There’s of course a couple of notes on combating this attack: most compilers of today don’t actually produce exactly the same code if you run them twice. In broad strokes they do but often they’ll have randomness creep in, such as different build hashes or iteration order of associative containers. To truly get a bit-for-bit identical output you may need to do some extra work, or perhaps run yet another step in a controlled environment to protect against this.
Second, and more importantly, many people carry a copy of a trusted compiler around, though it’s rarely mention in attacks like these: their head. In a pinch people can do spot checks to verify codegen to see whether it looks correct, unless the backdoor is incredibly subtle. But experience shows us that the more complex and hidden a backdoor is the more likely it is to break when subjected to unfamiliar examination.
Second, and more importantly, many people carry a copy of a trusted compiler around, though it’s rarely mention in attacks like these: their head. In a pinch people can do spot checks to verify codegen to see whether it looks correct, unless the backdoor is incredibly subtle. But experience shows us that the more complex and hidden a backdoor is the more likely it is to break when subjected to unfamiliar examination.