Example: pointer_copy_user_ctrlflow_bitwise.c

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    #include <stdio.h>
    #include <inttypes.h>
    #include <limits.h>
    int x=1;
    int main() {
      int *p = &x;
      uintptr_t i = (uintptr_t)p;
      int uintptr_t_width = sizeof(uintptr_t) * CHAR_BIT;
      uintptr_t bit, j;
      int k;
      j=0;
      for (k=0; k<uintptr_t_width; k++) {
        bit = (i & (((uintptr_t)1) << k)) >> k;
        if (bit == 1) 
          j = j | ((uintptr_t)1 << k);
        else
          j = j;
      }
      int *q = (int *)j;
      *q = 11; // is this free of 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-plain *p=11  *q=11


cerberus-concrete-PVI-ae *p=11  *q=11


cerberus-concrete-PVI-ae-udi *p=11  *q=11


gcc-8.3-O0 *p=11  *q=11


gcc-8.3-O2 *p=11  *q=11


gcc-8.3-O3 *p=11  *q=11


gcc-8.3-O2-no-strict-aliasing *p=11  *q=11


gcc-8.3-O3-no-strict-aliasing *p=11  *q=11


clang-7.0.1-O0 pointer_copy_user_ctrlflow_bitwise.c:17:9: warning: explicitly assigning value of variable of type 'uintptr_t' (aka 'unsigned long') to itself [-Wself-assign]
      j = j;
      ~ ^ ~
1 warning generated.
*p=11  *q=11


clang-7.0.1-O2 pointer_copy_user_ctrlflow_bitwise.c:17:9: warning: explicitly assigning value of variable of type 'uintptr_t' (aka 'unsigned long') to itself [-Wself-assign]
      j = j;
      ~ ^ ~
1 warning generated.
*p=11  *q=11


clang-7.0.1-O3 pointer_copy_user_ctrlflow_bitwise.c:17:9: warning: explicitly assigning value of variable of type 'uintptr_t' (aka 'unsigned long') to itself [-Wself-assign]
      j = j;
      ~ ^ ~
1 warning generated.
*p=11  *q=11


clang-7.0.1-O2-no-strict-aliasing pointer_copy_user_ctrlflow_bitwise.c:17:9: warning: explicitly assigning value of variable of type 'uintptr_t' (aka 'unsigned long') to itself [-Wself-assign]
      j = j;
      ~ ^ ~
1 warning generated.
*p=11  *q=11


clang-7.0.1-O3-no-strict-aliasing pointer_copy_user_ctrlflow_bitwise.c:17:9: warning: explicitly assigning value of variable of type 'uintptr_t' (aka 'unsigned long') to itself [-Wself-assign]
      j = j;
      ~ ^ ~
1 warning generated.
*p=11  *q=11


icc-19-O0 *p=11  *q=11


icc-19-O2 *p=11  *q=11


icc-19-O3 *p=11  *q=11


icc-19-O2-no-strict-aliasing *p=11  *q=11


icc-19-O3-no-strict-aliasing *p=11  *q=11