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More information. Especially about RE and AREXX automation
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05_reversing/static/compilers/aztec_c.md
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[← Home](../../../README.md) · [Reverse Engineering](../../README.md) · [Static Analysis](../README.md) · [Compilers](README.md)
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# Manx Aztec C — Reverse Engineering Field Manual
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## Overview
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**Manx Aztec C** (versions 3.x–5.x, 1985–1992) was the first widely used C compiler for the Amiga, predating Lattice C's market dominance. It targets early AmigaOS (1.1–1.3) and produces code with a distinctive **`LINK A5, #-N` + `MOVEM.L D3-D7, -(SP)`** prologue — saving only 5 data registers (D3–D7) instead of SAS/C's 9 registers. This narrower save set is the single most reliable Aztec C fingerprint.
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Key constraints:
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- **5-register data save (D3–D7 only)** — Aztec C preserves fewer registers than any other Amiga C compiler. D2 is considered scratch by Aztec, while SAS/C, GCC, and VBCC all preserve D2.
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- **A5 frame pointer** — standard `LINK A5, #-N` convention, like SAS/C.
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- **Absolute string addressing** — like SAS/C, strings are in DATA with `HUNK_RELOC32` relocation.
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- **Pre-MakeLibrary era** — Aztec C libraries use a different initialization pattern than later RTF_AUTOINIT libraries.
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- **Early AmigaOS focus** — code may assume OS 1.1/1.2 behavior that changed in 2.0+.
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```asm
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; Aztec C function prologue (THE signature):
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_func:
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LINK A5, #-$14 ; allocate frame
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MOVEM.L D3-D7, -(SP) ; save D3-D7 ONLY (5 regs!)
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; Note: D2 is NOT saved (unlike SAS/C, GCC, VBCC)
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; Note: A2-A4 are not saved (unlike SAS/C)
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```
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---
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## Binary Identification
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| Criterion | Aztec C | SAS/C |
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|---|---|---|
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| **Register save** | `D3-D7` (5 regs) | `D2-D7/A2-A4` (9 regs) |
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| **D2 preservation** | NOT preserved — call-clobbered | Preserved — callee-saved |
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| **A2-A4 preservation** | NOT preserved by default | Always preserved |
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| **Frame pointer** | A5 (`LINK A5`) | A5 (`LINK A5`) |
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| **String addressing** | Absolute + relocation | Absolute + relocation |
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| **Startup module** | `aztec.o` | `c.o` |
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| **Hunk names** | `CODE`, `DATA`, `BSS` | `CODE`, `DATA`, `BSS` |
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| **Era** | 1985–1992 (OS 1.1–1.3) | 1988–1996 (OS 1.2–3.1) |
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### Detecting D2 as Scratch Register
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The most distinctive Aztec C behavior: **D2 is call-clobbered**. After a function call, Aztec C must reload D2 if it was using it. SAS/C, GCC, and VBCC all preserve D2 across calls.
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```asm
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; Aztec C: D2 is NOT preserved across calls
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MOVE.L #value, D2 ; D2 = important value
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BSR _some_func ; D2 may be destroyed!
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MOVEQ #0, D2 ; reload D2 (Aztec C knows D2 is scratch)
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; SAS/C would NOT need this reload — D2 is callee-saved there
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```
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---
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## Historical Context
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Manx Software Systems produced Aztec C for multiple platforms (CP/M, DOS, Macintosh, Amiga, Atari ST). The Amiga version was one of the earliest C compilers available — released in 1985 alongside the Amiga 1000 launch. Its 5-register save convention (D3-D7 only) reflects the era's emphasis on minimizing prologue/epilogue overhead on the 7.14 MHz 68000.
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Aztec C was superceded by Lattice C (which became SAS/C) in the late 1980s, though Manx continued to release versions into the early 1990s. Most Aztec C binaries date from 1985–1989 — the Amiga's formative years.
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Software known to use Aztec C:
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- Early Amiga utilities (1985–1987 era)
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- Some Commodore-developed tools
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- ABasiC (the Amiga BASIC compiler)
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- Early versions of certain games ported from other platforms
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---
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## Same C Function — Aztec C Output
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```asm
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; CountWords() — Manx Aztec C 5.x:
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; (Note: smaller register save set, but structurally similar to SAS/C)
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_CountWords:
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LINK A5, #-$08
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MOVEM.L D3-D4, -(SP) ; ONLY D3-D4 (not D2-D3!)
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MOVEQ #0, D3 ; D3 = count
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MOVEQ #0, D4 ; D4 = in_word
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MOVEA.L $08(A5), A0 ; str
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BRA.S .loop_test
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.loop_body:
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MOVEQ #' ', D0
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CMP.B (A0), D0
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BEQ.S .not_word
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MOVEQ #'\t', D0
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CMP.B (A0), D0
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BEQ.S .not_word
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MOVEQ #'\n', D0
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CMP.B (A0), D0
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BEQ.S .not_word
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TST.B D4
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BNE.S .next_char
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ADDQ.L #1, D3
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MOVEQ #1, D4
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BRA.S .next_char
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.not_word:
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MOVEQ #0, D4
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.next_char:
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ADDQ.L #1, A0
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.loop_test:
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TST.B (A0)
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BNE.S .loop_body
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MOVE.L D3, D0
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MOVEM.L (SP)+, D3-D4
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UNLK A5
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RTS
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```
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**Aztec C observations**: The function body is nearly identical to SAS/C, but notice D2 is **not used** — Aztec C skips D2 and starts local register allocation at D3. If you see functions that never touch D2, it's likely Aztec C (or early Lattice C).
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---
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## References
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- [compiler_fingerprints.md](../../compiler_fingerprints.md) — Quick identification
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- Aztec C 68k Manual (archive.org)
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- See also: [sasc.md](sasc.md), [lattice_c.md](lattice_c.md) — compare with other compilers
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