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/MCObjectWriter.h"
20 #include "llvm/MC/MCSubtargetInfo.h"
21 #include "llvm/MC/MCSymbol.h"
22 #include "llvm/MC/MCValue.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:
WebAssemblyAsmBackend(bool Is64Bit,bool IsEmscripten)35 explicit WebAssemblyAsmBackend(bool Is64Bit, bool IsEmscripten)
36 : MCAsmBackend(llvm::endianness::little), Is64Bit(Is64Bit),
37 IsEmscripten(IsEmscripten) {}
38
39 MCFixupKindInfo getFixupKindInfo(MCFixupKind Kind) const override;
40
41 void applyFixup(const MCFragment &, const MCFixup &, const MCValue &Target,
42 MutableArrayRef<char> Data, uint64_t Value, bool) override;
43
44 std::unique_ptr<MCObjectTargetWriter>
45 createObjectTargetWriter() const override;
46
47 bool writeNopData(raw_ostream &OS, uint64_t Count,
48 const MCSubtargetInfo *STI) const override;
49 };
50
51 MCFixupKindInfo
getFixupKindInfo(MCFixupKind Kind) const52 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
53 const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
54 // This table *must* be in the order that the fixup_* kinds are defined in
55 // WebAssemblyFixupKinds.h.
56 //
57 // Name Offset (bits) Size (bits) Flags
58 {"fixup_sleb128_i32", 0, 5 * 8, 0},
59 {"fixup_sleb128_i64", 0, 10 * 8, 0},
60 {"fixup_uleb128_i32", 0, 5 * 8, 0},
61 {"fixup_uleb128_i64", 0, 10 * 8, 0},
62 };
63
64 if (Kind < FirstTargetFixupKind)
65 return MCAsmBackend::getFixupKindInfo(Kind);
66
67 assert(unsigned(Kind - FirstTargetFixupKind) <
68 WebAssembly::NumTargetFixupKinds &&
69 "Invalid kind!");
70 return Infos[Kind - FirstTargetFixupKind];
71 }
72
writeNopData(raw_ostream & OS,uint64_t Count,const MCSubtargetInfo * STI) const73 bool WebAssemblyAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
74 const MCSubtargetInfo *STI) const {
75 for (uint64_t I = 0; I < Count; ++I)
76 OS << char(WebAssembly::Nop);
77
78 return true;
79 }
80
applyFixup(const MCFragment & F,const MCFixup & Fixup,const MCValue & Target,MutableArrayRef<char> Data,uint64_t Value,bool IsResolved)81 void WebAssemblyAsmBackend::applyFixup(const MCFragment &F,
82 const MCFixup &Fixup,
83 const MCValue &Target,
84 MutableArrayRef<char> Data,
85 uint64_t Value, bool IsResolved) {
86 if (!IsResolved)
87 Asm->getWriter().recordRelocation(F, Fixup, Target, Value);
88
89 MCFixupKindInfo Info = getFixupKindInfo(Fixup.getKind());
90 assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags");
91
92 unsigned NumBytes = alignTo(Info.TargetSize, 8) / 8;
93 if (Value == 0)
94 return; // Doesn't change encoding.
95
96 // Shift the value into position.
97 Value <<= Info.TargetOffset;
98
99 unsigned Offset = Fixup.getOffset();
100 assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!");
101
102 // For each byte of the fragment that the fixup touches, mask in the
103 // bits from the fixup value.
104 for (unsigned I = 0; I != NumBytes; ++I)
105 Data[Offset + I] |= uint8_t((Value >> (I * 8)) & 0xff);
106 }
107
108 std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const109 WebAssemblyAsmBackend::createObjectTargetWriter() const {
110 return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten);
111 }
112
113 } // end anonymous namespace
114
createWebAssemblyAsmBackend(const Triple & TT)115 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
116 return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten());
117 }
118