Add unwinding strategy for panics

ctr-std/src/collections/hash/table.rs

@@ -44,7 +44,7 @@ impl TaggedHashUintPtr {
     #[inline]
     unsafe fn new(ptr: *mut HashUint) -> Self {
         debug_assert!(ptr as usize & 1 == 0 || ptr as usize == EMPTY as usize);
-        TaggedHashUintPtr(Unique::new(ptr))
+        TaggedHashUintPtr(Unique::new_unchecked(ptr))
     }
 
     #[inline]
@@ -56,7 +56,7 @@ impl TaggedHashUintPtr {
             } else {
                 usize_ptr &= !1;
             }
-            self.0 = Unique::new(usize_ptr as *mut HashUint)
+            self.0 = Unique::new_unchecked(usize_ptr as *mut HashUint)
         }
     }
 
@@ -877,7 +877,7 @@ impl<K, V> RawTable<K, V> {
                 elems_left: elems_left,
                 marker: marker::PhantomData,
             },
-            table: unsafe { Shared::new(self) },
+            table: Shared::from(self),
             marker: marker::PhantomData,
         }
     }

ctr-std/src/lib.rs

@@ -26,6 +26,7 @@
 #![feature(lang_items)]
 #![feature(macro_reexport)]
 #![feature(needs_drop)]
+#![feature(needs_panic_runtime)]
 #![feature(oom)]
 #![feature(on_unimplemented)]
 #![feature(optin_builtin_traits)]
@@ -45,10 +46,13 @@
 #![feature(unicode)]
 #![feature(unique)]
 #![feature(untagged_unions)]
+#![feature(unwind_attributes)]
 #![feature(zero_one)]
 #![allow(non_camel_case_types, dead_code, unused_features)]
 #![no_std]
 
+#![needs_panic_runtime]
+
 #![cfg_attr(not(stage0), default_lib_allocator)]
 #![stable(feature = "rust1", since = "1.0.0")]
 
@@ -197,20 +201,3 @@ pub mod rt;
 pub mod __rand {
     pub use rand::{thread_rng, ThreadRng, Rng};
 }
-
-// NOTE: These two are "undefined" symbols that LLVM emits but that
-// we never actually use
-#[doc(hidden)]
-
-#[stable(feature = "3ds", since = "1.0.0")]
-#[no_mangle]
-pub unsafe extern "C" fn __aeabi_unwind_cpp_pr0() {
-    intrinsics::unreachable()
-}
-
-#[stable(feature = "3ds", since = "1.0.0")]
-#[doc(hidden)]
-#[no_mangle]
-pub unsafe extern "C" fn __aeabi_unwind_cpp_pr1() {
-    intrinsics::unreachable()
-}

ctr-std/src/panic.rs

@@ -22,8 +22,8 @@ use rc::Rc;
 use sync::{Arc, Mutex, RwLock, atomic};
 use thread::Result;
 
-//#[stable(feature = "panic_hooks", since = "1.10.0")]
-//pub use panicking::{take_hook, set_hook, PanicInfo, Location};
+#[stable(feature = "panic_hooks", since = "1.10.0")]
+pub use panicking::{take_hook, set_hook, PanicInfo, Location};
 
 /// A marker trait which represents "panic safe" types in Rust.
 ///
@@ -112,7 +112,7 @@ pub trait UnwindSafe {}
 /// This is a "helper marker trait" used to provide impl blocks for the
 /// `UnwindSafe` trait, for more information see that documentation.
 #[stable(feature = "catch_unwind", since = "1.9.0")]
-#[rustc_on_unimplemented = "the type {Self} contains interior mutability \
+#[rustc_on_unimplemented = "the type {Self} may contain interior mutability \
                             and a reference may not be safely transferrable \
                             across a catch_unwind boundary"]
 pub trait RefUnwindSafe {}
@@ -388,7 +388,6 @@ pub fn catch_unwind<F: FnOnce() -> R + UnwindSafe, R>(f: F) -> Result<R> {
 /// }
 /// ```
 #[stable(feature = "resume_unwind", since = "1.9.0")]
-// we always abort so I'm pretty sure there's no reason to ever call this
-pub fn resume_unwind(_payload: Box<Any + Send>) -> ! {
-    unimplemented!()
+pub fn resume_unwind(payload: Box<Any + Send>) -> ! {
+    panicking::update_count_then_panic(payload)
 }

