oasm: Add initial support for labels

A label is like a pin on a map with a number attached to it. OASM keeps track
of a number referred to as the psuedo instruction pointer (PIP). This value is
initially zero by default and is incremented every instruction. The purpose of
this value is to pin a location in the code and mark it to be at a specific address
so that further references to that label would be translated to the previous PIP value
at the time of encountering the label.

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

1 files changed, 29 insertions, 3 deletions

diff --git a/usr.bin/oasm/lex.c b/usr.bin/oasm/lex.c
index a33a570..87ac464 100644
--- a/usr.bin/oasm/lex.c
+++ b/usr.bin/oasm/lex.c
@@ -50,6 +50,20 @@ static char putback = '\0';
 #define S_IMN_HLT  "hlt"
 #define S_IMN_BR   "br"
 
+/* Instruction length */
+#define OSMX64_INST_LEN 4
+
+/*
+ * Update the state when the caller encounters
+ * a newline.
+ */
+static inline void
+lex_newline(struct oasm_state *state)
+{
+    ++state->line;
+    state->pip += OSMX64_INST_LEN;
+}
+
 /*
  * Returns 0 if a char is counted as a
  * skippable token. Otherwise, -1
@@ -63,7 +77,7 @@ lex_skippable(struct oasm_state *state, char c)
     case '\t': return 0;
     case '\r': return 0;
     case '\n':
-        ++state->line;
+        lex_newline(state);
         return 0;
     }
 
@@ -154,6 +168,10 @@ lex_nomstr(struct oasm_state *state, char **res)
             retval = tmp;
             break;
         }
+        if (tmp == ':') {
+            retval = tmp;
+            break;
+        }
         if (tmp == '\n') {
             ++state->line;
             retval = tmp;
@@ -295,7 +313,7 @@ lex_tok(struct oasm_state *state, struct oasm_token *ttp)
 
     switch (c) {
     case '\n':
-        ++state->line;
+        lex_newline(state);
         return 0;
     case '\0':
         return -1;
@@ -306,7 +324,14 @@ lex_tok(struct oasm_state *state, struct oasm_token *ttp)
         ttp->raw = NULL;
 
         lex_putback(c);
-        lex_nomstr(state, &p);
+        c = lex_nomstr(state, &p);
+
+        while (c == ':') {
+            ttp->type = TT_LABEL;
+            ttp->raw = p;
+            state->label_ip = state->pip;
+            return 0;
+        }
 
         /* Arithmetic operation? */
         if ((tok = token_arith(p)) != TT_UNKNOWN) {
@@ -340,6 +365,7 @@ lex_tok(struct oasm_state *state, struct oasm_token *ttp)
             ttp->raw = p;
             return 0;
         }
+
         oasm_err("bad token \"%s\"\n", p);
         lex_try_free(p);
         return -1;