forked from OSchip/llvm-project
116 lines
4.0 KiB
C++
116 lines
4.0 KiB
C++
//===- Relocations.cpp ----------------------------------------------------===//
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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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#include "Relocations.h"
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#include "InputChunks.h"
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#include "SyntheticSections.h"
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using namespace llvm;
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using namespace llvm::wasm;
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using namespace lld;
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using namespace lld::wasm;
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static bool requiresGOTAccess(const Symbol *sym) {
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return config->isPic && !sym->isHidden() && !sym->isLocal();
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}
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static bool allowUndefined(const Symbol* sym) {
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// Historically --allow-undefined doesn't work for data symbols since we don't
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// have any way to represent these as imports in the final binary. The idea
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// behind allowing undefined symbols is to allow importing these symbols from
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// the embedder and we can't do this for data symbols (at least not without
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// compiling with -fPIC)
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if (isa<DataSymbol>(sym))
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return false;
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return (config->allowUndefined ||
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config->allowUndefinedSymbols.count(sym->getName()) != 0);
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}
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static void reportUndefined(const Symbol* sym) {
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assert(sym->isUndefined());
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assert(!sym->isWeak());
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if (!allowUndefined(sym))
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error(toString(sym->getFile()) + ": undefined symbol: " + toString(*sym));
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}
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static void addGOTEntry(Symbol *sym) {
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// In PIC mode a GOT entry is an imported global that the dynamic linker
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// will assign.
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// In non-PIC mode (i.e. when code compiled as fPIC is linked into a static
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// binary) we create an internal wasm global with a fixed value that takes the
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// place of th GOT entry and effectivly acts as an i32 const. This can
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// potentially be optimized away at runtime or with a post-link tool.
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// TODO(sbc): Linker relaxation might also be able to optimize this away.
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if (config->isPic)
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out.importSec->addGOTEntry(sym);
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else
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out.globalSec->addDummyGOTEntry(sym);
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}
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void lld::wasm::scanRelocations(InputChunk *chunk) {
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if (!chunk->live)
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return;
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ObjFile *file = chunk->file;
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ArrayRef<WasmSignature> types = file->getWasmObj()->types();
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for (const WasmRelocation &reloc : chunk->getRelocations()) {
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if (reloc.Type == R_WASM_TYPE_INDEX_LEB) {
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// Mark target type as live
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file->typeMap[reloc.Index] =
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out.typeSec->registerType(types[reloc.Index]);
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file->typeIsUsed[reloc.Index] = true;
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continue;
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}
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// Other relocation types all have a corresponding symbol
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Symbol *sym = file->getSymbols()[reloc.Index];
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switch (reloc.Type) {
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case R_WASM_TABLE_INDEX_I32:
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case R_WASM_TABLE_INDEX_SLEB:
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case R_WASM_TABLE_INDEX_REL_SLEB:
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if (requiresGOTAccess(sym))
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break;
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out.elemSec->addEntry(cast<FunctionSymbol>(sym));
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break;
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case R_WASM_GLOBAL_INDEX_LEB:
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if (!isa<GlobalSymbol>(sym))
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addGOTEntry(sym);
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break;
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}
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if (config->isPic) {
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switch (reloc.Type) {
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case R_WASM_TABLE_INDEX_SLEB:
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case R_WASM_MEMORY_ADDR_SLEB:
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case R_WASM_MEMORY_ADDR_LEB:
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// Certain relocation types can't be used when building PIC output,
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// since they would require absolute symbol addresses at link time.
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error(toString(file) + ": relocation " + relocTypeToString(reloc.Type) +
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" cannot be used against symbol " + toString(*sym) +
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"; recompile with -fPIC");
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break;
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case R_WASM_TABLE_INDEX_I32:
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case R_WASM_MEMORY_ADDR_I32:
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// These relocation types are only present in the data section and
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// will be converted into code by `generateRelocationCode`. This code
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// requires the symbols to have GOT entires.
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if (requiresGOTAccess(sym))
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addGOTEntry(sym);
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break;
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}
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} else {
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// Report undefined symbols
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if (sym->isUndefined() && !config->relocatable && !sym->isWeak())
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reportUndefined(sym);
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}
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}
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}
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