ctr-std/src/panicking.rs

@@ -10,16 +10,26 @@
 
 //! Implementation of various bits and pieces of the `panic!` macro and
 //! associated runtime pieces.
+//!
+//! Specifically, this module contains the implementation of:
+//!
+//! * Panic hooks
+//! * Executing a panic up to doing the actual implementation
+//! * Shims around "try"
 
 use io::prelude::*;
 
 use any::Any;
 use cell::RefCell;
-use fmt::{self, Display};
+use fmt;
+use intrinsics;
 use mem;
 use ptr;
 use raw;
+use sys_common::rwlock::RWLock;
 use sys_common::thread_info;
+use sys_common::util;
+use thread;
 
 thread_local! {
     pub static LOCAL_STDERR: RefCell<Option<Box<Write + Send>>> = {
@@ -27,97 +37,416 @@ thread_local! {
     }
 }
 
-///The compiler wants this to be here. Otherwise it won't be happy. And we like happy compilers.
-#[lang = "eh_personality"]
-pub extern fn eh_personality() {}
+#[allow(improper_ctypes)]
+extern {
+    fn __rust_maybe_catch_panic(f: fn(*mut u8),
+                                data: *mut u8,
+                                data_ptr: *mut usize,
+                                vtable_ptr: *mut usize) -> u32;
+    #[unwind]
+    fn __rust_start_panic(data: usize, vtable: usize) -> u32;
+}
 
-/// Determines whether the current thread is unwinding because of panic.
-// Which it won't be, since we still don't have stack unwinding.
-pub fn panicking() -> bool {
-    false
+#[derive(Copy, Clone)]
+enum Hook {
+    Default,
+    Custom(*mut (Fn(&PanicInfo) + 'static + Sync + Send)),
 }
 
-/// Entry point of panic from the libcore crate.
-#[lang = "panic_fmt"]
-pub extern fn rust_begin_panic(msg: fmt::Arguments,
-                               file: &'static str,
-                               line: u32,
-                               col: u32) -> ! {
-    begin_panic_fmt(&msg, &(file, line, col))
+static HOOK_LOCK: RWLock = RWLock::new();
+static mut HOOK: Hook = Hook::Default;
+
+/// Registers a custom panic hook, replacing any that was previously registered.
+///
+/// The panic hook is invoked when a thread panics, but before the panic runtime
+/// is invoked. As such, the hook will run with both the aborting and unwinding
+/// runtimes. The default hook prints a message to standard error and generates
+/// a backtrace if requested, but this behavior can be customized with the
+/// `set_hook` and `take_hook` functions.
+///
+/// The hook is provided with a `PanicInfo` struct which contains information
+/// about the origin of the panic, including the payload passed to `panic!` and
+/// the source code location from which the panic originated.
+///
+/// The panic hook is a global resource.
+///
+/// # Panics
+///
+/// Panics if called from a panicking thread.
+///
+/// # Examples
+///
+/// The following will print "Custom panic hook":
+///
+/// ```should_panic
+/// use std::panic;
+///
+/// panic::set_hook(Box::new(|_| {
+///     println!("Custom panic hook");
+/// }));
+///
+/// panic!("Normal panic");
+/// ```
+#[stable(feature = "panic_hooks", since = "1.10.0")]
+pub fn set_hook(hook: Box<Fn(&PanicInfo) + 'static + Sync + Send>) {
+    if thread::panicking() {
+        panic!("cannot modify the panic hook from a panicking thread");
+    }
+
+    unsafe {
+        HOOK_LOCK.write();
+        let old_hook = HOOK;
+        HOOK = Hook::Custom(Box::into_raw(hook));
+        HOOK_LOCK.write_unlock();
+
+        if let Hook::Custom(ptr) = old_hook {
+            Box::from_raw(ptr);
+        }
+    }
 }
 
