How I'm supposed to use the sanitizer in clang?

Question

I\'m sorry if this is a uber-easy concept, but I find hard to acquire the right mindset in order to correctly use the sanitizer provided by clang.

Answer 1

So if we look at the documentation in the the Controlling Code Generation it says (emphasis mine):

Turn on runtime checks for various forms of undefined or suspicious behavior.

This option controls whether Clang adds runtime checks for various forms of undefined or suspicious behavior, and is disabled by default. If a check fails, a diagnostic message is produced at runtime explaining the problem.

so these are runtime checks not compile time checks. So if you used foo in your code then you would see the following output:

runtime error: division by zero

See this example live using -fsanitize=undefined:

float foo(float f) { return (f / 0); }

int main()
{
    int x = 1 << 100 ;
    foo( 2.0f ) ;
}

it generates two run-time messages:

main.cpp:6:19: runtime error: shift exponent 100 is too large for 32-bit type 'int'

main.cpp:2:36: runtime error: division by zero

Update

With respect to static checkers, in my answer to A C++ implementation that detects undefined behavior? I mention several tools: STACK, kcc and of course Frama-C.

Apparently clang allows you to use --analyze to run it's static checker but it seems like it may be disabled eventually and the the correct way to run it would be through scan-build.

Also in my self-answered question Why do constant expressions have an exclusion for undefined behavior? I show how constexprs can be used to catch undefined behavior at compile time.