compiler/rustc_middle/src/middle/codegen_fn_attrs.rs

use std::borrow::Cow;

use rustc_abi::Align;
use rustc_hir::attrs::{InlineAttr, InstructionSetAttr, Linkage, OptimizeAttr, RtsanSetting};
use rustc_hir::def_id::DefId;
use rustc_macros::{StableHash, TyDecodable, TyEncodable};
use rustc_span::Symbol;
use rustc_target::spec::SanitizerSet;

use crate::mono::Visibility;
use crate::ty::{InstanceKind, ShimKind, TyCtxt};

impl<'tcx> TyCtxt<'tcx> {
    pub fn codegen_instance_attrs(
        self,
        instance_kind: InstanceKind<'_>,
    ) -> Cow<'tcx, CodegenFnAttrs> {
        // NOTE: we try to not clone the `CodegenFnAttrs` when that is not needed.
        // The `to_mut` method used below clones the inner value.
        let mut attrs = Cow::Borrowed(self.codegen_fn_attrs(instance_kind.def_id()));

        // Drop the `#[naked]` attribute on non-item `InstanceKind`s, like the shims that
        // are generated for indirect function calls.
        if !matches!(instance_kind, InstanceKind::Item(_)) {
            if attrs.flags.contains(CodegenFnAttrFlags::NAKED) {
                attrs.to_mut().flags.remove(CodegenFnAttrFlags::NAKED);
            }
        }

        // A shim created by `#[track_caller]` should not inherit any attributes
        // that modify the symbol name. Failing to remove these attributes from
        // the shim leads to errors like `symbol `foo` is already defined`.
        //
        // A `ClosureOnceShim` with the track_caller attribute does not have a symbol,
        // and therefore can be skipped here.
        if let InstanceKind::Shim(ShimKind::Reify(_, _)) = instance_kind
            && attrs.flags.contains(CodegenFnAttrFlags::TRACK_CALLER)
        {
            if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
                attrs.to_mut().flags.remove(CodegenFnAttrFlags::NO_MANGLE);
            }

            if attrs.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL) {
                attrs.to_mut().flags.remove(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL);
            }

            if attrs.flags.contains(CodegenFnAttrFlags::EXTERNALLY_IMPLEMENTABLE_ITEM) {
                attrs.to_mut().flags.remove(CodegenFnAttrFlags::EXTERNALLY_IMPLEMENTABLE_ITEM);
            }

            if attrs.symbol_name.is_some() {
                attrs.to_mut().symbol_name = None;
            }
        }

        // Ensure closure shims have the optimization properties of their closure applied to them.
        if let InstanceKind::Shim(ShimKind::ClosureOnce {
            call_once: _,
            closure,
            track_caller: _,
        }) = instance_kind
        {
            let closure_attrs = self.codegen_fn_attrs(closure);
            attrs.to_mut().optimize = closure_attrs.optimize;
        }

        attrs
    }
}

#[derive(Clone, TyEncodable, TyDecodable, StableHash, Debug)]
pub struct CodegenFnAttrs {
    pub flags: CodegenFnAttrFlags,
    /// Parsed representation of the `#[inline]` attribute
    pub inline: InlineAttr,
    /// Parsed representation of the `#[optimize]` attribute
    pub optimize: OptimizeAttr,
    /// The name this function will be imported/exported under. This can be set
    /// using the `#[export_name = "..."]` or `#[link_name = "..."]` attribute
    /// depending on if this is a function definition or foreign function.
    pub symbol_name: Option<Symbol>,
    /// Defids of foreign items somewhere that this function should "satisfy".
    /// i.e., if a foreign function has some symbol foo,
    /// generate this function under its real name,
    /// but *also* under the same name as this foreign function so that the foreign function has an implementation.
    // FIXME: make "SymbolName<'tcx>"
    pub foreign_item_symbol_aliases: Vec<(DefId, Linkage, Visibility)>,
    /// The `#[link_ordinal = "..."]` attribute, indicating an ordinal an
    /// imported function has in the dynamic library. Note that this must not
    /// be set when `link_name` is set. This is for foreign items with the
    /// "raw-dylib" kind.
    pub link_ordinal: Option<u16>,
    /// The `#[target_feature(enable = "...")]` attribute and the enabled
    /// features (only enabled features are supported right now).
    /// Implied target features have already been applied.
    pub target_features: Vec<TargetFeature>,
    /// Whether the function was declared safe, but has target features
    pub safe_target_features: bool,
    /// The `#[linkage = "..."]` attribute on Rust-defined items and the value we found.
    pub linkage: Option<Linkage>,
    /// The `#[linkage = "..."]` attribute on foreign items and the value we found.
    pub import_linkage: Option<Linkage>,
    /// The `#[link_section = "..."]` attribute, or what executable section this
    /// should be placed in.
    pub link_section: Option<Symbol>,
    /// The `#[sanitize(xyz = "off")]` attribute. Indicates the settings for each
    /// sanitizer for this function.
    pub sanitizers: SanitizerFnAttrs,
    /// The `#[instruction_set(set)]` attribute. Indicates if the generated code should
    /// be generated against a specific instruction set. Only usable on architectures which allow
    /// switching between multiple instruction sets.
    pub instruction_set: Option<InstructionSetAttr>,
    /// The `#[align(...)]` attribute. Determines the alignment of the function body.
    // FIXME(#82232, #143834): temporarily renamed to mitigate `#[align]` nameres ambiguity
    pub alignment: Option<Align>,
    /// The `#[patchable_function_entry(...)]` attribute. Indicates how many nops should be around
    /// the function entry, or override default section to record entry location.
    pub patchable_function_entry: Option<PatchableFunctionEntry>,
    /// The `#[rustc_objc_class = "..."]` attribute.
    pub objc_class: Option<Symbol>,
    /// The `#[rustc_objc_selector = "..."]` attribute.
    pub objc_selector: Option<Symbol>,
    /// The `#[instrument_fn]` attribute.
    pub instrument_fn: InstrumentFnAttr,
}

