loongarch.h

Go to the documentation of this file.

//= loongarch.h - Generic JITLink loongarch 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 loongarch objects.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_EXECUTIONENGINE_JITLINK_LOONGARCH_H
#define LLVM_EXECUTIONENGINE_JITLINK_LOONGARCH_H
 
#include "TableManager.h"
#include "llvm/ExecutionEngine/JITLink/JITLink.h"
#include "llvm/ExecutionEngine/Orc/Shared/MemoryFlags.h"
 
namespace llvm {
namespace jitlink {
namespace loongarch {
 
/// Represents loongarch fixups.
enum EdgeKind_loongarch : Edge::Kind {
  /// A plain 64-bit pointer value relocation.
  ///
  /// Fixup expression:
  ///   Fixup <- Target + Addend : uint64
  ///
  Pointer64 = 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 26-bit PC-relative branch.
  ///
  /// Represents a PC-relative call or branch to a target within +/-128Mb. The
  /// target must be 4-byte aligned.
  ///
  /// Fixup expression:
  ///   Fixup <- (Target - Fixup + Addend) >> 2 : int26
  ///
  /// Notes:
  ///   The '26' in the name refers to the number operand bits and follows the
  /// naming convention used by the corresponding ELF relocations. Since the low
  /// two bits must be zero (because of the 4-byte alignment of the target) the
  /// operand is effectively a signed 28-bit number.
  ///
  /// Errors:
  ///   - The result of the unshifted part of the fixup expression must be
  ///     4-byte aligned otherwise an alignment error will be returned.
  ///   - The result of the fixup expression must fit into an int26 otherwise an
  ///     out-of-range error will be returned.
  ///
  Branch26PCRel,
 
  /// A 32-bit delta.
  ///
  /// Delta from the fixup to the target.
  ///
  /// Fixup expression:
  ///   Fixup <- Target - Fixup + Addend : int32
  ///
  /// 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 negative delta.
  ///
  /// Delta from the target back to the fixup.
  ///
  /// Fixup expression:
  ///   Fixup <- Fixup - Target + Addend : int32
  ///
  /// Errors:
  ///   - The result of the fixup expression must fit into an int32, otherwise
  ///     an out-of-range error will be returned.
  ///
  NegDelta32,
 
  /// A 64-bit delta.
  ///
  /// Delta from the fixup to the target.
  ///
  /// Fixup expression:
  ///   Fixup <- Target - Fixup + Addend : int64
  ///
  Delta64,
 
  /// The signed 20-bit delta from the fixup page to the page containing the
  /// target.
  ///
  /// Fixup expression:
  ///   Fixup <- (((Target + Addend + ((Target + Addend) & 0x800)) & ~0xfff)
  //              - (Fixup & ~0xfff)) >> 12 : int20
  ///
  /// Notes:
  ///   For PCALAU12I fixups.
  ///
  /// Errors:
  ///   - The result of the fixup expression must fit into an int20 otherwise an
  ///     out-of-range error will be returned.
  ///
  Page20,
 
  /// The 12-bit offset of the target within its page.
  ///
  /// Typically used to fix up ADDI/LD_W/LD_D immediates.
  ///
  /// Fixup expression:
  ///   Fixup <- ((Target + Addend) >> Shift) & 0xfff : int12
  ///
  PageOffset12,
 
  /// A GOT entry getter/constructor, transformed to Page20 pointing at the GOT
  /// entry for the original target.
  ///
  /// Indicates that this edge should be transformed into a Page20 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/PLT 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.
  ///
  RequestGOTAndTransformToPage20,
 
  /// A GOT entry getter/constructor, transformed to Pageoffset12 pointing at
  /// the GOT entry for the original target.
  ///
  /// Indicates that this edge should be transformed into a PageOffset12
  /// 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/PLT builder pass inserted
  /// by default.
  ///
  /// Fixup expression:
  ///   NONE
  ///
  RequestGOTAndTransformToPageOffset12,
};
 
/// Returns a string name for the given loongarch edge. For debugging purposes
/// only.
const char *getEdgeKindName(Edge::Kind K);
 
