gasm-sdk/docs/DEFERRED.md

# Deferred decisions

Design decisions deliberately postponed, with enough context to pick them up
again without re-deriving the analysis.  Each entry records what is deferred,
why, the options on the table, and the trigger that should reopen it.

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## GOOBJ external (cross-package) symbol references

**Status:** resolved (v0.29.0+, 2026-08-07).

**Approach taken.**  Instead of parsing the compiler's iexport data (which
would have required either `golang.org/x/tools` or an in-house parser), the
resolver reads the **GOOBJ data directly** from the target package's `.a`
archive.  The `.a` file contains a `_go_.o` member whose GOOBJ format is the
same one gasm writes — the parser reuses the same layout (`blkSymdef`,
`blkNonpkgdef`, the string table), so no new dependency was needed.

**How it works.**

1. `go list -json -export <pkg>` finds the target package's `.a` file.
2. `extractGOOBJ` reads the ar archive, finds the `_go_.o` member, skips
   the `"go object …\n!\n"` preamble and parses the GOOBJ header.
3. `goobjFile.symbols()` walks `blkSymdef` and `blkNonpkgdef` in definition
   order — the same order the linker uses — to build the symbol → index
   mapping.
4. `resolveExternalSymbols` wires the resolved `{PkgIdx, SymIdx}` into the
   GOOBJ emission.

The resolver is invoked automatically when `img.Externals` is non-empty; it
runs `go list` as a subprocess (consistent with `toolchainObjectPreamble`
which already calls `go tool asm`).  All symbol data is cached per package
for the lifetime of the GOOBJ emission.