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fix(portkit): redesign sym_static!
This commit addresses multiple issues in `sym_static!`, including: - If a program contains multiple instances of the variables defined by `static_sym!`, the compiler can merge them into one because, from the compiler's point of view they are identically-defined functions. This phenomenon was observed in `r3_smp_rp_pico` under certain compile options. - The defined variable might not have a unique address if it's generic, and dynamic linking is in use. This is actually rather hard to deal with on Windows, which is why Rust doesn't have generic `static`s[1]. - It only supports zero-initialization. The new `sym_static!` addresses these problems by using real `static`s as its storage. For inline assembly access, it provides a `#[naked]` "function", which contains a pointer to the referenced variable. This approach is much more reliable but has a few drawbacks: - Inline assembly needs one extra indirection to access the variable. - The variable can no longer be implicitly instantiated. Each instantia- tion must be made by an invocation of `static_sym!`. [1]: https://internals.rust-lang.org/t/how-about-generic-global-variables/8351/19
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‎README.md

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@@ -50,7 +50,9 @@ The R3 original kernel is provided as a separate package [`r3_kernel`][].
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#![feature(const_fn_trait_bound)]
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#![feature(const_refs_to_cell)]
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#![feature(const_trait_impl)]
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#![feature(naked_functions)]
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#![feature(const_mut_refs)]
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#![feature(asm_const)]
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#![feature(asm_sym)]
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#![no_std]
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#![no_main]

‎examples/basic_gr_peach/src/main.rs

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@@ -4,6 +4,7 @@
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#![feature(const_trait_impl)]
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#![feature(const_mut_refs)]
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#![feature(naked_functions)]
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#![feature(asm_const)]
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#![feature(asm_sym)]
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#![deny(unsafe_op_in_unsafe_fn)]
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#![no_std]

‎examples/basic_nucleo_f401re/src/main.rs

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@@ -2,7 +2,9 @@
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#![feature(const_fn_trait_bound)]
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#![feature(const_refs_to_cell)]
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#![feature(const_trait_impl)]
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#![feature(naked_functions)]
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#![feature(const_mut_refs)]
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#![feature(asm_const)]
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#![feature(asm_sym)]
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#![deny(unsafe_op_in_unsafe_fn)]
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#![no_std]

‎examples/basic_rp_pico/src/main.rs

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@@ -2,7 +2,9 @@
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#![feature(const_fn_trait_bound)]
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#![feature(const_refs_to_cell)]
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#![feature(const_trait_impl)]
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#![feature(naked_functions)]
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#![feature(const_mut_refs)]
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#![feature(asm_const)]
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#![feature(asm_sym)]
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#![deny(unsafe_op_in_unsafe_fn)]
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#![no_std]

‎examples/basic_wio_terminal/src/main.rs

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@@ -2,7 +2,9 @@
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#![feature(const_fn_trait_bound)]
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#![feature(const_refs_to_cell)]
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#![feature(const_trait_impl)]
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#![feature(naked_functions)]
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#![feature(const_mut_refs)]
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#![feature(asm_const)]
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#![feature(let_else)]
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#![feature(asm_sym)]
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#![deny(unsafe_op_in_unsafe_fn)]

‎examples/smp_rp_pico/src/main.rs

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@@ -2,7 +2,9 @@
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#![feature(const_fn_trait_bound)]
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#![feature(const_refs_to_cell)]
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#![feature(const_trait_impl)]
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#![feature(naked_functions)]
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#![feature(const_mut_refs)]
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#![feature(asm_const)]
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#![feature(asm_sym)]
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#![deny(unsafe_op_in_unsafe_fn)]
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#![no_std]

‎src/r3_port_arm/src/lib.rs

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@@ -27,7 +27,7 @@ pub extern crate r3_core;
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#[doc(hidden)]
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pub extern crate r3_kernel;
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30-
/// Used by `use_sp804!`
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/// Used by `use_sp804!` and `use_port!`
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#[doc(hidden)]
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pub extern crate r3_portkit;
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‎src/r3_port_arm/src/threading/cfg.rs