// Returns extract bits Val[Hi:Lo].
inline uint32_t extractBits(uint32_t Val, unsigned Hi, unsigned Lo) {
  return (Val & (((1UL << (Hi + 1)) - 1))) >> Lo;
}
 
/// Apply fixup expression for edge to block content.
inline Error applyFixup(LinkGraph &G, Block &B, const Edge &E) {
  using namespace support;
 
  char *BlockWorkingMem = B.getAlreadyMutableContent().data();
  char *FixupPtr = BlockWorkingMem + E.getOffset();
  uint64_t FixupAddress = (B.getAddress() + E.getOffset()).getValue();
  uint64_t TargetAddress = E.getTarget().getAddress().getValue();
  int64_t Addend = E.getAddend();
 
  switch (E.getKind()) {
  case Pointer64:
    *(ulittle64_t *)FixupPtr = TargetAddress + Addend;
    break;
  case Pointer32: {
    uint64_t Value = TargetAddress + Addend;
    if (Value > std::numeric_limits<uint32_t>::max())
      return makeTargetOutOfRangeError(G, B, E);
    *(ulittle32_t *)FixupPtr = Value;
    break;
  }
  case Branch26PCRel: {
    int64_t Value = TargetAddress - FixupAddress + Addend;
 
    if (!isInt<28>(Value))
      return makeTargetOutOfRangeError(G, B, E);
 
    if (!isShiftedInt<26, 2>(Value))
      return makeAlignmentError(orc::ExecutorAddr(FixupAddress), Value, 4, E);
 
    uint32_t RawInstr = *(little32_t *)FixupPtr;
    uint32_t Imm = static_cast<uint32_t>(Value >> 2);
    uint32_t Imm15_0 = extractBits(Imm, /*Hi=*/15, /*Lo=*/0) << 10;
    uint32_t Imm25_16 = extractBits(Imm, /*Hi=*/25, /*Lo=*/16);
    *(little32_t *)FixupPtr = RawInstr | Imm15_0 | Imm25_16;
    break;
  }
  case Delta32: {
    int64_t Value = TargetAddress - FixupAddress + Addend;
 
    if (!isInt<32>(Value))
      return makeTargetOutOfRangeError(G, B, E);
    *(little32_t *)FixupPtr = Value;
    break;
  }
  case NegDelta32: {
    int64_t Value = FixupAddress - TargetAddress + Addend;
    if (!isInt<32>(Value))
      return makeTargetOutOfRangeError(G, B, E);
    *(little32_t *)FixupPtr = Value;
    break;
  }
  case Delta64:
    *(little64_t *)FixupPtr = TargetAddress - FixupAddress + Addend;
    break;
  case Page20: {
    uint64_t Target = TargetAddress + Addend;
    uint64_t TargetPage =
        (Target + (Target & 0x800)) & ~static_cast<uint64_t>(0xfff);
    uint64_t PCPage = FixupAddress & ~static_cast<uint64_t>(0xfff);
 
    int64_t PageDelta = TargetPage - PCPage;
    if (!isInt<32>(PageDelta))
      return makeTargetOutOfRangeError(G, B, E);
 
    uint32_t RawInstr = *(little32_t *)FixupPtr;
    uint32_t Imm31_12 = extractBits(PageDelta, /*Hi=*/31, /*Lo=*/12) << 5;
    *(little32_t *)FixupPtr = RawInstr | Imm31_12;
    break;
  }
  case PageOffset12: {
    uint64_t TargetOffset = (TargetAddress + Addend) & 0xfff;
 
    uint32_t RawInstr = *(ulittle32_t *)FixupPtr;
    uint32_t Imm11_0 = TargetOffset << 10;
    *(ulittle32_t *)FixupPtr = RawInstr | Imm11_0;
    break;
  }
  default:
    return make_error<JITLinkError>(
        "In graph " + G.getName() + ", section " + B.getSection().getName() +
        " unsupported edge kind " + getEdgeKindName(E.getKind()));
  }
 
  return Error::success();
}
 
/// loongarch null pointer content.
extern const char NullPointerContent[8];
inline ArrayRef<char> getGOTEntryBlockContent(LinkGraph &G) {
  return {reinterpret_cast<const char *>(NullPointerContent),
          G.getPointerSize()};
}
 
