forked from OSchip/llvm-project
1951 lines
67 KiB
C++
1951 lines
67 KiB
C++
//===- Writer.cpp ---------------------------------------------------------===//
|
|
//
|
|
// The LLVM Linker
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "Writer.h"
|
|
#include "Config.h"
|
|
#include "Filesystem.h"
|
|
#include "LinkerScript.h"
|
|
#include "MapFile.h"
|
|
#include "Memory.h"
|
|
#include "OutputSections.h"
|
|
#include "Relocations.h"
|
|
#include "Strings.h"
|
|
#include "SymbolTable.h"
|
|
#include "SyntheticSections.h"
|
|
#include "Target.h"
|
|
#include "Threads.h"
|
|
#include "llvm/ADT/StringMap.h"
|
|
#include "llvm/ADT/StringSwitch.h"
|
|
#include "llvm/Support/FileOutputBuffer.h"
|
|
#include <climits>
|
|
|
|
using namespace llvm;
|
|
using namespace llvm::ELF;
|
|
using namespace llvm::object;
|
|
using namespace llvm::support;
|
|
using namespace llvm::support::endian;
|
|
|
|
using namespace lld;
|
|
using namespace lld::elf;
|
|
|
|
namespace {
|
|
// The writer writes a SymbolTable result to a file.
|
|
template <class ELFT> class Writer {
|
|
public:
|
|
typedef typename ELFT::Shdr Elf_Shdr;
|
|
typedef typename ELFT::Ehdr Elf_Ehdr;
|
|
typedef typename ELFT::Phdr Elf_Phdr;
|
|
|
|
void run();
|
|
|
|
private:
|
|
void createSyntheticSections();
|
|
void copyLocalSymbols();
|
|
void addSectionSymbols();
|
|
void addReservedSymbols();
|
|
void createSections();
|
|
void forEachRelSec(std::function<void(InputSectionBase &)> Fn);
|
|
void sortSections();
|
|
void finalizeSections();
|
|
void addPredefinedSections();
|
|
void setReservedSymbolSections();
|
|
|
|
std::vector<PhdrEntry *> createPhdrs();
|
|
void removeEmptyPTLoad();
|
|
void addPtArmExid(std::vector<PhdrEntry *> &Phdrs);
|
|
void assignFileOffsets();
|
|
void assignFileOffsetsBinary();
|
|
void setPhdrs();
|
|
void fixSectionAlignments();
|
|
void openFile();
|
|
void writeTrapInstr();
|
|
void writeHeader();
|
|
void writeSections();
|
|
void writeSectionsBinary();
|
|
void writeBuildId();
|
|
|
|
std::unique_ptr<FileOutputBuffer> Buffer;
|
|
|
|
OutputSectionFactory Factory;
|
|
|
|
void addRelIpltSymbols();
|
|
void addStartEndSymbols();
|
|
void addStartStopSymbols(OutputSection *Sec);
|
|
uint64_t getEntryAddr();
|
|
OutputSection *findSection(StringRef Name);
|
|
|
|
std::vector<PhdrEntry *> Phdrs;
|
|
|
|
uint64_t FileSize;
|
|
uint64_t SectionHeaderOff;
|
|
|
|
bool HasGotBaseSym = false;
|
|
};
|
|
} // anonymous namespace
|
|
|
|
StringRef elf::getOutputSectionName(StringRef Name) {
|
|
// ".zdebug_" is a prefix for ZLIB-compressed sections.
|
|
// Because we decompressed input sections, we want to remove 'z'.
|
|
if (Name.startswith(".zdebug_"))
|
|
return Saver.save("." + Name.substr(2));
|
|
|
|
if (Config->Relocatable)
|
|
return Name;
|
|
|
|
for (StringRef V :
|
|
{".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
|
|
".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
|
|
".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab."}) {
|
|
StringRef Prefix = V.drop_back();
|
|
if (Name.startswith(V) || Name == Prefix)
|
|
return Prefix;
|
|
}
|
|
|
|
// CommonSection is identified as "COMMON" in linker scripts.
|
|
// By default, it should go to .bss section.
|
|
if (Name == "COMMON")
|
|
return ".bss";
|
|
|
|
return Name;
|
|
}
|
|
|
|
static bool needsInterpSection() {
|
|
return !SharedFiles.empty() && !Config->DynamicLinker.empty() &&
|
|
!Script->ignoreInterpSection();
|
|
}
|
|
|
|
template <class ELFT> void elf::writeResult() { Writer<ELFT>().run(); }
|
|
|
|
template <class ELFT> void Writer<ELFT>::removeEmptyPTLoad() {
|
|
llvm::erase_if(Phdrs, [&](const PhdrEntry *P) {
|
|
if (P->p_type != PT_LOAD)
|
|
return false;
|
|
if (!P->FirstSec)
|
|
return true;
|
|
uint64_t Size = P->LastSec->Addr + P->LastSec->Size - P->FirstSec->Addr;
|
|
return Size == 0;
|
|
});
|
|
}
|
|
|
|
template <class ELFT> static void combineEhFrameSections() {
|
|
for (InputSectionBase *&S : InputSections) {
|
|
EhInputSection *ES = dyn_cast<EhInputSection>(S);
|
|
if (!ES || !ES->Live)
|
|
continue;
|
|
|
|
In<ELFT>::EhFrame->addSection(ES);
|
|
S = nullptr;
|
|
}
|
|
|
|
std::vector<InputSectionBase *> &V = InputSections;
|
|
V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
|
|
}
|
|
|
|
// The main function of the writer.
|
|
template <class ELFT> void Writer<ELFT>::run() {
|
|
// Create linker-synthesized sections such as .got or .plt.
|
|
// Such sections are of type input section.
|
|
createSyntheticSections();
|
|
|
|
if (!Config->Relocatable)
|
|
combineEhFrameSections<ELFT>();
|
|
|
|
// We need to create some reserved symbols such as _end. Create them.
|
|
if (!Config->Relocatable)
|
|
addReservedSymbols();
|
|
|
|
// Create output sections.
|
|
if (Script->Opt.HasSections) {
|
|
// If linker script contains SECTIONS commands, let it create sections.
|
|
Script->processCommands(Factory);
|
|
|
|
// Linker scripts may have left some input sections unassigned.
|
|
// Assign such sections using the default rule.
|
|
Script->addOrphanSections(Factory);
|
|
} else {
|
|
// If linker script does not contain SECTIONS commands, create
|
|
// output sections by default rules. We still need to give the
|
|
// linker script a chance to run, because it might contain
|
|
// non-SECTIONS commands such as ASSERT.
|
|
Script->processCommands(Factory);
|
|
createSections();
|
|
}
|
|
|
|
if (Config->Discard != DiscardPolicy::All)
|
|
copyLocalSymbols();
|
|
|
|
if (Config->CopyRelocs)
|
|
addSectionSymbols();
|
|
|
|
// Now that we have a complete set of output sections. This function
|
|
// completes section contents. For example, we need to add strings
|
|
// to the string table, and add entries to .got and .plt.
|
|
// finalizeSections does that.
|
|
finalizeSections();
|
|
if (ErrorCount)
|
|
return;
|
|
|
|
// If -compressed-debug-sections is specified, we need to compress
|
|
// .debug_* sections. Do it right now because it changes the size of
|
|
// output sections.
|
|
parallelForEach(OutputSections,
|
|
[](OutputSection *Sec) { Sec->maybeCompress<ELFT>(); });
|
|
|
|
Script->assignAddresses();
|
|
Script->allocateHeaders(Phdrs);
|
|
|
|
// Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
|
|
// 0 sized region. This has to be done late since only after assignAddresses
|
|
// we know the size of the sections.
|
|
removeEmptyPTLoad();
|
|
|
|
if (!Config->OFormatBinary)
|
|
assignFileOffsets();
|
|
else
|
|
assignFileOffsetsBinary();
|
|
|
|
setPhdrs();
|
|
|
|
if (Config->Relocatable) {
|
|
for (OutputSection *Sec : OutputSections)
|
|
Sec->Addr = 0;
|
|
}
|
|
|
|
// It does not make sense try to open the file if we have error already.
|
|
if (ErrorCount)
|
|
return;
|
|
// Write the result down to a file.
|
|
openFile();
|
|
if (ErrorCount)
|
|
return;
|
|
|
|
if (!Config->OFormatBinary) {
|
|
writeTrapInstr();
|
|
writeHeader();
|
|
writeSections();
|
|
} else {
|
|
writeSectionsBinary();
|
|
}
|
|
|
|
// Backfill .note.gnu.build-id section content. This is done at last
|
|
// because the content is usually a hash value of the entire output file.
|
|
writeBuildId();
|
|
if (ErrorCount)
|
|
return;
|
|
|
|
// Handle -Map option.
|
|
writeMapFile<ELFT>();
|
|
if (ErrorCount)
|
|
return;
|
|
|
|
if (auto EC = Buffer->commit())
|
|
error("failed to write to the output file: " + EC.message());
|
|
|
|
// Flush the output streams and exit immediately. A full shutdown
|
|
// is a good test that we are keeping track of all allocated memory,
|
|
// but actually freeing it is a waste of time in a regular linker run.
|
|
if (Config->ExitEarly)
|
|
exitLld(0);
|
|
}
|
|
|
|
// Initialize Out members.
|
|
template <class ELFT> void Writer<ELFT>::createSyntheticSections() {
|
|
// Initialize all pointers with NULL. This is needed because
|
|
// you can call lld::elf::main more than once as a library.
|
|
memset(&Out::First, 0, sizeof(Out));
|
|
|
|
auto Add = [](InputSectionBase *Sec) { InputSections.push_back(Sec); };
|
|
|
|
InX::DynStrTab = make<StringTableSection>(".dynstr", true);
|
|
InX::Dynamic = make<DynamicSection<ELFT>>();
|
|
In<ELFT>::RelaDyn = make<RelocationSection<ELFT>>(
|
|
Config->IsRela ? ".rela.dyn" : ".rel.dyn", Config->ZCombreloc);
|
|
InX::ShStrTab = make<StringTableSection>(".shstrtab", false);
|
|
|
|
Out::ElfHeader = make<OutputSection>("", 0, SHF_ALLOC);
|
|
Out::ElfHeader->Size = sizeof(Elf_Ehdr);
|
|
Out::ProgramHeaders = make<OutputSection>("", 0, SHF_ALLOC);
|
|
Out::ProgramHeaders->updateAlignment(Config->Wordsize);
|
|
|
|
if (needsInterpSection()) {
|
|
InX::Interp = createInterpSection();
|
|
Add(InX::Interp);
|
|
} else {
|
|
InX::Interp = nullptr;
|
|
}
|
|
|
|
if (Config->Strip != StripPolicy::All) {
|
|
InX::StrTab = make<StringTableSection>(".strtab", false);
|
|
InX::SymTab = make<SymbolTableSection<ELFT>>(*InX::StrTab);
|
|
}
|
|
|
|
if (Config->BuildId != BuildIdKind::None) {
|
|
InX::BuildId = make<BuildIdSection>();
|
|
Add(InX::BuildId);
|
|
}
|
|
|
|
for (InputSection *S : createCommonSections())
|
|
Add(S);
|
|
|
|
InX::Bss = make<BssSection>(".bss");
|
|
Add(InX::Bss);
|
|
InX::BssRelRo = make<BssSection>(".bss.rel.ro");
|
|
Add(InX::BssRelRo);
|
|
|
|
// Add MIPS-specific sections.
