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(llvm::endianness::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 bool writeNopData(raw_ostream &OS, uint64_t Count,
56 const MCSubtargetInfo *STI) const override;
57 };
58
59 const MCFixupKindInfo &
getFixupKindInfo(MCFixupKind Kind) const60 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
61 const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = {
62 // This table *must* be in the order that the fixup_* kinds are defined in
63 // WebAssemblyFixupKinds.h.
64 //
65 // Name Offset (bits) Size (bits) Flags
66 {"fixup_sleb128_i32", 0, 5 * 8, 0},
67 {"fixup_sleb128_i64", 0, 10 * 8, 0},
68 {"fixup_uleb128_i32", 0, 5 * 8, 0},
69 {"fixup_uleb128_i64", 0, 10 * 8, 0},
70 };
71
72 if (Kind < FirstTargetFixupKind)
73 return MCAsmBackend::getFixupKindInfo(Kind);
74
75 assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
76 "Invalid kind!");
77 return Infos[Kind - FirstTargetFixupKind];
78 }
79
writeNopData(raw_ostream & OS,uint64_t Count,const MCSubtargetInfo * STI) const80 bool WebAssemblyAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
81 const MCSubtargetInfo *STI) const {
82 for (uint64_t I = 0; I < Count; ++I)
83 OS << char(WebAssembly::Nop);
84
85 return true;
86 }
87
applyFixup(const MCAssembler & Asm,const MCFixup & Fixup,const MCValue & Target,MutableArrayRef<char> Data,uint64_t Value,bool IsPCRel,const MCSubtargetInfo * STI) const88 void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm,
89 const MCFixup &Fixup,
90 const MCValue &Target,
91 MutableArrayRef<char> Data,
92 uint64_t Value, bool IsPCRel,
93 const MCSubtargetInfo *STI) const {
94 const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind());
95 assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags");
96
97 unsigned NumBytes = alignTo(Info.TargetSize, 8) / 8;
98 if (Value == 0)
99 return; // Doesn't change encoding.
100
101 // Shift the value into position.
102 Value <<= Info.TargetOffset;
103
104 unsigned Offset = Fixup.getOffset();
105 assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!");
106
107 // For each byte of the fragment that the fixup touches, mask in the
108 // bits from the fixup value.
109 for (unsigned I = 0; I != NumBytes; ++I)
110 Data[Offset + I] |= uint8_t((Value >> (I * 8)) & 0xff);
111 }
112
113 std::unique_ptr<MCObjectTargetWriter>
createObjectTargetWriter() const114 WebAssemblyAsmBackend::createObjectTargetWriter() const {
115 return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten);
116 }
117
118 } // end anonymous namespace
119
createWebAssemblyAsmBackend(const Triple & TT)120 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) {
121 return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten());
122 }
123