-/// The entry point for panicking with a formatted message.
+/// Unregisters the current panic hook, returning it.
 ///
-/// This is designed to reduce the amount of code required at the call
-/// site as much as possible (so that `panic!()` has as low an impact
-/// on (e.g.) the inlining of other functions as possible), by moving
-/// the actual formatting into this shared place.
-#[unstable(feature = "libstd_sys_internals",
-           reason = "used by the panic! macro",
-           issue = "0")]
-#[inline(never)] #[cold]
-pub fn begin_panic_fmt(msg: &fmt::Arguments, file_line_col: &(&'static str, u32, u32)) -> ! {
-    use fmt::Write;
+/// If no custom hook is registered, the default hook will be returned.
+///
+/// # Panics
+///
+/// Panics if called from a panicking thread.
+///
+/// # Examples
+///
+/// The following will print "Normal panic":
+///
+/// ```should_panic
+/// use std::panic;
+///
+/// panic::set_hook(Box::new(|_| {
+///     println!("Custom panic hook");
+/// }));
+///
+/// let _ = panic::take_hook();
+///
+/// panic!("Normal panic");
+/// ```
+#[stable(feature = "panic_hooks", since = "1.10.0")]
+pub fn take_hook() -> Box<Fn(&PanicInfo) + 'static + Sync + Send> {
+    if thread::panicking() {
+        panic!("cannot modify the panic hook from a panicking thread");
+    }
 
