Code Review

Review llama.cpp changes

This skill reviews changes against llama.cpp's conventions and the pitfalls that reviewers flag most often, so the contributor can fix them before a maintainer has to. It has two modes:

• Self-review (default): review the contributor's own local changes (uncommitted work, or a branch vs master) as a pre-PR pass. Ask which if it's ambiguous; default to git diff master...HEAD plus any uncommitted changes.
• Read-only review of a PR/file: if the user points at a PR number or specific files (including code they didn't write), review those and report findings.

In both modes the output is private review notes for the user to read and act on - it is never something to post. This is a hard rule from AGENTS.md: an agent must NEVER write, or help write, a PR comment, a review comment, or a reply to a reviewer, by any means including gh. Do not offer to. If the user asks you to post the notes, refuse and point them at that rule. Present findings in the conversation only.

Before starting, read AGENTS.md and CONTRIBUTING.md if not already in context - the "Coding guidelines", "Naming guidelines", and AI usage sections are the baseline this review enforces. For a diff that adds a new model architecture, also read docs/development/HOWTO-add-model.md and consider the dedicated add-new-model skill.

Step 0 - Scope the diff and pick the checklists

Identify what actually changed and which area checklists below apply. Run git diff --stat (or gh pr view <n> --json files for PR mode) and bucket the touched paths:

• conversion/, gguf-py/, src/models/, src/llama-arch.* -> New model / architecture
• ggml/ (any backend, op, or ggml.h) -> ggml / backend
• include/llama.h and other public headers -> Public API
• tools/server/ -> Server
• anything else, plus all of the above -> General (always runs)

Always run the Scope and quick-reject gate, the Security review, and the General checklist. Run each area checklist whose paths were touched. Additionally, if the diff introduces a new component, subsystem, or piece of infrastructure (a new file/class/module, a new abstraction, or hand-rolled machinery), run the Approach and design review. Tell the user which checklists you're running and why.

Scope and quick-reject gate (always)

These are the patterns that get PRs closed without a full review. Check them first - a finding here is more important than any code nit, because it can mean the change shouldn't be a PR in its current form at all.

• Is there a prior issue/discussion for this? Features are supposed to start as an issue, not a PR (CONTRIBUTING.md). If this is a nontrivial feature with no linked issue, flag it and suggest opening one first.
• Is it a duplicate of existing/in-flight work? Suggest gh search prs / gh search issues for the feature. Many closed PRs were duplicates of something already queued.
• Is it self-contained and single-purpose? Multiple unrelated changes/optimizations bundled together get sent back to be split. Flag unrelated changes and suggest separate PRs.
• Does it touch multiple ggml backends at once? Initial support should be CPU-only, other backends as follow-ups (CONTRIBUTING.md). Flag CUDA/Metal/Vulkan/etc. changes bundled into a feature's first PR.
• Does it add a new ggml_type / quantization type? That carries a disproportionate maintenance burden and needs the full justification package (GGUF sample upload, perplexity vs FP16/BF16 and similar sizes, KL-divergence data, CPU perf numbers). Absent that, it will be rejected regardless of code quality.
• Is it invasive - new subsystem, core-API reshaping, changes to shared graph/sampler code that other models don't need? Flag it and suggest a discussion with maintainers before investing further.
• Is it niche/vendor-specific in a way that adds a maintenance burden nobody will own long-term? Flag the maintenance-ownership question.
• Is the change semantically correct, or a plausible-looking "fix" that misunderstands the code? Sanity-check the actual behavior, not just that it compiles.
• AI-disclosure: if AI meaningfully contributed, is the PR template's disclosure section filled in? Remind the user. Never suggest writing the PR description or commit message for them.

Security review (mandatory)

Mandatory on every review; any finding here is blocking. Rule of thumb: GGUF metadata, tensor shapes, tokenizer/grammar input, and all server/RPC fields are attacker-controlled - bound them before use.

