IJ22942: BRANCH TO NULL WHEN TLS VARIABLE HELPER FUNCTION IS IN LIBRARY WITH RUNTIME LINKING

APAR status

• Closed as program error.

Error description

• An illegal instruction runtime error is encountered after a
  branch to NULL caused by an invalid branch location loaded for a
  TLS (Thread Local Storage) init function,
  _ZTH#<tls_variable_name>.  This occurs for C11 thread_local TLS
  variables.
  
  The error occurs when calling the function in a shared library
  with runtime linking enabled.  Static linking is unaffected.
  

Local fix

Problem summary

• PROBLEM DESCRIPTION:
  Runtime fault when entering an extern alias function inside a
  dynamically linked library.  The function descriptor for the
  target function is not populated correctly, for example with a
  function called 'tlsTest':
  
  .csect _ZTH7tlsTest{DS}, 3
  .long 0x00000000
  .long 0x00000000
  .long 0x00000000
  .long 0x00000380
  .long 0x00000000
  .long 0x00000000
  
  
  .toc
  # End csect _ZTH7tlsTest{DS}
  
  The function descriptor should look like:
  
  .csect _ZTH7tlsTest{DS}, 3
  .llong ._ZTH7tlsTest
  .llong TOC{TC0}
  .long 0x00000000
  .long 0x00000000
  # End csect _ZTH7tlsTest{DS}
  
  
  USERS AFFECTED:
  Users of thread_local or function alias attribute
  __attribute__((__alias__('func_name')));
  

Problem conclusion

• The alias issue was resolved, and the function descriptor is
  populated correctly now.
  

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