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Agent skill

Struct Layout Analysis

by isc-projects in isc-projects/bind9

Measure and fix C struct layout in BIND 9 — pahole on the build's DWARF for sizes, padding holes, and cacheline boundaries, plus the house cacheline-padding idiom.

MPL-2.0Auto-check passedDevelopment

Install Struct Layout Analysis

skills CLI
$ npx skills add isc-projects/bind9 --skill struct-layout-analysis -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install isc-projects/bind9 struct-layout-analysis --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/isc-projects/bind9.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/struct-layout-analysis .claude/skills/struct-layout-analysis && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
struct-layout-analysis
GitHub stars
780
Token cost
~461 tokens
SKILL.md length
170 words
Files
1
Skills in repo
9
Repo updated
First seen
Licence
MPL-2.0

At a glance

Measure and fix C struct layout in BIND 9 — pahole on the build's DWARF for sizes, padding holes, and cacheline boundaries, plus the house cacheline-padding idiom.

  • Asked about struct size
  • SKILL.md covers Measuring — pahole, never… and Padding to cachelines — union…
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
  • Adding/reordering members in hot structures

What it does

Struct Layout Analysis is an agent skill from isc-projects/bind9. Measure and fix C struct layout in BIND 9 — pahole on the build's DWARF for sizes, padding holes, and cacheline boundaries, plus the house cacheline-padding idiom. Use when asked about struct size, padding, false sharing, or when adding/reordering members in hot structures.

Its SKILL.md is about 460 tokens, which your agent loads only when the skill is triggered. It is a single SKILL.md file with no bundled scripts.

It sits in Development. The repository describes itself as: Archived mirror of https://gitlab.isc.org/isc-projects/bind9, please submit issues and PR/MRs in the GitLab. The licence is MPL-2.0.

When your agent uses it

  • Asked about struct size
  • Adding/reordering members in hot structures

Example prompts

  • “/struct-layout-analysis”

What it can do on your machine

Read from SKILL.md and the folder at commit 784d666. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md (its code samples are bash and c).

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    No URLs in SKILL.md.

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Struct Layout Analysis loads about 461 tokens when it runs. Until then it costs about 74 tokens; SKILL.md has 170 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~74
When it runs · the whole SKILL.md, loaded when a task matches
~461

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from isc-projects/bind9 at commit 784d666, republished under its MPL-2.0 licence (© isc-projects). 170 words, ~461 tokens.

Download SKILL.mdSave it as .claude/skills/struct-layout-analysis/SKILL.md (or your agent's skills folder).
name
struct-layout-analysis
description
Measure and fix C struct layout in BIND 9 — pahole on the build's DWARF for sizes, padding holes, and cacheline boundaries, plus the house cacheline-padding idiom. Use when asked about struct size, padding, false sharing, or when adding/reordering members in hot structures.

Struct layout: measure with pahole, pad with a multiplier

Measuring — pahole, never throwaway sizeof programs

The developer build (-Og -ggdb) already carries DWARF; read it instead of compiling sizeof/offsetof snippets:

sh
pahole -C <struct_name> build/lib/dns/libdns*.so.p/<file>.c.o
pahole --holes -C <struct_name> <object-or-binary>

pahole prints member offsets, padding holes, total size, and cacheline boundaries — complete layout information the compiler already computed, with no boilerplate to write. Any object file under build/ or the final binary works as input.

Padding to cachelines — union arm with a plain multiplier

Pad a struct to a whole number of cache lines with a union arm sized by a plain multiplier, always paired with a static assert:

c
struct foo {
	union {
		struct {
			/* members */
		};
		uint8_t __padding[ISC_OS_CACHELINE_SIZE * 6];
	};
};
STATIC_ASSERT(sizeof(struct foo) % ISC_OS_CACHELINE_SIZE == 0,
	      "struct foo size must be a multiple of the cacheline size");

Pick the smallest n that fits; when members outgrow the arm to a non-multiple size, the STATIC_ASSERT fires and prompts a bump of n.

Do NOT use the enumerated-sizeof trailing formula uint8_t __padding[CACHELINE - (sizeof(a) + sizeof(b) + ...) % CACHELINE] (the historical qpzone style): it must enumerate every member's sizeof, so adding a member silently miscounts unless the formula is updated in lockstep. The multiplier form has no such coupling and is easier to read.

© isc-projects, MPL-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .agents/skills/struct-layout-analysis of isc-projects/bind9.

Open the folder on GitHubat commit 784d666

Compare with similar skills

Struct Layout Analysis next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

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Struct Layout Analysis this skillisc-projects/bind9780—~461Automated safety check: PassMPL-2.0
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Code Review ChecklistshareAI-lab/learn-claude-code78k5 repos~1.1kAutomated safety check: PassMIT
Greplooponyx-dot-app/onyx32k4 repos~3.3kAutomated safety check: PassMIT

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Categories

Questions about Struct Layout Analysis

What does Struct Layout Analysis do?

Measure and fix C struct layout in BIND 9 — pahole on the build's DWARF for sizes, padding holes, and cacheline boundaries, plus the house cacheline-padding idiom. Struct Layout Analysis is an agent skill from isc-projects/bind9. Measure and fix C struct layout in BIND 9 — pahole on the build's DWARF for sizes, padding holes, and cacheline boundaries, plus the house cacheline-padding idiom.

When should I use Struct Layout Analysis?

Struct Layout Analysis fits situations like: asked about struct size; adding/reordering members in hot structures.

How do I install Struct Layout Analysis in Claude Code?

Run `npx skills add isc-projects/bind9 --skill struct-layout-analysis -a claude-code`. Or copy the skill folder (.agents/skills/struct-layout-analysis in isc-projects/bind9) into .claude/skills/struct-layout-analysis in your project. Claude Code loads it when a task matches its description.

How do I install Struct Layout Analysis in Codex?

Run `npx skills add isc-projects/bind9 --skill struct-layout-analysis -a codex`. Or copy the skill folder (.agents/skills/struct-layout-analysis in isc-projects/bind9) into .agents/skills/struct-layout-analysis in your project. Codex loads it when a task matches its description.

Can I use Struct Layout Analysis in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add isc-projects/bind9 --skill struct-layout-analysis -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/struct-layout-analysis, .gemini/skills/struct-layout-analysis, .github/skills/struct-layout-analysis and .opencode/skills/struct-layout-analysis in your project.

What does Struct Layout Analysis need to run?

SKILL.md names no scripts, command-line tools or credentials: Struct Layout Analysis is instructions for the agent only.

Does Struct Layout Analysis access the network?

SKILL.md contains no URLs. Any network use would come from the scripts or tools the agent runs. This is read from the text; nothing was executed.

Is Struct Layout Analysis safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does Struct Layout Analysis use?

Struct Layout Analysis is published under the MPL-2.0 licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Struct Layout Analysis use?

About 461 tokens (SKILL.md is roughly 1.8k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Struct Layout Analysis?

Skills that share tags, products or a category with Struct Layout Analysis: Finishing a Development Branch (obra/superpowers, 296k stars), Typescript Advanced Types (rolling-scopes/rsschool-app, 10k stars), PR Babysitter (openinterpreter/openinterpreter, 69k stars) and Code Review Checklist (shareAI-lab/learn-claude-code, 78k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Struct Layout Analysis?

isc-projects (a GitHub organization) maintains it in isc-projects/bind9, which has 780 GitHub stars. The repository holds 9 skills in this directory. The repository was last updated on October 7, 2026.

Source: isc-projects/bind9 on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.