rslr/amiga-bootcamp
1
0
Fork 0
mirror of https://github.com/alfishe/amiga-bootcamp.git synced 2026-06-12 16:16:28 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions
amiga-bootcamp/03_loader_and_exec_format/README.md
Ilia Sharin 4593ff135a 03: new article — exe_crunchers.md (executable packers deep dive) 
New comprehensive article on Amiga executable crunchers covering:
- Architecture: how crunched files remain valid HUNK executables
- Major crunchers: PowerPacker, Imploder, Shrinkler, ByteKiller,
  Titanics, CrunchMania, PackFire, XPK framework
- PP20 format: efficiency table, decrunch info, decrunch colours
- Shrinkler internals: 1536-context adaptive probability model,
  range coder, parity context flag, stack-based context table,
  actual 68000 decompressor source from GitHub
- LZ77/LZSS vs context-modelling+range-coding algorithms
- Relocation handling: 3 strategies (compressed relocs, delta
  table, merged single-hunk)
- Memory layout diagrams: before/during/after decompression
- Detection: magic signatures table, fake header warning,
  Python scanner script
- Tools: xfdmaster modular architecture, Ancient C++ library,
  debugger-based extraction (last resort)
- FPGA/emulation impact: timing, self-modifying code, cache

Based on web research: verified PP20 format spec, Shrinkler
source (askeksa/Shrinkler), Ancient library (temisu/ancient),
xfdmaster slave module architecture.

Updated indexes: 03/README.md, root README.md
2026-04-23 18:41:07 -04:00

2.9 KiB
Raw Permalink Blame History

← Home

Executable Loader & HUNK Format

Overview

This section covers the complete lifecycle of an AmigaOS executable:

  1. HUNK file format — the binary container for all AmigaOS executables, libraries, and object files
  2. Loader pipeline — how dos.library loads and relocates an executable into memory
  3. Object files — how compilers produce relocatable object files for the linker
  4. Overlays — how programs larger than available memory use the overlay system

Contents

File Topic
hunk_format.md Complete HUNK binary specification — all 22 hunk type codes with wire format, memory flags, advisory bits
hunk_ext_deep_dive.md HUNK_EXT: exports (EXT_DEF), imports (EXT_REF32), commons, linker resolution
hunk_relocation.md Relocation mechanics: visual before/after, patching algorithm, RELOC32/SHORT/DREL32, PC-relative impact
hunk_debug_info.md HUNK_SYMBOL and HUNK_DEBUG: stabs format (SAS/C, GCC), debugger consumption, stripping
exe_load_pipeline.md LoadSeg → AllocMem → relocation → segment chain → CreateProc → entry point
object_file_format.md Compiler object files (HUNK_UNIT), multi-section layout, HUNK_LIB archives, linker operation
overlay_system.md HUNK_OVERLAY: tree architecture, runtime overlay manager, worked binary example, modern alternatives
exe_crunchers.md Executable packers: PowerPacker/Imploder/Shrinkler, decrunch stubs, compression algorithms, detection

Why HUNK?

HUNK is the native AmigaOS executable format, used from AmigaOS 1.0 through 3.x. It predates ELF/COFF and has these key properties:

  • Segmented: separate code, data, and BSS hunks with independent memory allocation
  • Relocatable: all absolute references are patched at load time (no ASLR; base address changes each run)
  • Typed memory: each hunk can request CHIP or FAST memory independently
  • Symbol-complete: optional HUNK_SYMBOL and HUNK_DEBUG hunks carry debugging information

Key Concepts

Term Meaning
Hunk One contiguous block in the binary (code, data, BSS, etc.)
Segment A loaded hunk at runtime — a BPTR-linked list
Segment list Chain of loaded hunks returned by LoadSeg()
BPTR Amiga byte pointer — 32-bit value right-shifted by 2 (ptr >> 2)
Relocation Patching absolute addresses based on actual load address
LVO Library Vector Offset — negative offset from library base

References