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//! Type metadata identifiers for LLVM Kernel Control Flow Integrity (KCFI) and cross-language LLVM
//! KCFI support for the Rust compiler.
//!
//! For more information about LLVM KCFI and cross-language LLVM KCFI support for the Rust compiler,
//! see the tracking issue #123479.
use std::hash::Hasher;
use rustc_middle::ty::{Instance, InstanceKind, ReifyReason, Ty, TyCtxt};
use rustc_target::abi::call::FnAbi;
use twox_hash::XxHash64;
pub use crate::cfi::typeid::{itanium_cxx_abi, TypeIdOptions};
/// Returns a KCFI type metadata identifier for the specified FnAbi.
pub fn typeid_for_fnabi<'tcx>(
tcx: TyCtxt<'tcx>,
fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
options: TypeIdOptions,
) -> u32 {
// A KCFI type metadata identifier is a 32-bit constant produced by taking the lower half of the
// xxHash64 of the type metadata identifier. (See llvm/llvm-project@cff5bef.)
let mut hash: XxHash64 = Default::default();
hash.write(itanium_cxx_abi::typeid_for_fnabi(tcx, fn_abi, options).as_bytes());
hash.finish() as u32
}
/// Returns a KCFI type metadata identifier for the specified Instance.
pub fn typeid_for_instance<'tcx>(
tcx: TyCtxt<'tcx>,
instance: Instance<'tcx>,
mut options: TypeIdOptions,
) -> u32 {
// KCFI support for Rust shares most of its implementation with the CFI support, with some key
// differences:
//
// 1. KCFI performs type tests differently and are implemented as different LLVM passes than CFI
// to not require LTO.
// 2. KCFI has the limitation that a function or method may have one type id assigned only.
//
// Because of the limitation listed above (2), the current KCFI implementation (not CFI) does
// reifying of types (i.e., adds shims/trampolines for indirect calls in these cases) for:
//
// * Supporting casting between function items, closures, and Fn trait objects.
// * Supporting methods being cast as function pointers.
//
// This was implemented for KCFI support in #123106 and #123052 (which introduced the
// ReifyReason). The tracking issue for KCFI support for Rust is #123479.
if matches!(instance.def, InstanceKind::ReifyShim(_, Some(ReifyReason::FnPtr))) {
options.insert(TypeIdOptions::USE_CONCRETE_SELF);
}
// A KCFI type metadata identifier is a 32-bit constant produced by taking the lower half of the
// xxHash64 of the type metadata identifier. (See llvm/llvm-project@cff5bef.)
let mut hash: XxHash64 = Default::default();
hash.write(itanium_cxx_abi::typeid_for_instance(tcx, instance, options).as_bytes());
hash.finish() as u32
}