llvm-project/lld/MachO/Arch/ARM64.cpp

//===- ARM64.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 "Arch/ARM64Common.h"
#include "InputFiles.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"

#include "lld/Common/ErrorHandler.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/MathExtras.h"

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

namespace {

struct ARM64 : ARM64Common {
  ARM64();
  void writeStub(uint8_t *buf, const Symbol &) const override;
  void writeStubHelperHeader(uint8_t *buf) const override;
  void writeStubHelperEntry(uint8_t *buf, const DylibSymbol &,
                            uint64_t entryAddr) const override;
  const RelocAttrs &getRelocAttrs(uint8_t type) const override;
  void populateThunk(InputSection *thunk, Symbol *funcSym) override;
};

} // namespace

// Random notes on reloc types:
// ADDEND always pairs with BRANCH26, PAGE21, or PAGEOFF12
// POINTER_TO_GOT: ld64 supports a 4-byte pc-relative form as well as an 8-byte
// absolute version of this relocation. The semantics of the absolute relocation
// are weird -- it results in the value of the GOT slot being written, instead
// of the address. Let's not support it unless we find a real-world use case.

const RelocAttrs &ARM64::getRelocAttrs(uint8_t type) const {
  static const std::array<RelocAttrs, 11> relocAttrsArray{{
#define B(x) RelocAttrBits::x
      {"UNSIGNED",
       B(UNSIGNED) | B(ABSOLUTE) | B(EXTERN) | B(LOCAL) | B(BYTE4) | B(BYTE8)},
      {"SUBTRACTOR", B(SUBTRAHEND) | B(EXTERN) | B(BYTE4) | B(BYTE8)},
      {"BRANCH26", B(PCREL) | B(EXTERN) | B(BRANCH) | B(BYTE4)},
      {"PAGE21", B(PCREL) | B(EXTERN) | B(BYTE4)},
      {"PAGEOFF12", B(ABSOLUTE) | B(EXTERN) | B(BYTE4)},
      {"GOT_LOAD_PAGE21", B(PCREL) | B(EXTERN) | B(GOT) | B(BYTE4)},
      {"GOT_LOAD_PAGEOFF12",
       B(ABSOLUTE) | B(EXTERN) | B(GOT) | B(LOAD) | B(BYTE4)},
      {"POINTER_TO_GOT", B(PCREL) | B(EXTERN) | B(GOT) | B(POINTER) | B(BYTE4)},
      {"TLVP_LOAD_PAGE21", B(PCREL) | B(EXTERN) | B(TLV) | B(BYTE4)},
      {"TLVP_LOAD_PAGEOFF12",
       B(ABSOLUTE) | B(EXTERN) | B(TLV) | B(LOAD) | B(BYTE4)},
      {"ADDEND", B(ADDEND)},
#undef B
  }};
  assert(type < relocAttrsArray.size() && "invalid relocation type");
  if (type >= relocAttrsArray.size())
    return invalidRelocAttrs;
  return relocAttrsArray[type];
}

static constexpr uint32_t stubCode[] = {
    0x90000010, // 00: adrp  x16, __la_symbol_ptr@page
    0xf9400210, // 04: ldr   x16, [x16, __la_symbol_ptr@pageoff]
    0xd61f0200, // 08: br    x16
};

void ARM64::writeStub(uint8_t *buf8, const Symbol &sym) const {
  ::writeStub<LP64>(buf8, stubCode, sym);
}

static constexpr uint32_t stubHelperHeaderCode[] = {
    0x90000011, // 00: adrp  x17, _dyld_private@page
    0x91000231, // 04: add   x17, x17, _dyld_private@pageoff
    0xa9bf47f0, // 08: stp   x16/x17, [sp, #-16]!
    0x90000010, // 0c: adrp  x16, dyld_stub_binder@page
    0xf9400210, // 10: ldr   x16, [x16, dyld_stub_binder@pageoff]
    0xd61f0200, // 14: br    x16
};

void ARM64::writeStubHelperHeader(uint8_t *buf8) const {
  ::writeStubHelperHeader<LP64>(buf8, stubHelperHeaderCode);
}

static constexpr uint32_t stubHelperEntryCode[] = {
    0x18000050, // 00: ldr  w16, l0
    0x14000000, // 04: b    stubHelperHeader
    0x00000000, // 08: l0: .long 0
};

void ARM64::writeStubHelperEntry(uint8_t *buf8, const DylibSymbol &sym,
                                 uint64_t entryVA) const {
  ::writeStubHelperEntry(buf8, stubHelperEntryCode, sym, entryVA);
}

// A thunk is the relaxed variation of stubCode. We don't need the
// extra indirection through a lazy pointer because the target address
// is known at link time.
static constexpr uint32_t thunkCode[] = {
    0x90000010, // 00: adrp  x16, <thunk.ptr>@page
    0x91000210, // 04: add   x16, [x16,<thunk.ptr>@pageoff]
    0xd61f0200, // 08: br    x16
};

void ARM64::populateThunk(InputSection *thunk, Symbol *funcSym) {
  thunk->align = 4;
  thunk->data = {reinterpret_cast<const uint8_t *>(thunkCode),
                 sizeof(thunkCode)};
  thunk->relocs.push_back({/*type=*/ARM64_RELOC_PAGEOFF12,
                           /*pcrel=*/false, /*length=*/2,
                           /*offset=*/4, /*addend=*/0,
                           /*referent=*/funcSym});
  thunk->relocs.push_back({/*type=*/ARM64_RELOC_PAGE21,
                           /*pcrel=*/true, /*length=*/2,
                           /*offset=*/0, /*addend=*/0,
                           /*referent=*/funcSym});
}

ARM64::ARM64() : ARM64Common(LP64()) {
  cpuType = CPU_TYPE_ARM64;
  cpuSubtype = CPU_SUBTYPE_ARM64_ALL;

  stubSize = sizeof(stubCode);
  thunkSize = sizeof(thunkCode);

  // Branch immediate is two's complement 26 bits, which is implicitly
  // multiplied by 4 (since all functions are 4-aligned: The branch range
  // is -4*(2**(26-1))..4*(2**(26-1) - 1).
  backwardBranchRange = 128 * 1024 * 1024;
  forwardBranchRange = backwardBranchRange - 4;

  stubHelperHeaderSize = sizeof(stubHelperHeaderCode);
  stubHelperEntrySize = sizeof(stubHelperEntryCode);
}

TargetInfo *macho::createARM64TargetInfo() {
  static ARM64 t;
  return &t;
}