check_unreachable.c

   1 /*
   2  * Copyright (C) 2014 Oracle.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 #include "smatch.h"
  19
  20 static int my_id;
  21
  22 static int print_unreached = 1;
  23 static struct string_list *turn_off_names;
  24 static struct string_list *ignore_names;
  25
  26 static bool empty_statement(struct statement *stmt)
  27 {
  28         if (!stmt)
  29                 return false;
  30         if (stmt->type == STMT_EXPRESSION && !stmt->expression)
  31                 return true;
  32         return false;
  33 }
  34
  35 static void print_unreached_initializers(struct symbol_list *sym_list)
  36 {
  37         struct symbol *sym;
  38
  39         FOR_EACH_PTR(sym_list, sym) {
  40                 if (sym->initializer && !(sym->ctype.modifiers & MOD_STATIC))
  41                         sm_msg("info: '%s' is not actually initialized (unreached code).",
  42                                 (sym->ident ? sym->ident->name : "this variable"));
  43         } END_FOR_EACH_PTR(sym);
  44 }
  45
  46 static bool is_ignored_macro(struct statement *stmt)
  47 {
  48         char *name;
  49         char *tmp;
  50
  51         name = get_macro_name(stmt->pos);
  52         if (!name)
  53                 return false;
  54
  55         if (strncmp(name, "for_", 4) == 0)
  56                 return true;
  57
  58         FOR_EACH_PTR(ignore_names, tmp) {
  59                 if (strcmp(tmp, name) == 0)
  60                         return true;
  61         } END_FOR_EACH_PTR(tmp);
  62
  63         return false;
  64 }
  65
  66 static bool prev_line_was_endif(struct statement *stmt)
  67 {
  68         struct token *token;
  69         struct position pos = stmt->pos;
  70
  71         pos.line--;
  72         pos.pos = 2;
  73
  74         token = pos_get_token(pos);
  75         if (token && token_type(token) == TOKEN_IDENT &&
  76             strcmp(show_ident(token->ident), "endif") == 0)
  77                 return true;
  78
  79         pos.line--;
  80         token = pos_get_token(pos);
  81         if (token && token_type(token) == TOKEN_IDENT &&
  82             strcmp(show_ident(token->ident), "endif") == 0)
  83                 return true;
  84
  85         return false;
  86 }
  87
  88 static bool we_jumped_into_the_middle_of_a_loop(struct statement *stmt)
  89 {
  90         struct statement *prev;
  91
  92         /*
  93          * Smatch doesn't handle loops correctly and this is a hack.  What we
  94          * do is that if the first unreachable statement is a loop and the
  95          * previous statement was a goto then it's probably code like this:
  96          *      goto first;
  97          *      for (;;) {
  98          *              frob();
  99          * first:
 100          *              more_frob();
 101          *      }
 102          * Every statement is reachable but only on the second iteration.
 103          */
 104
 105         if (stmt->type != STMT_ITERATOR)
 106                 return false;
 107         prev = get_prev_statement();
 108         if (prev && prev->type == STMT_GOTO)
 109                 return true;
 110         return false;
 111 }
 112
 113 static void unreachable_stmt(struct statement *stmt)
 114 {
 115
 116         if (__inline_fn)
 117                 return;
 118
 119         if (!__path_is_null()) {
 120                 print_unreached = 1;
 121                 return;
 122         }
 123
 124         /* if we hit a label then assume there is a matching goto */
 125         if (stmt->type == STMT_LABEL)
 126                 print_unreached = 0;
 127         if (prev_line_was_endif(stmt))
 128                 print_unreached = 0;
 129         if (we_jumped_into_the_middle_of_a_loop(stmt))
 130                 print_unreached = 0;
 131
 132         if (!print_unreached)
 133                 return;
 134         if (empty_statement(stmt))
 135                 return;
 136         if (is_ignored_macro(stmt))
 137                 return;
 138
 139         switch (stmt->type) {
 140         case STMT_COMPOUND: /* after a switch before a case stmt */
 141         case STMT_RANGE:
 142         case STMT_CASE:
 143                 return;
 144         case STMT_DECLARATION: /* switch (x) { int a; case foo: ... */
 145                 print_unreached_initializers(stmt->declaration);
 146                 return;