-    let mut s = String::new();
-    let _ = s.write_fmt(*msg);
-    begin_panic(s, file_line_col);
+    unsafe {
+        HOOK_LOCK.write();
+        let hook = HOOK;
+        HOOK = Hook::Default;
+        HOOK_LOCK.write_unlock();
+
+        match hook {
+            Hook::Default => Box::new(default_hook),
+            Hook::Custom(ptr) => Box::from_raw(ptr),
+        }
+    }
+}
+
+/// A struct providing information about a panic.
+///
+/// `PanicInfo` structure is passed to a panic hook set by the [`set_hook`]
+/// function.
+///
+/// [`set_hook`]: ../../std/panic/fn.set_hook.html
+///
+/// # Examples
+///
+/// ```should_panic
+/// use std::panic;
+///
+/// panic::set_hook(Box::new(|panic_info| {
+///     println!("panic occured: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
+/// }));
+///
+/// panic!("Normal panic");
+/// ```
+#[stable(feature = "panic_hooks", since = "1.10.0")]
+#[derive(Debug)]
+pub struct PanicInfo<'a> {
+    payload: &'a (Any + Send),
+    location: Location<'a>,
+}
+
+impl<'a> PanicInfo<'a> {
+    /// Returns the payload associated with the panic.
+    ///
+    /// This will commonly, but not always, be a `&'static str` or [`String`].
+    ///
+    /// [`String`]: ../../std/string/struct.String.html
+    ///
+    /// # Examples
+    ///
+    /// ```should_panic
+    /// use std::panic;
+    ///
+    /// panic::set_hook(Box::new(|panic_info| {
+    ///     println!("panic occured: {:?}", panic_info.payload().downcast_ref::<&str>().unwrap());
+    /// }));
+    ///
+    /// panic!("Normal panic");
+    /// ```
+    #[stable(feature = "panic_hooks", since = "1.10.0")]
+    pub fn payload(&self) -> &(Any + Send) {
+        self.payload
+    }
+
+    /// Returns information about the location from which the panic originated,
+    /// if available.
+    ///
+    /// This method will currently always return [`Some`], but this may change
+    /// in future versions.
+    ///
+    /// [`Some`]: ../../std/option/enum.Option.html#variant.Some
+    ///
+    /// # Examples
+    ///
+    /// ```should_panic
+    /// use std::panic;
+    ///
+    /// panic::set_hook(Box::new(|panic_info| {
+    ///     if let Some(location) = panic_info.location() {
+    ///         println!("panic occured in file '{}' at line {}", location.file(), location.line());
+    ///     } else {
+    ///         println!("panic occured but can't get location information...");
+    ///     }
+    /// }));
+    ///
+    /// panic!("Normal panic");
+    /// ```
+    #[stable(feature = "panic_hooks", since = "1.10.0")]
+    pub fn location(&self) -> Option<&Location> {
+        Some(&self.location)
+    }
+}
+
+/// A struct containing information about the location of a panic.
+///
+/// This structure is created by the [`location`] method of [`PanicInfo`].
+///
+/// [`location`]: ../../std/panic/struct.PanicInfo.html#method.location
+/// [`PanicInfo`]: ../../std/panic/struct.PanicInfo.html
+///
+/// # Examples
+///
+/// ```should_panic
+/// use std::panic;
+///
+/// panic::set_hook(Box::new(|panic_info| {
+///     if let Some(location) = panic_info.location() {
+///         println!("panic occured in file '{}' at line {}", location.file(), location.line());
+///     } else {
+///         println!("panic occured but can't get location information...");
+///     }
+/// }));
+///
+/// panic!("Normal panic");
+/// ```
+#[derive(Debug)]
+#[stable(feature = "panic_hooks", since = "1.10.0")]
+pub struct Location<'a> {
+    file: &'a str,
+    line: u32,
+    col: u32,
+}
+
+impl<'a> Location<'a> {
+    /// Returns the name of the source file from which the panic originated.
+    ///
+    /// # Examples
+    ///
+    /// ```should_panic
+    /// use std::panic;
+    ///
+    /// panic::set_hook(Box::new(|panic_info| {
+    ///     if let Some(location) = panic_info.location() {
+    ///         println!("panic occured in file '{}'", location.file());
+    ///     } else {
+    ///         println!("panic occured but can't get location information...");
+    ///     }
+    /// }));
+    ///
+    /// panic!("Normal panic");
+    /// ```
+    #[stable(feature = "panic_hooks", since = "1.10.0")]
+    pub fn file(&self) -> &str {
+        self.file
+    }
+
+    /// Returns the line number from which the panic originated.
+    ///
+    /// # Examples
+    ///
+    /// ```should_panic
+    /// use std::panic;
+    ///
+    /// panic::set_hook(Box::new(|panic_info| {
+    ///     if let Some(location) = panic_info.location() {
+    ///         println!("panic occured at line {}", location.line());
+    ///     } else {
+    ///         println!("panic occured but can't get location information...");
+    ///     }
+    /// }));
+    ///
+    /// panic!("Normal panic");
+    /// ```
+    #[stable(feature = "panic_hooks", since = "1.10.0")]
+    pub fn line(&self) -> u32 {
+        self.line
+    }
+
+    /// Returns the column from which the panic originated.
+    ///
+    /// # Examples
+    ///
+    /// ```should_panic
+    /// #![feature(panic_col)]
+    /// use std::panic;
+    ///
+    /// panic::set_hook(Box::new(|panic_info| {
+    ///     if let Some(location) = panic_info.location() {
+    ///         println!("panic occured at column {}", location.column());
+    ///     } else {
+    ///         println!("panic occured but can't get location information...");
+    ///     }
+    /// }));
+    ///
+    /// panic!("Normal panic");
+    /// ```
+    #[unstable(feature = "panic_col", reason = "recently added", issue = "42939")]
+    pub fn column(&self) -> u32 {
+        self.col
+    }
 }
 
