Update to nightly-2025-07-20 (#2160)

Currently, Hubris' Rust toolchain is pinned to `nightly-2024-09-17`,
which is from 10 months ago. This is kind of unfortunate, especially
because that nightly is too old to support the Rust 2024 edition, which
means we cannot update our dependencies on any crates where the latest
version is built with Rust 2024.

Beyond just updating the toolchain, there were some noteworthy changes:

- Naked functions are now stable (yay!), but the attribute changed to
  `#[unsafe(naked)]`. Inline assembly in naked functions must now use
  `core::arch::naked_asm!` rather than normal `asm!`. As far as I can
  tell, the only difference between this and regular `asm!` is that it
  does not support `options(noreturn)`, as I believe the `naked_asm!`
  block kind of implies at least some of the codegen differences for
  `noreturn`.
- New warnings on creation of temporary shared references to mutable
  statics showed up in `stm32h7-update-server`, where we were using
  `[T]::as_ptr()` on zero-sized slices in mutable statics that were used
  to get linker-generated addresses. `[T]::as_ptr()` takes an `&self`
  receiver, so this was generating a temporary shared reference to the
  mutable static. I changed this to use `&raw const`, which takes the
  address of the static without creating a shared reference.
- There was a substantial regression in flash and RAM usage on the new
  toolchain due to [a change in the behavior of the `#[used]`
  attribute][1] which revealed [an underlying issue where ringbufs were
  not zero initialized][2]. These issues were resolved separately in
  #2167, #2168, #2170, and oxidecomputer/idolatry#65.

In addition, there were a variety of unremarkable linting changes,
including slightly better dead code detection (which detected some new
dead code), and some annoying clippy nonsense.

Note that this branch requires oxidecomputer/idolatry#65, which updates
`idol` to generate code that doesn't emit warnings with the new
toolchain, and fixes some of the flash/RAM size regression in code
generated by `idol`.

Fixes #2165

[1]: #2165 (comment)
[2]: #2165 (comment)

Author: hawkw

.cargo/config.toml

@@ -7,7 +7,7 @@ xtask = "run --package xtask --"
 # version_detect is basically "if nightly { return true; }". This setting gets
 # overridden within xtask for Hubris programs, so this only affects host tools like
 # xtask.
-rustflags = ["-Zallow-features=proc_macro_diagnostic,asm_const,naked_functions,used_with_arg"]
+rustflags = ["-Zallow-features=proc_macro_diagnostic,used_with_arg"]
 
 [unstable]
 bindeps = true

Cargo.lock

@@ -115,7 +115,7 @@ priority = 3
 max-sizes = {flash = 16384, ram = 4096}
 uses = ["rng", "pmc"]
 start = true
-stacksize = 2200
+stacksize = 2216
 task-slots = ["syscon_driver"]
 
 [tasks.pong]

app/lpc55xpresso/app.toml

@@ -6,12 +6,14 @@ version = "0.1.0"
 
 [features]
 dump = ["kern/dump"]
+traptrace = ["ringbuf"]
 
 [dependencies]
 cortex-m = { workspace = true }
 cortex-m-rt = { workspace = true }
 cfg-if = { workspace = true }
 stm32h7 = { workspace = true, features = ["rt", "stm32h753"] }
+ringbuf = { path = "../../lib/ringbuf", optional = true }
 
 drv-stm32h7-startup = { path = "../../drv/stm32h7-startup", features = ["h753"] }
 kern = { path = "../../sys/kern" }

app/medusa/Cargo.toml

@@ -15,6 +15,9 @@ use drv_stm32h7_startup::ClockConfig;
 
 use cortex_m_rt::entry;
 
+#[cfg(feature = "traptrace")]
+mod tracing;
+
 #[entry]
 fn main() -> ! {
     system_init();

