init segfaulting

[anholt]

As of recent rust nightlies, I get:

cargo run --target riscv64gc-unknown-none-elf 
   Compiling octox v0.1.0 (/home/anholt/src/octox)
warning: the feature `asm_const` has been stable since 1.82.0 and no longer requires an attribute to enable
  --> src/kernel/lib.rs:10:12
   |
10 | #![feature(asm_const)]
   |            ^^^^^^^^^
   |
   = note: `#[warn(stable_features)]` on by default

warning: the feature `new_uninit` has been stable since 1.82.0 and no longer requires an attribute to enable
 --> src/kernel/lib.rs:6:66
  |
6 | #![cfg_attr(all(target_os = "none", feature = "kernel"), feature(new_uninit))]
  |                                                                  ^^^^^^^^^^

warning: `libkernel` (lib) generated 2 warnings
warning: octox@0.1.0: nmeta 70 (boot, super, log blocks 30 inode blocks 13, bitmap blocks 25) blocks 199930 total 200000
warning: octox@0.1.0: mkfs:balloc: first 3221 blocks have benen allocated
warning: octox@0.1.0: mkfs:balloc: write bitmap block at sector 45
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.40s
     Running `qemu-system-riscv64 -machine virt -bios none -m 524M -smp 4 -nographic -serial 'mon:stdio' -global virtio-mmio.force-legacy=false -drive file=target/fs.img,if=none,format=raw,id=x0 -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0 -kernel target/riscv64gc-unknown-none-elf/debug/octox`

octox kernel is booting

bd: memory sz is 535633920 bytes; allocate an size array of length 26
bd: 12584176 meta bytes for managing 536870912 bytes of memory
bd: 1236992 bytes unavailable
hart 2 starting
hart 3 starting
hart 1 starting
usertrap(): unexcepted scause Exception(StorePageFault), pid=PId(0)
            sepc=3B0, stval=B010
core 1: panicked at src/kernel/proc.rs:726:5:
init exiting

By dropping channel = "nightly" from config.toml, I've bisected a bit, and it seems it's between nightly 2024-07-25 and 2024-09-01 that it fails. In between, there are a lot of compile failures about:

  --> src/kernel/trampoline.rs:96:5
   |
94 |     #[naked]
   |     -------- function marked with `#[naked]` here
95 |     #[no_mangle]
96 |     #[repr(align(16))]
   | ^^^^^^^^^^^^^^^^^^ the `repr` attribute is incompatible with `#[naked]`