#[derive(Copy, Clone, TyEncodable, TyDecodable, StableHash, Debug)]
pub enum InstrumentFnAttr {
    /// Always instrument function
    On,
    /// Never instrument function
    Off,
    /// Instrument based on command line options, if any.
    Default,
}

const impl Default for InstrumentFnAttr {
    fn default() -> Self {
        InstrumentFnAttr::Default
    }
}

#[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, StableHash, PartialEq, Eq)]
pub enum TargetFeatureKind {
    /// The feature is implied by another feature, rather than explicitly added by the
    /// `#[target_feature]` attribute
    Implied,
    /// The feature is added by the regular `target_feature` attribute.
    Enabled,
    /// The feature is added by the unsafe `force_target_feature` attribute.
    Forced,
}

#[derive(Copy, Clone, Debug, Eq, PartialEq, TyEncodable, TyDecodable, StableHash)]
pub struct TargetFeature {
    /// The name of the target feature (e.g. "avx")
    pub name: Symbol,
    /// The way this feature was enabled.
    pub kind: TargetFeatureKind,
}

#[derive(Copy, Clone, Debug, TyEncodable, TyDecodable, StableHash)]
pub struct PatchableFunctionEntry {
    /// Nops to prepend to the function
    prefix: Option<u8>,
    /// Nops after entry, but before body
    entry: Option<u8>,
    /// Optional, specific section to record entry location in
    section: Option<Symbol>,
}

impl PatchableFunctionEntry {
    pub fn from_prefix_entry_and_section(
        prefix: Option<u8>,
        entry: Option<u8>,
        section: Option<Symbol>,
    ) -> Self {
        Self { prefix, entry, section }
    }
    pub fn from_prefix_and_entry(prefix: u8, entry: u8) -> Self {
        Self { prefix: Some(prefix), entry: Some(entry), section: None }
    }
    pub fn prefix(&self) -> Option<u8> {
        self.prefix
    }
    pub fn entry(&self) -> Option<u8> {
        self.entry
    }
    pub fn section(&self) -> Option<Symbol> {
        self.section
    }
}