-// Citra doesn't support the Error applet yet
 #[cfg(feature = "citra")]
-#[unstable(feature = "libstd_sys_internals",
-           reason = "used by the panic! macro",
-           issue = "0")]
-#[inline(never)] #[cold]
-pub fn begin_panic<M: Any + Send + Display>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
-    let msg = Box::new(msg);
-    let (file, line, col) = *file_line_col;
+fn default_hook(info: &PanicInfo) {
+    #[cfg(feature = "backtrace")]
+    use sys_common::backtrace;
+
+    // If this is a double panic, make sure that we print a backtrace
+    // for this panic. Otherwise only print it if logging is enabled.
+    #[cfg(feature = "backtrace")]
+    let log_backtrace = {
+        let panics = update_panic_count(0);
+
+        if panics >= 2 {
+            Some(backtrace::PrintFormat::Full)
+        } else {
+            backtrace::log_enabled()
+        }
+    };
+
+    let file = info.location.file;
+    let line = info.location.line;
+    let col = info.location.col;
+
+    let msg = match info.payload.downcast_ref::<&'static str>() {
+        Some(s) => *s,
+        None => match info.payload.downcast_ref::<String>() {
+            Some(s) => &s[..],
+            None => "Box<Any>",
+        }
+    };
 
     // 3DS-specific code begins here
-    use libctru::{consoleInit, consoleClear, gfxScreen_t, threadGetCurrent};
+    use libctru::{consoleInit, consoleDebugInit, debugDevice,
+                  consoleClear, gfxScreen_t, threadGetCurrent};
+    use sys::stdio::Stderr;
+
+    let mut err = Stderr::new().ok();
+    let thread = thread_info::current_thread();
+    let name;
 
     unsafe {
-        // Set up a new console, overwriting whatever was on the top screen
+        // Set up a new console, overwriting whatever was on the bottom screen
         // before we started panicking
-        let _console = consoleInit(gfxScreen_t::GFX_TOP, ptr::null_mut());
+        let _console = consoleInit(gfxScreen_t::GFX_BOTTOM, ptr::null_mut());
         consoleClear();
+        consoleDebugInit(debugDevice::debugDevice_CONSOLE);
 
         // Determine thread name
-        let thread = thread_info::current_thread();
-        let name = thread.as_ref()
+        name = thread.as_ref()
             .and_then(|t| t.name())
             .unwrap_or(if threadGetCurrent() == ptr::null_mut() {"main"} else {"<unnamed>"});
+    }
+
+    let write = |err: &mut ::io::Write| {
+        let _ = writeln!(err, "thread '{}' panicked at '{}', {}:{}:{}",
+                         name, msg, file, line, col);
 
-        println!("thread '{}' panicked at '{}', {}:{}:{}",
-                 name, msg, file, line, col);
+        #[cfg(feature = "backtrace")]
+        {
+            use sync::atomic::{AtomicBool, Ordering};
 
-        // Citra seems to ignore calls to svcExitProcess, and libc::abort()
-        // causes it to lock up and fill the console with endless debug statements.
-        // So instead of terminating the program, we just let it spin in the following
-        // loop. This means that any background threads might continue to run after
-        // this thread panics, but there's not a lot we can do about that currently.
-        loop { }
+            static FIRST_PANIC: AtomicBool = AtomicBool::new(true);
+
+            if let Some(format) = log_backtrace {
+                let _ = backtrace::print(err, format);
+            } else if FIRST_PANIC.compare_and_swap(true, false, Ordering::SeqCst) {
+                let _ = writeln!(err, "note: Run with `RUST_BACKTRACE=1` for a backtrace.");
+            }
+        }
+    };
+
+    let prev = LOCAL_STDERR.with(|s| s.borrow_mut().take());
+    match (prev, err.as_mut()) {
+        (Some(mut stderr), _) => {
+            write(&mut *stderr);
+            let mut s = Some(stderr);
+            LOCAL_STDERR.with(|slot| {
+                *slot.borrow_mut() = s.take();
+            });
+        }
+        (None, Some(ref mut err)) => { write(err) }
+        _ => {}
     }
+    // Citra will crash and die horribly if we allow it to go further than this,
+    // So we just trap control flow in this loop instead. You'll still see the panic
+    // message, and Citra won't die quite as horribly. It's a win-win! Well, mostly.
+    loop { }
 }
 
