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stm32: Improve dualcore safety #3687

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merged 2 commits into from
Dec 25, 2024
Merged

stm32: Improve dualcore safety #3687

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92a489b
Make SharedData repr C
diondokter Dec 25, 2024
595ce48
Write the flag sooner with a known value
diondokter Dec 25, 2024
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44 changes: 42 additions & 2 deletions embassy-stm32/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -326,10 +326,11 @@ mod dual_core {
/// ```
///
/// This static must be placed in the same position for both cores. How and where this is done is left to the user.
#[repr(C)]
pub struct SharedData {
init_flag: AtomicUsize,
clocks: UnsafeCell<MaybeUninit<Clocks>>,
config: UnsafeCell<MaybeUninit<Config>>,
config: UnsafeCell<MaybeUninit<SharedConfig>>,
}

unsafe impl Sync for SharedData {}
Expand All @@ -349,10 +350,15 @@ mod dual_core {
pub fn init_primary(config: Config, shared_data: &'static MaybeUninit<SharedData>) -> Peripherals {
let shared_data = unsafe { shared_data.assume_init_ref() };

// Write the flag as soon as possible. Reading this flag uninitialized in the `init_secondary`
// is maybe unsound? Unclear. If it is indeed unsound, writing it sooner doesn't fix it all,
// but improves the odds of it going right
shared_data.init_flag.store(0, Ordering::SeqCst);

rcc::set_freqs_ptr(shared_data.clocks.get());
let p = init_hw(config);

unsafe { *shared_data.config.get() }.write(config);
unsafe { *shared_data.config.get() }.write(config.into());

shared_data.init_flag.store(INIT_DONE_FLAG, Ordering::SeqCst);

Expand Down Expand Up @@ -424,6 +430,40 @@ mod dual_core {

Peripherals::take()
}

#[repr(C)]
#[derive(Clone, Copy)]
struct SharedConfig {
#[cfg(bdma)]
bdma_interrupt_priority: Priority,
#[cfg(dma)]
dma_interrupt_priority: Priority,
#[cfg(gpdma)]
gpdma_interrupt_priority: Priority,
}

impl From<Config> for SharedConfig {
fn from(value: Config) -> Self {
let Config {
#[cfg(bdma)]
bdma_interrupt_priority,
#[cfg(dma)]
dma_interrupt_priority,
#[cfg(gpdma)]
gpdma_interrupt_priority,
..
} = value;

SharedConfig {
#[cfg(bdma)]
bdma_interrupt_priority,
#[cfg(dma)]
dma_interrupt_priority,
#[cfg(gpdma)]
gpdma_interrupt_priority,
}
}
}
}

#[cfg(feature = "_dual-core")]
Expand Down
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