• Sizes/counts from tensor dims: validate before allocating. Products like ne[i]*nb[i]/nbytes can overflow on crafted dims into an undersized alloc then heap overflow. Overflow checks must run BEFORE the arithmetic they guard - padding/alignment macros wrap to 0 near SIZE_MAX, so a guard after the pad passes.
• GGUF strings/arrays: cap declared lengths and element counts before using them to size a loop or buffer; validate element type and length before casting an array to a pointer or reading fixed indices ([i+1], [0..2]).
• File-supplied counts indexing fixed arrays: bound any count (e.g. layer/block count into a LLAMA_MAX_* array) before indexing; watch checks that only fire when an optional key is present.
• Bounds comparisons: flag narrowing casts (size_t->int32_t) and signed/unsigned mixing that can bypass a length check and copy past a buffer.
• Parsed/derived indices: range-check stoi/atoi results and catch parse throws; never use a default or derived token id (EOS/BOS/...) as an index without a bounds check.
• Reused/reserved buffers: recheck bounds after a buffer is shrunk or reused; watch reserve() then index-by-assumed-size, and header fields read before their length is checked.
• Server JSON ints: clamp client-supplied integers (token/discard counts, offsets) to non-negative and an upper bound before they reach index/pointer arithmetic.
• RPC-deserialized fields: treat every field (type/buffer/data/ne/nb/op_params) as hostile - validate before use. Null/zero buffers skipping validation, attacker data pointers, out-of-range type indices, and negative strides sign-extending past a corner-only assert all give arbitrary read/write.
• Lifetime/UAF: flag stored raw pointers to caller/temporary storage, cached pointers to buffers a later free releases, async ops whose source may drop before completion, and structures not invalidated on free/realloc. Null-check conditionally-built or "not required" tensors before dereferencing.

Approach and design (when a new component/infra is introduced)

Run this whenever the diff adds a new component, subsystem, or piece of infrastructure. Reviews too often stop at "does it work" - a diff can be correct and still be the wrong approach, and a messy design costs more long-term than a bug. Evaluate the approach, not just the behavior; raising a cleaner one is a high-value finding, not a nit. If you see a better design, describe it concretely rather than just calling the current one bad.

• Simpler approach upstream: the biggest win is often a different data model or design that removes whole subsystems, not tweaks to the code as written. Complexity must be justified by the problem, not by the first thing that worked.
• Reuse over reinvention: grep for an existing helper, library, object, or mechanism before adding a new one. Reimplementing what the codebase already has reintroduces solved bugs and adds maintenance surface.
• Clear ownership/lifetime: prefer RAII and obvious ownership over manual liveness flags, hand-tracked pointers, and "is it still alive?" checks - manual lifetime tracking is a recurring source of subtle bugs.
• Right-sized machinery: flag redundant, overkill, or heavier-than-needed primitives and abstractions; use the minimum the design actually needs.
• Right structure and fit: a new type should earn its place (split it if it serves two roles); follow existing patterns, idioms, and naming, and avoid constructs the project shuns.
• Root cause vs symptom: fixes layered on fixes signal a design to correct, not guard around.

New model / architecture

See the add-new-model skill and docs/development/HOWTO-add-model.md for the full workflow; this is the review-time subset that reviewers most often catch:

• Don't branch on model.arch when the real dependency is a config/capability value - gate on the hparam/capability, not the architecture enum.
• If the model is a close variant of an existing arch, is the delta justified? Prefer reusing or subclassing the existing arch/model class over duplicating it. A near-duplicate class or src/models/<name>.cpp will be asked to merge with its sibling.
• New tensor names go through tensor_mapping.py, not ad-hoc name matching.
• For QKV, split the activation with ggml_view, not the weight tensor; rely on ggml broadcasting instead of manually duplicating tensors.
• New graph inputs are declared at the top of the graph-build function, not inline where first used.
• Hparams that the model can't run correctly without must be mandatory (hard-error if missing), not read with a silent default fallback. Only genuinely-optional-across-configs values get a fallback accessor.
• New/optional weight tensors (scales, etc.) must route through build_lora_mm and the existing helpers, matching convention - don't leave raw matmuls copied from another arch.
• Don't hack RoPE with a custom sin/cos implementation. If ggml_rope_ext genuinely can't express it, that's an issue for discussion, not a PR.
• Test the quantized-KV path (-ctk/-ctv q8_0), not just default f16 - new speculative/attention features silently break there.
• Preserve existing explanatory comments about model-specific quirks when copying code; note the provenance ("copied from X, with Y added").
• Remove dead code/branches left over from adapting a reference implementation.

ggml / backend

• supports_op (and any dispatch/gating condition) must be scoped exactly to the cases being changed - a condition meant for a few quant types must not silently disable or enable everything else.
• No hardcoded warp/lane size - use ggml_cuda_get_physical_warp_size() (32 on CUDA, 64 on HIP/ROCm) and the portable helpers.
• Strip leftover debug/profiling/logging code before review.
• New or changed op? Update docs/ops.md and the relevant docs/ops/*.csv for the touched backend.
• New op or operator change needs corresponding test-backend-ops cases, and (per CONTRIBUTING.md) consistency across at least two backends.
• New kernels are expected to come with concrete perf data (throughput across realistic tensor shapes), not just correctness.
• Don't have a backend mutate the cgraph as a shortcut - that's an unresolved architectural question, not something to slip in.
• Expect this to need two maintainer approvals; that's normal for ggml/ changes, not a sign something is wrong.
• For CUDA: Avoid excessively templating kernels, only add this where it shows visible performance gain.

