COFF_x86_64.cpp

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//===----- COFF_x86_64.cpp - JIT linker implementation for COFF/x86_64 ----===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// COFF/x86_64 jit-link implementation.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/ExecutionEngine/JITLink/COFF_x86_64.h"
#include "COFFLinkGraphBuilder.h"
#include "JITLinkGeneric.h"
#include "SEHFrameSupport.h"
#include "llvm/BinaryFormat/COFF.h"
#include "llvm/ExecutionEngine/JITLink/COFF.h"
#include "llvm/ExecutionEngine/JITLink/x86_64.h"
#include "llvm/Object/COFF.h"
#include "llvm/Support/Endian.h"
 
#define DEBUG_TYPE "jitlink"
 
using namespace llvm;
using namespace llvm::jitlink;
 
namespace {
 
enum EdgeKind_coff_x86_64 : Edge::Kind {
  PCRel32 = x86_64::FirstPlatformRelocation,
  Pointer32NB,
  Pointer64,
  SectionIdx16,
  SecRel32,
};
 
class COFFJITLinker_x86_64 : public JITLinker<COFFJITLinker_x86_64> {
  friend class JITLinker<COFFJITLinker_x86_64>;
 
public:
  COFFJITLinker_x86_64(std::unique_ptr<JITLinkContext> Ctx,
                       std::unique_ptr<LinkGraph> G,
                       PassConfiguration PassConfig)
      : JITLinker(std::move(Ctx), std::move(G), std::move(PassConfig)) {}
 
private:
  Error applyFixup(LinkGraph &G, Block &B, const Edge &E) const {
    return x86_64::applyFixup(G, B, E, nullptr);
  }
};
 
class COFFLinkGraphBuilder_x86_64 : public COFFLinkGraphBuilder {
private:
  Error addRelocations() override {
    LLVM_DEBUG(dbgs() << "Processing relocations:\n");
 
    for (const auto &RelSect : sections())
      if (Error Err = COFFLinkGraphBuilder::forEachRelocation(
              RelSect, this, &COFFLinkGraphBuilder_x86_64::addSingleRelocation))
        return Err;
 
    return Error::success();
  }
 
  Error addSingleRelocation(const object::RelocationRef &Rel,
                            const object::SectionRef &FixupSect,
                            Block &BlockToFix) {
    const object::coff_relocation *COFFRel = getObject().getCOFFRelocation(Rel);
    auto SymbolIt = Rel.getSymbol();
    if (SymbolIt == getObject().symbol_end()) {
      return make_error<StringError>(
          formatv("Invalid symbol index in relocation entry. "
                  "index: {0}, section: {1}",
                  COFFRel->SymbolTableIndex, FixupSect.getIndex()),
          inconvertibleErrorCode());
    }
 
    object::COFFSymbolRef COFFSymbol = getObject().getCOFFSymbol(*SymbolIt);
    COFFSymbolIndex SymIndex = getObject().getSymbolIndex(COFFSymbol);
 
    Symbol *GraphSymbol = getGraphSymbol(SymIndex);
    if (!GraphSymbol)
      return make_error<StringError>(
          formatv("Could not find symbol at given index, did you add it to "
                  "JITSymbolTable? index: {0}, section: {1}",
                  SymIndex, FixupSect.getIndex()),
          inconvertibleErrorCode());
 
    int64_t Addend = 0;
    orc::ExecutorAddr FixupAddress =
        orc::ExecutorAddr(FixupSect.getAddress()) + Rel.getOffset();
    Edge::OffsetT Offset = FixupAddress - BlockToFix.getAddress();
 
    Edge::Kind Kind = Edge::Invalid;
    const char *FixupPtr = BlockToFix.getContent().data() + Offset;
    Symbol *ImageBase = GetImageBaseSymbol()(getGraph());
 
    switch (Rel.getType()) {
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_ADDR32NB: {
      if (!ImageBase)
        ImageBase = &addImageBaseSymbol();
      Kind = EdgeKind_coff_x86_64::Pointer32NB;
      Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_REL32: {
      Kind = EdgeKind_coff_x86_64::PCRel32;
      Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_REL32_1: {
      Kind = EdgeKind_coff_x86_64::PCRel32;
      Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
      Addend -= 1;
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_REL32_2: {
      Kind = EdgeKind_coff_x86_64::PCRel32;
      Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
      Addend -= 2;
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_REL32_3: {
      Kind = EdgeKind_coff_x86_64::PCRel32;
      Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
      Addend -= 3;
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_REL32_4: {
      Kind = EdgeKind_coff_x86_64::PCRel32;
      Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
      Addend -= 4;
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_REL32_5: {
      Kind = EdgeKind_coff_x86_64::PCRel32;
      Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
      Addend -= 5;
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_ADDR64: {
      Kind = EdgeKind_coff_x86_64::Pointer64;
      Addend = *reinterpret_cast<const support::little64_t *>(FixupPtr);
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_SECTION: {
      Kind = EdgeKind_coff_x86_64::SectionIdx16;
      Addend = *reinterpret_cast<const support::little16_t *>(FixupPtr);
      uint64_t SectionIdx = 0;
      if (COFFSymbol.isAbsolute())
        SectionIdx = getObject().getNumberOfSections() + 1;
      else
        SectionIdx = COFFSymbol.getSectionNumber();
 
