1 2 #include <stdio.h> 3 #include <stdlib.h> 4 #include <string.h> 5 6 int main ( void ) 7 { 8 char* x = strdup("hello"); 9 char c; 10 char c0[8], c1[8], c2[8], c3[8], c4[8]; 11 12 // Each of these pointers has a different alignment 13 char** p0 = (char**)&c0[0]; char** p1 = (char**)&c1[1]; 14 char** p2 = (char**)&c2[2]; char** p3 = (char**)&c3[3]; 15 char** p4 = (char**)&c4[4]; 16 *p0 = x; *p1 = x; *p2 = x; 17 *p3 = x; *p4 = x; 18 19 // These 10 are ok 20 c = (*p0)[0]; 21 c = (*p1)[0]; 22 c = (*p2)[0]; 23 c = (*p3)[0]; 24 c = (*p4)[0]; 25 26 c = (*p0)[5]; 27 c = (*p1)[5]; 28 c = (*p2)[5]; 29 c = (*p3)[5]; 30 c = (*p4)[5]; 31 32 // These 10 are bad 33 c = (*p0)[-1]; // always word aligned, so det 34 c = (*p1)[-1]; // undet 35 c = (*p2)[-1]; // undet 36 c = (*p3)[-1]; // undet 37 c = (*p4)[-1]; // undet on 64-bit since not 64-bit aligned 38 39 c = (*p0)[6]; // always word aligned, so det 40 c = (*p1)[6]; // undet 41 c = (*p2)[6]; // undet 42 c = (*p3)[6]; // undet 43 c = (*p4)[6]; // undet on 64-bit since not 64-bit aligned 44 45 return 0; 46 } 47 48 /* What this program does: verifies that (unfortunately) if you store a 49 pointer misaligned, then the associated shadow value decays to Unknown, 50 and so when you retrieve the pointer later and dereference it, you 51 get no check :-( */ 52
