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Compiling Rust with GCC: an update

Compiling Rust with GCC: an update

Posted Sep 12, 2022 22:12 UTC (Mon) by himi (subscriber, #340)
In reply to: Compiling Rust with GCC: an update by mjg59
Parent article: Compiling Rust with GCC: an update

I'd have to actually check the bootstrap process for rust (it's probably been five years since I last tried), but I have a feeling you have a second step beyond just building rustc with mrustc, though that may be more of a verification step. mrustc doesn't have a lot of the memory safety features of rustc, and only implements the minimal features needed to compile rustc, so I don't think a compiler built by it will behave the same as the compiler built by rustc, even if it's the same version (i.e. mrustc building rustc 1.54 compared with rustc 1.54 building rustc 1.54).

It does still break (or dilute greatly) the chain of trust, but you'd need a more careful verification to make sure nothing hinky was going on.

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Compiling Rust with GCC: an update

Posted Sep 13, 2022 2:39 UTC (Tue) by mjg59 (subscriber, #23239) [Link]

I'd expect rustc built with mrustc to behave differently in various ways (such as plausibly not being correctly memory safe in the face of malformed input), but I'd expect the actual compilation process to be the same? It doesn't really matter, though, since you can just do another round of building rustc and you should have the same assertions around it being trustworthy.

Compiling Rust with GCC: an update

Posted Sep 13, 2022 8:30 UTC (Tue) by farnz (subscriber, #17727) [Link]

Assuming mrustc is bug-free against its own spec, the rule is that it'll compile all code that rustc does with the same behaviour in the final compiled binary, but it will also compile programs that rustc rejects as invalid. For this comparison purpose, that's good enough - you can't trust an mrustc-built compiler if you don't also have a rustc-built compiler from the same source.


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