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Revert r319090, "COFF: Do not create SectionChunks for discarded comdat sections." 

Caused test failures in check-cfi on Windows.
http://lab.llvm.org:8011/builders/sanitizer-windows/builds/20284

llvm-svn: 319100
This commit is contained in:
Peter Collingbourne 2017-11-27 21:37:51 +00:00
parent 06b891f693
commit c8477b8234
10 changed files with 169 additions and 243 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
lld/COFF/Chunks.cpp
View File

@ -38,6 +38,9 @@ SectionChunk::SectionChunk(ObjFile *F, const coff_section *H)
Alignment = Header->getAlignment();
// Chunks may be discarded during comdat merging.
Discarded = false;
// If linker GC is disabled, every chunk starts out alive. If linker GC is
// enabled, treat non-comdat sections as roots. Generally optimized object
// files will be built with -ffunction-sections or /Gy, so most things worth
@ -359,8 +362,12 @@ bool SectionChunk::isCOMDAT() const {
void SectionChunk::printDiscardedMessage() const {
// Removed by dead-stripping. If it's removed by ICF, ICF already
// printed out the name, so don't repeat that here.
if (Sym && this == Repl)
message("Discarded " + Sym->getName());
if (Sym && this == Repl) {
if (Discarded)
message("Discarded comdat symbol " + Sym->getName());
else if (!Live)
message("Discarded " + Sym->getName());
}
}
StringRef SectionChunk::getDebugName() {

21
lld/COFF/Chunks.h
View File

@ -159,9 +159,10 @@ public:
void addAssociative(SectionChunk *Child);
StringRef getDebugName() override;
void setSymbol(DefinedRegular *S) { if (!Sym) Sym = S; }
// Returns true if the chunk was not dropped by GC.
bool isLive() { return Live; }
// Returns true if the chunk was not dropped by GC or COMDAT deduplication.
bool isLive() { return Live && !Discarded; }
// Used by the garbage collector.
void markLive() {
@ -170,6 +171,13 @@ public:
Live = true;
}
// Returns true if this chunk was dropped by COMDAT deduplication.
bool isDiscarded() const { return Discarded; }
// Used by the SymbolTable when discarding unused comdat sections. This is
// redundant when GC is enabled, as all comdat sections will start out dead.
void markDiscarded() { Discarded = true; }
// True if this is a codeview debug info chunk. These will not be laid out in
// the image. Instead they will end up in the PDB, if one is requested.
bool isCodeView() const {
@ -205,21 +213,24 @@ public:
// The file that this chunk was created from.
ObjFile *File;
// The COMDAT leader symbol if this is a COMDAT chunk.
DefinedRegular *Sym = nullptr;
private:
StringRef SectionName;
std::vector<SectionChunk *> AssocChildren;
llvm::iterator_range<const coff_relocation *> Relocs;
size_t NumRelocs;
// True if this chunk was discarded because it was a duplicate comdat section.
bool Discarded;
// Used by the garbage collector.
bool Live;
// Used for ICF (Identical COMDAT Folding)
void replace(SectionChunk *Other);
uint32_t Class[2] = {0, 0};
// Sym points to a section symbol if this is a COMDAT chunk.
DefinedRegular *Sym = nullptr;
};
// A chunk for common symbols. Common chunks don't have actual data.

