amiga-bootcamp/03_loader_and_exec_format

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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

• ADCD 2.1: Includes_and_Autodocs_3._guide/ — dos.library LoadSeg autodoc
• NDK39: dos/dos.h — BPTR, segment handling macros
• Amiga ROM Kernel Reference Manual: Libraries — AmigaDOS chapter
• http://amigadev.elowar.com/read/ADCD_2.1/Libraries_Manual_guide/node0150.html