Fortran ABI Instability After Major Upgrade

Question

A major Fortran compiler upgrade may alter the binary interface between compiled object files and runtime libraries, creating compatibility risks for existing applications. The affected feature is the compiler-generated module layout and intrinsic interface signatures, which are not standardized across major releases. This goal examines whether object code produced by a previous compiler version can be linked and executed without modification after an upgrade, and what implications arise for long-term project maintenance.

Fortran compilers do not mandate a stable binary ABI across major releases; changes in symbol naming, data layout, and intrinsic function signatures can cause linker errors or runtime crashes if the upgrade is interrupted or performed without recompilation. Additionally, official recovery guidance is sparse, with most documentation recommending a full reinstall or the use of vendor-specific flags, but no standardized rollback procedure exists for failed upgrades. These factors introduce uncertainty regarding the feasibility of safe, incremental upgrades.

Can a linker-level compatibility layer mitigate symbol mismatches between object files from different compiler versions? Does the compiler's module interoperability flag guarantee binary compatibility across major releases? What is the minimum set of recompilation requirements to ensure functional equivalence across upgrade cycles?

Tasadduq Burney · Answer

ABI Stability After Fortran Compiler Upgrade
No, a linker-level compatibility layer cannot reliably mitigate deep symbol mismatches between object files generated by significantly different Fortran compiler versions. Furthermore, a compiler's module interoperability flag does not guarantee binary compatibility across major releases.

Confirmed Facts and Implications

Fortran compilers generally do not mandate a stable binary ABI across major releases.
Changes in symbol naming, data layout, and intrinsic function signatures are common during major revisions.
Linking object code from a previous version against a new compiler's runtime libraries is likely to cause linker errors or runtime crashes.

Required Steps for Functional Equivalence

Identify the specific compiler vendor and the exact major version change.
Consult the vendor's official release notes and ABI compatibility matrix for that specific upgrade path.
Perform a complete recompilation of the entire codebase using the new compiler.

The minimum set of recompilation requirements to ensure functional equivalence across upgrade cycles is a full recompilation of all source files and dependent modules.

Diagnostic Requirement
To refine this guidance, please specify the compiler vendor and the major version numbers involved in the upgrade.

Fortran ABI Instability After Major Upgrade

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ABI Stability After Fortran Compiler Upgrade

Confirmed Facts and Implications

Required Steps for Functional Equivalence

Diagnostic Requirement

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