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Revert r297008: [ELF] - Make Bss and BssRelRo sections to be synthetic (#2). 

This reverts commit r297008 because it's reported that that
change broke AArch64 bots.

llvm-svn: 297297
This commit is contained in:
Rui Ueyama 2017-03-08 17:24:24 +00:00
parent 9f495695bb
commit 007c002cb6
8 changed files with 78 additions and 59 deletions
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2
lld/ELF/OutputSections.cpp
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@ -31,6 +31,8 @@ using namespace lld;
using namespace lld::elf;
uint8_t Out::First;
OutputSection *Out::Bss;
OutputSection *Out::BssRelRo;
OutputSection *Out::Opd;
uint8_t *Out::OpdBuf;
PhdrEntry *Out::TlsPhdr;

2
lld/ELF/OutputSections.h
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@ -98,6 +98,8 @@ public:
// until Writer is initialized.
struct Out {
static uint8_t First;
static OutputSection *Bss;
static OutputSection *BssRelRo;
static OutputSection *Opd;
static uint8_t *OpdBuf;
static PhdrEntry *TlsPhdr;

27
lld/ELF/Relocations.cpp
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@ -479,20 +479,23 @@ template <class ELFT> static void addCopyRelSymbol(SharedSymbol *SS) {
// See if this symbol is in a read-only segment. If so, preserve the symbol's
// memory protection by reserving space in the .bss.rel.ro section.
bool IsReadOnly = isReadOnly<ELFT>(SS);
BssRelSection<ELFT> *RelSec = IsReadOnly ? In<ELFT>::BssRelRo : In<ELFT>::Bss;
uintX_t Off = RelSec->addCopyRelocation(SS->getAlignment<ELFT>(), SymSize);
OutputSection *OSec = IsReadOnly ? Out::BssRelRo : Out::Bss;
// Create a SyntheticSection in Out to hold the .bss and the Copy Reloc.
auto *ISec =
make<CopyRelSection<ELFT>>(IsReadOnly, SS->getAlignment<ELFT>(), SymSize);
OSec->addSection(ISec);
// Look through the DSO's dynamic symbol table for aliases and create a
// dynamic symbol for each one. This causes the copy relocation to correctly
// interpose any aliases.
for (SharedSymbol *Sym : getSymbolsAt<ELFT>(SS)) {
Sym->NeedsCopy = true;
Sym->Section = ISec;
Sym->symbol()->IsUsedInRegularObj = true;
replaceBody<DefinedRegular>(Sym->symbol(), Sym->getName(),
/*IsLocal=*/false, Sym->StOther, Sym->Type, Off,
Sym->getSize<ELFT>(), RelSec, nullptr);
}
In<ELFT>::RelaDyn->addReloc({Target->CopyRel, RelSec, Off, false, SS, 0});
In<ELFT>::RelaDyn->addReloc({Target->CopyRel, ISec, 0, false, SS, 0});
}
template <class ELFT>
@ -532,12 +535,14 @@ static RelExpr adjustExpr(const elf::ObjectFile<ELFT> &File, SymbolBody &Body,
if (Body.isObject()) {
// Produce a copy relocation.
auto *B = cast<SharedSymbol>(&Body);
if (Config->ZNocopyreloc)
error(S.getLocation<ELFT>(RelOff) + ": unresolvable relocation " +
toString(Type) + " against symbol '" + toString(*B) +
"'; recompile with -fPIC or remove '-z nocopyreloc'");
if (!B->NeedsCopy) {
if (Config->ZNocopyreloc)
error(S.getLocation<ELFT>(RelOff) + ": unresolvable relocation " +
toString(Type) + " against symbol '" + toString(*B) +
"'; recompile with -fPIC or remove '-z nocopyreloc'");
addCopyRelSymbol<ELFT>(B);
addCopyRelSymbol<ELFT>(B);
}
return Expr;
}
if (Body.isFunc()) {

