lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp

   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);
  35
  36 private:
  37   unsigned getRelocType(const MCValue &Target,
  38                         const MCFixup &Fixup) const override;
  39 };
  40 } // end anonymous namespace
  41
  42 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit)
  43     : MCWasmObjectTargetWriter(Is64Bit) {}
  44
  45 static const MCSection *getFixupSection(const MCExpr *Expr) {
  46   if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) {
  47     if (SyExp->getSymbol().isInSection())
  48       return &SyExp->getSymbol().getSection();
  49     return nullptr;
  50   }
  51
  52   if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) {
  53     auto SectionLHS = getFixupSection(BinOp->getLHS());
  54     auto SectionRHS = getFixupSection(BinOp->getRHS());
  55     return SectionLHS == SectionRHS ? nullptr : SectionLHS;
  56   }
  57
  58   if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr))
  59     return getFixupSection(UnOp->getSubExpr());
  60
  61   return nullptr;
  62 }
  63
  64 unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
  65                                                    const MCFixup &Fixup) const {
  66   const MCSymbolRefExpr *RefA = Target.getSymA();
  67   assert(RefA);
  68   auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol());
  69
  70   MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
  71
  72   switch (Modifier) {
  73     case MCSymbolRefExpr::VK_GOT:
  74       return wasm::R_WASM_GLOBAL_INDEX_LEB;
  75     case MCSymbolRefExpr::VK_WASM_TBREL:
  76       assert(SymA.isFunction());
  77       return wasm::R_WASM_TABLE_INDEX_REL_SLEB;
  78     case MCSymbolRefExpr::VK_WASM_MBREL:
  79       assert(SymA.isData());
  80       return wasm::R_WASM_MEMORY_ADDR_REL_SLEB;
  81     case MCSymbolRefExpr::VK_WASM_TYPEINDEX:
  82       return wasm::R_WASM_TYPE_INDEX_LEB;
  83     default:
  84       break;
  85   }
  86
  87   switch (unsigned(Fixup.getKind())) {
  88   case WebAssembly::fixup_sleb128_i32:
  89     if (SymA.isFunction())
  90       return wasm::R_WASM_TABLE_INDEX_SLEB;
  91     return wasm::R_WASM_MEMORY_ADDR_SLEB;
  92   case WebAssembly::fixup_sleb128_i64:
  93     llvm_unreachable("fixup_sleb128_i64 not implemented yet");
  94   case WebAssembly::fixup_uleb128_i32:
  95     if (SymA.isGlobal())
  96       return wasm::R_WASM_GLOBAL_INDEX_LEB;
  97     if (SymA.isFunction())
  98       return wasm::R_WASM_FUNCTION_INDEX_LEB;
  99     if (SymA.isEvent())
 100       return wasm::R_WASM_EVENT_INDEX_LEB;
 101     return wasm::R_WASM_MEMORY_ADDR_LEB;
 102   case FK_Data_4:
 103     if (SymA.isFunction())
 104       return wasm::R_WASM_TABLE_INDEX_I32;
 105     if (auto Section = static_cast<const MCSectionWasm *>(
 106             getFixupSection(Fixup.getValue()))) {
 107       if (Section->getKind().isText())
 108         return wasm::R_WASM_FUNCTION_OFFSET_I32;
 109       else if (!Section->isWasmData())
 110         return wasm::R_WASM_SECTION_OFFSET_I32;
 111     }
 112     return wasm::R_WASM_MEMORY_ADDR_I32;
 113   default:
 114     llvm_unreachable("unimplemented fixup kind");
 115   }
 116 }
 117
 118 std::unique_ptr<MCObjectTargetWriter>
 119 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit) {
 120   return llvm::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit);
 121 }