llvm-project/lld/MachO/Arch/X86_64.cpp

//===- X86_64.cpp ---------------------------------------------------------===//
//
// 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 "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"

#include "lld/Common/ErrorHandler.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/Support/Endian.h"

using namespace llvm::MachO;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::macho;

namespace {

struct X86_64 : TargetInfo {
  X86_64();

  uint64_t getImplicitAddend(const uint8_t *loc, uint8_t type) const override;
  void relocateOne(uint8_t *loc, uint8_t type, uint64_t val) const override;

  void writeStub(uint8_t *buf, const DylibSymbol &) const override;
  void writeStubHelperHeader(uint8_t *buf) const override;
  void writeStubHelperEntry(uint8_t *buf, const DylibSymbol &,
                            uint64_t entryAddr) const override;

  void prepareDylibSymbolRelocation(DylibSymbol &, uint8_t type) override;
  uint64_t getDylibSymbolVA(const DylibSymbol &, uint8_t type) const override;
};

} // namespace

uint64_t X86_64::getImplicitAddend(const uint8_t *loc, uint8_t type) const {
  switch (type) {
  case X86_64_RELOC_BRANCH:
  case X86_64_RELOC_SIGNED:
  case X86_64_RELOC_SIGNED_1:
  case X86_64_RELOC_SIGNED_2:
  case X86_64_RELOC_SIGNED_4:
  case X86_64_RELOC_GOT_LOAD:
    return read32le(loc);
  case X86_64_RELOC_UNSIGNED:
    return read64le(loc);
  default:
    error("TODO: Unhandled relocation type " + std::to_string(type));
    return 0;
  }
}

void X86_64::relocateOne(uint8_t *loc, uint8_t type, uint64_t val) const {
  switch (type) {
  case X86_64_RELOC_BRANCH:
  case X86_64_RELOC_SIGNED:
  case X86_64_RELOC_SIGNED_1:
  case X86_64_RELOC_SIGNED_2:
  case X86_64_RELOC_SIGNED_4:
  case X86_64_RELOC_GOT_LOAD:
    // These types are only used for pc-relative relocations, so offset by 4
    // since the RIP has advanced by 4 at this point.
    write32le(loc, val - 4);
    break;
  case X86_64_RELOC_UNSIGNED:
    write64le(loc, val);
    break;
  default:
    llvm_unreachable(
        "getImplicitAddend should have flagged all unhandled relocation types");
  }
}

// The following methods emit a number of assembly sequences with RIP-relative
// addressing. Note that RIP-relative addressing on X86-64 has the RIP pointing
// to the next instruction, not the current instruction, so we always have to
// account for the current instruction's size when calculating offsets.
// writeRipRelative helps with that.
//
// bufAddr:  The virtual address corresponding to buf[0].
// bufOff:   The offset within buf of the next instruction.
// destAddr: The destination address that the current instruction references.
static void writeRipRelative(uint8_t *buf, uint64_t bufAddr, uint64_t bufOff,
                             uint64_t destAddr) {
  uint64_t rip = bufAddr + bufOff;
  // For the instructions we care about, the RIP-relative address is always
  // stored in the last 4 bytes of the instruction.
  write32le(buf + bufOff - 4, destAddr - rip);
}

static constexpr uint8_t stub[] = {
    0xff, 0x25, 0, 0, 0, 0, // jmpq *__la_symbol_ptr(%rip)
};

void X86_64::writeStub(uint8_t *buf, const DylibSymbol &sym) const {
  memcpy(buf, stub, 2); // just copy the two nonzero bytes
  uint64_t stubAddr = in.stubs->addr + sym.stubsIndex * sizeof(stub);
  writeRipRelative(buf, stubAddr, sizeof(stub),
                   in.lazyPointers->addr + sym.stubsIndex * WordSize);
}

static constexpr uint8_t stubHelperHeader[] = {
    0x4c, 0x8d, 0x1d, 0, 0, 0, 0, // 0x0: leaq ImageLoaderCache(%rip), %r11
    0x41, 0x53,                   // 0x7: pushq %r11
    0xff, 0x25, 0,    0, 0, 0,    // 0x9: jmpq *dyld_stub_binder@GOT(%rip)
    0x90,                         // 0xf: nop
};

static constexpr uint8_t stubHelperEntry[] = {
    0x68, 0, 0, 0, 0, // 0x0: pushq <bind offset>
    0xe9, 0, 0, 0, 0, // 0x5: jmp <__stub_helper>
};

void X86_64::writeStubHelperHeader(uint8_t *buf) const {
  memcpy(buf, stubHelperHeader, sizeof(stubHelperHeader));
  writeRipRelative(buf, in.stubHelper->addr, 7, in.imageLoaderCache->getVA());
  writeRipRelative(buf, in.stubHelper->addr, 0xf,
                   in.got->addr +
                       in.stubHelper->stubBinder->gotIndex * WordSize);
}

void X86_64::writeStubHelperEntry(uint8_t *buf, const DylibSymbol &sym,
                                  uint64_t entryAddr) const {
  memcpy(buf, stubHelperEntry, sizeof(stubHelperEntry));
  write32le(buf + 1, sym.lazyBindOffset);
  writeRipRelative(buf, entryAddr, sizeof(stubHelperEntry),
                   in.stubHelper->addr);
}

void X86_64::prepareDylibSymbolRelocation(DylibSymbol &sym, uint8_t type) {
  switch (type) {
  case X86_64_RELOC_GOT_LOAD:
    in.got->addEntry(sym);
    break;
  case X86_64_RELOC_BRANCH:
    in.stubs->addEntry(sym);
    break;
  case X86_64_RELOC_GOT:
    fatal("TODO: Unhandled dylib symbol relocation X86_64_RELOC_GOT");
  default:
    llvm_unreachable("Unexpected dylib relocation type");
  }
}

uint64_t X86_64::getDylibSymbolVA(const DylibSymbol &sym, uint8_t type) const {
  switch (type) {
  case X86_64_RELOC_GOT_LOAD:
    return in.got->addr + sym.gotIndex * WordSize;
  case X86_64_RELOC_BRANCH:
    return in.stubs->addr + sym.stubsIndex * sizeof(stub);
  case X86_64_RELOC_GOT:
    fatal("TODO: Unhandled dylib symbol relocation X86_64_RELOC_GOT");
  default:
    llvm_unreachable("Unexpected dylib relocation type");
  }
}

X86_64::X86_64() {
  cpuType = CPU_TYPE_X86_64;
  cpuSubtype = CPU_SUBTYPE_X86_64_ALL;

  stubSize = sizeof(stub);
  stubHelperHeaderSize = sizeof(stubHelperHeader);
  stubHelperEntrySize = sizeof(stubHelperEntry);
}

TargetInfo *macho::createX86_64TargetInfo() {
  static X86_64 t;
  return &t;
}