LI78989: DWARF DW_AT_TYPE : 0X0 WITH MULTI-DIMENSIONAL ARRAYS CAUSING DEBUGGER ERROR

IBM XL C/C++ for Linux 13.1.4
IBM XL C/C++ for Linux 13.1.5
IBM XL C/C++ for Linux 13.1.6
XL C/C++ for Linux, V13.1.6.1 Fix Pack (December 2017)

APAR status

• Closed as fixed if next.

Error description

• Incorrect DWARF debugging information is generated when
  multi-dimensional arrays are used, causing debugger errors when
  debugging the code.
  
  The specific code pattern causing the problem is the presence of
  a multi-dimensional array definition, followed immediately by
  another array of the same TYPE which is also the same SIZE as
  the second dimension of the multi-dimensional array.
  
  The compiler is incorrectly flagging some of the required debug
  type information of the multi-dimensional array as duplicate
  information.  The compiler then deleted the required type debug
  information; generating incorrect DWARF debugging information.
  This can cause errors when running the code with a debugger.
  
  
  An example of an error from the GDB debugger is:
  
     Dwarf Error: Cannot find DIE at 0x5ee6c2 referenced from DIE
     at 0x5f414c [in module test]
  
  This is caused by the incorrect DWARF debug information, as read
  by 'readelf -wi':
  
     <5abb>   DW_AT_type        : 0x0
  
  
  
     === TEST CASE ===
  
  char bad[5][10];
  struct a{
     char space[10];
  };
  int main(){
     struct a a1;
      return 0;
  }
  
  
  
  $ xlc -c t.c -g
  $ readelf -wi t.o | grep "DW_AT_type        : 0x0"
      <b1>   DW_AT_type        : 0x0
  $
  

Local fix

• The issue can be worked around by modifying the code near the
  multi-dimensional array definition:
  
  - Change the array types so they do not match
  - Change the array sizes so they do not match
  - Move the multi-dimensional array definition AFTER the other
  array
  

Problem summary

• The DWARF debug generation issue has been corrected, and
  'readelf -wi' output should no longer display "DW_AT_type
   : 0x0".  Debugging is no longer impaired.  The fix will be
  available in a future MOD release.
  

Problem conclusion

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

Applicable component levels

• RD13 PSY

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