When unwinding, create DwarfUnwinder after the trampoline

So that we don't try to clean it up during the unwind.

Author: philipc

unwind/src/glue.rs

@@ -1,7 +1,13 @@
 use gimli::X86_64;
-use super::{UnwindPayload, StackFrames};
 use registers::Registers;
 
+type UnwindPayload<'a> = &'a mut dyn FnMut(Registers);
+
+pub fn registers<F>(mut f: F) where F: FnMut(Registers) {
+    let mut f = &mut f as UnwindPayload;
+    unsafe { unwind_trampoline(&mut f) };
+}
+
 #[allow(improper_ctypes)] // trampoline just forwards the ptr
 extern "C" {
     #[cfg(not(feature = "asm"))]
@@ -106,13 +112,7 @@ pub unsafe extern "C" fn unwind_recorder(payload: *mut UnwindPayload, stack: u64
     registers[X86_64::R15] = Some(saved_regs.r15);
     registers[X86_64::RA] = Some(*(stack as *const u64));
 
-    let mut frames = StackFrames {
-        unwinder: payload.unwinder,
-        registers,
-        state: None,
-    };
-
-    (payload.tracer)(&mut frames);
+    payload(registers);
 }
 
 pub unsafe fn land(regs: &Registers) {

unwind/src/lib.rs

@@ -82,23 +82,15 @@ impl Default for DwarfUnwinder {
     }
 }
 
-pub struct UnwindPayload<'a> {
-    unwinder: &'a mut DwarfUnwinder,
-    tracer: &'a mut FnMut(&mut StackFrames),
-}
-
 impl Unwinder for DwarfUnwinder {
     fn trace<F>(&mut self, mut f: F) where F: FnMut(&mut StackFrames) {
-        let mut payload = UnwindPayload {
-            unwinder: self,
-            tracer: &mut f,
-        };
-
-        unsafe { glue::unwind_trampoline(&mut payload) };
+        glue::registers(|registers| {
+            let mut frames = StackFrames::new(self, registers);
+            f(&mut frames)
+        });
     }
 }
 
-
 struct UnwindInfo<R: Reader> {
     row: UnwindTableRow<R>,
     personality: Option<Pointer>,
@@ -156,6 +148,14 @@ unsafe fn deref_ptr(ptr: Pointer) -> u64 {
 
 
 impl<'a> StackFrames<'a> {
+    pub fn new(unwinder: &'a mut DwarfUnwinder, registers: Registers) -> Self {
+        StackFrames {
+            unwinder,
+            registers,
+            state: None,
+        }
+    }
+
     pub fn registers(&mut self) -> &mut Registers {
         &mut self.registers
     }

unwind/src/libunwind_shim.rs

@@ -5,7 +5,7 @@ use fallible_iterator::FallibleIterator;
 use gimli::X86_64;
 
 use registers::Registers;
-use super::{DwarfUnwinder, Unwinder};
+use super::{DwarfUnwinder, Unwinder, StackFrames};
 
 #[repr(C)]
 #[derive(Copy, Clone, PartialEq)]
@@ -58,7 +58,7 @@ type PersonalityRoutine = extern "C" fn(version: c_int, actions: c_int, class: u
 // it never needs any cleanup. Currently this is not true.
 #[no_mangle]
 pub unsafe extern "C" fn _Unwind_Resume(exception: *mut _Unwind_Exception) -> ! {
-    DwarfUnwinder::default().trace(|frames| unwind_tracer(frames, exception));
+    ::glue::registers(|registers| unwind_tracer(registers, exception));
     unreachable!();
 }
 
@@ -120,11 +120,14 @@ pub unsafe extern "C" fn _Unwind_FindEnclosingFunction(pc: *mut c_void) -> *mut
 #[no_mangle]
 pub unsafe extern "C" fn _Unwind_RaiseException(exception: *mut _Unwind_Exception) -> _Unwind_Reason_Code {
     (*exception).private_contptr = None;
-    DwarfUnwinder::default().trace(|frames| unwind_tracer(frames, exception));
+    ::glue::registers(|registers| unwind_tracer(registers, exception));
     unreachable!();
 }
 
-unsafe fn unwind_tracer(frames: &mut ::StackFrames, exception: *mut _Unwind_Exception) {
+unsafe fn unwind_tracer(registers: Registers, exception: *mut _Unwind_Exception) {
+    let mut unwinder = DwarfUnwinder::default();
+    let mut frames = StackFrames::new(&mut unwinder, registers);
+
     if let Some(contptr) = (*exception).private_contptr {
         loop {
             if let Some(frame) = frames.next().unwrap() {