Bus Address Crash in ckh unit test

Christopher Ferris cferris at google.com
Mon Feb 1 15:51:20 PST 2016

When I compiled the ckh unit test with a newer version of clang, it was
crashing. I tracked the problem down to an implicit assumption that a value
passed to chk_search is 4 byte aligned. Specifically, the code in
test/unit/ckh.c, the test test_count_insert_search_remove, makes this call:

  assert_true(ckh_search(&ckh, missing, NULL, NULL),
      "Unexpected ckh_search() success");

The problem is that the definition of missing is:

  char *missing = "A string not in the hash table.";

Which means missing is not guaranteed to be of any alignment.

I'm not sure on what platforms jemalloc needs to be compiled, so I think
that something like this:

  #define HASH_TABLE_STRING "A string not in the hash table."
  union { char char_data[sizeof(HASH_TABLE_STRING)]; uint32_t uint_data; }
  memcpy(missing.char_data, HASH_TABLE_STRING, sizeof(HASH_TABLE_STRING));
  assert_true(ckh_search(&ckh, missing.char_data, NULL, NULL),
      "Unexpected ckh_search() success");

Would guarantee the needed alignment.

Does this seem reasonable?

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