# debug-optimized-builds

Walks an agent through debugging code compiled with optimization, including the "value optimized out" message and inlined frames in GDB.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 533 installs · ★ 267
- Author: mohitmishra786
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/debuggers/debug-optimized-builds/SKILL.md
- Updated: 2026-06-27
- HTML: https://affpapa.org/en/nevibecode/skills/debug-optimized-builds

## What it does

The skill guides an agent through debugging optimized builds: which optimization level to pick, how to read inlined frames, and what "value optimized out" actually means. It lays out a workflow in steps — choosing a build configuration, working around optimized-out variables, reading inline frames in GDB, handling line number drift, `scheduler-locking` for multithreaded code, and split-DWARF.

Build flags come with ready recipes: `-O0 -g` for full debuggability, `-Og -g` as the balance for everyday work, `-O2 -g -gsplit-dwarf` for a release build that still carries debug info. CMake build types are covered too — `Debug`, `RelWithDebInfo`, `Release` — with the flags behind each one.

When a variable vanishes from the output, the skill lists workarounds: `volatile`, the `used` attribute, dropping optimization for a single file via `set_source_files_properties`, or reading registers directly. Note that `volatile` changes program semantics, so it is worth checking whether it belongs in that spot at all. The skill text cuts off in the related skills section, so the full list of links is not shown.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill debug-optimized-builds -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/debug-optimized-builds/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/debug-optimized-builds/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill debug-optimized-builds -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/debug-optimized-builds/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill debug-optimized-builds -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/debug-optimized-builds/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install mohitmishra786/low-level-dev-skills debug-optimized-builds
```

2. **Manually: put the files in place**
- File: `.github/skills/debug-optimized-builds/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill debug-optimized-builds -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/mohitmishra786/low-level-dev-skills --path skills/debuggers/debug-optimized-builds
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/debug-optimized-builds/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill debug-optimized-builds -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/debuggers/debug-optimized-builds/SKILL.md

## When to use it
- figure out what "value optimized out" means in GDB output
- pick an optimization level that still allows debugging
- see frames of functions the optimizer inlined
- keep other threads from interfering while stepping
- cut debug build time with split-DWARF

## Example prompts
- GDB says "value optimized out" — what does that mean and how do I see the value?
- How do I debug a RelWithDebInfo build with CMake?
- Show me inlined function frames in GDB and explain why my breakpoint landed on the wrong line

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 1765dd8505db98b5.

BEGIN THIRD-PARTY FILE 1765dd8505db98b5
````text
---
name: debug-optimized-builds
description: Debugging optimized builds skill for diagnosing issues in release code. Use when debugging RelWithDebInfo builds, using -Og for debuggable optimization, working with split-DWARF, applying GDB scheduler-locking, reading inlined frames, or understanding "value optimized out" messages. Activates on queries about debugging optimized code, RelWithDebInfo, -Og, inlined functions in GDB, value optimized out, GDB with -O2, or debugging release builds.
---

# Debugging Optimized Builds

## Purpose

Guide agents through debugging code compiled with optimization: choosing the right debug-friendly optimization level, reading inlined frames, diagnosing "value optimized out", using split-DWARF for faster debug builds, and applying GDB techniques specific to optimized code.

## Triggers

- "GDB says 'value optimized out' — what does that mean?"
- "How do I debug a release build?"
- "How do I see inlined function frames in GDB?"
- "What's the difference between -O0 and -Og for debugging?"
- "How do I use RelWithDebInfo with CMake?"
- "Breakpoints in optimized code land on wrong lines"

## Workflow

### 1. Choose the right build configuration

```
Goal?
├── Full debuggability, no optimization
│   → -O0 -g                        (slowest, all vars visible)
├── Debuggable, some optimization (recommended for most dev work)
│   → -Og -g                        (-Og keeps debug experience good)
├── Release build with debug info (shipped, debuggable crashes)
│   → -O2 -g -gsplit-dwarf          (or -O2 -g1 for lighter info)
└── Full release (no debug symbols)
    → -O2 -DNDEBUG
```

**`-Og`**: GCC's "debug-friendly optimization" — enables optimizations that don't interfere with debugging. Variables stay in registers where GDB can see them. Line numbers stay accurate. **Best balance for development.**

```bash
# GCC / Clang
gcc -Og -g -Wall main.c -o prog

# CMake build types
cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug          # -O0 -g
cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo # -O2 -g -DNDEBUG
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release        # -O2 -DNDEBUG
```

### 2. "Value optimized out" — causes and workarounds

```text
(gdb) print my_variable
$1 = <optimized out>
```
````
END THIRD-PARTY FILE 1765dd8505db98b5

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