llvm/bolt/lib/Rewrite/JITLinkLinker.cpp

//===- bolt/Rewrite/JITLinkLinker.cpp - BOLTLinker using JITLink ----------===//
//
// 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/Rewrite/JITLinkLinker.h"
#include "bolt/Core/BinaryData.h"
#include "bolt/Rewrite/RewriteInstance.h"
#include "llvm/ExecutionEngine/JITLink/JITLink.h"
#include "llvm/ExecutionEngine/Orc/Shared/ExecutorAddress.h"
#include "llvm/ExecutionEngine/Orc/Shared/ExecutorSymbolDef.h"
#include "llvm/Support/Debug.h"

#define DEBUG_TYPE "bolt"

namespace llvm {
namespace bolt {

namespace {

bool hasSymbols(const jitlink::Block &B) {
  return llvm::any_of(B.getSection().symbols(),
                      [&B](const auto &S) { return &S->getBlock() == &B; });
}

/// Liveness in JITLink is based on symbols so sections that do not contain
/// any symbols will always be pruned. This pass adds anonymous symbols to
/// needed sections to prevent pruning.
Error markSectionsLive(jitlink::LinkGraph &G) {
  for (auto &Section : G.sections()) {
    // We only need allocatable sections.
    if (Section.getMemLifetimePolicy() == orc::MemLifetimePolicy::NoAlloc)
      continue;

    // Skip empty sections.
    if (JITLinkLinker::sectionSize(Section) == 0)
      continue;

    for (auto *Block : Section.blocks()) {
      // No need to add symbols if it already has some.
      if (hasSymbols(*Block))
        continue;

      G.addAnonymousSymbol(*Block, /*Offset=*/0, /*Size=*/0,
                           /*IsCallable=*/false, /*IsLive=*/true);
    }
  }

  return jitlink::markAllSymbolsLive(G);
}

void reassignSectionAddress(jitlink::LinkGraph &LG,
                            const BinarySection &BinSection, uint64_t Address) {
  auto *JLSection = LG.findSectionByName(BinSection.getSectionID());
  assert(JLSection && "cannot find section in LinkGraph");

  auto BlockAddress = Address;
  for (auto *Block : JITLinkLinker::orderedBlocks(*JLSection)) {
    // FIXME it would seem to make sense to align here. However, in
    // non-relocation mode, we simply use the original address of functions
    // which might not be aligned with the minimum alignment used by
    // BinaryFunction (2). Example failing test when aligning:
    // bolt/test/X86/addr32.s
    Block->setAddress(orc::ExecutorAddr(BlockAddress));
    BlockAddress += Block->getSize();
  }
}

} // anonymous namespace

struct JITLinkLinker::Context : jitlink::JITLinkContext {
  JITLinkLinker &Linker;
  JITLinkLinker::SectionsMapper MapSections;

  Context(JITLinkLinker &Linker, JITLinkLinker::SectionsMapper MapSections)
      : JITLinkContext(&Linker.Dylib), Linker(Linker),
        MapSections(MapSections) {}

  jitlink::JITLinkMemoryManager &getMemoryManager() override {
    return *Linker.MM;
  }

  bool shouldAddDefaultTargetPasses(const Triple &TT) const override {
    // The default passes manipulate DWARF sections in a way incompatible with
    // BOLT.
    // TODO check if we can actually use these passes to remove some of the
    // DWARF manipulation done in BOLT.
    return false;
  }

  Error modifyPassConfig(jitlink::LinkGraph &G,
                         jitlink::PassConfiguration &Config) override {
    Config.PrePrunePasses.push_back(markSectionsLive);
    return Error::success();
  }

  void notifyFailed(Error Err) override {
    errs() << "BOLT-ERROR: JITLink failed: " << Err << '\n';
    exit(1);
  }

  void
  lookup(const LookupMap &Symbols,
         std::unique_ptr<jitlink::JITLinkAsyncLookupContinuation> LC) override {
    jitlink::AsyncLookupResult AllResults;

    for (const auto &Symbol : Symbols) {
      std::string SymName = Symbol.first.str();
      LLVM_DEBUG(dbgs() << "BOLT: looking for " << SymName << "\n");

      if (auto Address = Linker.lookupSymbol(SymName)) {
        LLVM_DEBUG(dbgs() << "Resolved to address 0x"
                          << Twine::utohexstr(*Address) << "\n");
        AllResults[Symbol.first] = orc::ExecutorSymbolDef(
            orc::ExecutorAddr(*Address), JITSymbolFlags());
        continue;
      }

      if (const BinaryData *I = Linker.BC.getBinaryDataByName(SymName)) {
        uint64_t Address = I->isMoved() && !I->isJumpTable()
                               ? I->getOutputAddress()
                               : I->getAddress();
        LLVM_DEBUG(dbgs() << "Resolved to address 0x"
                          << Twine::utohexstr(Address) << "\n");
        AllResults[Symbol.first] = orc::ExecutorSymbolDef(
            orc::ExecutorAddr(Address), JITSymbolFlags());
        continue;
      }
      LLVM_DEBUG(dbgs() << "Resolved to address 0x0\n");
      AllResults[Symbol.first] =
          orc::ExecutorSymbolDef(orc::ExecutorAddr(0), JITSymbolFlags());
    }

    LC->run(std::move(AllResults));
  }

  Error notifyResolved(jitlink::LinkGraph &G) override {
    MapSections([&G](const BinarySection &Section, uint64_t Address) {
      reassignSectionAddress(G, Section, Address);
    });

    for (auto *Symbol : G.defined_symbols()) {
      Linker.Symtab.insert(
          {Symbol->getName().str(), Symbol->getAddress().getValue()});
    }

    return Error::success();
  }

  void notifyFinalized(
      jitlink::JITLinkMemoryManager::FinalizedAlloc Alloc) override {
    Linker.Allocs.push_back(std::move(Alloc));
    ++Linker.MM->ObjectsLoaded;
  }
};

JITLinkLinker::JITLinkLinker(BinaryContext &BC,
                             std::unique_ptr<ExecutableFileMemoryManager> MM)
    : BC(BC), MM(std::move(MM)) {}

JITLinkLinker::~JITLinkLinker() { cantFail(MM->deallocate(std::move(Allocs))); }

void JITLinkLinker::loadObject(MemoryBufferRef Obj,
                               SectionsMapper MapSections) {
  auto LG = jitlink::createLinkGraphFromObject(Obj);
  if (auto E = LG.takeError()) {
    errs() << "BOLT-ERROR: JITLink failed: " << E << '\n';
    exit(1);
  }

  auto Ctx = std::make_unique<Context>(*this, MapSections);
  jitlink::link(std::move(*LG), std::move(Ctx));
}

std::optional<uint64_t> JITLinkLinker::lookupSymbol(StringRef Name) const {
  auto It = Symtab.find(Name.data());
  if (It == Symtab.end())
    return std::nullopt;

  return It->second;
}

SmallVector<jitlink::Block *, 2>
JITLinkLinker::orderedBlocks(const jitlink::Section &Section) {
  SmallVector<jitlink::Block *, 2> Blocks(Section.blocks());
  llvm::sort(Blocks, [](const auto *LHS, const auto *RHS) {
    return LHS->getAddress() < RHS->getAddress();
  });
  return Blocks;
}

size_t JITLinkLinker::sectionSize(const jitlink::Section &Section) {
  size_t Size = 0;

  for (const auto *Block : orderedBlocks(Section)) {
    Size = jitlink::alignToBlock(Size, *Block);
    Size += Block->getSize();
  }

  return Size;
}

} // namespace bolt
} // namespace llvm