/// loongarch stub content.
///
/// Contains the instruction sequence for an indirect jump via an in-memory
/// pointer:
///   pcalau12i $t8, %page20(ptr)
///   ld.[w/d]  $t8, %pageoff12(ptr)
///   jr        $t8
constexpr size_t StubEntrySize = 12;
extern const uint8_t LA64StubContent[StubEntrySize];
extern const uint8_t LA32StubContent[StubEntrySize];
inline ArrayRef<char> getStubBlockContent(LinkGraph &G) {
  auto StubContent =
      G.getPointerSize() == 8 ? LA64StubContent : LA32StubContent;
  return {reinterpret_cast<const char *>(StubContent), StubEntrySize};
}
 
/// Creates a new pointer block in the given section and returns an
/// Anonymous symbol pointing to it.
///
/// If InitialTarget is given then an Pointer64 relocation will be added to the
/// block pointing at InitialTarget.
///
/// The pointer block will have the following default values:
///   alignment: PointerSize
///   alignment-offset: 0
inline Symbol &createAnonymousPointer(LinkGraph &G, Section &PointerSection,
                                      Symbol *InitialTarget = nullptr,
                                      uint64_t InitialAddend = 0) {
  auto &B = G.createContentBlock(PointerSection, getGOTEntryBlockContent(G),
                                 orc::ExecutorAddr(), G.getPointerSize(), 0);
  if (InitialTarget)
    B.addEdge(G.getPointerSize() == 8 ? Pointer64 : Pointer32, 0,
              *InitialTarget, InitialAddend);
  return G.addAnonymousSymbol(B, 0, G.getPointerSize(), false, false);
}
 
/// Create a jump stub that jumps via the pointer at the given symbol and
/// an anonymous symbol pointing to it. Return the anonymous symbol.
inline Symbol &createAnonymousPointerJumpStub(LinkGraph &G,
                                              Section &StubSection,
                                              Symbol &PointerSymbol) {
  Block &StubContentBlock = G.createContentBlock(
      StubSection, getStubBlockContent(G), orc::ExecutorAddr(), 4, 0);
  StubContentBlock.addEdge(Page20, 0, PointerSymbol, 0);
  StubContentBlock.addEdge(PageOffset12, 4, PointerSymbol, 0);
  return G.addAnonymousSymbol(StubContentBlock, 0, StubEntrySize, true, 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 RequestGOTAndTransformToPage20:
      KindToSet = Page20;
      break;
    case RequestGOTAndTransformToPageOffset12:
      KindToSet = PageOffset12;
      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 | orc::MemProt::Exec);
    return *GOTSection;
  }
 
  Section *GOTSection = nullptr;
};
 
/// Procedure Linkage Table Builder.
class PLTTableManager : public TableManager<PLTTableManager> {
public:
  PLTTableManager(GOTTableManager &GOT) : GOT(GOT) {}
 
  static StringRef getSectionName() { return "$__STUBS"; }
 
  bool visitEdge(LinkGraph &G, Block *B, Edge &E) {
    if (E.getKind() == Branch26PCRel && !E.getTarget().isDefined()) {
      DEBUG_WITH_TYPE("jitlink", {
        dbgs() << "  Fixing " << G.getEdgeKindName(E.getKind()) << " edge at "
               << B->getFixupAddress(E) << " (" << B->getAddress() << " + "
               << formatv("{0:x}", E.getOffset()) << ")\n";
      });
      E.setTarget(getEntryForTarget(G, E.getTarget()));
      return true;
    }
    return false;
  }
 
  Symbol &createEntry(LinkGraph &G, Symbol &Target) {
    return createAnonymousPointerJumpStub(G, getStubsSection(G),
                                          GOT.getEntryForTarget(G, Target));
  }
 
public:
  Section &getStubsSection(LinkGraph &G) {
    if (!StubsSection)
      StubsSection = &G.createSection(getSectionName(),
                                      orc::MemProt::Read | orc::MemProt::Exec);
    return *StubsSection;
  }
 
  GOTTableManager &GOT;
  Section *StubsSection = nullptr;
};
 
} // namespace loongarch
} // namespace jitlink
} // namespace llvm
 
#endif