bjoernager/rust
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mark some target features as 'forbidden' so they cannot be (un)set

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For now, this is just a warning, but should become a hard error in the future
This commit is contained in:
Ralf Jung 2024-09-02 11:45:59 +02:00
parent 2dece5bb62
commit ffad9aac27
23 changed files with 372 additions and 158 deletions
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117
compiler/rustc_codegen_llvm/src/llvm_util.rs
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@ -16,12 +16,12 @@ use rustc_session::Session;
use rustc_session::config::{PrintKind, PrintRequest};
use rustc_span::symbol::Symbol;
use rustc_target::spec::{MergeFunctions, PanicStrategy, SmallDataThresholdSupport};
use rustc_target::target_features::{RUSTC_SPECIAL_FEATURES, RUSTC_SPECIFIC_FEATURES};
use rustc_target::target_features::{RUSTC_SPECIAL_FEATURES, RUSTC_SPECIFIC_FEATURES, Stability};
use crate::back::write::create_informational_target_machine;
use crate::errors::{
FixedX18InvalidArch, InvalidTargetFeaturePrefix, PossibleFeature, UnknownCTargetFeature,
UnknownCTargetFeaturePrefix, UnstableCTargetFeature,
FixedX18InvalidArch, ForbiddenCTargetFeature, InvalidTargetFeaturePrefix, PossibleFeature,
UnknownCTargetFeature, UnknownCTargetFeaturePrefix, UnstableCTargetFeature,
};
use crate::llvm;
@ -280,19 +280,29 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
}
}
/// Used to generate cfg variables and apply features
/// Must express features in the way Rust understands them
/// Used to generate cfg variables and apply features.
/// Must express features in the way Rust understands them.
///
/// We do not have to worry about RUSTC_SPECIFIC_FEATURES here, those are handled outside codegen.
pub fn target_features(sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
let mut features = vec![];
let mut features: FxHashSet<Symbol> = Default::default();
// Add base features for the target
// Add base features for the target.
// We do *not* add the -Ctarget-features there, and instead duplicate the logic for that below.
// The reason is that if LLVM considers a feature implied but we do not, we don't want that to
// show up in `cfg`. That way, `cfg` is entirely under our control -- except for the handling of
// the target CPU, that is still expanded to target features (with all their implied features) by
// LLVM.
let target_machine = create_informational_target_machine(sess, true);
// Compute which of the known target features are enabled in the 'base' target machine.
// We only consider "supported" features; "forbidden" features are not reflected in `cfg` as of now.
features.extend(
sess.target
.supported_target_features()
.rust_target_features()
.iter()
.filter(|(_, gate, _)| gate.is_supported())
.filter(|(feature, _, _)| {
// skip checking special features, as LLVM may not understands them
// skip checking special features, as LLVM may not understand them
if RUSTC_SPECIAL_FEATURES.contains(feature) {
return true;
}
@ -323,7 +333,12 @@ pub fn target_features(sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
if enabled {
features.extend(sess.target.implied_target_features(std::iter::once(feature)));
} else {
// We don't care about the order in `features` since the only thing we use it for is the
// `features.contains` below.
#[allow(rustc::potential_query_instability)]
features.retain(|f| {
// Keep a feature if it does not imply `feature`. Or, equivalently,
// remove the reverse-dependencies of `feature`.
!sess.target.implied_target_features(std::iter::once(*f)).contains(&feature)
});
}
@ -331,8 +346,9 @@ pub fn target_features(sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
// Filter enabled features based on feature gates
sess.target
.supported_target_features()
.rust_target_features()
.iter()
.filter(|(_, gate, _)| gate.is_supported())
.filter_map(|&(feature, gate, _)| {
if sess.is_nightly_build() || allow_unstable || gate.is_stable() {
Some(feature)
@ -392,9 +408,13 @@ fn print_target_features(out: &mut String, sess: &Session, tm: &llvm::TargetMach
let mut known_llvm_target_features = FxHashSet::<&'static str>::default();
let mut rustc_target_features = sess
.target
.supported_target_features()
.rust_target_features()
.iter()
.filter_map(|(feature, _gate, _implied)| {
.filter_map(|(feature, gate, _implied)| {
if !gate.is_supported() {
// Only list (experimentally) supported features.
return None;
}
// LLVM asserts that these are sorted. LLVM and Rust both use byte comparison for these
// strings.
let llvm_feature = to_llvm_features(sess, *feature)?.llvm_feature_name;
@ -567,7 +587,7 @@ pub(crate) fn global_llvm_features(
// -Ctarget-features
if !only_base_features {
let supported_features = sess.target.supported_target_features();
let known_features = sess.target.rust_target_features();
let mut featsmap = FxHashMap::default();
// insert implied features
@ -601,50 +621,53 @@ pub(crate) fn global_llvm_features(
}
};
// Get the backend feature name, if any.
// This excludes rustc-specific features, which do not get passed to LLVM.
let feature = backend_feature_name(sess, s)?;
// Warn against use of LLVM specific feature names and unstable features on the CLI.
if diagnostics {
let feature_state = supported_features.iter().find(|&&(v, _, _)| v == feature);
if feature_state.is_none() {
let rust_feature =
supported_features.iter().find_map(|&(rust_feature, _, _)| {
let llvm_features = to_llvm_features(sess, rust_feature)?;
if llvm_features.contains(feature)
&& !llvm_features.contains(rust_feature)
{
Some(rust_feature)
} else {
None
let feature_state = known_features.iter().find(|&&(v, _, _)| v == feature);
match feature_state {
None => {
let rust_feature =
known_features.iter().find_map(|&(rust_feature, _, _)| {
let llvm_features = to_llvm_features(sess, rust_feature)?;
if llvm_features.contains(feature)
&& !llvm_features.contains(rust_feature)
{
Some(rust_feature)
} else {
None
}
});
let unknown_feature = if let Some(rust_feature) = rust_feature {
UnknownCTargetFeature {
feature,
rust_feature: PossibleFeature::Some { rust_feature },
}
});
let unknown_feature = if let Some(rust_feature) = rust_feature {
UnknownCTargetFeature {
feature,
rust_feature: PossibleFeature::Some { rust_feature },
}
} else {
UnknownCTargetFeature { feature, rust_feature: PossibleFeature::None }
};
sess.dcx().emit_warn(unknown_feature);
} else if feature_state
.is_some_and(|(_name, feature_gate, _implied)| !feature_gate.is_stable())
{
// An unstable feature. Warn about using it.
sess.dcx().emit_warn(UnstableCTargetFeature { feature });
} else {
UnknownCTargetFeature {
feature,
rust_feature: PossibleFeature::None,
}
};
sess.dcx().emit_warn(unknown_feature);
}
Some((_, Stability::Stable, _)) => {}
Some((_, Stability::Unstable(_), _)) => {
// An unstable feature. Warn about using it.
sess.dcx().emit_warn(UnstableCTargetFeature { feature });
}
Some((_, Stability::Forbidden { reason }, _)) => {
sess.dcx().emit_warn(ForbiddenCTargetFeature { feature, reason });
}
}
}
if diagnostics {
// FIXME(nagisa): figure out how to not allocate a full hashset here.
featsmap.insert(feature, enable_disable == '+');
}
// rustc-specific features do not get passed down to LLVM…
if RUSTC_SPECIFIC_FEATURES.contains(&feature) {
return None;
}
// ... otherwise though we run through `to_llvm_features` when
// We run through `to_llvm_features` when
// passing requests down to LLVM. This means that all in-language
// features also work on the command line instead of having two
// different names when the LLVM name and the Rust name differ.