check_unused_ret.c

   1 /*
   2  * sparse/check_unused_ret.c
   3  *
   4  * Copyright (C) 2009 Dan Carpenter.
   5  *
   6  * Licensed under the Open Software License version 1.1
   7  *
   8  */
   9
  10 /*
  11  * This check is supposed to find places like this:
  12  * err = foo();
  13  * err = bar();
  14  * if (err)
  15  *         return err;
  16  * (the first assignment isn't used)
  17  *
  18  * How the check works is that every assignment gets an ID.
  19  * We store that assignment ID in a list of assignments that
  20  * haven't been used.  We also set the state of 'err' from
  21  * the example above to be.  Then when we use 'err' we remove
  22  * it from the list.  At the end of the function we print
  23  * a list of assignments that still haven't been used.
  24  *
  25  * Note that this check only works for assignments to
  26  * EXPR_SYMBOL.  Maybe it could be modified to cover other
  27  * assignments later but then you would have to deal with
  28  * scope issues.
  29  *
  30  * Also this state is quite tied to the order the callbacks
  31  * are called in smatch_flow.c.  (If the order changed it
  32  * would break).
  33  *
  34  */
  35
  36 #include "smatch.h"
  37 #include "smatch_slist.h"
  38 #include "smatch_function_hashtable.h"
  39
  40 static int my_id;
  41
  42 struct assignment {
  43         int assign_id;
  44         char *name;
  45         char *function;
  46         int line;
  47 };
  48 ALLOCATOR(assignment, "assignment id");
  49 DECLARE_PTR_LIST(assignment_list, struct assignment);
  50 static struct assignment_list *assignment_list;
  51
  52 static struct expression *skip_this;
  53 static int assign_id;
  54
  55 static DEFINE_HASHTABLE_INSERT(insert_func, char, int);
  56 static DEFINE_HASHTABLE_SEARCH(search_func, char, int);
  57 static struct hashtable *ignored_funcs;
  58
  59 static const char *kernel_ignored[] = {
  60         "inb",
  61         "inl",
  62         "inw",
  63         "readb",
  64         "readl",
  65         "readw",
  66 };
  67
  68 static char *get_fn_name(struct expression *expr)
  69 {
  70         if (expr->type != EXPR_CALL)
  71                 return NULL;
  72         if (expr->fn->type != EXPR_SYMBOL)
  73                 return NULL;
  74         return get_variable_from_expr(expr->fn, NULL);
  75 }
  76
  77 static int ignored_function(struct expression *expr)
  78 {
  79         char *func;
  80         int ret = 0;
  81
  82         func = get_fn_name(expr);
  83         if (!func)
  84                 return 0;
  85         if (search_func(ignored_funcs, func))
  86                 ret = 1;
  87         free_string(func);
  88         return ret;
  89 }
  90
  91 static void match_assign_call(struct expression *expr)
  92 {
  93         struct expression *left;
  94         struct assignment *assign;
  95
  96         if (final_pass)
  97                 return;
  98         if (in_condition())
  99                 return;
 100         if (expr->op != '=')
 101                 return;
 102         if (unreachable())
 103                 return;
 104         if (ignored_function(expr->right))
 105                 return;
 106         left = strip_expr(expr->left);
 107         if (!left || left->type != EXPR_SYMBOL)
 108                 return;
 109         if (left->symbol->ctype.modifiers & (MOD_TOPLEVEL | MOD_EXTERN | MOD_STATIC))
 110                 return;
 111
 112         skip_this = left;
 113
 114         set_state_expr(my_id, left, alloc_state_num(assign_id));
 115
 116         assign = __alloc_assignment(0);
 117         assign->assign_id = assign_id++;
 118         assign->name = get_variable_from_expr(left, NULL);
 119         assign->function = get_fn_name(expr->right);
 120         assign->line = get_lineno();
 121         add_ptr_list(&assignment_list, assign);
 122 }
 123
 124 static void match_assign(struct expression *expr)
 125 {
 126         struct expression *left;
 127
 128         if (expr->op != '=')
 129                 return;
 130         left = strip_expr(expr->left);
 131         if (!left || left->type != EXPR_SYMBOL)
 132                 return;
 133         delete_state_expr(my_id, left);
 134 }
 135
 136 static void delete_used(int assign_id)
 137 {
 138         struct assignment *tmp;
 139
 140         FOR_EACH_PTR(assignment_list, tmp) {
 141                 if (tmp->assign_id == assign_id) {
 142                         DELETE_CURRENT_PTR(tmp);
 143                         return;
 144                 }
 145         } END_FOR_EACH_PTR(tmp);
 146 }
 147
 148 static void delete_used_symbols(struct state_list *possible)
 149 {
 150         struct sm_state *tmp;
 151
 152         FOR_EACH_PTR(possible, tmp) {
 153                 delete_used(PTR_INT(tmp->state->data));
 154         } END_FOR_EACH_PTR(tmp);
 155 }
 156
 157 static void match_symbol(struct expression *expr)
 158 {
 159         struct sm_state *sm;
 160
 161         expr = strip_expr(expr);
 162         if (expr == skip_this)
 163                 return;
 164         sm = get_sm_state_expr(my_id, expr);
 165         if (!sm)
 166                 return;
 167         delete_used_symbols(sm->possible);
 168         delete_state_expr(my_id, expr);
 169 }
 170
 171 static void match_end_func(struct symbol *sym)
 172 {
 173         struct assignment *tmp;
 174
 175         FOR_EACH_PTR(assignment_list, tmp) {
 176                 sm_printf("%s:%d %s ", get_filename(), tmp->line, get_function());
 177                 sm_printf("warn: unused return: %s = %s()\n",
 178                         tmp->name, tmp->function);
 179         } END_FOR_EACH_PTR(tmp);
 180         clear_assignment_alloc();
 181         __free_ptr_list((struct ptr_list **)&assignment_list);
 182 }
 183
 184 void check_unused_ret(int id)
 185 {
 186         my_id = id;
 187
 188         /* It turns out that this test is worthless unless you use --two-passes.  */
 189         if (!option_two_passes)
 190                 return;
 191         add_hook(&match_assign_call, CALL_ASSIGNMENT_HOOK);
 192         add_hook(&match_assign, ASSIGNMENT_HOOK);
 193         add_hook(&match_symbol, SYM_HOOK);
 194         add_hook(&match_end_func, END_FUNC_HOOK);
 195         ignored_funcs = create_function_hashtable(100);
 196         if (option_project == PROJ_KERNEL) {
 197                 int i;
 198
 199                 for (i = 0; i < ARRAY_SIZE(kernel_ignored); i++)
 200                         insert_func(ignored_funcs, (char *)kernel_ignored[i], (int *)1);
 201         }
 202 }