rustc: Add official support for weak failure

This commit is part of the ongoing libstd facade efforts (cc #13851). The
compiler now recognizes some language items as "extern { fn foo(...); }" and
will automatically perform the following actions:

1. The foreign function has a pre-defined name.
2. The crate and downstream crates can only be built as rlibs until a crate
   defines the lang item itself.
3. The actual lang item has a pre-defined name.

This is essentially nicer compiler support for the hokey
core-depends-on-std-failure scheme today, but it is implemented the same way.
The details are a little more hidden under the covers.

In addition to failure, this commit promotes the eh_personality and
rust_stack_exhausted functions to official lang items. The compiler can generate
calls to these functions, causing linkage errors if they are left undefined. The
checking for these items is not as precise as it could be. Crates compiling with
`-Z no-landing-pads` will not need the eh_personality lang item, and crates
compiling with no split stacks won't need the stack exhausted lang item. For
ease, however, these items are checked for presence in all final outputs of the
compiler.

It is quite easy to define dummy versions of the functions necessary:

    #[lang = "stack_exhausted"]
    extern fn stack_exhausted() { /* ... */ }

    #[lang = "eh_personality"]
    extern fn eh_personality() { /* ... */ }

cc #11922, rust_stack_exhausted is now a lang item
cc #13851, libcollections is blocked on eh_personality becoming weak

1 files changed, 32 insertions, 6 deletions

diff --git a/src/libstd/rt/stack.rs b/src/libstd/rt/stack.rs
index b9bcd1de8fc..b3be742e1ed 100644
--- a/src/libstd/rt/stack.rs
+++ b/src/libstd/rt/stack.rs
@@ -30,12 +30,9 @@ pub static RED_ZONE: uint = 20 * 1024;
 /// stacks are currently not enabled as segmented stacks, but rather one giant
 /// stack segment. This means that whenever we run out of stack, we want to
 /// truly consider it to be stack overflow rather than allocating a new stack.
-#[no_mangle]      // - this is called from C code
-#[no_split_stack] // - it would be sad for this function to trigger __morestack
-#[doc(hidden)]    // - Function must be `pub` to get exported, but it's
-                  //   irrelevant for documentation purposes.
-#[cfg(not(test))] // in testing, use the original libstd's version
-pub extern "C" fn rust_stack_exhausted() {
+#[cfg(not(test), not(stage0))] // in testing, use the original libstd's version
+#[lang = "stack_exhausted"]
+extern fn stack_exhausted() {
     use option::{Option, None, Some};
     use owned::Box;
     use rt::local::Local;
@@ -106,6 +103,35 @@ pub extern "C" fn rust_stack_exhausted() {
     }
 }
 
+#[no_mangle]      // - this is called from C code
+#[no_split_stack] // - it would be sad for this function to trigger __morestack
+#[doc(hidden)]    // - Function must be `pub` to get exported, but it's
+                  //   irrelevant for documentation purposes.
+#[cfg(stage0, not(test))] // in testing, use the original libstd's version
+pub extern "C" fn rust_stack_exhausted() {
+    use option::{Option, None, Some};
+    use owned::Box;
+    use rt::local::Local;
+    use rt::task::Task;
+    use str::Str;
+    use intrinsics;
+
+    unsafe {
+        let limit = get_sp_limit();
+        record_sp_limit(limit - RED_ZONE / 2);
+        let task: Option<Box<Task>> = Local::try_take();
+        let name = match task {
+            Some(ref task) => {
+                task.name.as_ref().map(|n| n.as_slice())
+            }
+            None => None
+        };
+        let name = name.unwrap_or("<unknown>");
+        rterrln!("task '{}' has overflowed its stack", name);
+        intrinsics::abort();
+    }
+}
+
 #[inline(always)]
 pub unsafe fn record_stack_bounds(stack_lo: uint, stack_hi: uint) {
     // When the old runtime had segmented stacks, it used a calculation that was