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 case MCSymbolRefExpr::VK_WASM_GOT_TLS:
78 return wasm::R_WASM_GLOBAL_INDEX_LEB;
79 case MCSymbolRefExpr::VK_WASM_TBREL:
80 assert(SymA.isFunction());
81 return is64Bit() ? wasm::R_WASM_TABLE_INDEX_REL_SLEB64
82 : wasm::R_WASM_TABLE_INDEX_REL_SLEB;
83 case MCSymbolRefExpr::VK_WASM_TLSREL:
84 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64
85 : wasm::R_WASM_MEMORY_ADDR_TLS_SLEB;
86 case MCSymbolRefExpr::VK_WASM_MBREL:
87 assert(SymA.isData());
88 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_REL_SLEB64
89 : wasm::R_WASM_MEMORY_ADDR_REL_SLEB;
90 case MCSymbolRefExpr::VK_WASM_TYPEINDEX:
91 return wasm::R_WASM_TYPE_INDEX_LEB;
92 case MCSymbolRefExpr::VK_None:
93 break;
94 default:
95 report_fatal_error("unknown VariantKind");
96 break;
97 }
98
99 switch (unsigned(Fixup.getKind())) {
100 case WebAssembly::fixup_sleb128_i32:
101 if (SymA.isFunction())
102 return wasm::R_WASM_TABLE_INDEX_SLEB;
103 return wasm::R_WASM_MEMORY_ADDR_SLEB;
104 case WebAssembly::fixup_sleb128_i64:
105 if (SymA.isFunction())
106 return wasm::R_WASM_TABLE_INDEX_SLEB64;
107 return wasm::R_WASM_MEMORY_ADDR_SLEB64;
108 case WebAssembly::fixup_uleb128_i32:
109 if (SymA.isGlobal())
110 return wasm::R_WASM_GLOBAL_INDEX_LEB;
111 if (SymA.isFunction())
112 return wasm::R_WASM_FUNCTION_INDEX_LEB;
113 if (SymA.isTag())
114 return wasm::R_WASM_TAG_INDEX_LEB;
115 if (SymA.isTable())
116 return wasm::R_WASM_TABLE_NUMBER_LEB;
117 return wasm::R_WASM_MEMORY_ADDR_LEB;
118 case WebAssembly::fixup_uleb128_i64:
119 assert(SymA.isData());
120 return wasm::R_WASM_MEMORY_ADDR_LEB64;
121 case FK_Data_4:
122 if (SymA.isFunction()) {
123 if (FixupSection.getKind().isMetadata())
124 return wasm::R_WASM_FUNCTION_OFFSET_I32;
125 assert(FixupSection.isWasmData());
126 return wasm::R_WASM_TABLE_INDEX_I32;
127 }
128 if (SymA.isGlobal())
129 return wasm::R_WASM_GLOBAL_INDEX_I32;
130 if (auto Section = static_cast<const MCSectionWasm *>(
131 getTargetSection(Fixup.getValue()))) {
132 if (Section->getKind().isText())
133 return wasm::R_WASM_FUNCTION_OFFSET_I32;
134 else if (!Section->isWasmData())
135 return wasm::R_WASM_SECTION_OFFSET_I32;
136 }
137 return IsLocRel ? wasm::R_WASM_MEMORY_ADDR_LOCREL_I32
138 : wasm::R_WASM_MEMORY_ADDR_I32;
139 case FK_Data_8:
140 if (SymA.isFunction()) {
141 if (FixupSection.getKind().isMetadata())
142 return wasm::R_WASM_FUNCTION_OFFSET_I64;
143 return wasm::R_WASM_TABLE_INDEX_I64;
144 }
145 if (SymA.isGlobal())
146 llvm_unreachable("unimplemented R_WASM_GLOBAL_INDEX_I64");
147 if (auto Section = static_cast<const MCSectionWasm *>(
148 getTargetSection(Fixup.getValue()))) {
149 if (Section->getKind().isText())
150 return wasm::R_WASM_FUNCTION_OFFSET_I64;
151 else if (!Section->isWasmData())
152 llvm_unreachable("unimplemented R_WASM_SECTION_OFFSET_I64");
153 }
154 assert(SymA.isData());
155 return wasm::R_WASM_MEMORY_ADDR_I64;
156 default:
157 llvm_unreachable("unimplemented fixup kind");
158 }
159 }
160
161 std::unique_ptr<MCObjectTargetWriter>
createWebAssemblyWasmObjectWriter(bool Is64Bit,bool IsEmscripten)162 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) {
163 return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten);
164 }
165