Rust: "Move fast and break things" as a moral imperative February 9, 2021 on Drew DeVault's blog

Rust breaks a lot of stuff, and in ways that are difficult to fix. This can have a chilling effect on users, particularly those on older or slower hardware. Rust has only one implementation, with a very narrow set of supported platforms, tens of millions of lines of C++ code, and no specification. Rust ostensibly supports several dozen targets, but only the tier 1 platforms can be reasonably expected to work. As someone who has tried to bootstrap Rust (and failed) for even a tier-two platform, I can assure you that it’s a nightmare. Bringing it up for an entirely new target would be a hellish experience. Ask any distribution packager who works with Rust to share their horror stories — they have many.

The Rust cargo cult needs to pause and re-evaluate. Switching to Rust breaks things for anyone who steps even a toe out of the norm of Linux/macOS/Windows on x86_64 or aarch64. Even on the supported platforms it comes with a substantial burden on build requirements, calling for 10× to 100× or more RAM, CPU time, and power usage. Whatever its benefits, choosing Rust is ultimately choosing to lock a large group of people out of your project, and dooming many more to struggle and frustration. These are real trade-offs that you need to seriously consider.

Rewrite-it-in-Rust has become a moral imperative. Well, here’s a moral argument: throwing away serviceable computers every couple of years to upgrade is a privilege that not all of your users have, contributes to climate change, and fills up landfills. As far as security is concerned, some matters demand leaving the norm: old hardware is the only kind that can avoid proprietary firmware blobs, Intel ME or AMD PSP, and UEFI. Novel hardware which addresses issues like microcode and open hardware, like POWER9 and RISC-V, are also suffering under Rust’s mainstream-or-bust regime. Anyone left behind is forced to use the legacy C codebase you’ve abandoned, which is much worse for their security than the hypothetical bugs you’re trying to save them from.

C is not memory safe. It suffers from undefined behavior. These are valid complaints. However, C code can be secure! Just look at seL4, which I guarantee you has fewer bugs than, say, RedoxOS. There are plenty of C programs which aren’t formally verified that work fine, too. Rewriting your code in Rust is always going to introduce new bugs, including security bugs, that wouldn’t be there if you just maintained the C code. Maybe there are undiscovered bugs lurking in your C codebase, but as your codebase ages under continuous maintenance, that number will only shrink.

A working C toolchain (say, cproc and qbe) can be written in a couple tens of thousands of lines of code. The only working Rust toolchain is tens of millions of lines of C++ and Rust code. How many undiscovered bugs do you think these two toolchains have when compared? How many of those are security issues? How much relative work would it be to debug them, or port them to new — or old — platforms? How often do these respective codebases churn, creating a larger maintenance burden and introducing new bugs/vulnerabilities? I can bootstrap a working C toolchain in about 10 minutes. I spent a week trying to do that for Rust, and failed. That matters.

Rust is kind of cool, but it’s not a panacea. There are legitimate reasons to prefer C, both technical and moral, and Rust still needs a lot of work before it’s ready for the prime time in systems which prioritize stability, reliability, simplicity, and accessibility. Those of us who work with such systems, we feel like the Rust community has put its thumbs into its collective ears, sung “la la la” to our problems, and proceeded to stomp all over the software ecosystem like a toddler playing “Godzilla” with their Lego, all the while yelling at us old fogies for being old and fogey.

To the Rust team: it’s time to calm down. Slow down the language, write a specification, focus on improving your tier 2 and tier 3 targets, expand to more platforms, and work on performance, stability, and accessibility. Invest more in third-party implementations like rust-gcc. I spent almost a week, full-time, trying to bring up Rust for riscv64-musl. The bootstrap process is absolutely miserable. Your ecosystem has real problems that affect real people. It’s time to stop ignoring them.

⇒ This article is also available on gemini.

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