OpenVMS Migration Software for VAX to Alpha Systems Release Notes

This document, the "OpenVMS Migration Software for VAX to Alpha Systems Release Notes" (formerly DECmigrate), dated June 2002, provides information for migrating OpenVMS VAX applications to OpenVMS Alpha systems using the VAX Environment Software Translator (VEST).

Key Points:

• Purpose: The software enables the translation of VAX executable and shareable images into functionally equivalent Alpha images, allowing them to run on OpenVMS Alpha systems.
• Version: This is Release 1.2, an update to DECmigrate V1.1A, and introduces native OpenVMS Alpha utilities for better performance, image reference renaming during translation, and new translated runtime libraries from OpenVMS VAX 7.3.
• Compatibility:
  • Translates images from OpenVMS VAX Version 7.3 or later (non-privileged, linked on VAX/VMS 4.0+).
  • Translated images require OpenVMS Alpha Version 6.2 or higher to execute.
  • Translated images are generally forward-compatible but not backward-compatible.

Restrictions and Known Problems (Major Focus of the Document):

• General: VEST cannot translate DECnet-accessed images directly; issues can arise if the maximum number of open files is reached. Installation requires sufficient global pagelets and sections.

• Interoperability:

  • Native and translated images can interoperate, but native routines must be compiled with /TIE and linked with /NONATIVE_ONLY when calling or being called by translated images.
  • Indirect calls from non-/TIE native code to translated routines may cause access violations.
  • Sharing shared PSECTs (e.g., COBOL EXTERNAL, BASIC COMMON, FORTRAN COMMON) between translated and native images is not supported.
  • The OpenVMS Alpha calling standard only supports call entries; jsbentry calls between native and translated code are not supported.

• Layered Products: Some layered products (e.g., DECwindows Motif) may have incompatible translated and native shareable libraries, prohibiting their mixed use within a single process.

• Dependencies: Circular dependencies between translated shareable images with initialization code will be reported as an error.
• Bugs: VEST may sometimes fail to report certain issues like call mask overlaps, invalid case statements, or environment-related translation failures (e.g., insufficient quotas).
• Instruction Atomicity: The /PRESERVE=INSTRUCTION_ATOMICITY qualifier has limitations; it doesn't apply to complex VAX instructions, and specific VAX instructions (e.g., CALLG, CALLS, JSB) never preserve atomicity.

• Language-Specific Restrictions:

  • VAX Ada and DEC C: Applications cannot be translated; must be recompiled/relinked natively on Alpha.
  • VAX BASIC: WHEN ERROR construct requires /OPTIMIZE=NOSCHEDULE.
  • VAX COBOL: Programs using CANCEL or IS INITIAL may require relinking with SYS$LIBRARY:COBRESTVA.OBJ before translation.
  • VAX DIBOL: Requires /PRESERVE=SAFETY.
  • VAX C: Issues with brk() for releasing memory if complex VAX instructions are used; vfork() with executive functions may hang. Relinking to share VAXCRTL is recommended.

• Floating Point: Potential inaccuracies if VEST's default D53 precision is used with code assuming D56 precision (e.g., MTHRTL); retranslation with /FLOAT=D56_FLOAT may be necessary. Handling of "dirty zeros" requires /PRESERVE=FLOAT_EXCEPTIONS to avoid traps. Rounding issues can occur during D_floating conversion.

• Condition/Exception Handlers: Native and translated routines cannot establish each other's condition handlers. VAX-specific routines like LIB$DECODE_FAULT and DECthreads TRY/CATCH exception handling are not translatable.
• DECthreads: Images using DECthreads are not translatable; they must be ported to OpenVMS Alpha and linked with native libraries.
• System Quotas: Translating large images may require increasing system quotas (e.g., BYTLM, WSQUO).

Unsupported Feature:

• The kit includes an unsupported program called the GIRDLE Information File Compressor, which merges and sorts information files but comes with no performance guarantee or support.