app/medusa/src/main.rs

@@ -0,0 +1,90 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//
+// If you are cutting-and-pasting this code into another kernel (and that
+// kernel is armv6m), it is hoped that you will cut-and-paste this compile
+// error along with it and take heed of its admonition!
+//
+#[cfg(not(any(armv7m, armv8m)))]
+compile_error!("ringbuf is unsound in the kernel on armv6m");
+
+use ringbuf::*;
+
+#[derive(Copy, Clone, PartialEq)]
+enum Event {
+    SyscallEnter(u32),
+    SyscallExit,
+    SecondarySyscallEnter,
+    SecondarySyscallExit,
+    IsrEnter,
+    IsrExit,
+    TimerIsrEnter,
+    TimerIsrExit,
+    ContextSwitch(usize),
+}
+
+#[derive(Copy, Clone, PartialEq)]
+enum Trace {
+    None,
+    Event(Event),
+}
+
+ringbuf!(Trace, 128, Trace::None);
+
+fn trace(event: Event) {
+    ringbuf_entry!(Trace::Event(event));
+}
+
+fn syscall_enter(nr: u32) {
+    trace(Event::SyscallEnter(nr));
+}
+
+fn syscall_exit() {
+    trace(Event::SyscallExit);
+}
+
+fn secondary_syscall_enter() {
+    trace(Event::SecondarySyscallEnter);
+}
+
+fn secondary_syscall_exit() {
+    trace(Event::SecondarySyscallExit);
+}
+
+fn isr_enter() {
+    trace(Event::IsrEnter);
+}
+
+fn isr_exit() {
+    trace(Event::IsrExit);
+}
+
+fn timer_isr_enter() {
+    trace(Event::TimerIsrEnter);
+}
+
+fn timer_isr_exit() {
+    trace(Event::TimerIsrExit);
+}
+
+fn context_switch(addr: usize) {
+    trace(Event::ContextSwitch(addr));
+}
+
+static TRACING: kern::profiling::EventsTable = kern::profiling::EventsTable {
+    syscall_enter,
+    syscall_exit,
+    secondary_syscall_enter,
+    secondary_syscall_exit,
+    isr_enter,
+    isr_exit,
+    timer_isr_enter,
+    timer_isr_exit,
+    context_switch,
+};
+
+pub fn table() -> &'static kern::profiling::EventsTable {
+    &TRACING
+}

app/medusa/src/tracing.rs

@@ -95,7 +95,7 @@ priority = 5
 max-sizes = {flash = 16384, ram = 4096}
 uses = ["rng", "pmc"]
 start = true
-stacksize = 2200
+stacksize = 2216
 task-slots = ["syscon_driver"]
 
 [tasks.sprot]

app/rot-carrier/app.toml

@@ -20,11 +20,11 @@ pub fn rustfmt(path: impl AsRef<Path>) -> Result<()> {
 
     let out_str = std::str::from_utf8(&which_out.stdout)?.trim();
 
-    println!("will invoke: {}", out_str);
+    println!("will invoke: {out_str}");
 
     let fmt_status = Command::new(out_str).arg(path.as_ref()).status()?;
     if !fmt_status.success() {
-        bail!("rustfmt returned status {}", fmt_status);
+        bail!("rustfmt returned status {fmt_status}");
     }
     Ok(())
 }

build/call_rustfmt/src/lib.rs

@@ -113,7 +113,7 @@ fn recurse_addr_map(
                 )
                 .unwrap();
             }
-            _ => panic!("unexpected child {:?}", child),
+            _ => panic!("unexpected child {child:?}"),
         }
     }
 }
@@ -607,10 +607,8 @@ pub fn build_peripheral(
 
         let inst_name = inst_name.to_upper_camel_case();
         let struct_name: syn::Ident = syn::parse_str(&inst_name).unwrap();
-        let handle_name: syn::Ident =
-            syn::parse_str(&format!("{}Handle", inst_name)).unwrap();
-        let view_name: syn::Ident =
-            syn::parse_str(&format!("{}View", inst_name)).unwrap();
+        let handle_name: syn::Ident = quote::format_ident!("{inst_name}Handle");
+        let view_name: syn::Ident = quote::format_ident!("{inst_name}View");
         let reg_addr = base_addr
             + u32::try_from(*periph_offset).unwrap()
             + u32::try_from(*addr_offset).unwrap();
@@ -738,7 +736,7 @@ pub fn read_parse(p: &std::path::Path) -> anyhow::Result<Node> {
     std::fs::File::open(p)
         .with_context(|| format!("failed to open {p:?}"))?
         .read_to_end(&mut data)?;
-    println!("cargo:rerun-if-changed={:?}", p);
+    println!("cargo::rerun-if-changed={p:?}");
     let src = std::str::from_utf8(&data)?;
     let node: Node = serde_json::from_str(src)?;
     Ok(node)