ELF_riscv.cpp

Go to the documentation of this file.

//===------- ELF_riscv.cpp -JIT linker implementation for ELF/riscv -------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// ELF/riscv jit-link implementation.
//
//===----------------------------------------------------------------------===//
 
#include "llvm/ExecutionEngine/JITLink/ELF_riscv.h"
#include "ELFLinkGraphBuilder.h"
#include "JITLinkGeneric.h"
#include "PerGraphGOTAndPLTStubsBuilder.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/ExecutionEngine/JITLink/JITLink.h"
#include "llvm/ExecutionEngine/JITLink/riscv.h"
#include "llvm/Object/ELF.h"
#include "llvm/Object/ELFObjectFile.h"
 
#define DEBUG_TYPE "jitlink"
using namespace llvm;
using namespace llvm::jitlink;
using namespace llvm::jitlink::riscv;
 
namespace {
 
class PerGraphGOTAndPLTStubsBuilder_ELF_riscv
    : public PerGraphGOTAndPLTStubsBuilder<
          PerGraphGOTAndPLTStubsBuilder_ELF_riscv> {
public:
  static constexpr size_t StubEntrySize = 16;
  static const uint8_t NullGOTEntryContent[8];
  static const uint8_t RV64StubContent[StubEntrySize];
  static const uint8_t RV32StubContent[StubEntrySize];
 
  using PerGraphGOTAndPLTStubsBuilder<
      PerGraphGOTAndPLTStubsBuilder_ELF_riscv>::PerGraphGOTAndPLTStubsBuilder;
 
  bool isRV64() const { return G.getPointerSize() == 8; }
 
  bool isGOTEdgeToFix(Edge &E) const { return E.getKind() == R_RISCV_GOT_HI20; }
 
  Symbol &createGOTEntry(Symbol &Target) {
    Block &GOTBlock = G.createContentBlock(
        getGOTSection(), getGOTEntryBlockContent(), 0, G.getPointerSize(), 0);
    GOTBlock.addEdge(isRV64() ? R_RISCV_64 : R_RISCV_32, 0, Target, 0);
    return G.addAnonymousSymbol(GOTBlock, 0, G.getPointerSize(), false, false);
  }
 
  Symbol &createPLTStub(Symbol &Target) {
    Block &StubContentBlock =
        G.createContentBlock(getStubsSection(), getStubBlockContent(), 0, 4, 0);
    auto &GOTEntrySymbol = getGOTEntry(Target);
    StubContentBlock.addEdge(R_RISCV_CALL, 0, GOTEntrySymbol, 0);
    return G.addAnonymousSymbol(StubContentBlock, 0, StubEntrySize, true,
                                false);
  }
 
  void fixGOTEdge(Edge &E, Symbol &GOTEntry) {
    // Replace the relocation pair (R_RISCV_GOT_HI20, R_RISCV_PCREL_LO12)
    // with (R_RISCV_PCREL_HI20, R_RISCV_PCREL_LO12)
    // Therefore, here just change the R_RISCV_GOT_HI20 to R_RISCV_PCREL_HI20
    E.setKind(R_RISCV_PCREL_HI20);
    E.setTarget(GOTEntry);
  }
 
  void fixPLTEdge(Edge &E, Symbol &PLTStubs) {
    assert(E.getKind() == R_RISCV_CALL_PLT && "Not a R_RISCV_CALL_PLT edge?");
    E.setKind(R_RISCV_CALL);
    E.setTarget(PLTStubs);
  }
 
  bool isExternalBranchEdge(Edge &E) const {
    return E.getKind() == R_RISCV_CALL_PLT;
  }
 
private:
  Section &getGOTSection() const {
    if (!GOTSection)
      GOTSection = &G.createSection("$__GOT", MemProt::Read);
    return *GOTSection;
  }
 
  Section &getStubsSection() const {
    if (!StubsSection)
      StubsSection =
          &G.createSection("$__STUBS", MemProt::Read | MemProt::Exec);
    return *StubsSection;
  }
 
  ArrayRef<char> getGOTEntryBlockContent() {
    return {reinterpret_cast<const char *>(NullGOTEntryContent),
            G.getPointerSize()};
  }
 
