ValidateMemRefs.cpp

//===- bolt/Passes/ValidateMemRefs.cpp ------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include"bolt/Passes/ValidateMemRefs.h"
#include"bolt/Core/ParallelUtilities.h"

#defineDEBUG_TYPE"bolt-memrefs"

namespaceopts {
extern llvm::cl::opt<llvm::bolt::JumpTableSupportLevel> JumpTables;
}

namespacellvm::bolt {

std::atomic<std::uint64_t> ValidateMemRefs::ReplacedReferences{0};

boolValidateMemRefs::checkAndFixJTReference(BinaryFunction &BF, MCInst &Inst,
uint32_t OperandNum,
const MCSymbol *Sym,
uint64_t Offset) {
 BinaryContext &BC = BF.getBinaryContext();
auto L = BC.scopeLock();
 BinaryData *BD = BC.getBinaryDataByName(Sym->getName());
if (!BD)
returnfalse;

 JumpTable *JT = BC.getJumpTableContainingAddress(BD->getAddress());
if (!JT)
returnfalse;

constbool IsLegitAccess = llvm::is_contained(JT->Parents, &BF);
if (IsLegitAccess)
returntrue;

// Accessing a jump table in another function. This is not a
// legitimate jump table access, we need to replace the reference to
// the jump table label with a regular rodata reference. Get a
// non-JT reference by fetching the symbol 1 byte before the JT
// label.
 MCSymbol *NewSym = BC.getOrCreateGlobalSymbol(BD->getAddress() - 1, "DATAat");
 BC.MIB->setOperandToSymbolRef(Inst, OperandNum, NewSym, Offset + 1, &*BC.Ctx,
0);
LLVM_DEBUG(dbgs() << "BOLT-DEBUG: replaced reference @" << BF.getPrintName()
 << " from " << BD->getName() << " to " << NewSym->getName()
 << " + 1\n");
 ++ReplacedReferences;
returntrue;
}

voidValidateMemRefs::runOnFunction(BinaryFunction &BF) {
 MCPlusBuilder *MIB = BF.getBinaryContext().MIB.get();

for (BinaryBasicBlock &BB : BF) {
for (MCInst &Inst : BB) {
for (int I = 0, E = MCPlus::getNumPrimeOperands(Inst); I != E; ++I) {
const MCOperand &Operand = Inst.getOperand(I);
if (!Operand.isExpr())
continue;

constauto [Sym, Offset] = MIB->getTargetSymbolInfo(Operand.getExpr());
if (!Sym)
continue;

checkAndFixJTReference(BF, Inst, I, Sym, Offset);
 }
 }
 }
}

Error ValidateMemRefs::runOnFunctions(BinaryContext &BC) {
if (!BC.isX86())
returnError::success();

// Skip validation if not moving JT
if (opts::JumpTables == JTS_NONE || opts::JumpTables == JTS_BASIC)
returnError::success();

 ParallelUtilities::WorkFuncWithAllocTy ProcessFunction =
 [&](BinaryFunction &BF, MCPlusBuilder::AllocatorIdTy AllocId) {
runOnFunction(BF);
 };
 ParallelUtilities::PredicateTy SkipPredicate = [&](const BinaryFunction &BF) {
return !BF.hasCFG();
 };
LLVM_DEBUG(dbgs() << "BOLT-DEBUG: starting memrefs validation pass\n");
ParallelUtilities::runOnEachFunctionWithUniqueAllocId(
 BC, ParallelUtilities::SchedulingPolicy::SP_INST_LINEAR, ProcessFunction,
 SkipPredicate, "validate-mem-refs", /*ForceSequential=*/true);
LLVM_DEBUG(dbgs() << "BOLT-DEBUG: memrefs validation is concluded\n");

if (!ReplacedReferences)
returnError::success();

 BC.outs() << "BOLT-INFO: validate-mem-refs updated " << ReplacedReferences
 << " object references\n";
returnError::success();
}

} // namespace llvm::bolt