PH07579: UNABLE TO USERMOD MODULE DFSMDA00 DUE TO BASE REGISTER LIMITATIONS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Module DFSMDA00 is a very common module modified by users with
  USERMODs.  The module is real tight on base registers.  There
  are two base registers defined in the module.  Label WRTMSGM is
  located at x'1FFA'.  Any USERMOD modification of the module can
  easily push the label beyond the defined base registers.  Adding
  an additional base register does not appear to be an option.
  .
  The module may needed to be modified to use a Branch Relative
  approach.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All users of IMS v15                                         *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * Applying a USERMOD to DFSMDA00 may result in assembly errors *
  * due to base register limitations                             *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * INSTALL CORRECTIVE SERVICE FOR APAR/PTF                      *
  ****************************************************************
  Module DFSMDA00 uses two base registers, which is sufficient to
  address 8192 bytes (0x2000 hex) of executable code.  Almost all
  of this area is used.  The branch target with the highest
  offset, WRTMSGM, is at offset 0x1FFA from the beginning of the
  CSECT.  Therefore, if a USERMOD, even a very small one, adds
  code to DFSMDA00, this label and possibly others may be pushed
  beyond offset 0x2000, which is not addressable by the module?s
  base registers.  This results in an assembly error ASMA034E for
  BEYOND ACTIVE USING.
  

Problem conclusion

• Module DFSMDA00 is changed to use branch relative addressing.
  As a result, a USERMOD may add lines of code to the module
  without causing assembly errors due to base register
  limitations.
  
  There are two main components to this conversion.  First, a
  BRREL=YES statement is added to the CHANGEID statement for the
  main CSECT and subroutines to direct the assembler to convert
  branch instructions that depend on a base register to jump
  instructions that use relative addressing, according to the
  definitions in DFSBRREL MACRO.  Second, a static area is defined
  so that local variables may be addressed using a register that
  points to the static area, rather than relying on a base
  register.
  
  Additional smaller changes are required in order to support this
  conversion to branch relative addressing and the use of a static
  area:
  - Rearrange the module so that all data definitions that need to
  be in the static area are contiguous.
  - Modify CHANGEID statements to specify both branch relative
  addressing and the static area.  Remove the specification of R12
  and R10 as base registers.
  - Remove USING statements and code used to set up the base
  registers.
  - Relocate instructions that are the target of EXECUTE
  instructions from the main CSECT to the static area.
  - Modify branch tables to use relative addressing to calculate
  the correct branch target.
  - For certain branch instructions that do not depend on the base
  register (such as at label LOAD089), add an underscore to tell
  the assembler not to try to convert it to a branch relative
  instruction.
  - Remove LTORG statements so that all literals appear in the
  static area.
  

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:

  UI61720 PH16171

Modules/Macros

• DFSMDA00
  

Fix information

• Fixed component name

  IMS V15

• Fixed component ID

  5635A0600

Applicable component levels

• R500 PSY UI61720

     UP19/03/12 P F903

Fix is available

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