|
|
if (Config->EMachine == EM_MIPS) {
|
|
if (!Config->Shared && Config->HasDynSymTab) {
|
|
InX::MipsRldMap = make<MipsRldMapSection>();
|
|
Add(InX::MipsRldMap);
|
|
}
|
|
if (auto *Sec = MipsAbiFlagsSection<ELFT>::create())
|
|
Add(Sec);
|
|
if (auto *Sec = MipsOptionsSection<ELFT>::create())
|
|
Add(Sec);
|
|
if (auto *Sec = MipsReginfoSection<ELFT>::create())
|
|
Add(Sec);
|
|
}
|
|
|
|
if (Config->HasDynSymTab) {
|
|
InX::DynSymTab = make<SymbolTableSection<ELFT>>(*InX::DynStrTab);
|
|
Add(InX::DynSymTab);
|
|
|
|
In<ELFT>::VerSym = make<VersionTableSection<ELFT>>();
|
|
Add(In<ELFT>::VerSym);
|
|
|
|
if (!Config->VersionDefinitions.empty()) {
|
|
In<ELFT>::VerDef = make<VersionDefinitionSection<ELFT>>();
|
|
Add(In<ELFT>::VerDef);
|
|
}
|
|
|
|
In<ELFT>::VerNeed = make<VersionNeedSection<ELFT>>();
|
|
Add(In<ELFT>::VerNeed);
|
|
|
|
if (Config->GnuHash) {
|
|
InX::GnuHashTab = make<GnuHashTableSection>();
|
|
Add(InX::GnuHashTab);
|
|
}
|
|
|
|
if (Config->SysvHash) {
|
|
In<ELFT>::HashTab = make<HashTableSection<ELFT>>();
|
|
Add(In<ELFT>::HashTab);
|
|
}
|
|
|
|
Add(InX::Dynamic);
|
|
Add(InX::DynStrTab);
|
|
Add(In<ELFT>::RelaDyn);
|
|
}
|
|
|
|
// Add .got. MIPS' .got is so different from the other archs,
|
|
// it has its own class.
|
|
if (Config->EMachine == EM_MIPS) {
|
|
InX::MipsGot = make<MipsGotSection>();
|
|
Add(InX::MipsGot);
|
|
} else {
|
|
InX::Got = make<GotSection>();
|
|
Add(InX::Got);
|
|
}
|
|
|
|
InX::GotPlt = make<GotPltSection>();
|
|
Add(InX::GotPlt);
|
|
InX::IgotPlt = make<IgotPltSection>();
|
|
Add(InX::IgotPlt);
|
|
|
|
if (Config->GdbIndex) {
|
|
InX::GdbIndex = createGdbIndex<ELFT>();
|
|
Add(InX::GdbIndex);
|
|
}
|
|
|
|
// We always need to add rel[a].plt to output if it has entries.
|
|
// Even for static linking it can contain R_[*]_IRELATIVE relocations.
|
|
In<ELFT>::RelaPlt = make<RelocationSection<ELFT>>(
|
|
Config->IsRela ? ".rela.plt" : ".rel.plt", false /*Sort*/);
|
|
Add(In<ELFT>::RelaPlt);
|
|
|
|
// The RelaIplt immediately follows .rel.plt (.rel.dyn for ARM) to ensure
|
|
// that the IRelative relocations are processed last by the dynamic loader
|
|
In<ELFT>::RelaIplt = make<RelocationSection<ELFT>>(
|
|
(Config->EMachine == EM_ARM) ? ".rel.dyn" : In<ELFT>::RelaPlt->Name,
|
|
false /*Sort*/);
|
|
Add(In<ELFT>::RelaIplt);
|
|
|
|
InX::Plt = make<PltSection>(Target->PltHeaderSize);
|
|
Add(InX::Plt);
|
|
InX::Iplt = make<PltSection>(0);
|
|
Add(InX::Iplt);
|
|
|
|
if (!Config->Relocatable) {
|
|
if (Config->EhFrameHdr) {
|
|
In<ELFT>::EhFrameHdr = make<EhFrameHeader<ELFT>>();
|
|
Add(In<ELFT>::EhFrameHdr);
|
|
}
|
|
In<ELFT>::EhFrame = make<EhFrameSection<ELFT>>();
|
|
Add(In<ELFT>::EhFrame);
|
|
}
|
|
|
|
if (InX::SymTab)
|
|
Add(InX::SymTab);
|
|
Add(InX::ShStrTab);
|
|
if (InX::StrTab)
|
|
Add(InX::StrTab);
|
|
}
|
|
|
|
static bool shouldKeepInSymtab(SectionBase *Sec, StringRef SymName,
|
|
const SymbolBody &B) {
|
|
if (B.isFile() || B.isSection())
|
|
return false;
|
|
|
|
// If sym references a section in a discarded group, don't keep it.
|
|
if (Sec == &InputSection::Discarded)
|
|
return false;
|
|
|
|
if (Config->Discard == DiscardPolicy::None)
|
|
return true;
|
|
|
|
// In ELF assembly .L symbols are normally discarded by the assembler.
|
|
// If the assembler fails to do so, the linker discards them if
|
|
// * --discard-locals is used.
|
|
// * The symbol is in a SHF_MERGE section, which is normally the reason for
|
|
// the assembler keeping the .L symbol.
|
|
if (!SymName.startswith(".L") && !SymName.empty())
|
|
return true;
|
|
|
|
if (Config->Discard == DiscardPolicy::Locals)
|
|
return false;
|
|
|
|
return !Sec || !(Sec->Flags & SHF_MERGE);
|
|
}
|
|
|
|
static bool includeInSymtab(const SymbolBody &B) {
|
|
if (!B.isLocal() && !B.symbol()->IsUsedInRegularObj)
|
|
return false;
|
|
|
|
if (auto *D = dyn_cast<DefinedRegular>(&B)) {
|
|
// Always include absolute symbols.
|
|
SectionBase *Sec = D->Section;
|
|
if (!Sec)
|
|
return true;
|
|
if (auto *IS = dyn_cast<InputSectionBase>(Sec)) {
|
|
Sec = IS->Repl;
|
|
IS = cast<InputSectionBase>(Sec);
|
|
// Exclude symbols pointing to garbage-collected sections.
|
|
if (!IS->Live)
|
|
return false;
|
|
}
|
|
if (auto *S = dyn_cast<MergeInputSection>(Sec))
|
|
if (!S->getSectionPiece(D->Value)->Live)
|
|
return false;
|
|
return true;
|
|
}
|
|
|
|
if (auto *Sym = dyn_cast<DefinedCommon>(&B))
|
|
return Sym->Live;
|
|
return true;
|
|
}
|
|
|
|
// Local symbols are not in the linker's symbol table. This function scans
|
|
// each object file's symbol table to copy local symbols to the output.
|
|
template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
|
|
if (!InX::SymTab)
|
|
return;
|
|
for (InputFile *File : ObjectFiles) {
|
|
ObjFile<ELFT> *F = cast<ObjFile<ELFT>>(File);
|
|
for (SymbolBody *B : F->getLocalSymbols()) {
|
|
if (!B->IsLocal)
|
|
fatal(toString(F) +
|
|
": broken object: getLocalSymbols returns a non-local symbol");
|
|
auto *DR = dyn_cast<DefinedRegular>(B);
|
|
|
|
// No reason to keep local undefined symbol in symtab.
|
|
if (!DR)
|
|
continue;
|
|
if (!includeInSymtab(*B))
|
|
continue;
|
|
|
|
SectionBase *Sec = DR->Section;
|
|
if (!shouldKeepInSymtab(Sec, B->getName(), *B))
|
|
continue;
|
|
InX::SymTab->addSymbol(B);
|
|
}
|
|
}
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
|
|
// Create one STT_SECTION symbol for each output section we might
|
|
// have a relocation with.
|
|
for (BaseCommand *Base : Script->Opt.Commands) {
|
|
auto *Sec = dyn_cast<OutputSection>(Base);
|
|
if (!Sec)
|
|
continue;
|
|
auto I = llvm::find_if(Sec->Commands, [](BaseCommand *Base) {
|
|
if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
|
|
return !ISD->Sections.empty();
|
|
return false;
|
|
});
|
|
if (I == Sec->Commands.end())
|
|
continue;
|
|
InputSection *IS = cast<InputSectionDescription>(*I)->Sections[0];
|
|
if (isa<SyntheticSection>(IS) || IS->Type == SHT_REL ||
|
|
IS->Type == SHT_RELA)
|
|
continue;
|
|
|
|
auto *Sym =
|
|
make<DefinedRegular>("", /*IsLocal=*/true, /*StOther=*/0, STT_SECTION,
|
|
/*Value=*/0, /*Size=*/0, IS);
|
|
InX::SymTab->addSymbol(Sym);
|
|
}
|
|
}
|
|
|
|
// Today's loaders have a feature to make segments read-only after
|
|
// processing dynamic relocations to enhance security. PT_GNU_RELRO
|
|
// is defined for that.
|
|
//
|
|
// This function returns true if a section needs to be put into a
|
|
// PT_GNU_RELRO segment.
|
|
static bool isRelroSection(const OutputSection *Sec) {
|
|
if (!Config->ZRelro)
|
|
return false;
|
|
|
|
uint64_t Flags = Sec->Flags;
|
|
|
|
// Non-allocatable or non-writable sections don't need RELRO because
|
|
// they are not writable or not even mapped to memory in the first place.
|
|
// RELRO is for sections that are essentially read-only but need to
|
|
// be writable only at process startup to allow dynamic linker to
|
|
// apply relocations.
|
|
if (!(Flags & SHF_ALLOC) || !(Flags & SHF_WRITE))
|
|
return false;
|
|
|
|
// Once initialized, TLS data segments are used as data templates
|
|
// for a thread-local storage. For each new thread, runtime
|
|
// allocates memory for a TLS and copy templates there. No thread
|
|
// are supposed to use templates directly. Thus, it can be in RELRO.
|
|
if (Flags & SHF_TLS)
|
|
return true;
|
|
|
|
// .init_array, .preinit_array and .fini_array contain pointers to
|
|
// functions that are executed on process startup or exit. These
|
|
// pointers are set by the static linker, and they are not expected
|
|
// to change at runtime. But if you are an attacker, you could do
|
|
// interesting things by manipulating pointers in .fini_array, for
|
|
// example. So they are put into RELRO.
|
|
uint32_t Type = Sec->Type;
|
|
if (Type == SHT_INIT_ARRAY || Type == SHT_FINI_ARRAY ||
|
|
Type == SHT_PREINIT_ARRAY)
|
|
return true;
|
|
|
|
// .got contains pointers to external symbols. They are resolved by
|
|
// the dynamic linker when a module is loaded into memory, and after
|
|
// that they are not expected to change. So, it can be in RELRO.
