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 bool IsEmscripten;
35
36 public:
WebAssemblyAsmBackend(bool Is64Bit,bool IsEmscripten)37 explicit WebAssemblyAsmBackend(bool Is64Bit, bool IsEmscripten)
38 : MCAsmBackend(support::little), Is64Bit(Is64Bit),
39 IsEmscripten(IsEmscripten) {}
40
getNumFixupKinds() const41 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
fixupNeedsRelaxation(const MCFixup & Fixup,uint64_t Value,const MCRelaxableFragment * DF,const MCAsmLayout & Layout) const56 bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
57 const MCRelaxableFragment *DF,
58 const MCAsmLayout &Layout) const override {
59 return false;
60 }
61
mayNeedRelaxation(const MCInst & Inst,const MCSubtargetInfo & STI) const62 bool mayNeedRelaxation(const MCInst &Inst,
63 const MCSubtargetInfo &STI) const override {
64 return false;
65 }
66
67 bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
68 };
69
70 const MCFixupKindInfo &
getFixupKindInfo(MCFixupKind Kind) const71 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
72 const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
73 // This table *must* be in the order that the fixup_* kinds are defined in
74 // WebAssemblyFixupKinds.h.
75 //
76 // Name Offset (bits) Size (bits) Flags
77 {"fixup_sleb128_i32", 0, 5 * 8, 0},
78 {"fixup_sleb128_i64", 0, 10 * 8, 0},
79 {"fixup_uleb128_i32", 0, 5 * 8, 0},
80 {"fixup_uleb128_i64", 0, 10 * 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
writeNopData(raw_ostream & OS,uint64_t Count) const91 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
applyFixup(const MCAssembler & Asm,const MCFixup & Fixup,const MCValue & Target,MutableArrayRef<char> Data,uint64_t Value,bool IsPCRel,const MCSubtargetInfo * STI) const99 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>
createObjectTargetWriter() const125 WebAssemblyAsmBackend::createObjectTargetWriter() const {
126 return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten);
127 }
128
129 } // end anonymous namespace
130
createWebAssemblyAsmBackend(const Triple & TT)131 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
132 return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten());
133 }
134