rustc: Switch extern functions to abort by default on panic

src/librustc_codegen_llvm/attributes.rs

@@ -15,14 +15,15 @@ use rustc::hir::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
 use rustc::session::Session;
 use rustc::session::config::Sanitizer;
-use rustc::ty::TyCtxt;
+use rustc::ty::{self, TyCtxt, PolyFnSig};
 use rustc::ty::layout::HasTyCtxt;
 use rustc::ty::query::Providers;
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_target::spec::PanicStrategy;
 use rustc_codegen_ssa::traits::*;
 
+use abi::Abi;
 use attributes;
 use llvm::{self, Attribute};
 use llvm::AttributePlace::Function;
@@ -60,7 +61,7 @@ pub fn emit_uwtable(val: &'ll Value, emit: bool) {
 
 /// Tell LLVM whether the function can or cannot unwind.
 #[inline]
-pub fn unwind(val: &'ll Value, can_unwind: bool) {
+fn unwind(val: &'ll Value, can_unwind: bool) {
     Attribute::NoUnwind.toggle_llfn(Function, val, !can_unwind);
 }
 
@@ -150,9 +151,10 @@ pub fn non_lazy_bind(sess: &Session, llfn: &'ll Value) {
 /// Composite function which sets LLVM attributes for function depending on its AST (`#[attribute]`)
 /// attributes.
 pub fn from_fn_attrs(
-    cx: &CodegenCx<'ll, '_>,
+    cx: &CodegenCx<'ll, 'tcx>,
     llfn: &'ll Value,
     id: Option<DefId>,
+    sig: PolyFnSig<'tcx>,
 ) {
     let codegen_fn_attrs = id.map(|id| cx.tcx.codegen_fn_attrs(id))
         .unwrap_or_else(|| CodegenFnAttrs::new());
@@ -194,28 +196,37 @@ pub fn from_fn_attrs(
             llvm::AttributePlace::ReturnValue, llfn);
     }
 
-    let can_unwind = if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::UNWIND) {
-        Some(true)
+    unwind(llfn, if cx.tcx.sess.panic_strategy() != PanicStrategy::Unwind {
+        // In panic=abort mode we assume nothing can unwind anywhere, so
+        // optimize based on this!
+        false
+    } else if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::UNWIND) {
+        // If a specific #[unwind] attribute is present, use that
+        true
     } else if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND) {
-        Some(false)
-
-    // Perhaps questionable, but we assume that anything defined
-    // *in Rust code* may unwind. Foreign items like `extern "C" {
-    // fn foo(); }` are assumed not to unwind **unless** they have
-    // a `#[unwind]` attribute.
-    } else if id.map(|id| !cx.tcx.is_foreign_item(id)).unwrap_or(false) {
-        Some(true)
-    } else {
-        None
-    };
-
-    match can_unwind {
-        Some(false) => attributes::unwind(llfn, false),
-        Some(true) if cx.tcx.sess.panic_strategy() == PanicStrategy::Unwind => {
-            attributes::unwind(llfn, true);
+        // Special attribute for allocator functions, which can't unwind
+        false
+    } else if let Some(id) = id {
+        let sig = cx.tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
+        if cx.tcx.is_foreign_item(id) {
+            // Foreign items like `extern "C" { fn foo(); }` are assumed not to
+            // unwind
+            false
+        } else if sig.abi != Abi::Rust && sig.abi != Abi::RustCall {
+            // Any items defined in Rust that *don't* have the `extern` ABI are
+            // defined to not unwind. We insert shims to abort if an unwind
+            // happens to enforce this.
+            false
+        } else {
+            // Anything else defined in Rust is assumed that it can possibly
+            // unwind
+            true
         }
-        Some(true) | None => {}
-    }
+    } else {
+        // assume this can possibly unwind, avoiding the application of a
+        // `nounwind` attribute below.
+        true
+    });
 
