ELF2: Split Writer::createSections into small functions.
Also added a few comments. llvm-svn: 249781
This commit is contained in:
Rui Ueyama
parent
55a7a2481b
commit
5a9640be32
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@ -75,6 +75,7 @@ public:
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void run();
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private:
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void copyLocalSymbols();
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void createSections();
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template <bool isRela>
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void scanRelocs(const InputSection<ELFT> &C,
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@ -162,6 +163,8 @@ void lld::elf2::writeResult(SymbolTable *Symtab) {
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// The main function of the writer.
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template <class ELFT> void Writer<ELFT>::run() {
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if (!Config->DiscardAll)
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copyLocalSymbols();
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createSections();
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assignAddresses();
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openFile(Config->OutputFile);
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@ -282,6 +285,91 @@ static void reportUndefined(const SymbolTable &S, const SymbolBody &Sym) {
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error(Message);
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}
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// Local symbols are not in the linker's symbol table. This function scans
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// each object file's symbol table to copy local symbols to the output.
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template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
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for (const std::unique_ptr<ObjectFileBase> &FileB : Symtab.getObjectFiles()) {
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auto &File = cast<ObjectFile<ELFT>>(*FileB);
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for (const Elf_Sym &Sym : File.getLocalSymbols()) {
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ErrorOr<StringRef> SymNameOrErr = Sym.getName(File.getStringTable());
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error(SymNameOrErr);
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StringRef SymName = *SymNameOrErr;
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if (shouldKeepInSymtab<ELFT>(SymName, Sym))
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Out<ELFT>::SymTab->addSymbol(SymName, true);
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}
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}
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}
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// Output section ordering is determined by this function.
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template <class ELFT>
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static bool compareOutputSections(OutputSectionBase<ELFT::Is64Bits> *A,
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OutputSectionBase<ELFT::Is64Bits> *B) {
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typedef typename ELFFile<ELFT>::uintX_t uintX_t;
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uintX_t AFlags = A->getFlags();
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uintX_t BFlags = B->getFlags();
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// Allocatable sections go first to reduce the total PT_LOAD size and
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// so debug info doesn't change addresses in actual code.
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bool AIsAlloc = AFlags & SHF_ALLOC;
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bool BIsAlloc = BFlags & SHF_ALLOC;
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if (AIsAlloc != BIsAlloc)
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return AIsAlloc;
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// We don't have any special requirements for the relative order of
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// two non allocatable sections.
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if (!AIsAlloc)
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return false;
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// We want the read only sections first so that they go in the PT_LOAD
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// covering the program headers at the start of the file.
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bool AIsWritable = AFlags & SHF_WRITE;
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bool BIsWritable = BFlags & SHF_WRITE;
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if (AIsWritable != BIsWritable)
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return BIsWritable;
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// For a corresponding reason, put non exec sections first (the program
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// header PT_LOAD is not executable).
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bool AIsExec = AFlags & SHF_EXECINSTR;
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bool BIsExec = BFlags & SHF_EXECINSTR;
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if (AIsExec != BIsExec)
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return BIsExec;
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// If we got here we know that both A and B and in the same PT_LOAD.
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// The last requirement we have is to put nobits section last. The
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// reason is that the only thing the dynamic linker will see about
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// them is a p_memsz that is larger than p_filesz. Seeing that it
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// zeros the end of the PT_LOAD, so that has to correspond to the
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// nobits sections.
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return A->getType() != SHT_NOBITS && B->getType() == SHT_NOBITS;
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}
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// Until this function is called, common symbols do not belong to any section.
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// This function adds them to end of BSS section.
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template <class ELFT>
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static void addCommonSymbols(std::vector<DefinedCommon<ELFT> *> &Syms) {
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typedef typename ELFFile<ELFT>::uintX_t uintX_t;
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typedef typename ELFFile<ELFT>::Elf_Sym Elf_Sym;
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// Sort the common symbols by alignment as an heuristic to pack them better.
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std::stable_sort(
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Syms.begin(), Syms.end(),
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[](const DefinedCommon<ELFT> *A, const DefinedCommon<ELFT> *B) {
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return A->MaxAlignment > B->MaxAlignment;
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});
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uintX_t Off = Out<ELFT>::Bss->getSize();
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for (DefinedCommon<ELFT> *C : Syms) {
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const Elf_Sym &Sym = C->Sym;
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uintX_t Align = C->MaxAlignment;
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Off = RoundUpToAlignment(Off, Align);
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C->OffsetInBSS = Off;
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Off += Sym.st_size;
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}
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Out<ELFT>::Bss->setSize(Off);
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}
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// Create output section objects and add them to OutputSections.
