From 0f33e9f2816358a4d8afd02af35bd23a4d6d0857 Mon Sep 17 00:00:00 2001 From: "katelyn a. martin" Date: Thu, 10 Sep 2020 13:38:39 -0400 Subject: [PATCH] implement unwinding abi's (RFC 2945) ### Changes This commit implements unwind ABI's, specified in RFC 2945. We adjust the `rustc_middle::ty::layout::fn_can_unwind` function, used to compute whether or not a `FnAbi` object represents a function that should be able to unwind when `panic=unwind` is in use. Changes are also made to `rustc_mir_build::build::should_abort_on_panic` so that the function ABI is used to determind whether it should abort, assuming that the `panic=unwind` strategy is being used, and no explicit unwind attribute was provided. ### Tests Unit tests, checking that the behavior is correct for `C-unwind`, `stdcall-unwind`, `system-unwind`, and `thiscall-unwind`, are included. These alternative `unwind` ABI strings are specified in RFC 2945, in the "_Other `unwind` ABI strings_" section. Additionally, a test case is included to assert that the LLVM IR generated for an external function defined with the `C-unwind` ABI will be appropriately labeled with the `nounwind` LLVM attribute when the `panic=abort` compilation flag is used. ### Ignore Directives This commit uses `ignore-*` directives in two of our `*-unwind` ABI test cases. Specifically, the `stdcall-unwind` and `thiscall-unwind` test cases ignore architectures that do not support `stdcall` and `thiscall`, respectively. These directives are cribbed from `src/test/ui/c-variadic/variadic-ffi-1.rs` for `stdcall`, and `src/test/ui/extern/extern-thiscall.rs` for `thiscall`. --- compiler/rustc_middle/src/ty/layout.rs | 29 +++++++++------- compiler/rustc_mir_build/src/build/mod.rs | 22 ++++++++++--- .../unwind-abis/c-unwind-abi-panic-abort.rs | 18 ++++++++++ src/test/codegen/unwind-abis/c-unwind-abi.rs | 29 ++++++++++++++++ .../codegen/unwind-abis/stdcall-unwind-abi.rs | 32 ++++++++++++++++++ .../codegen/unwind-abis/system-unwind-abi.rs | 29 ++++++++++++++++ .../unwind-abis/thiscall-unwind-abi.rs | 33 +++++++++++++++++++ 7 files changed, 176 insertions(+), 16 deletions(-) create mode 100644 src/test/codegen/unwind-abis/c-unwind-abi-panic-abort.rs create mode 100644 src/test/codegen/unwind-abis/c-unwind-abi.rs create mode 100644 src/test/codegen/unwind-abis/stdcall-unwind-abi.rs create mode 100644 src/test/codegen/unwind-abis/system-unwind-abi.rs create mode 100644 src/test/codegen/unwind-abis/thiscall-unwind-abi.rs diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs index 2f5380861c4..ee2dffd8bae 100644 --- a/compiler/rustc_middle/src/ty/layout.rs +++ b/compiler/rustc_middle/src/ty/layout.rs @@ -2562,6 +2562,7 @@ fn fn_can_unwind( panic_strategy: PanicStrategy, codegen_fn_attr_flags: CodegenFnAttrFlags, call_conv: Conv, + abi: SpecAbi, ) -> bool { if panic_strategy != PanicStrategy::Unwind { // In panic=abort mode we assume nothing can unwind anywhere, so @@ -2586,17 +2587,16 @@ fn fn_can_unwind( // // 2. A Rust item using a non-Rust ABI (like `extern "C" fn foo() { ... }`). // - // Foreign items (case 1) are assumed to not unwind; it is - // UB otherwise. (At least for now; see also - // rust-lang/rust#63909 and Rust RFC 2753.) - // - // Items defined in Rust with non-Rust ABIs (case 2) are also - // not supposed to unwind. Whether this should be enforced - // (versus stating it is UB) and *how* it would be enforced - // is currently under discussion; see rust-lang/rust#58794. - // - // In either case, we mark item as explicitly nounwind. - false + // In both of these cases, we should refer to the ABI to determine whether or not we + // should unwind. See Rust RFC 2945 for more information on this behavior, here: + // https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md + use SpecAbi::*; + match abi { + C { unwind } | Stdcall { unwind } | System { unwind } | Thiscall { unwind } => { + unwind + } + _ => false, + } } } } @@ -2823,7 +2823,12 @@ where c_variadic: sig.c_variadic, fixed_count: inputs.len(), conv, - can_unwind: fn_can_unwind(cx.tcx().sess.panic_strategy(), codegen_fn_attr_flags, conv), + can_unwind: fn_can_unwind( + cx.tcx().sess.panic_strategy(), + codegen_fn_attr_flags, + conv, + sig.abi, + ), }; fn_abi.adjust_for_abi(cx, sig.abi); debug!