Fix undefined behavior compile error (#346)

CHANGELOG.md

@@ -22,6 +22,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Deprecate `Toggle` enum and use `Switch` instead for better naming purposes
   ([#334])
   - Add `impl From<Toggle> for Switch` to reduce churn.
+- Fix undefined behavior in SPI implementation ([#346])
+  - Add `num_traits::PrimInt` bounds to `Word`
 
 ### Added
 
@@ -595,6 +597,7 @@ let clocks = rcc
 [defmt]: https://github.com/knurling-rs/defmt
 [filter]: https://defmt.ferrous-systems.com/filtering.html
 
+[#346]: https://github.com/stm32-rs/stm32f3xx-hal/pull/346
 [#340]: https://github.com/stm32-rs/stm32f3xx-hal/pull/340
 [#338]: https://github.com/stm32-rs/stm32f3xx-hal/pull/338
 [#337]: https://github.com/stm32-rs/stm32f3xx-hal/pull/337

Cargo.toml

@@ -37,6 +37,7 @@ embedded-hal = { version = "0.2.5", features = ["unproven"] }
 embedded-time = "0.12.0"
 enumset = { version = "1.0.6", optional = true }
 nb = "1.0.0"
+num-traits = { version = "0.2.17", default-features = false}
 paste = "1.0.5"
 rtcc = { version = "0.3.0", optional = true }
 stm32-usbd = { version = "0.6.0", optional = true }

src/spi.rs

@@ -6,7 +6,7 @@
 //!
 //! [examples/spi.rs]: https://github.com/stm32-rs/stm32f3xx-hal/blob/v0.9.1/examples/spi.rs
 
-use core::{fmt, marker::PhantomData, ops::Deref, ptr};
+use core::{fmt, marker::PhantomData, ops::Deref};
 
 use crate::hal::blocking::spi;
 use crate::hal::spi::FullDuplex;
@@ -24,6 +24,7 @@ use crate::{
     rcc::{self, Clocks},
     time::rate,
 };
+use num_traits::{AsPrimitive, PrimInt};
 
 /// SPI error
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
@@ -337,6 +338,8 @@ where
     // SckPin could technically be omitted, though not advisable.
     Miso: MisoPin<SPI>,
     Mosi: MosiPin<SPI>,
+    Word: PrimInt + Into<u32> + 'static,
+    u32: AsPrimitive<Word>,
 {
     type Error = Error;
 
@@ -350,9 +353,9 @@ where
         } else if sr.crcerr().is_no_match() {
             nb::Error::Other(Error::Crc)
         } else if sr.rxne().is_not_empty() {
-            let read_ptr = &self.spi.dr as *const _ as *const Word;
-            // NOTE(unsafe) read from register owned by this Spi struct
-            let value = unsafe { ptr::read_volatile(read_ptr) };
+            let read_ptr = core::ptr::addr_of!(self.spi.dr) as *const Word;
+            // SAFETY: Read from register owned by this Spi struct
+            let value = unsafe { core::ptr::read_volatile(read_ptr) };
             return Ok(value);
         } else {
             nb::Error::WouldBlock
@@ -369,9 +372,9 @@ where
         } else if sr.crcerr().is_no_match() {
             nb::Error::Other(Error::Crc)
         } else if sr.txe().is_empty() {
-            let write_ptr = &self.spi.dr as *const _ as *mut Word;
-            // NOTE(unsafe) write to register owned by this Spi struct
-            unsafe { ptr::write_volatile(write_ptr, word) };
+            let write_ptr = core::ptr::addr_of!(self.spi.dr) as *mut Word;
+            // SAFETY: Write to register owned by this Spi struct
+            unsafe { core::ptr::write_volatile(write_ptr, word) };
             return Ok(());
         } else {
             nb::Error::WouldBlock
@@ -384,6 +387,8 @@ where
     SPI: Instance,
     Miso: MisoPin<SPI>,
     Mosi: MosiPin<SPI>,
+    Word: PrimInt + Into<u32> + 'static,
+    u32: AsPrimitive<Word>,
 {
 }
 
@@ -392,6 +397,8 @@ where
     SPI: Instance,
     Miso: MisoPin<SPI>,
     Mosi: MosiPin<SPI>,
+    Word: PrimInt + Into<u32> + 'static,
+    u32: AsPrimitive<Word>,
 {
 }