arm32 (GOARCH=arm) builds are not supported

[unxed]

Currently, goffi does not support building 32-bit ARM (GOARCH=arm) binaries.

This became apparent while trying to build the f4 project (relevant issue) for armv7/OpenWRT devices. The GitHub Actions job fails because arm32 is not a supported target:

https://github.com/unxed/f4/actions/runs/30841038017/job/91777851957

Supporting GOARCH=arm (at least GOARM=5/6/7) would make it possible to build binaries for many older ARM devices, including routers and embedded systems running OpenWRT.

If there are technical limitations preventing arm32 support, it would be helpful to document them. Otherwise, adding GOARCH=arm support would significantly improve compatibility with legacy ARM hardware.

Original report:
https://habr.com/ru/articles/1030444/#comment_29921510

[kolkov]

Looked into this in detail. The compile failure is because ffi/dl_unix.go has (amd64 || arm64) in its build tags — ARM32 isn't covered, so LoadLibrary/GetSymbol are missing at link time.

ARM32 is fundamentally different from ARM64: only 4 GP registers (R0-R3 vs X0-X7), 64-bit arguments span two registers with alignment rules, Thumb interworking needs BLX which Go's assembler doesn't even support directly (requires raw WORD encoding), and GOARM=5 vs 7 changes the entire float calling convention. It's not a build tag fix — it's a new architecture.

That said, we're going to do it properly. purego has a working ARM32 reference implementation, Go's runtime fully supports linux/arm (FirstClass, asmcgocall present), and libffi has a well-documented ARM32 backend.

The plan (ADR-014 written):

1. TASK-052: Core Go→C FFI — AAPCS trampoline, arg classification, errno capture, dl loading (5 pts)
2. TASK-053: fakecgo for CGO_ENABLED=0 — crosscall2, trampolines (3 pts)
3. TASK-054: C→Go callbacks — 2000-entry table, dispatcher (3 pts)
4. TASK-055: CI via QEMU + tests (2 pts)

Targeting GOARM=7 (hard-float, ARMv7) on Linux only. GOARM=5 soft-float is out of scope — practically nobody ships new ARMv5 embedded Linux in 2026.

Total: ~5,500 lines (4,100 generated callback table + ~1,400 real logic), 13 story points. Milestone: v0.8.0.

Quick question — does f4 actually call C functions through goffi on ARM32, or is goffi a transitive dependency? If transitive, we can ship a stubs-only patch immediately (compiles clean, FFI returns error at runtime) while the full implementation is in progress.