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Ilia Sharin 7df1f11f15 03/04: deep enrichment of loader/exec format and linking/libraries 
Sections 03 and 04 augmented to bootcamp quality with targeted
enrichment based on content analysis (not just file size).

03_loader_and_exec_format:
- overlay_system.md: full rewrite — tree architecture diagram,
  HUNK_OVERLAY binary format, overlay manager runtime internals,
  worked binary example, linker support, modern alternatives
- hunk_relocation.md: full rewrite — visual before/after diagram,
  patching algorithm with code, RELOC32SHORT and DREL32 formats,
  PC-relative impact comparison table, self-referencing relocs,
  error scenarios, Python reloc scanner tool

04_linking_and_libraries:
- library_structure.md: full rewrite — ASCII memory layout diagram,
  JMP table encoding (why 6 bytes), MakeLibrary internals with both
  function array formats, complete library creation example with
  .fd file, checksum verification, lifecycle state diagram
- shared_libraries_runtime.md: full rewrite — OpenLibrary 4-step
  resolution path, ramlib disk loader internals, disk search path,
  version negotiation table (v33-v47), CloseLibrary/Expunge deep
  dive, memory-low sweep, common pitfalls table
- register_conventions.md: full rewrite — FPU register map,
  inter-library A6 save/restore pattern, small-data model with
  __saveds keyword, varargs/TagItem pattern deep dive,
  stack-based wrapper explanation, disassembly identification

Updated indexes:
- 03_loader_and_exec_format/README.md
- 04_linking_and_libraries/README.md
- Root README.md (sections 03 and 04)
2026-04-23 18:30:45 -04:00
..
exe_load_pipeline.md docs(amiga): make cross-references clickable markdown links 2026-04-23 12:24:21 -04:00
hunk_debug_info.md docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections 2026-04-23 12:17:35 -04:00
hunk_ext_deep_dive.md docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections 2026-04-23 12:17:35 -04:00
hunk_format.md docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections 2026-04-23 12:17:35 -04:00
hunk_relocation.md 03/04: deep enrichment of loader/exec format and linking/libraries 2026-04-23 18:30:45 -04:00
object_file_format.md docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections 2026-04-23 12:17:35 -04:00
overlay_system.md 03/04: deep enrichment of loader/exec format and linking/libraries 2026-04-23 18:30:45 -04:00
README.md 03/04: deep enrichment of loader/exec format and linking/libraries 2026-04-23 18:30:45 -04:00

README.md

← 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

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