gasm-sdk/README.md

# gasm-devkit

Developer tooling for **GAsm** — Go's built-in Plan 9 assembler.

Go ships an assembler but no tooling for it.  There is no syntax highlighting,
no autocomplete, no linter, no static analyser, no formatter, no standalone
assembler and no debugger for `.s` files.  Developers write assembly blind,
validate it by benchmark, and debug it by print statement.

gasm-devkit is the missing toolkit.  It is a single, self-contained binary —
`gasm` — that brings proper developer tooling to Plan 9 assembly:

```
gasm tokens   dump the lexical token stream
gasm parse    parse and report syntax errors
gasm fmt      canonicalise formatting (gofmt for assembly)
gasm lint     static checks
gasm lsp      language server (completion, hover, symbols, diagnostics, highlighting)
gasm asm      standalone assembler
gasm verify   dynamic analysis & verification
gasm debug    source-level debugger
gasm diff     compare machine code of two .s files
gasm profile  show basic-block structure of functions
```

## Architecture support

gasm-devkit targets every architecture Go's assembler speaks.  The instruction
tables are **generated from the Go toolchain's own assembler source**
(`cmd/internal/obj/<arch>`), so gasm-devkit recognises *every* mnemonic the
real assembler accepts — not a hand-maintained subset that drifts and rots.

| Architecture | GOARCH      | File suffix    | Instructions recognised            |
|--------------|-------------|----------------|------------------------------------|
| AMD64        | `amd64`     | `_amd64.s`     | 1600 + common opcodes + traditional aliases |
| ARM64        | `arm64`     | `_arm64.s`     | 538 + common opcodes               |
| RISC-V       | `riscv64`   | `_riscv64.s`   | 961 + common opcodes               |
| LoongArch    | `loong64`   | `_loong64.s`   | 799 + common opcodes               |

"Common opcodes" are the instructions shared by every architecture (`RET`,
`JMP`, `NOP`, `CALL`, `TEXT`, `FUNCDATA`, `PCDATA`, …).  AMD64 additionally
carries the traditional conditional-jump spellings (`JZ`, `JNZ`, `JA`, `JC`,
…) that the assembler accepts as aliases.  Regenerating the tables is one
command — `just gen` — and requires only a Go installation; the committed
output has no runtime dependency on the toolchain.

## Supported Platforms

The toolkit runs on Linux.  All four Linux architectures are supported as
hosts — amd64, arm64, riscv64 and loong64 — and the release matrix
cross-compiles the same four targets.

**FreeBSD support is planned for a future release.**

## Principles

- **Pure Go and GAsm only.**  No C, no cgo, no external toolchains, no native
  binaries, no JavaScript runtimes.  The parser is hand-written; there is no
  parser generator.
- **Self-contained.**  The toolkit's production code depends only on the
  standard library; one binary, no runtime data files.  The single module
  dependency, `golang.org/x/arch`, is used **only in tests** to validate the
  instruction encoder by round-trip decoding — it is never linked into the
  `gasm` binary.
- **Linux-only.**  Runs natively on amd64, arm64, riscv64 and loong64 Linux
  hosts; the release matrix cross-compiles the same four targets.  Latest
  stable Go only.
- **No vendor lock-in.**  The integration surface is the Language Server
  Protocol and a command-line interface — both open standards.  No cloud
  service, no proprietary API, no dependence on any one editor's internals.
- **Complete and verifiable.**  Instruction coverage is generated from the
  assembler's own source and regenerated on demand, so it cannot silently fall
  behind the toolchain.

## Components

| Package | Purpose |
|---------|---------|
| `token` | Lexical token kinds and source positions. |
| `lexer` | Hand-written scanner for Plan 9 assembly. |
| `ast` | The abstract syntax tree. |
| `parser` | Line-oriented, error-tolerant parser producing the AST. |
| `arch` | amd64, arm64, riscv64 and loong64 register files and instruction tables. |
| `lint` | Conservative static checks (13 rules including unused-label, invalid-textflag, stack-imbalance). |
| `s` | A canonical formatter — `gofmt` for assembly. |
| `asm` | The standalone assembler: all four architecture encoders, linker, object-file emitters (ELF with DWARF5, GOOBJ). |
| `verify` | JIT execution substrate for dynamic analysis, combined ABI+fuzz differential testing.  Assembly trampolines for all four architectures. |
| `debug` | Interactive ptrace debugger for all four architectures: single-stepping, breakpoints, hardware watchpoints, register and memory inspection. |
| `lsp` | Language Server Protocol server: completion, hover, symbols, diagnostics, semantic tokens, find references, rename, formatting, inlay hints. |
| `cmd/gasm` | The `gasm` binary tying it all together. |
| `_gen` | The generator that rebuilds the instruction tables from the Go toolchain. |

See [`docs/ARCHITECTURE.md`](docs/ARCHITECTURE.md) for the design rationale and
data flow, and [`docs/DECISIONS.md`](docs/DECISIONS.md) for design decisions
deliberately postponed (with the analysis needed to pick them up again).

## Quick start

```sh
just install     # download dependencies (there are none)
just build       # go vet + gofmt check — zero errors, zero warnings
just test        # full suite, race detector, 80 % coverage gate
just fmt         # gofmt the tree
just gen         # regenerate the instruction tables from the Go toolchain
```

Install the binary and use it:

```sh
just install-bin                    # installs gasm into $GOBIN

gasm --help                         # overview of commands and flags
gasm tokens kernel_amd64.s          # dump the token stream
gasm parse  kernel_amd64.s          # parse, report syntax errors
gasm fmt    -w kernel_amd64.s       # canonicalise in place
gasm fmt                            # reformat every .s below here, like go fmt
gasm lint   *.s                     # static checks
gasm asm --format elf -o k.o k.s    # assemble to a linkable ELF object
gasm verify kernel_amd64.s           # JIT-load and report functions
gasm verify --ground-truth k.s      # byte-for-byte vs go tool asm
gasm verify --call decodeBlockAVX2 --buf src:64:hex...,dst:256:zero k.s
gasm verify --call sumTo --args n=57,base=0x1f k.s   # scalar arguments
gasm debug --func name k.s           # interactive debugger
gasm debug --func name --script cmds.txt --timeout 30s k.s   # headless run
gasm debug --func name --cover k.s   # which labels did execution reach?
gasm audit-instructions              # encoder vs go tool asm name diff
gasm scaffold differential k.s       # generate a differential test skeleton
gasm diff a.s b.s                    # compare machine code byte-for-byte
gasm diff --map wideCopyAVX2=wideCopyAVX512 avx2.s avx512.s
gasm profile k.s                     # show basic-block structure
```

See [CONTRIBUTING.md](CONTRIBUTING.md) for the full development workflow,
[docs/CLI.md](docs/CLI.md) for the command reference, and
[docs/DEVELOPMENT.md](docs/DEVELOPMENT.md) for setup and recipes.

## Editor integration

`gasm lsp` speaks the Language Server Protocol over standard input/output, so
any LSP-capable editor can use it — point your editor's LSP client at the
binary and associate it with `.s` files.  Syntax highlighting is delivered as
**LSP semantic tokens**, so no editor-specific grammar is required.  The server
infers the target architecture from the file-name suffix
(`_amd64.s` / `_arm64.s` / `_riscv64.s` / `_loong64.s`).

## License

BSD-3-Clause — see [LICENSE](LICENSE).  
Copyright © 2026 [Petr Balvín](https://petrbalvin.org)