PI96691: 1-BYTE ENUM SAVED IN INCORRECT OS64_NOSTACK LINKAGE PARAMETER LIST POSITION AFTER OPTIMIZATION

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When calling an external function that uses
  OS_NOSTACK/OS64_NOSTACK linkage, an issue is encountered with
  the parameter list for a 1-byte enum value, when optimization is
  used.
  
  When no optimization is used, the parameter list temp value for
  the 1-byte enum is correct - i.e. the value is loaded, then
  stored into a temp area as a full 32-bit value, per the #pragma
  linkage documentation:
  
     #pragma linkage (C only)
     https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.2.0/
     com.ibm.zos.v2r1.cbclx01/zos_pragma_linkage.htm
  
        OS_NOSTACK
        For integer type arguments, the value passed is widened
        to the size of the int type, that is 4-byte.
  
  The code appears as:
  
  000B6  E300  7008  0090  000019  | LLGC
                              r0,(*)mystruct.mystruct.val(,r7,8)
  0000BC  5000  48C0       000019 | ST r0,#wtemp_1(,r4,2240)
  0000C0  4100  48C0       000019 | LA r0,#wtemp_1(,r4,2240)
  ...
  0000EE  E300  4888  0024 000019 | STG r0,#MX_TEMP1(,r4,2184)
  
  
  When optimization is used, the parameter list temp value for the
  1-byte enum is incorrect.  THe LLC/STC instructions are used to
  load and save only the 1-byte instead of a full 32-bit word.
  The 1-byte enum ends up being stored in the first 8-bits of the
  temp area:
  
  0000A4  E300  1008  0094 000019 | LLC
                              r0,(*)mystruct.mystruct.val(,r1,8)
  ...
  0000B6  4200  4958       000019 | STC r0,<a1:d2392:l1>(,r4,2392)
  0000BA  4100  4958       000019 | LA r0,#wtemp_1(,r4,2392)
  ...
  0000DE  E300  4888  0024 000019 | STG r0,#MX_TEMP1(,r4,2184)
  
  
  
     === TEST CASE ===
  
  > xlc_64 -O2 apar.c
  
  typedef enum myenum
  {
     ZERO  = 0,
     ONE   = 1
  } ONEBYTEENUM;
  
  #pragma linkage(my_extern_func,OS64_NOSTACK)
  int  my_extern_func(const char *a, ONEBYTEENUM  b);
  
  typedef struct mystruct
  {
     char         *name;
     ONEBYTEENUM  val;
  } my_values;
  
  
  void test( my_values *c)
  {
  my_extern_func( c->name, c->val );
  }
  

Local fix

• Do not use optimization.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: Users of compiler options: XPLINK, LP32 with *
  *                 HGPR, or LP64, plus OPT, and ARCH(7) &  *
  *                 above; and calling a function with linkage   *
  *                 OS, and char or short parameter              *
  ****************************************************************
  * PROBLEM DESCRIPTION: The affected users will get an          *
  *                      incorrect value from loading the        *
  *                      argument address from the argument      *
  *                      list                                    *
  ****************************************************************
  .
  

Problem conclusion

• Apply service provided.
  

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:

  PI99715

Modules/Macros

• CCNECICS CCNECWI  CCNED220 CCNEDSCT CCNEDWRT CCNEFILT CCNEHIFC
  CCNEMDEP CCNEOPTP CCNEP    CCNEPP   CCNETBY  CCNMSGE  CCNMSGT
  

Fix information

• Fixed component name

  C/C++ FOR MVS

• Fixed component ID

  56551210A

Applicable component levels

• R7A0 PSY UI55634

     UP18/05/30 P F805

Fix is available

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