 +12,5 @@ some_label:      ! X
     inc x1       ! ~ 0x00000018
     add x2, #3   ! ~ 0x0000001C
     mrow x4, #0  ! ~ 0x00000020
-    hlt          ! ~ 0x00000024
+    nop          ! ~ 0x00000024
+    hlt          ! ~ 0x00000028
diff --git a/usr.bin/oasm/emit.c b/usr.bin/oasm/emit.c
index 3261522..139cf47 100644
--- a/usr.bin/oasm/emit.c
+++ b/usr.bin/oasm/emit.c
@@ -357,6 +357,26 @@ emit_encode_mro(struct emit_state *state, struct oasm_token *tok)
     return TAILQ_NEXT(tok, link);
 }
 
+/*
+ * Encode a NOP instruction
+ *
+ * 'nop' - no operands
+ *
+ * Returns the next token on success,
+ * otherwise NULL.
+ */
+static struct oasm_token *
+emit_encode_nop(struct emit_state *state, struct oasm_token *tok)
+{
+    inst_t curinst;
+
+    curinst.opcode = OSMX64_NOP;
+    curinst.rd = 0;
+    curinst.unused = 0;
+    emit_bytes(state, &curinst, sizeof(curinst));
+    return TAILQ_NEXT(tok, link);
+}
+
 int
 emit_osmx64(struct emit_state *state, struct oasm_token *tp)
 {
@@ -428,6 +448,9 @@ emit_process(struct oasm_state *oasm, struct emit_state *emit)
     curtok = TAILQ_FIRST(&emit->ir);
     while (curtok != NULL) {
         switch (curtok->type) {
+        case TT_NOP:
+            curtok = emit_encode_nop(emit, curtok);
+            break;
         case TT_MOV:
             curtok = emit_encode_mov(emit, curtok);
             break;
diff --git a/usr.bin/oasm/include/oasm/lex.h b/usr.bin/oasm/include/oasm/lex.h
index b392403..375771e 100644
--- a/usr.bin/oasm/include/oasm/lex.h
+++ b/usr.bin/oasm/include/oasm/lex.h
@@ -90,6 +90,7 @@ struct oasm_state;
  */
 typedef enum {
     TT_UNKNOWN,     /* Unknown token */
+    TT_NOP,         /* No operation */
 
     /* Arithmetic instructions */
     TT_ADD,         /* 'add' */
diff --git a/usr.bin/oasm/lex.c b/usr.bin/oasm/lex.c
index dcd7c1f..fea9dc3 100644
--- a/usr.bin/oasm/lex.c
+++ b/usr.bin/oasm/lex.c
@@ -40,6 +40,7 @@
 static char putback = '\0';
 
 /* Instruction mnemonic strings */
+#define S_IMN_NOP  "nop"
 #define S_IMN_MOV  "mov"
 #define S_IMN_ADD  "add"
 #define S_IMN_SUB  "sub"
@@ -372,6 +373,13 @@ lex_tok(struct oasm_state *state, struct oasm_token *ttp)
             return 0;
         }
 
+        /* No operation? */
+        if (strcmp(p, S_IMN_NOP) == 0) {
+            ttp->type = TT_NOP;
+            ttp->raw = p;
+            return 0;
+        }
+
         /* Arithmetic operation? */
         if ((tok = token_arith(p)) != TT_UNKNOWN) {
             ttp->type = tok;
diff --git a/usr.bin/oasm/parse.c b/usr.bin/oasm/parse.c
index 229455b..ba97306 100644
--- a/usr.bin/oasm/parse.c
+++ b/usr.bin/oasm/parse.c
@@ -39,6 +39,7 @@
 static struct emit_state emit_state;
 static const char *tokstr[] = {
     [ TT_UNKNOWN] = "bad",
+    [ TT_NOP ]    = "nop",
     [ TT_ADD ] = "add",
     [ TT_SUB ] = "sub",
     [ TT_MUL ] = "mul",
@@ -154,6 +155,10 @@ parse_tok(struct oasm_state *state, struct oasm_token *tok)
     int error;
 
     switch (tok->type) {
+    case TT_NOP:
+        state->last = tok->type;
+        emit_osmx64(&emit_state, tok);
+        break;
     case TT_BR:
         state->last = tok->type;
         emit_osmx64(&emit_state, tok);