Add support for x86-interrupt calling convention

Tracking issue: https://github.com/rust-lang/rust/issues/40180

This calling convention can be used for definining interrupt handlers on
32-bit and 64-bit x86 targets. The compiler then uses `iret` instead of
`ret` for returning and ensures that all registers are restored to their
original values.

Usage:

```
extern "x86-interrupt" fn handler(stack_frame: &ExceptionStackFrame) {…}
```

for interrupts and exceptions without error code and

```
extern "x86-interrupt" fn page_fault_handler(stack_frame: &ExceptionStackFrame,
                                             error_code: u64) {…}
```

for exceptions that push an error code (e.g., page faults or general
protection faults). The programmer must ensure that the correct version
is used for each interrupt.

For more details see the [LLVM PR][1] and the corresponding [proposal][2].

[1]: https://reviews.llvm.org/D15567
[2]: http://lists.llvm.org/pipermail/cfe-dev/2015-September/045171.html

2 files changed, 9 insertions, 0 deletions

diff --git a/src/libsyntax/abi.rs b/src/libsyntax/abi.rs
index 42f3aa5ffd6..30641515a41 100644
--- a/src/libsyntax/abi.rs
+++ b/src/libsyntax/abi.rs
@@ -25,6 +25,7 @@ pub enum Abi {
     SysV64,
     PtxKernel,
     Msp430Interrupt,
+    X86Interrupt,
 
     // Multiplatform / generic ABIs
     Rust,
@@ -59,6 +60,7 @@ const AbiDatas: &'static [AbiData] = &[
     AbiData {abi: Abi::SysV64, name: "sysv64", generic: false },
     AbiData {abi: Abi::PtxKernel, name: "ptx-kernel", generic: false },
     AbiData {abi: Abi::Msp430Interrupt, name: "msp430-interrupt", generic: false },
+    AbiData {abi: Abi::X86Interrupt, name: "x86-interrupt", generic: false },
 
     // Cross-platform ABIs
     AbiData {abi: Abi::Rust, name: "Rust", generic: true },
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index c2b72edb66c..78f13c18dc1 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -330,6 +330,9 @@ declare_features! (
     // Used to identify crates that contain sanitizer runtimes
     // rustc internal
     (active, sanitizer_runtime, "1.17.0", None),
+
+    // `extern "x86-interrupt" fn()`
+    (active, abi_x86_interrupt, "1.17.0", Some(40180)),
 );
 
 declare_features! (
@@ -1036,6 +1039,10 @@ impl<'a> PostExpansionVisitor<'a> {
                 gate_feature_post!(&self, abi_msp430_interrupt, span,
                                    "msp430-interrupt ABI is experimental and subject to change");
             },
+            Abi::X86Interrupt => {
+                gate_feature_post!(&self, abi_x86_interrupt, span,
+                                   "x86-interrupt ABI is experimental and subject to change");
+            },
             // Stable
             Abi::Cdecl |
             Abi::Stdcall |