Implement basic panic handler

Cargo.toml

@@ -22,6 +22,7 @@ personality = []
 personality-dummy = []
 print = ["libc"]
 panic = ["alloc"]
+panic-handler = ["print", "panic"]
 system-alloc = []
 default = ["dwarf-expr", "hide-trace", "fde-phdr", "fde-registry"]
 

src/lib.rs

@@ -6,6 +6,7 @@
     feature(lang_items)
 )]
 #![cfg_attr(feature = "panic", feature(core_intrinsics))]
+#![cfg_attr(feature = "panic-handler", feature(thread_local))]
 #![warn(rust_2018_idioms)]
 #![warn(unsafe_op_in_unsafe_fn)]
 #![no_std]
@@ -31,5 +32,8 @@ mod personality_dummy;
 #[cfg(feature = "panic")]
 pub mod panic;
 
+#[cfg(feature = "panic-handler")]
+pub mod panic_handler;
+
 #[cfg(feature = "system-alloc")]
 mod system_alloc;

src/panic.rs

@@ -3,6 +3,8 @@ use core::any::Any;
 use core::mem::ManuallyDrop;
 
 use crate::abi::*;
+#[cfg(feature = "panic-handler")]
+pub use crate::panic_handler::*;
 
 #[repr(C)]
 struct Exception {
@@ -20,7 +22,14 @@ pub fn begin_panic(payload: Box<dyn Any + Send>) -> UnwindReasonCode {
         unsafe {
             let _ = Box::from_raw(exception as *mut Exception);
         }
-        core::intrinsics::abort();
+        #[cfg(feature = "panic-handler")]
+        {
+            drop_panic();
+        }
+        #[cfg(not(feature = "panic-handler"))]
+        {
+            core::intrinsics::abort();
+        }
     }
 
     let mut unwind_ex = UnwindException::new();
@@ -38,7 +47,18 @@ unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send + 'static> {
     let exception = payload as *mut UnwindException;
     if unsafe { (*exception).exception_class } != RUST_EXCEPTION_CLASS {
         unsafe { _Unwind_DeleteException(exception) };
-        core::intrinsics::abort();
+        #[cfg(feature = "panic-handler")]
+        {
+            foreign_exception();
+        }
+        #[cfg(not(feature = "panic-handler"))]
+        {
+            core::intrinsics::abort();
+        }
+    }
+    #[cfg(feature = "panic-handler")]
+    {
+        panic_caught();
     }
     let unwind_ex = unsafe { Box::from_raw(exception as *mut Exception) };
     unwind_ex.payload

src/panic_handler.rs

@@ -0,0 +1,48 @@
+use crate::print::*;
+use alloc::boxed::Box;
+use core::any::Any;
+use core::cell::Cell;
+use core::panic::{Location, PanicInfo};
+
+#[thread_local]
+static PANIC_COUNT: Cell<usize> = Cell::new(0);
+
+#[link(name = "c")]
+extern "C" {}
+
+pub(crate) fn drop_panic() {
+    eprintln!("Rust panics must be rethrown");
+}
+
+pub(crate) fn foreign_exception() {
+    eprintln!("Rust cannot catch foreign exceptions");
+}
+
+pub(crate) fn panic_caught() {
+    PANIC_COUNT.set(0);
+}
+
+fn do_panic(msg: Box<dyn Any + Send>) -> ! {
+    if PANIC_COUNT.get() >= 1 {
+        eprintln!("thread panicked while processing panic. aborting.");
+        core::intrinsics::abort();
+    }
+    PANIC_COUNT.set(1);
+    let code = crate::panic::begin_panic(Box::new(msg));
+    eprintln!("failed to initiate panic, error {}", code.0);
+    core::intrinsics::abort();
+}
+
+#[panic_handler]
+fn panic(info: &PanicInfo<'_>) -> ! {
+    eprintln!("{}", info);
+
+    struct NoPayload;
+    do_panic(Box::new(NoPayload))
+}
+
+#[track_caller]
+pub fn panic_any<M: 'static + Any + Send>(msg: M) -> ! {
+    eprintln!("panicked at {}", Location::caller());
+    do_panic(Box::new(msg))
+}