1 //===-- WebAssemblyWasmObjectWriter.cpp - WebAssembly Wasm Writer ---------===//
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 handles Wasm-specific object emission, converting LLVM's
11 /// internal fixups into the appropriate relocations.
12 ///
13 //===----------------------------------------------------------------------===//
14
15 #include "MCTargetDesc/WebAssemblyFixupKinds.h"
16 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
17 #include "llvm/BinaryFormat/Wasm.h"
18 #include "llvm/MC/MCAsmBackend.h"
19 #include "llvm/MC/MCFixup.h"
20 #include "llvm/MC/MCFixupKindInfo.h"
21 #include "llvm/MC/MCObjectWriter.h"
22 #include "llvm/MC/MCSectionWasm.h"
23 #include "llvm/MC/MCSymbolWasm.h"
24 #include "llvm/MC/MCValue.h"
25 #include "llvm/MC/MCWasmObjectWriter.h"
26 #include "llvm/Support/Casting.h"
27 #include "llvm/Support/ErrorHandling.h"
28
29 using namespace llvm;
30
31 namespace {
32 class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter {
33 public:
34 explicit WebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten);
35
36 private:
37 unsigned getRelocType(const MCValue &Target, const MCFixup &Fixup,
38 const MCSectionWasm &FixupSection,
39 bool IsLocRel) const override;
40 };
41 } // end anonymous namespace
42
WebAssemblyWasmObjectWriter(bool Is64Bit,bool IsEmscripten)43 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit,
44 bool IsEmscripten)
45 : MCWasmObjectTargetWriter(Is64Bit, IsEmscripten) {}
46
getTargetSection(const MCExpr * Expr)47 static const MCSection *getTargetSection(const MCExpr *Expr) {
48 if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) {
49 if (SyExp->getSymbol().isInSection())
50 return &SyExp->getSymbol().getSection();
51 return nullptr;
52 }
53
54 if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) {
55 auto SectionLHS = getTargetSection(BinOp->getLHS());
56 auto SectionRHS = getTargetSection(BinOp->getRHS());
57 return SectionLHS == SectionRHS ? nullptr : SectionLHS;
58 }
59
60 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr))
61 return getTargetSection(UnOp->getSubExpr());
62
63 return nullptr;
64 }
65
getRelocType(const MCValue & Target,const MCFixup & Fixup,const MCSectionWasm & FixupSection,bool IsLocRel) const66 unsigned WebAssemblyWasmObjectWriter::getRelocType(
67 const MCValue &Target, const MCFixup &Fixup,
68 const MCSectionWasm &FixupSection, bool IsLocRel) const {
69 const MCSymbolRefExpr *RefA = Target.getSymA();
70 assert(RefA);
71 auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol());
72
73 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
74
75 switch (Modifier) {
76 case MCSymbolRefExpr::VK_GOT:
77 return wasm::R_WASM_GLOBAL_INDEX_LEB;
78 case MCSymbolRefExpr::VK_WASM_TBREL:
79 assert(SymA.isFunction());
80 return is64Bit() ? wasm::R_WASM_TABLE_INDEX_REL_SLEB64
81 : wasm::R_WASM_TABLE_INDEX_REL_SLEB;
82 case MCSymbolRefExpr::VK_WASM_TLSREL:
83 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64
84 : wasm::R_WASM_MEMORY_ADDR_TLS_SLEB;
85 case MCSymbolRefExpr::VK_WASM_MBREL:
86 assert(SymA.isData());
87 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_REL_SLEB64
88 : wasm::R_WASM_MEMORY_ADDR_REL_SLEB;
89 case MCSymbolRefExpr::VK_WASM_TYPEINDEX:
90 return wasm::R_WASM_TYPE_INDEX_LEB;
91 default:
92 break;
93 }
94
95 switch (unsigned(Fixup.getKind())) {
96 case WebAssembly::fixup_sleb128_i32:
97 if (SymA.isFunction())
98 return wasm::R_WASM_TABLE_INDEX_SLEB;
99 return wasm::R_WASM_MEMORY_ADDR_SLEB;
100 case WebAssembly::fixup_sleb128_i64:
101 if (SymA.isFunction())
102 return wasm::R_WASM_TABLE_INDEX_SLEB64;
103 return wasm::R_WASM_MEMORY_ADDR_SLEB64;
104 case WebAssembly::fixup_uleb128_i32:
105 if (SymA.isGlobal())
106 return wasm::R_WASM_GLOBAL_INDEX_LEB;
107 if (SymA.isFunction())
108 return wasm::R_WASM_FUNCTION_INDEX_LEB;
109 if (SymA.isTag())
110 return wasm::R_WASM_TAG_INDEX_LEB;
111 if (SymA.isTable())
112 return wasm::R_WASM_TABLE_NUMBER_LEB;
113 return wasm::R_WASM_MEMORY_ADDR_LEB;
114 case WebAssembly::fixup_uleb128_i64:
115 assert(SymA.isData());
116 return wasm::R_WASM_MEMORY_ADDR_LEB64;
117 case FK_Data_4:
118 if (SymA.isFunction()) {
119 if (FixupSection.getKind().isMetadata())
120 return wasm::R_WASM_FUNCTION_OFFSET_I32;
121 assert(FixupSection.isWasmData());
122 return wasm::R_WASM_TABLE_INDEX_I32;
123 }
124 if (SymA.isGlobal())
125 return wasm::R_WASM_GLOBAL_INDEX_I32;
126 if (auto Section = static_cast<const MCSectionWasm *>(
127 getTargetSection(Fixup.getValue()))) {
128 if (Section->getKind().isText())
129 return wasm::R_WASM_FUNCTION_OFFSET_I32;
130 else if (!Section->isWasmData())
131 return wasm::R_WASM_SECTION_OFFSET_I32;
132 }
133 return IsLocRel ? wasm::R_WASM_MEMORY_ADDR_LOCREL_I32
134 : wasm::R_WASM_MEMORY_ADDR_I32;
135 case FK_Data_8:
136 if (SymA.isFunction()) {
137 if (FixupSection.getKind().isMetadata())
138 return wasm::R_WASM_FUNCTION_OFFSET_I64;
139 return wasm::R_WASM_TABLE_INDEX_I64;
140 }
141 if (SymA.isGlobal())
142 llvm_unreachable("unimplemented R_WASM_GLOBAL_INDEX_I64");
143 if (auto Section = static_cast<const MCSectionWasm *>(
144 getTargetSection(Fixup.getValue()))) {
145 if (Section->getKind().isText())
146 return wasm::R_WASM_FUNCTION_OFFSET_I64;
147 else if (!Section->isWasmData())
148 llvm_unreachable("unimplemented R_WASM_SECTION_OFFSET_I64");
149 }
150 assert(SymA.isData());
151 return wasm::R_WASM_MEMORY_ADDR_I64;
152 default:
153 llvm_unreachable("unimplemented fixup kind");
154 }
155 }
156
157 std::unique_ptr<MCObjectTargetWriter>
createWebAssemblyWasmObjectWriter(bool Is64Bit,bool IsEmscripten)158 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) {
159 return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten);
160 }
161