20
lld/ELF/Symbols.cpp
View File

@ -112,10 +112,14 @@ static typename ELFT::uint getSymVA(const SymbolBody &Body, int64_t &Addend) {
return 0;
return In<ELFT>::Common->OutSec->Addr + In<ELFT>::Common->OutSecOff +
cast<DefinedCommon>(Body).Offset;
case SymbolBody::SharedKind:
if (cast<SharedSymbol>(Body).NeedsPltAddr)
case SymbolBody::SharedKind: {
auto &SS = cast<SharedSymbol>(Body);
if (SS.NeedsCopy)
return SS.Section->OutSec->Addr + SS.Section->OutSecOff;
if (SS.NeedsPltAddr)
return Body.getPltVA<ELFT>();
return 0;
}
case SymbolBody::UndefinedKind:
return 0;
case SymbolBody::LazyArchiveKind:
@ -128,7 +132,7 @@ static typename ELFT::uint getSymVA(const SymbolBody &Body, int64_t &Addend) {
SymbolBody::SymbolBody(Kind K, StringRefZ Name, bool IsLocal, uint8_t StOther,
uint8_t Type)
: SymbolKind(K), NeedsPltAddr(false), IsLocal(IsLocal),
: SymbolKind(K), NeedsCopy(false), NeedsPltAddr(false), IsLocal(IsLocal),
IsInGlobalMipsGot(false), Is32BitMipsGot(false), IsInIplt(false),
IsInIgot(false), Type(Type), StOther(StOther), Name(Name) {}
@ -139,9 +143,10 @@ bool SymbolBody::isPreemptible() const {
return false;
// Shared symbols resolve to the definition in the DSO. The exceptions are
// symbols that needs plt entries (which resolve to that plt entry).
// symbols with copy relocations (which resolve to .bss) or preempt plt
// entries (which resolve to that plt entry).
if (isShared())
return !NeedsPltAddr;
return !NeedsCopy && !NeedsPltAddr;
// That's all that can be preempted in a non-DSO.
if (!Config->Shared)
@ -210,8 +215,11 @@ const OutputSection *SymbolBody::getOutputSection() const {
return nullptr;
}
if (isa<SharedSymbol>(this))
if (auto *S = dyn_cast<SharedSymbol>(this)) {
if (S->NeedsCopy)
return S->Section->OutSec;
return nullptr;
}
if (isa<DefinedCommon>(this)) {
if (Config->DefineCommon)

7
lld/ELF/Symbols.h
View File

@ -102,6 +102,10 @@ protected:
const unsigned SymbolKind : 8;
public:
// True if the linker has to generate a copy relocation.
// For SharedSymbol only.
unsigned NeedsCopy : 1;
// True the symbol should point to its PLT entry.
// For SharedSymbol only.
unsigned NeedsPltAddr : 1;
@ -266,6 +270,9 @@ public:
// This field is a pointer to the symbol's version definition.
const void *Verdef;
// Section is significant only when NeedsCopy is true.
InputSection *Section = nullptr;
private:
template <class ELFT> const typename ELFT::Sym &getSym() const {
return *(const typename ELFT::Sym *)ElfSym;

23
lld/ELF/SyntheticSections.cpp
View File

@ -377,17 +377,10 @@ void BuildIdSection<ELFT>::computeHash(
}
template <class ELFT>
BssRelSection<ELFT>::BssRelSection(bool RelRo)
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, 0,
RelRo ? ".bss.rel.ro" : ".bss"),
Size(0) {}
template <class ELFT>
size_t BssRelSection<ELFT>::addCopyRelocation(uintX_t AddrAlign, size_t Size) {
OutSec->updateAlignment(AddrAlign);
this->Size = alignTo(this->Size, AddrAlign) + Size;
return this->Size - Size;
}
CopyRelSection<ELFT>::CopyRelSection(bool ReadOnly, uintX_t AddrAlign, size_t S)
: SyntheticSection(SHF_ALLOC, SHT_NOBITS, AddrAlign,
ReadOnly ? ".bss.rel.ro" : ".bss"),
Size(S) {}
template <class ELFT>
void BuildIdSection<ELFT>::writeBuildId(ArrayRef<uint8_t> Buf) {
@ -2311,10 +2304,10 @@ template class elf::BuildIdSection<ELF32BE>;
template class elf::BuildIdSection<ELF64LE>;
template class elf::BuildIdSection<ELF64BE>;
template class elf::BssRelSection<ELF32LE>;
template class elf::BssRelSection<ELF32BE>;
template class elf::BssRelSection<ELF64LE>;
template class elf::BssRelSection<ELF64BE>;
template class elf::CopyRelSection<ELF32LE>;
template class elf::CopyRelSection<ELF32BE>;
template class elf::CopyRelSection<ELF64LE>;
template class elf::CopyRelSection<ELF64BE>;
template class elf::GotSection<ELF32LE>;
template class elf::GotSection<ELF32BE>;

14
lld/ELF/SyntheticSections.h
View File

@ -152,16 +152,14 @@ private:
uint8_t *HashBuf;
};
// Section used for storing copy relocations. We create two sections now,
// .bss.rel.ro for RelRo case and .bss for regular case.
template <class ELFT> class BssRelSection final : public SyntheticSection {
// For each copy relocation, we create an instance of this class to
// reserve space in .bss or .bss.rel.ro.
template <class ELFT> class CopyRelSection final : public SyntheticSection {
typedef typename ELFT::uint uintX_t;
public:
BssRelSection(bool RelRo);
CopyRelSection(bool ReadOnly, uintX_t AddrAlign, size_t Size);
void writeTo(uint8_t *) override {}
bool empty() const override { return getSize() == 0; }
size_t addCopyRelocation(uintX_t AddrAlign, size_t Size);
size_t getSize() const override { return Size; }
size_t Size;
};
@ -764,8 +762,6 @@ SymbolBody *addSyntheticLocal(StringRef Name, uint8_t Type, uint64_t Value,
template <class ELFT> struct In {
static InputSection *ARMAttributes;
static BuildIdSection<ELFT> *BuildId;
static BssRelSection<ELFT> *Bss;
static BssRelSection<ELFT> *BssRelRo;
static InputSection *Common;
static DynamicSection<ELFT> *Dynamic;
static StringTableSection<ELFT> *DynStrTab;
@ -795,8 +791,6 @@ template <class ELFT> struct In {
};
template <class ELFT> InputSection *In<ELFT>::ARMAttributes;
template <class ELFT> BssRelSection<ELFT> *In<ELFT>::Bss;
template <class ELFT> BssRelSection<ELFT> *In<ELFT>::BssRelRo;
template <class ELFT> BuildIdSection<ELFT> *In<ELFT>::BuildId;
template <class ELFT> InputSection *In<ELFT>::Common;
template <class ELFT> DynamicSection<ELFT> *In<ELFT>::Dynamic;

