IJ25964: INCORRECT OFFSET USED FOR 8-BYTE STDX STORE INSTRUCTION

APAR status

• Closed as program error.

Error description

• When using the -O2 optimization level, an 8-byte store operation
  is using an incorrect offset value as the target memory address.
  This results in memory stored in an incorrect location on the
  stack.
  
  The cause of the bad offset calculation is due to an
  optimization that implements stores of 8-bytes with the stdx
  instruction, where the base offset is the stack pointer, and the
  offset value is NOT a multiple of 4.  In these cases, the offset
  into the stackframe from the stack pointer is not included in
  the overall offset calculation.
  

Local fix

• - Use lower optimization level, or
  - If 8-byte store is due to memset(), avoid usage of the XLC
  compiler built-in __memcpy found in the string.h header file
  

Problem summary

• USERS AFFECTED:
  Users who compile with -O2 and have memcpy statements may be
  affected by this issue.
  
  PROBLEM DESCRIPTION:
  The compiler was incorrectly optimizing the memcpy instruction
  leading to incorrect results at runtime
  

Problem conclusion

• The compiler otpimizer has been fixed.
  

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

• Fixed component name

  XL C FOR AIX

• Fixed component ID

  5725C7100

Applicable component levels