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template <class ELFT> void Writer<ELFT>::createSections() {
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SmallDenseMap<SectionKey<ELFT::Is64Bits>, OutputSection<ELFT> *> Map;
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@ -308,16 +396,6 @@ template <class ELFT> void Writer<ELFT>::createSections() {
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for (const std::unique_ptr<ObjectFileBase> &FileB : Symtab.getObjectFiles()) {
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auto &File = cast<ObjectFile<ELFT>>(*FileB);
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if (!Config->DiscardAll) {
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Elf_Sym_Range Syms = File.getLocalSymbols();
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for (const Elf_Sym &Sym : Syms) {
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ErrorOr<StringRef> SymNameOrErr = Sym.getName(File.getStringTable());
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error(SymNameOrErr);
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StringRef SymName = *SymNameOrErr;
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if (shouldKeepInSymtab<ELFT>(SymName, Sym))
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Out<ELFT>::SymTab->addSymbol(SymName, true);
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}
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}
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for (InputSection<ELFT> *C : File.getSections()) {
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if (!C)
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continue;
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@ -376,27 +454,9 @@ template <class ELFT> void Writer<ELFT>::createSections() {
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if (needsDynamicSections() && includeInDynamicSymtab(*Body))
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Out<ELFT>::HashTab->addSymbol(Body);
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}
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// Sort the common symbols by alignment as an heuristic to pack them better.
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std::stable_sort(
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CommonSymbols.begin(), CommonSymbols.end(),
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[](const DefinedCommon<ELFT> *A, const DefinedCommon<ELFT> *B) {
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return A->MaxAlignment > B->MaxAlignment;
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});
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uintX_t Off = Out<ELFT>::Bss->getSize();
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for (DefinedCommon<ELFT> *C : CommonSymbols) {
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const Elf_Sym &Sym = C->Sym;
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uintX_t Align = C->MaxAlignment;
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Off = RoundUpToAlignment(Off, Align);
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C->OffsetInBSS = Off;
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Off += Sym.st_size;
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}
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Out<ELFT>::Bss->setSize(Off);
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addCommonSymbols(CommonSymbols);
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OutputSections.push_back(Out<ELFT>::SymTab);
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if (needsDynamicSections()) {
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if (needsInterpSection())
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OutputSections.push_back(Out<ELFT>::Interp);
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@ -412,47 +472,8 @@ template <class ELFT> void Writer<ELFT>::createSections() {
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if (!Out<ELFT>::Plt->empty())
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OutputSections.push_back(Out<ELFT>::Plt);
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std::stable_sort(
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OutputSections.begin(), OutputSections.end(),
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[](OutputSectionBase<ELFT::Is64Bits> *A,
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OutputSectionBase<ELFT::Is64Bits> *B) {
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uintX_t AFlags = A->getFlags();
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uintX_t BFlags = B->getFlags();
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// Allocatable sections go first to reduce the total PT_LOAD size and
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// so debug info doesn't change addresses in actual code.
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bool AIsAlloc = AFlags & SHF_ALLOC;
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bool BIsAlloc = BFlags & SHF_ALLOC;
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if (AIsAlloc != BIsAlloc)
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return AIsAlloc;
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// We don't have any special requirements for the relative order of
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// two non allocatable sections.
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if (!AIsAlloc)
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return false;
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// We want the read only sections first so that they go in the PT_LOAD
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// covering the program headers at the start of the file.
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bool AIsWritable = AFlags & SHF_WRITE;
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bool BIsWritable = BFlags & SHF_WRITE;
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if (AIsWritable != BIsWritable)
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return BIsWritable;
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// For a corresponding reason, put non exec sections first (the program
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// header PT_LOAD is not executable).
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bool AIsExec = AFlags & SHF_EXECINSTR;
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bool BIsExec = BFlags & SHF_EXECINSTR;
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if (AIsExec != BIsExec)
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return BIsExec;
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// If we got here we know that both A and B and in the same PT_LOAD.
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// The last requirement we have is to put nobits section last. The
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// reason is that the only thing the dynamic linker will see about
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// them is a p_memsz that is larger than p_filesz. Seeing that it
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// zeros the end of the PT_LOAD, so that has to correspond to the
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// nobits sections.
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return A->getType() != SHT_NOBITS && B->getType() == SHT_NOBITS;
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});
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std::stable_sort(OutputSections.begin(), OutputSections.end(),
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compareOutputSections<ELFT>);
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// Always put StrTabSec last so that no section names are added to it after
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// it's finalized.
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