rust/src/librustc_mir/transform/add_validation.rs

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! This pass adds validation calls (AcquireValid, ReleaseValid) where appropriate.
//! It has to be run really early, before transformations like inlining, because
//! introducing these calls *adds* UB -- so, conceptually, this pass is actually part
//! of MIR building, and only after this pass we think of the program has having the
//! normal MIR semantics.

use rustc::ty::{self, TyCtxt, RegionKind};
use rustc::hir;
use rustc::mir::*;
use rustc::mir::transform::{MirPass, MirSource};
use rustc::middle::region::CodeExtent;

pub struct AddValidation;

/// Determine the "context" of the lval: Mutability and region.
fn lval_context<'a, 'tcx, D>(
    lval: &Lvalue<'tcx>,
    local_decls: &D,
    tcx: TyCtxt<'a, 'tcx, 'tcx>
) -> (Option<CodeExtent>, hir::Mutability)
    where D: HasLocalDecls<'tcx>
{
    use rustc::mir::Lvalue::*;

    match *lval {
        Local { .. } => (None, hir::MutMutable),
        Static(_) => (None, hir::MutImmutable),
        Projection(ref proj) => {
            match proj.elem {
                ProjectionElem::Deref => {
                    // Computing the inside the recursion makes this quadratic.
                    // We don't expect deep paths though.
                    let ty = proj.base.ty(local_decls, tcx).to_ty(tcx);
                    // A Deref projection may restrict the context, this depends on the type
                    // being deref'd.
                    let context = match ty.sty {
                        ty::TyRef(re, tam) => {
                            let re = match re {
                                &RegionKind::ReScope(ce) => Some(ce),
                                &RegionKind::ReErased =>
                                    bug!("AddValidation pass must be run before erasing lifetimes"),
                                _ => None
                            };
                            (re, tam.mutbl)
                        }
                        ty::TyRawPtr(_) =>
                            // There is no guarantee behind even a mutable raw pointer,
                            // no write locks are acquired there, so we also don't want to
                            // release any.
                            (None, hir::MutImmutable),
                        ty::TyAdt(adt, _) if adt.is_box() => (None, hir::MutMutable),
                        _ => bug!("Deref on a non-pointer type {:?}", ty),
                    };
                    // "Intersect" this restriction with proj.base.
                    if let (Some(_), hir::MutImmutable) = context {
                        // This is already as restricted as it gets, no need to even recurse
                        context
                    } else {
                        let base_context = lval_context(&proj.base, local_decls, tcx);
                        // The region of the outermost Deref is always most restrictive.
                        let re = context.0.or(base_context.0);
                        let mutbl = context.1.and(base_context.1);
                        (re, mutbl)
                    }

                }
                _ => lval_context(&proj.base, local_decls, tcx),
            }
        }
    }
}

impl MirPass for AddValidation {
    fn run_pass<'a, 'tcx>(&self,
                          tcx: TyCtxt<'a, 'tcx, 'tcx>,
                          _: MirSource,
                          mir: &mut Mir<'tcx>) {
        if !tcx.sess.opts.debugging_opts.mir_emit_validate {
            return;
        }

        let local_decls = mir.local_decls.clone(); // FIXME: Find a way to get rid of this clone.

        /// Convert an lvalue to a validation operand.
        let lval_to_operand = |lval: Lvalue<'tcx>| -> ValidationOperand<'tcx, Lvalue<'tcx>> {
            let (re, mutbl) = lval_context(&lval, &local_decls, tcx);
            let ty = lval.ty(&local_decls, tcx).to_ty(tcx);
            ValidationOperand { lval, ty, re, mutbl }
        };

        // PART 1
        // Add an AcquireValid at the beginning of the start block.
        if mir.arg_count > 0 {
            let acquire_stmt = Statement {
                source_info: SourceInfo {
                    scope: ARGUMENT_VISIBILITY_SCOPE,
                    span: mir.span, // FIXME: Consider using just the span covering the function
                                    // argument declaration.
                },
                kind: StatementKind::Validate(ValidationOp::Acquire,
                    // Skip return value, go over all the arguments
                    mir.local_decls.iter_enumerated().skip(1).take(mir.arg_count)
                    .map(|(local, _)| lval_to_operand(Lvalue::Local(local))).collect()
                )
            };
            mir.basic_blocks_mut()[START_BLOCK].statements.insert(0, acquire_stmt);
        }

