IJ23820: STORE TO NULL WHEN INITIALIZING GLOBAL THREAD_LOCAL ARRAY

APAR status

• Closed as program error.

Error description

• When initializing a thread_local array, a store to NULL occurs
  causing a segmentation fault.  The stacktrace shows the code
  going through the "TLS init function" and "TLS wrapper
  function", until it tries to create a Class
  __compressed_pair_elem - the bad store happens in the
  constructor for this class:
  
     std::__1::__compressed_pair_elem<std::__1::basic_string<char,
     std::__1::char_traits<char>, std::__1::allocator<char>
     >::__rep,0, false>::__compressed_pair_elem()(this = (nil)),
     line 2043 in "memory"
     _ZTH3str() at 0x100000da8          ==> TLS init function
     _ZTW3str(), line 2062 in "memory"  ==> TLS wrapper function
     main(), line 9 in "main.cpp"
  
  
     === TEST CASE ===
  
  #include <iostream>
  #include <string>
  using namespace std;
  
  thread_local string str[5];
  
  int main()
  {
     str[1] = "ThreadLocal";
     cout << "String: " << str[1] << endl;
  }
  
  
  
  $ xlclang++ main.cpp
  $ ./a.out
  Segmentation fault (core dumped)
  $
  

Local fix

Problem summary

• USERS AFFECTED:
  Users of non-local arrays with thread_local storage duration
  that have or might have
  non-constant initialization maybe affected by this issue.
  Users of similar thread_local references to functions may also
  be affected by this issue.
  
  PROBLEM DESCRIPTION:
  The thread-local wrapper function that is meant to cause
  initialization of a
  thread-local array with non-local possibly-non-constant
  initialization
  on its first use may be incorrectly generated and/or
  incorrectly called.
  This may manifest as a compile-time abend, a runtime abend, or
  incorrect output at runtime.
  

Problem conclusion

• The generation of thread-local wrapper functions is corrected
  to
  avoid issues related to array-to-pointer conversion,
  function-to-pointer conversion, etc.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  XL C/C++ FOR AI

• Fixed component ID

  5725C7200

Applicable component levels