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@@ -93,12 +93,17 @@ macro_rules! use_port {
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cfg::{ThreadingOptions, EntryPoint},
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};
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96-
unsafe impl PortInstance for $Traits {}
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static PORT_STATE: State = $crate::r3_core::utils::Init::INIT;
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98+
unsafe impl PortInstance for $Traits {
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$crate::r3_portkit::sym::sym_static!(
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#[sym(p_port_state)] fn port_state() -> &State { &PORT_STATE });
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}
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98103
impl EntryPoint for $Traits {
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#[inline]
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unsafe fn start() -> ! {
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unsafe { <Self as PortInstance>::port_state().port_boot::<Self>() }
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unsafe { PORT_STATE.port_boot::<Self>() }
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}
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104109
const IRQ_ENTRY: unsafe extern "C" fn() -> ! = State::irq_entry::<Self>;
@@ -122,52 +127,52 @@ macro_rules! use_port {
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123128
#[inline(always)]
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unsafe fn dispatch_first_task() -> ! {
125-
<Self as PortInstance>::port_state().dispatch_first_task::<Self>()
130+
PORT_STATE.dispatch_first_task::<Self>()
126131
}
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128133
#[inline(always)]
129134
unsafe fn yield_cpu() {
130-
<Self as PortInstance>::port_state().yield_cpu::<Self>()
135+
PORT_STATE.yield_cpu::<Self>()
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}
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133138
#[inline(always)]
134139
unsafe fn exit_and_dispatch(task: &'static TaskCb<Self>) -> ! {
135-
<Self as PortInstance>::port_state().exit_and_dispatch::<Self>(task)
140+
PORT_STATE.exit_and_dispatch::<Self>(task)
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}
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138143
#[inline(always)]
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unsafe fn enter_cpu_lock() {
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<Self as PortInstance>::port_state().enter_cpu_lock::<Self>()
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PORT_STATE.enter_cpu_lock::<Self>()
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}
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143148
#[inline(always)]
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unsafe fn leave_cpu_lock() {
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<Self as PortInstance>::port_state().leave_cpu_lock::<Self>()
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PORT_STATE.leave_cpu_lock::<Self>()
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}
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148153
#[inline(always)]
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unsafe fn initialize_task_state(task: &'static TaskCb<Self>) {
150-
<Self as PortInstance>::port_state().initialize_task_state::<Self>(task)
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PORT_STATE.initialize_task_state::<Self>(task)
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}
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153158
#[inline(always)]
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fn is_cpu_lock_active() -> bool {
155-
<Self as PortInstance>::port_state().is_cpu_lock_active::<Self>()
160+
PORT_STATE.is_cpu_lock_active::<Self>()
156161
}
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158163
#[inline(always)]
159164
fn is_task_context() -> bool {
160-
<Self as PortInstance>::port_state().is_task_context::<Self>()
165+
PORT_STATE.is_task_context::<Self>()
161166
}
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163168
#[inline(always)]
164169
fn is_interrupt_context() -> bool {
165-
<Self as PortInstance>::port_state().is_interrupt_context::<Self>()
170+
PORT_STATE.is_interrupt_context::<Self>()
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}
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168173
#[inline(always)]
169174
fn is_scheduler_active() -> bool {
170-
<Self as PortInstance>::port_state().is_scheduler_active::<Self>()
175+
PORT_STATE.is_scheduler_active::<Self>()
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}
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}
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}

