smatch_struct_assignment.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 /*
  19  * This file started out by saying that if you have:
  20  *
  21  *      struct foo one, two;
  22  *      ...
  23  *      one = two;
  24  *
  25  * That's equivalent to saying:
  26  *
  27  *      one.x = two.x;
  28  *      one.y = two.y;
  29  *
  30  * Turning an assignment like that into a bunch of small fake assignments is
  31  * really useful.
  32  *
  33  * The call to memcpy(&one, &two, sizeof(foo)); is the same as "one = two;" so
  34  * we can re-use the code.  And we may as well use it for memset() too.
  35  * Assigning pointers is almost the same:
  36  *
  37  *      p1 = p2;
  38  *
  39  * Is the same as:
  40  *
  41  *      p1->x = p2->x;
  42  *      p1->y = p2->y;
  43  *
  44  * The problem is that you can go a bit crazy with pointers to pointers.
  45  *
  46  *      p1->x->y->z->one->two->three = p2->x->y->z->one->two->three;
  47  *
  48  * I don't have a proper solution for this problem right now.  I just copy one
  49  * level and don't nest.  It should handle limitted nesting but intelligently.
  50  *
  51  * The other thing is that you end up with a lot of garbage assignments where
  52  * we record "x could be anything. x->y could be anything. x->y->z->a->b->c
  53  * could *also* be anything!".  There should be a better way to filter this
  54  * useless information.
  55  *
  56  */
  57
  58 #include "scope.h"
  59 #include "smatch.h"
  60 #include "smatch_slist.h"
  61 #include "smatch_extra.h"
  62
  63 static struct symbol *get_struct_type(struct expression *expr)
  64 {
  65         struct symbol *type;
  66
  67         type = get_type(expr);
  68         if (!type)
  69                 return NULL;
  70         if (type->type == SYM_PTR)
  71                 type = get_real_base_type(type);
  72         if (type && type->type == SYM_STRUCT)
  73                 return type;
  74         return NULL;
  75 }
  76
  77 static struct expression *get_matching_member_expr(struct symbol *left_type, struct expression *right, struct symbol *left_member)
  78 {
  79         struct symbol *struct_type;
  80         int op = '.';
  81
  82         if (!left_member->ident)
  83                 return NULL;
  84
  85         struct_type = get_struct_type(right);
  86         if (!struct_type)
  87                 return NULL;
  88         if (struct_type != left_type)
  89                 return NULL;
  90
  91         if (right->type == EXPR_PREOP && right->op == '&')
  92                 right = strip_expr(right->unop);
  93
  94         if (is_pointer(right)) {
  95                 right = deref_expression(right);
  96                 op = '*';
  97         }
  98
  99         return member_expression(right, op, left_member->ident);
 100 }
 101
 102 static struct expression *remove_addr(struct expression *expr)
 103 {
 104         expr = strip_expr(expr);
 105
 106         if (expr->type == EXPR_PREOP && expr->op == '&')
 107                 return strip_expr(expr->unop);
 108         return expr;
 109 }
 110
 111 void __struct_members_copy(int mode, struct expression *left, struct expression *right)
 112 {
 113         struct symbol *struct_type, *tmp, *type;
 114         struct expression *left_member;
 115         struct expression *right_member = NULL;
 116         struct expression *assign;
 117         int op = '.';
 118
 119
 120         if (__in_fake_assign)
 121                 return;
 122
 123         left = strip_expr(left);
 124         right = strip_expr(right);
 125
 126         struct_type = get_struct_type(left);
 127         if (!struct_type) {
 128                 /*
 129                  * This is not a struct assignment obviously.  But this is where
 130                  * memcpy() is handled so it feels like a good place to add this
 131                  * code.
