LLVM  10.0.0svn
WebAssemblyAsmBackend.cpp
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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 
16 #include "llvm/MC/MCAsmBackend.h"
17 #include "llvm/MC/MCAssembler.h"
18 #include "llvm/MC/MCDirectives.h"
19 #include "llvm/MC/MCExpr.h"
21 #include "llvm/MC/MCObjectWriter.h"
23 #include "llvm/MC/MCSymbol.h"
27 
28 using namespace llvm;
29 
30 namespace {
31 
32 class WebAssemblyAsmBackend final : public MCAsmBackend {
33  bool Is64Bit;
34  bool IsEmscripten;
35 
36 public:
37  explicit WebAssemblyAsmBackend(bool Is64Bit, bool IsEmscripten)
38  : MCAsmBackend(support::little), Is64Bit(Is64Bit),
39  IsEmscripten(IsEmscripten) {}
40 
41  unsigned getNumFixupKinds() const override {
43  }
44 
45  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
46 
47  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
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 
73 const MCFixupKindInfo &
74 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
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 
93 bool 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 
101 void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm,
102  const MCFixup &Fixup,
103  const MCValue &Target,
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 
126 std::unique_ptr<MCObjectTargetWriter>
127 WebAssemblyAsmBackend::createObjectTargetWriter() const {
128  return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten);
129 }
130 
131 } // end anonymous namespace
132 
134  return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten());
135 }
bool isOSEmscripten() const
Tests whether the OS is Emscripten.
Definition: Triple.h:606
This class represents lattice values for constants.
Definition: AllocatorList.h:23
This represents an "assembler immediate".
Definition: MCValue.h:39
virtual const MCFixupKindInfo & getFixupKindInfo(MCFixupKind Kind) const
Get information on a fixup kind.
unsigned TargetOffset
The bit offset to write the relocation into.
Encode information on a single operation to perform on a byte sequence (e.g., an encoded instruction)...
Definition: MCFixup.h:77
Encapsulates the layout of an assembly file at a particular point in time.
Definition: MCAsmLayout.h:28
Analysis containing CSE Info
Definition: CSEInfo.cpp:20
Instances of this class represent a single low-level machine instruction.
Definition: MCInst.h:158
A relaxable fragment holds on to its MCInst, since it may need to be relaxed during the assembler lay...
Definition: MCFragment.h:272
MutableArrayRef - Represent a mutable reference to an array (0 or more elements consecutively in memo...
Definition: ArrayRef.h:290
size_t size() const
size - Get the array size.
Definition: ArrayRef.h:148
This file provides WebAssembly-specific target descriptions.
MCFixupKind
Extensible enumeration to represent the type of a fixup.
Definition: MCFixup.h:22
uint32_t getOffset() const
Definition: MCFixup.h:130
Triple - Helper class for working with autoconf configuration names.
Definition: Triple.h:43
unsigned TargetSize
The number of bits written by this fixup.
MCAsmBackend * createWebAssemblyAsmBackend(const Triple &TT)
Target - Wrapper for Target specific information.
uint64_t alignTo(uint64_t Size, Align A)
Returns a multiple of A needed to store Size bytes.
Definition: Alignment.h:126
bool isArch64Bit() const
Test whether the architecture is 64-bit.
Definition: Triple.cpp:1292
#define I(x, y, z)
Definition: MD5.cpp:58
Generic base class for all target subtargets.
Target independent information on a fixup kind.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
LLVM Value Representation.
Definition: Value.h:73
Generic interface to target specific assembler backends.
Definition: MCAsmBackend.h:41
static const unsigned Nop
Instruction opcodes emitted via means other than CodeGen.
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:45
std::unique_ptr< MCObjectTargetWriter > createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten)
unsigned Flags
Flags describing additional information on this fixup kind.
MCFixupKind getKind() const
Definition: MCFixup.h:126