‎src/r3_port_arm/src/threading/imp.rs

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@@ -1,11 +1,8 @@
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use core::{arch::asm, cell::UnsafeCell, mem::MaybeUninit, slice};
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use memoffset::offset_of;
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use r3_core::{
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kernel::traits,
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utils::{Init, ZeroInit},
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};
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use r3_core::{kernel::traits, utils::Init};
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use r3_kernel::{KernelTraits, Port, PortToKernel, System, TaskCb};
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use r3_portkit::sym::{sym_static, SymStaticExt};
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use r3_portkit::sym::sym_static;
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use super::cfg::{InterruptController, ThreadingOptions, Timer};
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@@ -17,12 +14,7 @@ use super::cfg::{InterruptController, ThreadingOptions, Timer};
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pub unsafe trait PortInstance:
1815
KernelTraits + Port<PortTaskState = TaskState> + ThreadingOptions + InterruptController + Timer
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{
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sym_static!(static PORT_STATE: SymStatic<State> = zeroed!());
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22-
#[inline(always)]
23-
fn port_state() -> &'static State {
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sym_static(Self::PORT_STATE).as_ref()
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}
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sym_static!(#[sym(p_port_state)] fn port_state() -> &State);
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}
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2820
#[repr(C)]
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}
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4436
unsafe impl Sync for State {}
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unsafe impl ZeroInit for State {}
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impl Init for State {
39+
const INIT: Self = Self {
40+
dispatch_pending: UnsafeCell::new(false),
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main_stack: UnsafeCell::new(0),
42+
running_task_ptr: UnsafeCell::new(core::ptr::null_mut()),
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};
44+
}
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4746
#[derive(Debug)]
4847
#[repr(C)]
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180179

181180
unsafe {
182181
asm!("
183-
movw r0, :lower16:{PORT_STATE}_
184-
movt r0, :upper16:{PORT_STATE}_
182+
movw r0, :lower16:{p_port_state}_
183+
movt r0, :upper16:{p_port_state}_
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ldr r0, [r0]
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186186
# Skip saving the second-level state if the current context
187187
# is an idle task. Also, in this case, we don't have a stack,
@@ -205,8 +205,8 @@ impl State {
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206206
# Store SP to `TaskState`.
207207
#
208-
# <r0 = &PORT_STATE>
209-
# r0 = *PORT_STATE.running_task_ptr // == running_task
208+
# <r0 = &port_state>
209+
# r0 = *port_state.running_task_ptr // == running_task
210210
# r0.port_task_state.sp = sp_usr
211211
#
212212
ldr r0, [r0, #{OFFSET_RUNNING_TASK_PTR}]
@@ -260,7 +260,7 @@ impl State {
260260
push_second_level_state_and_dispatch =
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sym Self::push_second_level_state_and_dispatch::<Traits>,
262262
idle_task = sym Self::idle_task::<Traits>,
263-
PORT_STATE = sym Traits::PORT_STATE,
263+
p_port_state = sym Traits::p_port_state,
264264
OFFSET_RUNNING_TASK_PTR = const Self::OFFSET_RUNNING_TASK_PTR,
265265
OFFSET_MAIN_STACK = const Self::OFFSET_MAIN_STACK,
266266
options(noreturn),
@@ -278,8 +278,9 @@ impl State {
278278
asm!("
279279
# Read `port_state().dispatch_pending`. If it's clear, branch
280280
# to `NotShortcutting`
281-
movw r0, :lower16:{PORT_STATE}_
282-
movt r0, :upper16:{PORT_STATE}_
281+
movw r0, :lower16:{p_port_state}_
282+
movt r0, :upper16:{p_port_state}_
283+
ldr r0, [r0]
283284
ldrb r1, [r0, #{OFFSET_DISPATCH_PENDING}]
284285
tst r1, r1
285286
bne 0f
@@ -307,7 +308,7 @@ impl State {
307308
push_second_level_state_and_dispatch =
308309
sym Self::push_second_level_state_and_dispatch::<Traits>,
309310
idle_task = sym Self::idle_task::<Traits>,
310-
PORT_STATE = sym Traits::PORT_STATE,
311+
p_port_state = sym Traits::p_port_state,
311312
OFFSET_DISPATCH_PENDING = const Self::OFFSET_DISPATCH_PENDING,
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options(noreturn),
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);

‎src/r3_port_arm_m/src/lib.rs

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@@ -60,5 +60,8 @@ pub extern crate r3_core;
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pub extern crate r3_kernel;
6161
/// Used by `use_port!`
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#[doc(hidden)]
63+
pub extern crate r3_portkit;
64+
/// Used by `use_port!`
65+
#[doc(hidden)]
6366
#[cfg(target_os = "none")]
6467
pub use cortex_m_rt;

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