Public API (include/llama.h)

Public API changes carry a higher bar than internal ones (CONTRIBUTING.md). Review for:

• Justification: why doesn't an existing mechanism (e.g. cb_eval, existing batch/sampler knobs) suffice? If it does, the change likely shouldn't add public surface. This is the single most common reason these PRs are rejected.
• Experimental or stop-gap surface belongs in a side header (llama-ext.h), not in llama.h.
• Keep it minimal and general: prefer one general call over several narrow convenience wrappers; make new calls forward-compatible (e.g. mixed-modality batches) rather than assuming today's shape.
• The C API is the first-class, stable, ABI-defining surface - don't propose a parallel C++ API as a replacement. llama-cpp.h stays a thin convenience layer.
• Types and naming: sized integer types (int32_t, size_t for sizes/offsets); snake_case; <class>_<method> = <class>_<action>_<noun>; enum values upper-case and prefixed with the enum name; _t suffix for opaque types. Avoid gratuitous signature/ABI changes to existing exported functions.
• Every new API needs a working example/tool exercising it in the same PR - reviewers find real bugs by requiring it to be wired into server, embedding, perplexity, etc.

Server (tools/server/)

• Is the feature within server's defined scope? Check tools/server/README-dev.md - out-of-scope features get declined.
• Security: don't trust client-supplied headers (e.g. X-Forwarded-For) or add footguns; things like IP allowlisting belong at a reverse proxy unless there's a trusted-proxy design.
• Wire new behavior into the existing request/response and checkpoint paths correctly; watch for resource leaks across requests.

Multimodal (tools/mtmd/)

• Tensor names must be prefixed by v., a., mm. or a.mm. (legacy naming doesn't follow this convention - this is expected, but new code should follow it).
• Do not use explicit sin/cos for RoPE; use ggml_rope_ext instead, see HOWTO-add-model.md. If it can't express the needed behavior, that's a design discussion, not a PR.
• New GGML ops must not be introduced in the same PR, you must push it as a separate PR.
• In most cases, build_vit should be enough to build the transformer graph for vision models. Do not add a loop to build the transformer graph manually, unless you have a very good reason to do so. If you do, please explain why in the PR description.
• If you need a dedicated preprocessor, there is a high chance that it can be a derived class from one of the existing preprocessors. Check carefully before adding a new preprocessor class.
• If the model need a new public API in mtmd.h, open a discussion first.

General (always)

Enforce the AGENTS.md / CONTRIBUTING.md coding and naming guidelines on every changed line - this is a distinct pass from checking that the code works, and matters just as much for review speed:

• ASCII only in code and comments - no emdash, unicode arrows, x, ... used as unicode; use -, ->, x, ... ASCII equivalents.
• Comments are concise and explain non-obvious why, not what. Flag verbose comments, comments that restate the code, comments that reference the current task/PR, and comments hard-wrapped to a fixed column width.
• Do not force-wrap prose/comments to a fixed character count or split a sentence across lines.
• snake_case names; kebab-case (lowercase-with-dashes) file names for C/C++, .h headers; Python files lowercase-with-underscores. Naming optimizes for longest common prefix (number_small, not small_number).
• 4-space indentation, brackets on the same line, void * ptr, int & a, no trailing whitespace; match the surrounding style.
• Reuse existing infrastructure over introducing new components; no new third-party dependencies, extra headers, or files unless clearly justified.
• Keep it simple: a simpler change doing 90% is often preferable to a complex one doing 100%. Flag unnecessary templates/fancy STL; basic for loops are fine here.
• Every added line should be something the contributor can explain and defend to a reviewer without AI help - flag anything that looks copied-in without understanding.

Reporting

Group findings by severity so the user knows what actually blocks a merge:

1. Blocking - quick-reject/scope issues and correctness bugs; these can sink the PR regardless of everything else.
2. Will slow the review - convention/naming/comment violations, missing tests/docs/perf data, missing API justification or example.
3. Nits - minor style, optional cleanups.

For each finding, point to the file and line and say concretely what to change and why. Do not rewrite the whole diff unprompted; let the contributor make the fixes so they own and understand them. And do not draft any PR text, commit message, or reviewer reply - that is the contributor's to write.