forked from OSchip/llvm-project
436 lines
14 KiB
C++
436 lines
14 KiB
C++
//===- OutputSections.cpp -------------------------------------------------===//
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//
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// The LLVM Linker
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "OutputSections.h"
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#include "Config.h"
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#include "LinkerScript.h"
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#include "SymbolTable.h"
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#include "SyntheticSections.h"
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#include "Target.h"
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#include "lld/Common/Memory.h"
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#include "lld/Common/Strings.h"
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#include "lld/Common/Threads.h"
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#include "llvm/BinaryFormat/Dwarf.h"
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#include "llvm/Support/Compression.h"
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#include "llvm/Support/MD5.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/Support/SHA1.h"
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using namespace llvm;
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using namespace llvm::dwarf;
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using namespace llvm::object;
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using namespace llvm::ELF;
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using namespace lld;
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using namespace lld::elf;
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uint8_t Out::First;
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PhdrEntry *Out::TlsPhdr;
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OutputSection *Out::DebugInfo;
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OutputSection *Out::ElfHeader;
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OutputSection *Out::ProgramHeaders;
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OutputSection *Out::PreinitArray;
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OutputSection *Out::InitArray;
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OutputSection *Out::FiniArray;
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std::vector<OutputSection *> elf::OutputSections;
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uint32_t OutputSection::getPhdrFlags() const {
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uint32_t Ret = 0;
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if (Config->EMachine != EM_ARM || !(Flags & SHF_ARM_PURECODE))
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Ret |= PF_R;
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if (Flags & SHF_WRITE)
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Ret |= PF_W;
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if (Flags & SHF_EXECINSTR)
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Ret |= PF_X;
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return Ret;
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}
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template <class ELFT>
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void OutputSection::writeHeaderTo(typename ELFT::Shdr *Shdr) {
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Shdr->sh_entsize = Entsize;
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Shdr->sh_addralign = Alignment;
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Shdr->sh_type = Type;
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Shdr->sh_offset = Offset;
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Shdr->sh_flags = Flags;
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Shdr->sh_info = Info;
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Shdr->sh_link = Link;
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Shdr->sh_addr = Addr;
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Shdr->sh_size = Size;
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Shdr->sh_name = ShName;
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}
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OutputSection::OutputSection(StringRef Name, uint32_t Type, uint64_t Flags)
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: BaseCommand(OutputSectionKind),
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SectionBase(Output, Name, Flags, /*Entsize*/ 0, /*Alignment*/ 1, Type,
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/*Info*/ 0, /*Link*/ 0) {
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Live = false;
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}
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// We allow sections of types listed below to merged into a
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// single progbits section. This is typically done by linker
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// scripts. Merging nobits and progbits will force disk space
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// to be allocated for nobits sections. Other ones don't require
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// any special treatment on top of progbits, so there doesn't
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// seem to be a harm in merging them.
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static bool canMergeToProgbits(unsigned Type) {
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return Type == SHT_NOBITS || Type == SHT_PROGBITS || Type == SHT_INIT_ARRAY ||
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Type == SHT_PREINIT_ARRAY || Type == SHT_FINI_ARRAY ||
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Type == SHT_NOTE;
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}
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void OutputSection::addSection(InputSection *IS) {
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if (!Live) {
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// If IS is the first section to be added to this section,
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// initialize Type, Entsize and flags from IS.
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Live = true;
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Type = IS->Type;
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Entsize = IS->Entsize;
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Flags = IS->Flags;
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} else {
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// Otherwise, check if new type or flags are compatible with existing ones.
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unsigned Mask = SHF_ALLOC | SHF_TLS | SHF_LINK_ORDER;
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if ((Flags & Mask) != (IS->Flags & Mask))
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error("incompatible section flags for " + Name + "\n>>> " + toString(IS) +
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": 0x" + utohexstr(IS->Flags) + "\n>>> output section " + Name +
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": 0x" + utohexstr(Flags));
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if (Type != IS->Type) {
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if (!canMergeToProgbits(Type) || !canMergeToProgbits(IS->Type))
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error("section type mismatch for " + IS->Name + "\n>>> " +
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toString(IS) + ": " +
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getELFSectionTypeName(Config->EMachine, IS->Type) +
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"\n>>> output section " + Name + ": " +
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getELFSectionTypeName(Config->EMachine, Type));
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Type = SHT_PROGBITS;
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}
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}
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IS->Parent = this;
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uint64_t AndMask =
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Config->EMachine == EM_ARM ? (uint64_t)SHF_ARM_PURECODE : 0;
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uint64_t OrMask = ~AndMask;
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uint64_t AndFlags = (Flags & IS->Flags) & AndMask;
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uint64_t OrFlags = (Flags | IS->Flags) & OrMask;
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Flags = AndFlags | OrFlags;
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Alignment = std::max(Alignment, IS->Alignment);
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// If this section contains a table of fixed-size entries, sh_entsize
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// holds the element size. If it contains elements of different size we
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// set sh_entsize to 0.