272
lld/COFF/InputFiles.cpp
View File

@ -119,158 +119,86 @@ void ObjFile::parse() {
initializeSEH();
}
// We set SectionChunk pointers in the SparseChunks vector to this value
// temporarily to mark comdat sections as having an unknown resolution. As we
// walk the object file's symbol table, once we visit either a leader symbol or
// an associative section definition together with the parent comdat's leader,
// we set the pointer to either nullptr (to mark the section as discarded) or a
// valid SectionChunk for that section.
static SectionChunk *const PendingComdat = reinterpret_cast<SectionChunk *>(1);
void ObjFile::initializeChunks() {
uint32_t NumSections = COFFObj->getNumberOfSections();
Chunks.reserve(NumSections);
SparseChunks.resize(NumSections + 1);
for (uint32_t I = 1; I < NumSections + 1; ++I) {
const coff_section *Sec;
StringRef Name;
if (auto EC = COFFObj->getSection(I, Sec))
fatal("getSection failed: #" + Twine(I) + ": " + EC.message());
if (auto EC = COFFObj->getSectionName(Sec, Name))
fatal("getSectionName failed: #" + Twine(I) + ": " + EC.message());
if (Name == ".sxdata") {
SXData = Sec;
continue;
}
if (Name == ".drectve") {
ArrayRef<uint8_t> Data;
COFFObj->getSectionContents(Sec, Data);
Directives = std::string((const char *)Data.data(), Data.size());
continue;
}
if (Sec->Characteristics & IMAGE_SCN_LNK_COMDAT)
SparseChunks[I] = PendingComdat;
// Object files may have DWARF debug info or MS CodeView debug info
// (or both).
//
// DWARF sections don't need any special handling from the perspective
// of the linker; they are just a data section containing relocations.
// We can just link them to complete debug info.
//
// CodeView needs a linker support. We need to interpret and debug
// info, and then write it to a separate .pdb file.
// Ignore debug info unless /debug is given.
if (!Config->Debug && Name.startswith(".debug"))
continue;
if (Sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_REMOVE)
continue;
auto *C = make<SectionChunk>(this, Sec);
// CodeView sections are stored to a different vector because they are not
// linked in the regular manner.
if (C->isCodeView())
DebugChunks.push_back(C);
else
SparseChunks[I] = readSection(I, nullptr);
Chunks.push_back(C);
SparseChunks[I] = C;
}
}
SectionChunk *ObjFile::readSection(uint32_t SectionNumber,
const coff_aux_section_definition *Def) {
const coff_section *Sec;
StringRef Name;
if (auto EC = COFFObj->getSection(SectionNumber, Sec))
fatal("getSection failed: #" + Twine(SectionNumber) + ": " + EC.message());
if (auto EC = COFFObj->getSectionName(Sec, Name))
fatal("getSectionName failed: #" + Twine(SectionNumber) + ": " +
EC.message());
if (Name == ".sxdata") {
SXData = Sec;
return nullptr;
}
if (Name == ".drectve") {
ArrayRef<uint8_t> Data;
COFFObj->getSectionContents(Sec, Data);
Directives = std::string((const char *)Data.data(), Data.size());
return nullptr;
}
// Object files may have DWARF debug info or MS CodeView debug info
// (or both).
//
// DWARF sections don't need any special handling from the perspective
// of the linker; they are just a data section containing relocations.
// We can just link them to complete debug info.
//
// CodeView needs a linker support. We need to interpret and debug
// info, and then write it to a separate .pdb file.
// Ignore debug info unless /debug is given.
if (!Config->Debug && Name.startswith(".debug"))
return nullptr;
if (Sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_REMOVE)
return nullptr;
auto *C = make<SectionChunk>(this, Sec);
if (Def)
C->Checksum = Def->CheckSum;
// CodeView sections are stored to a different vector because they are not
// linked in the regular manner.
if (C->isCodeView())
DebugChunks.push_back(C);
else
Chunks.push_back(C);
return C;
}
void ObjFile::readAssociativeDefinition(
