fix: handle potentially unaligned frame pointer (#217)

Signed-off-by: Gen Xu <xgbarry@gmail.com>

CHANGELOG.md

@@ -4,6 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+- Handle potentially unaligned frame pointer (#217)
+
 ## [0.12.0] - 2023-07-03
 
 ### Added

src/backtrace/frame_pointer.rs

@@ -36,6 +36,20 @@ impl super::Frame for Frame {
  }
 }
 
+/// helper to read a pointer from a potentially unaligned address
+///
+/// # Safety
+///
+/// Same as [`std::ptr::read_unaligned`]
+#[inline]
+unsafe fn read_ptr<T>(ptr: *const T) -> T {
+ if ptr.align_offset(std::mem::align_of::<T>()) == 0 {
+ std::ptr::read(ptr)
+ } else {
+ std::ptr::read_unaligned(ptr)
+ }
+}
+
 pub struct Trace {}
 impl super::Trace for Trace {
  type Frame = Frame;
@@ -104,13 +118,13 @@ impl super::Trace for Trace {
 
  // iterate to the next frame
  let frame = Frame {
- ip: unsafe { (*frame_pointer).ret },
+ ip: unsafe { read_ptr(frame_pointer).ret },
  };
 
  if !cb(&frame) {
  break;
  }
- frame_pointer = unsafe { (*frame_pointer).frame_pointer };
+ frame_pointer = unsafe { read_ptr(frame_pointer).frame_pointer };
  }
  }
 }
@@ -120,3 +134,33 @@ struct FramePointerLayout {
  frame_pointer: *mut FramePointerLayout,
  ret: usize,
 }
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ #[repr(C, align(64))]
+ struct AlignToSixtyFour([u8; 64]);
+
+ impl Default for AlignToSixtyFour {
+ fn default() -> Self {
+ AlignToSixtyFour([0; 64])
+ }
+ }
+
+ #[test]
+ fn test_read_ptr_aligned() {
+ let x = AlignToSixtyFour::default();
+ let ptr = &x.0[0] as *const u8;
+ assert_eq!(unsafe { read_ptr(ptr) }, x.0[0]);
+ }
+
+ #[test]
+ fn test_read_ptr_unaligned() {
+ let mut x = AlignToSixtyFour::default();
+ let expected = usize::MAX / 2;
+ x.0[1..9].copy_from_slice(&expected.to_ne_bytes()[..]);
+ let ptr: *const usize = unsafe { std::mem::transmute(&x.0[1] as *const u8) };
+ assert_eq!(unsafe { read_ptr(ptr) }, expected);
+ }
+}