While compiling tock with the latest nightly version of rust, nightly-2024-02-08, I encounter 25 warnings regarding the usage of shared references of mutable static in folders such as arch/, kernel/, chips/ and boards/ as it can be seen bellow:

warning: shared reference of mutable static is discouraged
   --> kernel/src/deferred_call.rs:145:28
    |
145 |         let ctr = unsafe { &CTR };
    |                            ^^^^ shared reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
    = note: reference of mutable static is a hard error from 2024 edition
    = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
    = note: `#[warn(static_mut_ref)]` on by default
help: shared references are dangerous since if there's any kind of mutation of that static while the reference lives, that's UB; use `addr_of!` instead to create a raw pointer
    |
145 |         let ctr = unsafe { addr_of!(CTR) };

If I understand correctly, for the moment this is just a warning, but it will soon become a compile error. We will need some workarounds for this.

Todo

• Stopgap using addr_of to allow us to update nightlies still
• Decide on an approach for avoiding the warning or more safely handling mutable statics. kernel: add SingleThreadValue type for !Sync statics, using atomics for synchronization #4551
• Fix deferred call DeferredCall: Port to SingleThreadValue #4566
• Fix debug writer static mut: Convert DEBUG_WRITER to SingleThreadValue, rename type Chip to type ChipHw in boards #4624
• Fix debug gpio static mut: Use STV for debug_gpios #4635
• Handle PROCESSES, CHIP, etc. in boards. Board Panic Handler static muts: Port to SingleThreadValue #4519
• Fix chips
  • chips/nrf5x/src/aes.rs chips: nrf5x: forbid unsafe #4626
  • chips/nrf5x/src/pinmux.rs chips: nrf5x: forbid unsafe #4626
  • chips/e310x/src/plic.rs
  • chips/earlgrey/src/plic.rs
  • chips/esp32-c3/src/chip.rs
  • chips/nrf52/src/acomp.rs chips: nrf52: acomp: remove static mut #4625
  • chips/nrf52/src/ficr.rs
  • chips/qemu_rv32_virt_chip/src/plic.rs
  • chips/stm32f303xc/src/exti.rs
  • chips/stm32f4xx/src/exti.rs
  • chips/veer_el2/src/chip.rs
  • chips/apollo3/src/ble.rs
  • chips/arty_e21_chip/src/chip.rs
  • chips/e310x/src/chip.rs
  • chips/earlgrey/src/chip.rs
  • chips/esp32-c3/src/chip.rs
  • chips/litex_vexriscv/src/chip.rs
  • chips/nrf52/src/adc.rs
  • chips/nrf52/src/ble_radio.rs
  • chips/nrf52/src/pwm.rs
  • chips/nrf52/src/uart.rs
  • chips/qemu_rv32_virt_chip/src/chip.rs
  • chips/veer_el2/src/chip.rs