Merge #259

259: Rust assembly stubs r=thalesfragoso a=jonas-schievink

Disclaimer: I have not tested any of this (help wanted, we have no tests in here).

Thanks to @therealprof for nerd-sniping me into oblivion.

Fixes #254
Fixes #194
Fixes #139

# Summary

* Remove the assembly files in favor of a new `asm.rs`, which uses unstable inline assembly and provides a C ABI interface.
* Replace the shell scripts by a [`cargo-xtask`](https://github.com/matklad/cargo-xtask/).
* While we're at it, also pre-build artifacts that are compatible with linker-plugin LTO, fixing #139 (again, not tested)

This means that contributors and maintainers just need ~~a nightly Rust compiler installed~~ to run `cargo xtask assemble`. No binutils, no assembler, no `ar`, no GCC/Clang, and especially nothing from the godawful Arm servers, fixing #194. You don't even have to install the correct nightly Rust toolchain, `cargo xtask` does it for you (and installs all the thumb targets too).

Co-authored-by: Jonas Schievink <[email protected]>

Author: bors[bot]

.cargo/config

@@ -0,0 +1,2 @@
+[alias]
+xtask = "run --package xtask --bin xtask --"

.travis.yml

@@ -72,7 +72,6 @@ before_install: set -e
 
 install:
   - bash ci/install.sh
-  - export PATH="$PATH:$PWD/gcc/bin"
 
 script:
   - bash ci/script.sh

Cargo.toml

@@ -21,6 +21,14 @@ volatile-register = "0.2.0"
 bitfield = "0.13.2"
 embedded-hal = "0.2.4"
 
+[features]
+cm7-r0p1 = []
+inline-asm = []
+linker-plugin-lto = []
+
+[workspace]
+members = ["xtask"]
+
 [package.metadata.docs.rs]
 targets = [
     "thumbv8m.main-none-eabihf",
@@ -31,7 +39,3 @@ targets = [
     "thumbv8m.base-none-eabi",
     "thumbv8m.main-none-eabi"
 ]
-
-[features]
-cm7-r0p1 = []
-inline-asm = []

asm-cm7-r0p1.s

@@ -0,0 +1 @@
+nightly-2020-08-26