# Qemu Tcg Frontend Instruction

> Use for adding, reviewing, or debugging a guest ISA instruction in a QEMU TCG frontend. Extends qemu-flow-plan and qemu-rlcr-loop; this skill only defines frontend decode/translation decisions.

- **Type:** Skill
- **Install:** `agentstack add skill-processmission-oh-my-qemu-qemu-tcg-frontend-instruction`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [processmission](https://agentstack.voostack.com/s/processmission)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [processmission](https://github.com/processmission)
- **Source:** https://github.com/processmission/oh-my-qemu/tree/main/.agents/skills/qemu-tcg-frontend-instruction
- **Website:** https://processmission.github.io/oh-my-qemu/

## Install

```sh
agentstack add skill-processmission-oh-my-qemu-qemu-tcg-frontend-instruction
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# QEMU TCG Frontend Instruction

Use this domain skill for guest ISA decode/translation work in `target//`: decodetree patterns, `trans_*` functions, feature gates, helpers, PC updates, exceptions, and tests.

## Flow dependencies

1. Start with `qemu-flow-plan`.
2. Put decode notes, generated decoder inspection, TCG logs, test outputs, and scratch files under `build/agent//`.
3. Use `qemu-rlcr-loop` for iterative work.
4. Use `qemu-build` for target builds.
5. Use `qemu-debug` for TCG logs and `one-insn-per-tb` debugging.
6. Use `qemu-model-verification` for evidence reporting.

## Hard policy boundary

Do not produce source code intended for QEMU upstream submission. Do not add DCO or review trailers.

## Frontend contract

A frontend maps guest instructions to TCG IR while preserving architectural exceptions, feature gating, PC state, and TB termination.

Record in the plan:

- ISA extension/version and privilege requirements;
- instruction encoding and aliases;
- operand fields and sign/zero extension;
- XLEN/vector/FPU state constraints;
- expected illegal-instruction cases;
- helper vs direct TCG-op decision;
- tests that prove semantics and invalid encodings.

## Decoder rules

For decodetree targets:

- reuse existing fields, formats, and argument sets;
- confirm fixedmask/fixedbits uniqueness;
- handle overlap groups intentionally;
- use field functions for transformed immediates;
- keep decoder ordering consistent with nearby extensions.

For hand decoders, preserve existing fallback and illegal-instruction behavior.

## `trans_*` rules

Before emitting IR, gate:

- CPU/ISA feature;
- privilege/virtualization mode;
- XLEN/operand width;
- reserved bits and invalid immediates;
- vector/FPU state where relevant;
- alignment or memory-mode constraints if architectural.

Use direct TCG ops for simple integer/logical/shift/select operations. Use helpers for complex state, softfloat/crypto/vector libraries, or exception-heavy semantics.

Helper calls must use correct side-effect flags. Do not mark a helper no-side-effects if it can raise or mutate CPU state.

## PC and TB rules

Check target conventions for:

- `pc_next` advancement;
- PC update before exceptions;
- branch/direct-block chaining;
- `ctx->base.is_jmp` state;
- page-boundary behavior;
- single-step and interrupt trigger behavior.

Wrong PC state corrupts exceptions, gdbstub state, and replay/debug evidence.

## Verification expectations

- Build the target translator.
- Add/run focused `tests/tcg//` coverage when applicable.
- Cover edge values, invalid encodings, feature-disabled behavior, and privilege errors.
- Use `-accel tcg,one-insn-per-tb=on` when debugging instruction boundaries.
- Store TCG logs under `build/agent//logs/`.

## Upstream references

- QEMU code provenance and AI policy: `docs/devel/code-provenance.rst`.
- Decodetree: `docs/devel/decodetree.rst`.
- TCG internals: `docs/devel/tcg.rst`.
- TCG IR/helper semantics: `docs/devel/tcg-ops.rst`.
- Target examples: `target/riscv/translate.c`, `target/riscv/*.decode`, `target/riscv/insn_trans/`.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [processmission](https://github.com/processmission)
- **Source:** [processmission/oh-my-qemu](https://github.com/processmission/oh-my-qemu)
- **License:** MIT
- **Homepage:** https://processmission.github.io/oh-my-qemu/

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-processmission-oh-my-qemu-qemu-tcg-frontend-instruction
- Seller: https://agentstack.voostack.com/s/processmission
- Browse the marketplace: https://agentstack.voostack.com/browse

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