Add attribute nodebug support and skip bitfield padding

The following code:
typedef struct {
  unsigned int a __attribute__((nodebug));
  unsigned int b;
  unsigned int : 32;
  unsigned int c;
} tst;

Supresses a and also suppresses bitfield padding.
So debugger shows only b and c in above example.

Author: hermantb

tcc.h

@@ -548,7 +548,8 @@ struct SymAttr {
     nodecorate  : 1,
     dllimport   : 1,
     addrtaken   : 1,
-    xxxx        : 3; /* not used */
+    nodebug     : 1,
+    xxxx        : 2; /* not used */
 };
 
 /* function attributes or temporary attributes for parsing */

tccdbg.c

@@ -1285,6 +1285,15 @@ static void tcc_debug_remove(TCCState *s1, Sym *t)
 	}
 }
 
+#define	STRUCT_NODEBUG(s) 			       \
+    (s->a.nodebug ||                           \
+     ((s->v & ~SYM_FIELD) >= SYM_FIRST_ANOM && \
+      ((s->type.t & VT_BTYPE) == VT_BYTE ||    \
+       (s->type.t & VT_BTYPE) == VT_BOOL ||    \
+       (s->type.t & VT_BTYPE) == VT_SHORT ||   \
+       (s->type.t & VT_BTYPE) == VT_INT ||     \
+       (s->type.t & VT_BTYPE) == VT_LLONG)))
+
 static void tcc_get_debug_info(TCCState *s1, Sym *s, CString *result)
 {
     int type;
@@ -1320,9 +1329,10 @@ static void tcc_get_debug_info(TCCState *s1, Sym *s, CString *result)
                 int pos, size, align;
 
                 t = t->next;
+		if (STRUCT_NODEBUG(t))
+		    continue;
                 cstr_printf (&str, "%s:",
-                             (t->v & ~SYM_FIELD) >= SYM_FIRST_ANOM
-                             ? "" : get_tok_str(t->v & ~SYM_FIELD, NULL));
+                             get_tok_str(t->v & ~SYM_FIELD, NULL));
                 tcc_get_debug_info (s1, t, &str);
                 if (t->type.t & VT_BITFIELD) {
                     pos = t->c * 8 + BIT_POS(t->type.t);
@@ -1430,6 +1440,8 @@ static int tcc_get_dwarf_info(TCCState *s1, Sym *s)
 	    i = 0;
 	    while (e->next) {
 		e = e->next;
+		if (STRUCT_NODEBUG(e))
+		    continue;
 		i++;
 	    }
 	    pos_type = (int *) tcc_malloc(i * sizeof(int));
@@ -1453,12 +1465,13 @@ static int tcc_get_dwarf_info(TCCState *s1, Sym *s)
 	    i = 0;
             while (e->next) {
                 e = e->next;
+		if (STRUCT_NODEBUG(e))
+		    continue;
 	        dwarf_data1(dwarf_info_section,
 			    e->type.t & VT_BITFIELD ? DWARF_ABBREV_MEMBER_BF
 						    : DWARF_ABBREV_MEMBER);
 		dwarf_strp(dwarf_info_section,
-			   (e->v & ~SYM_FIELD) >= SYM_FIRST_ANOM
-			   ? "" : get_tok_str(e->v & ~SYM_FIELD, NULL));
+			   get_tok_str(e->v & ~SYM_FIELD, NULL));
 		dwarf_uleb128(dwarf_info_section, dwarf_line.cur_file);
 		dwarf_uleb128(dwarf_info_section, file->line_num);
 		pos_type[i++] = dwarf_info_section->data_offset;
@@ -1482,6 +1495,8 @@ static int tcc_get_dwarf_info(TCCState *s1, Sym *s)
 	    i = 0;
 	    while (e->next) {
 		e = e->next;
+		if (STRUCT_NODEBUG(e))
+		    continue;
 		type = tcc_get_dwarf_info(s1, e);
 		tcc_debug_check_anon(s1, e, pos_type[i]);
 		write32le(dwarf_info_section->data + pos_type[i++],

tccgen.c

@@ -1067,6 +1067,7 @@ static void merge_symattr(struct SymAttr *sa, struct SymAttr *sa1)
       sa->aligned = sa1->aligned;
     sa->packed |= sa1->packed;
     sa->weak |= sa1->weak;
+    sa->nodebug |= sa1->nodebug;
     if (sa1->visibility != STV_DEFAULT) {
 	int vis = sa->visibility;
 	if (vis == STV_DEFAULT
@@ -3823,6 +3824,10 @@ static void parse_attribute(AttributeDef *ad)
         case TOK_WEAK2:
             ad->a.weak = 1;
             break;
+        case TOK_NODEBUG1:
+        case TOK_NODEBUG2:
+            ad->a.nodebug = 1;
+            break;
         case TOK_UNUSED1:
         case TOK_UNUSED2:
             /* currently, no need to handle it because tcc does not

tcctok.h

@@ -124,6 +124,8 @@
      DEF(TOK_ALIAS2, "__alias__")
      DEF(TOK_UNUSED1, "unused")
      DEF(TOK_UNUSED2, "__unused__")
+     DEF(TOK_NODEBUG1, "nodebug")
+     DEF(TOK_NODEBUG2, "__nodebug__")
      DEF(TOK_CDECL1, "cdecl")
      DEF(TOK_CDECL2, "__cdecl")
      DEF(TOK_CDECL3, "__cdecl__")