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amiga-bootcamp/04_linking_and_libraries/README.md
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

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Linking & Library Integration

Overview

This section documents how AmigaOS shared libraries work at the binary level — how compilers produce library call stubs, how the linker wires them up, and how to reconstruct this mechanism during reverse engineering.

Contents

File Topic
library_structure.md Library memory layout, JMP table encoding, MakeLibrary construction, complete library creation example
shared_libraries_runtime.md OpenLibrary resolution path, ramlib disk loader, version negotiation, expunge mechanics
register_conventions.md Register ABI: integer, FPU, varargs/TagItem, small-data model, __saveds, inter-library calls
fd_files.md Function Definition files — the library ABI source of truth, LVO calculation
lvo_table.md JMP table layout, complete exec.library LVO table, IDA reconstruction script
compiler_stubs.md How SAS/C, GCC, VBCC call libraries — compiler signature identification
inline_stubs.md Compiler inline stubs: pragma (SAS/C), inline asm (GCC), __reg (VBCC), stub generation tools
link_libraries.md Static linking: amiga.lib, sc.lib, libnix, auto.lib, WBStartup glue, stack cookie
startup_code.md c.o / gcrt0.S: entry contract, CLI vs WB detection, argument parsing, WBStartup message
setfunction.md Runtime function patching: canonical pattern, chaining, removal, RE detection heuristics

The Library ABI Model

Every AmigaOS shared library exposes its functions through a negative-offset JMP table relative to the library base pointer:

Library base:  LIB+0    → Library node (struct Library)
               LIB-6    → JMP _Open        (mandatory)
               LIB-12   → JMP _Close       (mandatory)
               LIB-18   → JMP _Expunge     (mandatory)
               LIB-24   → JMP _Reserved    (mandatory)
               LIB-30   → JMP _func1       (first user function)
               LIB-36   → JMP _func2
               ...

A C call like OpenLibrary("graphics.library", 0) compiles to:

MOVE.L  4.W, A6          ; A6 = SysBase (exec)
JSR     -552(A6)          ; LVO for OpenLibrary = -552

The negative offset (-552) is the Library Vector Offset (LVO) — a fixed ABI value defined in the library's .fd file and proto/ include.

References