Example: pointer_copy_user_ctrlflow_bytewise.c

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    #include <stdio.h>
    #include <string.h>
    #include <assert.h>
    #include <limits.h>
    int x=1;
    unsigned char control_flow_copy(unsigned char c) {
      assert(UCHAR_MAX==255);
      switch (c) {
      case 0: return(0);
      case 1: return(1);
      case 2: return(2);
      case 3: return(3);
      case 4: return(4);
      case 5: return(5);
      case 6: return(6);
      case 7: return(7);
      case 8: return(8);
      case 9: return(9);
      case 10: return(10);
      case 11: return(11);
      case 12: return(12);
      case 13: return(13);
      case 14: return(14);
      case 15: return(15);
      case 16: return(16);
      case 17: return(17);
      case 18: return(18);
      case 19: return(19);
      case 20: return(20);
      case 21: return(21);
      case 22: return(22);
      case 23: return(23);
      case 24: return(24);
      case 25: return(25);
      case 26: return(26);
      case 27: return(27);
      case 28: return(28);
      case 29: return(29);
      case 30: return(30);
      case 31: return(31);
      case 32: return(32);
      case 33: return(33);
      case 34: return(34);
      case 35: return(35);
      case 36: return(36);
      case 37: return(37);
      case 38: return(38);
      case 39: return(39);
      case 40: return(40);
      case 41: return(41);
      case 42: return(42);
      case 43: return(43);
      case 44: return(44);
      case 45: return(45);
      case 46: return(46);
      case 47: return(47);
      case 48: return(48);
      case 49: return(49);
      case 50: return(50);
      case 51: return(51);
      case 52: return(52);
      case 53: return(53);
      case 54: return(54);
      case 55: return(55);
      case 56: return(56);
      case 57: return(57);
      case 58: return(58);
      case 59: return(59);
      case 60: return(60);
      case 61: return(61);
      case 62: return(62);
      case 63: return(63);
      case 64: return(64);
      case 65: return(65);
      case 66: return(66);
      case 67: return(67);
      case 68: return(68);
      case 69: return(69);
      case 70: return(70);
      case 71: return(71);
      case 72: return(72);
      case 73: return(73);
      case 74: return(74);
      case 75: return(75);
      case 76: return(76);
      case 77: return(77);
      case 78: return(78);
      case 79: return(79);
      case 80: return(80);
      case 81: return(81);
      case 82: return(82);
      case 83: return(83);
      case 84: return(84);
      case 85: return(85);
      case 86: return(86);
      case 87: return(87);
      case 88: return(88);
      case 89: return(89);
      case 90: return(90);
      case 91: return(91);
      case 92: return(92);
      case 93: return(93);
      case 94: return(94);
      case 95: return(95);
      case 96: return(96);
      case 97: return(97);
      case 98: return(98);
      case 99: return(99);
      case 100: return(100);
      case 101: return(101);
      case 102: return(102);
      case 103: return(103);
      case 104: return(104);
      case 105: return(105);
      case 106: return(106);
      case 107: return(107);
      case 108: return(108);
      case 109: return(109);
      case 110: return(110);
      case 111: return(111);
      case 112: return(112);
      case 113: return(113);
      case 114: return(114);
      case 115: return(115);
      case 116: return(116);
      case 117: return(117);
      case 118: return(118);
      case 119: return(119);
      case 120: return(120);
      case 121: return(121);
      case 122: return(122);
      case 123: return(123);
      case 124: return(124);
      case 125: return(125);
      case 126: return(126);
      case 127: return(127);
      case 128: return(128);
      case 129: return(129);
      case 130: return(130);
      case 131: return(131);
      case 132: return(132);
      case 133: return(133);
      case 134: return(134);
      case 135: return(135);
      case 136: return(136);
      case 137: return(137);
      case 138: return(138);
      case 139: return(139);
      case 140: return(140);
      case 141: return(141);
      case 142: return(142);
      case 143: return(143);
      case 144: return(144);
      case 145: return(145);
      case 146: return(146);
      case 147: return(147);
      case 148: return(148);
      case 149: return(149);
      case 150: return(150);
      case 151: return(151);
      case 152: return(152);
      case 153: return(153);
      case 154: return(154);
      case 155: return(155);
      case 156: return(156);
      case 157: return(157);
      case 158: return(158);
      case 159: return(159);
      case 160: return(160);
      case 161: return(161);
      case 162: return(162);
      case 163: return(163);
      case 164: return(164);
      case 165: return(165);
      case 166: return(166);
      case 167: return(167);
      case 168: return(168);
      case 169: return(169);
      case 170: return(170);
      case 171: return(171);
      case 172: return(172);
      case 173: return(173);
      case 174: return(174);
      case 175: return(175);
      case 176: return(176);
      case 177: return(177);
      case 178: return(178);
      case 179: return(179);
      case 180: return(180);
      case 181: return(181);
      case 182: return(182);
      case 183: return(183);
      case 184: return(184);
      case 185: return(185);
      case 186: return(186);
      case 187: return(187);
      case 188: return(188);
      case 189: return(189);
      case 190: return(190);
      case 191: return(191);
      case 192: return(192);
      case 193: return(193);
      case 194: return(194);
      case 195: return(195);
      case 196: return(196);
      case 197: return(197);
      case 198: return(198);
      case 199: return(199);
      case 200: return(200);
      case 201: return(201);
      case 202: return(202);
      case 203: return(203);
      case 204: return(204);
      case 205: return(205);
      case 206: return(206);
      case 207: return(207);
      case 208: return(208);
      case 209: return(209);
      case 210: return(210);
      case 211: return(211);
      case 212: return(212);
      case 213: return(213);
      case 214: return(214);
      case 215: return(215);
      case 216: return(216);
      case 217: return(217);
      case 218: return(218);
      case 219: return(219);
      case 220: return(220);
      case 221: return(221);
      case 222: return(222);
      case 223: return(223);
      case 224: return(224);
      case 225: return(225);
      case 226: return(226);
      case 227: return(227);
      case 228: return(228);
      case 229: return(229);
      case 230: return(230);
      case 231: return(231);
      case 232: return(232);
      case 233: return(233);
      case 234: return(234);
      case 235: return(235);
      case 236: return(236);
      case 237: return(237);
      case 238: return(238);
      case 239: return(239);
      case 240: return(240);
      case 241: return(241);
      case 242: return(242);
      case 243: return(243);
      case 244: return(244);
      case 245: return(245);
      case 246: return(246);
      case 247: return(247);
      case 248: return(248);
      case 249: return(249);
      case 250: return(250);
      case 251: return(251);
      case 252: return(252);
      case 253: return(253);
      case 254: return(254);
      case 255: return(255);
      }
    }
    void user_memcpy2(unsigned char* dest, 
                      unsigned char *src, size_t n) {
      while (n > 0)  {      
        *dest = control_flow_copy(*src);
        src += 1;
        dest += 1;
        n -= 1;
      }
    }
    int main() {
      int *p = &x;
      int *q;
      user_memcpy2((unsigned char*)&q, (unsigned char*)&p, 
                  sizeof(p));
      *q = 11; // does this have undefined behaviour?
      printf("*p=%d  *q=%d\n",*p,*q);
    }
[link to run test in Cerberus]

