LI76118: INCORRECT BRANCH WITH BUILTINS

XL C/C++ for Linux Fix Pack 9 (August 2013 Update) for 11.1
April 2011 Update for XL C/C++ for Linux, V11.1
July 2011 Update for XL C/C++ for Linux, V11.1
October 2011 Update for XL C/C++ for Linux, V11.1
June 2012 Update for XL C/C++ for Linux, V11.1
October 2012 Update for XL C/C++ for Linux, V11.1
XL C/C++ for Linux Fix Pack 8 (June 2013 Update) for 11.1

APAR status

• Closed as program error.

Error description

• This is a test for the builtin long __fetch_and_swaplp(volatile
  long*, long);
  
  inline intptr_t Atomic::xchg_ptr(intptr_t exchange_value,
  volatile intptr_t* dest) {
    long old_value;
    __lwsync();
    old_value = __fetch_and_swaplp(dest, exchange_value);
    __isync();
    return (intptr_t) old_value;
  }
  
  And this is the disassembled code:
  
  $ dbx cpp_test
  Type 'help' for help.
  reading symbolic information ...
  (dbx) listi test_xchg_ptr
  0x100000c00 (test_xchg_ptr(long,volatile long*))      7c2004ac
  sync
  0x100000c04 (test_xchg_ptr(long,volatile long*)+0x4)  7c0020a8
  ldarx   r0,r0,r4
  0x100000c08 (test_xchg_ptr(long,volatile long*)+0x8)  7c6021ad
  stdcx.   r3,r0,r4
  0x100000c0c (test_xchg_ptr(long,volatile long*)+0xc)  40a2fff8
  bne   0x100000c14 (test_xchg_ptr(long,volatile long*)+0x4)
  0x100000c10 (test_xchg_ptr(long,volatile long*)+0x10) 4c00012c
  isync
  0x100000c14 (test_xchg_ptr(long,volatile long*)+0x14) 60030000
  ori   r3,r0,0x0
  0x100000c18 (test_xchg_ptr(long,volatile long*)+0x18) 4e800020
  blr
  
  The problem is the bne at 0x100000c0c. It should branch back to
  the ldarx at 0x100000c04, if the stdcx fails,
  but instead it branches forward to 0x100000c14 and then
  xchg_ptr() returns without having stored exchange_value to dest.
  
  The problem seems to occur when mixing inline assembler with
  built-ins.
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Users who inter-mix asm statements and compiler built-ins may
  be affected by this issue.
  
  PROBLEM DESCRIPTION:
  The resulting assembler file contained incorrect assembly code
  for branches, which resulted in incorrect execution
  of the code at runtime.
  

Problem conclusion

• The compiler has been fixed so that it will generate correct
  assembly code for branches.
  

Temporary fix

Comments

APAR Information

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

  IZ94262

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

Fix information

• Fixed component name

  XL C/C++ FOR LI

• Fixed component ID

  5724X1400

Applicable component levels

• RB10 PSN IZ94262

     UP06/09/13