("FnAbi::new_internal = {:?}", fn_abi); diff --git a/compiler/rustc_mir_build/src/build/mod.rs b/compiler/rustc_mir_build/src/build/mod.rs index b928458df8e..dd9c859544f 100644 --- a/compiler/rustc_mir_build/src/build/mod.rs +++ b/compiler/rustc_mir_build/src/build/mod.rs @@ -548,7 +548,7 @@ macro_rules! unpack { }}; } -fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, _abi: Abi) -> bool { +fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, abi: Abi) -> bool { // Validate `#[unwind]` syntax regardless of platform-specific panic strategy. let attrs = &tcx.get_attrs(fn_def_id.to_def_id()); let unwind_attr = attr::find_unwind_attr(&tcx.sess, attrs); @@ -558,12 +558,26 @@ fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, _abi: Abi) -> b return false; } - // This is a special case: some functions have a C abi but are meant to - // unwind anyway. Don't stop them. match unwind_attr { - None => false, // FIXME(#58794); should be `!(abi == Abi::Rust || abi == Abi::RustCall)` + // If an `#[unwind]` attribute was found, we should adhere to it. Some(UnwindAttr::Allowed) => false, Some(UnwindAttr::Aborts) => true, + // If no attribute was found and the panic strategy is `unwind`, then we should examine + // the function's ABI string to determine whether it should abort upon panic. + None => { + use Abi::*; + match abi { + // In the case of ABI's that have an `-unwind` equivalent, check whether the ABI + // permits unwinding. If so, we should not abort. Otherwise, we should. + C { unwind } | Stdcall { unwind } | System { unwind } | Thiscall { unwind } => { + !unwind + } + // Rust and `rust-call` functions are allowed to unwind, and should not abort. + Rust | RustCall => false, + // Other ABI's should abort. + _ => true, + } + } } } diff --git a/src/test/codegen/unwind-abis/c-unwind-abi-panic-abort.rs b/src/test/codegen/unwind-abis/c-unwind-abi-panic-abort.rs new file mode 100644 index 00000000000..afd65ff6741 --- /dev/null +++ b/src/test/codegen/unwind-abis/c-unwind-abi-panic-abort.rs @@ -0,0 +1,18 @@ +// compile-flags: -C panic=abort -C opt-level=0 + +// Test that `nounwind` atributes are applied to `C-unwind` extern functions when the +// code is compiled with `panic=abort`. We disable optimizations above to prevent LLVM from +// inferring the attribute. + +#![crate_type = "lib"] +#![feature(c_unwind)] + +// CHECK: @rust_item_that_can_unwind() unnamed_addr #0 { +#[no_mangle] +pub extern "C-unwind" fn rust_item_that_can_unwind() { +} + +// Now, make sure that the LLVM attributes for this functions are correct. First, make +// sure that the first item is correctly marked with the `nounwind` attribute: +// +// CHECK: attributes #0 = { {{.*}}nounwind{{.*}} } diff --git a/src/test/codegen/unwind-abis/c-unwind-abi.rs b/src/test/codegen/unwind-abis/c-unwind-abi.rs new file mode 100644 index 00000000000..f1576536753 --- /dev/null +++ b/src/test/codegen/unwind-abis/c-unwind-abi.rs @@ -0,0 +1,29 @@ +// compile-flags: -C opt-level=0 + +// Test that `nounwind` atributes are correctly applied to exported `C` and `C-unwind` extern +// functions. `C-unwind` functions MUST NOT have this attribute. We disable optimizations above +// to prevent LLVM from inferring the attribute. + +#![crate_type = "lib"] +#![feature(c_unwind)] + +// CHECK: @rust_item_that_cannot_unwind() unnamed_addr #0 { +#[no_mangle] +pub extern "C" fn rust_item_that_cannot_unwind() { +} + +// CHECK: @rust_item_that_can_unwind() unnamed_addr #1 { +#[no_mangle] +pub extern "C-unwind" fn rust_item_that_can_unwind() { +} + +// Now, make some assertions that the LLVM attributes for these functions are correct. First, make +// sure that the first item is correctly marked with the `nounwind` attribute: +// +// CHECK: attributes #0 = { {{.*}}nounwind{{.