llvm-project

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//===- bolt/Passes/FixRelaxationPass.cpp ------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "bolt/Passes/FixRelaxationPass.h"
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#include "bolt/Core/ParallelUtilities.h"
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using namespace llvm;
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namespace llvm {
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namespace bolt {
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// This function finds ADRP+ADD instruction sequences that originally before
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// linker relaxations were ADRP+LDR. We've modified LDR/ADD relocation properly
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// during relocation reading, so its targeting right symbol. As for ADRP its
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// target is wrong before this pass since we won't be able to recognize and
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// properly change R_AARCH64_ADR_GOT_PAGE relocation to
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// R_AARCH64_ADR_PREL_PG_HI21 during relocation reading. Now we're searching for
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// ADRP+ADD sequences, checking that ADRP points to the GOT-table symbol and the
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// target of ADD is another symbol. When found change ADRP symbol reference to
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// the ADDs one.
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void FixRelaxations::runOnFunction(BinaryFunction &BF) {
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  BinaryContext &BC = BF.getBinaryContext();
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  for (BinaryBasicBlock &BB : BF) {
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    for (auto II = BB.begin(); II != BB.end(); ++II) {
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      MCInst &Adrp = *II;
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      if (BC.MIB->isPseudo(Adrp) || !BC.MIB->isADRP(Adrp))
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        continue;
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      const MCSymbol *AdrpSymbol = BC.MIB->getTargetSymbol(Adrp);
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      if (!AdrpSymbol || AdrpSymbol->getName() != "__BOLT_got_zero")
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        continue;
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      auto NextII = std::next(II);
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      if (NextII == BB.end())
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        continue;
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      const MCInst &Add = *NextII;
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      if (!BC.MIB->matchAdrpAddPair(Adrp, Add))
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        continue;
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      const MCSymbol *Symbol = BC.MIB->getTargetSymbol(Add);
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      if (!Symbol || AdrpSymbol == Symbol)
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        continue;
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      auto L = BC.scopeLock();
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      const int64_t Addend = BC.MIB->getTargetAddend(Add);
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      BC.MIB->setOperandToSymbolRef(Adrp, /*OpNum*/ 1, Symbol, Addend,
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                                    BC.Ctx.get(), ELF::R_AARCH64_NONE);
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    }
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  }
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}
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Error FixRelaxations::runOnFunctions(BinaryContext &BC) {
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  if (!BC.isAArch64() || !BC.HasRelocations)
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    return Error::success();
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  ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
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    runOnFunction(BF);
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  };
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  ParallelUtilities::runOnEachFunction(
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      BC, ParallelUtilities::SchedulingPolicy::SP_INST_LINEAR, WorkFun, nullptr,
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      "FixRelaxations");
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  return Error::success();
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}
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} // namespace bolt
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} // namespace llvm
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