      auto *AbsSym = &getGraph().addAbsoluteSymbol(
          "secidx", orc::ExecutorAddr(SectionIdx), 2, Linkage::Strong,
          Scope::Local, false);
      GraphSymbol = AbsSym;
      break;
    }
    case COFF::RelocationTypeAMD64::IMAGE_REL_AMD64_SECREL: {
      // FIXME: SECREL to external symbol should be handled
      if (!GraphSymbol->isDefined())
        return Error::success();
      Kind = EdgeKind_coff_x86_64::SecRel32;
      Addend = *reinterpret_cast<const support::little32_t *>(FixupPtr);
      break;
    }
    default: {
      return make_error<JITLinkError>("Unsupported x86_64 relocation:" +
                                      formatv("{0:d}", Rel.getType()));
    }
    };
 
    Edge GE(Kind, Offset, *GraphSymbol, Addend);
    LLVM_DEBUG({
      dbgs() << "    ";
      printEdge(dbgs(), BlockToFix, GE, getCOFFX86RelocationKindName(Kind));
      dbgs() << "\n";
    });
 
    BlockToFix.addEdge(std::move(GE));
 
    return Error::success();
  }
 
public:
  COFFLinkGraphBuilder_x86_64(const object::COFFObjectFile &Obj,
                              std::shared_ptr<orc::SymbolStringPool> SSP,
                              const Triple T, const SubtargetFeatures Features)
      : COFFLinkGraphBuilder(Obj, std::move(SSP), std::move(T),
                             std::move(Features),
                             getCOFFX86RelocationKindName) {}
};
 
class COFFLinkGraphLowering_x86_64 {
public:
  // Lowers COFF x86_64 specific edges to generic x86_64 edges.
  Error operator()(LinkGraph &G) {
    for (auto *B : G.blocks()) {
      for (auto &E : B->edges()) {
        switch (E.getKind()) {
        case EdgeKind_coff_x86_64::Pointer32NB: {
          auto ImageBase = GetImageBase(G);
          assert(ImageBase && "__ImageBase symbol must be defined");
          E.setAddend(E.getAddend() - ImageBase->getAddress().getValue());
          E.setKind(x86_64::Pointer32);
          break;
        }
        case EdgeKind_coff_x86_64::PCRel32: {
          E.setKind(x86_64::PCRel32);
          break;
        }
        case EdgeKind_coff_x86_64::Pointer64: {
          E.setKind(x86_64::Pointer64);
          break;
        }
        case EdgeKind_coff_x86_64::SectionIdx16: {
          E.setKind(x86_64::Pointer16);
          break;
        }
        case EdgeKind_coff_x86_64::SecRel32: {
          E.setAddend(E.getAddend() -
                      getSectionStart(E.getTarget().getSection()).getValue());
          E.setKind(x86_64::Pointer32);
          break;
        }
        default:
          break;
        }
      }
    }
    return Error::success();
  }
 
private:
  orc::ExecutorAddr getSectionStart(Section &Sec) {
    auto [It, Inserted] = SectionStartCache.try_emplace(&Sec);
    if (Inserted) {
      SectionRange Range(Sec);
      It->second = Range.getStart();
    }
    return It->second;
  }
 
  GetImageBaseSymbol GetImageBase;
  DenseMap<Section *, orc::ExecutorAddr> SectionStartCache;
};
 
// Synthesize COFF __imp_ Import Address Table (IAT) entries.
//
// For a dllimport reference, codegen emits an indirect access through a named
// __imp_X symbol, e.g.
//
//     callq *__imp_bar(%rip)        ; or, for data: movq __imp_g(%rip), %rax
//
// where __imp_X is an undefined external. This pass supplies the missing IAT
// entry by defining __imp_X over an 8-byte pointer slot that holds X's address:
//
//     __imp_bar:
//         .quad bar                 ; X is resolved as an ordinary external
//
// X is left external, so its address is provided by whatever resolves the
// JITDylib's externals (an import library, a DynamicLibrarySearchGenerator,
// AutoImportGenerator, ...). If X is unresolvable the link fails, exactly as a
// static link against the corresponding import library would.
//
// This is the COFF analog of the ELF/Mach-O GOT builder, but deliberately NOT
// written as a TableManager/visitEdge pass like x86_64::GOTTableManager. ELF's
// GOT references are *nameless* edge kinds, so that builder has to create an
// anonymous entry and redirect every edge to it (and, for our case, would then
// have to delete the now-orphaned __imp_X external so it isn't looked up).
// COFF instead references a *named* __imp_X symbol, so the simpler and more
// natural thing is to define that symbol over the slot: edges to __imp_X then
// resolve to it with no edge rewriting and no orphan cleanup, call and
// data-access references are handled identically, and sharing is automatic
// because there is exactly one __imp_X symbol per import.
//
// Direct (non-dllimport) references such as `callq foo` are intentionally not
// handled here: those are either kept in range by the slab allocator or thunked
// by the opt-in AutoImportGenerator -- both outside this pass.
Error synthesizeIATEntries_COFF_x86_64(LinkGraph &G) {
  static constexpr StringRef ImpPrefix = "__imp_";
 