  ArrayRef<char> getStubBlockContent() {
    auto StubContent = isRV64() ? RV64StubContent : RV32StubContent;
    return {reinterpret_cast<const char *>(StubContent), StubEntrySize};
  }
 
  mutable Section *GOTSection = nullptr;
  mutable Section *StubsSection = nullptr;
};
 
const uint8_t PerGraphGOTAndPLTStubsBuilder_ELF_riscv::NullGOTEntryContent[8] =
    {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
 
const uint8_t
    PerGraphGOTAndPLTStubsBuilder_ELF_riscv::RV64StubContent[StubEntrySize] = {
        0x17, 0x0e, 0x00, 0x00,  // auipc t3, literal
        0x03, 0x3e, 0x0e, 0x00,  // ld    t3, literal(t3)
        0x67, 0x00, 0x0e, 0x00,  // jr    t3
        0x13, 0x00, 0x00, 0x00}; // nop
 
const uint8_t
    PerGraphGOTAndPLTStubsBuilder_ELF_riscv::RV32StubContent[StubEntrySize] = {
        0x17, 0x0e, 0x00, 0x00,  // auipc t3, literal
        0x03, 0x2e, 0x0e, 0x00,  // lw    t3, literal(t3)
        0x67, 0x00, 0x0e, 0x00,  // jr    t3
        0x13, 0x00, 0x00, 0x00}; // nop
} // namespace
namespace llvm {
namespace jitlink {
 
static Expected<const Edge &> getRISCVPCRelHi20(const Edge &E) {
  using namespace riscv;
  assert((E.getKind() == R_RISCV_PCREL_LO12_I ||
          E.getKind() == R_RISCV_PCREL_LO12_S) &&
         "Can only have high relocation for R_RISCV_PCREL_LO12_I or "
         "R_RISCV_PCREL_LO12_S");
 
  const Symbol &Sym = E.getTarget();
  const Block &B = Sym.getBlock();
  JITTargetAddress Offset = Sym.getOffset();
 
  struct Comp {
    bool operator()(const Edge &Lhs, JITTargetAddress Offset) {
      return Lhs.getOffset() < Offset;
    }
    bool operator()(JITTargetAddress Offset, const Edge &Rhs) {
      return Offset < Rhs.getOffset();
    }
  };
 
  auto Bound =
      std::equal_range(B.edges().begin(), B.edges().end(), Offset, Comp{});
 
  for (auto It = Bound.first; It != Bound.second; ++It) {
    if (It->getKind() == R_RISCV_PCREL_HI20)
      return *It;
  }
 
  return make_error<JITLinkError>(
      "No HI20 PCREL relocation type be found for LO12 PCREL relocation type");
}
 
static uint32_t extractBits(uint64_t Num, unsigned High, unsigned Low) {
  return (Num & ((1ULL << (High + 1)) - 1)) >> Low;
}
 
class ELFJITLinker_riscv : public JITLinker<ELFJITLinker_riscv> {
  friend class JITLinker<ELFJITLinker_riscv>;
 
public:
  ELFJITLinker_riscv(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 {
    using namespace riscv;
    using namespace llvm::support;
 
