Make fmtscan support '__asm__' alternative keyword

According to the GCC documentation, the 'asm' keyword is a GNU extension
and the alternative '__asm__' can be used when writing code compiled
with '-ansi' and various '-std' options.

Change-Id: Icb6c052a92894839b99640641964f0e99e16eb30

Author: lumynou5

tools/fmtscan.c

@@ -629,7 +629,7 @@ static get_char_t skip_macros(parser_t *p)
     return PARSER_EOF;
 }
 
-static get_char_t skip_inline_asm(parser_t *p)
+static get_char_t skip_inline_asm(parser_t *p, bool underscore)
 {
     get_char_t ch = get_char(p);
     if (ch != 's')
@@ -642,6 +642,19 @@ static get_char_t skip_inline_asm(parser_t *p)
     if (UNLIKELY(ch == PARSER_EOF))
         return ch;
 
+    if (underscore) {
+        ch = get_char(p);
+        if (ch != '_')
+            goto check_underline_1_failed;
+        if (UNLIKELY(ch == PARSER_EOF))
+            return ch;
+        ch = get_char(p);
+        if (ch != '_')
+            goto check_underline_2_failed;
+        if (UNLIKELY(ch == PARSER_EOF))
+            return ch;
+    }
+
     int paren = 0;
     do {
         ch = get_char(p);
@@ -665,6 +678,10 @@ static get_char_t skip_inline_asm(parser_t *p)
     } while (paren);
     return PARSER_COMMENT_FOUND;
 
+check_underline_2_failed:
+    unget_char(p);
+check_underline_1_failed:
+    unget_char(p);
 check_m_failed:
     unget_char(p);
 check_s_failed:
@@ -791,7 +808,31 @@ static get_char_t parse_inline_asm(parser_t *restrict p,
                                    token_t *restrict t,
                                    get_char_t ch)
 {
-    get_char_t ret = skip_inline_asm(p);
+    get_char_t ret = skip_inline_asm(p, false);
+
+    if (ret == PARSER_COMMENT_FOUND) {
+        ret |= PARSER_CONTINUE;
+        return ret;
+    }
+    if (UNLIKELY(ret == PARSER_EOF))
+        return ret;
+
+    return parse_identifier(p, t, ch);
+}
+
+/* Parse an potential inline assembly wraped with double underscores. */
+static get_char_t parse_inline_asm_underscore(parser_t *restrict p,
+                                              token_t *restrict t,
+                                              get_char_t ch)
+{
+    get_char_t ret = get_char(p);
+    if (ret != '_') {
+        unget_char(p);
+        return parse_identifier(p, t, ch);
+    }
+    if (UNLIKELY(ret == PARSER_EOF))
+        return ret;
+    ret = skip_inline_asm(p, true);
 
     if (ret == PARSER_COMMENT_FOUND) {
         ret |= PARSER_CONTINUE;
@@ -1224,7 +1265,7 @@ static get_token_action_t get_token_actions[] = {
     ['X'] = parse_identifier,
     ['Y'] = parse_identifier,
     ['Z'] = parse_identifier,
-    ['_'] = parse_identifier,
+    ['_'] = parse_inline_asm_underscore,
     ['"'] = parse_literal_string,
     ['\''] = parse_literal_char,
     ['\\'] = parse_backslash,