respect declared unsafety

the `#[entry]` and `#[exception]` attributes ignored the declared unsafety and
always expanded to a safe function. This caused the following valid code to
error at compile time:

``` rust
 #[entry]
unsafe fn main() -> ! {
    foo();
    //~^ ERROR call to unsafe function is unsafe and requires unsafe function or block

    loop {}
}

unsafe fn foo() {}
```

1 files changed, 36 insertions, 0 deletions

diff --git a/cortex-m-rt/examples/unsafety.rs b/cortex-m-rt/examples/unsafety.rs
new file mode 100644
index 0000000..a9f0234
--- /dev/null
+++ b/cortex-m-rt/examples/unsafety.rs
@@ -0,0 +1,36 @@
+//! Checks that the declared unsafety is respected by the attributes
+
+#![deny(warnings)]
+#![no_main]
+#![no_std]
+
+extern crate cortex_m_rt;
+extern crate panic_semihosting;
+
+use cortex_m_rt::{entry, exception, ExceptionFrame};
+
+#[entry]
+unsafe fn main() -> ! {
+    foo();
+
+    loop {}
+}
+
+#[exception]
+unsafe fn DefaultHandler(_irqn: i16) {
+    foo();
+}
+
+#[exception]
+unsafe fn HardFault(_ef: &ExceptionFrame) -> ! {
+    foo();
+
+    loop {}
+}
+
+#[exception]
+unsafe fn SysTick() {
+    foo();
+}
+
+unsafe fn foo() {}