COFFSymbolRef Sym, const coff_aux_section_definition *Def) {
SectionChunk *Parent = SparseChunks[Def->getNumber(Sym.isBigObj())];
// If the parent is pending, it probably means that its section definition
// appears after us in the symbol table. Leave the associated section as
// pending; we will handle it during the second pass in initializeSymbols().
if (Parent == PendingComdat)
return;
// Check whether the parent is prevailing. If it is, so are we, and we read
// the section; otherwise mark it as discarded.
int32_t SectionNumber = Sym.getSectionNumber();
if (Parent) {
SparseChunks[SectionNumber] = readSection(SectionNumber, Def);
Parent->addAssociative(SparseChunks[SectionNumber]);
} else {
SparseChunks[SectionNumber] = nullptr;
}
}
Symbol *ObjFile::createRegular(COFFSymbolRef Sym) {
SectionChunk *SC = SparseChunks[Sym.getSectionNumber()];
if (Sym.isExternal()) {
StringRef Name;
COFFObj->getSymbolName(Sym, Name);
if (SC)
return Symtab->addRegular(this, Name, Sym.getGeneric(), SC);
return Symtab->addUndefined(Name, this, false);
}
if (SC)
return make<DefinedRegular>(this, /*Name*/ "", false,
/*IsExternal*/ false, Sym.getGeneric(), SC);
return nullptr;
}
void ObjFile::initializeSymbols() {
uint32_t NumSymbols = COFFObj->getNumberOfSymbols();
Symbols.resize(NumSymbols);
SmallVector<std::pair<Symbol *, uint32_t>, 8> WeakAliases;
std::vector<uint32_t> PendingIndexes;
PendingIndexes.reserve(NumSymbols);
std::vector<const coff_aux_section_definition *> ComdatDefs(
COFFObj->getNumberOfSections() + 1);
int32_t LastSectionNumber = 0;
for (uint32_t I = 0; I < NumSymbols; ++I) {
COFFSymbolRef COFFSym = check(COFFObj->getSymbol(I));
if (COFFSym.isUndefined()) {
Symbols[I] = createUndefined(COFFSym);
} else if (COFFSym.isWeakExternal()) {
Symbols[I] = createUndefined(COFFSym);
uint32_t TagIndex = COFFSym.getAux<coff_aux_weak_external>()->TagIndex;
WeakAliases.emplace_back(Symbols[I], TagIndex);
} else if (Optional<Symbol *> OptSym = createDefined(COFFSym, ComdatDefs)) {
Symbols[I] = *OptSym;
} else {
// createDefined() returns None if a symbol belongs to a section that
// was pending at the point when the symbol was read. This can happen in
// two cases:
// 1) section definition symbol for a comdat leader;
// 2) symbol belongs to a comdat section associated with a section whose
// section definition symbol appears later in the symbol table.
// In both of these cases, we can expect the section to be resolved by
// the time we finish visiting the remaining symbols in the symbol
// table. So we postpone the handling of this symbol until that time.
PendingIndexes.push_back(I);
}
I += COFFSym.getNumberOfAuxSymbols();
}
for (uint32_t I : PendingIndexes) {
COFFSymbolRef Sym = check(COFFObj->getSymbol(I));
if (auto *Def = Sym.getSectionDefinition())
if (Def->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)
readAssociativeDefinition(Sym, Def);
Symbols[I] = createRegular(Sym);
const void *AuxP = nullptr;
if (COFFSym.getNumberOfAuxSymbols())
AuxP = check(COFFObj->getSymbol(I + 1)).getRawPtr();
bool IsFirst = (LastSectionNumber != COFFSym.getSectionNumber());
Symbol *Sym = nullptr;
if (COFFSym.isUndefined()) {
Sym = createUndefined(COFFSym);
} else if (COFFSym.isWeakExternal()) {
Sym = createUndefined(COFFSym);
uint32_t TagIndex =
static_cast<const coff_aux_weak_external *>(AuxP)->TagIndex;
WeakAliases.emplace_back(Sym, TagIndex);
} else {
Sym = createDefined(COFFSym, AuxP, IsFirst);
}
Symbols[I] = Sym;
I += COFFSym.getNumberOfAuxSymbols();
LastSectionNumber = COFFSym.getSectionNumber();
}
for (auto &KV : WeakAliases) {
@ -286,9 +214,8 @@ Symbol *ObjFile::createUndefined(COFFSymbolRef Sym) {
return Symtab->addUndefined(Name, this, Sym.isWeakExternal());
}
Optional<Symbol *> ObjFile::createDefined(
COFFSymbolRef Sym,
std::vector<const coff_aux_section_definition *> &ComdatDefs) {
