IV49625: SEGFAULT WITH LIMITED SCOPE VARIABLES

XL C/C++ for AIX Fix Pack 5 (September 2013 PTF) for 12.1
XL C/C++ for AIX Fix Pack 7 (January 2014 PTF) for 12.1
XL C for AIX Fix Pack 8 (March 2014 PTF) for 12.1
XL C/C++ for AIX Fix Pack 8 (March 2014 PTF) for 12.1
XL C/C++ for AIX Fix Pack 11 (February 2015 PTF) for 12.1
XL C for AIX Fix Pack 12 (May 2015 PTF) for 12.1
XL C/C++ for AIX Fix Pack 12 (May 2015 PTF) for 12.1
XL C/C++ for AIX Fix Pack 13 (August 2015 Update) for 12.1
XL C/C++ for AIX Fix Pack 14 (December 2015 Update) for 12.1
XL C for AIX Fix Pack 15 (April 2016 Update) for 12.1
XL C/C++ for AIX Fix Pack 15 (April 2016 Update) for 12.1
XL C for AIX Fix Pack 16 (July 2016 Update) for 12.1
XL C/C++ for AIX Fix Pack 16 (July 2016 Update) for 12.1
XL C/C++ for AIX Fix Pack 17 (November 2016 Update) for 12.1
XL C for AIX Fix Pack 17 (November 2016 Update) for 12.1
XL C for AIX Fix Pack 18 (February 2017 Update) for 12.1
XL C/C++ for AIX Fix Pack 18 (February 2017 Update) for 12.1
XL C for AIX Fix Pack 19 (August 2017 Update) for 12.1
XL C/C++ for AIX Fix Pack 19 (August 2017 Update) for 12.1
XL C for AIX Fix Pack 20 (March 2018 Update) for 12.1
XL C/C++ for AIX Fix Pack 20 (March 2018 Update) for 12.1
XL C for AIX Fix Pack 5 (September 2013 PTF) for 12.1
XL C for AIX Fix Pack 6 (December 2013 PTF) for 12.1
XL C/C++ for AIX Fix Pack 6 (December 2013 PTF) for 12.1
XL C for AIX Fix Pack 7 (January 2014 PTF) for 12.1
XL C for AIX Fix Pack 9 (July 2014 PTF) for 12.1
XL C/C++ for AIX Fix Pack 9 (July 2014 PTF) for 12.1
XL C for AIX Fix Pack 10 (October 2014 PTF) for 12.1
XL C/C++ for AIX Fix Pack 10 (October 2014 PTF) for 12.1
XL C for AIX Fix Pack 11 (February 2015 PTF) for 12.1
XL C for AIX Fix Pack 13 (August 2015 Update) for 12.1
XL C for AIX Fix Pack 14 (December 2015 Update) for 12.1
XL C/C++ for AIX Fix Pack 21 (January 2019 Update) for 12.1
XL C for AIX Fix Pack 21 (January 2019 Update) for 12.1

APAR status

• Closed as program error.

Error description

• When { } scope limit braces on line 1 and line 10 are added in
  the code block below, the program segfaults at runtime with
  violation inside that block of code.
   {// limit scope, line 1
        // get remote velocities and store in state.
        unsigned nRemoteEvents = parms->lrList.size;
        unsigned rList[nRemoteEvents];     //----> segfault here
        RemoteData vRemote[nRemoteEvents];
  .......
   } // limit scope, line 10
  If the limit scope braces on line 1 and line 10 are commented,
  the recompiled program will run successfully.
  The scope limit shall not affect semantics. The compiler is
  handling the variables inside it incorrectly.
  Below is reduced test case:
  void foo(int n)
  {
    for (int i=0; i<100; i++)
    {
    }
    { // extra scope delimiter
      unsigned vla[n];
      printf("foo: %d\n", n);
    } // extra scope delimiter
  }
  int main()
  {
    int m=0;
    printf("main: len=%d\n", m);
    foo(m);
  }
  xlc t.c
  $./a.out
  main: len=0
  Segmentation fault(coredump)
  

Local fix

• Remove the scope limit braces.
  

Problem summary

• PROBLEM DESCRIPTION: incorrect code gen variable length array
  with zero size
  
  USERS AFFECTED: any use of VLA that may have zero length
  

Problem conclusion

• code generation is correct to properly handle VLA with zero
  length.
  

Temporary fix

Comments

APAR Information

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

  LI77209

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

Fix information

• Fixed component name

  XL C FOR AIX

• Fixed component ID

  5725C7100

Applicable component levels

• RC10 PSN UP06/09/13

     C