Add safety docs

Author: jonas-schievink

cortex-m-rt/src/lib.rs

@@ -472,41 +472,81 @@ impl ExceptionFrame {
     }
 
     /// Sets the stacked value of (general purpose) register 0.
+    ///
+    /// # Safety
+    ///
+    /// This affects the `r0` register of the preempted code, which must not rely on it getting
+    /// restored to its previous value.
     pub unsafe fn set_r0(&mut self, value: u32) {
         self.r0 = value;
     }
 
     /// Sets the stacked value of (general purpose) register 1.
+    ///
+    /// # Safety
+    ///
+    /// This affects the `r1` register of the preempted code, which must not rely on it getting
+    /// restored to its previous value.
     pub unsafe fn set_r1(&mut self, value: u32) {
         self.r1 = value;
     }
 
     /// Sets the stacked value of (general purpose) register 2.
+    ///
+    /// # Safety
+    ///
+    /// This affects the `r2` register of the preempted code, which must not rely on it getting
+    /// restored to its previous value.
     pub unsafe fn set_r2(&mut self, value: u32) {
         self.r2 = value;
     }
 
     /// Sets the stacked value of (general purpose) register 3.
+    ///
+    /// # Safety
+    ///
+    /// This affects the `r3` register of the preempted code, which must not rely on it getting
+    /// restored to its previous value.
     pub unsafe fn set_r3(&mut self, value: u32) {
         self.r3 = value;
     }
 
     /// Sets the stacked value of (general purpose) register 12.
+    ///
+    /// # Safety
+    ///
+    /// This affects the `r12` register of the preempted code, which must not rely on it getting
+    /// restored to its previous value.
     pub unsafe fn set_r12(&mut self, value: u32) {
         self.r12 = value;
     }
 
     /// Sets the stacked value of the Link Register.
+    ///
+    /// # Safety
+    ///
+    /// This affects the `lr` register of the preempted code, which must not rely on it getting
+    /// restored to its previous value.
     pub unsafe fn set_lr(&mut self, value: u32) {
         self.lr = value;
     }
 
     /// Sets the stacked value of the Program Counter.
+    ///
+    /// # Safety
+    ///
+    /// This affects the `pc` register of the preempted code, which must not rely on it getting
+    /// restored to its previous value.
     pub unsafe fn set_pc(&mut self, value: u32) {
         self.pc = value;
     }
 
     /// Sets the stacked value of the Program Status Register.
+    ///
+    /// # Safety
+    ///
+    /// This affects the `xPSR` registers (`IPSR`, `APSR`, and `EPSR`) of the preempted code, which
+    /// must not rely on them getting restored to their previous value.
     pub unsafe fn set_xpsr(&mut self, value: u32) {
         self.xpsr = value;
     }