Symbol *ObjFile::createDefined(COFFSymbolRef Sym, const void *AuxP,
bool IsFirst) {
StringRef Name;
if (Sym.isCommon()) {
auto *C = make<CommonChunk>(Sym);
@ -327,46 +254,37 @@ Optional<Symbol *> ObjFile::createDefined(
if ((uint32_t)SectionNumber >= SparseChunks.size())
fatal("broken object file: " + toString(this));
// Handle comdat leader symbols.
if (const coff_aux_section_definition *Def = ComdatDefs[SectionNumber]) {
ComdatDefs[SectionNumber] = nullptr;
Symbol *Leader;
bool Prevailing;
if (Sym.isExternal()) {
COFFObj->getSymbolName(Sym, Name);
std::tie(Leader, Prevailing) =
Symtab->addComdat(this, Name, Sym.getGeneric());
} else {
Leader = make<DefinedRegular>(this, /*Name*/ "", false,
/*IsExternal*/ false, Sym.getGeneric());
Prevailing = true;
}
if (Prevailing) {
SectionChunk *C = readSection(SectionNumber, Def);
SparseChunks[SectionNumber] = C;
C->Sym = cast<DefinedRegular>(Leader);
cast<DefinedRegular>(Leader)->Data = &C->Repl;
} else {
SparseChunks[SectionNumber] = nullptr;
}
return Leader;
// Nothing else to do without a section chunk.
auto *SC = SparseChunks[SectionNumber];
if (!SC)
return nullptr;
// Handle section definitions
if (IsFirst && AuxP) {
auto *Aux = reinterpret_cast<const coff_aux_section_definition *>(AuxP);
if (Aux->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)
if (auto *ParentSC = SparseChunks[Aux->getNumber(Sym.isBigObj())]) {
ParentSC->addAssociative(SC);
// If we already discarded the parent, discard the child.
if (ParentSC->isDiscarded())
SC->markDiscarded();
}
SC->Checksum = Aux->CheckSum;
}
// Read associative section definitions and prepare to handle the comdat
// leader symbol by setting the section's ComdatDefs pointer if we encounter a
// non-associative comdat.
if (SparseChunks[SectionNumber] == PendingComdat) {
if (auto *Def = Sym.getSectionDefinition()) {
if (Def->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)
readAssociativeDefinition(Sym, Def);
else
ComdatDefs[SectionNumber] = Def;
}
}
DefinedRegular *B;
if (Sym.isExternal()) {
COFFObj->getSymbolName(Sym, Name);
Symbol *S =
Symtab->addRegular(this, Name, SC->isCOMDAT(), Sym.getGeneric(), SC);
B = cast<DefinedRegular>(S);
} else
B = make<DefinedRegular>(this, /*Name*/ "", SC->isCOMDAT(),
/*IsExternal*/ false, Sym.getGeneric(), SC);
if (SC->isCOMDAT() && Sym.getValue() == 0 && !AuxP)
SC->setSymbol(B);
if (SparseChunks[SectionNumber] == PendingComdat)
return None;
return createRegular(Sym);
return B;
}
void ObjFile::initializeSEH() {
@ -443,12 +361,8 @@ void ImportFile::parse() {
void BitcodeFile::parse() {
Obj = check(lto::InputFile::create(MemoryBufferRef(
MB.getBuffer(), Saver.save(ParentName + MB.getBufferIdentifier()))));
std::vector<std::pair<Symbol *, bool>> Comdat(Obj->getComdatTable().size());
for (size_t I = 0; I != Obj->getComdatTable().size(); ++I)
Comdat[I] = Symtab->addComdat(this, Saver.save(Obj->getComdatTable()[I]));
for (const lto::InputFile::Symbol &ObjSym : Obj->symbols()) {
StringRef SymName = Saver.save(ObjSym.getName());
int ComdatIndex = ObjSym.getComdatIndex();
Symbol *Sym;
if (ObjSym.isUndefined()) {
Sym = Symtab->addUndefined(SymName, this, false);
@ -460,15 +374,9 @@ void BitcodeFile::parse() {
std::string Fallback = ObjSym.getCOFFWeakExternalFallback();
Symbol *Alias = Symtab->addUndefined(Saver.save(Fallback));
checkAndSetWeakAlias(Symtab, this, Sym, Alias);
} else if (ComdatIndex != -1) {
if (SymName == Obj->getComdatTable()[ComdatIndex])
Sym = Comdat[ComdatIndex].first;
else if (Comdat[ComdatIndex].second)
Sym = Symtab->addRegular(this, SymName);
else
Sym = Symtab->addUndefined(SymName, this, false);
} else {
Sym = Symtab->addRegular(this, SymName);
bool IsCOMDAT = ObjSym.getComdatIndex() != -1;
Sym = Symtab->addRegular(this, SymName, IsCOMDAT);
}
SymbolBodies.push_back(Sym);
}