|
|
if (InX::Got && Sec == InX::Got->getParent())
|
|
return true;
|
|
|
|
// .got.plt contains pointers to external function symbols. They are
|
|
// by default resolved lazily, so we usually cannot put it into RELRO.
|
|
// However, if "-z now" is given, the lazy symbol resolution is
|
|
// disabled, which enables us to put it into RELRO.
|
|
if (Sec == InX::GotPlt->getParent())
|
|
return Config->ZNow;
|
|
|
|
// .dynamic section contains data for the dynamic linker, and
|
|
// there's no need to write to it at runtime, so it's better to put
|
|
// it into RELRO.
|
|
if (Sec == InX::Dynamic->getParent())
|
|
return true;
|
|
|
|
// .bss.rel.ro is used for copy relocations for read-only symbols.
|
|
// Since the dynamic linker needs to process copy relocations, the
|
|
// section cannot be read-only, but once initialized, they shouldn't
|
|
// change.
|
|
if (Sec == InX::BssRelRo->getParent())
|
|
return true;
|
|
|
|
// Sections with some special names are put into RELRO. This is a
|
|
// bit unfortunate because section names shouldn't be significant in
|
|
// ELF in spirit. But in reality many linker features depend on
|
|
// magic section names.
|
|
StringRef S = Sec->Name;
|
|
return S == ".data.rel.ro" || S == ".ctors" || S == ".dtors" || S == ".jcr" ||
|
|
S == ".eh_frame" || S == ".openbsd.randomdata";
|
|
}
|
|
|
|
// We compute a rank for each section. The rank indicates where the
|
|
// section should be placed in the file. Instead of using simple
|
|
// numbers (0,1,2...), we use a series of flags. One for each decision
|
|
// point when placing the section.
|
|
// Using flags has two key properties:
|
|
// * It is easy to check if a give branch was taken.
|
|
// * It is easy two see how similar two ranks are (see getRankProximity).
|
|
enum RankFlags {
|
|
RF_NOT_ADDR_SET = 1 << 16,
|
|
RF_NOT_INTERP = 1 << 15,
|
|
RF_NOT_ALLOC = 1 << 14,
|
|
RF_WRITE = 1 << 13,
|
|
RF_EXEC_WRITE = 1 << 12,
|
|
RF_EXEC = 1 << 11,
|
|
RF_NON_TLS_BSS = 1 << 10,
|
|
RF_NON_TLS_BSS_RO = 1 << 9,
|
|
RF_NOT_TLS = 1 << 8,
|
|
RF_BSS = 1 << 7,
|
|
RF_PPC_NOT_TOCBSS = 1 << 6,
|
|
RF_PPC_OPD = 1 << 5,
|
|
RF_PPC_TOCL = 1 << 4,
|
|
RF_PPC_TOC = 1 << 3,
|
|
RF_PPC_BRANCH_LT = 1 << 2,
|
|
RF_MIPS_GPREL = 1 << 1,
|
|
RF_MIPS_NOT_GOT = 1 << 0
|
|
};
|
|
|
|
static unsigned getSectionRank(const OutputSection *Sec) {
|
|
unsigned Rank = 0;
|
|
|
|
// We want to put section specified by -T option first, so we
|
|
// can start assigning VA starting from them later.
|
|
if (Config->SectionStartMap.count(Sec->Name))
|
|
return Rank;
|
|
Rank |= RF_NOT_ADDR_SET;
|
|
|
|
// Put .interp first because some loaders want to see that section
|
|
// on the first page of the executable file when loaded into memory.
|
|
if (Sec->Name == ".interp")
|
|
return Rank;
|
|
Rank |= RF_NOT_INTERP;
|
|
|
|
// Allocatable sections go first to reduce the total PT_LOAD size and
|
|
// so debug info doesn't change addresses in actual code.
|
|
if (!(Sec->Flags & SHF_ALLOC))
|
|
return Rank | RF_NOT_ALLOC;
|
|
|
|
// Sort sections based on their access permission in the following
|
|
// order: R, RX, RWX, RW. This order is based on the following
|
|
// considerations:
|
|
// * Read-only sections come first such that they go in the
|
|
// PT_LOAD covering the program headers at the start of the file.
|
|
// * Read-only, executable sections come next, unless the
|
|
// -no-rosegment option is used.
|
|
// * Writable, executable sections follow such that .plt on
|
|
// architectures where it needs to be writable will be placed
|
|
// between .text and .data.
|
|
// * Writable sections come last, such that .bss lands at the very
|
|
// end of the last PT_LOAD.
|
|
bool IsExec = Sec->Flags & SHF_EXECINSTR;
|
|
bool IsWrite = Sec->Flags & SHF_WRITE;
|
|
|
|
if (IsExec) {
|
|
if (IsWrite)
|
|
Rank |= RF_EXEC_WRITE;
|
|
else if (!Config->SingleRoRx)
|
|
Rank |= RF_EXEC;
|
|
} else {
|
|
if (IsWrite)
|
|
Rank |= RF_WRITE;
|
|
}
|
|
|
|
// If we got here we know that both A and B are in the same PT_LOAD.
|
|
|
|
bool IsTls = Sec->Flags & SHF_TLS;
|
|
bool IsNoBits = Sec->Type == SHT_NOBITS;
|
|
|
|
// The first requirement we have is to put (non-TLS) nobits sections last. The
|
|
// reason is that the only thing the dynamic linker will see about them is a
|
|
// p_memsz that is larger than p_filesz. Seeing that it zeros the end of the
|
|
// PT_LOAD, so that has to correspond to the nobits sections.
|
|
bool IsNonTlsNoBits = IsNoBits && !IsTls;
|
|
if (IsNonTlsNoBits)
|
|
Rank |= RF_NON_TLS_BSS;
|
|
|
|
// We place nobits RelRo sections before plain r/w ones, and non-nobits RelRo
|
|
// sections after r/w ones, so that the RelRo sections are contiguous.
|
|
bool IsRelRo = isRelroSection(Sec);
|
|
if (IsNonTlsNoBits && !IsRelRo)
|
|
Rank |= RF_NON_TLS_BSS_RO;
|
|
if (!IsNonTlsNoBits && IsRelRo)
|
|
Rank |= RF_NON_TLS_BSS_RO;
|
|
|
|
// The TLS initialization block needs to be a single contiguous block in a R/W
|
|
// PT_LOAD, so stick TLS sections directly before the other RelRo R/W
|
|
// sections. The TLS NOBITS sections are placed here as they don't take up
|
|
// virtual address space in the PT_LOAD.
|
|
if (!IsTls)
|
|
Rank |= RF_NOT_TLS;
|
|
|
|
// Within the TLS initialization block, the non-nobits sections need to appear
|
|
// first.
|
|
if (IsNoBits)
|
|
Rank |= RF_BSS;
|
|
|
|
// Some architectures have additional ordering restrictions for sections
|
|
// within the same PT_LOAD.
|
|
if (Config->EMachine == EM_PPC64) {
|
|
// PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections
|
|
// that we would like to make sure appear is a specific order to maximize
|
|
// their coverage by a single signed 16-bit offset from the TOC base
|
|
// pointer. Conversely, the special .tocbss section should be first among
|
|
// all SHT_NOBITS sections. This will put it next to the loaded special
|
|
// PPC64 sections (and, thus, within reach of the TOC base pointer).
|
|
StringRef Name = Sec->Name;
|
|
if (Name != ".tocbss")
|
|
Rank |= RF_PPC_NOT_TOCBSS;
|
|
|
|
if (Name == ".opd")
|
|
Rank |= RF_PPC_OPD;
|
|
|
|
if (Name == ".toc1")
|
|
Rank |= RF_PPC_TOCL;
|
|
|
|
if (Name == ".toc")
|
|
Rank |= RF_PPC_TOC;
|
|
|
|
if (Name == ".branch_lt")
|
|
Rank |= RF_PPC_BRANCH_LT;
|
|
}
|
|
if (Config->EMachine == EM_MIPS) {
|
|
// All sections with SHF_MIPS_GPREL flag should be grouped together
|
|
// because data in these sections is addressable with a gp relative address.
|
|
if (Sec->Flags & SHF_MIPS_GPREL)
|
|
Rank |= RF_MIPS_GPREL;
|
|
|
|
if (Sec->Name != ".got")
|
|
Rank |= RF_MIPS_NOT_GOT;
|
|
}
|
|
|
|
return Rank;
|
|
}
|
|
|
|
static bool compareSections(const BaseCommand *ACmd, const BaseCommand *BCmd) {
|
|
const OutputSection *A = cast<OutputSection>(ACmd);
|
|
const OutputSection *B = cast<OutputSection>(BCmd);
|
|
if (A->SortRank != B->SortRank)
|
|
return A->SortRank < B->SortRank;
|
|
if (!(A->SortRank & RF_NOT_ADDR_SET))
|
|
return Config->SectionStartMap.lookup(A->Name) <
|
|
Config->SectionStartMap.lookup(B->Name);
|
|
return false;
|
|
}
|
|
|
|
void PhdrEntry::add(OutputSection *Sec) {
|
|
LastSec = Sec;
|
|
if (!FirstSec)
|
|
FirstSec = Sec;
|
|
p_align = std::max(p_align, Sec->Alignment);
|
|
if (p_type == PT_LOAD)
|
|
Sec->PtLoad = this;
|
|
}
|
|
|
|
template <class ELFT>
|
|
static Symbol *addRegular(StringRef Name, SectionBase *Sec, uint64_t Value,
|
|
uint8_t StOther = STV_HIDDEN,
|
|
uint8_t Binding = STB_WEAK) {
|
|
// The linker generated symbols are added as STB_WEAK to allow user defined
|
|
// ones to override them.
|
|
return Symtab->addRegular<ELFT>(Name, StOther, STT_NOTYPE, Value,
|
|
/*Size=*/0, Binding, Sec,
|
|
/*File=*/nullptr);
|
|
}
|
|
|
|
template <class ELFT>
|
|
static DefinedRegular *
|
|
addOptionalRegular(StringRef Name, SectionBase *Sec, uint64_t Val,
|
|
uint8_t StOther = STV_HIDDEN, uint8_t Binding = STB_GLOBAL) {
|
|
SymbolBody *S = Symtab->find(Name);
|
|
if (!S)
|
|
return nullptr;
|
|
if (S->isInCurrentDSO())
|
|
return nullptr;
|
|
return cast<DefinedRegular>(
|
|
addRegular<ELFT>(Name, Sec, Val, StOther, Binding)->body());
|
|
}
|
|
|
|
// The beginning and the ending of .rel[a].plt section are marked
|
|
// with __rel[a]_iplt_{start,end} symbols if it is a statically linked
|
|
// executable. The runtime needs these symbols in order to resolve
|
|
// all IRELATIVE relocs on startup. For dynamic executables, we don't
|
|
// need these symbols, since IRELATIVE relocs are resolved through GOT
|
|
// and PLT. For details, see http://www.airs.com/blog/archives/403.
