arm-trusted-firmware VS rustc_codegen_gcc

I have a PinePhone Pro, and I'm trying to figure out a reasonable way to get more than one half of ten minutes of battery life out of it, while still receiving notifications. I figure the best route to go will be to create a service that holds ports open, while the CPU is completely asleep, and either run it on the modem's processor or, as an possibility for the PinePhone Pro, but not the original Pinephone, run it on the m0 core used for power management.

Arm v7 was a Wild West, but with v8, Arm tried to standardize a lot. The Arm Trusted Firmware is the reference boot firmware implementation for v8+ CPUs: https://github.com/ARM-software/arm-trusted-firmware.

I'd think most of the referece documents can be discovered from that code base.

Relatedly, from the perspective of hands-on programming, the System Programmer's guide is the manual to start with.

I assure you that there is no lack of skill; that is just what happens over the course of ten years in a 300,000 line code-base and multiple hundreds of contributors: https://github.com/ARM-software/arm-trusted-firmware/blob/master/Makefile

The ARM Trusted Firmware is what typically runs in the secure world, and it is indeed open source: https://github.com/ARM-software/arm-trusted-firmware

ROM code generally speaking is not open source, but has been dumped on occasion.

The reference Trustzone implementation for ARM is open source https://github.com/ARM-software/arm-trusted-firmware , so I really can't think of some reason the ARM license would have to do with it.

SMP support (at least as far as CPU suspend and hotplug goes) is usually handled by TrustZone firmware on aarch64, not by the kernel (see PSCI). If you write your own OS on a bare-metal platform you can of course do what you want, but if you're looking for existing sources that's where you'd have to look. https://github.com/ARM-software/arm-trusted-firmware is a common reference implementation that supports a bunch of platforms, but many others (e.g. all Samsung and Qualcomm phones) also use their own proprietary stuff which is not publicly available.

Come again? https://github.com/ARM-software/arm-trusted-firmware

Alternatively, there's another initiative called codegen_gcc which is about using GCC as a backend for the rustc compiler. It's (much) more advanced in Rust support, but I am not sure how easy it would be to use a modified libgccjit from there.

In addition to what others have said about platform support, Rust is also on its way to gaining more platform support through rustc_codegen_gcc, the GCC codegen backend for rustc, as an alternative to the LLVM backend. That means many of the platforms GCC supports will suddenly become available with Rust.

Yeah, rustc_codegen_gcc is a GCC backend for rustc, and its making a lot of good regular progress.

gcc-rs is one of two projects for bringing Rust to gcc. gcc-rs is the more ambitious of the two, with an entirely new frontend. There is also rustc_codegen_gcc (https://github.com/rust-lang/rustc_codegen_gcc) that keeps the rustc frontend, and only swaps out LLVM for GCC at the codegen stage.

Fixing unwinding in release mode is still ungoing. I could use some help here, so anyone with some understanding of unwinding, landing pads or GCC, please come on this issue to discuss this.

Additionally, there is gcc codegen for rustc (https://github.com/rust-lang/rustc_codegen_gcc), which is not a compiler per se, but an alternative code generator, with more architectures supported and other nice things. It's also coming along, but there's still a lot of work to do there too. There's also Cranelift codegen (https://github.com/bjorn3/rustc_codegen_cranelift), which is designed to make debug builds faster, but this is not as exciting/useful as the other 2.

Good idea. I added the tag "help wanted" to the issue.

Also, there are indeed ABI issues, e.g. for 128-bit integers and NaN.

I'm excited about both the backend & the frontend.

There is also a project for rustc to use GCC instead of LLVM for codegen.

https://github.com/rust-lang/rustc_codegen_gcc