Experimental data (what does this mean?) 



cerberus-concrete-PVI Undefined behaviour: the operand of the unary '*' operator has an invalid value at 282:3-5


cerberus-concrete-PNVI *p=11  *q=11


gcc-8.1-O0 *p=11  *q=11


gcc-8.1-O2 *p=11  *q=11


gcc-8.1-O3 *p=11  *q=11


gcc-8.1-O2-no-strict-aliasing *p=11  *q=11


gcc-8.1-O3-no-strict-aliasing *p=11  *q=11


clang-6.0-O0 pointer_copy_user_ctrlflow_bytewise.c:266:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
*p=11  *q=11


clang-6.0-O2 pointer_copy_user_ctrlflow_bytewise.c:266:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
*p=11  *q=11


clang-6.0-O3 pointer_copy_user_ctrlflow_bytewise.c:266:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
*p=11  *q=11


clang-6.0-O2-no-strict-aliasing pointer_copy_user_ctrlflow_bytewise.c:266:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
*p=11  *q=11


clang-6.0-O3-no-strict-aliasing pointer_copy_user_ctrlflow_bytewise.c:266:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
*p=11  *q=11


clang-6.0-UBSAN pointer_copy_user_ctrlflow_bytewise.c:266:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
*p=11  *q=11


clang-6.0-ASAN pointer_copy_user_ctrlflow_bytewise.c:266:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
*p=11  *q=11


clang-6.0-MSAN pointer_copy_user_ctrlflow_bytewise.c:266:1: warning: control may reach end of non-void function [-Wreturn-type]
}
^
1 warning generated.
*p=11  *q=11


icc-19-O0 pointer_copy_user_ctrlflow_bytewise.c(266): warning #1011: missing return statement at end of non-void function "control_flow_copy"
  }
  ^

