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Move #[used] check for Mach-O to rustc_typeck from rustc_codegen_llvm

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Thom Chiovoloni 2022-05-11 01:55:00 -07:00
parent da72295411
commit a64b2a95ff
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GPG Key ID: E2EFD4309E11C8A8
2 changed files with 38 additions and 28 deletions
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34
compiler/rustc_codegen_llvm/src/consts.rs
View File

@ -543,33 +543,13 @@ impl<'ll> StaticMethods for CodegenCx<'ll, '_> {
// in the handling of `.init_array` (the static constructor list) in versions of
// the gold linker (prior to the one released with binutils 2.36).
//
// However, unconditional use of `llvm.compiler.used` caused a nontrivial amount of
// ecosystem breakage, especially on Mach-O targets. To resolve this, we compile it
// as llvm.compiler.used on ELF targets and llvm.used elsewhere, which should be
// equivalent to how we compiled `#[used]` before LLVM 13, as `llvm.used` and
// `llvm.compiler.used` were treated the same on ELF targets prior in earlier LLVM
// versions (additionally, it seems to be how Clang handles `__attribute__((used))`,
// perhaps for similar compatibility-motivated reasons).
//
// See https://github.com/rust-lang/rust/issues/47384#issuecomment-1019080146 and
// following comments for some discussion of this.
//
// The final wrinkle is it's not really clear how to tell if we're going to output
// ELF, so it's been approximated as "not like wasm, osx, or windows", which is
// not exactly correct, but is pretty close and hopefully handles all the platforms
// platforms where old versions of `ld.gold` are likely to show up.
//
// All this is subject to change in the future. Which is a good thing, because this
// probably should be firmed up somehow!
let seems_like_elf = !(self.tcx.sess.target.is_like_osx
|| self.tcx.sess.target.is_like_windows
|| self.tcx.sess.target.is_like_wasm);
if seems_like_elf {
self.add_compiler_used_global(g);
} else {
self.add_used_global(g);
}
// That said, we only ever emit these when compiling for ELF targets, unless
// `#[used(compiler)]` is explicitly requested. This is to avoid similar breakage
// on other targets, in particular MachO targets have *their* static constructor
// lists broken if `llvm.compiler.used` is emitted rather than llvm.used. However,
// that check happens when assigning the `CodegenFnAttrFlags` in `rustc_typeck`,
// so we don't need to take care of it here.
self.add_compiler_used_global(g);
}
if attrs.flags.contains(CodegenFnAttrFlags::USED_LINKER) {
// `USED` and `USED_LINKER` can't be used together.

32
compiler/rustc_typeck/src/collect.rs
View File

@ -2850,7 +2850,37 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: DefId) -> CodegenFnAttrs {
)
.emit();
}
None => codegen_fn_attrs.flags |= CodegenFnAttrFlags::USED,
None => {
// Unfortunately, unconditionally using `llvm.used` causes
// issues in handling `.init_array` with the gold linker,
// but using `llvm.compiler.used` caused a nontrival amount
// of unintentional ecosystem breakage -- particularly on
// Mach-O targets.
//
// As a result, we emit `llvm.compiler.used` only on ELF
// targets. This is somewhat ad-hoc, but actually follows
// our pre-LLVM 13 behavior (prior to the ecosystem
// breakage), and seems to match `clang`'s behavior as well
// (both before and after LLVM 13), possibly because they
// have similar compatibility concerns to us. See
// https://github.com/rust-lang/rust/issues/47384#issuecomment-1019080146
// and following comments for some discussion of this, as
// well as the comments in `rustc_codegen_llvm` where these
// flags are handled.
//
// Anyway, to be clear: this is still up in the air
// somewhat, and is subject to change in the future (which
// is a good thing, because this would ideally be a bit
// more firmed up).
let is_like_elf = !(tcx.sess.target.is_like_osx
|| tcx.sess.target.is_like_windows
|| tcx.sess.target.is_like_wasm);
codegen_fn_attrs.flags = if is_like_elf {
CodegenFnAttrFlags::USED
} else {
CodegenFnAttrFlags::USED_LINKER
};
}
}
} else if attr.has_name(sym::cmse_nonsecure_entry) {
if !matches!(tcx.fn_sig(did).abi(), abi::Abi::C { .. }) {