Allow foreign exceptions to unwind through Rust code

Author: Amanieu

src/doc/unstable-book/src/language-features/lang-items.md

@@ -249,9 +249,8 @@ the source code.
 - Runtime
   - `start`: `libstd/rt.rs`
   - `eh_personality`: `libpanic_unwind/emcc.rs` (EMCC)
-  - `eh_personality`: `libpanic_unwind/seh64_gnu.rs` (SEH64 GNU)
+  - `eh_personality`: `libpanic_unwind/gcc.rs` (GNU)
   - `eh_personality`: `libpanic_unwind/seh.rs` (SEH)
-  - `eh_unwind_resume`: `libpanic_unwind/seh64_gnu.rs` (SEH64 GNU)
   - `eh_unwind_resume`: `libpanic_unwind/gcc.rs` (GCC)
   - `msvc_try_filter`: `libpanic_unwind/seh.rs` (SEH)
   - `panic`: `libcore/panicking.rs`

src/libpanic_unwind/dwarf/eh.rs

@@ -51,7 +51,7 @@ pub enum EHAction {
 
 pub const USING_SJLJ_EXCEPTIONS: bool = cfg!(all(target_os = "ios", target_arch = "arm"));
 
-pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>)
+pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>, foreign_exception: bool)
     -> Result<EHAction, ()>
 {
     if lsda.is_null() {
@@ -96,7 +96,7 @@ pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>)
                     return Ok(EHAction::None)
                 } else {
                     let lpad = lpad_base + cs_lpad;
-                    return Ok(interpret_cs_action(cs_action, lpad))
+                    return Ok(interpret_cs_action(cs_action, lpad, foreign_exception))
                 }
             }
         }
@@ -121,16 +121,23 @@ pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>)
                 // Can never have null landing pad for sjlj -- that would have
                 // been indicated by a -1 call site index.
                 let lpad = (cs_lpad + 1) as usize;
-                return Ok(interpret_cs_action(cs_action, lpad))
+                return Ok(interpret_cs_action(cs_action, lpad, foreign_exception))
             }
         }
     }
 }
 
-fn interpret_cs_action(cs_action: u64, lpad: usize) -> EHAction {
+fn interpret_cs_action(cs_action: u64, lpad: usize, foreign_exception: bool) -> EHAction {
     if cs_action == 0 {
+        // If cs_action is 0 then this is a cleanup (Drop::drop). We run these
+        // for both Rust panics and foriegn exceptions.
         EHAction::Cleanup(lpad)
+    } else if foreign_exception {
+        // catch_unwind should not catch foreign exceptions, only Rust panics.
+        // Instead just continue unwinding.
+        EHAction::None
     } else {
+        // Stop unwinding Rust panics at catch_unwind.
         EHAction::Catch(lpad)
     }
 }

src/libpanic_unwind/gcc.rs

@@ -5,9 +5,8 @@
 //! essentially gets categorized into three buckets currently:
 //!
 //! 1. MSVC targets use SEH in the `seh.rs` file.
-//! 2. The 64-bit MinGW target half-uses SEH and half-use gcc-like information
-//!    in the `seh64_gnu.rs` module.
-//! 3. All other targets use libunwind/libgcc in the `gcc/mod.rs` module.
+//! 2. Emscripten uses C++ exceptions in the `emcc.rs` file.
+//! 3. All other targets use libunwind/libgcc in the `gcc.rs` file.
 //!
 //! More documentation about each implementation can be found in the respective
 //! module.
@@ -52,9 +51,6 @@ cfg_if::cfg_if! {
     } else if #[cfg(target_env = "msvc")] {
         #[path = "seh.rs"]
         mod imp;
-    } else if #[cfg(all(windows, target_arch = "x86_64", target_env = "gnu"))] {
-        #[path = "seh64_gnu.rs"]
-        mod imp;
     } else {
         // Rust runtime's startup objects depend on these symbols, so make them public.
         #[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]

src/libpanic_unwind/lib.rs

@@ -244,3 +244,30 @@ if #[cfg(not(all(target_os = "ios", target_arch = "arm")))] {
     }
 }
 } // cfg_if!
+
+cfg_if::cfg_if! {
+if #[cfg(all(windows, target_arch = "x86_64", target_env = "gnu"))] {
+    // We declare these as opaque types. This is fine since you just need to
+    // pass them to _GCC_specific_handler and forget about them.
+    pub enum EXCEPTION_RECORD {}
+    pub type LPVOID = *mut c_void;
+    pub enum CONTEXT {}
+    pub enum DISPATCHER_CONTEXT {}
+    pub type EXCEPTION_DISPOSITION = c_int;
+    type PersonalityFn = unsafe extern "C" fn(version: c_int,
+                                              actions: _Unwind_Action,
+                                              exception_class: _Unwind_Exception_Class,
+                                              exception_object: *mut _Unwind_Exception,
+                                              context: *mut _Unwind_Context)
+                                              -> _Unwind_Reason_Code;
+
+    extern "C" {
+        pub fn _GCC_specific_handler(exceptionRecord: *mut EXCEPTION_RECORD,
+                                establisherFrame: LPVOID,
+                                contextRecord: *mut CONTEXT,
+                                dispatcherContext: *mut DISPATCHER_CONTEXT,
+                                personality: PersonalityFn)
+                                -> EXCEPTION_DISPOSITION;
+    }
+}
+} // cfg_if!

