IV80372: SEGMENTATION FAULT IN BASIC_STRING CODE USING _NULLSTR

XL C/C++ Runtime for AIX Fix Pack 1 (March 2016 PTF) for 13.1.3
XL C/C++ for AIX Fix Pack 7 (May 2016 PTF) for 13.1
XL C/C++ for AIX Fix Pack 8 (August 2016 PTF) for 13.1
XL C/C++ Runtime for AIX, V13.1.3.2 Fix Pack (April 2017)
XL C/C++ for AIX Fix Pack 9 (June 2017 PTF) for 13.1
XL C/C++ Runtime for AIX, V13.1.3.3 Fix Pack (June 2017)
XL C/C++ for AIX Fix Pack 10 (February 2018 PTF) for 13.1
XL C/C++ for AIX Fix Pack 11 (November 2018 PTF) for 13.1

APAR status

• Closed as program error.

Error description

• An application runtime segmentation fault occurs when using
  basic_string objects and the <xstring> _Nullstr() function.
  This function is used by the c_str() function when processing
  NULL strings.
  
  The segmentation fault occurs after the XL C++ Runtime level is
  updated to V13.1 .  Previous XL C++ Runtime releases do not
  encounter the issue.
  
  The segmentation fault is caused by an STH store instruction to
  an XL C++ Runtime symbol that is found in the read-only data
  section of the library.  Code may appear similar to:
  
  
  ------------------------------
  
      003088 lwz   80620120 1 L4A
                 gr3=.guard__C1___Nullstr__Q3_3std7_LFS_ON12bas
                 ic_stringXTwTQ2_3std11char_traitsXTw_TQ2_3std9
                 allocatorXTw__Fv(gr2,0)
  
      00308C lwz   80C20124 1 L4A
                 gr6=._C___Nullstr__Q3_3std7_LFS_ON12basic_stri
                 ngXTwTQ2_3std11char_traitsXTw_TQ2_3std9allocat
                 orXTw__Fv__1(gr2,0)
  
      003090 lwz   80030000 1 L4A
                 gr0=guard__C1___Nullstr__Q3_3std7_LFS_ON12basi
                 c_stringXTwTQ2_3std11char_traitsXTw_TQ2_3std9a
                 llocatorXTw__Fv(gr3,0)
  
      003094 cmpwi 2C000000 1 C4 cr0=gr0,0
  
      003098 bc    40820014 1 BF CL.254,cr0,0x4/eq,taken=50%(0,0)
  
      00309C addi  38800001 1 LI gr4=1
  
      0030A0 addi  38000000 1 LI gr0=0
  
      0030A4 stw   90830000 1 ST4A
                 guard__C1___Nullstr__Q3_3std7_LFS_ON12basic_st
                 ringXTwTQ2_3std11char_traitsXTw_TQ2_3std9alloc
                 atorXTw__Fv(gr3,0)=gr4
  
  **  0030A8 sth   B0060000 1 ST2Z
                 _C___Nullstr__Q3_3std7_LFS_ON12basic_stringXTw
                 TQ2_3std11char_traitsXTw_TQ2_3std9allocatorXTw
                 __Fv__1(gr6,0)=gr0
  
  ------------------------------
  
  
  Analysis of the memory location of the _C___Nullstr__Q3_3std
  7_LFS_ON12basic_stringXTwTQ2_3std11char_traitsXTw_TQ2_3std9a
  llocatorXTw__Fv__1 symbol symbol using the DBX debugger will
  show that it is found in the 0xD shared memory data section
  (read only section):
  
  
  ------------------------------
     (dbx) p
     &_C___Nullstr__Q3_3std7_LFS_ON12basic_stringXTwTQ2_3std11char
     _traitsXTw_TQ2_3std9allocatorXTw__Fv__1
     0xd3755bd4
     (dbx)
  ------------------------------
  

Local fix

• N/A
  

Problem summary

• PROBLEM DESCRIPTION:
  C++ code containing string usage compiled with the V11.1.0.13
  compiler or earlier encounters runtime segmentation faults after
  upgrading to the XL C++ Runtime, V13.1 (fileset:  xlC.rte).  The
  XL C++ Runtime, V12.1 works correctly.
  
  The root issue of the problem is fixed in the XL C/C++ for AIX,
  V11.1.0.14 compiler PTF release, and corrects invalid _Nullstr()
  function code generation.  Code compiled with the V11.1.0.14
  release and later will not encounter the problem with the XL C++
  Runtime, V13.1 .
  
  For users with existing code compiled with V11.1.0.13 and
  earlier, this APAR will modify the XL C++ Runtime, V13.1 to
  accept the old code safely.
  
  USERS AFFECTED:
  Users with code compiled with the V11.1.0.13 release and
  earlier.
  

Problem conclusion

• In the XL C++ Runtime, V13.1 release, the _Nullstr() runtime
  symbol
  '_C___Nullstr__Q3_3std7_LFS_ON12basic_stringXTwTQ2_3std11char_tr
  aitsXTw_TQ2_3std9allocatorXTw__Fv__1' was made read-only text,
  when it had been read/write data in the past.  This change
  caused the runtime segmentation fault when older pre-V11.1.0.14
  code would attempt to write to the symbol.  Code compiled with
  V11.1.0.14 and later does not write to this symbol.
  
  The symbol in the XL C++ Runtime, V13.1 has been made read/write
  data again to support older code.
  

Temporary fix

Comments

APAR Information

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

  IV79436

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

Fix information

• Fixed component name

  XL C/C++ RUNTIM

• Fixed component ID

  5725C7201

Applicable component levels

• RD13 PSY

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