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, bool IsEmscripten);
  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                                                          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) 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>
 120 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) {
 121   return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten);
 122 }