LI77209: SEGFAULT WITH LIMITED SCOPE VARIABLES

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You can track all active APARs for this component.

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 number

    LI77209

  • Reported component name

    XL C/C++ FOR BG

  • Reported component ID

    5799AG100

  • Reported release

    C10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2013-01-30

  • Closed date

    2013-09-11

  • Last modified date

    2013-09-11

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

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

    IV49625 LI77614

Fix information

  • Fixed component name

    XL C/C++ FOR BG

  • Fixed component ID

    5799AG100

Applicable component levels

  • RC10 PSY

       UP



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Document information


More support for:

XL C/C++ for Blue Gene/Q
Compiler

Software version:

12.1

Reference #:

LI77209

Modified date:

2013-09-11

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