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//===-- WebAssemblyWasmObjectWriter.cpp - WebAssembly Wasm Writer ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file handles Wasm-specific object emission, converting LLVM's
/// internal fixups into the appropriate relocations.
///
//===----------------------------------------------------------------------===//
#include "MCTargetDesc/WebAssemblyFixupKinds.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "llvm/BinaryFormat/Wasm.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCFixup.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionWasm.h"
#include "llvm/MC/MCSymbolWasm.h"
#include "llvm/MC/MCValue.h"
#include "llvm/MC/MCWasmObjectWriter.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
using namespace llvm;
namespace {
class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter {
public:
explicit WebAssemblyWasmObjectWriter(bool Is64Bit);
private:
unsigned getRelocType(const MCValue &Target,
const MCFixup &Fixup) const override;
};
} // end anonymous namespace
WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit)
: MCWasmObjectTargetWriter(Is64Bit) {}
// Test whether the given expression computes a function address.
static bool IsFunctionExpr(const MCExpr *Expr) {
if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr))
return cast<MCSymbolWasm>(SyExp->getSymbol()).isFunction();
if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr))
return IsFunctionExpr(BinOp->getLHS()) != IsFunctionExpr(BinOp->getRHS());
if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr))
return IsFunctionExpr(UnOp->getSubExpr());
return false;
}
static bool IsFunctionType(const MCValue &Target) {
const MCSymbolRefExpr *RefA = Target.getSymA();
return RefA && RefA->getKind() == MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX;
}
static const MCSection *GetFixupSection(const MCExpr *Expr) {
if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) {
if (SyExp->getSymbol().isInSection())
return &SyExp->getSymbol().getSection();
return nullptr;
}
if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) {
auto SectionLHS = GetFixupSection(BinOp->getLHS());
auto SectionRHS = GetFixupSection(BinOp->getRHS());
return SectionLHS == SectionRHS ? nullptr : SectionLHS;
}
if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr))
return GetFixupSection(UnOp->getSubExpr());
return nullptr;
}
unsigned
WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
const MCFixup &Fixup) const {
// WebAssembly functions are not allocated in the data address space. To
// resolve a pointer to a function, we must use a special relocation type.
bool IsFunction = IsFunctionExpr(Fixup.getValue());
switch (unsigned(Fixup.getKind())) {
case WebAssembly::fixup_code_global_index:
return wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB;
case WebAssembly::fixup_code_sleb128_i32:
if (IsFunction)
return wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB;
return wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB;
case WebAssembly::fixup_code_sleb128_i64:
llvm_unreachable("fixup_sleb128_i64 not implemented yet");
case WebAssembly::fixup_code_uleb128_i32:
if (IsFunctionType(Target))
return wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB;
if (IsFunction)
return wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB;
return wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB;
case FK_Data_4:
if (IsFunction)
return wasm::R_WEBASSEMBLY_TABLE_INDEX_I32;
if (auto Section = static_cast<const MCSectionWasm *>(
GetFixupSection(Fixup.getValue()))) {
if (Section->getKind().isText())
return wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32;
else if (!Section->isWasmData())
return wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32;
}
return wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32;
case FK_Data_8:
llvm_unreachable("FK_Data_8 not implemented yet");
default:
llvm_unreachable("unimplemented fixup kind");
}
}
std::unique_ptr<MCObjectTargetWriter>
llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit) {
return llvm::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit);
}
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