Agent Skills: Sanitizers

Sanitizers

Description

Interpreting AddressSanitizer, UndefinedBehaviorSanitizer, and ThreadSanitizer output.

Build Modes

make BUILD=sanitize check   # ASan + UBSan
make BUILD=tsan check       # ThreadSanitizer (incompatible with ASan)

AddressSanitizer (ASan)

Detects buffer overflows, use-after-free, use-after-return, memory leaks.

Sample Output

==12345==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x...
READ of size 4 at 0x... thread T0
    #0 0x... in function_name file.c:42
    #1 0x... in caller file.c:100

0x... is located 0 bytes to the right of 100-byte region [0x...,0x...)
allocated by thread T0 here:
    #0 0x... in malloc (...)
    #1 0x... in allocate_buffer file.c:30

Error Types

• heap-buffer-overflow - Read/write past heap allocation
• stack-buffer-overflow - Read/write past stack buffer
• global-buffer-overflow - Read/write past global
• heap-use-after-free - Accessing freed heap memory
• stack-use-after-return - Accessing returned stack frame
• double-free - Freeing already-freed memory

Environment Variables

ASAN_OPTIONS=detect_leaks=1:abort_on_error=1 ./ikigai

• detect_leaks=1 - Enable leak detection
• abort_on_error=1 - Abort on first error (for core dumps)
• halt_on_error=0 - Continue after error
• print_stats=1 - Print memory stats

UndefinedBehaviorSanitizer (UBSan)

Detects undefined behavior: integer overflow, null dereference, alignment issues.

Sample Output

file.c:42:15: runtime error: signed integer overflow:
2147483647 + 1 cannot be represented in type 'int'

Error Types

• signed integer overflow - Arithmetic overflow
• null pointer passed - NULL where non-null expected
• load of misaligned address - Alignment violation
• member access within null pointer - NULL struct dereference
• division by zero - Self-explanatory
• shift exponent is negative - Invalid shift

Environment Variables

UBSAN_OPTIONS=print_stacktrace=1:halt_on_error=1 ./ikigai

ThreadSanitizer (TSan)

Detects data races and deadlocks.

Sample Output

WARNING: ThreadSanitizer: data race (pid=12345)
  Write of size 4 at 0x... by thread T1:
    #0 function_name file.c:42
  Previous read of size 4 at 0x... by main thread:
    #0 other_function file.c:100
  Location is global 'shared_var' of size 4 at 0x...

Error Types

• data race - Unsynchronized access to shared data
• lock-order-inversion - Potential deadlock
• thread leak - Thread not joined

Environment Variables

TSAN_OPTIONS=halt_on_error=1:second_deadlock_stack=1 ./ikigai

Debugging Workflow

1. Run with sanitizer enabled
2. Read error message top-to-bottom
3. First stack trace = where error detected
4. Second stack trace = where memory allocated/related operation
5. Fix root cause, not symptom

Limitations

• ASan and TSan are mutually exclusive (can't use both)
• Sanitizers add ~2x memory overhead, ~2x slowdown
• Some false positives possible with complex code

References

• ASan docs: https://clang.llvm.org/docs/AddressSanitizer.html
• UBSan docs: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html
• TSan docs: https://clang.llvm.org/docs/ThreadSanitizer.html