 #[cfg(not(feature = "citra"))]
-#[unstable(feature = "libstd_sys_internals",
-           reason = "used by the panic! macro",
-           issue = "0")]
-#[inline(never)] #[cold]
-pub fn begin_panic<M: Any + Send + Display>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
-    let msg = Box::new(msg);
-    let (file, line, col) = *file_line_col;
+fn default_hook(info: &PanicInfo) {
+    #[cfg(feature = "backtrace")]
+    use sys_common::backtrace;
+
+    // If this is a double panic, make sure that we print a backtrace
+    // for this panic. Otherwise only print it if logging is enabled.
+    #[cfg(feature = "backtrace")]
+    let log_backtrace = {
+        let panics = update_panic_count(0);
+
+        if panics >= 2 {
+            Some(backtrace::PrintFormat::Full)
+        } else {
+            backtrace::log_enabled()
+        }
+    };
+
+    let file = info.location.file;
+    let line = info.location.line;
+    let col = info.location.col;
+
+    let msg = match info.payload.downcast_ref::<&'static str>() {
+        Some(s) => *s,
+        None => match info.payload.downcast_ref::<String>() {
+            Some(s) => &s[..],
+            None => "Box<Any>",
+        }
+    };
 
     // 3DS-specific code begins here
-    use libctru::{errorInit, errorText, errorDisp,
-                  APT_HardwareResetAsync, svcExitProcess, threadGetCurrent,
+    use libctru::{errorInit, errorText, errorDisp, threadGetCurrent,
                   errorConf, errorType, CFG_Language};
     use libc;
 
     unsafe {
-        // Determine thread name
         let thread = thread_info::current_thread();
         let name = thread.as_ref()
             .and_then(|t| t.name())
@@ -126,6 +455,7 @@ pub fn begin_panic<M: Any + Send + Display>(msg: M, file_line_col: &(&'static st
         // Setup error payload
         let error_text = format!("thread '{}' panicked at '{}', {}:{}:{}",
                                  name, msg, file, line, col);
+
         let mut error_conf: errorConf = mem::uninitialized();
         errorInit(&mut error_conf,
                   errorType::ERROR_TEXT_WORD_WRAP,
@@ -134,16 +464,26 @@ pub fn begin_panic<M: Any + Send + Display>(msg: M, file_line_col: &(&'static st
 
         // Display error
         errorDisp(&mut error_conf);
+    }
+}
 
-        // Now that we're all done printing, it's time to exit the program.
-        // We don't have stack unwinding yet, so let's just trigger a reboot
-        APT_HardwareResetAsync();
+#[cfg(not(test))]
+#[doc(hidden)]
+#[unstable(feature = "update_panic_count", issue = "0")]
+pub fn update_panic_count(amt: isize) -> usize {
+    use cell::Cell;
+    thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }
 
-        // If rebooting fails for some reason, we extra-forcibly end the program
-        svcExitProcess()
-    }
+    PANIC_COUNT.with(|c| {
+        let next = (c.get() as isize + amt) as usize;
+        c.set(next);
+        return next
+    })
 }
 
+#[cfg(test)]
+pub use realstd::rt::update_panic_count;
+
 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
 pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<Any + Send>> {
     #[allow(unions_with_drop_fields)]
@@ -209,29 +549,129 @@ pub unsafe fn try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<Any + Send>> {
     }
 }
 
-#[cfg(not(test))]
-#[doc(hidden)]
-#[unstable(feature = "update_panic_count", issue = "0")]
-pub fn update_panic_count(amt: isize) -> usize {
-    use cell::Cell;
-    thread_local! { static PANIC_COUNT: Cell<usize> = Cell::new(0) }
+/// Determines whether the current thread is unwinding because of panic.
+pub fn panicking() -> bool {
+    update_panic_count(0) != 0
+}
 
