llvm/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/MCExpr.h"
  19 #include "llvm/MC/MCFixupKindInfo.h"
  20 #include "llvm/MC/MCObjectWriter.h"
  21 #include "llvm/MC/MCSubtargetInfo.h"
  22 #include "llvm/MC/MCSymbol.h"
  23 #include "llvm/MC/MCWasmObjectWriter.h"
  24 #include "llvm/Support/raw_ostream.h"
  25
  26 using namespace llvm;
  27
  28 namespace {
  29
  30 class WebAssemblyAsmBackend final : public MCAsmBackend {
  31   bool Is64Bit;
  32   bool IsEmscripten;
  33
  34 public:
  35   explicit WebAssemblyAsmBackend(bool Is64Bit, bool IsEmscripten)
  36       : MCAsmBackend(llvm::endianness::little), Is64Bit(Is64Bit),
  37         IsEmscripten(IsEmscripten) {}
  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   bool writeNopData(raw_ostream &OS, uint64_t Count,
  54                     const MCSubtargetInfo *STI) const override;
  55 };
  56
  57 const MCFixupKindInfo &
  58 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
  59   const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
  60       // This table *must* be in the order that the fixup_* kinds are defined in
  61       // WebAssemblyFixupKinds.h.
  62       //
  63       // Name                     Offset (bits) Size (bits)     Flags
  64       {"fixup_sleb128_i32", 0, 5 * 8, 0},
  65       {"fixup_sleb128_i64", 0, 10 * 8, 0},
  66       {"fixup_uleb128_i32", 0, 5 * 8, 0},
  67       {"fixup_uleb128_i64", 0, 10 * 8, 0},
  68   };
  69
  70   if (Kind < FirstTargetFixupKind)
  71     return MCAsmBackend::getFixupKindInfo(Kind);
  72
  73   assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
  74          "Invalid kind!");
  75   return Infos[Kind - FirstTargetFixupKind];
  76 }
  77
  78 bool WebAssemblyAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
  79                                          const MCSubtargetInfo *STI) const {
  80   for (uint64_t I = 0; I < Count; ++I)
  81     OS << char(WebAssembly::Nop);
  82
  83   return true;
  84 }
  85
  86 void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm,
  87                                        const MCFixup &Fixup,
  88                                        const MCValue &Target,
  89                                        MutableArrayRef<char> Data,
  90                                        uint64_t Value, bool IsPCRel,
  91                                        const MCSubtargetInfo *STI) const {
  92   const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind());
  93   assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags");
  94
  95   unsigned NumBytes = alignTo(Info.TargetSize, 8) / 8;
  96   if (Value == 0)
  97     return; // Doesn't change encoding.
  98
  99   // Shift the value into position.
 100   Value <<= Info.TargetOffset;
 101
 102   unsigned Offset = Fixup.getOffset();
 103   assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!");
 104
 105   // For each byte of the fragment that the fixup touches, mask in the
 106   // bits from the fixup value.
 107   for (unsigned I = 0; I != NumBytes; ++I)
 108     Data[Offset + I] |= uint8_t((Value >> (I * 8)) & 0xff);
 109 }
 110
 111 std::unique_ptr<MCObjectTargetWriter>
 112 WebAssemblyAsmBackend::createObjectTargetWriter() const {
 113   return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten);
 114 }
 115
 116 } // end anonymous namespace
 117
 118 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
 119   return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten());
 120 }