|
|
template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
|
|
if (!Config->Static)
|
|
return;
|
|
StringRef S = Config->IsRela ? "__rela_iplt_start" : "__rel_iplt_start";
|
|
addOptionalRegular<ELFT>(S, In<ELFT>::RelaIplt, 0, STV_HIDDEN, STB_WEAK);
|
|
|
|
S = Config->IsRela ? "__rela_iplt_end" : "__rel_iplt_end";
|
|
addOptionalRegular<ELFT>(S, In<ELFT>::RelaIplt, -1, STV_HIDDEN, STB_WEAK);
|
|
}
|
|
|
|
// The linker is expected to define some symbols depending on
|
|
// the linking result. This function defines such symbols.
|
|
template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
|
|
if (Config->EMachine == EM_MIPS) {
|
|
// Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
|
|
// so that it points to an absolute address which by default is relative
|
|
// to GOT. Default offset is 0x7ff0.
|
|
// See "Global Data Symbols" in Chapter 6 in the following document:
|
|
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
|
|
ElfSym::MipsGp = Symtab->addAbsolute<ELFT>("_gp", STV_HIDDEN, STB_LOCAL);
|
|
|
|
// On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
|
|
// start of function and 'gp' pointer into GOT.
|
|
if (Symtab->find("_gp_disp"))
|
|
ElfSym::MipsGpDisp =
|
|
Symtab->addAbsolute<ELFT>("_gp_disp", STV_HIDDEN, STB_LOCAL);
|
|
|
|
// The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
|
|
// pointer. This symbol is used in the code generated by .cpload pseudo-op
|
|
// in case of using -mno-shared option.
|
|
// https://sourceware.org/ml/binutils/2004-12/msg00094.html
|
|
if (Symtab->find("__gnu_local_gp"))
|
|
ElfSym::MipsLocalGp =
|
|
Symtab->addAbsolute<ELFT>("__gnu_local_gp", STV_HIDDEN, STB_LOCAL);
|
|
}
|
|
|
|
// The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention to
|
|
// be at some offset from the base of the .got section, usually 0 or the end
|
|
// of the .got
|
|
InputSection *GotSection = InX::MipsGot ? cast<InputSection>(InX::MipsGot)
|
|
: cast<InputSection>(InX::Got);
|
|
ElfSym::GlobalOffsetTable = addOptionalRegular<ELFT>(
|
|
"_GLOBAL_OFFSET_TABLE_", GotSection, Target->GotBaseSymOff);
|
|
|
|
// __tls_get_addr is defined by the dynamic linker for dynamic ELFs. For
|
|
// static linking the linker is required to optimize away any references to
|
|
// __tls_get_addr, so it's not defined anywhere. Create a hidden definition
|
|
// to avoid the undefined symbol error.
|
|
if (!InX::DynSymTab)
|
|
Symtab->addIgnored<ELFT>("__tls_get_addr");
|
|
|
|
// __ehdr_start is the location of ELF file headers. Note that we define
|
|
// this symbol unconditionally even when using a linker script, which
|
|
// differs from the behavior implemented by GNU linker which only define
|
|
// this symbol if ELF headers are in the memory mapped segment.
|
|
// __executable_start is not documented, but the expectation of at
|
|
// least the android libc is that it points to the elf header too.
|
|
// __dso_handle symbol is passed to cxa_finalize as a marker to identify
|
|
// each DSO. The address of the symbol doesn't matter as long as they are
|
|
// different in different DSOs, so we chose the start address of the DSO.
|
|
for (const char *Name :
|
|
{"__ehdr_start", "__executable_start", "__dso_handle"})
|
|
addOptionalRegular<ELFT>(Name, Out::ElfHeader, 0, STV_HIDDEN);
|
|
|
|
// If linker script do layout we do not need to create any standart symbols.
|
|
if (Script->Opt.HasSections)
|
|
return;
|
|
|
|
auto Add = [](StringRef S, int64_t Pos) {
|
|
return addOptionalRegular<ELFT>(S, Out::ElfHeader, Pos, STV_DEFAULT);
|
|
};
|
|
|
|
ElfSym::Bss = Add("__bss_start", 0);
|
|
ElfSym::End1 = Add("end", -1);
|
|
ElfSym::End2 = Add("_end", -1);
|
|
ElfSym::Etext1 = Add("etext", -1);
|
|
ElfSym::Etext2 = Add("_etext", -1);
|
|
ElfSym::Edata1 = Add("edata", -1);
|
|
ElfSym::Edata2 = Add("_edata", -1);
|
|
}
|
|
|
|
// Sort input sections by section name suffixes for
|
|
// __attribute__((init_priority(N))).
|
|
static void sortInitFini(OutputSection *Cmd) {
|
|
if (Cmd)
|
|
Cmd->sortInitFini();
|
|
}
|
|
|
|
// Sort input sections by the special rule for .ctors and .dtors.
|
|
static void sortCtorsDtors(OutputSection *Cmd) {
|
|
if (Cmd)
|
|
Cmd->sortCtorsDtors();
|
|
}
|
|
|
|
// Sort input sections using the list provided by --symbol-ordering-file.
|
|
static void sortBySymbolsOrder() {
|
|
if (Config->SymbolOrderingFile.empty())
|
|
return;
|
|
|
|
// Sort sections by priority.
|
|
DenseMap<SectionBase *, int> SectionOrder = buildSectionOrder();
|
|
for (BaseCommand *Base : Script->Opt.Commands)
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base))
|
|
Sec->sort([&](InputSectionBase *S) { return SectionOrder.lookup(S); });
|
|
}
|
|
|
|
template <class ELFT>
|
|
void Writer<ELFT>::forEachRelSec(std::function<void(InputSectionBase &)> Fn) {
|
|
// Scan all relocations. Each relocation goes through a series
|
|
// of tests to determine if it needs special treatment, such as
|
|
// creating GOT, PLT, copy relocations, etc.
|
|
// Note that relocations for non-alloc sections are directly
|
|
// processed by InputSection::relocateNonAlloc.
|
|
for (InputSectionBase *IS : InputSections)
|
|
if (IS->Live && isa<InputSection>(IS) && (IS->Flags & SHF_ALLOC))
|
|
Fn(*IS);
|
|
for (EhInputSection *ES : In<ELFT>::EhFrame->Sections)
|
|
Fn(*ES);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::createSections() {
|
|
std::vector<BaseCommand *> Old = Script->Opt.Commands;
|
|
Script->Opt.Commands.clear();
|
|
for (InputSectionBase *IS : InputSections)
|
|
if (IS)
|
|
Factory.addInputSec(IS, getOutputSectionName(IS->Name));
|
|
Script->Opt.Commands.insert(Script->Opt.Commands.end(), Old.begin(),
|
|
Old.end());
|
|
|
|
Script->fabricateDefaultCommands();
|
|
sortBySymbolsOrder();
|
|
sortInitFini(findSection(".init_array"));
|
|
sortInitFini(findSection(".fini_array"));
|
|
sortCtorsDtors(findSection(".ctors"));
|
|
sortCtorsDtors(findSection(".dtors"));
|
|
}
|
|
|
|
// This function generates assignments for predefined symbols (e.g. _end or
|
|
// _etext) and inserts them into the commands sequence to be processed at the
|
|
// appropriate time. This ensures that the value is going to be correct by the
|
|
// time any references to these symbols are processed and is equivalent to
|
|
// defining these symbols explicitly in the linker script.
|
|
template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
|
|
PhdrEntry *Last = nullptr;
|
|
PhdrEntry *LastRO = nullptr;
|
|
PhdrEntry *LastRW = nullptr;
|
|
|
|
for (PhdrEntry *P : Phdrs) {
|
|
if (P->p_type != PT_LOAD)
|
|
continue;
|
|
Last = P;
|
|
if (P->p_flags & PF_W)
|
|
LastRW = P;
|
|
else
|
|
LastRO = P;
|
|
}
|
|
|
|
// _end is the first location after the uninitialized data region.
|
|
if (Last) {
|
|
if (ElfSym::End1)
|
|
ElfSym::End1->Section = Last->LastSec;
|
|
if (ElfSym::End2)
|
|
ElfSym::End2->Section = Last->LastSec;
|
|
}
|
|
|
|
// _etext is the first location after the last read-only loadable segment.
|
|
if (LastRO) {
|
|
if (ElfSym::Etext1)
|
|
ElfSym::Etext1->Section = LastRO->LastSec;
|
|
if (ElfSym::Etext2)
|
|
ElfSym::Etext2->Section = LastRO->LastSec;
|
|
}
|
|
|
|
// _edata points to the end of the last non SHT_NOBITS section.
|
|
if (LastRW) {
|
|
size_t I = 0;
|
|
for (; I < OutputSections.size(); ++I)
|
|
if (OutputSections[I] == LastRW->FirstSec)
|
|
break;
|
|
|
|
for (; I < OutputSections.size(); ++I) {
|
|
if (OutputSections[I]->Type != SHT_NOBITS)
|
|
continue;
|
|
break;
|
|
}
|
|
if (ElfSym::Edata1)
|
|
ElfSym::Edata1->Section = OutputSections[I - 1];
|
|
if (ElfSym::Edata2)
|
|
ElfSym::Edata2->Section = OutputSections[I - 1];
|
|
}
|
|
|
|
if (ElfSym::Bss)
|
|
ElfSym::Bss->Section = findSection(".bss");
|
|
|
|
// Setup MIPS _gp_disp/__gnu_local_gp symbols which should
|
|
// be equal to the _gp symbol's value.
|
|
if (ElfSym::MipsGp) {
|
|
// Find GP-relative section with the lowest address
|
|
// and use this address to calculate default _gp value.
|
|
for (OutputSection *OS : OutputSections) {
|
|
if (OS->Flags & SHF_MIPS_GPREL) {
|
|
ElfSym::MipsGp->Section = OS;
|
|
ElfSym::MipsGp->Value = 0x7ff0;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// We want to find how similar two ranks are.
|
|
// The more branches in getSectionRank that match, the more similar they are.
|
|
// Since each branch corresponds to a bit flag, we can just use
|
|
// countLeadingZeros.
|
|
static int getRankProximityAux(OutputSection *A, OutputSection *B) {
|
|
return countLeadingZeros(A->SortRank ^ B->SortRank);
|
|
}
|
|
|
|
static int getRankProximity(OutputSection *A, BaseCommand *B) {
|
|
if (auto *Sec = dyn_cast<OutputSection>(B))
|
|
if (Sec->Live)
|
|
return getRankProximityAux(A, Sec);
|
|
return -1;
|
|
}
|
|
|
|
// When placing orphan sections, we want to place them after symbol assignments
|
|
// so that an orphan after
|
|
// begin_foo = .;
|
|
// foo : { *(foo) }
|
|
// end_foo = .;
|
|
// doesn't break the intended meaning of the begin/end symbols.
|
|
// We don't want to go over sections since findOrphanPos is the
|
|
// one in charge of deciding the order of the sections.
