efipack — self-extracting EFI

github.com/go-coff/efipack is a pure-Go library that compresses PE32+/EFI binaries into a self-extracting PE32+/EFI image — the UPX-equivalent that does not otherwise exist for this format. It was designed to mitigate the EDK2 OVMF amd64 CpuPageTableLib #GP that fires on LoadImage / StartImage of sufficiently large EFI binaries (cloud-boot M6.2 milestone).

go get github.com/go-coff/efipack

Host side only (as of this revision)

This revision ships the host side: it compresses an input and assembles the self-extracting envelope, but the emitted .stub section still carries a TODO_STUB placeholder — the output is not yet a runnable EFI. The per-arch runtime decompressor stub, the pectl pack integration and the cross-arch boot-smoke matrix land in later PRs.

API surface

import "github.com/go-coff/efipack"

// Detect the architecture of an input PE32+ from its COFF header.
arch, err := efipack.InferArch(peBytes)
// arch ∈ {AmdArch, ArmArch, RiscvArch, LoongArch}

in, _  := os.Open("BOOTX64.EFI")
out, _ := os.Create("BOOTX64-packed.EFI")
res, err := efipack.Pack(in, out, efipack.Options{
    Compressor: efipack.Flate, // default; zero stub cost
    Level:      0,             // 0 → codec default
})
// res.OriginalSize, res.CompressedSize, res.PackedSize, res.Arch, res.Compressor

Type / constant	Purpose
`Pack(in, out, opts) (PackResult, error)`	host-side compress + envelope
`Options{Compressor, Level}`	knobs; zero value = Flate at default level
`PackResult{OriginalSize, CompressedSize, PackedSize, Compressor, Arch}`	summary
`Compressor` (`Flate` / `LZFSE` / `LZ4`)	algorithm switch
`Arch` (`AmdArch` / `ArmArch` / `RiscvArch` / `LoongArch`)	PE machine
`InferArch(pe) (Arch, error)`	read COFF.Machine without `debug/pe` (works on loong64)
`ReadPayload(pe) (algo, uncompressedSize, body, err)`	inverse of `Pack`'s envelope
`ErrCompressorNotImplemented`	sentinel for codecs not yet wired (`LZ4`)

The envelope is a standard PE32+/EFI structure: DOS stub + PE signature + COFF + optional header + section table + a .stub placeholder + a .payload body.

`.payload` wire format

PE/COFF — and this envelope — are little-endian:

.payload section body:
  magic         [4]byte   "CBP0"   — cloud-boot pack v0
  algo          [4]byte   "FLAT" | "LZFS" | "LZ4 "
  uncompressed  uint64    little-endian — host-input size in bytes
  compressed    uint64    little-endian — body size in bytes
  body          [N]byte   exactly N=compressed bytes; codec-specific stream

The (future) runtime stub reads this header, allocates exactly the right number of EfiBootServicesCode pages, decompresses, then chain-loads via gBS->LoadImage + gBS->StartImage.

Why Flate as the default?

Cloud-boot binaries already link compress/gzip, so a Flate-based stub adds zero bytes versus LZFSE's ~100–200 KiB cost. The ~1-point raw-ratio gap (LZFSE 40.13 % vs Flate 39.11 %) is negligible against the multi-MiB binaries being compressed. Flate is therefore the zero-value default; LZFSE is host-side only and LZ4 is reserved.

Licensed BSD-3-Clause.

efipack — self-extracting EFI

API surface

.payload wire format

Why Flate as the default?

`.payload` wire format