GSoC 2025 – Improving Fortran Interfacing in PETSc

Projects GSoC-2025
4

Weekly Progress Update: As of 24th June 2025

This week I focused on understanding and automating character argument handling in PETSc’s Fortran bindings.

Concepts learnt

  • PeNS Functions and Character Arguments: PETSc uses PeNS macro to mark non-standard functions that bypass automatic Fortran binding generation. Many contain character arguments (char*, const char[], single char) requiring manual Fortran interfaces.
  • C-fortran String Interoperability: C uses null-terminated strings while Fortran uses space-padded strings with hidden length parameters. PETSc provides FIXCHAR/FREECHAR macros for conversion, handling memory allocation and null termination between languages.
  • PETSc Automation Tools: Went through getAPI.py (function signature parser) and generateFortranBindings.py (binding generator). Current limitations include incomplete character type detection and exclusion of PeNS-marked functions from automation.

Work Done

For automation of fortran bindings generation for functions with char arguments:

  • Extended the getAPI.py to recognize and categorize different character argument types, storing metadata about input/output direction and string vs single character use.
  • Modified the generateFortranBindings.py with templates to automatically generate appropriate Fortran interfaces and C stub functions for each character argument pattern.
  • As proof-of-concept, automated PetscTestFile() bindings that compile correctly and match PETSc’s Fortran conventions, eliminating need for manual binding.
  • Wrote tests verifying generated bindings work correctly for string input/output scenarios.

Merge Requests Status

Active MRs (as author)

  • !8492 - under review
  • !8437 - 1 job failed in stage 3
  • !8436 - 1 job failed in stage 3

Issues Assigned:

  • #1779 - Keep C variable names for Fortran interfaces

Next steps:

  • Resolve the pipeline issues
  • Implement review feedback
  • Work on fixing assigned issue
  • Meeting with mentors to discuss the next incremental step.
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