[gnutls-devel] libtasn1 | Fix handling of code which uses NULL pointers + offset (fixes issue #30) (!71)

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Wed Feb 3 07:27:13 CET 2021

Stefan Weil commented:

Code constructs like (NULL + offset) are undefined, so clang may handle that as NULL and ignore the offset. This can also be a security feature to avoid illegal memory access. Try this test program with `-O2`:

    #include <stdio.h>
    static void f(int offset, const void *p) {
      if (p != NULL) {
        printf("NULL+%d => %p\n", offset, p + offset);
      } else {
        printf("NULL+%d => NULL\n", offset);
    int main(int argc, char *argv[]) {
      void *p = NULL;
      f(argc, p);
      return 0;

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