42
lld/ELF/Writer.cpp
View File

@ -111,8 +111,8 @@ StringRef elf::getOutputSectionName(StringRef Name) {
}
for (StringRef V :
{".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
{".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.",
".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
".gcc_except_table.", ".tdata.", ".ARM.exidx."}) {
StringRef Prefix = V.drop_back();
if (Name.startswith(V) || Name == Prefix)
@ -309,6 +309,10 @@ template <class ELFT> void Writer<ELFT>::createSyntheticSections() {
auto Add = [](InputSectionBase *Sec) { InputSections.push_back(Sec); };
// Create singleton output sections.
Out::Bss = make<OutputSection>(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
Out::BssRelRo =
make<OutputSection>(".bss.rel.ro", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
In<ELFT>::DynStrTab = make<StringTableSection<ELFT>>(".dynstr", true);
In<ELFT>::Dynamic = make<DynamicSection<ELFT>>();
In<ELFT>::RelaDyn = make<RelocationSection<ELFT>>(
@ -346,11 +350,6 @@ template <class ELFT> void Writer<ELFT>::createSyntheticSections() {
Add(Common);
}
In<ELFT>::Bss = make<BssRelSection<ELFT>>(false /*RelRo*/);
Add(In<ELFT>::Bss);
In<ELFT>::BssRelRo = make<BssRelSection<ELFT>>(true /*RelRo*/);
Add(In<ELFT>::BssRelRo);
// Add MIPS-specific sections.
bool HasDynSymTab =
!Symtab<ELFT>::X->getSharedFiles().empty() || Config->pic() ||
@ -596,7 +595,7 @@ template <class ELFT> bool elf::isRelroSection(const OutputSection *Sec) {
return true;
if (In<ELFT>::Got && Sec == In<ELFT>::Got->OutSec)
return true;
if (Sec == In<ELFT>::BssRelRo->OutSec)
if (Sec == Out::BssRelRo)
return true;
StringRef S = Sec->Name;
@ -1150,15 +1149,14 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
// Dynamic section must be the last one in this list and dynamic
// symbol table section (DynSymTab) must be the first one.
applySynthetic<ELFT>(
{In<ELFT>::DynSymTab, In<ELFT>::Bss, In<ELFT>::BssRelRo,
In<ELFT>::GnuHashTab, In<ELFT>::HashTab, In<ELFT>::SymTab,
In<ELFT>::ShStrTab, In<ELFT>::StrTab, In<ELFT>::VerDef,
In<ELFT>::DynStrTab, In<ELFT>::GdbIndex, In<ELFT>::Got,
In<ELFT>::MipsGot, In<ELFT>::IgotPlt, In<ELFT>::GotPlt,
In<ELFT>::RelaDyn, In<ELFT>::RelaIplt, In<ELFT>::RelaPlt,
In<ELFT>::Plt, In<ELFT>::Iplt, In<ELFT>::Plt,
In<ELFT>::EhFrameHdr, In<ELFT>::VerSym, In<ELFT>::VerNeed,
In<ELFT>::Dynamic},
{In<ELFT>::DynSymTab, In<ELFT>::GnuHashTab, In<ELFT>::HashTab,
In<ELFT>::SymTab, In<ELFT>::ShStrTab, In<ELFT>::StrTab,
In<ELFT>::VerDef, In<ELFT>::DynStrTab, In<ELFT>::GdbIndex,
In<ELFT>::Got, In<ELFT>::MipsGot, In<ELFT>::IgotPlt,
In<ELFT>::GotPlt, In<ELFT>::RelaDyn, In<ELFT>::RelaIplt,
In<ELFT>::RelaPlt, In<ELFT>::Plt, In<ELFT>::Iplt,
In<ELFT>::Plt, In<ELFT>::EhFrameHdr, In<ELFT>::VerSym,
In<ELFT>::VerNeed, In<ELFT>::Dynamic},
[](SyntheticSection *SS) { SS->finalizeContents(); });
// Some architectures use small displacements for jump instructions.
@ -1187,6 +1185,16 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
}
template <class ELFT> void Writer<ELFT>::addPredefinedSections() {
// Add BSS sections.
auto Add = [=](OutputSection *Sec) {
if (!Sec->Sections.empty()) {
Sec->assignOffsets<ELFT>();
OutputSections.push_back(Sec);
}
};
Add(Out::Bss);
Add(Out::BssRelRo);
// 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.
auto *OS = dyn_cast_or_null<OutputSection>(findSection(".ARM.exidx"));