|
|
// We don't want to go over changes to '.', since doing so in
|
|
// rx_sec : { *(rx_sec) }
|
|
// . = ALIGN(0x1000);
|
|
// /* The RW PT_LOAD starts here*/
|
|
// rw_sec : { *(rw_sec) }
|
|
// would mean that the RW PT_LOAD would become unaligned.
|
|
static bool shouldSkip(BaseCommand *Cmd) {
|
|
if (isa<OutputSection>(Cmd))
|
|
return false;
|
|
if (auto *Assign = dyn_cast<SymbolAssignment>(Cmd))
|
|
return Assign->Name != ".";
|
|
return true;
|
|
}
|
|
|
|
// We want to place orphan sections so that they share as much
|
|
// characteristics with their neighbors as possible. For example, if
|
|
// both are rw, or both are tls.
|
|
template <typename ELFT>
|
|
static std::vector<BaseCommand *>::iterator
|
|
findOrphanPos(std::vector<BaseCommand *>::iterator B,
|
|
std::vector<BaseCommand *>::iterator E) {
|
|
OutputSection *Sec = cast<OutputSection>(*E);
|
|
|
|
// Find the first element that has as close a rank as possible.
|
|
auto I = std::max_element(B, E, [=](BaseCommand *A, BaseCommand *B) {
|
|
return getRankProximity(Sec, A) < getRankProximity(Sec, B);
|
|
});
|
|
if (I == E)
|
|
return E;
|
|
|
|
// Consider all existing sections with the same proximity.
|
|
int Proximity = getRankProximity(Sec, *I);
|
|
for (; I != E; ++I) {
|
|
auto *CurSec = dyn_cast<OutputSection>(*I);
|
|
if (!CurSec || !CurSec->Live)
|
|
continue;
|
|
if (getRankProximity(Sec, CurSec) != Proximity ||
|
|
Sec->SortRank < CurSec->SortRank)
|
|
break;
|
|
}
|
|
auto J = std::find_if(
|
|
llvm::make_reverse_iterator(I), llvm::make_reverse_iterator(B),
|
|
[](BaseCommand *Cmd) { return isa<OutputSection>(Cmd); });
|
|
I = J.base();
|
|
|
|
// As a special case, if the orphan section is the last section, put
|
|
// it at the very end, past any other commands.
|
|
// This matches bfd's behavior and is convenient when the linker script fully
|
|
// specifies the start of the file, but doesn't care about the end (the non
|
|
// alloc sections for example).
|
|
auto NextSec = std::find_if(
|
|
I, E, [](BaseCommand *Cmd) { return isa<OutputSection>(Cmd); });
|
|
if (NextSec == E)
|
|
return E;
|
|
|
|
while (I != E && shouldSkip(*I))
|
|
++I;
|
|
return I;
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::sortSections() {
|
|
if (Script->Opt.HasSections)
|
|
Script->adjustSectionsBeforeSorting();
|
|
|
|
// Don't sort if using -r. It is not necessary and we want to preserve the
|
|
// relative order for SHF_LINK_ORDER sections.
|
|
if (Config->Relocatable)
|
|
return;
|
|
|
|
for (BaseCommand *Base : Script->Opt.Commands)
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base))
|
|
Sec->SortRank = getSectionRank(Sec);
|
|
|
|
if (!Script->Opt.HasSections) {
|
|
// We know that all the OutputSections are contiguous in
|
|
// this case.
|
|
auto E = Script->Opt.Commands.end();
|
|
auto I = Script->Opt.Commands.begin();
|
|
auto IsSection = [](BaseCommand *Base) { return isa<OutputSection>(Base); };
|
|
I = std::find_if(I, E, IsSection);
|
|
E = std::find_if(llvm::make_reverse_iterator(E),
|
|
llvm::make_reverse_iterator(I), IsSection)
|
|
.base();
|
|
std::stable_sort(I, E, compareSections);
|
|
return;
|
|
}
|
|
|
|
// Orphan sections are sections present in the input files which are
|
|
// not explicitly placed into the output file by the linker script.
|
|
//
|
|
// The sections in the linker script are already in the correct
|
|
// order. We have to figuere out where to insert the orphan
|
|
// sections.
|
|
//
|
|
// The order of the sections in the script is arbitrary and may not agree with
|
|
// compareSections. This means that we cannot easily define a strict weak
|
|
// ordering. To see why, consider a comparison of a section in the script and
|
|
// one not in the script. We have a two simple options:
|
|
// * Make them equivalent (a is not less than b, and b is not less than a).
|
|
// The problem is then that equivalence has to be transitive and we can
|
|
// have sections a, b and c with only b in a script and a less than c
|
|
// which breaks this property.
|
|
// * Use compareSectionsNonScript. Given that the script order doesn't have
|
|
// to match, we can end up with sections a, b, c, d where b and c are in the
|
|
// script and c is compareSectionsNonScript less than b. In which case d
|
|
// can be equivalent to c, a to b and d < a. As a concrete example:
|
|
// .a (rx) # not in script
|
|
// .b (rx) # in script
|
|
// .c (ro) # in script
|
|
// .d (ro) # not in script
|
|
//
|
|
// The way we define an order then is:
|
|
// * Sort only the orphan sections. They are in the end right now.
|
|
// * Move each orphan section to its preferred position. We try
|
|
// to put each section in the last position where it it can share
|
|
// a PT_LOAD.
|
|
//
|
|
// There is some ambiguity as to where exactly a new entry should be
|
|
// inserted, because Opt.Commands contains not only output section
|
|
// commands but also other types of commands such as symbol assignment
|
|
// expressions. There's no correct answer here due to the lack of the
|
|
// formal specification of the linker script. We use heuristics to
|
|
// determine whether a new output command should be added before or
|
|
// after another commands. For the details, look at shouldSkip
|
|
// function.
|
|
|
|
auto I = Script->Opt.Commands.begin();
|
|
auto E = Script->Opt.Commands.end();
|
|
auto NonScriptI = std::find_if(I, E, [](BaseCommand *Base) {
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base))
|
|
return Sec->Live && Sec->SectionIndex == INT_MAX;
|
|
return false;
|
|
});
|
|
|
|
// Sort the orphan sections.
|
|
std::stable_sort(NonScriptI, E, compareSections);
|
|
|
|
// As a horrible special case, skip the first . assignment if it is before any
|
|
// section. We do this because it is common to set a load address by starting
|
|
// the script with ". = 0xabcd" and the expectation is that every section is
|
|
// after that.
|
|
auto FirstSectionOrDotAssignment =
|
|
std::find_if(I, E, [](BaseCommand *Cmd) { return !shouldSkip(Cmd); });
|
|
if (FirstSectionOrDotAssignment != E &&
|
|
isa<SymbolAssignment>(**FirstSectionOrDotAssignment))
|
|
++FirstSectionOrDotAssignment;
|
|
I = FirstSectionOrDotAssignment;
|
|
|
|
while (NonScriptI != E) {
|
|
auto Pos = findOrphanPos<ELFT>(I, NonScriptI);
|
|
OutputSection *Orphan = cast<OutputSection>(*NonScriptI);
|
|
|
|
// As an optimization, find all sections with the same sort rank
|
|
// and insert them with one rotate.
|
|
unsigned Rank = Orphan->SortRank;
|
|
auto End = std::find_if(NonScriptI + 1, E, [=](BaseCommand *Cmd) {
|
|
return cast<OutputSection>(Cmd)->SortRank != Rank;
|
|
});
|
|
std::rotate(Pos, NonScriptI, End);
|
|
NonScriptI = End;
|
|
}
|
|
|
|
Script->adjustSectionsAfterSorting();
|
|
}
|
|
|
|
static void applySynthetic(const std::vector<SyntheticSection *> &Sections,
|
|
std::function<void(SyntheticSection *)> Fn) {
|
|
for (SyntheticSection *SS : Sections)
|
|
if (SS && SS->getParent() && !SS->empty())
|
|
Fn(SS);
|
|
}
|
|
|
|
// We need to add input synthetic sections early in createSyntheticSections()
|
|
// to make them visible from linkescript side. But not all sections are always
|
|
// required to be in output. For example we don't need dynamic section content
|
|
// sometimes. This function filters out such unused sections from the output.
|
|
static void removeUnusedSyntheticSections() {
|
|
// All input synthetic sections that can be empty are placed after
|
|
// all regular ones. We iterate over them all and exit at first
|
|
// non-synthetic.
|
|
for (InputSectionBase *S : llvm::reverse(InputSections)) {
|
|
SyntheticSection *SS = dyn_cast<SyntheticSection>(S);
|
|
if (!SS)
|
|
return;
|
|
OutputSection *OS = SS->getParent();
|
|
if (!SS->empty() || !OS)
|
|
continue;
|
|
if ((SS == InX::Got || SS == InX::MipsGot) && ElfSym::GlobalOffsetTable)
|
|
continue;
|
|
|
|
std::vector<BaseCommand *>::iterator Empty = OS->Commands.end();
|
|
for (auto I = OS->Commands.begin(), E = OS->Commands.end(); I != E; ++I) {
|
|
BaseCommand *B = *I;
|
|
if (auto *ISD = dyn_cast<InputSectionDescription>(B)) {
|
|
llvm::erase_if(ISD->Sections,
|
|
[=](InputSection *IS) { return IS == SS; });
|
|
if (ISD->Sections.empty())
|
|
Empty = I;
|
|
}
|
|
}
|
|
if (Empty != OS->Commands.end())
|
|
OS->Commands.erase(Empty);
|
|
|
|
// If there are no other sections in the output section, remove it from the
|
|
// output.
|
|
if (OS->Commands.empty())
|
|
llvm::erase_if(Script->Opt.Commands,
|
|
[&](BaseCommand *Cmd) { return Cmd == OS; });
|
|
}
|
|
}
|
|
|
|
// Returns true if a symbol can be replaced at load-time by a symbol
|
|
// with the same name defined in other ELF executable or DSO.
|
|
static bool computeIsPreemptible(const SymbolBody &B) {
|
|
assert(!B.isLocal());
|
|
// Only symbols that appear in dynsym can be preempted.
|
|
if (!B.symbol()->includeInDynsym())
|
|
return false;
|
|
|
|
// Only default visibility symbols can be preempted.
|
|
if (B.symbol()->Visibility != STV_DEFAULT)
|
|
return false;
|
|
|
|
// At this point copy relocations have not been created yet, so any
|
|
// symbol that is not defined locally is preemptible.
|
|
if (!B.isInCurrentDSO())
|
|
return true;
|
|
|
|
// If we have a dynamic list it specifies which local symbols are preemptible.
|
|
if (Config->HasDynamicList)
|
|
return false;
|
|
|
|
if (!Config->Shared)
|
|
return false;
|
|
|
|
// -Bsymbolic means that definitions are not preempted.
|
|
if (Config->Bsymbolic || (Config->BsymbolicFunctions && B.isFunc()))
|
|
return false;
|
|
return true;
|
|
}
|
|
|
|
// Create output section objects and add them to OutputSections.
