feat: add aarch64 as target

1 files changed, 11 insertions, 1 deletions

diff --git a/docs/language.md b/docs/language.md
index 79d7866..a4743b3 100644
--- a/docs/language.md
+++ b/docs/language.md
@@ -1,6 +1,16 @@
 # hdass language reference
 
-hdass emits NASM or FASM for x86-64 (`-t nasm` by default, `-t fasm`); masm is planned. The instruction bodies are the same Intel syntax for both — only the framing (headers, sections, constants, data) differs. The compiler output itself isn't tied to an OS, but the examples and toolchain here target Linux (Linux syscall numbers, ELF64, `ld`). Pipeline: `lex → parse → analyze → emit`.
+hdass has two independent axes: the **architecture** (which instructions and registers) and the **assembler syntax** (how they are written). A target is a pairing:
+
+| `-t` | architecture | assembler |
+| --- | --- | --- |
+| `nasm` (default) | x86-64 | NASM |
+| `fasm` | x86-64 | fasm |
+| `arm64` | AArch64 | GNU as |
+
+For x86-64 the two syntaxes emit the same Intel instruction bodies and differ only in framing (headers, sections, constants, data). `arm64` is a separate instruction selector — different registers, three-operand arithmetic, `ldr`/`str`, `cmp`+`b.cond`, `svc #0` — and is early: assignments, arithmetic (`+ - * /`), control flow, calls, `syscall`, and the raw instruction statement work; floats, stack buffers, and division-remainder do not yet. masm is planned. Pipeline: `lex → parse → analyze → emit`.
+
+The portable way to write for more than one architecture is the [`logical_registers`](#extensions) extension: `r1..r14` are the general-purpose registers, mapped per target (x86-64 `r1 = rax`; AArch64 `r1 = x0`, i.e. `rN → x(N-1)`). Architecture-native register names (`rax`, `x0`) and the raw instruction statement are, by definition, locked to one architecture. Syscall ABIs also differ per architecture — Linux exit is `60` in `rax` on x86-64 but `93` in `x8` (logical `r9`) on AArch64 — so programs still carry arch-specific ABI constants even when the language is portable. The output isn't tied to an OS, but the examples and toolchain here target Linux (ELF, `ld` / `qemu-aarch64`).
 
 ## A first program