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Auto merge of #128004 - folkertdev:naked-fn-asm, r=Amanieu

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codegen `#[naked]` functions using global asm

tracking issue: https://github.com/rust-lang/rust/issues/90957

Fixes #124375

This implements the approach suggested in the tracking issue: use the existing global assembly infrastructure to emit the body of `#[naked]` functions. The main advantage is that we now have full control over what gets generated, and are no longer dependent on LLVM not sneakily messing with our output (inlining, adding extra instructions, etc).

I discussed this approach with `@Amanieu` and while I think the general direction is correct, there is probably a bunch of stuff that needs to change or move around here. I'll leave some inline comments on things that I'm not sure about.

Combined with https://github.com/rust-lang/rust/pull/127853, if both accepted, I think that resolves all steps from the tracking issue.

r? `@Amanieu`
This commit is contained in:
bors 2024-12-11 21:51:07 +00:00
commit 1daec069fb
18 changed files with 635 additions and 106 deletions
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11
compiler/rustc_codegen_ssa/src/codegen_attrs.rs
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@ -550,6 +550,13 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
}
});
// naked function MUST NOT be inlined! This attribute is required for the rust compiler itself,
// but not for the code generation backend because at that point the naked function will just be
// a declaration, with a definition provided in global assembly.
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
codegen_fn_attrs.inline = InlineAttr::Never;
}
codegen_fn_attrs.optimize = attrs.iter().fold(OptimizeAttr::None, |ia, attr| {
if !attr.has_name(sym::optimize) {
return ia;
@ -634,10 +641,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
}
}
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
codegen_fn_attrs.inline = InlineAttr::Never;
}
// Weak lang items have the same semantics as "std internal" symbols in the
// sense that they're preserved through all our LTO passes and only
// strippable by the linker.