AD5040: DoNotUseUncheckedOptimization¶

Summary¶

Description¶

Mach-O binaries should not use aggressive optimization flags that sacrifice safety for performance, potentially introducing undefined behavior.

How It Works¶

The rule checks for dangerous optimization indicators:

1. -ffast-math usage patterns
2. -fno-strict-overflow (actually safer, not flagged)
3. Other unsafe optimization patterns

Why This Matters¶

Some optimization flags assume the program has no undefined behavior. If it does, these flags can cause unexpected security issues.

Dangerous Optimizations¶

-ffast-math Security Issues¶

// With -ffast-math:
if (x != x) {
    // NaN check - optimizer may remove this!
    handle_nan();
}

// This can cause security issues if NaN
// indicates an attack or data corruption

Safer Alternatives¶

Checking for Fast-Math¶

# Check if fast-math was used
otool -l binary | grep FAST_MATH
# Or check for reassociated math patterns

Resolution¶

Avoid unsafe optimization flags:

# Bad
clang -O3 -ffast-math program.c

# Good
clang -O3 program.c

# If you need some math optimizations:
clang -O3 -fno-math-errno -fno-signed-zeros program.c
# These are safer than full -ffast-math

CMake Configuration¶

# Do NOT use:
# add_compile_options(-ffast-math)

# Instead, use targeted options if needed:
add_compile_options(-fno-math-errno)  # Safe

Xcode Settings¶

Avoid setting "Relax IEEE Compliance" to Yes.