Subversion Repositories QNX 8.QNX8 LLVM/Clang compiler suite

//=== i386.h - Generic JITLink i386 edge kinds, utilities -*- 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

//

//===----------------------------------------------------------------------===//

//

// Generic utilities for graphs representing i386 objects.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_EXECUTIONENGINE_JITLINK_I386_H

#define LLVM_EXECUTIONENGINE_JITLINK_I386_H

#include "llvm/ExecutionEngine/JITLink/JITLink.h"

#include "llvm/ExecutionEngine/JITLink/TableManager.h"

namespace llvm::jitlink::i386 {

/// Represets i386 fixups

enum EdgeKind_i386 : Edge::Kind {

  /// None

  None = Edge::FirstRelocation,

  /// A plain 32-bit pointer value relocation.

  ///

  /// Fixup expression:

  ///   Fixup <- Target + Addend : uint32

  ///

  /// Errors:

  ///   - The target must reside in the low 32-bits of the address space,

  ///     otherwise an out-of-range error will be returned.

  ///

  Pointer32,

  /// A 32-bit PC-relative relocation.

  ///

  /// Represents a data/control flow instruction using PC-relative addressing

  /// to a target.

  ///

  /// The fixup expression for this kind includes an implicit offset to account

  /// for the PC (unlike the Delta edges) so that a PCRel32 with a target

  /// T and addend zero is a call/branch to the start (offset zero) of T.

  ///

  /// Fixup expression:

  ///   Fixup <- Target - (Fixup + 4) + Addend : int32

  ///

  /// Errors:

  ///   - The result of the fixup expression must fit into an int32, otherwise

  ///     an out-of-range error will be returned.

  ///

  PCRel32,

  /// A plain 16-bit pointer value relocation.

  ///

  /// Fixup expression:

  ///   Fixup <- Target + Addend : uint16

  ///

  /// Errors:

  ///   - The target must reside in the low 16-bits of the address space,

  ///     otherwise an out-of-range error will be returned.

  ///

  Pointer16,

  /// A 16-bit PC-relative relocation.

  ///

  /// Represents a data/control flow instruction using PC-relative addressing

  /// to a target.

  ///

  /// The fixup expression for this kind includes an implicit offset to account

  /// for the PC (unlike the Delta edges) so that a PCRel16 with a target

  /// T and addend zero is a call/branch to the start (offset zero) of T.

  ///

  /// Fixup expression:

  ///   Fixup <- Target - (Fixup + 4) + Addend : int16

  ///

  /// Errors:

  ///   - The result of the fixup expression must fit into an int16, otherwise

  ///     an out-of-range error will be returned.

  ///

  PCRel16,

  /// A 32-bit delta.

  ///

  /// Delta from the fixup to the target.

  ///

  /// Fixup expression:

  ///   Fixup <- Target - Fixup + Addend : int64

  ///

  /// Errors:

  ///   - The result of the fixup expression must fit into an int32, otherwise

  ///     an out-of-range error will be returned.

  Delta32,

  /// A 32-bit GOT delta.

  ///

  /// Delta from the global offset table to the target.

  ///

  /// Fixup expression:

  ///   Fixup <- Target - GOTSymbol + Addend : int32

  ///

  /// Errors:

  ///   - *ASSERTION* Failure to a null pointer GOTSymbol, which the GOT section

  ///     symbol was not been defined.

  Delta32FromGOT,

  /// A GOT entry offset within GOT getter/constructor, transformed to

  /// Delta32FromGOT pointing at the GOT entry for the original target.

  ///

  /// Indicates that this edge should be transformed into a Delta32FromGOT

  /// targeting the GOT entry for the edge's current target, maintaining the

  /// same addend.

  /// A GOT entry for the target should be created if one does not already

  /// exist.

  ///

  /// Edges of this kind are usually handled by a GOT builder pass inserted by

  /// default

  ///

  /// Fixup expression:

  ///   NONE

  ///

  /// Errors:

  ///   - *ASSERTION* Failure to handle edges of this kind prior to the fixup

  ///     phase will result in an assert/unreachable during the fixup phase

  RequestGOTAndTransformToDelta32FromGOT,

};

/// Returns a string name for the given i386 edge. For debugging purposes

/// only

const char *getEdgeKindName(Edge::Kind K);

/// Returns true if the given uint32_t value is in range for a uint16_t.

inline bool isInRangeForImmU16(uint32_t Value) {

  return Value <= std::numeric_limits<uint16_t>::max();

}

/// Returns true if the given int32_t value is in range for an int16_t.

inline bool isInRangeForImmS16(int32_t Value) {

  return (Value >= std::numeric_limits<int16_t>::min() &&

          Value <= std::numeric_limits<int16_t>::max());

}

/// Apply fixup expression for edge to block content.