-    PANIC_COUNT.with(|c| {
-        let next = (c.get() as isize + amt) as usize;
-        c.set(next);
-        return next
-    })
+/// Entry point of panic from the libcore crate.
+#[lang = "panic_fmt"]
+#[unwind]
+pub extern fn rust_begin_panic(msg: fmt::Arguments,
+                               file: &'static str,
+                               line: u32,
+                               col: u32) -> ! {
+    begin_panic_fmt(&msg, &(file, line, col))
 }
 
-// *Implementation borrowed from the libpanic_abort crate*
-//
-// Rust's "try" function, but if we're aborting on panics we just call the
-// function as there's nothing else we need to do here.
-#[allow(improper_ctypes)]
-extern fn __rust_maybe_catch_panic(f: fn(*mut u8),
-                                data: *mut u8,
-                                _data_ptr: *mut usize,
-								_vtable_ptr: *mut usize) -> u32 {
-    f(data);
-    0
+/// The entry point for panicking with a formatted message.
+///
+/// This is designed to reduce the amount of code required at the call
+/// site as much as possible (so that `panic!()` has as low an impact
+/// on (e.g.) the inlining of other functions as possible), by moving
+/// the actual formatting into this shared place.
+#[unstable(feature = "libstd_sys_internals",
+           reason = "used by the panic! macro",
+           issue = "0")]
+#[inline(never)] #[cold]
+pub fn begin_panic_fmt(msg: &fmt::Arguments,
+                       file_line_col: &(&'static str, u32, u32)) -> ! {
+    use fmt::Write;
+
+    // We do two allocations here, unfortunately. But (a) they're
+    // required with the current scheme, and (b) we don't handle
+    // panic + OOM properly anyway (see comment in begin_panic
+    // below).
+
+    let mut s = String::new();
+    let _ = s.write_fmt(*msg);
+    begin_panic(s, file_line_col)
+}
+
+/// This is the entry point of panicking for panic!() and assert!().
+#[unstable(feature = "libstd_sys_internals",
+           reason = "used by the panic! macro",
+           issue = "0")]
+#[inline(never)] #[cold] // avoid code bloat at the call sites as much as possible
+pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
+    // Note that this should be the only allocation performed in this code path.
+    // Currently this means that panic!() on OOM will invoke this code path,
+    // but then again we're not really ready for panic on OOM anyway. If
+    // we do start doing this, then we should propagate this allocation to
+    // be performed in the parent of this thread instead of the thread that's
+    // panicking.
+
+    rust_panic_with_hook(Box::new(msg), file_line_col)
+}
+
+/// Executes the primary logic for a panic, including checking for recursive
+/// panics and panic hooks.
+///
+/// This is the entry point or panics from libcore, formatted panics, and
+/// `Box<Any>` panics. Here we'll verify that we're not panicking recursively,
+/// run panic hooks, and then delegate to the actual implementation of panics.
+#[inline(never)]
+#[cold]
+fn rust_panic_with_hook(msg: Box<Any + Send>,
+                        file_line_col: &(&'static str, u32, u32)) -> ! {
+    let (file, line, col) = *file_line_col;
+
+    let panics = update_panic_count(1);
+
+    // If this is the third nested call (e.g. panics == 2, this is 0-indexed),
+    // the panic hook probably triggered the last panic, otherwise the
+    // double-panic check would have aborted the process. In this case abort the
+    // process real quickly as we don't want to try calling it again as it'll
+    // probably just panic again.
+    if panics > 2 {
+        util::dumb_print(format_args!("thread panicked while processing \
+                                       panic. aborting.\n"));
+        unsafe { intrinsics::abort() }
+    }
+
+    unsafe {
+        let info = PanicInfo {
+            payload: &*msg,
+            location: Location {
+                file,
+                line,
+                col,
+            },
+        };
+        HOOK_LOCK.read();
+        match HOOK {
+            Hook::Default => default_hook(&info),
+            Hook::Custom(ptr) => (*ptr)(&info),
+        }
+        HOOK_LOCK.read_unlock();
+    }
+
+    if panics > 1 {
+        // If a thread panics while it's already unwinding then we
+        // have limited options. Currently our preference is to
+        // just abort. In the future we may consider resuming
+        // unwinding or otherwise exiting the thread cleanly.
+        util::dumb_print(format_args!("thread panicked while panicking. \
+                                       aborting.\n"));
+        unsafe { intrinsics::abort() }
+    }
+
+    rust_panic(msg)
+}
+
+/// Shim around rust_panic. Called by resume_unwind.
+pub fn update_count_then_panic(msg: Box<Any + Send>) -> ! {
+    update_panic_count(1);
+    rust_panic(msg)
+}
+
+/// A private no-mangle function on which to slap yer breakpoints.
+#[no_mangle]
+#[allow(private_no_mangle_fns)] // yes we get it, but we like breakpoints
+pub fn rust_panic(msg: Box<Any + Send>) -> ! {
+    let code = unsafe {
+        let obj = mem::transmute::<_, raw::TraitObject>(msg);
+        __rust_start_panic(obj.data as usize, obj.vtable as usize)
+    };
+    rtabort!("failed to initiate panic, error {}", code)
 }

