strongSwan

When this code is built with Clang, parts of plugin_feature_t are left uninitialized.

You've got a union with fields of varying size. Clang does not clear padding bytes when a shorter field is initialized. I believe it is aligned with the standard, because reading from a field of a union other the last assigned one is UB, so you should never be able to observe this uninitialized padding.

Find a relevant compiler issue by this link: http://llvm.org/bugs/show_bug.cgi?id=14352

struct S {
  int a;
  int b;
  union {
    struct {
      void * p;
      void * q;
    } a;
    int b;
  } c;
};

void g(struct S*);

void f(int x, int y) {
  struct S s = (struct S){x, x, {.b = y}};
  g(s);
}

f():
   0:   48 83 ec 18             sub    $0x18,%rsp
   4:   89 3c 24                mov    %edi,(%rsp)
   7:   89 7c 24 04             mov    %edi,0x4(%rsp)
   b:   89 74 24 08             mov    %esi,0x8(%rsp)
   f:   48 8d 3c 24             lea    (%rsp),%rdi
  13:   e8 00 00 00 00          callq  18 <f+0x18>
                        14: R_X86_64_PC32       g-0x4
  18:   48 83 c4 18             add    $0x18,%rsp
  1c:   c3                      retq