|
|
template <class ELFT> void Writer<ELFT>::finalizeSections() {
|
|
Out::DebugInfo = findSection(".debug_info");
|
|
Out::PreinitArray = findSection(".preinit_array");
|
|
Out::InitArray = findSection(".init_array");
|
|
Out::FiniArray = findSection(".fini_array");
|
|
|
|
// The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
|
|
// symbols for sections, so that the runtime can get the start and end
|
|
// addresses of each section by section name. Add such symbols.
|
|
if (!Config->Relocatable) {
|
|
addStartEndSymbols();
|
|
for (BaseCommand *Base : Script->Opt.Commands)
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base))
|
|
addStartStopSymbols(Sec);
|
|
}
|
|
|
|
// Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
|
|
// It should be okay as no one seems to care about the type.
|
|
// Even the author of gold doesn't remember why gold behaves that way.
|
|
// https://sourceware.org/ml/binutils/2002-03/msg00360.html
|
|
if (InX::DynSymTab)
|
|
addRegular<ELFT>("_DYNAMIC", InX::Dynamic, 0);
|
|
|
|
// Define __rel[a]_iplt_{start,end} symbols if needed.
|
|
addRelIpltSymbols();
|
|
|
|
// This responsible for splitting up .eh_frame section into
|
|
// pieces. The relocation scan uses those pieces, so this has to be
|
|
// earlier.
|
|
applySynthetic({In<ELFT>::EhFrame},
|
|
[](SyntheticSection *SS) { SS->finalizeContents(); });
|
|
|
|
for (Symbol *S : Symtab->getSymbols())
|
|
S->body()->IsPreemptible |= computeIsPreemptible(*S->body());
|
|
|
|
// Scan relocations. This must be done after every symbol is declared so that
|
|
// we can correctly decide if a dynamic relocation is needed.
|
|
if (!Config->Relocatable)
|
|
forEachRelSec(scanRelocations<ELFT>);
|
|
|
|
if (InX::Plt && !InX::Plt->empty())
|
|
InX::Plt->addSymbols();
|
|
if (InX::Iplt && !InX::Iplt->empty())
|
|
InX::Iplt->addSymbols();
|
|
|
|
// Now that we have defined all possible global symbols including linker-
|
|
// synthesized ones. Visit all symbols to give the finishing touches.
|
|
for (Symbol *S : Symtab->getSymbols()) {
|
|
SymbolBody *Body = S->body();
|
|
|
|
if (!includeInSymtab(*Body))
|
|
continue;
|
|
if (InX::SymTab)
|
|
InX::SymTab->addSymbol(Body);
|
|
|
|
if (InX::DynSymTab && S->includeInDynsym()) {
|
|
InX::DynSymTab->addSymbol(Body);
|
|
if (auto *SS = dyn_cast<SharedSymbol>(Body))
|
|
if (cast<SharedFile<ELFT>>(S->File)->isNeeded())
|
|
In<ELFT>::VerNeed->addSymbol(SS);
|
|
}
|
|
}
|
|
|
|
// Do not proceed if there was an undefined symbol.
|
|
if (ErrorCount)
|
|
return;
|
|
|
|
addPredefinedSections();
|
|
removeUnusedSyntheticSections();
|
|
|
|
sortSections();
|
|
|
|
// Now that we have the final list, create a list of all the
|
|
// OutputSections for convenience.
|
|
for (BaseCommand *Base : Script->Opt.Commands)
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base))
|
|
OutputSections.push_back(Sec);
|
|
|
|
// Prefer command line supplied address over other constraints.
|
|
for (OutputSection *Sec : OutputSections) {
|
|
auto I = Config->SectionStartMap.find(Sec->Name);
|
|
if (I != Config->SectionStartMap.end())
|
|
Sec->AddrExpr = [=] { return I->second; };
|
|
}
|
|
|
|
// This is a bit of a hack. A value of 0 means undef, so we set it
|
|
// to 1 t make __ehdr_start defined. The section number is not
|
|
// particularly relevant.
|
|
Out::ElfHeader->SectionIndex = 1;
|
|
|
|
unsigned I = 1;
|
|
for (OutputSection *Sec : OutputSections) {
|
|
Sec->SectionIndex = I++;
|
|
Sec->ShName = InX::ShStrTab->addString(Sec->Name);
|
|
}
|
|
|
|
// Binary and relocatable output does not have PHDRS.
|
|
// The headers have to be created before finalize as that can influence the
|
|
// image base and the dynamic section on mips includes the image base.
|
|
if (!Config->Relocatable && !Config->OFormatBinary) {
|
|
Phdrs = Script->hasPhdrsCommands() ? Script->createPhdrs() : createPhdrs();
|
|
addPtArmExid(Phdrs);
|
|
Out::ProgramHeaders->Size = sizeof(Elf_Phdr) * Phdrs.size();
|
|
}
|
|
|
|
// Some symbols are defined in term of program headers. Now that we
|
|
// have the headers, we can find out which sections they point to.
|
|
setReservedSymbolSections();
|
|
|
|
// Dynamic section must be the last one in this list and dynamic
|
|
// symbol table section (DynSymTab) must be the first one.
|
|
applySynthetic({InX::DynSymTab, InX::Bss,
|
|
InX::BssRelRo, InX::GnuHashTab,
|
|
In<ELFT>::HashTab, InX::SymTab,
|
|
InX::ShStrTab, InX::StrTab,
|
|
In<ELFT>::VerDef, InX::DynStrTab,
|
|
InX::Got, InX::MipsGot,
|
|
InX::IgotPlt, InX::GotPlt,
|
|
In<ELFT>::RelaDyn, In<ELFT>::RelaIplt,
|
|
In<ELFT>::RelaPlt, InX::Plt,
|
|
InX::Iplt, In<ELFT>::EhFrameHdr,
|
|
In<ELFT>::VerSym, In<ELFT>::VerNeed,
|
|
InX::Dynamic},
|
|
[](SyntheticSection *SS) { SS->finalizeContents(); });
|
|
|
|
if (!Script->Opt.HasSections && !Config->Relocatable)
|
|
fixSectionAlignments();
|
|
|
|
// Some architectures use small displacements for jump instructions.
|
|
// It is linker's responsibility to create thunks containing long
|
|
// jump instructions if jump targets are too far. Create thunks.
|
|
if (Target->NeedsThunks) {
|
|
// FIXME: only ARM Interworking and Mips LA25 Thunks are implemented,
|
|
// these
|
|
// do not require address information. To support range extension Thunks
|
|
// we need to assign addresses so that we can tell if jump instructions
|
|
// are out of range. This will need to turn into a loop that converges
|
|
// when no more Thunks are added
|
|
ThunkCreator TC;
|
|
Script->assignAddresses();
|
|
if (TC.createThunks(OutputSections)) {
|
|
applySynthetic({InX::MipsGot},
|
|
[](SyntheticSection *SS) { SS->updateAllocSize(); });
|
|
if (TC.createThunks(OutputSections))
|
|
fatal("All non-range thunks should be created in first call");
|
|
}
|
|
}
|
|
|
|
// Fill other section headers. The dynamic table is finalized
|
|
// at the end because some tags like RELSZ depend on result
|
|
// of finalizing other sections.
|
|
for (OutputSection *Sec : OutputSections)
|
|
Sec->finalize<ELFT>();
|
|
|
|
// createThunks may have added local symbols to the static symbol table
|
|
applySynthetic({InX::SymTab, InX::ShStrTab, InX::StrTab},
|
|
[](SyntheticSection *SS) { SS->postThunkContents(); });
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
|
|
// ARM ABI requires .ARM.exidx to be terminated by some piece of data.
|
|
// We have the terminater synthetic section class. Add that at the end.
|
|
OutputSection *Cmd = findSection(".ARM.exidx");
|
|
if (!Cmd || !Cmd->Live || Config->Relocatable)
|
|
return;
|
|
|
|
auto *Sentinel = make<ARMExidxSentinelSection>();
|
|
Cmd->addSection(Sentinel);
|
|
}
|
|
|
|
// The linker is expected to define SECNAME_start and SECNAME_end
|
|
// symbols for a few sections. This function defines them.
|
|
template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
|
|
auto Define = [&](StringRef Start, StringRef End, OutputSection *OS) {
|
|
// These symbols resolve to the image base if the section does not exist.
|
|
// A special value -1 indicates end of the section.
|
|
if (OS) {
|
|
addOptionalRegular<ELFT>(Start, OS, 0);
|
|
addOptionalRegular<ELFT>(End, OS, -1);
|
|
} else {
|
|
if (Config->Pic)
|
|
OS = Out::ElfHeader;
|
|
addOptionalRegular<ELFT>(Start, OS, 0);
|
|
addOptionalRegular<ELFT>(End, OS, 0);
|
|
}
|
|
};
|
|
|
|
Define("__preinit_array_start", "__preinit_array_end", Out::PreinitArray);
|
|
Define("__init_array_start", "__init_array_end", Out::InitArray);
|
|
Define("__fini_array_start", "__fini_array_end", Out::FiniArray);
|
|
|
|
if (OutputSection *Sec = findSection(".ARM.exidx"))
|
|
Define("__exidx_start", "__exidx_end", Sec);
|
|
}
|
|
|
|
// If a section name is valid as a C identifier (which is rare because of
|
|
// the leading '.'), linkers are expected to define __start_<secname> and
|
|
// __stop_<secname> symbols. They are at beginning and end of the section,
|
|
// respectively. This is not requested by the ELF standard, but GNU ld and
|
|
// gold provide the feature, and used by many programs.
|
|
template <class ELFT>
|
|
void Writer<ELFT>::addStartStopSymbols(OutputSection *Sec) {
|
|
StringRef S = Sec->Name;
|
|
if (!isValidCIdentifier(S))
|
|
return;
|
|
addOptionalRegular<ELFT>(Saver.save("__start_" + S), Sec, 0, STV_DEFAULT);
|
|
addOptionalRegular<ELFT>(Saver.save("__stop_" + S), Sec, -1, STV_DEFAULT);
|
|
}
|
|
|
|
template <class ELFT> OutputSection *Writer<ELFT>::findSection(StringRef Name) {
|
|
for (BaseCommand *Base : Script->Opt.Commands)
|
|
if (auto *Sec = dyn_cast<OutputSection>(Base))
|
|
if (Sec->Name == Name)
|
|
return Sec;
|
|
return nullptr;
|
|
}
|
|
|
|
static bool needsPtLoad(OutputSection *Sec) {
|
|
if (!(Sec->Flags & SHF_ALLOC))
|
|
return false;
|
|
|
|
// Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
|
|
// responsible for allocating space for them, not the PT_LOAD that
|
|
// contains the TLS initialization image.
|
|
if (Sec->Flags & SHF_TLS && Sec->Type == SHT_NOBITS)
|
|
return false;
|
|
return true;
|
|
}
|
|
|
|
// Linker scripts are responsible for aligning addresses. Unfortunately, most
|
|
// linker scripts are designed for creating two PT_LOADs only, one RX and one
|
|
// RW. This means that there is no alignment in the RO to RX transition and we
|
|
// cannot create a PT_LOAD there.
