rustc: Always emit the `uwtable` attribute on Windows
This commit alters the translation layer to unconditionally emit the `uwtable` LLVM attribute on Windows regardless of the `no_landing_pads` setting. Previously I believe we omitted this attribute as an optimization when the `-Cpanic=abort` flag was passed, but this unfortunately caused problems for Gecko. It [was discovered] that there was trouble unwinding through Rust functions due to foreign exceptions such as illegal instructions or otherwise in-practice methods used to abort a process. In testing it looked like the major difference between a working binary and a non-working binary is indeed this `uwtable` attribute, but this PR has unfortunately not been thoroughly tested in terms of compiling Gecko with `-C panic=abort` *and* this PR to see whether it works, so this is still somewhat working on just suspicion. [was discovered]: https://bugzilla.mozilla.org/show_bug.cgi?id=1302078
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@ -583,7 +583,24 @@ pub fn trans_instance<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, instance: Instance
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ccx.stats().n_closures.set(ccx.stats().n_closures.get() + 1);
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ccx.stats().n_closures.set(ccx.stats().n_closures.get() + 1);
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if !ccx.sess().no_landing_pads() {
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// The `uwtable` attribute according to LLVM is:
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//
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// This attribute indicates that the ABI being targeted requires that an
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// unwind table entry be produced for this function even if we can show
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// that no exceptions passes by it. This is normally the case for the
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// ELF x86-64 abi, but it can be disabled for some compilation units.
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//
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// Typically when we're compiling with `-C panic=abort` (which implies this
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// `no_landing_pads` check) we don't need `uwtable` because we can't
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// generate any exceptions! On Windows, however, exceptions include other
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// events such as illegal instructions, segfaults, etc. This means that on
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// Windows we end up still needing the `uwtable` attribute even if the `-C
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// panic=abort` flag is passed.
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//
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// You can also find more info on why Windows is whitelisted here in:
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// https://bugzilla.mozilla.org/show_bug.cgi?id=1302078
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if !ccx.sess().no_landing_pads() ||
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ccx.sess().target.target.options.is_like_windows {
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attributes::emit_uwtable(lldecl, true);
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attributes::emit_uwtable(lldecl, true);
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}
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}
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@ -0,0 +1,41 @@
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// ignore-tidy-linelength
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// This test is for *-windows-msvc only.
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// ignore-android
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// ignore-bitrig
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// ignore-macos
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// ignore-dragonfly
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// ignore-freebsd
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// ignore-haiku
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// ignore-ios
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// ignore-linux
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// ignore-netbsd
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// ignore-openbsd
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// ignore-solaris
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// ignore-emscripten
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// compile-flags: -C no-prepopulate-passes -C panic=abort -O
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#![crate_type = "lib"]
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// CHECK: Function Attrs: uwtable
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// CHECK-NEXT: define void @normal_uwtable()
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#[no_mangle]
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pub fn normal_uwtable() {
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}
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// CHECK: Function Attrs: nounwind uwtable
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// CHECK-NEXT: define void @extern_uwtable()
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#[no_mangle]
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pub extern fn extern_uwtable() {
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}
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