valgrind

Q: How do I install valgrind?

Run npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill valgrind in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/valgrind/ (personal) or .claude/skills/valgrind/ (project).

by mohitmishra786

Valgrind profiler skill for memory error detection and cache profiling. Use when running Memcheck to find heap corruption, use-after-free, memory leaks, or uninitialised reads; or Cachegrind/Callgrind for cache simulation and function-level profiling. Activates on queries about valgrind, memcheck, heap leaks, use-after-free without sanitizers, cachegrind, callgrind, KCachegrind, or massif memory profiling.

Installs: 683
Last 24h: —
Trending rank: —
Security: Not audited

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill valgrind

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads valgrind automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

SKILL.md

The instructions your agent reads when the skill is triggered.

Valgrind

Purpose

Guide agents through Valgrind tools: Memcheck for memory errors, Cachegrind for cache simulation, Callgrind for call graphs, and Massif for heap profiling.

Triggers

"My program has a memory leak / use-after-free"
"I can't use ASan — can I use Valgrind instead?"
"How do I profile cache behaviour without perf?"
"How do I visualize call graphs with Callgrind?"
"How do I profile heap allocation patterns?"
"Valgrind reports errors in third-party code I can't fix"

Workflow

1. Memcheck — memory error detection

Compile with -g -O1 for best results. -O0 is also fine; avoid -O2+ which can produce false positives.

valgrind --tool=memcheck \
         --leak-check=full \
         --show-leak-kinds=all \
         --track-origins=yes \
         --error-exitcode=1 \
         ./prog [args]

Key flags:

Flag	Default	Effect
`--leak-check=full`	summary	Full leak details
`--show-leak-kinds=all`	definite	Show all leak kinds
`--track-origins=yes`	no	Show where uninit values came from (slow)
`--error-exitcode=N`	0	Exit N if errors found (CI integration)
`--log-file=file`	stderr	Save report to file
`--suppressions=file`	none	Suppress known FPs
`--gen-suppressions=yes`	no	Print suppression directives for errors
`--max-stackframe=N`	2000000	Increase for deep stacks
`--malloc-fill=0xAB`	off	Fill allocated memory (detect uninit use)
`--free-fill=0xCD`	off	Fill freed memory (detect use-after-free)

2. Understanding Memcheck output

==12345== Invalid read of size 4
==12345==    at 0x4007A2: foo (main.c:15)
==12345==    by 0x400846: main (main.c:30)
==12345==  Address 0x5204040 is 0 bytes after a block of size 40 alloc'd
==12345==    at 0x4C2FB0F: malloc (in /usr/lib/valgrind/vgpreload_memcheck.so)
==12345==    by 0x40074B: main (main.c:25)

Invalid read/write: out-of-bounds access; check array bounds
Use of uninitialised value: read before write; use --track-origins=yes
Invalid free / double free: mismatched malloc/free; check ownership
Definitely lost: reachable via no pointers; clear leak
Indirectly lost: lost through a chain; usually means one root leak
Possibly lost: might be pointing into the middle of a block; often FP with custom allocators

3. Leak kinds

Kind	Meaning
Definitely lost	No pointer to block
Indirectly lost	Lost via another lost block
Possibly lost	Pointer into middle of block
Still reachable	Pointer exists at exit; not a leak but never freed

For library code: --show-leak-kinds=definite,indirect reduces noise from still-reachable.

4. Suppressions

# Generate suppression for current error
valgrind --gen-suppressions=yes ./prog 2>&1 | grep -A20 '{'

# Example suppression file (valgrind.supp)
{
   openssl_uninit
   Memcheck:Cond
   fun:SHA256_Init
   ...
}

# Use suppression file
valgrind --suppressions=valgrind.supp ./prog

5. Cachegrind — cache simulation

valgrind --tool=cachegrind ./prog

# Output: cachegrind.out.PID
# Annotate source
cg_annotate cachegrind.out.12345 --auto=yes

# Diff two runs
cg_diff cachegrind.out.before cachegrind.out.after

Key metrics:

I1mr / ILmr: L1/LL instruction cache miss rate
D1mr / DLmr: L1/LL data read miss rate
D1mw / DLmw: L1/LL data write miss rate

6. Callgrind — call graph profiling

valgrind --tool=callgrind --callgrind-out-file=callgrind.out ./prog

# Analyse
callgrind_annotate callgrind.out

# Visualise in KCachegrind (GUI)
kcachegrind callgrind.out

Callgrind is slower than perf but works without root and provides exact call counts.

7. Massif — heap profiling

valgrind --tool=massif ./prog

# Visualise
ms_print massif.out.PID | less

# GUI
massif-visualizer massif.out.PID

Massif shows heap usage over time; useful for finding peak allocation sites and tracking gradual leaks.

8. Performance considerations

Valgrind Memcheck runs ~10-50x slower than native. Mitigations:

Use a shorter representative workload
Use --error-exitcode=1 to fail fast in CI
Use ASan (-fsanitize=address) for faster memory checking during development
Reserve Valgrind for cases where ASan can't be used (old toolchains, production-like environments)

For a comparison of Valgrind vs ASan, see references/valgrind-vs-asan.md.

Related skills

Use skills/runtimes/sanitizers for faster ASan/UBSan alternatives
Use skills/profilers/linux-perf for CPU-level profiling (faster than Cachegrind)
Use skills/profilers/flamegraphs to visualise Callgrind output

FAQ

What does the valgrind skill do?

How do I install valgrind?

Run npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill valgrind in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/valgrind/ (personal) or .claude/skills/valgrind/ (project).

Which AI agents can use valgrind?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is valgrind safe to install?

No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.

Who maintains valgrind?

It is published by mohitmishra786 in mohitmishra786/low-level-dev-skills. It has 683 recorded installs.