*}} } +// +// Next, let's assert that the second item, which CAN unwind, does not have this attribute. +// +// CHECK: attributes #1 = { +// CHECK-NOT: nounwind +// CHECK: } diff --git a/src/test/codegen/unwind-abis/stdcall-unwind-abi.rs b/src/test/codegen/unwind-abis/stdcall-unwind-abi.rs new file mode 100644 index 00000000000..ed804ca278d --- /dev/null +++ b/src/test/codegen/unwind-abis/stdcall-unwind-abi.rs @@ -0,0 +1,32 @@ +// compile-flags: -C opt-level=0 +// ignore-arm stdcall isn't supported +// ignore-aarch64 stdcall isn't supported +// ignore-riscv64 stdcall isn't supported + +// Test that `nounwind` atributes are correctly applied to exported `stdcall` and `stdcall-unwind` +// extern functions. `stdcall-unwind` functions MUST NOT have this attribute. We disable +// optimizations above to prevent LLVM from inferring the attribute. + +#![crate_type = "lib"] +#![feature(c_unwind)] + +// CHECK: @rust_item_that_cannot_unwind() unnamed_addr #0 { +#[no_mangle] +pub extern "stdcall" fn rust_item_that_cannot_unwind() { +} + +// CHECK: @rust_item_that_can_unwind() unnamed_addr #1 { +#[no_mangle] +pub extern "stdcall-unwind" fn rust_item_that_can_unwind() { +} + +// Now, make some assertions that the LLVM attributes for these functions are correct. First, make +// sure that the first item is correctly marked with the `nounwind` attribute: +// +// CHECK: attributes #0 = { {{.*}}nounwind{{.*}} } +// +// Next, let's assert that the second item, which CAN unwind, does not have this attribute. +// +// CHECK: attributes #1 = { +// CHECK-NOT: nounwind +// CHECK: } diff --git a/src/test/codegen/unwind-abis/system-unwind-abi.rs b/src/test/codegen/unwind-abis/system-unwind-abi.rs new file mode 100644 index 00000000000..c4d51328352 --- /dev/null +++ b/src/test/codegen/unwind-abis/system-unwind-abi.rs @@ -0,0 +1,29 @@ +// compile-flags: -C opt-level=0 + +// Test that `nounwind` atributes are correctly applied to exported `system` and `system-unwind` +// extern functions. `system-unwind` functions MUST NOT have this attribute. We disable +// optimizations above to prevent LLVM from inferring the attribute. + +#![crate_type = "lib"] +#![feature(c_unwind)] + +// CHECK: @rust_item_that_cannot_unwind() unnamed_addr #0 { +#[no_mangle] +pub extern "system" fn rust_item_that_cannot_unwind() { +} + +// CHECK: @rust_item_that_can_unwind() unnamed_addr #1 { +#[no_mangle] +pub extern "system-unwind" fn rust_item_that_can_unwind() { +} + +// Now, make some assertions that the LLVM attributes for these functions are correct. First, make +// sure that the first item is correctly marked with the `nounwind` attribute: +// +// CHECK: attributes #0 = { {{.*}}nounwind{{.*}} } +// +// Next, let's assert that the second item, which CAN unwind, does not have this attribute. +// +// CHECK: attributes #1 = { +// CHECK-NOT: nounwind +// CHECK: } diff --git a/src/test/codegen/unwind-abis/thiscall-unwind-abi.rs b/src/test/codegen/unwind-abis/thiscall-unwind-abi.rs new file mode 100644 index 00000000000..aaa63ae55c3 --- /dev/null +++ b/src/test/codegen/unwind-abis/thiscall-unwind-abi.rs @@ -0,0 +1,33 @@ +// compile-flags: -C opt-level=0 +// ignore-arm thiscall isn't supported +// ignore-aarch64 thiscall isn't supported +// ignore-riscv64 thiscall isn't supported + +// Test that `nounwind` atributes are correctly applied to exported `thiscall` and +// `thiscall-unwind` extern functions. `thiscall-unwind` functions MUST NOT have this attribute. We +// disable optimizations above to prevent LLVM from inferring the attribute. + +#![crate_type = "lib"] +#![feature(abi_thiscall)] +#![feature(c_unwind)] + +// CHECK: @rust_item_that_cannot_unwind() unnamed_addr #0 { +#[no_mangle] +pub extern "thiscall" fn rust_item_that_cannot_unwind() { +} + +// CHECK: @rust_item_that_can_unwind() unnamed_addr #1 { +#[no_mangle] +pub extern "thiscall-unwind" fn rust_item_that_can_unwind() { +} + +// Now, make some assertions that the LLVM attributes for these functions are correct. First, make +// sure that the first item is correctly marked with the `nounwind` attribute: +// +// CHECK: attributes #0 = { {{.*}}nounwind{{.*}} } +// +// Next, let's assert that the second item, which CAN unwind, does not have this attribute. +// +// CHECK: attributes #1 = { +// CHECK-NOT: nounwind +// CHECK: }