Sanitizers

What it does

When your agent uses it

• Enabling and interpreting AddressSanitizer (ASan)
• UndefinedBehaviorSanitizer (UBSan)
• ThreadSanitizer (TSan)
• MemorySanitizer (MSan)

Example prompts

• “/sanitizers”

Workflow steps

12 steps, taken from the step headings in SKILL.md.

1. 1Decision tree: which sanitizer?
2. 2AddressSanitizer (ASan)
3. 3UndefinedBehaviorSanitizer (UBSan)
4. 4ThreadSanitizer (TSan)
5. 5MemorySanitizer (MSan)
6. 6ASan + UBSan combined
7. 7Suppressions
8. 8CMake integration
9. 9CI integration
10. 10HWASan (Hardware-Assisted AddressSanitizer)
11. 11MemTagSanitizer (ARM MTE)
12. 12GWP-ASan (production sampling)

What it can do on your machine

Read from SKILL.md and the folder at commit bdc5847. 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, cmake and yaml).

  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

Sanitizers loads about 2.1k tokens when it runs, and up to ~4k if it reads all its reference files. Until then it costs about 116 tokens; SKILL.md has 415 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~116

When it runs · the whole SKILL.md, loaded when a task matches

~2.1k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~4k

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

• NoteRuns commands with sudoSKILL.md:251

  sudo insmod mymod.ko

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 mohitmishra786/low-level-dev-skills at commit bdc5847, republished under its MIT licence (© mohitmishra786). 415 words, ~2,127 tokens.

name

sanitizers

description

Compiler sanitizer skill for runtime bug detection in C/C++. Use when enabling and interpreting AddressSanitizer (ASan), UndefinedBehaviorSanitizer (UBSan), ThreadSanitizer (TSan), MemorySanitizer (MSan), or LeakSanitizer (LSan) with GCC or Clang. Activates on queries about sanitizer flags, sanitizer reports, ASAN_OPTIONS, memory errors, data races, undefined behaviour, uninitialised reads, or choosing which sanitizer to use for a given bug class.

Bug class?
├── Memory OOB, use-after-free, double-free → AddressSanitizer (ASan)
├── Stack OOB, global OOB → ASan (all three covered)
├── Uninitialised reads → MemorySanitizer (MSan, Clang only, requires all-clang build)
├── Undefined behaviour (int overflow, null deref, bad cast) → UBSan
├── Data races (multi-thread) → ThreadSanitizer (TSan)
├── Memory leaks only → LeakSanitizer (LSan, standalone or via ASan)
└── Multiple classes → ASan + UBSan (common combo); cannot combine with TSan or MSan

# GCC or Clang
gcc -fsanitize=address -fno-omit-frame-pointer -g -O1 -o prog main.c
# Or
clang -fsanitize=address -fno-omit-frame-pointer -g -O1 -o prog main.c

ASAN_OPTIONS=detect_leaks=1:abort_on_error=1:log_path=/tmp/asan.log ./prog

==12345==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000050
READ of size 4 at 0x602000000050 thread T0
    #0 0x401234 in foo /home/user/src/main.c:15
    #1 0x401567 in main /home/user/src/main.c:42

0x602000000050 is located 0 bytes after a 40-byte region
[0x602000000028, 0x602000000050) allocated at:
    #0 0x7f12345 in malloc ...
    #1 0x401234 in main /home/user/src/main.c:10

gcc -fsanitize=undefined -g -O1 -o prog main.c
# More complete: add specific checks
gcc -fsanitize=undefined,integer -g -O1 -o prog main.c

# Enable everything including integer overflow
gcc -fsanitize=undefined \
    -fsanitize=signed-integer-overflow,unsigned-integer-overflow,float-cast-overflow \
    -fno-sanitize-recover=all \   # abort instead of continue
    -g -O1 -o prog main.c

src/main.c:15:12: runtime error: signed integer overflow: 2147483647 + 1 cannot be represented in type 'int'

# Clang or GCC (GCC ≥ 4.8)
clang -fsanitize=thread -g -O1 -o prog main.c

# TSan is incompatible with ASan and MSan

WARNING: ThreadSanitizer: data race (pid=12345)
  Write of size 4 at 0x7f... by thread T2:
    #0 increment /home/user/src/counter.c:8
  Previous read of size 4 at 0x7f... by thread T1:
    #0 read_counter /home/user/src/counter.c:3

clang -fsanitize=memory -fno-omit-frame-pointer -g -O1 -o prog main.c
# With origin tracking (slower but shows where uninit value came from)
clang -fsanitize=memory -fsanitize-memory-track-origins=2 -g -O1 -o prog main.c

gcc -fsanitize=address,undefined -fno-sanitize-recover=all \
    -fno-omit-frame-pointer -g -O1 -o prog main.c

# ASan suppression file
cat > asan.supp << 'EOF'
# Suppress leaks from OpenSSL init
leak:CRYPTO_malloc
EOF

LSAN_OPTIONS=suppressions=asan.supp ./prog

# UBSan suppression
cat > ubsan.supp << 'EOF'
signed-integer-overflow:third_party/fast_math.c
EOF
UBSAN_OPTIONS=suppressions=ubsan.supp:print_stacktrace=1 ./prog

option(SANITIZE "Enable sanitizers" OFF)
if(SANITIZE)
    set(san_flags -fsanitize=address,undefined -fno-sanitize-recover=all
                  -fno-omit-frame-pointer -g -O1)
    add_compile_options(${san_flags})
    add_link_options(${san_flags})
endif()

# GitHub Actions example
- name: Build with ASan+UBSan
  run: |
    cmake -S . -B build -DSANITIZE=ON
    cmake --build build -j$(nproc)

- name: Run tests under sanitizers
  run: |
    ASAN_OPTIONS=abort_on_error=1:detect_leaks=1 \
    UBSAN_OPTIONS=print_stacktrace=1:halt_on_error=1 \
    ctest --test-dir build -j$(nproc) --output-on-failure

# Clang/LLVM HWASan (userspace)
clang -fsanitize=hwaddress -g -O1 -o app app.c

# Requires ARM64 with TBI (most Android/arm64 servers) or HWASan tagging support
# Cannot combine with ASan on same build

# Experimental — LLVM with MTE-capable hardware (arm64)
clang -fsanitize=memtag -g -O1 -o app app.c

# Kernel MTE (separate from userspace MemTagSanitizer)
# CONFIG_ARM64_MTE=y — hardware tagging in kernel allocator

# LLVM GWP-ASan (link-time, sampled allocations)
clang -fsanitize=gwp-asan -O2 -o app app.c

# Android: enabled in some system components for sampled crash detection
# glibc: experimental GWP-ASan allocator integration (check distro release notes)

# Build test kernel with KASAN
# CONFIG_KASAN=y CONFIG_KASAN_INLINE=y or CONFIG_KASAN_OUTLINE=y

# Boot KASAN kernel in QEMU for module development
qemu-system-x86_64 -kernel bzImage -append "kasan=on" ...

# Load module — KASAN reports appear in dmesg
sudo insmod mymod.ko
dmesg | tail -30

© mohitmishra786, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 2 other files (references) in skills/runtimes/sanitizers of mohitmishra786/low-level-dev-skills.

• SKILL.md
• references/flags.md
• references/reports.md

Open the folder on GitHubat commit bdc5847