IJ51032: ALIGNMENT OF STATIC_RO_DR IS NOT RESPECTED IN THE FINAL OBJECT EMITTER

APAR status

• Closed as program error.

Error description

• The following testcase demonstrates an alignment issue for
  STATIC_RO_DR:
  
  ======COMPILE COMMAND:
  xlc test.c -q64
  
  
  ======TESTCASE:
  $ cat test.c
  #include <stdio.h>
  #include <stdint.h>
  
  /* add a byte so the compiler has to go out of its way to
  achieve alignment for
     consecutive instances */
  typedef union PGIOAlignedBlock
  {
    __attribute__((aligned(4096)))
    char            data[1 + 8192];
  } PGIOAlignedBlock;
  
  
  static const PGIOAlignedBlock al4096_static_const_initialized =
  {{0}};
  
  #define DUMP(want_align, var) dump_internal(#var, (want_align),
  &(var))
  
  static void
  dump_internal(const char *ident, unsigned want_align, const void
  *addr)
  {
    unsigned        mod = (uintptr_t) addr % want_align;
  
    printf("%-32s %4u @ 0x%p (mod %u%s)\n", ident, want_align,
  addr,
           mod, mod ? " - BUG" : "");
  }
  
  int main(int argc, char **argv)
  {
    DUMP(4096, al4096_static_const_initialized);
    return 0;
  }
  $
  
  =======ACTUAL OUTPUT:
  $./a.out
  al4096_static_const_initialized  4096 @ 0x100000650 (mod 1616 -
  BUG)
  
  
  =======EXPECTED OUTPUT:
  $./a.out
  al4096_static_const_initialized  4096 @ 0x100001000 (mod 0)
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Users who rely on specific alignments of unions may be affected
  by this issue.
  
  PROBLEM DESCRIPTION:
  The C++ Compiler was incorrectly aligning static readonly
  sections causing the incorrect output at runtime.
  

Problem conclusion

• The alignment of static readonly sections is now 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/C++ FOR AI

• Fixed component ID

  5725C7200

Applicable component levels