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llvm-project/llvm/lib/MC/MCContext.cpp
Rafael Espindola 13a79bbfe5 Change how we handle section symbols on ELF. 
On ELF every section can have a corresponding section symbol. When in
an assembly file we have

.quad .text

the '.text' refers to that symbol.

The way we used to handle them is to leave .text an undefined symbol
until the very end when the object writer would map them to the
actual section symbol.

The problem with that is that anything before the end would see an
undefined symbol. This could result in bad diagnostics
(test/MC/AArch64/label-arithmetic-diags-elf.s), or incorrect results
when using the asm streamer (est/MC/Mips/expansion-jal-sym-pic.s).

Fixing this will also allow using the section symbol earlier for
setting sh_link of SHF_METADATA sections.

This patch includes a few hacks to avoid changing our behaviour when
handling conflicts between section symbols and other symbols. I
reported pr31850 to track that.

llvm-svn: 293936
2017-02-02 21:26:06 +00:00

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//===- lib/MC/MCContext.cpp - Machine Code Context ------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/MC/MCContext.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCCodeView.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCLabel.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSectionCOFF.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCSectionMachO.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbolCOFF.h"
#include "llvm/MC/MCSymbolELF.h"
#include "llvm/MC/MCSymbolMachO.h"
#include "llvm/Support/COFF.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ELF.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/SourceMgr.h"
using namespace llvm;
static cl::opt<char*>
AsSecureLogFileName("as-secure-log-file-name",
cl::desc("As secure log file name (initialized from "
"AS_SECURE_LOG_FILE env variable)"),
cl::init(getenv("AS_SECURE_LOG_FILE")), cl::Hidden);
MCContext::MCContext(const MCAsmInfo *mai, const MCRegisterInfo *mri,
const MCObjectFileInfo *mofi, const SourceMgr *mgr,
bool DoAutoReset)
: SrcMgr(mgr), MAI(mai), MRI(mri), MOFI(mofi), Allocator(),
Symbols(Allocator), UsedNames(Allocator),
CurrentDwarfLoc(0, 0, 0, DWARF2_FLAG_IS_STMT, 0, 0), DwarfLocSeen(false),
GenDwarfForAssembly(false), GenDwarfFileNumber(0), DwarfVersion(4),
AllowTemporaryLabels(true), DwarfCompileUnitID(0),
AutoReset(DoAutoReset), HadError(false) {
SecureLogFile = AsSecureLogFileName;
SecureLog = nullptr;
SecureLogUsed = false;
if (SrcMgr && SrcMgr->getNumBuffers())
MainFileName =
SrcMgr->getMemoryBuffer(SrcMgr->getMainFileID())->getBufferIdentifier();
}
MCContext::~MCContext() {
if (AutoReset)
reset();
// NOTE: The symbols are all allocated out of a bump pointer allocator,
// we don't need to free them here.
}
//===----------------------------------------------------------------------===//
// Module Lifetime Management
//===----------------------------------------------------------------------===//
void MCContext::reset() {
// Call the destructors so the fragments are freed
COFFAllocator.DestroyAll();
ELFAllocator.DestroyAll();
MachOAllocator.DestroyAll();
MCSubtargetAllocator.DestroyAll();
UsedNames.clear();
Symbols.clear();
Allocator.Reset();
Instances.clear();
CompilationDir.clear();
MainFileName.clear();
MCDwarfLineTablesCUMap.clear();
SectionsForRanges.clear();
MCGenDwarfLabelEntries.clear();
DwarfDebugFlags = StringRef();
DwarfCompileUnitID = 0;
CurrentDwarfLoc = MCDwarfLoc(0, 0, 0, DWARF2_FLAG_IS_STMT, 0, 0);
CVContext.reset();
MachOUniquingMap.clear();
ELFUniquingMap.clear();
COFFUniquingMap.clear();
NextID.clear();
AllowTemporaryLabels = true;
DwarfLocSeen = false;
GenDwarfForAssembly = false;
GenDwarfFileNumber = 0;
HadError = false;
}
//===----------------------------------------------------------------------===//
// Symbol Manipulation
//===----------------------------------------------------------------------===//
MCSymbol *MCContext::getOrCreateSymbol(const Twine &Name) {
SmallString<128> NameSV;
StringRef NameRef = Name.toStringRef(NameSV);
assert(!NameRef.empty() && "Normal symbols cannot be unnamed!");
MCSymbol *&Sym = Symbols[NameRef];
if (!Sym)
Sym = createSymbol(NameRef, false, false);
return Sym;
}
MCSymbol *MCContext::getOrCreateFrameAllocSymbol(StringRef FuncName,
unsigned Idx) {
return getOrCreateSymbol(Twine(MAI->getPrivateGlobalPrefix()) + FuncName +
"$frame_escape_" + Twine(Idx));
}
MCSymbol *MCContext::getOrCreateParentFrameOffsetSymbol(StringRef FuncName) {
return getOrCreateSymbol(Twine(MAI->getPrivateGlobalPrefix()) + FuncName +
"$parent_frame_offset");
}
MCSymbol *MCContext::getOrCreateLSDASymbol(StringRef FuncName) {