    char *BlockWorkingMem = B.getAlreadyMutableContent().data();
    char *FixupPtr = BlockWorkingMem + E.getOffset();
    JITTargetAddress FixupAddress = B.getAddress() + E.getOffset();
    switch (E.getKind()) {
    case R_RISCV_32: {
      int64_t Value = E.getTarget().getAddress() + E.getAddend();
      *(little32_t *)FixupPtr = static_cast<uint32_t>(Value);
      break;
    }
    case R_RISCV_64: {
      int64_t Value = E.getTarget().getAddress() + E.getAddend();
      *(little64_t *)FixupPtr = static_cast<uint64_t>(Value);
      break;
    }
    case R_RISCV_HI20: {
      int64_t Value = E.getTarget().getAddress() + E.getAddend();
      int32_t Hi = (Value + 0x800) & 0xFFFFF000;
      uint32_t RawInstr = *(little32_t *)FixupPtr;
      *(little32_t *)FixupPtr = (RawInstr & 0xFFF) | static_cast<uint32_t>(Hi);
      break;
    }
    case R_RISCV_LO12_I: {
      int64_t Value = E.getTarget().getAddress() + E.getAddend();
      int32_t Lo = Value & 0xFFF;
      uint32_t RawInstr = *(little32_t *)FixupPtr;
      *(little32_t *)FixupPtr =
          (RawInstr & 0xFFFFF) | (static_cast<uint32_t>(Lo & 0xFFF) << 20);
      break;
    }
    case R_RISCV_CALL: {
      int64_t Value = E.getTarget().getAddress() + E.getAddend() - FixupAddress;
      int32_t Hi = (Value + 0x800) & 0xFFFFF000;
      int32_t Lo = Value & 0xFFF;
      uint32_t RawInstrAuipc = *(little32_t *)FixupPtr;
      uint32_t RawInstrJalr = *(little32_t *)(FixupPtr + 4);
      *(little32_t *)FixupPtr = RawInstrAuipc | static_cast<uint32_t>(Hi);
      *(little32_t *)(FixupPtr + 4) =
          RawInstrJalr | (static_cast<uint32_t>(Lo) << 20);
      break;
    }
    case R_RISCV_PCREL_HI20: {
      int64_t Value = E.getTarget().getAddress() + E.getAddend() - FixupAddress;
      int32_t Hi = (Value + 0x800) & 0xFFFFF000;
      uint32_t RawInstr = *(little32_t *)FixupPtr;
      *(little32_t *)FixupPtr = (RawInstr & 0xFFF) | static_cast<uint32_t>(Hi);
      break;
    }
    case R_RISCV_PCREL_LO12_I: {
      auto RelHI20 = getRISCVPCRelHi20(E);
      if (!RelHI20)
        return RelHI20.takeError();
      int64_t Value = RelHI20->getTarget().getAddress() +
                      RelHI20->getAddend() - E.getTarget().getAddress();
      int64_t Lo = Value & 0xFFF;
      uint32_t RawInstr = *(little32_t *)FixupPtr;
      *(little32_t *)FixupPtr =
          (RawInstr & 0xFFFFF) | (static_cast<uint32_t>(Lo & 0xFFF) << 20);
      break;
    }
    case R_RISCV_PCREL_LO12_S: {
      auto RelHI20 = getRISCVPCRelHi20(E);
      int64_t Value = RelHI20->getTarget().getAddress() +
                      RelHI20->getAddend() - E.getTarget().getAddress();
      int64_t Lo = Value & 0xFFF;
      uint32_t Imm31_25 = extractBits(Lo, 11, 5) << 25;
      uint32_t Imm11_7 = extractBits(Lo, 4, 0) << 7;
      uint32_t RawInstr = *(little32_t *)FixupPtr;
 
      *(little32_t *)FixupPtr = (RawInstr & 0x1FFF07F) | Imm31_25 | Imm11_7;
      break;
    }
    }
    return Error::success();
  }
};
 
template <typename ELFT>
class ELFLinkGraphBuilder_riscv : public ELFLinkGraphBuilder<ELFT> {
private:
  static Expected<riscv::EdgeKind_riscv>
  getRelocationKind(const uint32_t Type) {
    using namespace riscv;
    switch (Type) {
    case ELF::R_RISCV_32:
      return EdgeKind_riscv::R_RISCV_32;
    case ELF::R_RISCV_64:
      return EdgeKind_riscv::R_RISCV_64;
    case ELF::R_RISCV_HI20:
      return EdgeKind_riscv::R_RISCV_HI20;
    case ELF::R_RISCV_LO12_I:
      return EdgeKind_riscv::R_RISCV_LO12_I;
    case ELF::R_RISCV_CALL:
      return EdgeKind_riscv::R_RISCV_CALL;
    case ELF::R_RISCV_PCREL_HI20:
      return EdgeKind_riscv::R_RISCV_PCREL_HI20;
    case ELF::R_RISCV_PCREL_LO12_I:
      return EdgeKind_riscv::R_RISCV_PCREL_LO12_I;
    case ELF::R_RISCV_PCREL_LO12_S:
      return EdgeKind_riscv::R_RISCV_PCREL_LO12_S;
    case ELF::R_RISCV_GOT_HI20:
      return EdgeKind_riscv::R_RISCV_GOT_HI20;
    case ELF::R_RISCV_CALL_PLT:
      return EdgeKind_riscv::R_RISCV_CALL_PLT;
    }
 
    return make_error<JITLinkError>("Unsupported riscv relocation:" +
                                    formatv("{0:d}", Type));
  }
 