  // Collect the external __imp_ symbols up front: we mutate the symbol lists
  // below (makeDefined / addExternalSymbol).
  SmallVector<Symbol *, 8> Imps;
  for (auto *Sym : G.external_symbols())
    if (Sym->hasName() && (*Sym->getName()).starts_with(ImpPrefix))
      Imps.push_back(Sym);
  if (Imps.empty())
    return Error::success();
 
  auto FindByName = [&](const orc::SymbolStringPtr &Name) -> Symbol * {
    if (auto *Sym = G.findExternalSymbolByName(Name))
      return Sym;
    if (auto *Sym = G.findDefinedSymbolByName(Name))
      return Sym;
    return nullptr;
  };
 
  Section &IATSec = G.createSection("$__IAT", orc::MemProt::Read);
 
  for (auto *Imp : Imps) {
    orc::SymbolStringPtr Base =
        G.intern((*Imp->getName()).drop_front(ImpPrefix.size()));
 
    // Find the real target X, or add it as an external to be resolved normally.
    Symbol *Target = FindByName(std::move(Base));
    if (!Target)
      Target = &G.addExternalSymbol(std::move(Base), 0,
                                    /*IsWeaklyReferenced=*/false);
 
    // 8-byte slot holding &X, with __imp_X defined over it.
    Symbol &Slot = x86_64::createAnonymousPointer(G, IATSec, Target);
    G.makeDefined(*Imp, Slot.getBlock(), 0, G.getPointerSize(), Linkage::Strong,
                  Scope::Local, /*IsLive=*/true);
  }
 
  return Error::success();
}
} // namespace
 
namespace llvm {
namespace jitlink {
 
/// Return the string name of the given COFF x86_64 edge kind.
const char *getCOFFX86RelocationKindName(Edge::Kind R) {
  switch (R) {
  case PCRel32:
    return "PCRel32";
  case Pointer32NB:
    return "Pointer32NB";
  case Pointer64:
    return "Pointer64";
  case SectionIdx16:
    return "SectionIdx16";
  case SecRel32:
    return "SecRel32";
  default:
    return x86_64::getEdgeKindName(R);
  }
}
 
Expected<std::unique_ptr<LinkGraph>> createLinkGraphFromCOFFObject_x86_64(
    MemoryBufferRef ObjectBuffer, std::shared_ptr<orc::SymbolStringPool> SSP) {
  LLVM_DEBUG({
    dbgs() << "Building jitlink graph for new input "
           << ObjectBuffer.getBufferIdentifier() << "...\n";
  });
 
  auto COFFObj = object::ObjectFile::createCOFFObjectFile(ObjectBuffer);
  if (!COFFObj)
    return COFFObj.takeError();
 
  auto Features = (*COFFObj)->getFeatures();
  if (!Features)
    return Features.takeError();
 
  return COFFLinkGraphBuilder_x86_64(**COFFObj, std::move(SSP),
                                     (*COFFObj)->makeTriple(),
                                     std::move(*Features))
      .buildGraph();
}
 
void link_COFF_x86_64(std::unique_ptr<LinkGraph> G,
                      std::unique_ptr<JITLinkContext> Ctx) {
  PassConfiguration Config;
  const Triple &TT = G->getTargetTriple();
  if (Ctx->shouldAddDefaultTargetPasses(TT)) {
    // Add a mark-live pass.
    if (auto MarkLive = Ctx->getMarkLivePass(TT)) {
      Config.PrePrunePasses.push_back(std::move(MarkLive));
      Config.PrePrunePasses.push_back(SEHFrameKeepAlivePass(".pdata"));
    } else
      Config.PrePrunePasses.push_back(markAllSymbolsLive);
 
    // Synthesize __imp_X IAT entries for dllimport references, like the GOT/PLT
    // builders for ELF/Mach-O. Runs in PostPrune (before external-symbol
    // lookup) so the X targets it introduces are resolved normally.
    Config.PostPrunePasses.push_back(synthesizeIATEntries_COFF_x86_64);
 
    // Add COFF edge lowering passes.
    Config.PreFixupPasses.push_back(COFFLinkGraphLowering_x86_64());
  }
 
  if (auto Err = Ctx->modifyPassConfig(*G, Config))
    return Ctx->notifyFailed(std::move(Err));
 
  COFFJITLinker_x86_64::link(std::move(Ctx), std::move(G), std::move(Config));
}
 
} // namespace jitlink
} // namespace llvm