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,
38 const MCFixup &Fixup) const override;
39 };
40 } // end anonymous namespace
41
WebAssemblyWasmObjectWriter(bool Is64Bit,bool IsEmscripten)42 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit,
43 bool IsEmscripten)
44 : MCWasmObjectTargetWriter(Is64Bit, IsEmscripten) {}
45
getFixupSection(const MCExpr * Expr)46 static const MCSection *getFixupSection(const MCExpr *Expr) {
47 if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) {
48 if (SyExp->getSymbol().isInSection())
49 return &SyExp->getSymbol().getSection();
50 return nullptr;
51 }
52
53 if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) {
54 auto SectionLHS = getFixupSection(BinOp->getLHS());
55 auto SectionRHS = getFixupSection(BinOp->getRHS());
56 return SectionLHS == SectionRHS ? nullptr : SectionLHS;
57 }
58
59 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr))
60 return getFixupSection(UnOp->getSubExpr());
61
62 return nullptr;
63 }
64
getRelocType(const MCValue & Target,const MCFixup & Fixup) const65 unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
66 const MCFixup &Fixup) const {
67 const MCSymbolRefExpr *RefA = Target.getSymA();
68 assert(RefA);
69 auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol());
70
71 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
72
73 switch (Modifier) {
74 case MCSymbolRefExpr::VK_GOT:
75 return wasm::R_WASM_GLOBAL_INDEX_LEB;
76 case MCSymbolRefExpr::VK_WASM_TBREL:
77 assert(SymA.isFunction());
78 return wasm::R_WASM_TABLE_INDEX_REL_SLEB;
79 case MCSymbolRefExpr::VK_WASM_MBREL:
80 assert(SymA.isData());
81 return wasm::R_WASM_MEMORY_ADDR_REL_SLEB;
82 case MCSymbolRefExpr::VK_WASM_TYPEINDEX:
83 return wasm::R_WASM_TYPE_INDEX_LEB;
84 default:
85 break;
86 }
87
88 switch (unsigned(Fixup.getKind())) {
89 case WebAssembly::fixup_sleb128_i32:
90 if (SymA.isFunction())
91 return wasm::R_WASM_TABLE_INDEX_SLEB;
92 return wasm::R_WASM_MEMORY_ADDR_SLEB;
93 case WebAssembly::fixup_sleb128_i64:
94 llvm_unreachable("fixup_sleb128_i64 not implemented yet");
95 case WebAssembly::fixup_uleb128_i32:
96 if (SymA.isGlobal())
97 return wasm::R_WASM_GLOBAL_INDEX_LEB;
98 if (SymA.isFunction())
99 return wasm::R_WASM_FUNCTION_INDEX_LEB;
100 if (SymA.isEvent())
101 return wasm::R_WASM_EVENT_INDEX_LEB;
102 return wasm::R_WASM_MEMORY_ADDR_LEB;
103 case FK_Data_4:
104 if (SymA.isFunction())
105 return wasm::R_WASM_TABLE_INDEX_I32;
106 if (auto Section = static_cast<const MCSectionWasm *>(
107 getFixupSection(Fixup.getValue()))) {
108 if (Section->getKind().isText())
109 return wasm::R_WASM_FUNCTION_OFFSET_I32;
110 else if (!Section->isWasmData())
111 return wasm::R_WASM_SECTION_OFFSET_I32;
112 }
113 return wasm::R_WASM_MEMORY_ADDR_I32;
114 default:
115 llvm_unreachable("unimplemented fixup kind");
116 }
117 }
118
119 std::unique_ptr<MCObjectTargetWriter>
createWebAssemblyWasmObjectWriter(bool Is64Bit,bool IsEmscripten)120 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) {
121 return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten);
122 }
123