*p=11  *q=11


icc-19-O2 pointer_copy_user_ctrlflow_bytewise.c(266): warning #1011: missing return statement at end of non-void function "control_flow_copy"
  }
  ^

*p=11  *q=11


icc-19-O3 pointer_copy_user_ctrlflow_bytewise.c(266): warning #1011: missing return statement at end of non-void function "control_flow_copy"
  }
  ^

*p=11  *q=11


icc-19-O2-no-strict-aliasing pointer_copy_user_ctrlflow_bytewise.c(266): warning #1011: missing return statement at end of non-void function "control_flow_copy"
  }
  ^

*p=11  *q=11


icc-19-O3-no-strict-aliasing pointer_copy_user_ctrlflow_bytewise.c(266): warning #1011: missing return statement at end of non-void function "control_flow_copy"
  }
  ^

*p=11  *q=11


compcert-3.4 pointer_copy_user_ctrlflow_bytewise.c:6: warning: control reaches end of non-void function [-Wreturn-type]
*p=11  *q=11


compcert-3.4-O pointer_copy_user_ctrlflow_bytewise.c:6: warning: control reaches end of non-void function [-Wreturn-type]
*p=11  *q=11


kcc-1.0 exit codes: compile 0 / execute 139
Switching on an unspecified controlling expression:
      > in control_flow_copy at pointer_copy_user_ctrlflow_bytewise.c:8:3
        in user_memcpy2 at pointer_copy_user_ctrlflow_bytewise.c:271:5
        in main at pointer_copy_user_ctrlflow_bytewise.c:280:3

    Unspecified value or behavior (USP-ESS1):
        see C11 section 6.8.4.2:5 http://rvdoc.org/C11/6.8.4.2
        see MISRA-C section 8.1:3 http://rvdoc.org/MISRA-C/8.1

Casting empty value to type other than void:
      > in control_flow_copy at pointer_copy_user_ctrlflow_bytewise.c:8:3
        in user_memcpy2 at pointer_copy_user_ctrlflow_bytewise.c:271:5
        in main at pointer_copy_user_ctrlflow_bytewise.c:280:3

    Undefined behavior (UB-CCV5):
        see C11 section 6.3.2.2:1 http://rvdoc.org/C11/6.3.2.2
        see C11 section J.2:1 item 23 http://rvdoc.org/C11/J.2
        see CERT-C section MSC15-C http://rvdoc.org/CERT-C/MSC15-C
        see CERT-C section MSC37-C http://rvdoc.org/CERT-C/MSC37-C
        see MISRA-C section 8.1:3 http://rvdoc.org/MISRA-C/8.1

Indeterminate value used in an expression:
      > in user_memcpy2 at pointer_copy_user_ctrlflow_bytewise.c:271:5
        in main at pointer_copy_user_ctrlflow_bytewise.c:280:3

    Undefined behavior (UB-CEE2):
        see C11 section 6.2.4 http://rvdoc.org/C11/6.2.4
        see C11 section 6.7.9 http://rvdoc.org/C11/6.7.9
        see C11 section 6.8 http://rvdoc.org/C11/6.8
        see C11 section J.2:1 item 11 http://rvdoc.org/C11/J.2
        see CERT-C section EXP33-C http://rvdoc.org/CERT-C/EXP33-C
        see MISRA-C section 8.9:1 http://rvdoc.org/MISRA-C/8.9
        see MISRA-C section 8.1:3 http://rvdoc.org/MISRA-C/8.1

Dereferencing a null pointer:
      > in main at pointer_copy_user_ctrlflow_bytewise.c:282:3

    Undefined behavior (UB-CER3):
        see C11 section 6.5.3.2:4 http://rvdoc.org/C11/6.5.3.2
        see C11 section J.2:1 item 43 http://rvdoc.org/C11/J.2
        see CERT-C section EXP34-C http://rvdoc.org/CERT-C/EXP34-C
        see MISRA-C section 8.1:3 http://rvdoc.org/MISRA-C/8.1

Execution failed (configuration dumped)