Rust works great in embedded. You do have to learn some things about how to get binary sizes down, depending on how resource constrained you are. If you're on a device that's running Linux, you probably don't need to think about it at all. If you're on a device and writing 100% of the code yourself, you may have to watch out for certain things, like formatting code, that can add a bunch of bloat, and choose alternatives.

At work we have a de novo microkernel we're using for the firmware of a few things inside of our product. A recent build we did to check on binary size of OS + 5 simple tasks using 22kb of flash and 3.5 kb of RAM. Those tasks are all separately compiled programs, it all gets put together on one single image to flash.

If you're talking 8 bit micros, you run into platform support issues before you even get to the binary size stuff, but if you're on Arm, even the low end, size is not the primary issue when it comes to doing Rust projects.

>Can you point out an example on reading a bunch of structs from a file? Without std? Now I'm really curious.

Not really, but here is really simple example:

  use std::fs::File;
  use std::io::Read;
  
  #[derive(Debug)]
  struct Point {
      x: i32,
      y: i32,
  }
  
  fn bytes2point(buf: [u8; 8]) -> Point {
      Point {
          // Slices to arrays is a bit unwieldy...
          x: i32::from_le_bytes(buf[..4].try_into().unwrap()),
          y: i32::from_le_bytes(buf[4..].try_into().unwrap()),
      }
  }
  
  fn main() {
      let mut buf: [u8; 8] = [0; 8];
      let mut file: File = File::open("data.txt").unwrap();
      Read::read(&mut file, &mut buf).unwrap();
      let point: Point = bytes2point(buf);
      println!("{:?}", point);
  }

It doesn't do any extra i/o compared to C. Std is only used for filesystem access and printing. It does require extra buffer.

I'd be surprised if you see that Rust code is significantly slower than equivalent C code; this isn't how it pans out in most benchmarks. The killer for Rust is executable binary size, which even with no-std and other tricks can still balloon to an enormous size.