  Error addRelocations() override {
    LLVM_DEBUG(dbgs() << "Processing relocations:\n");
 
    using Base = ELFLinkGraphBuilder<ELFT>;
    using Self = ELFLinkGraphBuilder_riscv<ELFT>;
    for (const auto &RelSect : Base::Sections)
      if (Error Err = Base::forEachRelocation(RelSect, this,
                                              &Self::addSingleRelocation))
        return Err;
 
    return Error::success();
  }
 
  Error addSingleRelocation(const typename ELFT::Rela &Rel,
                            const typename ELFT::Shdr &FixupSect,
                            Section &GraphSection) {
    using Base = ELFLinkGraphBuilder<ELFT>;
 
    uint32_t SymbolIndex = Rel.getSymbol(false);
    auto ObjSymbol = Base::Obj.getRelocationSymbol(Rel, Base::SymTabSec);
    if (!ObjSymbol)
      return ObjSymbol.takeError();
 
    Symbol *GraphSymbol = Base::getGraphSymbol(SymbolIndex);
    if (!GraphSymbol)
      return make_error<StringError>(
          formatv("Could not find symbol at given index, did you add it to "
                  "JITSymbolTable? index: {0}, shndx: {1} Size of table: {2}",
                  SymbolIndex, (*ObjSymbol)->st_shndx,
                  Base::GraphSymbols.size()),
          inconvertibleErrorCode());
 
    uint32_t Type = Rel.getType(false);
    Expected<riscv::EdgeKind_riscv> Kind = getRelocationKind(Type);
    if (!Kind)
      return Kind.takeError();
 
    int64_t Addend = Rel.r_addend;
    Block *BlockToFix = *(GraphSection.blocks().begin());
    JITTargetAddress FixupAddress = FixupSect.sh_addr + Rel.r_offset;
    Edge::OffsetT Offset = FixupAddress - BlockToFix->getAddress();
    Edge GE(*Kind, Offset, *GraphSymbol, Addend);
    LLVM_DEBUG({
      dbgs() << "    ";
      printEdge(dbgs(), *BlockToFix, GE, riscv::getEdgeKindName(*Kind));
      dbgs() << "\n";
    });
 
    BlockToFix->addEdge(std::move(GE));
    return Error::success();
  }
 
public:
  ELFLinkGraphBuilder_riscv(StringRef FileName,
                            const object::ELFFile<ELFT> &Obj, const Triple T)
      : ELFLinkGraphBuilder<ELFT>(Obj, std::move(T), FileName,
                                  riscv::getEdgeKindName) {}
};
 
Expected<std::unique_ptr<LinkGraph>>
createLinkGraphFromELFObject_riscv(MemoryBufferRef ObjectBuffer) {
  LLVM_DEBUG({
    dbgs() << "Building jitlink graph for new input "
           << ObjectBuffer.getBufferIdentifier() << "...\n";
  });
 
  auto ELFObj = object::ObjectFile::createELFObjectFile(ObjectBuffer);
  if (!ELFObj)
    return ELFObj.takeError();
 
  if ((*ELFObj)->getArch() == Triple::riscv64) {
    auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF64LE>>(**ELFObj);
    return ELFLinkGraphBuilder_riscv<object::ELF64LE>(
               (*ELFObj)->getFileName(), ELFObjFile.getELFFile(),
               (*ELFObj)->makeTriple())
        .buildGraph();
  } else {
    assert((*ELFObj)->getArch() == Triple::riscv32 &&
           "Invalid triple for RISCV ELF object file");
    auto &ELFObjFile = cast<object::ELFObjectFile<object::ELF32LE>>(**ELFObj);
    return ELFLinkGraphBuilder_riscv<object::ELF32LE>(
               (*ELFObj)->getFileName(), ELFObjFile.getELFFile(),
               (*ELFObj)->makeTriple())
        .buildGraph();
  }
}
 
void link_ELF_riscv(std::unique_ptr<LinkGraph> G,
                    std::unique_ptr<JITLinkContext> Ctx) {
  PassConfiguration Config;
  const Triple &TT = G->getTargetTriple();
  if (Ctx->shouldAddDefaultTargetPasses(TT)) {
    if (auto MarkLive = Ctx->getMarkLivePass(TT))
      Config.PrePrunePasses.push_back(std::move(MarkLive));
    else
      Config.PrePrunePasses.push_back(markAllSymbolsLive);
    Config.PostPrunePasses.push_back(
        PerGraphGOTAndPLTStubsBuilder_ELF_riscv::asPass);
  }
  if (auto Err = Ctx->modifyPassConfig(*G, Config))
    return Ctx->notifyFailed(std::move(Err));
 
  ELFJITLinker_riscv::link(std::move(Ctx), std::move(G), std::move(Config));
}
 
} // namespace jitlink
} // namespace llvm