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162 changes: 162 additions & 0 deletions
162
compiler/rustc_codegen_ssa/src/mir/pointer_alignment_check.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,162 @@ | ||
| use rustc_hir::LangItem; | ||
| use rustc_middle::mir; | ||
| use rustc_middle::mir::visit::Visitor; | ||
| use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext}; | ||
| use rustc_span::Span; | ||
|
|
||
| use super::FunctionCx; | ||
| use crate::base; | ||
| use crate::common; | ||
| use crate::mir::OperandValue; | ||
| use crate::traits::*; | ||
|
|
||
| pub fn pointers_to_check<F>( | ||
| statement: &mir::Statement<'_>, | ||
| required_align_of: F, | ||
| ) -> Vec<(mir::Local, u64)> | ||
| where | ||
| F: Fn(mir::Local) -> Option<u64>, | ||
| { | ||
| let mut finder = PointerFinder { required_align_of, pointers: Vec::new() }; | ||
| finder.visit_statement(statement, rustc_middle::mir::Location::START); | ||
| finder.pointers | ||
| } | ||
|
|
||
| struct PointerFinder<F> { | ||
| pointers: Vec<(mir::Local, u64)>, | ||
| required_align_of: F, | ||
| } | ||
|
|
||
| impl<'tcx, F> Visitor<'tcx> for PointerFinder<F> | ||
| where | ||
| F: Fn(mir::Local) -> Option<u64>, | ||
| { | ||
| fn visit_place( | ||
| &mut self, | ||
| place: &mir::Place<'tcx>, | ||
| context: PlaceContext, | ||
| location: mir::Location, | ||
| ) { | ||
| // We want to only check reads and writes to Places, so we specifically exclude | ||
| // Borrows and AddressOf. | ||
| match context { | ||
| PlaceContext::MutatingUse( | ||
| MutatingUseContext::Store | ||
| | MutatingUseContext::AsmOutput | ||
| | MutatingUseContext::Call | ||
| | MutatingUseContext::Yield | ||
| | MutatingUseContext::Drop, | ||
| ) => {} | ||
| PlaceContext::NonMutatingUse( | ||
| NonMutatingUseContext::Copy | NonMutatingUseContext::Move, | ||
| ) => {} | ||
| _ => { | ||
| return; | ||
| } | ||
| } | ||
|
|
||
| if !place.is_indirect() { | ||
| return; | ||
| } | ||
|
|
||
| let pointer = place.local; | ||
| let Some(required_alignment) = (self.required_align_of)(pointer) else { | ||
| return; | ||
| }; | ||
|
|
||
| if required_alignment == 1 { | ||
| return; | ||
| } | ||
|
|
||
| // Ensure that this place is based on an aligned pointer. | ||
| self.pointers.push((pointer, required_alignment)); | ||
|
|
||
| self.super_place(place, context, location); | ||
| } | ||
| } | ||
|
|
||
| impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { | ||
| #[instrument(level = "debug", skip(self, bx))] | ||
| pub fn codegen_alignment_check( | ||
| &mut self, | ||
| bx: &mut Bx, | ||
| pointer: mir::Operand<'tcx>, | ||
| required_alignment: u64, | ||
| source_info: mir::SourceInfo, | ||
| ) { | ||
| // Compute the alignment mask | ||
| let mask = bx.const_usize(required_alignment - 1); | ||
| let zero = bx.const_usize(0); | ||
| let required_alignment = bx.const_usize(required_alignment); | ||
|
|
||
| // And the pointer with the mask | ||
| let pointer = match self.codegen_operand(bx, &pointer).val { | ||
| OperandValue::Immediate(imm) => imm, | ||
| OperandValue::Pair(ptr, _) => ptr, | ||
| _ => { | ||
| unreachable!("{pointer:?}"); | ||
| } | ||
| }; | ||
| let addr = bx.ptrtoint(pointer, bx.cx().type_isize()); | ||
| let masked = bx.and(addr, mask); | ||
|
|
||
| // Branch on whether the masked value is zero | ||
| let is_zero = bx.icmp( | ||
| base::bin_op_to_icmp_predicate(mir::BinOp::Eq.to_hir_binop(), false), | ||
| masked, | ||
| zero, | ||
| ); | ||
|
|
||
| // Create destination blocks, branching on is_zero | ||
| let panic = bx.append_sibling_block("panic"); | ||
| let success = bx.append_sibling_block("success"); | ||
| bx.cond_br(is_zero, success, panic); | ||
|
|
||
| // Switch to the failure block and codegen a call to the panic intrinsic | ||
| bx.switch_to_block(panic); | ||
| self.set_debug_loc(bx, source_info); | ||
| let location = self.get_caller_location(bx, source_info).immediate(); | ||
| self.codegen_nounwind_panic( | ||
| bx, | ||
| LangItem::PanicMisalignedPointerDereference, | ||
| &[required_alignment, addr, location], | ||
| source_info.span, | ||
| ); | ||
|
|
||
| // Continue codegen in the success block. | ||
| bx.switch_to_block(success); | ||
| self.set_debug_loc(bx, source_info); | ||
| } | ||
|
|
||
| /// Emit a call to a diverging and `rustc_nounwind` panic helper. | ||
| #[instrument(level = "debug", skip(self, bx))] | ||
| fn codegen_nounwind_panic( | ||
| &mut self, | ||
| bx: &mut Bx, | ||
| lang_item: LangItem, | ||
| args: &[Bx::Value], | ||
| span: Span, | ||
| ) { | ||
| let (fn_abi, fn_ptr, instance) = common::build_langcall(bx, Some(span), lang_item); | ||
| let fn_ty = bx.fn_decl_backend_type(&fn_abi); | ||
| let fn_attrs = if bx.tcx().def_kind(self.instance.def_id()).has_codegen_attrs() { | ||
| Some(bx.tcx().codegen_fn_attrs(self.instance.def_id())) | ||
| } else { | ||
| None | ||
| }; | ||
|
|
||
| // bx.call requires that the call not unwind. Double-check that this LangItem can't unwind. | ||
| assert!(!fn_abi.can_unwind); | ||
|
|
||
| bx.call( | ||
| fn_ty, | ||
| fn_attrs, | ||
| Some(&fn_abi), | ||
| fn_ptr, | ||
| args, | ||
| None, /* funclet */ | ||
| Some(instance), | ||
| ); | ||
| bx.unreachable(); | ||
| } | ||
| } |
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