|
|
static uint64_t computeFlags(uint64_t Flags) {
|
|
if (Config->Omagic)
|
|
return PF_R | PF_W | PF_X;
|
|
if (Config->SingleRoRx && !(Flags & PF_W))
|
|
return Flags | PF_X;
|
|
return Flags;
|
|
}
|
|
|
|
// Decide which program headers to create and which sections to include in each
|
|
// one.
|
|
template <class ELFT> std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs() {
|
|
std::vector<PhdrEntry *> Ret;
|
|
auto AddHdr = [&](unsigned Type, unsigned Flags) -> PhdrEntry * {
|
|
Ret.push_back(make<PhdrEntry>(Type, Flags));
|
|
return Ret.back();
|
|
};
|
|
|
|
// The first phdr entry is PT_PHDR which describes the program header itself.
|
|
AddHdr(PT_PHDR, PF_R)->add(Out::ProgramHeaders);
|
|
|
|
// PT_INTERP must be the second entry if exists.
|
|
if (OutputSection *Cmd = findSection(".interp"))
|
|
AddHdr(PT_INTERP, Cmd->getPhdrFlags())->add(Cmd);
|
|
|
|
// Add the first PT_LOAD segment for regular output sections.
|
|
uint64_t Flags = computeFlags(PF_R);
|
|
PhdrEntry *Load = AddHdr(PT_LOAD, Flags);
|
|
|
|
// Add the headers. We will remove them if they don't fit.
|
|
Load->add(Out::ElfHeader);
|
|
Load->add(Out::ProgramHeaders);
|
|
|
|
for (OutputSection *Sec : OutputSections) {
|
|
if (!(Sec->Flags & SHF_ALLOC))
|
|
break;
|
|
if (!needsPtLoad(Sec))
|
|
continue;
|
|
|
|
// Segments are contiguous memory regions that has the same attributes
|
|
// (e.g. executable or writable). There is one phdr for each segment.
|
|
// Therefore, we need to create a new phdr when the next section has
|
|
// different flags or is loaded at a discontiguous address using AT linker
|
|
// script command.
|
|
uint64_t NewFlags = computeFlags(Sec->getPhdrFlags());
|
|
if (Sec->LMAExpr || Flags != NewFlags) {
|
|
Load = AddHdr(PT_LOAD, NewFlags);
|
|
Flags = NewFlags;
|
|
}
|
|
|
|
Load->add(Sec);
|
|
}
|
|
|
|
// Add a TLS segment if any.
|
|
PhdrEntry *TlsHdr = make<PhdrEntry>(PT_TLS, PF_R);
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->Flags & SHF_TLS)
|
|
TlsHdr->add(Sec);
|
|
if (TlsHdr->FirstSec)
|
|
Ret.push_back(TlsHdr);
|
|
|
|
// Add an entry for .dynamic.
|
|
if (InX::DynSymTab)
|
|
AddHdr(PT_DYNAMIC, InX::Dynamic->getParent()->getPhdrFlags())
|
|
->add(InX::Dynamic->getParent());
|
|
|
|
// PT_GNU_RELRO includes all sections that should be marked as
|
|
// read-only by dynamic linker after proccessing relocations.
|
|
PhdrEntry *RelRo = make<PhdrEntry>(PT_GNU_RELRO, PF_R);
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (needsPtLoad(Sec) && isRelroSection(Sec))
|
|
RelRo->add(Sec);
|
|
if (RelRo->FirstSec)
|
|
Ret.push_back(RelRo);
|
|
|
|
// PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
|
|
if (!In<ELFT>::EhFrame->empty() && In<ELFT>::EhFrameHdr &&
|
|
In<ELFT>::EhFrame->getParent() && In<ELFT>::EhFrameHdr->getParent())
|
|
AddHdr(PT_GNU_EH_FRAME, In<ELFT>::EhFrameHdr->getParent()->getPhdrFlags())
|
|
->add(In<ELFT>::EhFrameHdr->getParent());
|
|
|
|
// PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
|
|
// the dynamic linker fill the segment with random data.
|
|
if (OutputSection *Cmd = findSection(".openbsd.randomdata"))
|
|
AddHdr(PT_OPENBSD_RANDOMIZE, Cmd->getPhdrFlags())->add(Cmd);
|
|
|
|
// PT_GNU_STACK is a special section to tell the loader to make the
|
|
// pages for the stack non-executable. If you really want an executable
|
|
// stack, you can pass -z execstack, but that's not recommended for
|
|
// security reasons.
|
|
unsigned Perm;
|
|
if (Config->ZExecstack)
|
|
Perm = PF_R | PF_W | PF_X;
|
|
else
|
|
Perm = PF_R | PF_W;
|
|
AddHdr(PT_GNU_STACK, Perm)->p_memsz = Config->ZStackSize;
|
|
|
|
// PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
|
|
// is expected to perform W^X violations, such as calling mprotect(2) or
|
|
// mmap(2) with PROT_WRITE | PROT_EXEC, which is prohibited by default on
|
|
// OpenBSD.
|
|
if (Config->ZWxneeded)
|
|
AddHdr(PT_OPENBSD_WXNEEDED, PF_X);
|
|
|
|
// Create one PT_NOTE per a group of contiguous .note sections.
|
|
PhdrEntry *Note = nullptr;
|
|
for (OutputSection *Sec : OutputSections) {
|
|
if (Sec->Type == SHT_NOTE) {
|
|
if (!Note || Sec->LMAExpr)
|
|
Note = AddHdr(PT_NOTE, PF_R);
|
|
Note->add(Sec);
|
|
} else {
|
|
Note = nullptr;
|
|
}
|
|
}
|
|
return Ret;
|
|
}
|
|
|
|
template <class ELFT>
|
|
void Writer<ELFT>::addPtArmExid(std::vector<PhdrEntry *> &Phdrs) {
|
|
if (Config->EMachine != EM_ARM)
|
|
return;
|
|
auto I = llvm::find_if(OutputSections, [](OutputSection *Cmd) {
|
|
return Cmd->Type == SHT_ARM_EXIDX;
|
|
});
|
|
if (I == OutputSections.end())
|
|
return;
|
|
|
|
// PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
|
|
PhdrEntry *ARMExidx = make<PhdrEntry>(PT_ARM_EXIDX, PF_R);
|
|
ARMExidx->add(*I);
|
|
Phdrs.push_back(ARMExidx);
|
|
}
|
|
|
|
// The first section of each PT_LOAD, the first section in PT_GNU_RELRO and the
|
|
// first section after PT_GNU_RELRO have to be page aligned so that the dynamic
|
|
// linker can set the permissions.
|
|
template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
|
|
auto PageAlign = [](OutputSection *Cmd) {
|
|
if (Cmd && !Cmd->AddrExpr)
|
|
Cmd->AddrExpr = [=] {
|
|
return alignTo(Script->getDot(), Config->MaxPageSize);
|
|
};
|
|
};
|
|
|
|
for (const PhdrEntry *P : Phdrs)
|
|
if (P->p_type == PT_LOAD && P->FirstSec)
|
|
PageAlign(P->FirstSec);
|
|
|
|
for (const PhdrEntry *P : Phdrs) {
|
|
if (P->p_type != PT_GNU_RELRO)
|
|
continue;
|
|
if (P->FirstSec)
|
|
PageAlign(P->FirstSec);
|
|
// Find the first section after PT_GNU_RELRO. If it is in a PT_LOAD we
|
|
// have to align it to a page.
|
|
auto End = OutputSections.end();
|
|
auto I = std::find(OutputSections.begin(), End, P->LastSec);
|
|
if (I == End || (I + 1) == End)
|
|
continue;
|
|
OutputSection *Cmd = (*(I + 1));
|
|
if (needsPtLoad(Cmd))
|
|
PageAlign(Cmd);
|
|
}
|
|
}
|
|
|
|
// Adjusts the file alignment for a given output section and returns
|
|
// its new file offset. The file offset must be the same with its
|
|
// virtual address (modulo the page size) so that the loader can load
|
|
// executables without any address adjustment.
|
|
static uint64_t getFileAlignment(uint64_t Off, OutputSection *Cmd) {
|
|
// If the section is not in a PT_LOAD, we just have to align it.
|
|
if (!Cmd->PtLoad)
|
|
return alignTo(Off, Cmd->Alignment);
|
|
|
|
OutputSection *First = Cmd->PtLoad->FirstSec;
|
|
// The first section in a PT_LOAD has to have congruent offset and address
|
|
// module the page size.
|
|
if (Cmd == First)
|
|
return alignTo(Off, std::max<uint64_t>(Cmd->Alignment, Config->MaxPageSize),
|
|
Cmd->Addr);
|
|
|
|
// If two sections share the same PT_LOAD the file offset is calculated
|
|
// using this formula: Off2 = Off1 + (VA2 - VA1).
|
|
return First->Offset + Cmd->Addr - First->Addr;
|
|
}
|
|
|
|
static uint64_t setOffset(OutputSection *Cmd, uint64_t Off) {
|
|
if (Cmd->Type == SHT_NOBITS) {
|
|
Cmd->Offset = Off;
|
|
return Off;
|
|
}
|
|
|
|
Off = getFileAlignment(Off, Cmd);
|
|
Cmd->Offset = Off;
|
|
return Off + Cmd->Size;
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
|
|
uint64_t Off = 0;
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->Flags & SHF_ALLOC)
|
|
Off = setOffset(Sec, Off);
|
|
FileSize = alignTo(Off, Config->Wordsize);
|
|
}
|
|
|
|
// Assign file offsets to output sections.
|
|
template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
|
|
uint64_t Off = 0;
|
|
Off = setOffset(Out::ElfHeader, Off);
|
|
Off = setOffset(Out::ProgramHeaders, Off);
|
|
|
|
PhdrEntry *LastRX = nullptr;
|
|
for (PhdrEntry *P : Phdrs)
|
|
if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
|
|
LastRX = P;
|
|
|
|
for (OutputSection *Sec : OutputSections) {
|
|
Off = setOffset(Sec, Off);
|
|
if (Script->Opt.HasSections)
|
|
continue;
|
|
// If this is a last section of the last executable segment and that
|
|
// segment is the last loadable segment, align the offset of the
|
|
// following section to avoid loading non-segments parts of the file.
|
|
if (LastRX && LastRX->LastSec == Sec)
|
|
Off = alignTo(Off, Target->PageSize);
|
|
}
|
|
|
|
SectionHeaderOff = alignTo(Off, Config->Wordsize);
|
|
FileSize = SectionHeaderOff + (OutputSections.size() + 1) * sizeof(Elf_Shdr);
|
|
}
|
|
|
|
// Finalize the program headers. We call this function after we assign
|
|
// file offsets and VAs to all sections.
