LI82915: MEMORY FAULT WHEN COMPILING WITH -O2

APAR status

• Closed as program error.

Error description

• When compiling with -O2, the resulting binary produces a memory
  fault.
  
  ===== COMPILE COMMAND:
  xlC -std=c++14 -O2 -g  -DONE_PARAM -DTWO_PARAM xl-reproducer.cpp
   -o pgm.both
  
  ===== TESTCASE:
  $ cat xl-reproducer.cpp
  #include <iostream>
  
  struct PodStruct {
    int i;
    double d;
  };
  
  #ifdef ONE_PARAM
  namespace one_param_initializer {
  struct B {
    PodStruct& some_struct;
  };
  
  struct D : public B {
    D(PodStruct& s) : B{s} {}
  };
  }  // namespace one_param_initializer
  #endif // ONE_PARAM
  
  #ifdef TWO_PARAM
  namespace two_param_initializer {
  struct B {
    int some_int;
    PodStruct& some_struct;
  };
  struct D : public B {
    D(int i, PodStruct& s) : B{i, s} {}
  };
  }  // namespace two_param_initializer
  #endif // TWO_PARAM
  
  int main() {
    PodStruct main_struct;
    main_struct.i = 42;
    main_struct.d = .123;
  
  #ifdef ONE_PARAM
    {
      one_param_initializer::D d(main_struct);
  
      std::cout << "one_param_initializer::D::some_struct.i -> "
                << d.some_struct.i << " (address " <<
  &d.some_struct.i << ")"
                << std::endl;
      std::cout << "one_param_initializer::D::some_struct.d -> "
                << d.some_struct.d << " (address " <<
  &d.some_struct.d << ")"
                << std::endl;
    }
  #endif
  
  #ifdef TWO_PARAM
    {
      int main_int = 5;
      two_param_initializer::D d(main_int, main_struct);
  
      std::cout << "two_param_initializer::D::some_struct.i -> "
                << d.some_struct.i << " (address " <<
  &d.some_struct.i << ")"
                << std::endl;
      std::cout << "two_param_initializer::D::some_struct.d -> "
                << d.some_struct.d << " (address " <<
  &d.some_struct.d << ")"
                << std::endl;
    }
  #endif
  
    return 0;
  }
  $
  
  
  ====== ACTUAL OUTPUT:
  $ ./pgm.both
  Memory fault
  $
  
  ===== EXPECTED OUTPUT:
  $ ./pgm.both
  one_param_initializer::D::some_struct.i -> 42 (address
  0x7ffff30e99e0)
  one_param_initializer::D::some_struct.d -> 0.123 (address
  0x7ffff30e99e8)
  two_param_initializer::D::some_struct.i -> 42 (address
  0x10027f00)
  two_param_initializer::D::some_struct.d -> 0.123 (address
  0x10027f08)
  $
  

Local fix

• Temporarily remove -O2 from the compile line
  

Problem summary

• USERS AFFECTED:
  Users of the legacy C++ compiler (ie xlC stanza) who make use of
  a brace-list for initialization of a reference member of a base
  class may be affected by this isue.
  
  PROBLEM DESCRIPTION:
  Initialization of a reference member of a base class through a
  brace-list specification in a constructor initializer list was
  not correct
  (ie, a uniform init for a reference in a base clas was
  incorrect).
  

Problem conclusion

• The legacy C++ compiler was changed to generate correct code
  where the target of a brace-list initializer (a "uniform-init")
  is a reference member of a base class.
  

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++ LINUX

• Fixed component ID

  5725C7310

Applicable component levels