LI83059: MEMBER OBJECT 'THIS' POINTER INCORRECT WHEN CALLING DESTRUC AFTER EXCEPTION

APAR status

• Closed as program error.

Error description

• ERROR DESCRIPTION:
  When using optimization, a base class destructor called during
  exception handling appears to have the wrong 'this' pointer.
  
  The class object is a member is a different class, and is
  preceded in the object by another data member (in the example
  below, 'd_data').  The positioning of the members affects the
  memory offset into the class, and appears to affect the
  incorrect value of the problem class's 'this' pointer.
  
  This issue affects object compiled with both the legacy xlC
  compiler, and the xlclang++ compiler.
  
  
     === TEST CASE ===
  
  #include <cstdio>
  
  class Base {
    int    d_value;
  
    public:
      Base() : d_value(0) { std::printf("ct:  this=%p\n",this); }
      ~Base() { std::printf("dt:  this=%p d_value=%d\n", this,
                d_value); }
  };
  
  class Derived : public Base {
    public:
      Derived() : Base() { throw 77; }
  };
  
  class DerivedHolder {
    private:
      int d_data;  // Member causing offset of d_derived 'this'
      Derived d_derived;
  
    public:
      explicit DerivedHolder() : d_data(42) , d_derived() { }
  };
  
  int main()
  {
      try {
          DerivedHolder *const holder = ::new DerivedHolder();
          ::delete holder;
      }
      catch (...) { }
      return 0;
  }
  
  
  $ xlC test.cpp
  $ ./a.out
  ct:  this=20002d0c
  dt:  this=20002d0c d_value=0
  $ xlC -O test.cpp
  $ ./a.out
  ct:  this=20002b0c
  dt:  this=20002b08 d_value=42
  
  LOCAL FIX:
  Do not use optimization.
  

Local fix

• Do not use optimization.
  

Problem summary

• PROBLEM DESCRIPTION:
  An incorrect memory address is referenced when accessing an
  object member when optimization is used.
  
  USERS AFFECTED:
  Users of optimization, exception handling, and objects
  containing sub-object members.
  

Problem conclusion

• An issue with code inlining that was affecting how offsets into
  an object were calculated was fixed.
  

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