Allocation mémoire et addresses
Bonsoir,
J'ai remarqué en executant le programme ci dessous que mon ordi allouait 2 fois la taille demandé pour une variable, si quelqu'un pouvait m'expliquer pourquoi..
Code:
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| #include <stdio.h>
#include <string.h>
int main(int argc, char *argv[]) {
int value = 5;
char buffer_one[8], buffer_two[8];
strcpy(buffer_one, "one"); /* Put "one" into buffer_one. */
strcpy(buffer_two, "two"); /* Put "two" into buffer_two. */
printf("[BEFORE] buffer_two is at %p and contains \'%s\'\n", buffer_two, buffer_two);
printf("[BEFORE] buffer_one is at %p and contains \'%s\'\n", buffer_one, buffer_one);
printf("[BEFORE] value is at %p and is %d (0x%08x)\n", &value, value, value);
printf("\n[STRCPY] copying %d bytes into buffer_two\n\n", (int)strlen(argv[1]));
strcpy(buffer_two, argv[1]); /* Copy first argument into buffer_two. */
printf("[AFTER] buffer_two is at %p and contains \'%s\'\n", buffer_two, buffer_two);
printf("[AFTER] buffer_one is at %p and contains \'%s\'\n", buffer_one, buffer_one);
printf("[AFTER] value is at %p and is %d (0x%08x)\n", &value, value, value);
} |
Exemple d'execution:
Citation:
$ ./overflow_exemple 1234567890
[BEFORE] buffer_two is at 0x7fff62e3d7c0 and contains 'two'
[BEFORE] buffer_one is at 0x7fff62e3d7d0 and contains 'one'
[BEFORE] value is at 0x7fff62e3d7bc and is 5 (0x00000005)
[STRCPY] copying 10 bytes into buffer_two
[AFTER] buffer_two is at 0x7fff62e3d7c0 and contains '1234567890'
[AFTER] buffer_one is at 0x7fff62e3d7d0 and contains 'one'
[AFTER] value is at 0x7fff62e3d7bc and is 5 (0x00000005)
Les 16 premiers caractères sont insérés dans buffer_two alors que je ne lui ai alloué que 8 cases, la suite va dans buffer_one.
Si quelqu'un peut m'eclaircir..
