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Auto merge of #129884 - RalfJung:forbidden-target-features, r=workingjubilee

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mark some target features as 'forbidden' so they cannot be (un)set with -Ctarget-feature

The context for this is https://github.com/rust-lang/rust/issues/116344: some target features change the way floats are passed between functions. Changing those target features is unsound as code compiled for the same target may now use different ABIs.

So this introduces a new concept of "forbidden" target features (on top of the existing "stable " and "unstable" categories), and makes it a hard error to (un)set such a target feature. For now, the x86 and ARM feature `soft-float` is on that list. We'll have to make some effort to collect more relevant features, and similar features from other targets, but that can happen after the basic infrastructure for this landed. (These features are being collected in https://github.com/rust-lang/rust/issues/131799.)

I've made this a warning for now to give people some time to speak up if this would break something.

MCP: https://github.com/rust-lang/compiler-team/issues/780
This commit is contained in:
bors 2024-11-05 16:25:45 +00:00
commit e8c698bb3b
23 changed files with 372 additions and 158 deletions
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14
compiler/rustc_codegen_ssa/src/codegen_attrs.rs
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@ -20,8 +20,8 @@ use rustc_span::symbol::Ident;
use rustc_span::{Span, sym};
use rustc_target::spec::{SanitizerSet, abi};
use crate::errors::{self, MissingFeatures, TargetFeatureDisableOrEnable};
use crate::target_features::{check_target_feature_trait_unsafe, from_target_feature};
use crate::errors;
use crate::target_features::{check_target_feature_trait_unsafe, from_target_feature_attr};
fn linkage_by_name(tcx: TyCtxt<'_>, def_id: LocalDefId, name: &str) -> Linkage {
use rustc_middle::mir::mono::Linkage::*;
@ -73,7 +73,7 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_BUILTINS;
}
let supported_target_features = tcx.supported_target_features(LOCAL_CRATE);
let rust_target_features = tcx.rust_target_features(LOCAL_CRATE);
let mut inline_span = None;
let mut link_ordinal_span = None;
@ -281,10 +281,10 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
check_target_feature_trait_unsafe(tcx, did, attr.span);
}
}
from_target_feature(
from_target_feature_attr(
tcx,
attr,
supported_target_features,
rust_target_features,
&mut codegen_fn_attrs.target_features,
);
}
@ -676,10 +676,10 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
.next()
.map_or_else(|| tcx.def_span(did), |a| a.span);
tcx.dcx()
.create_err(TargetFeatureDisableOrEnable {
.create_err(errors::TargetFeatureDisableOrEnable {
features,
span: Some(span),
missing_features: Some(MissingFeatures),
missing_features: Some(errors::MissingFeatures),
})
.emit();
}