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23fe8db89f
This change implements lowering of references global symbols in PIC mode. This change implements lowering of global references in PIC mode using a new @GOT reference type. @GOT references can be used with function or data symbol names combined with the get_global instruction. In this case the linker will insert the wasm global that stores the address of the symbol (either in memory for data symbols or in the wasm table for function symbols). For now I'm continuing to use the R_WASM_GLOBAL_INDEX_LEB relocation type for this type of reference which means that this relocation type can refer to either a global or a function or data symbol. We could choose to introduce specific relocation types for GOT entries in the future. See the current dynamic linking proposal: https://github.com/WebAssembly/tool-conventions/blob/master/DynamicLinking.md Differential Revision: https://reviews.llvm.org/D54647 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357022 91177308-0d34-0410-b5e6-96231b3b80d8
119 lines
4.0 KiB
C++
119 lines
4.0 KiB
C++
//===-- WebAssemblyWasmObjectWriter.cpp - WebAssembly Wasm Writer ---------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// This file handles Wasm-specific object emission, converting LLVM's
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/// internal fixups into the appropriate relocations.
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///
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//===----------------------------------------------------------------------===//
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#include "MCTargetDesc/WebAssemblyFixupKinds.h"
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#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
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#include "llvm/BinaryFormat/Wasm.h"
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#include "llvm/MC/MCAsmBackend.h"
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#include "llvm/MC/MCFixup.h"
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#include "llvm/MC/MCFixupKindInfo.h"
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#include "llvm/MC/MCObjectWriter.h"
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#include "llvm/MC/MCSectionWasm.h"
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#include "llvm/MC/MCSymbolWasm.h"
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#include "llvm/MC/MCValue.h"
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#include "llvm/MC/MCWasmObjectWriter.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/ErrorHandling.h"
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using namespace llvm;
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namespace {
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class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter {
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public:
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explicit WebAssemblyWasmObjectWriter(bool Is64Bit);
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private:
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unsigned getRelocType(const MCValue &Target,
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const MCFixup &Fixup) const override;
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};
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} // end anonymous namespace
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WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit)
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: MCWasmObjectTargetWriter(Is64Bit) {}
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static bool isFunctionSignatureRef(const MCSymbolRefExpr *Ref) {
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return Ref->getKind() == MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX;
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}
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static bool isGOTRef(const MCSymbolRefExpr *Ref) {
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return Ref->getKind() == MCSymbolRefExpr::VK_GOT;
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}
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static const MCSection *getFixupSection(const MCExpr *Expr) {
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if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) {
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if (SyExp->getSymbol().isInSection())
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return &SyExp->getSymbol().getSection();
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return nullptr;
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}
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if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) {
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auto SectionLHS = getFixupSection(BinOp->getLHS());
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auto SectionRHS = getFixupSection(BinOp->getRHS());
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return SectionLHS == SectionRHS ? nullptr : SectionLHS;
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}
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if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr))
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return getFixupSection(UnOp->getSubExpr());
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return nullptr;
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}
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unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
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const MCFixup &Fixup) const {
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const MCSymbolRefExpr *RefA = Target.getSymA();
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assert(RefA);
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auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol());
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switch (unsigned(Fixup.getKind())) {
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case WebAssembly::fixup_code_sleb128_i32:
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if (SymA.isFunction())
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return wasm::R_WASM_TABLE_INDEX_SLEB;
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return wasm::R_WASM_MEMORY_ADDR_SLEB;
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case WebAssembly::fixup_code_sleb128_i64:
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llvm_unreachable("fixup_sleb128_i64 not implemented yet");
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case WebAssembly::fixup_code_uleb128_i32:
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if (SymA.isGlobal() || isGOTRef(RefA))
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return wasm::R_WASM_GLOBAL_INDEX_LEB;
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if (SymA.isFunction()) {
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if (isFunctionSignatureRef(RefA))
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return wasm::R_WASM_TYPE_INDEX_LEB;
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else
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return wasm::R_WASM_FUNCTION_INDEX_LEB;
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}
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if (SymA.isEvent())
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return wasm::R_WASM_EVENT_INDEX_LEB;
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return wasm::R_WASM_MEMORY_ADDR_LEB;
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case FK_Data_4:
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if (SymA.isFunction())
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return wasm::R_WASM_TABLE_INDEX_I32;
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if (auto Section = static_cast<const MCSectionWasm *>(
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getFixupSection(Fixup.getValue()))) {
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if (Section->getKind().isText())
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return wasm::R_WASM_FUNCTION_OFFSET_I32;
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else if (!Section->isWasmData())
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return wasm::R_WASM_SECTION_OFFSET_I32;
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}
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return wasm::R_WASM_MEMORY_ADDR_I32;
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case FK_Data_8:
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llvm_unreachable("FK_Data_8 not implemented yet");
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default:
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llvm_unreachable("unimplemented fixup kind");
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}
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}
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std::unique_ptr<MCObjectTargetWriter>
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llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit) {
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return llvm::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit);
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}
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