Merge #2915

2915: Update rust-toolchain to 2021-12-04 r=ppannuto a=lschuermann

### Pull Request Overview

This pull request updates the Rust toolchain to version `1.59.0-nightly (efec54529 2021-12-04)`. The motivation for this change is that the `litex-sim-ci` breaks when compiling `elf2tab` on the previous toolchain version:

```
error[E0658]: use of unstable library feature 'proc_macro_is_available'
  --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.33/src/detection.rs:28:21
   |
28 |     let available = proc_macro::is_available();
   |                     ^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #71436 <rust-lang/rust#71436> for more information
   = help: add `#![feature(proc_macro_is_available)]` to the crate attributes to enable

For more information about this error, try `rustc --explain E0658`.
error: could not compile `proc-macro2` due to previous error
warning: build failed, waiting for other jobs to finish...
error: failed to compile `elf2tab v0.8.0`, intermediate artifacts can be found at `/tmp/cargo-installl05bA0`
```

Now, I'm not entirely sure as to why this happens. We haven't upgraded either of the Rust toolchain or `elf2tab`, and -- as far as I understand -- `cargo install elf2tab` should use the `Cargo.lock` file, so dependencies shouldn't change.

In any case, this update seems to fix it. Besides the failing `litex-sim-ci` workflow, it seems like a good idea to pin a `rustc` version on which vital tools such as `elf2tab` properly compile. I can also reproduce the `elf2tab` build failure locally while the `rust-toolchain` of the Tock repository is used.


### Testing Strategy

This pull request was tested by CI.


### TODO or Help Wanted

N/A


### Documentation Updated

- [x] ~Updated the relevant files in `/docs`,~ or no updates are required.

### Formatting

- [x] Ran `make prepush`.


Co-authored-by: Leon Schuermann <leon@is.currently.online>

.github/workflows/litex_sim.yml

@@ -56,6 +56,11 @@ jobs:
         with:
           components: rustfmt, clippy
 
+      # Install elf2tabl to be able to build userspace apps
+      - name: Install elf2tab
+        run: |
+          cargo install elf2tab
+
       # Install tockloader, which is used to prepare binaries with userspace
       # applications.
       - name: Install tockloader

.vscode/settings.json

@@ -1,4 +1,4 @@
 {
     "editor.formatOnSave": true,
-    "rust-client.channel": "nightly-2021-10-05",
+    "rust-client.channel": "nightly-2021-12-04",
 }

arch/cortex-m/src/lib.rs

@@ -2,7 +2,7 @@
 
 #![crate_name = "cortexm"]
 #![crate_type = "rlib"]
-#![feature(asm)]
+#![feature(asm, asm_sym)]
 #![feature(naked_functions)]
 #![no_std]
 

arch/cortex-m0/src/lib.rs

@@ -2,7 +2,7 @@
 
 #![crate_name = "cortexm0"]
 #![crate_type = "rlib"]
-#![feature(asm, naked_functions)]
+#![feature(asm, asm_sym, naked_functions)]
 #![no_std]
 
 // Re-export the base generic cortex-m functions here as they are

arch/rv32i/src/lib.rs

@@ -2,7 +2,7 @@
 
 #![crate_name = "rv32i"]
 #![crate_type = "rlib"]
-#![feature(asm, const_fn_trait_bound, naked_functions)]
+#![feature(asm, asm_sym, const_fn_trait_bound, naked_functions)]
 #![no_std]
 
 use core::fmt::Write;

chips/litex_vexriscv/src/lib.rs

@@ -1,6 +1,6 @@
 //! LiteX SoCs based around a VexRiscv CPU
 
-#![feature(asm, const_fn_trait_bound)]
+#![feature(asm, asm_const, const_fn_trait_bound)]
 #![no_std]
 #![crate_name = "litex_vexriscv"]
 #![crate_type = "rlib"]

doc/Getting_Started.md

@@ -75,7 +75,7 @@ of installing some of these tools, but you can also install them yourself.
 
 #### Rust (nightly)
 
-We are using `nightly-2021-10-05`. We require
+We are using `nightly-2021-12-04`. We require
 installing it with [rustup](http://www.rustup.rs) so you can manage multiple
 versions of Rust and continue using stable versions for other Rust code:
 
@@ -90,7 +90,7 @@ to your `$PATH`.
 Then install the correct nightly version of Rust:
 
 ```bash
-$ rustup install nightly-2021-10-05
+$ rustup install nightly-2021-12-04
 ```
 
 #### Tockloader

libraries/riscv-csr/src/lib.rs

@@ -2,7 +2,7 @@
 //!
 //! Uses the Tock Register Interface to control RISC-V CSRs.
 
-#![feature(asm)]
+#![feature(asm, asm_const)]
 #![feature(const_fn_trait_bound)]
 #![no_std]
 

rust-toolchain

@@ -1 +1 @@
-nightly-2021-10-05
+nightly-2021-12-04

tools/netlify-build.sh

@@ -12,7 +12,7 @@ set -u
 set -x
 
 # Install rust stuff that we need
-curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain nightly-2021-10-05
+curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain nightly-2021-12-04
 
 # And fixup path for the newly installed rust stuff
 export PATH="$PATH:$HOME/.cargo/bin"