Agent Skills: Valgrind

Valgrind

Description

Interpreting Valgrind memcheck output for memory debugging.

Running Valgrind

# Via Makefile
make check-valgrind

# Direct invocation
valgrind --leak-check=full --track-origins=yes ./ikigai

Error Types

Invalid Read/Write

==12345== Invalid read of size 4
==12345==    at 0x... function_name (file.c:42)
==12345==  Address 0x... is 0 bytes after a block of size 100 alloc'd

Meaning: Reading/writing past buffer bounds or freed memory. Fix: Check array indices, buffer sizes, use-after-free.

Use of Uninitialized Value

==12345== Conditional jump or move depends on uninitialised value(s)
==12345==    at 0x... function_name (file.c:42)
==12345==  Uninitialised value was created by a heap allocation
==12345==    at 0x... malloc (...)

Meaning: Using memory before setting it. Fix: Initialize variables, use memset, check all code paths.

Invalid Free

==12345== Invalid free() / delete / delete[]
==12345==    at 0x... free (...)
==12345==  Address 0x... is 0 bytes inside a block of size 100 free'd

Meaning: Double-free or freeing invalid pointer. Fix: Track ownership, use talloc's hierarchical free.

Memory Leaks

==12345== LEAK SUMMARY:
==12345==    definitely lost: 100 bytes in 1 blocks
==12345==    indirectly lost: 200 bytes in 2 blocks
==12345==    possibly lost: 0 bytes in 0 blocks
==12345==    still reachable: 500 bytes in 5 blocks

• definitely lost - Memory with no pointer to it (real leak)
• indirectly lost - Memory reachable only through definitely lost
• possibly lost - Interior pointer exists (may be intentional)
• still reachable - Memory still accessible at exit (often acceptable)

Common Options

--leak-check=full          # Detailed leak info
--track-origins=yes        # Where uninitialized values came from
--show-reachable=yes       # Show still-reachable blocks
--suppressions=file.supp   # Ignore known issues
--gen-suppressions=all     # Generate suppression entries

Reading Stack Traces

==12345== Invalid read of size 4
==12345==    at 0x401234: parse_json (parser.c:142)
==12345==    by 0x401567: load_config (config.c:89)
==12345==    by 0x401890: main (main.c:23)

Read bottom-up: main called load_config called parse_json where error occurred.

Helgrind (Thread Debugging)

valgrind --tool=helgrind ./ikigai

Detects:

• Data races
• Lock order violations
• Misuse of POSIX threading API

References

• Valgrind manual: https://valgrind.org/docs/manual/
• See gdbserver.md for live debugging
• See coredump.md for crash analysis