$devvkit learn --librarie valgrind-guide

Valgrind Guide

[memory][debugging][profiling][c-cpp]

Performance & Profiling

Install

sudo apt install valgrind
brew install valgrind
# Windows: use Dr.Memory or WSL

Valgrind runs your program in a virtual machine (dynamic binary instrumentation), detecting memory leaks, invalid reads/writes, use-after-free, and double frees. The default Memcheck tool is the gold standard for C/C++ memory safety.

Beyond Memcheck, Valgrind includes: Cachegrind (cache profiling), Callgrind (call-graph profiling with `callgrind_annotate`), Helgrind (thread race detection), Massif (heap profiler), and DHAT (heap allocation analysis).

Expect a 5-20x slowdown under Valgrind — use it for debugging, not production. Run with `--tool=memcheck --leak-check=full`. GUI alternatives: AddressSanitizer (ASan) for faster runs, Heaptrack for KDE-integrated heap analysis.

Memcheck

Memory leak check— Find unreleased memory.

valgrind --leak-check=full --show-leak-kinds=all ./myapp
valgrind --leak-check=full --track-origins=yes ./myapp   # Show where uninit vals come from

Invalid access— Buffer overflow detection.

valgrind --tool=memcheck --vgdb=yes --vgdb-error=0 ./myapp
# Then attach with gdb for fine-grained inspection:
# gdb ./myapp
# (gdb) target remote | vgdb

Trick: shallow with ASan— Faster alternative.

# ASan is 2x faster than Valgrind:
clang -fsanitize=address -fno-omit-frame-pointer -g -O1 -o myapp-asan myapp.c
./myapp-asan

# Also: LeakSanitizer for leaks only
clang -fsanitize=leak -g -o myapp-lsan myapp.c

Cachegrind

Cache profiling— L1/L2/LLC misses.

valgrind --tool=cachegrind ./myapp
# Output: cachegrind.out.PID
cg_annotate cachegrind.out.PID    # Annotated source with miss counts
# Use KCachegrind for GUI visualization

Call-graph profiling— Function call counts.

valgrind --tool=callgrind ./myapp
callgrind_annotate callgrind.out.PID
# Open in KCachegrind (GUI) for interactive caller/callee tree
# qcachegrind on macOS

Massif

Heap profiler— Memory usage over time.

valgrind --tool=massif ./myapp
# Output: massif.out.PID
ms_print massif.out.PID | head -50  # Text chart of heap usage over time
# Use massif-visualizer for GUI

Helgrind

Thread race detection— Find data races.

valgrind --tool=helgrind ./myapp-threaded
# Reports: conflicting accesses, lock ordering violations

Suppressions

Suppression file— Ignore known false positives.

# Create suppression file:
cat > suppressions.txt <<EOF
{
   ignore_libc_memcpy
   Memcheck:Overlap
   fun:memcpy
}
EOF

valgrind --suppressions=suppressions.txt ./myapp