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if (Entsize != IS->Entsize)
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Entsize = 0;
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if (!IS->Assigned) {
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IS->Assigned = true;
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if (SectionCommands.empty() ||
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!isa<InputSectionDescription>(SectionCommands.back()))
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SectionCommands.push_back(make<InputSectionDescription>(""));
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auto *ISD = cast<InputSectionDescription>(SectionCommands.back());
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ISD->Sections.push_back(IS);
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}
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}
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static void sortByOrder(MutableArrayRef<InputSection *> In,
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llvm::function_ref<int(InputSectionBase *S)> Order) {
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typedef std::pair<int, InputSection *> Pair;
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auto Comp = [](const Pair &A, const Pair &B) { return A.first < B.first; };
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std::vector<Pair> V;
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for (InputSection *S : In)
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V.push_back({Order(S), S});
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std::stable_sort(V.begin(), V.end(), Comp);
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for (size_t I = 0; I < V.size(); ++I)
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In[I] = V[I].second;
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}
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uint64_t elf::getHeaderSize() {
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if (Config->OFormatBinary)
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return 0;
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return Out::ElfHeader->Size + Out::ProgramHeaders->Size;
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}
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bool OutputSection::classof(const BaseCommand *C) {
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return C->Kind == OutputSectionKind;
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}
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void OutputSection::sort(llvm::function_ref<int(InputSectionBase *S)> Order) {
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assert(Live);
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for (BaseCommand *B : SectionCommands)
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if (auto *ISD = dyn_cast<InputSectionDescription>(B))
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sortByOrder(ISD->Sections, Order);
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}
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// Fill [Buf, Buf + Size) with Filler.
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// This is used for linker script "=fillexp" command.
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static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
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size_t I = 0;
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for (; I + 4 < Size; I += 4)
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memcpy(Buf + I, &Filler, 4);
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memcpy(Buf + I, &Filler, Size - I);
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}
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// Compress section contents if this section contains debug info.
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template <class ELFT> void OutputSection::maybeCompress() {
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typedef typename ELFT::Chdr Elf_Chdr;
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// Compress only DWARF debug sections.
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if (!Config->CompressDebugSections || (Flags & SHF_ALLOC) ||
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!Name.startswith(".debug_"))
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return;
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// Create a section header.
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ZDebugHeader.resize(sizeof(Elf_Chdr));
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auto *Hdr = reinterpret_cast<Elf_Chdr *>(ZDebugHeader.data());
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Hdr->ch_type = ELFCOMPRESS_ZLIB;
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Hdr->ch_size = Size;
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Hdr->ch_addralign = Alignment;
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// Write section contents to a temporary buffer and compress it.
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std::vector<uint8_t> Buf(Size);
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writeTo<ELFT>(Buf.data());
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if (Error E = zlib::compress(toStringRef(Buf), CompressedData))
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fatal("compress failed: " + llvm::toString(std::move(E)));
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// Update section headers.
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Size = sizeof(Elf_Chdr) + CompressedData.size();
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Flags |= SHF_COMPRESSED;
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}
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static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
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if (Size == 1)
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*Buf = Data;
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else if (Size == 2)
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write16(Buf, Data);
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else if (Size == 4)
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write32(Buf, Data);
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else if (Size == 8)
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write64(Buf, Data);
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else
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llvm_unreachable("unsupported Size argument");
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}
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template <class ELFT> void OutputSection::writeTo(uint8_t *Buf) {
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if (Type == SHT_NOBITS)
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return;
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Loc = Buf;
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// If -compress-debug-section is specified and if this is a debug seciton,
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// we've already compressed section contents. If that's the case,
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// just write it down.
