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amiga-bootcamp/06_exec_os/exec_base.md
Ilia Sharin 21751c0025 docs(amiga): complete AmigaOS 3.1/3.2 developer reference — 172 files across 17 sections 
Comprehensive technical documentation covering:
- Hardware: OCS/ECS/AGA custom chip registers, Copper & Blitter deep dives
- Boot sequence: cold boot through startup-sequence
- Binary format: HUNK executable spec, relocation, debug info
- Linking & ABI: .fd files, LVO tables, register calling conventions
- Exec kernel: tasks, interrupts, memory, signals, semaphores
- AmigaDOS: file I/O, FFS/OFS layout, CLI/Shell scripting
- Graphics: planar bitmaps, Copper programming, HAM/EHB modes
- Intuition: screens, windows, IDCMP, BOOPSI
- Devices: trackdisk, SCSI, serial, timer, audio, keyboard
- Libraries: utility, expansion, IFFParse, locale, ARexx
- Networking: bsdsocket API, SANA-II, TCP/IP stack comparison
- Toolchain: GCC, vasm/vlink, SAS/C, NDK, debugging
- Reverse engineering: IDA/Ghidra setup, compiler fingerprints, case studies
- CPU & MMU: 68040/060 emulation libs, PMMU, cache management
- Driver development: SANA-II, Picasso96/RTG, AHI audio

All files include breadcrumb navigation. No local paths or proprietary content.
2026-04-23 12:17:35 -04:00

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← Home · Exec Kernel

ExecBase — Full Structure Reference

Overview

ExecBase is the root structure of AmigaOS, located at absolute address $4. It is a struct Library extended with all exec kernel state: memory lists, task queues, interrupt vectors, library lists, and hardware abstraction fields.

Locating ExecBase

struct ExecBase *SysBase = *((struct ExecBase **)4);

In assembly:

MOVEA.L  4.W, A6   ; A6 = SysBase

Key Field Groups

Library Header (offset 0)

struct Library  LibNode;     /* +0  — ln_Name = "exec.library" */
                             /* +20 — lib_Version (40 = OS3.1, 44 = OS3.2) */

Interrupts (offset +84)

UWORD   AttnFlags;       /* +0x128 — processor capability flags */
UWORD   AttnResched;     /* +0x12A — reschedule attention flag */

Task Scheduling

Offset Field Description
+0x128 TaskReady struct List — tasks ready to run
+0x132 TaskWait struct List — tasks waiting on signals
+0x126 IDNestCnt Interrupt disable nesting count
+0x127 TDNestCnt Task disable nesting count

Memory

Offset Field Description
+0x130 MemList struct List of MemHeader regions
+0x134 ResourceList Resources list

Library and Device Lists

Offset Field Description
+0x17A LibList struct List — loaded libraries
+0x182 DeviceList struct List — loaded devices
+0x18A IntrList Interrupt server list
+0x192 PortList Public message ports
+0x19A TaskList All tasks (not just ready/waiting)

Vectors and ROM

Offset Field Description
+0x26 SoftVer Kickstart software revision
+0x10 ChkBase Checksum of library header
+0x222 PowerSupplyFrequency 50 or 60 Hz
+0x21E ChipRevBits0 Chip revision detection flags

Chip Revision Flags (ChipRevBits0)

Bit Constant Chip
4 ATNF_68010 68010 or better
5 ATNF_68020 68020 or better
6 ATNF_68030 68030
7 ATNF_68040 68040
10 ATNF_FPU40 68040 internal FPU

Detecting CPU and Chipset

/* CPU: */
if (SysBase->AttnFlags & AFF_68020) { /* 020+ */ }
if (SysBase->AttnFlags & AFF_68040) { /* 040 */ }

/* Chipset (via graphics.library): */
struct GfxBase *gfx = (struct GfxBase *)OpenLibrary("graphics.library", 36);
if (gfx->ChipRevBits0 & GFXB_AA_ALICE) { /* AGA Alice chip */ }

ExecBase in IDA Pro

After loading Kickstart ROM:

  1. Create a segment at $4 containing a pointer
  2. Follow the pointer to the ExecBase (in ROM)
  3. Apply struct ExecBase type (from NDK39 headers parsed via File → Parse C header)
  4. All N(A6) offsets auto-annotate as field names

References