In general, if Rust is significantly slower than equivalent C, it's a bug. We do care about bugs, and if you try some stuff and find them, please file them. (We track them via this tag: https://github.com/rust-lang/rust/labels/I-slow)
Embedded can be tricky at times; we've had a working group pushing on making stuff great all year. There's still a lot of work to be done. Sometimes you need to opt into nightly-only features. We'll get there!
(One major example is platform support: since we're built off of LLVM, we may not have a backend for more obscure architectures. ARM stuff works really well, generally. AVR is down to some codegen bugs...)
Hey Steve, thanks for commenting here. As a person who is trying to get into embedded development but who knows very little, can you explain the challenges of having a language support most/all embedded platforms? I’m guessing you would need to support old versions of gcc that or something like this? Or be able to compile things with each platform special flags?
It seems like even C projects have a hard time being portable. People even avoid cmake because of the large dependency and the fact that it is cross platform until it isn’t.
First of all, most embedded development makes use of bare metal, where the libraries take the role of an OS, or they use a specialized OS from the hardware vendor.
Just using pure ANSI C isn't possible, because the standard does not expose the hardware features from the underlying platform, so the alternatives are to use Assembly, or language extensions.
Naturally language extensions are more convenient to use, so that is what most developers end up doing.
Also there are many types of embedded platforms, you can be targeting anything between a tiny PIC with 8KB FLASH RAM to a powerful multi-core ARMv8-A with 8GB.
So the toolchain must allow for customization of what actually gets linked into the final binary, and the runtime must be as thin as possible.
Then there this the drivers story, each vendor gives you their own SDK, which most of the time is the only way to access their devices.
It is typical for open source projects to reverse engineer some of those SDKs to get the necessary information for linker maps, compiler flags and driver information.
Regarding Rust, there is an ongoing effort to create a embedded library for hardware drivers, as means to write portable code.