inline Error applyFixup(LinkGraph &G, Block &B, const Edge &E,

                        const Symbol *GOTSymbol) {

  using namespace i386;

  using namespace llvm::support;

  char *BlockWorkingMem = B.getAlreadyMutableContent().data();

  char *FixupPtr = BlockWorkingMem + E.getOffset();

  auto FixupAddress = B.getAddress() + E.getOffset();

  switch (E.getKind()) {

  case i386::None: {

    break;

  }

  case i386::Pointer32: {

    uint32_t Value = E.getTarget().getAddress().getValue() + E.getAddend();

    *(ulittle32_t *)FixupPtr = Value;

    break;

  }

  case i386::PCRel32: {

    int32_t Value =

        E.getTarget().getAddress() - (FixupAddress + 4) + E.getAddend();

    *(little32_t *)FixupPtr = Value;

    break;

  }

  case i386::Pointer16: {

    uint32_t Value = E.getTarget().getAddress().getValue() + E.getAddend();

    if (LLVM_LIKELY(isInRangeForImmU16(Value)))

      *(ulittle16_t *)FixupPtr = Value;

    else

      return makeTargetOutOfRangeError(G, B, E);

    break;

  }

  case i386::PCRel16: {

    int32_t Value =

        E.getTarget().getAddress() - (FixupAddress + 4) + E.getAddend();

    if (LLVM_LIKELY(isInRangeForImmS16(Value)))

      *(little16_t *)FixupPtr = Value;

    else

      return makeTargetOutOfRangeError(G, B, E);

    break;

  }

  case i386::Delta32: {

    int32_t Value = E.getTarget().getAddress() - FixupAddress + E.getAddend();

    *(little32_t *)FixupPtr = Value;

    break;

  }

  case i386::Delta32FromGOT: {

    assert(GOTSymbol && "No GOT section symbol");

    int32_t Value =

        E.getTarget().getAddress() - GOTSymbol->getAddress() + E.getAddend();

    *(little32_t *)FixupPtr = Value;

    break;

  }

  default:

    return make_error<JITLinkError>(

        "In graph " + G.getName() + ", section " + B.getSection().getName() +

        "unsupported edge kind" + getEdgeKindName(E.getKind()));

  }

  return Error::success();

}

/// i386 pointer size.

constexpr uint32_t PointerSize = 4;

/// i386 null pointer content.

extern const char NullPointerContent[PointerSize];

/// Creates a new pointer block in the given section and returns an anonymous

/// symbol pointing to it.

///

/// If InitialTarget is given then an Pointer32 relocation will be added to the

/// block pointing at InitialTarget.

///

/// The pointer block will have the following default values:

///   alignment: 32-bit

///   alignment-offset: 0

///   address: highest allowable (~7U)

inline Symbol &createAnonymousPointer(LinkGraph &G, Section &PointerSection,

                                      Symbol *InitialTarget = nullptr,

                                      uint64_t InitialAddend = 0) {

  auto &B = G.createContentBlock(PointerSection, NullPointerContent,

                                 orc::ExecutorAddr(), 8, 0);

  if (InitialTarget)

    B.addEdge(Pointer32, 0, *InitialTarget, InitialAddend);

  return G.addAnonymousSymbol(B, 0, PointerSize, false, false);

}

/// Global Offset Table Builder.

class GOTTableManager : public TableManager<GOTTableManager> {

public:

  static StringRef getSectionName() { return "$__GOT"; }

  bool visitEdge(LinkGraph &G, Block *B, Edge &E) {

    Edge::Kind KindToSet = Edge::Invalid;

    switch (E.getKind()) {

    case i386::Delta32FromGOT: {

      // we need to make sure that the GOT section exists, but don't otherwise

      // need to fix up this edge

      getGOTSection(G);

      return false;

    }

    case i386::RequestGOTAndTransformToDelta32FromGOT:

      KindToSet = i386::Delta32FromGOT;

      break;

    default:

      return false;

    }

    assert(KindToSet != Edge::Invalid &&

           "Fell through switch, but no new kind to set");

    DEBUG_WITH_TYPE("jitlink", {

      dbgs() << "  Fixing " << G.getEdgeKindName(E.getKind()) << " edge at "

             << B->getFixupAddress(E) << " (" << B->getAddress() << " + "

             << formatv("{0:x}", E.getOffset()) << ")\n";

    });

    E.setKind(KindToSet);

    E.setTarget(getEntryForTarget(G, E.getTarget()));

    return true;

  }

  Symbol &createEntry(LinkGraph &G, Symbol &Target) {

    return createAnonymousPointer(G, getGOTSection(G), &Target);

  }

private:

  Section &getGOTSection(LinkGraph &G) {

    if (!GOTSection)

      GOTSection = &G.createSection(getSectionName(), orc::MemProt::Read);

    return *GOTSection;

  }

  Section *GOTSection = nullptr;

};

} // namespace llvm::jitlink::i386

#endif // LLVM_EXECUTIONENGINE_JITLINK_I386_H