Add support for Miri backtraces

Companion to rust-lang/miri#1559

src/backtrace/miri.rs

@@ -0,0 +1,69 @@
+use std::boxed::Box;
+use std::ffi::c_void;
+
+extern "Rust" {
+    fn miri_get_backtrace(flags: u64) -> Box<[*mut ()]>;
+    fn miri_resolve_frame(ptr: *mut (), flags: u64) -> MiriFrame;
+}
+
+#[derive(Clone, Debug)]
+#[repr(C)]
+pub struct MiriFrame {
+    pub name: Box<[u8]>,
+    pub filename: Box<[u8]>,
+    pub lineno: u32,
+    pub colno: u32,
+}
+
+#[derive(Debug, Clone)]
+pub struct Frame {
+    pub addr: *mut c_void,
+    pub inner: MiriFrame,
+}
+
+// SAFETY: Miri guarantees that the returned pointer
+// can be used from any thread.
+unsafe impl Send for Frame {}
+unsafe impl Sync for Frame {}
+
+impl Frame {
+    pub fn ip(&self) -> *mut c_void {
+        self.addr
+    }
+
+    pub fn sp(&self) -> *mut c_void {
+        std::ptr::null_mut()
+    }
+
+    pub fn symbol_address(&self) -> *mut c_void {
+        self.addr
+    }
+
+    pub fn module_base_address(&self) -> Option<*mut c_void> {
+        None
+    }
+}
+
+pub fn trace<F: FnMut(&super::Frame) -> bool>(cb: F) {
+    // SAFETY: Miri guarnatees that the backtrace API functions
+    // can be called from any thread.
+    unsafe { trace_unsynchronized(cb) };
+}
+
+pub fn resolve_addr(ptr: *mut c_void) -> Frame {
+    // SAFETY: Miri will stop execution with an error if this pointer
+    // is invalid.
+    let frame: MiriFrame = unsafe { miri_resolve_frame(ptr as *mut (), 0) };
+    Frame {
+        addr: ptr,
+        inner: frame,
+    }
+}
+
+pub unsafe fn trace_unsynchronized<F: FnMut(&super::Frame) -> bool>(mut cb: F) {
+    let frames = miri_get_backtrace(0);
+    for ptr in frames.iter() {
+        let frame = resolve_addr(*ptr as *mut c_void);
+        cb(&super::Frame { inner: frame });
+    }
+}

src/backtrace/mod.rs

@@ -126,10 +126,12 @@ impl fmt::Debug for Frame {
 }
 
 cfg_if::cfg_if! {
+    // This needs to come first, to ensure that
+    // Miri takes priority over the host platform
     if #[cfg(miri)] {
-        mod noop;
-        use self::noop::trace as trace_imp;
-        pub(crate) use self::noop::Frame as FrameImp;
+        pub(crate) mod miri;
+        use self::miri::trace as trace_imp;
+        pub(crate) use self::miri::Frame as FrameImp;
     } else if #[cfg(
         any(
             all(

src/symbolize/miri.rs

@@ -0,0 +1,54 @@
+use core::ffi::c_void;
+use core::marker::PhantomData;
+
+use crate::backtrace::miri::{resolve_addr, Frame};
+use crate::symbolize::{ResolveWhat, SymbolName};
+use crate::types::BytesOrWideString;
+
+pub unsafe fn resolve(what: ResolveWhat<'_>, cb: &mut dyn FnMut(&super::Symbol)) {
+    let sym = match what {
+        ResolveWhat::Address(addr) => Symbol {
+            inner: resolve_addr(addr),
+            _unused: PhantomData,
+        },
+        ResolveWhat::Frame(frame) => Symbol {
+            inner: frame.inner.clone(),
+            _unused: PhantomData,
+        },
+    };
+    cb(&super::Symbol { inner: sym })
+}
+
+pub struct Symbol<'a> {
+    inner: Frame,
+    _unused: PhantomData<&'a ()>,
+}
+
+impl<'a> Symbol<'a> {
+    pub fn name(&self) -> Option<SymbolName<'_>> {
+        Some(SymbolName::new(&self.inner.inner.name))
+    }
+
+    pub fn addr(&self) -> Option<*mut c_void> {
+        Some(self.inner.addr)
+    }
+
+    pub fn filename_raw(&self) -> Option<BytesOrWideString<'_>> {
+        Some(BytesOrWideString::Bytes(&self.inner.inner.filename))
+    }
+
+    pub fn lineno(&self) -> Option<u32> {
+        Some(self.inner.inner.lineno)
+    }
+
+    pub fn colno(&self) -> Option<u32> {
+        Some(self.inner.inner.colno)
+    }
+
+    pub fn filename(&self) -> Option<&::std::path::Path> {
+        use std::path::Path;
+        Some(Path::new(
+            std::str::from_utf8(&self.inner.inner.filename).unwrap(),
+        ))
+    }
+}

src/symbolize/mod.rs

@@ -465,10 +465,9 @@ pub fn clear_symbol_cache() {
 
 cfg_if::cfg_if! {
     if #[cfg(miri)] {
-        mod noop;
-        use self::noop::resolve as resolve_imp;
-        use self::noop::Symbol as SymbolImp;
-        #[allow(unused)]
+        mod miri;
+        use self::miri::resolve as resolve_imp;
+        use self::miri::Symbol as SymbolImp;
         unsafe fn clear_symbol_cache_imp() {}
     } else if #[cfg(all(windows, target_env = "msvc", not(target_vendor = "uwp")))] {
         mod dbghelp;