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      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                         bool IsLocRel) const override;
     39 };
     40 } // end anonymous namespace
     41 
     42 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit,
     43                                                          bool IsEmscripten)
     44     : MCWasmObjectTargetWriter(Is64Bit, IsEmscripten) {}
     45 
     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 
     65 unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
     66                                                    const MCFixup &Fixup,
     67                                                    bool IsLocRel) const {
     68   const MCSymbolRefExpr *RefA = Target.getSymA();
     69   assert(RefA);
     70   auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol());
     71 
     72   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
     73 
     74   switch (Modifier) {
     75     case MCSymbolRefExpr::VK_GOT:
     76       return wasm::R_WASM_GLOBAL_INDEX_LEB;
     77     case MCSymbolRefExpr::VK_WASM_TBREL:
     78       assert(SymA.isFunction());
     79       return is64Bit() ? wasm::R_WASM_TABLE_INDEX_REL_SLEB64
     80                        : wasm::R_WASM_TABLE_INDEX_REL_SLEB;
     81     case MCSymbolRefExpr::VK_WASM_TLSREL:
     82       return wasm::R_WASM_MEMORY_ADDR_TLS_SLEB;
     83     case MCSymbolRefExpr::VK_WASM_MBREL:
     84       assert(SymA.isData());
     85       return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_REL_SLEB64
     86                        : wasm::R_WASM_MEMORY_ADDR_REL_SLEB;
     87     case MCSymbolRefExpr::VK_WASM_TYPEINDEX:
     88       return wasm::R_WASM_TYPE_INDEX_LEB;
     89     default:
     90       break;
     91   }
     92 
     93   switch (unsigned(Fixup.getKind())) {
     94   case WebAssembly::fixup_sleb128_i32:
     95     if (SymA.isFunction())
     96       return wasm::R_WASM_TABLE_INDEX_SLEB;
     97     return wasm::R_WASM_MEMORY_ADDR_SLEB;
     98   case WebAssembly::fixup_sleb128_i64:
     99     if (SymA.isFunction())
    100       return wasm::R_WASM_TABLE_INDEX_SLEB64;
    101     return wasm::R_WASM_MEMORY_ADDR_SLEB64;
    102   case WebAssembly::fixup_uleb128_i32:
    103     if (SymA.isGlobal())
    104       return wasm::R_WASM_GLOBAL_INDEX_LEB;
    105     if (SymA.isFunction())
    106       return wasm::R_WASM_FUNCTION_INDEX_LEB;
    107     if (SymA.isEvent())
    108       return wasm::R_WASM_EVENT_INDEX_LEB;
    109     if (SymA.isTable())
    110       return wasm::R_WASM_TABLE_NUMBER_LEB;
    111     return wasm::R_WASM_MEMORY_ADDR_LEB;
    112   case WebAssembly::fixup_uleb128_i64:
    113     assert(SymA.isData());
    114     return wasm::R_WASM_MEMORY_ADDR_LEB64;
    115   case FK_Data_4:
    116     if (SymA.isFunction())
    117       return wasm::R_WASM_TABLE_INDEX_I32;
    118     if (SymA.isGlobal())
    119       return wasm::R_WASM_GLOBAL_INDEX_I32;
    120     if (auto Section = static_cast<const MCSectionWasm *>(
    121             getFixupSection(Fixup.getValue()))) {
    122       if (Section->getKind().isText())
    123         return wasm::R_WASM_FUNCTION_OFFSET_I32;
    124       else if (!Section->isWasmData())
    125         return wasm::R_WASM_SECTION_OFFSET_I32;
    126     }
    127     return IsLocRel ? wasm::R_WASM_MEMORY_ADDR_LOCREL_I32
    128                     : wasm::R_WASM_MEMORY_ADDR_I32;
    129   case FK_Data_8:
    130     if (SymA.isFunction())
    131       return wasm::R_WASM_TABLE_INDEX_I64;
    132     if (SymA.isGlobal())
    133       llvm_unreachable("unimplemented R_WASM_GLOBAL_INDEX_I64");
    134     if (auto Section = static_cast<const MCSectionWasm *>(
    135             getFixupSection(Fixup.getValue()))) {
    136       if (Section->getKind().isText())
    137         return wasm::R_WASM_FUNCTION_OFFSET_I64;
    138       else if (!Section->isWasmData())
    139         llvm_unreachable("unimplemented R_WASM_SECTION_OFFSET_I64");
    140     }
    141     assert(SymA.isData());
    142     return wasm::R_WASM_MEMORY_ADDR_I64;
    143   default:
    144     llvm_unreachable("unimplemented fixup kind");
    145   }
    146 }
    147 
    148 std::unique_ptr<MCObjectTargetWriter>
    149 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) {
    150   return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten);
    151 }
    152