lib/Target/WebAssembly/MCTargetDesc/WebAssemblyAsmBackend.cpp

   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
  28 using namespace llvm;
  29
  30 namespace {
  31
  32 class WebAssemblyAsmBackend final : public MCAsmBackend {
  33   bool Is64Bit;
  34
  35 public:
  36   explicit WebAssemblyAsmBackend(bool Is64Bit)
  37       : MCAsmBackend(support::little), Is64Bit(Is64Bit) {}
  38
  39   unsigned getNumFixupKinds() const override {
  40     return WebAssembly::NumTargetFixupKinds;
  41   }
  42
  43   const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
  44
  45   void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
  46                   const MCValue &Target, MutableArrayRef<char> Data,
  47                   uint64_t Value, bool IsPCRel,
  48                   const MCSubtargetInfo *STI) const override;
  49
  50   std::unique_ptr<MCObjectTargetWriter>
  51   createObjectTargetWriter() const override;
  52
  53   // No instruction requires relaxation
  54   bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
  55                             const MCRelaxableFragment *DF,
  56                             const MCAsmLayout &Layout) const override {
  57     return false;
  58   }
  59
  60   bool mayNeedRelaxation(const MCInst &Inst,
  61                          const MCSubtargetInfo &STI) const override {
  62     return false;
  63   }
  64
  65   void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
  66                         MCInst &Res) const override {}
  67
  68   bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
  69 };
  70
  71 const MCFixupKindInfo &
  72 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
  73   const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
  74       // This table *must* be in the order that the fixup_* kinds are defined in
  75       // WebAssemblyFixupKinds.h.
  76       //
  77       // Name                     Offset (bits) Size (bits)     Flags
  78       {"fixup_code_sleb128_i32", 0, 5 * 8, 0},
  79       {"fixup_code_sleb128_i64", 0, 10 * 8, 0},
  80       {"fixup_code_uleb128_i32", 0, 5 * 8, 0},
  81   };
  82
  83   if (Kind < FirstTargetFixupKind)
  84     return MCAsmBackend::getFixupKindInfo(Kind);
  85
  86   assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
  87          "Invalid kind!");
  88   return Infos[Kind - FirstTargetFixupKind];
  89 }
  90
  91 bool WebAssemblyAsmBackend::writeNopData(raw_ostream &OS,
  92                                          uint64_t Count) const {
  93   for (uint64_t I = 0; I < Count; ++I)
  94     OS << char(WebAssembly::Nop);
  95
  96   return true;
  97 }
  98
  99 void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm,
 100                                        const MCFixup &Fixup,
 101                                        const MCValue &Target,
 102                                        MutableArrayRef<char> Data,
 103                                        uint64_t Value, bool IsPCRel,
 104                                        const MCSubtargetInfo *STI) const {
 105   const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind());
 106   assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags");
 107
 108   unsigned NumBytes = alignTo(Info.TargetSize, 8) / 8;
 109   if (Value == 0)
 110     return; // Doesn't change encoding.
 111
 112   // Shift the value into position.
 113   Value <<= Info.TargetOffset;
 114
 115   unsigned Offset = Fixup.getOffset();
 116   assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!");
 117
 118   // For each byte of the fragment that the fixup touches, mask in the
 119   // bits from the fixup value.
 120   for (unsigned I = 0; I != NumBytes; ++I)
 121     Data[Offset + I] |= uint8_t((Value >> (I * 8)) & 0xff);
 122 }
 123
 124 std::unique_ptr<MCObjectTargetWriter>
 125 WebAssemblyAsmBackend::createObjectTargetWriter() const {
 126   return createWebAssemblyWasmObjectWriter(Is64Bit);
 127 }
 128
 129 } // end anonymous namespace
 130
 131 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
 132   return new WebAssemblyAsmBackend(TT.isArch64Bit());
 133 }