        // PART 2
        // Add ReleaseValid/AcquireValid around function call terminators.  We don't use a visitor
        // because we need to access the block that a Call jumps to.
        let mut returns : Vec<(SourceInfo, Lvalue<'tcx>, BasicBlock)> = Vec::new();
        for block_data in mir.basic_blocks_mut() {
            match block_data.terminator {
                Some(Terminator { kind: TerminatorKind::Call { ref args, ref destination, .. },
                                  source_info }) => {
                    // Before the call: Release all arguments
                    let release_stmt = Statement {
                        source_info,
                        kind: StatementKind::Validate(ValidationOp::Release,
                            args.iter().filter_map(|op| {
                                match op {
                                    &Operand::Consume(ref lval) =>
                                        Some(lval_to_operand(lval.clone())),
                                    &Operand::Constant(..) => { None },
                                }
                            }).collect())
                    };
                    block_data.statements.push(release_stmt);
                    // Remember the return destination for later
                    if let &Some(ref destination) = destination {
                        returns.push((source_info, destination.0.clone(), destination.1));
                    }
                }
                Some(Terminator { kind: TerminatorKind::Drop { location: ref lval, .. },
                                  source_info }) |
                Some(Terminator { kind: TerminatorKind::DropAndReplace { location: ref lval, .. },
                                  source_info }) => {
                    // Before the call: Release all arguments
                    let release_stmt = Statement {
                        source_info,
                        kind: StatementKind::Validate(ValidationOp::Release,
                                vec![lval_to_operand(lval.clone())]),
                    };
                    block_data.statements.push(release_stmt);
                    // drop doesn't return anything, so we need no acquire.
                }
                _ => {
                    // Not a block ending in a Call -> ignore.
                }
            }
        }
        // Now we go over the returns we collected to acquire the return values.
        for (source_info, dest_lval, dest_block) in returns {
            let acquire_stmt = Statement {
                source_info,
                kind: StatementKind::Validate(ValidationOp::Acquire,
                        vec![lval_to_operand(dest_lval)]),
            };
            mir.basic_blocks_mut()[dest_block].statements.insert(0, acquire_stmt);
        }

        // PART 3
        // Add ReleaseValid/AcquireValid around Ref.  Again an iterator does not seem very suited
        // as we need to add new statements before and after each Ref.
        for block_data in mir.basic_blocks_mut() {
            // We want to insert statements around Ref commands as we iterate.  To this end, we
            // iterate backwards using indices.
            for i in (0..block_data.statements.len()).rev() {
                let (dest_lval, re, src_lval) = match block_data.statements[i].kind {
                    StatementKind::Assign(ref dest_lval, Rvalue::Ref(re, _, ref src_lval)) => {
                        (dest_lval.clone(), re, src_lval.clone())
                    },
                    _ => continue,
                };
                // So this is a ref, and we got all the data we wanted.
                // Do an acquire of the result -- but only what it points to, so add a Deref
                // projection.
                let dest_lval = Projection { base: dest_lval, elem: ProjectionElem::Deref };
                let dest_lval = Lvalue::Projection(Box::new(dest_lval));
                let acquire_stmt = Statement {
                    source_info: block_data.statements[i].source_info,
                    kind: StatementKind::Validate(ValidationOp::Acquire,
                            vec![lval_to_operand(dest_lval)]),
                };
                block_data.statements.insert(i+1, acquire_stmt);

                // The source is released until the region of the borrow ends.
                let op = match re {
                    &RegionKind::ReScope(ce) => ValidationOp::Suspend(ce),
                    &RegionKind::ReErased =>
                        bug!("AddValidation pass must be run before erasing lifetimes"),
                    _ => ValidationOp::Release,
                };
                let release_stmt = Statement {
                    source_info: block_data.statements[i].source_info,
                    kind: StatementKind::Validate(op, vec![lval_to_operand(src_lval)]),
                };
                block_data.statements.insert(i, release_stmt);
            }
        }
    }
}