#[derive(Clone, Copy, PartialEq, Eq, TyEncodable, TyDecodable, StableHash)]
pub struct CodegenFnAttrFlags(u32);
bitflags::bitflags! {
    impl CodegenFnAttrFlags: u32 {
        /// `#[cold]`: a hint to LLVM that this function, when called, is never on
        /// the hot path.
        const COLD                      = 1 << 0;
        /// `#[rustc_nounwind]`: An indicator that function will never unwind.
        const NEVER_UNWIND              = 1 << 1;
        /// `#[naked]`: an indicator to LLVM that no function prologue/epilogue
        /// should be generated.
        const NAKED                     = 1 << 2;
        /// `#[no_mangle]`: an indicator that the function's name should be the same
        /// as its symbol.
        const NO_MANGLE                 = 1 << 3;
        /// `#[rustc_std_internal_symbol]`: an indicator that this symbol is a
        /// "weird symbol" for the standard library in that it has slightly
        /// different linkage, visibility, and reachability rules.
        const RUSTC_STD_INTERNAL_SYMBOL = 1 << 4;
        /// `#[thread_local]`: indicates a static is actually a thread local
        /// piece of memory
        const THREAD_LOCAL              = 1 << 5;
        /// `#[used(compiler)]`: indicates that LLVM can't eliminate this function (but the
        /// linker can!).
        const USED_COMPILER             = 1 << 6;
        /// `#[used(linker)]`:
        /// indicates that neither LLVM nor the linker will eliminate this function.
        const USED_LINKER               = 1 << 7;
        /// `#[track_caller]`: allow access to the caller location
        const TRACK_CALLER              = 1 << 8;
        /// #[ffi_pure]: applies clang's `pure` attribute to a foreign function
        /// declaration.
        const FFI_PURE                  = 1 << 9;
        /// #[ffi_const]: applies clang's `const` attribute to a foreign function
        /// declaration.
        const FFI_CONST                 = 1 << 10;
        /// `#[rustc_allocator]`: a hint to LLVM that the pointer returned from this
        /// function is never null and the function has no side effects other than allocating.
        const ALLOCATOR                 = 1 << 11;
        /// `#[rustc_deallocator]`: a hint to LLVM that the function only deallocates memory.
        const DEALLOCATOR               = 1 << 12;
        /// `#[rustc_reallocator]`: a hint to LLVM that the function only reallocates memory.
        const REALLOCATOR               = 1 << 13;
        /// `#[rustc_allocator_zeroed]`: a hint to LLVM that the function only allocates zeroed memory.
        const ALLOCATOR_ZEROED          = 1 << 14;
        /// `#[no_builtins]`: indicates that disable implicit builtin knowledge of functions for the function.
        const NO_BUILTINS               = 1 << 15;
        /// Marks foreign items, to make `contains_extern_indicator` cheaper.
        const FOREIGN_ITEM              = 1 << 16;
        /// `#[rustc_offload_kernel]`: indicates that this is an offload kernel, an extra ptr arg will be added.
        const OFFLOAD_KERNEL = 1 << 17;
        /// Externally implementable item symbols act a little like `RUSTC_STD_INTERNAL_SYMBOL`.
        /// When a crate declares an EII and dependencies expect the symbol to exist,
        /// they will refer to this symbol name before a definition is given.
        /// As such, we must make sure these symbols really do exist in the final binary/library.
        /// This flag is put on both the implementations of EIIs and the foreign item they implement.
        const EXTERNALLY_IMPLEMENTABLE_ITEM = 1 << 18;
    }
}
rustc_data_structures::external_bitflags_debug! { CodegenFnAttrFlags }

impl CodegenFnAttrs {
    pub const EMPTY: &'static Self = &Self::new();

    pub const fn new() -> CodegenFnAttrs {
        CodegenFnAttrs {
            flags: CodegenFnAttrFlags::empty(),
            inline: InlineAttr::None,
            optimize: OptimizeAttr::Default,
            symbol_name: None,
            link_ordinal: None,
            target_features: vec![],
            foreign_item_symbol_aliases: vec![],
            safe_target_features: false,
            linkage: None,
            import_linkage: None,
            link_section: None,
            sanitizers: SanitizerFnAttrs::default(),
            instruction_set: None,
            alignment: None,
            patchable_function_entry: None,
            objc_class: None,
            objc_selector: None,
            instrument_fn: InstrumentFnAttr::default(),
        }
    }

    /// Returns `true` if it looks like this symbol needs to be exported, for example:
    ///
    /// * `#[no_mangle]` is present
    /// * `#[export_name(...)]` is present
    /// * `#[linkage]` is present
    ///
    /// Keep this in sync with the logic for the unused_attributes for `#[inline]` lint.
    pub fn contains_extern_indicator(&self) -> bool {
        if self.flags.contains(CodegenFnAttrFlags::FOREIGN_ITEM) {
            return false;
        }

        self.flags.contains(CodegenFnAttrFlags::NO_MANGLE)
            || self.flags.contains(CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL)
            // note: for these we do also set a symbol name so technically also handled by the
            // condition below. However, I think that regardless these should be treated as extern.
            || self.flags.contains(CodegenFnAttrFlags::EXTERNALLY_IMPLEMENTABLE_ITEM)
            || self.symbol_name.is_some()
            || match self.linkage {
                // These are private, so make sure we don't try to consider
                // them external.
                None | Some(Linkage::Internal) => false,
                Some(_) => true,
            }
    }
}

#[derive(Clone, Copy, Debug, StableHash, TyEncodable, TyDecodable, Eq, PartialEq)]
pub struct SanitizerFnAttrs {
    pub disabled: SanitizerSet,
    pub rtsan_setting: RtsanSetting,
}

const impl Default for SanitizerFnAttrs {
    fn default() -> Self {
        Self { disabled: SanitizerSet::empty(), rtsan_setting: RtsanSetting::default() }
    }
}