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if (!CompressedData.empty()) {
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memcpy(Buf, ZDebugHeader.data(), ZDebugHeader.size());
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memcpy(Buf + ZDebugHeader.size(), CompressedData.data(),
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CompressedData.size());
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return;
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}
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// Write leading padding.
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std::vector<InputSection *> Sections = getInputSections(this);
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uint32_t Filler = getFiller();
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if (Filler)
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fill(Buf, Sections.empty() ? Size : Sections[0]->OutSecOff, Filler);
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parallelForEachN(0, Sections.size(), [&](size_t I) {
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InputSection *IS = Sections[I];
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IS->writeTo<ELFT>(Buf);
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// Fill gaps between sections.
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if (Filler) {
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uint8_t *Start = Buf + IS->OutSecOff + IS->getSize();
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uint8_t *End;
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if (I + 1 == Sections.size())
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End = Buf + Size;
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else
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End = Buf + Sections[I + 1]->OutSecOff;
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fill(Start, End - Start, Filler);
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}
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});
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// Linker scripts may have BYTE()-family commands with which you
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// can write arbitrary bytes to the output. Process them if any.
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for (BaseCommand *Base : SectionCommands)
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if (auto *Data = dyn_cast<ByteCommand>(Base))
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writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
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}
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template <class ELFT>
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static void finalizeShtGroup(OutputSection *OS,
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InputSection *Section) {
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assert(Config->Relocatable);
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// sh_link field for SHT_GROUP sections should contain the section index of
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// the symbol table.
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OS->Link = In.SymTab->getParent()->SectionIndex;
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// sh_info then contain index of an entry in symbol table section which
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// provides signature of the section group.
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ObjFile<ELFT> *Obj = Section->getFile<ELFT>();
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ArrayRef<Symbol *> Symbols = Obj->getSymbols();
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OS->Info = In.SymTab->getSymbolIndex(Symbols[Section->Info]);
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}
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template <class ELFT> void OutputSection::finalize() {
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if (Type == SHT_NOBITS)
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for (BaseCommand *Base : SectionCommands)
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if (isa<ByteCommand>(Base))
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Type = SHT_PROGBITS;
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std::vector<InputSection *> V = getInputSections(this);
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InputSection *First = V.empty() ? nullptr : V[0];
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if (Flags & SHF_LINK_ORDER) {
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// We must preserve the link order dependency of sections with the
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// SHF_LINK_ORDER flag. The dependency is indicated by the sh_link field. We
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// need to translate the InputSection sh_link to the OutputSection sh_link,
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// all InputSections in the OutputSection have the same dependency.
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if (auto *D = First->getLinkOrderDep())
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Link = D->getParent()->SectionIndex;
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}
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if (Type == SHT_GROUP) {
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finalizeShtGroup<ELFT>(this, First);
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return;
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}
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if (!Config->CopyRelocs || (Type != SHT_RELA && Type != SHT_REL))
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return;
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if (isa<SyntheticSection>(First))
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return;
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Link = In.SymTab->getParent()->SectionIndex;
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// sh_info for SHT_REL[A] sections should contain the section header index of
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// the section to which the relocation applies.
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InputSectionBase *S = First->getRelocatedSection();
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Info = S->getOutputSection()->SectionIndex;
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Flags |= SHF_INFO_LINK;
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}
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// Returns true if S matches /Filename.?\.o$/.
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static bool isCrtBeginEnd(StringRef S, StringRef Filename) {
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if (!S.endswith(".o"))
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return false;
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S = S.drop_back(2);
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if (S.endswith(Filename))
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return true;
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return !S.empty() && S.drop_back().endswith(Filename);
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}
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static bool isCrtbegin(StringRef S) { return isCrtBeginEnd(S, "crtbegin"); }
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static bool isCrtend(StringRef S) { return isCrtBeginEnd(S, "crtend"); }
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// .ctors and .dtors are sorted by this priority from highest to lowest.
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//
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// 1. The section was contained in crtbegin (crtbegin contains
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// some sentinel value in its .ctors and .dtors so that the runtime
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// can find the beginning of the sections.)
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//
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// 2. The section has an optional priority value in the form of ".ctors.N"
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// or ".dtors.N" where N is a number. Unlike .{init,fini}_array,
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// they are compared as string rather than number.
