1//===-- WebAssemblyAsmBackend.cpp - WebAssembly Assembler Backend ---------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8///
9/// \file
10/// This file implements the WebAssemblyAsmBackend class.
11///
12//===----------------------------------------------------------------------===//
13
14#include "MCTargetDesc/WebAssemblyFixupKinds.h"
15#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
16#include "llvm/MC/MCAsmBackend.h"
17#include "llvm/MC/MCAssembler.h"
18#include "llvm/MC/MCDirectives.h"
19#include "llvm/MC/MCExpr.h"
20#include "llvm/MC/MCFixupKindInfo.h"
21#include "llvm/MC/MCObjectWriter.h"
22#include "llvm/MC/MCSubtargetInfo.h"
23#include "llvm/MC/MCSymbol.h"
24#include "llvm/MC/MCWasmObjectWriter.h"
25#include "llvm/Support/ErrorHandling.h"
26#include "llvm/Support/raw_ostream.h"
27
28using namespace llvm;
29
30namespace {
31
32class WebAssemblyAsmBackend final : public MCAsmBackend {
33  bool Is64Bit;
34  bool IsEmscripten;
35
36public:
37  explicit WebAssemblyAsmBackend(bool Is64Bit, bool IsEmscripten)
38      : MCAsmBackend(support::little), Is64Bit(Is64Bit),
39        IsEmscripten(IsEmscripten) {}
40
41  unsigned getNumFixupKinds() const override {
42    return WebAssembly::NumTargetFixupKinds;
43  }
44
45  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
46
47  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
48                  const MCValue &Target, MutableArrayRef<char> Data,
49                  uint64_t Value, bool IsPCRel,
50                  const MCSubtargetInfo *STI) const override;
51
52  std::unique_ptr<MCObjectTargetWriter>
53  createObjectTargetWriter() const override;
54
55  // No instruction requires relaxation
56  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
57                            const MCRelaxableFragment *DF,
58                            const MCAsmLayout &Layout) const override {
59    return false;
60  }
61
62  bool mayNeedRelaxation(const MCInst &Inst,
63                         const MCSubtargetInfo &STI) const override {
64    return false;
65  }
66
67  void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
68                        MCInst &Res) const override {}
69
70  bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
71};
72
73const MCFixupKindInfo &
74WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
75  const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
76      // This table *must* be in the order that the fixup_* kinds are defined in
77      // WebAssemblyFixupKinds.h.
78      //
79      // Name                     Offset (bits) Size (bits)     Flags
80      {"fixup_sleb128_i32", 0, 5 * 8, 0},
81      {"fixup_sleb128_i64", 0, 10 * 8, 0},
82      {"fixup_uleb128_i32", 0, 5 * 8, 0},
83  };
84
85  if (Kind < FirstTargetFixupKind)
86    return MCAsmBackend::getFixupKindInfo(Kind);
87
88  assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
89         "Invalid kind!");
90  return Infos[Kind - FirstTargetFixupKind];
91}
92
93bool WebAssemblyAsmBackend::writeNopData(raw_ostream &OS,
94                                         uint64_t Count) const {
95  for (uint64_t I = 0; I < Count; ++I)
96    OS << char(WebAssembly::Nop);
97
98  return true;
99}
100
101void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm,
102                                       const MCFixup &Fixup,
103                                       const MCValue &Target,
104                                       MutableArrayRef<char> Data,
105                                       uint64_t Value, bool IsPCRel,
106                                       const MCSubtargetInfo *STI) const {
107  const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind());
108  assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags");
109
110  unsigned NumBytes = alignTo(Info.TargetSize, 8) / 8;
111  if (Value == 0)
112    return; // Doesn't change encoding.
113
114  // Shift the value into position.
115  Value <<= Info.TargetOffset;
116
117  unsigned Offset = Fixup.getOffset();
118  assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!");
119
120  // For each byte of the fragment that the fixup touches, mask in the
121  // bits from the fixup value.
122  for (unsigned I = 0; I != NumBytes; ++I)
123    Data[Offset + I] |= uint8_t((Value >> (I * 8)) & 0xff);
124}
125
126std::unique_ptr<MCObjectTargetWriter>
127WebAssemblyAsmBackend::createObjectTargetWriter() const {
128  return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten);
129}
130
131} // end anonymous namespace
132
133MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
134  return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten());
135}
136