14
lld/COFF/InputFiles.h
View File

@ -142,19 +142,7 @@ private:
void initializeSymbols();
void initializeSEH();
SectionChunk *
readSection(uint32_t SectionNumber,
const llvm::object::coff_aux_section_definition *Def);
void readAssociativeDefinition(
COFFSymbolRef COFFSym,
const llvm::object::coff_aux_section_definition *Def);
llvm::Optional<Symbol *>
createDefined(COFFSymbolRef Sym,
std::vector<const llvm::object::coff_aux_section_definition *>
&ComdatDefs);
Symbol *createRegular(COFFSymbolRef Sym);
Symbol *createDefined(COFFSymbolRef Sym, const void *Aux, bool IsFirst);
Symbol *createUndefined(COFFSymbolRef Sym);
std::unique_ptr<COFFObjectFile> COFFObj;

7
lld/COFF/MarkLive.cpp
View File

@ -52,6 +52,13 @@ void markLive(const std::vector<Chunk *> &Chunks) {
while (!Worklist.empty()) {
SectionChunk *SC = Worklist.pop_back_val();
// If this section was discarded, there are relocations referring to
// discarded sections. Ignore these sections to avoid crashing. They will be
// diagnosed during relocation processing.
if (SC->isDiscarded())
continue;
assert(SC->isLive() && "We mark as live when pushing onto the worklist!");
// Mark all symbols listed in the relocation table for this section.

66
lld/COFF/SymbolTable.cpp
View File

@ -24,6 +24,36 @@ using namespace llvm;
namespace lld {
namespace coff {
enum SymbolPreference {
SP_EXISTING = -1,
SP_CONFLICT = 0,
SP_NEW = 1,
};
/// Checks if an existing symbol S should be kept or replaced by a new symbol.
/// Returns SP_EXISTING when S should be kept, SP_NEW when the new symbol
/// should be kept, and SP_CONFLICT if no valid resolution exists.
static SymbolPreference compareDefined(Symbol *S, bool WasInserted,
bool NewIsCOMDAT) {
// If the symbol wasn't previously known, the new symbol wins by default.
if (WasInserted || !isa<Defined>(S))
return SP_NEW;
// If the existing symbol is a DefinedRegular, both it and the new symbol
// must be comdats. In that case, we have no reason to prefer one symbol
// over the other, and we keep the existing one. If one of the symbols
// is not a comdat, we report a conflict.
if (auto *R = dyn_cast<DefinedRegular>(S)) {
if (NewIsCOMDAT && R->isCOMDAT())
return SP_EXISTING;
else
return SP_CONFLICT;
}
// Existing symbol is not a DefinedRegular; new symbol wins.
return SP_NEW;
}
SymbolTable *Symtab;
void SymbolTable::addFile(InputFile *File) {
@ -210,7 +240,7 @@ Symbol *SymbolTable::addSynthetic(StringRef N, Chunk *C) {
return S;
}
Symbol *SymbolTable::addRegular(InputFile *F, StringRef N,
Symbol *SymbolTable::addRegular(InputFile *F, StringRef N, bool IsCOMDAT,
const coff_symbol_generic *Sym,
SectionChunk *C) {
Symbol *S;
@ -218,30 +248,20 @@ Symbol *SymbolTable::addRegular(InputFile *F, StringRef N,
std::tie(S, WasInserted) = insert(N);
if (!isa<BitcodeFile>(F))
S->IsUsedInRegularObj = true;
if (WasInserted || !isa<DefinedRegular>(S))
replaceSymbol<DefinedRegular>(S, F, N, /*IsCOMDAT*/ false,
/*IsExternal*/ true, Sym, C);
else
SymbolPreference SP = compareDefined(S, WasInserted, IsCOMDAT);
if (SP == SP_CONFLICT) {
reportDuplicate(S, F);
return S;
}
std::pair<Symbol *, bool>
SymbolTable::addComdat(InputFile *F, StringRef N,
const coff_symbol_generic *Sym) {
Symbol *S;
bool WasInserted;
std::tie(S, WasInserted) = insert(N);
if (!isa<BitcodeFile>(F))
S->IsUsedInRegularObj = true;
if (WasInserted || !isa<DefinedRegular>(S)) {
replaceSymbol<DefinedRegular>(S, F, N, /*IsCOMDAT*/ true,
/*IsExternal*/ true, Sym, nullptr);
return {S, true};
} else if (SP == SP_NEW) {
replaceSymbol<DefinedRegular>(S, F, N, IsCOMDAT, /*IsExternal*/ true, Sym,
C);
} else if (SP == SP_EXISTING && IsCOMDAT && C) {
C->markDiscarded();
// Discard associative chunks that we've parsed so far. No need to recurse
// because an associative section cannot have children.
for (SectionChunk *Child : C->children())
Child->markDiscarded();
}
if (!cast<DefinedRegular>(S)->isCOMDAT())
reportDuplicate(S, F);
return {S, false};
return S;
}
Symbol *SymbolTable::addCommon(InputFile *F, StringRef N, uint64_t Size,