|
|
template <class ELFT> void Writer<ELFT>::setPhdrs() {
|
|
for (PhdrEntry *P : Phdrs) {
|
|
OutputSection *First = P->FirstSec;
|
|
OutputSection *Last = P->LastSec;
|
|
if (First) {
|
|
P->p_filesz = Last->Offset - First->Offset;
|
|
if (Last->Type != SHT_NOBITS)
|
|
P->p_filesz += Last->Size;
|
|
P->p_memsz = Last->Addr + Last->Size - First->Addr;
|
|
P->p_offset = First->Offset;
|
|
P->p_vaddr = First->Addr;
|
|
if (!P->HasLMA)
|
|
P->p_paddr = First->getLMA();
|
|
}
|
|
if (P->p_type == PT_LOAD)
|
|
P->p_align = std::max<uint64_t>(P->p_align, Config->MaxPageSize);
|
|
else if (P->p_type == PT_GNU_RELRO) {
|
|
P->p_align = 1;
|
|
// The glibc dynamic loader rounds the size down, so we need to round up
|
|
// to protect the last page. This is a no-op on FreeBSD which always
|
|
// rounds up.
|
|
P->p_memsz = alignTo(P->p_memsz, Target->PageSize);
|
|
}
|
|
|
|
// The TLS pointer goes after PT_TLS. At least glibc will align it,
|
|
// so round up the size to make sure the offsets are correct.
|
|
if (P->p_type == PT_TLS) {
|
|
Out::TlsPhdr = P;
|
|
if (P->p_memsz)
|
|
P->p_memsz = alignTo(P->p_memsz, P->p_align);
|
|
}
|
|
}
|
|
}
|
|
|
|
// The entry point address is chosen in the following ways.
|
|
//
|
|
// 1. the '-e' entry command-line option;
|
|
// 2. the ENTRY(symbol) command in a linker control script;
|
|
// 3. the value of the symbol start, if present;
|
|
// 4. the address of the first byte of the .text section, if present;
|
|
// 5. the address 0.
|
|
template <class ELFT> uint64_t Writer<ELFT>::getEntryAddr() {
|
|
// Case 1, 2 or 3. As a special case, if the symbol is actually
|
|
// a number, we'll use that number as an address.
|
|
if (SymbolBody *B = Symtab->find(Config->Entry))
|
|
return B->getVA();
|
|
uint64_t Addr;
|
|
if (to_integer(Config->Entry, Addr))
|
|
return Addr;
|
|
|
|
// Case 4
|
|
if (OutputSection *Sec = findSection(".text")) {
|
|
if (Config->WarnMissingEntry)
|
|
warn("cannot find entry symbol " + Config->Entry + "; defaulting to 0x" +
|
|
utohexstr(Sec->Addr));
|
|
return Sec->Addr;
|
|
}
|
|
|
|
// Case 5
|
|
if (Config->WarnMissingEntry)
|
|
warn("cannot find entry symbol " + Config->Entry +
|
|
"; not setting start address");
|
|
return 0;
|
|
}
|
|
|
|
static uint16_t getELFType() {
|
|
if (Config->Pic)
|
|
return ET_DYN;
|
|
if (Config->Relocatable)
|
|
return ET_REL;
|
|
return ET_EXEC;
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeHeader() {
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
memcpy(Buf, "\177ELF", 4);
|
|
|
|
// Write the ELF header.
|
|
auto *EHdr = reinterpret_cast<Elf_Ehdr *>(Buf);
|
|
EHdr->e_ident[EI_CLASS] = Config->Is64 ? ELFCLASS64 : ELFCLASS32;
|
|
EHdr->e_ident[EI_DATA] = Config->IsLE ? ELFDATA2LSB : ELFDATA2MSB;
|
|
EHdr->e_ident[EI_VERSION] = EV_CURRENT;
|
|
EHdr->e_ident[EI_OSABI] = Config->OSABI;
|
|
EHdr->e_type = getELFType();
|
|
EHdr->e_machine = Config->EMachine;
|
|
EHdr->e_version = EV_CURRENT;
|
|
EHdr->e_entry = getEntryAddr();
|
|
EHdr->e_shoff = SectionHeaderOff;
|
|
EHdr->e_ehsize = sizeof(Elf_Ehdr);
|
|
EHdr->e_phnum = Phdrs.size();
|
|
EHdr->e_shentsize = sizeof(Elf_Shdr);
|
|
EHdr->e_shnum = OutputSections.size() + 1;
|
|
EHdr->e_shstrndx = InX::ShStrTab->getParent()->SectionIndex;
|
|
|
|
if (Config->EMachine == EM_ARM)
|
|
// We don't currently use any features incompatible with EF_ARM_EABI_VER5,
|
|
// but we don't have any firm guarantees of conformance. Linux AArch64
|
|
// kernels (as of 2016) require an EABI version to be set.
|
|
EHdr->e_flags = EF_ARM_EABI_VER5;
|
|
else if (Config->EMachine == EM_MIPS)
|
|
EHdr->e_flags = getMipsEFlags<ELFT>();
|
|
|
|
if (!Config->Relocatable) {
|
|
EHdr->e_phoff = sizeof(Elf_Ehdr);
|
|
EHdr->e_phentsize = sizeof(Elf_Phdr);
|
|
}
|
|
|
|
// Write the program header table.
|
|
auto *HBuf = reinterpret_cast<Elf_Phdr *>(Buf + EHdr->e_phoff);
|
|
for (PhdrEntry *P : Phdrs) {
|
|
HBuf->p_type = P->p_type;
|
|
HBuf->p_flags = P->p_flags;
|
|
HBuf->p_offset = P->p_offset;
|
|
HBuf->p_vaddr = P->p_vaddr;
|
|
HBuf->p_paddr = P->p_paddr;
|
|
HBuf->p_filesz = P->p_filesz;
|
|
HBuf->p_memsz = P->p_memsz;
|
|
HBuf->p_align = P->p_align;
|
|
++HBuf;
|
|
}
|
|
|
|
// Write the section header table. Note that the first table entry is null.
|
|
auto *SHdrs = reinterpret_cast<Elf_Shdr *>(Buf + EHdr->e_shoff);
|
|
for (OutputSection *Sec : OutputSections)
|
|
Sec->writeHeaderTo<ELFT>(++SHdrs);
|
|
}
|
|
|
|
// Open a result file.
|
|
template <class ELFT> void Writer<ELFT>::openFile() {
|
|
if (!Config->Is64 && FileSize > UINT32_MAX) {
|
|
error("output file too large: " + Twine(FileSize) + " bytes");
|
|
return;
|
|
}
|
|
|
|
unlinkAsync(Config->OutputFile);
|
|
ErrorOr<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
|
|
FileOutputBuffer::create(Config->OutputFile, FileSize,
|
|
FileOutputBuffer::F_executable);
|
|
|
|
if (auto EC = BufferOrErr.getError())
|
|
error("failed to open " + Config->OutputFile + ": " + EC.message());
|
|
else
|
|
Buffer = std::move(*BufferOrErr);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->Flags & SHF_ALLOC)
|
|
Sec->writeTo<ELFT>(Buf + Sec->Offset);
|
|
}
|
|
|
|
static void fillTrap(uint8_t *I, uint8_t *End) {
|
|
for (; I + 4 <= End; I += 4)
|
|
memcpy(I, &Target->TrapInstr, 4);
|
|
}
|
|
|
|
// Fill the last page of executable segments with trap instructions
|
|
// instead of leaving them as zero. Even though it is not required by any
|
|
// standard, it is in general a good thing to do for security reasons.
|
|
//
|
|
// We'll leave other pages in segments as-is because the rest will be
|
|
// overwritten by output sections.
|
|
template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
|
|
if (Script->Opt.HasSections)
|
|
return;
|
|
|
|
// Fill the last page.
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
for (PhdrEntry *P : Phdrs)
|
|
if (P->p_type == PT_LOAD && (P->p_flags & PF_X))
|
|
fillTrap(Buf + alignDown(P->p_offset + P->p_filesz, Target->PageSize),
|
|
Buf + alignTo(P->p_offset + P->p_filesz, Target->PageSize));
|
|
|
|
// Round up the file size of the last segment to the page boundary iff it is
|
|
// an executable segment to ensure that other other tools don't accidentally
|
|
// trim the instruction padding (e.g. when stripping the file).
|
|
PhdrEntry *LastRX = nullptr;
|
|
for (PhdrEntry *P : Phdrs) {
|
|
if (P->p_type != PT_LOAD)
|
|
continue;
|
|
if (P->p_flags & PF_X)
|
|
LastRX = P;
|
|
else
|
|
LastRX = nullptr;
|
|
}
|
|
if (LastRX)
|
|
LastRX->p_memsz = LastRX->p_filesz =
|
|
alignTo(LastRX->p_filesz, Target->PageSize);
|
|
}
|
|
|
|
// Write section contents to a mmap'ed file.
|
|
template <class ELFT> void Writer<ELFT>::writeSections() {
|
|
uint8_t *Buf = Buffer->getBufferStart();
|
|
|
|
// PPC64 needs to process relocations in the .opd section
|
|
// before processing relocations in code-containing sections.
|
|
if (auto *OpdCmd = findSection(".opd")) {
|
|
Out::Opd = OpdCmd;
|
|
Out::OpdBuf = Buf + Out::Opd->Offset;
|
|
OpdCmd->template writeTo<ELFT>(Buf + Out::Opd->Offset);
|
|
}
|
|
|
|
OutputSection *EhFrameHdr =
|
|
(In<ELFT>::EhFrameHdr && !In<ELFT>::EhFrameHdr->empty())
|
|
? In<ELFT>::EhFrameHdr->getParent()
|
|
: nullptr;
|
|
|
|
// In -r or -emit-relocs mode, write the relocation sections first as in
|
|
// ELf_Rel targets we might find out that we need to modify the relocated
|
|
// section while doing it.
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
|
|
Sec->writeTo<ELFT>(Buf + Sec->Offset);
|
|
|
|
for (OutputSection *Sec : OutputSections)
|
|
if (Sec != Out::Opd && Sec != EhFrameHdr && Sec->Type != SHT_REL &&
|
|
Sec->Type != SHT_RELA)
|
|
Sec->writeTo<ELFT>(Buf + Sec->Offset);
|
|
|
|
// The .eh_frame_hdr depends on .eh_frame section contents, therefore
|
|
// it should be written after .eh_frame is written.
|
|
if (EhFrameHdr)
|
|
EhFrameHdr->writeTo<ELFT>(Buf + EhFrameHdr->Offset);
|
|
}
|
|
|
|
template <class ELFT> void Writer<ELFT>::writeBuildId() {
|
|
if (!InX::BuildId || !InX::BuildId->getParent())
|
|
return;
|
|
|
|
// Compute a hash of all sections of the output file.
|
|
uint8_t *Start = Buffer->getBufferStart();
|
|
uint8_t *End = Start + FileSize;
|
|
InX::BuildId->writeBuildId({Start, End});
|
|
}
|
|
|
|
template void elf::writeResult<ELF32LE>();
|
|
template void elf::writeResult<ELF32BE>();
|
|
template void elf::writeResult<ELF64LE>();
|
|
template void elf::writeResult<ELF64BE>();
|