Interesting, didn't hear from this system so far. Seems to be funded by the EU. Apparently it is written in pure Rust since 2020, and Andrew "bunnie" Huang seems to be involved.
From the talk linked above, they went to considerable effort to design a system with a cheap processor which nevertheless contains an mmu, and so most other embedded kernels, which assume the lack of one, are not applicable. So the point of writing in rust is that they can ensure that some of the guarantees of rust are enforced by the hardware. (It's been a while since I watched that talk, so I don't recall exactly which ones). And this is a microkernel, not a monolithic kernel, so they will be using hardware guarantees even between kernel components.
Use of "unsafe" is unavoidable. Various pieces of hardware are directly writing into the address space. Concepts of "ownership" and "mutability" go beyond code semantics.
It's not really about infrastructure but yes kernels and firmwares have to do a lot of stuff the compiler can't verify as safe, eg writing to a magic memory address you obtained from the datasheet that enables some feature of the chip. And that will need to happen in unsafe code blocks. I wouldn't call that a problem but it is a reality.
Are you one of the authors? Concerning the "infrastructure": Rust assumes a runtime, the standard library assumes a stack exists, a heap exists, and that main() is called by an OS; in a kernel, none of this is true. And the borrow checker cannot reason about things like e.g. DMA controllers mutating memory the CPU believes it owns, Memory-mapped I/O where a "read" has side effects (violating functional purity), context switches that require saving register state to arbitrary memory locations, or interrupt handlers that violate the call stack model. That's what I mean by "infrastructure". It's essentially the same issue with every programming language to some degree, but for Rust it is relevant to understand that the "safety guarantees" don't apply to all parts of an operating system, even if written in Rust.
Rust's safety model only applies to code you write in your program, and there's a lot that's unsafe (cannot be verified by the compiler) about writing a kernel or a firmware, agreed. You could have similar problems when doing FFI as well.
Here's their 39c3 talk about Xous: https://media.ccc.de/v/39c3-xous-a-pure-rust-rethink-of-the-...
Interesting, didn't hear from this system so far. Seems to be funded by the EU. Apparently it is written in pure Rust since 2020, and Andrew "bunnie" Huang seems to be involved.
Is there a PDF version of the book (https://betrusted.io/xous-book/)?
There is a single-page version of the book that you can save as a PDF: https://betrusted.io/xous-book/print.html
Great, thanks.
I assume the "kernel" makes heavy use of "unsafe", because all the infrastructure assumed by Rust is not available. Or how was this solved?
From the talk linked above, they went to considerable effort to design a system with a cheap processor which nevertheless contains an mmu, and so most other embedded kernels, which assume the lack of one, are not applicable. So the point of writing in rust is that they can ensure that some of the guarantees of rust are enforced by the hardware. (It's been a while since I watched that talk, so I don't recall exactly which ones). And this is a microkernel, not a monolithic kernel, so they will be using hardware guarantees even between kernel components.
Use of "unsafe" is unavoidable. Various pieces of hardware are directly writing into the address space. Concepts of "ownership" and "mutability" go beyond code semantics.
It's not really about infrastructure but yes kernels and firmwares have to do a lot of stuff the compiler can't verify as safe, eg writing to a magic memory address you obtained from the datasheet that enables some feature of the chip. And that will need to happen in unsafe code blocks. I wouldn't call that a problem but it is a reality.
Are you one of the authors? Concerning the "infrastructure": Rust assumes a runtime, the standard library assumes a stack exists, a heap exists, and that main() is called by an OS; in a kernel, none of this is true. And the borrow checker cannot reason about things like e.g. DMA controllers mutating memory the CPU believes it owns, Memory-mapped I/O where a "read" has side effects (violating functional purity), context switches that require saving register state to arbitrary memory locations, or interrupt handlers that violate the call stack model. That's what I mean by "infrastructure". It's essentially the same issue with every programming language to some degree, but for Rust it is relevant to understand that the "safety guarantees" don't apply to all parts of an operating system, even if written in Rust.
I have no affiliation, I'm just a commenter.
The standard library requires a heap and such, but you can enable the no_std attribute to work in environments where they don't exist. https://docs.rust-embedded.org/book/intro/no-std.html
Rust's safety model only applies to code you write in your program, and there's a lot that's unsafe (cannot be verified by the compiler) about writing a kernel or a firmware, agreed. You could have similar problems when doing FFI as well.
You can't write a kernel without `unsafe` appearing somewhere.
What problem is this solving? Are there no OSes for medium embedded systems? Are they too expensive?
Trust and transparency: https://betrusted.io