 132                  */
 133
 134                 type = get_type(left);
 135                 if (!type || type->type != SYM_BASETYPE)
 136                         return;
 137
 138                 right = strip_expr(right);
 139                 if (right && right->type == EXPR_PREOP && right->op == '&')
 140                         right = remove_addr(right);
 141                 else
 142                         right = unknown_value_expression(left);
 143                 assign = assign_expression(left, right);
 144                 __in_fake_assign++;
 145                 __split_expr(assign);
 146                 __in_fake_assign--;
 147                 return;
 148         }
 149
 150         if (is_pointer(left)) {
 151                 left = deref_expression(left);
 152                 op = '*';
 153         }
 154
 155         FOR_EACH_PTR(struct_type->symbol_list, tmp) {
 156                 type = get_real_base_type(tmp);
 157                 if (type && type->type == SYM_ARRAY)
 158                         continue;
 159
 160                 left_member = member_expression(left, op, tmp->ident);
 161
 162                 switch (mode) {
 163                 case COPY_NORMAL:
 164                 case COPY_MEMCPY:
 165                         right_member = get_matching_member_expr(struct_type, right, tmp);
 166                         break;
 167                 case COPY_MEMSET:
 168                         right_member = right;
 169                         break;
 170                 }
 171                 if (!right_member)
 172                         right_member = unknown_value_expression(left_member);
 173                 assign = assign_expression(left_member, right_member);
 174                 __in_fake_assign++;
 175                 __split_expr(assign);
 176                 __in_fake_assign--;
 177         } END_FOR_EACH_PTR(tmp);
 178 }
 179
 180 void __fake_struct_member_assignments(struct expression *expr)
 181 {
 182         struct symbol *struct_type;
 183
 184         if (is_zero(expr->right))
 185                 return;
 186
 187         struct_type = get_struct_type(expr->left);
 188         if (!struct_type)
 189                 return;
 190
 191         __struct_members_copy(COPY_NORMAL, expr->left, expr->right);
 192 }
 193
 194 static void match_memset(const char *fn, struct expression *expr, void *_size_arg)
 195 {
 196         struct expression *buf;
 197         struct expression *val;
 198
 199         buf = get_argument_from_call_expr(expr->args, 0);
 200         val = get_argument_from_call_expr(expr->args, 1);
 201
 202         buf = strip_expr(buf);
 203         __struct_members_copy(COPY_MEMSET, remove_addr(buf), val);
 204 }
 205
 206 static void match_memcpy(const char *fn, struct expression *expr, void *_arg)
 207 {
 208         struct expression *dest;
 209         struct expression *src;
 210
 211         dest = get_argument_from_call_expr(expr->args, 0);
 212         src = get_argument_from_call_expr(expr->args, 1);
 213
 214         __struct_members_copy(COPY_MEMCPY, remove_addr(dest), remove_addr(src));
 215 }
 216
 217 static void match_memcpy_unknown(const char *fn, struct expression *expr, void *_arg)
 218 {
 219         struct expression *dest;
 220
 221         dest = get_argument_from_call_expr(expr->args, 0);
 222         __struct_members_copy(COPY_MEMCPY, remove_addr(dest), NULL);
 223 }
 224
 225 static void register_clears_param(void)
 226 {
 227         struct token *token;
 228         char name[256];
 229         const char *function;
 230         int param;
 231
 232         if (option_project == PROJ_NONE)
 233                 return;
 234
 235         snprintf(name, 256, "%s.clears_argument", option_project_str);
 236
 237         token = get_tokens_file(name);
 238         if (!token)
 239                 return;
 240         if (token_type(token) != TOKEN_STREAMBEGIN)
 241                 return;
 242         token = token->next;
 243         while (token_type(token) != TOKEN_STREAMEND) {
 244                 if (token_type(token) != TOKEN_IDENT)
 245                         return;
 246                 function = show_ident(token->ident);
 247                 token = token->next;
 248                 if (token_type(token) != TOKEN_NUMBER)
 249                         return;
 250                 param = atoi(token->number);
 251                 add_function_hook(function, &match_memcpy_unknown, INT_PTR(param));
 252                 token = token->next;
 253         }
 254         clear_token_alloc();
 255 }
 256
 257 static void db_param_cleared(struct expression *expr, int param, char *key, char *value)
 258 {
 259         struct expression *arg;
 260
 261         while (expr->type == EXPR_ASSIGNMENT)
 262                 expr = strip_expr(expr->right);
 263         if (expr->type != EXPR_CALL)
 264                 return;
 265
 266         arg = get_argument_from_call_expr(expr->args, param);
 267         if (!arg)
 268                 return;
 269
 270         if (strcmp(value, "0") == 0)
 271                 __struct_members_copy(COPY_MEMSET, remove_addr(arg), zero_expr());
 272         else
 273                 __struct_members_copy(COPY_MEMCPY, remove_addr(arg), NULL);
 274
 275 }
 276
 277 void register_struct_assignment(int id)
 278 {
 279         add_function_hook("memset", &match_memset, NULL);
 280
 281         add_function_hook("memcpy", &match_memcpy, INT_PTR(0));
 282         add_function_hook("memmove", &match_memcpy, INT_PTR(0));
 283
 284         register_clears_param();
 285         select_return_states_hook(PARAM_CLEARED, &db_param_cleared);
 286 }