Provided you can trust the build tools. The compiler, linker, install package builder...

But yeah. Point taken. Ambiguous wording. What I meant to say was, "How do I know that any code does what its creator says it does and nothing else?"

Basically, it is just a matter of trust. You cannot go around worrying about everything and suspect everyone. You just have to trust someone. You have no choice. In fact, in every single product, from software to cars to groceries, there are many links in the chain and you have to trust every single one of them.