ctr-std/src/rt.rs

@@ -22,6 +22,7 @@
             issue = "0")]
 #![doc(hidden)]
 
+use panic;
 use mem;
 
 // Reexport some of our utilities which are expected by other crates.
@@ -31,6 +32,8 @@ pub use panicking::{begin_panic, begin_panic_fmt};
 #[lang = "start"]
 #[allow(unused_variables)]
 fn lang_start(main: *const u8, argc: isize, argv: *const *const u8) -> isize {
-    unsafe { mem::transmute::<_, fn()>(main)(); }
+    let _ = unsafe {
+        panic::catch_unwind(mem::transmute::<_, fn()>(main))
+    };
     0
 }

ctr-std/src/sys_common/mod.rs

@@ -77,6 +77,10 @@ pub fn at_exit<F: FnOnce() + Send + 'static>(f: F) -> Result<(), ()> {
     if at_exit_imp::push(Box::new(f)) {Ok(())} else {Err(())}
 }
 
+macro_rules! rtabort {
+    ($($t:tt)*) => (::sys_common::util::abort(format_args!($($t)*)))
+}
+
 // Computes (value*numer)/denom without overflow, as long as both
 // (numer*denom) and the overall result fit into i64 (which is the case
 // for our time conversions).

examples/.cargo/config

@@ -10,6 +10,9 @@ rustflags = [
     "-Clink-arg=-mtune=mpcore",
     "-Clink-arg=-mfpu=vfp",
     "-Clink-arg=-mtp=soft",
+    "-Clink-arg=-z",
+    "-Clink-arg=muldefs",
+    "-Clink-arg=-lgcc",
     "-Clink-arg=-lsysbase",
     "-Clink-arg=-lc"
 ]

examples/3ds.json

@@ -14,6 +14,5 @@
   "relocation-model": "static",
   "executables": true,
   "exe-suffix": ".elf",
-  "panic-strategy": "abort",
   "linker-flavor": "gcc"
 }

examples/Cargo.toml

@@ -5,5 +5,9 @@ version = "0.1.0"
 [dependencies]
 ctru-rs = { path = "../ctru-rs" }
 
+
+[profile.dev]
+lto = true
+
 [profile.release]
 lto = true

examples/Xargo.toml

@@ -1,5 +1,7 @@
 [dependencies.collections]
 [dependencies.rand]
+[dependencies.panic_abort]
+[dependencies.panic_unwind]
 
 [dependencies.std]
 path = "../ctr-std"