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//
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// 3. The section is just ".ctors" or ".dtors".
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//
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// 4. The section was contained in crtend, which contains an end marker.
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//
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// In an ideal world, we don't need this function because .init_array and
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// .ctors are duplicate features (and .init_array is newer.) However, there
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// are too many real-world use cases of .ctors, so we had no choice to
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// support that with this rather ad-hoc semantics.
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static bool compCtors(const InputSection *A, const InputSection *B) {
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bool BeginA = isCrtbegin(A->File->getName());
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bool BeginB = isCrtbegin(B->File->getName());
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if (BeginA != BeginB)
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return BeginA;
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bool EndA = isCrtend(A->File->getName());
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bool EndB = isCrtend(B->File->getName());
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if (EndA != EndB)
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return EndB;
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StringRef X = A->Name;
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StringRef Y = B->Name;
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assert(X.startswith(".ctors") || X.startswith(".dtors"));
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assert(Y.startswith(".ctors") || Y.startswith(".dtors"));
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X = X.substr(6);
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Y = Y.substr(6);
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return X < Y;
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}
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// Sorts input sections by the special rules for .ctors and .dtors.
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// Unfortunately, the rules are different from the one for .{init,fini}_array.
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// Read the comment above.
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void OutputSection::sortCtorsDtors() {
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assert(SectionCommands.size() == 1);
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auto *ISD = cast<InputSectionDescription>(SectionCommands[0]);
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std::stable_sort(ISD->Sections.begin(), ISD->Sections.end(), compCtors);
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}
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// If an input string is in the form of "foo.N" where N is a number,
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// return N. Otherwise, returns 65536, which is one greater than the
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// lowest priority.
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int elf::getPriority(StringRef S) {
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size_t Pos = S.rfind('.');
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if (Pos == StringRef::npos)
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return 65536;
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int V;
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if (!to_integer(S.substr(Pos + 1), V, 10))
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return 65536;
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return V;
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}
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std::vector<InputSection *> elf::getInputSections(OutputSection *OS) {
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std::vector<InputSection *> Ret;
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for (BaseCommand *Base : OS->SectionCommands)
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if (auto *ISD = dyn_cast<InputSectionDescription>(Base))
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Ret.insert(Ret.end(), ISD->Sections.begin(), ISD->Sections.end());
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return Ret;
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}
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// Sorts input sections by section name suffixes, so that .foo.N comes
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// before .foo.M if N < M. Used to sort .{init,fini}_array.N sections.
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// We want to keep the original order if the priorities are the same
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// because the compiler keeps the original initialization order in a
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// translation unit and we need to respect that.
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// For more detail, read the section of the GCC's manual about init_priority.
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void OutputSection::sortInitFini() {
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// Sort sections by priority.
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sort([](InputSectionBase *S) { return getPriority(S->Name); });
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}
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uint32_t OutputSection::getFiller() {
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if (Filler)
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return *Filler;
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if (Flags & SHF_EXECINSTR)
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return Target->TrapInstr;
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return 0;
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}
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template void OutputSection::writeHeaderTo<ELF32LE>(ELF32LE::Shdr *Shdr);
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template void OutputSection::writeHeaderTo<ELF32BE>(ELF32BE::Shdr *Shdr);
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template void OutputSection::writeHeaderTo<ELF64LE>(ELF64LE::Shdr *Shdr);
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template void OutputSection::writeHeaderTo<ELF64BE>(ELF64BE::Shdr *Shdr);
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template void OutputSection::writeTo<ELF32LE>(uint8_t *Buf);
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template void OutputSection::writeTo<ELF32BE>(uint8_t *Buf);
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template void OutputSection::writeTo<ELF64LE>(uint8_t *Buf);
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template void OutputSection::writeTo<ELF64BE>(uint8_t *Buf);
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template void OutputSection::maybeCompress<ELF32LE>();
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template void OutputSection::maybeCompress<ELF32BE>();
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template void OutputSection::maybeCompress<ELF64LE>();
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template void OutputSection::maybeCompress<ELF64BE>();
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template void OutputSection::finalize<ELF32LE>();
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template void OutputSection::finalize<ELF32BE>();
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template void OutputSection::finalize<ELF64LE>();
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template void OutputSection::finalize<ELF64BE>();
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