compiler-builtins

Rust does not rely on syscalls or libraries on embedded targets, which is what the #![no_std] marker at the top of the project indicates. On some platforms, like ESP32, Rust can make calls into the RTOS and don't need that marker, but other embedded targets don't provide access to the std crate and you need to interact with peripherals from Rust or by interfacing with C or assembly. Rust's only requirement is that memcpy, memmove, memset, memcmp, bcmp, and strlen are available, and it can provide them if needed: https://github.com/rust-lang/compiler-builtins

The runtime thing is the easy part. I was wondering about the stack probes, which require LLVM support. There's a comment in the sources that suggest it's still x86-only, but that may be outdated: “ //! Finally it's worth noting that at the time of this writing LLVM only has //! support for stack probes on x86 and x86_64. There's no support for stack //! probes on any other architecture like ARM or PowerPC64. LLVM I'm sure would //! be more than welcome to accept such a change! ” https://github.com/rust-lang/compiler-builtins/blob/master/s...

yes https://github.com/rust-lang/compiler-builtins/pull/370

Rust already ships with its own memcpy, so it should be possible: https://github.com/rust-lang/compiler-builtins/blob/master/s...

I believe between - this - https://docs.rs/gimli/0.23.0/gimli/ - https://github.com/rust-lang/compiler-builtins - https://github.com/redox-os/relibc - https://lld.llvm.org/ It finally possible to make Linux binaries in a high level language not involving anything written in C at build-time or run-time!!! (And I think with CraneLift + -Z build-std, but without any libc, one should be able to skip linking separately-compiled object files too, and thus skip LLD and C++.)

Hi, I believe they can be done for 32 bit platforms also with the multiword division in Knuth https://skanthak.homepage.t-online.de/division.html what I've chosen for fallback if not x86_64 platform. I will try to implement the same optimizations in Rust in the upcoming weeks UPD And we opened an issue :) https://github.com/rust-lang/compiler-builtins/issues/368

Very nice post! I remember helping to port the 128 bit integer functions in compiler-rt to Rust years ago [0], because clang only supported 128 bit integers on 64 bit platforms, but the goal of Rust was to support them on all platforms that Rust supports. Since then, all algorithms in compiler-rt have been ported to Rust and live in the compiler-builtins crate. This [1] is the source code file for unsigned division. The actual logic is inside a macro and used to implement both 128 bit division in terms of 64 bit numbers and 64 bit division in terms of 32 bit numbers. I wonder if similar optimizations can be done to that code. [1]: https://github.com/rust-lang/rust/pull/38482 [0]: https://github.com/rust-lang/compiler-builtins/blob/master/s...

IIUC Rust stack overflows are actually checked, hit a guard page, and unwind the stack https://github.com/rust-lang/compiler-builtins/blob/master/s... A cactusref is owned by a single thread so there's no STW issue, but you also can't share them mutably between threads like structures available in some GCed languages.