5
lld/COFF/SymbolTable.h
View File

@ -83,12 +83,9 @@ public:
Symbol *addUndefined(StringRef Name, InputFile *F, bool IsWeakAlias);
void addLazy(ArchiveFile *F, const Archive::Symbol Sym);
Symbol *addAbsolute(StringRef N, COFFSymbolRef S);
Symbol *addRegular(InputFile *F, StringRef N,
Symbol *addRegular(InputFile *F, StringRef N, bool IsCOMDAT,
const llvm::object::coff_symbol_generic *S = nullptr,
SectionChunk *C = nullptr);
std::pair<Symbol *, bool>
addComdat(InputFile *F, StringRef N,
const llvm::object::coff_symbol_generic *S = nullptr);
Symbol *addCommon(InputFile *F, StringRef N, uint64_t Size,
const llvm::object::coff_symbol_generic *S = nullptr,
CommonChunk *C = nullptr);

1
lld/COFF/Symbols.h
View File

@ -169,6 +169,7 @@ public:
SectionChunk *getChunk() const { return *Data; }
uint32_t getValue() const { return Sym->Value; }
private:
SectionChunk **Data;
};

1
lld/test/COFF/reloc-discarded.s
View File

@ -18,6 +18,7 @@ main_global:
.section .CRT$XCU,"dr",associative,main_global
.p2align 3
.globl assoc_global
assoc_global:
.quad main_global

14
llvm/include/llvm/Object/COFF.h
View File

@ -275,8 +275,6 @@ struct coff_symbol_generic {
support::ulittle32_t Value;
};
struct coff_aux_section_definition;
class COFFSymbolRef {
public:
COFFSymbolRef() = default;
@ -348,18 +346,6 @@ public:
return (getType() & 0xF0) >> COFF::SCT_COMPLEX_TYPE_SHIFT;
}
template <typename T> const T *getAux() const {
return CS16 ? reinterpret_cast<const T *>(CS16 + 1)
: reinterpret_cast<const T *>(CS32 + 1);
}
const coff_aux_section_definition *getSectionDefinition() const {
if (!getNumberOfAuxSymbols() ||
getStorageClass() != COFF::IMAGE_SYM_CLASS_STATIC)
return nullptr;
return getAux<coff_aux_section_definition>();
}
bool isAbsolute() const {
return getSectionNumber() == -1;
}