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//===- Relocations.cpp ----------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "Relocations.h"
#include "InputChunks.h"
#include "OutputSegment.h"
#include "SymbolTable.h"
#include "SyntheticSections.h"
using namespace llvm;
using namespace llvm::wasm;
namespace lld::wasm {
static bool requiresGOTAccess(const Symbol *sym) {
if (!config->isPic &&
config->unresolvedSymbols != UnresolvedPolicy::ImportDynamic)
return false;
if (sym->isHidden() || sym->isLocal())
return false;
// With `-Bsymbolic` (or when building an executable) as don't need to use
// the GOT for symbols that are defined within the current module.
if (sym->isDefined() && (!config->shared || config->bsymbolic))
return false;
return true;
}
static bool allowUndefined(const Symbol* sym) {
// Symbols that are explicitly imported are always allowed to be undefined at
// link time.
if (sym->isImported())
return true;
if (isa<UndefinedFunction>(sym) && config->importUndefined)
return true;
return config->allowUndefinedSymbols.count(sym->getName()) != 0;
}
static void reportUndefined(Symbol *sym) {
if (!allowUndefined(sym)) {
switch (config->unresolvedSymbols) {
case UnresolvedPolicy::ReportError:
error(toString(sym->getFile()) + ": undefined symbol: " + toString(*sym));
break;
case UnresolvedPolicy::Warn:
warn(toString(sym->getFile()) + ": undefined symbol: " + toString(*sym));
break;
case UnresolvedPolicy::Ignore:
LLVM_DEBUG(dbgs() << "ignoring undefined symbol: " + toString(*sym) +
"\n");
if (!config->importUndefined) {
if (auto *f = dyn_cast<UndefinedFunction>(sym)) {
if (!f->stubFunction) {
f->stubFunction = symtab->createUndefinedStub(*f->getSignature());
f->stubFunction->markLive();
// Mark the function itself as a stub which prevents it from being
// assigned a table entry.
f->isStub = true;
}
}
}
break;
case UnresolvedPolicy::ImportDynamic:
break;
}
}
}
static void addGOTEntry(Symbol *sym) {
if (requiresGOTAccess(sym))
out.importSec->addGOTEntry(sym);
else
out.globalSec->addInternalGOTEntry(sym);
}
void scanRelocations(InputChunk *chunk) {
if (!chunk->live)
return;
ObjFile *file = chunk->file;
ArrayRef<WasmSignature> types = file->getWasmObj()->types();
for (const WasmRelocation &reloc : chunk->getRelocations()) {
if (reloc.Type == R_WASM_TYPE_INDEX_LEB) {
// Mark target type as live
file->typeMap[reloc.Index] =
out.typeSec->registerType(types[reloc.Index]);
file->typeIsUsed[reloc.Index] = true;
continue;
}
// Other relocation types all have a corresponding symbol
Symbol *sym = file->getSymbols()[reloc.Index];
switch (reloc.Type) {
case R_WASM_TABLE_INDEX_I32:
case R_WASM_TABLE_INDEX_I64:
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_TABLE_INDEX_SLEB64:
case R_WASM_TABLE_INDEX_REL_SLEB:
case R_WASM_TABLE_INDEX_REL_SLEB64:
if (requiresGOTAccess(sym))
break;
out.elemSec->addEntry(cast<FunctionSymbol>(sym));
break;
case R_WASM_GLOBAL_INDEX_LEB:
case R_WASM_GLOBAL_INDEX_I32:
if (!isa<GlobalSymbol>(sym))
addGOTEntry(sym);
break;
case R_WASM_MEMORY_ADDR_TLS_SLEB:
case R_WASM_MEMORY_ADDR_TLS_SLEB64:
if (!sym->isDefined()) {
error(toString(file) + ": relocation " + relocTypeToString(reloc.Type) +
" cannot be used against an undefined symbol `" + toString(*sym) +
"`");
}
// In single-threaded builds TLS is lowered away and TLS data can be
// merged with normal data and allowing TLS relocation in non-TLS
// segments.
if (config->sharedMemory) {
if (!sym->isTLS()) {
error(toString(file) + ": relocation " +
relocTypeToString(reloc.Type) +
" cannot be used against non-TLS symbol `" + toString(*sym) +
"`");
}
if (auto *D = dyn_cast<DefinedData>(sym)) {
if (!D->segment->outputSeg->isTLS()) {
error(toString(file) + ": relocation " +
relocTypeToString(reloc.Type) + " cannot be used against `" +
toString(*sym) +
"` in non-TLS section: " + D->segment->outputSeg->name);
}
}
}
break;
}
if (config->isPic ||
(sym->isUndefined() &&
config->unresolvedSymbols == UnresolvedPolicy::ImportDynamic)) {
switch (reloc.Type) {
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_TABLE_INDEX_SLEB64:
case R_WASM_MEMORY_ADDR_SLEB:
case R_WASM_MEMORY_ADDR_LEB:
case R_WASM_MEMORY_ADDR_SLEB64:
case R_WASM_MEMORY_ADDR_LEB64:
// Certain relocation types can't be used when building PIC output,
// since they would require absolute symbol addresses at link time.
error(toString(file) + ": relocation " + relocTypeToString(reloc.Type) +
" cannot be used against symbol `" + toString(*sym) +
"`; recompile with -fPIC");
break;
case R_WASM_TABLE_INDEX_I32:
case R_WASM_TABLE_INDEX_I64:
case R_WASM_MEMORY_ADDR_I32:
case R_WASM_MEMORY_ADDR_I64:
// These relocation types are only present in the data section and
// will be converted into code by `generateRelocationCode`. This code
// requires the symbols to have GOT entries.
if (requiresGOTAccess(sym))
addGOTEntry(sym);
break;
}
} else if (sym->isUndefined() && !config->relocatable && !sym->isWeak()) {
// Report undefined symbols
reportUndefined(sym);
}
}
}
} // namespace lld::wasm
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