FixRelaxationPass.cpp

//===- bolt/Passes/FixRelaxationPass.cpp ------------------------*- C++ -*-===//
//
// 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/FixRelaxationPass.h"
#include"bolt/Core/ParallelUtilities.h"

usingnamespacellvm;

namespacellvm {
namespacebolt {

// This function finds ADRP+ADD instruction sequences that originally before
// linker relaxations were ADRP+LDR. We've modified LDR/ADD relocation properly
// during relocation reading, so its targeting right symbol. As for ADRP its
// target is wrong before this pass since we won't be able to recognize and
// properly change R_AARCH64_ADR_GOT_PAGE relocation to
// R_AARCH64_ADR_PREL_PG_HI21 during relocation reading. Now we're searching for
// ADRP+ADD sequences, checking that ADRP points to the GOT-table symbol and the
// target of ADD is another symbol. When found change ADRP symbol reference to
// the ADDs one.
voidFixRelaxations::runOnFunction(BinaryFunction &BF) {
 BinaryContext &BC = BF.getBinaryContext();
for (BinaryBasicBlock &BB : BF) {
for (auto II = BB.begin(); II != BB.end(); ++II) {
 MCInst &Adrp = *II;
if (BC.MIB->isPseudo(Adrp) || !BC.MIB->isADRP(Adrp))
continue;

const MCSymbol *AdrpSymbol = BC.MIB->getTargetSymbol(Adrp);
if (!AdrpSymbol || AdrpSymbol->getName() != "__BOLT_got_zero")
continue;

auto NextII = std::next(II);
if (NextII == BB.end())
continue;

const MCInst &Add = *NextII;
if (!BC.MIB->matchAdrpAddPair(Adrp, Add))
continue;

const MCSymbol *Symbol = BC.MIB->getTargetSymbol(Add);
if (!Symbol || AdrpSymbol == Symbol)
continue;

auto L = BC.scopeLock();
constint64_t Addend = BC.MIB->getTargetAddend(Add);
 BC.MIB->setOperandToSymbolRef(Adrp, /*OpNum*/1, Symbol, Addend,
 BC.Ctx.get(), ELF::R_AARCH64_NONE);
 }
 }
}

Error FixRelaxations::runOnFunctions(BinaryContext &BC) {
if (!BC.isAArch64() || !BC.HasRelocations)
returnError::success();

 ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
runOnFunction(BF);
 };

ParallelUtilities::runOnEachFunction(
 BC, ParallelUtilities::SchedulingPolicy::SP_INST_LINEAR, WorkFun, nullptr,
"FixRelaxations");
returnError::success();
}

} // namespace bolt
} // namespace llvm