 147         case STMT_RETURN: /* gcc complains if you don't have a return statement */
 148                 if (is_last_stmt(stmt))
 149                         return;
 150                 break;
 151         case STMT_GOTO:
 152                 /* people put extra breaks inside switch statements */
 153                 if (stmt->goto_label && stmt->goto_label->type == SYM_NODE &&
 154                     strcmp(stmt->goto_label->ident->name, "break") == 0)
 155                         return;
 156                 break;
 157         default:
 158                 break;
 159         }
 160         sm_warning("ignoring unreachable code.");
 161         print_unreached = 0;
 162 }
 163
 164 static bool is_turn_off(char *name)
 165 {
 166         char *tmp;
 167
 168         if (!name)
 169                 return false;
 170
 171         FOR_EACH_PTR(turn_off_names, tmp) {
 172                 if (strcmp(tmp, name) == 0)
 173                         return true;
 174         } END_FOR_EACH_PTR(tmp);
 175
 176         return false;
 177 }
 178
 179 static char *get_function_name(struct statement *stmt)
 180 {
 181         struct expression *expr;
 182
 183         if (stmt->type != STMT_EXPRESSION)
 184                 return NULL;
 185         expr = stmt->expression;
 186         if (!expr || expr->type != EXPR_CALL)
 187                 return NULL;
 188         if (expr->fn->type != EXPR_SYMBOL || !expr->fn->symbol_name)
 189                 return NULL;
 190         return expr->fn->symbol_name->name;
 191 }
 192
 193 static void turn_off_unreachable(struct statement *stmt)
 194 {
 195         char *name;
 196
 197         name = get_macro_name(stmt->pos);
 198         if (is_turn_off(name)) {
 199                 print_unreached = 0;
 200                 return;
 201         }
 202
 203         if (stmt->type == STMT_IF &&
 204             known_condition_true(stmt->if_conditional) && __path_is_null()) {
 205                 print_unreached = 0;
 206                 return;
 207         }
 208
 209         name = get_function_name(stmt);
 210         if (is_turn_off(name))
 211                 print_unreached = 0;
 212 }
 213
 214 static void register_turn_off_macros(void)
 215 {
 216         struct token *token;
 217         char *macro;
 218         char name[256];
 219
 220         if (option_project == PROJ_NONE)
 221                 strcpy(name, "unreachable.turn_off");
 222         else
 223                 snprintf(name, 256, "%s.unreachable.turn_off", option_project_str);
 224
 225         token = get_tokens_file(name);
 226         if (!token)
 227                 return;
 228         if (token_type(token) != TOKEN_STREAMBEGIN)
 229                 return;
 230         token = token->next;
 231         while (token_type(token) != TOKEN_STREAMEND) {
 232                 if (token_type(token) != TOKEN_IDENT)
 233                         return;
 234                 macro = alloc_string(show_ident(token->ident));
 235                 add_ptr_list(&turn_off_names, macro);
 236                 token = token->next;
 237         }
 238         clear_token_alloc();
 239 }
 240
 241 static void register_ignored_macros(void)
 242 {
 243         struct token *token;
 244         char *macro;
 245         char name[256];
 246
 247         if (option_project == PROJ_NONE)
 248                 strcpy(name, "unreachable.ignore");
 249         else
 250                 snprintf(name, 256, "%s.unreachable.ignore", option_project_str);
 251
 252         token = get_tokens_file(name);
 253         if (!token)
 254                 return;
 255         if (token_type(token) != TOKEN_STREAMBEGIN)
 256                 return;
 257         token = token->next;
 258         while (token_type(token) != TOKEN_STREAMEND) {
 259                 if (token_type(token) != TOKEN_IDENT)
 260                         return;
 261                 macro = alloc_string(show_ident(token->ident));
 262                 add_ptr_list(&ignore_names, macro);
 263                 token = token->next;
 264         }
 265         clear_token_alloc();
 266 }
 267
 268 void check_unreachable(int id)
 269 {
 270         my_id = id;
 271
 272         register_turn_off_macros();
 273         register_ignored_macros();
 274         add_hook(&unreachable_stmt, STMT_HOOK);
 275         add_hook(&turn_off_unreachable, STMT_HOOK_AFTER);
 276 }