src/libpanic_unwind/seh64_gnu.rs

@@ -0,0 +1,10 @@
+-include ../tools.mk
+
+all: foo
+	$(call RUN,foo)
+
+foo: foo.rs $(call NATIVE_STATICLIB,foo)
+	$(RUSTC) $< -lfoo $(EXTRACXXFLAGS)
+
+$(TMPDIR)/libfoo.o: foo.cpp
+	$(call COMPILE_OBJ_CXX,$@,$<)

src/libunwind/libunwind.rs

@@ -0,0 +1,59 @@
+#include <assert.h>
+#include <stddef.h>
+#include <stdio.h>
+
+void println(const char* s) {
+    puts(s);
+    fflush(stdout);
+}
+
+struct exception {};
+
+struct drop_check {
+    bool* ok;
+    ~drop_check() {
+        println("~drop_check");
+
+        if (ok)
+            *ok = true;
+    }
+};
+
+extern "C" {
+    void rust_catch_callback(void (*cb)(), bool* rust_ok);
+
+    static void callback() {
+        println("throwing C++ exception");
+        throw exception();
+    }
+
+    void throw_cxx_exception() {
+        bool rust_ok = false;
+        try {
+            rust_catch_callback(callback, &rust_ok);
+            assert(false && "unreachable");
+        } catch (exception e) {
+            println("caught C++ exception");
+            assert(rust_ok);
+            return;
+        }
+        assert(false && "did not catch thrown C++ exception");
+    }
+
+    void cxx_catch_callback(void (*cb)(), bool* cxx_ok) {
+        drop_check x;
+        x.ok = NULL;
+        try {
+            cb();
+        } catch (exception e) {
+            assert(false && "shouldn't be able to catch a rust panic");
+        } catch (...) {
+            println("caught foreign exception in catch (...)");
+            // Foreign exceptions are caught by catch (...). We only set the ok
+            // flag if we successfully caught the panic. The destructor of
+            // drop_check will then set the flag to true if it is executed.
+            x.ok = cxx_ok;
+            throw;
+        }
+    }
+}

src/test/run-make-fulldeps/foreign-exceptions/Makefile

@@ -0,0 +1,63 @@
+// Tests that C++ exceptions can unwind through Rust code, run destructors and
+// are ignored by catch_unwind. Also tests that Rust panics can unwind through
+// C++ code.
+
+#![feature(unwind_attributes)]
+
+use std::panic::{catch_unwind, AssertUnwindSafe};
+
+struct DropCheck<'a>(&'a mut bool);
+impl<'a> Drop for DropCheck<'a> {
+    fn drop(&mut self) {
+        println!("DropCheck::drop");
+        *self.0 = true;
+    }
+}
+
+extern "C" {
+    fn throw_cxx_exception();
+
+    #[unwind(allowed)]
+    fn cxx_catch_callback(cb: extern "C" fn(), ok: *mut bool);
+}
+
+#[no_mangle]
+#[unwind(allowed)]
+extern "C" fn rust_catch_callback(cb: extern "C" fn(), rust_ok: &mut bool) {
+    let _caught_unwind = catch_unwind(AssertUnwindSafe(|| {
+        let _drop = DropCheck(rust_ok);
+        cb();
+        unreachable!("should have unwound instead of returned");
+    }));
+    unreachable!("catch_unwind should not have caught foreign exception");
+}
+
+fn throw_rust_panic() {
+    #[unwind(allowed)]
+    extern "C" fn callback() {
+        println!("throwing rust panic");
+        panic!(1234i32);
+    }
+
+    let mut dropped = false;
+    let mut cxx_ok = false;
+    let caught_unwind = catch_unwind(AssertUnwindSafe(|| {
+        let _drop = DropCheck(&mut dropped);
+        unsafe {
+            cxx_catch_callback(callback, &mut cxx_ok);
+        }
+        unreachable!("should have unwound instead of returned");
+    }));
+    println!("caught rust panic");
+    assert!(dropped);
+    assert!(caught_unwind.is_err());
+    let panic_obj = caught_unwind.unwrap_err();
+    let panic_int = *panic_obj.downcast_ref::<i32>().unwrap();
+    assert_eq!(panic_int, 1234);
+    assert!(cxx_ok);
+}
+
+fn main() {
+    unsafe { throw_cxx_exception() };
+    throw_rust_panic();
+}