     // Always annotate functions with the target-cpu they are compiled for.
     // Without this, ThinLTO won't inline Rust functions into Clang generated

src/librustc_codegen_llvm/callee.rs

@@ -94,7 +94,7 @@ pub fn get_fn(
         if instance.def.is_inline(tcx) {
             attributes::inline(cx, llfn, attributes::InlineAttr::Hint);
         }
-        attributes::from_fn_attrs(cx, llfn, Some(instance.def.def_id()));
+        attributes::from_fn_attrs(cx, llfn, Some(instance.def.def_id()), sig);
 
         let instance_def_id = instance.def_id();
 

src/librustc_codegen_llvm/context.rs

@@ -409,7 +409,6 @@ impl MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         ));
 
         let llfn = self.declare_fn("rust_eh_unwind_resume", sig);
-        attributes::unwind(llfn, true);
         attributes::apply_target_cpu_attr(self, llfn);
         unwresume.set(Some(llfn));
         llfn

src/librustc_codegen_llvm/declare.rs

@@ -26,8 +26,7 @@ use rustc::ty::{self, PolyFnSig};
 use rustc::ty::layout::LayoutOf;
 use rustc::session::config::Sanitizer;
 use rustc_data_structures::small_c_str::SmallCStr;
-use rustc_target::spec::PanicStrategy;
-use abi::{Abi, FnType, FnTypeExt};
+use abi::{FnType, FnTypeExt};
 use attributes;
 use context::CodegenCx;
 use type_::Type;
@@ -86,10 +85,6 @@ fn declare_raw_fn(
         _ => {},
     }
 
-    if cx.tcx.sess.panic_strategy() != PanicStrategy::Unwind {
-        attributes::unwind(llfn, false);
-    }
-
     attributes::non_lazy_bind(cx.sess(), llfn);
 
     llfn
@@ -132,10 +127,6 @@ impl DeclareMethods<'tcx> for CodegenCx<'ll, 'tcx> {
             llvm::Attribute::NoReturn.apply_llfn(Function, llfn);
         }
 
-        if sig.abi != Abi::Rust && sig.abi != Abi::RustCall {
-            attributes::unwind(llfn, false);
-        }
-
         fty.apply_attrs_llfn(llfn);
 
         llfn

src/librustc_codegen_llvm/intrinsic.rs

@@ -1081,7 +1081,7 @@ fn gen_fn<'ll, 'tcx>(
         Abi::Rust
     ));
     let llfn = cx.define_internal_fn(name, rust_fn_sig);
-    attributes::from_fn_attrs(cx, llfn, None);
+    attributes::from_fn_attrs(cx, llfn, None, rust_fn_sig);
     let bx = Builder::new_block(cx, llfn, "entry-block");
     codegen(bx);
     llfn

src/librustc_codegen_llvm/mono_item.rs

@@ -82,7 +82,12 @@ impl PreDefineMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         if instance.def.is_inline(self.tcx) {
             attributes::inline(self, lldecl, attributes::InlineAttr::Hint);
         }
-        attributes::from_fn_attrs(self, lldecl, Some(instance.def.def_id()));
+        attributes::from_fn_attrs(
+            self,
+            lldecl,
+            Some(instance.def.def_id()),
+            mono_sig,
+        );
 
         self.instances.borrow_mut().insert(instance, lldecl);
     }

src/librustc_mir/build/mod.rs

@@ -628,12 +628,7 @@ fn should_abort_on_panic<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
     // unwind anyway. Don't stop them.
     let attrs = &tcx.get_attrs(fn_def_id);
     match attr::find_unwind_attr(Some(tcx.sess.diagnostic()), attrs) {
-        None => {
-            // FIXME(rust-lang/rust#48251) -- Had to disable
-            // abort-on-panic for backwards compatibility reasons.
-            false
-        }
-
+        None => true,
         Some(UnwindAttr::Allowed) => false,
         Some(UnwindAttr::Aborts) => true,
     }

src/test/codegen/nounwind-extern.rs

@@ -0,0 +1,16 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -O
+
+#![crate_type = "lib"]
+
+// CHECK: Function Attrs: norecurse nounwind
+pub extern fn foo() {}

src/test/run-pass/abort-on-c-abi.rs

@@ -15,14 +15,11 @@
 // ignore-cloudabi no env and process
 // ignore-emscripten no processes
 
-#![feature(unwind_attributes)]
-
 use std::{env, panic};
 use std::io::prelude::*;
 use std::io;
 use std::process::{Command, Stdio};
 
-#[unwind(aborts)]
 extern "C" fn panic_in_ffi() {
     panic!("Test");
 }

src/test/run-pass/extern/extern-call-deep.rs

@@ -10,6 +10,7 @@
 
 // run-pass
 // ignore-wasm32-bare no libc to test ffi with
+// ignore-emscripten blows the JS stack
 
 #![feature(rustc_private)]