return getOrCreateSymbol(Twine(MAI->getPrivateGlobalPrefix()) + "__ehtable$" +
FuncName);
}
MCSymbol *MCContext::createSymbolImpl(const StringMapEntry<bool> *Name,
bool IsTemporary) {
if (MOFI) {
switch (MOFI->getObjectFileType()) {
case MCObjectFileInfo::IsCOFF:
return new (Name, *this) MCSymbolCOFF(Name, IsTemporary);
case MCObjectFileInfo::IsELF:
return new (Name, *this) MCSymbolELF(Name, IsTemporary);
case MCObjectFileInfo::IsMachO:
return new (Name, *this) MCSymbolMachO(Name, IsTemporary);
}
}
return new (Name, *this) MCSymbol(MCSymbol::SymbolKindUnset, Name,
IsTemporary);
}
MCSymbol *MCContext::createSymbol(StringRef Name, bool AlwaysAddSuffix,
bool CanBeUnnamed) {
if (CanBeUnnamed && !UseNamesOnTempLabels)
return createSymbolImpl(nullptr, true);
// Determine whether this is a user written assembler temporary or normal
// label, if used.
bool IsTemporary = CanBeUnnamed;
if (AllowTemporaryLabels && !IsTemporary)
IsTemporary = Name.startswith(MAI->getPrivateGlobalPrefix());
SmallString<128> NewName = Name;
bool AddSuffix = AlwaysAddSuffix;
unsigned &NextUniqueID = NextID[Name];
for (;;) {
if (AddSuffix) {
NewName.resize(Name.size());
raw_svector_ostream(NewName) << NextUniqueID++;
}
auto NameEntry = UsedNames.insert(std::make_pair(NewName, true));
if (NameEntry.second || !NameEntry.first->second) {
// Ok, we found a name.
// Mark it as used for a non-section symbol.
NameEntry.first->second = true;
// Have the MCSymbol object itself refer to the copy of the string that is
// embedded in the UsedNames entry.
return createSymbolImpl(&*NameEntry.first, IsTemporary);
}
assert(IsTemporary && "Cannot rename non-temporary symbols");
AddSuffix = true;
}
llvm_unreachable("Infinite loop");
}
MCSymbol *MCContext::createTempSymbol(const Twine &Name, bool AlwaysAddSuffix,
bool CanBeUnnamed) {
SmallString<128> NameSV;
raw_svector_ostream(NameSV) << MAI->getPrivateGlobalPrefix() << Name;
return createSymbol(NameSV, AlwaysAddSuffix, CanBeUnnamed);
}
MCSymbol *MCContext::createLinkerPrivateTempSymbol() {
SmallString<128> NameSV;
raw_svector_ostream(NameSV) << MAI->getLinkerPrivateGlobalPrefix() << "tmp";
return createSymbol(NameSV, true, false);
}
MCSymbol *MCContext::createTempSymbol(bool CanBeUnnamed) {
return createTempSymbol("tmp", true, CanBeUnnamed);
}
unsigned MCContext::NextInstance(unsigned LocalLabelVal) {
MCLabel *&Label = Instances[LocalLabelVal];
if (!Label)
Label = new (*this) MCLabel(0);
return Label->incInstance();
}
unsigned MCContext::GetInstance(unsigned LocalLabelVal) {
MCLabel *&Label = Instances[LocalLabelVal];
if (!Label)
Label = new (*this) MCLabel(0);
return Label->getInstance();
}
MCSymbol *MCContext::getOrCreateDirectionalLocalSymbol(unsigned LocalLabelVal,
unsigned Instance) {
MCSymbol *&Sym = LocalSymbols[std::make_pair(LocalLabelVal, Instance)];
if (!Sym)
Sym = createTempSymbol(false);
return Sym;
}
MCSymbol *MCContext::createDirectionalLocalSymbol(unsigned LocalLabelVal) {
unsigned Instance = NextInstance(LocalLabelVal);
return getOrCreateDirectionalLocalSymbol(LocalLabelVal, Instance);
}
MCSymbol *MCContext::getDirectionalLocalSymbol(unsigned LocalLabelVal,
bool Before) {
unsigned Instance = GetInstance(LocalLabelVal);
if (!Before)
++Instance;
return getOrCreateDirectionalLocalSymbol(LocalLabelVal, Instance);
}
MCSymbol *MCContext::lookupSymbol(const Twine &Name) const {
SmallString<128> NameSV;
StringRef NameRef = Name.toStringRef(NameSV);
return Symbols.lookup(NameRef);
}
void MCContext::setSymbolValue(MCStreamer &Streamer,
StringRef Sym,
uint64_t Val) {
auto Symbol = getOrCreateSymbol(Sym);
Streamer.EmitAssignment(Symbol, MCConstantExpr::create(Val, *this));
}
//===----------------------------------------------------------------------===//
// Section Management
//===----------------------------------------------------------------------===//
MCSectionMachO *MCContext::getMachOSection(StringRef Segment, StringRef Section,
unsigned TypeAndAttributes,
unsigned Reserved2, SectionKind Kind,
const char *BeginSymName) {
// We unique sections by their segment/section pair. The returned section
// may not have the same flags as the requested section, if so this should be
// diagnosed by the client as an error.
// Form the name to look up.
SmallString<64> Name;
Name += Segment;
Name.push_back(',');
Name += Section;
// Do the lookup, if we have a hit, return it.
MCSectionMachO *&Entry = MachOUniquingMap[Name];
if (Entry)
return Entry;
MCSymbol *Begin = nullptr;
if (BeginSymName)
Begin = createTempSymbol(BeginSymName, false);
// Otherwise, return a new section.
return Entry = new (MachOAllocator.Allocate()) MCSectionMachO(
Segment, Section, TypeAndAttributes, Reserved2, Kind, Begin);
}
void MCContext::renameELFSection(MCSectionELF *Section, StringRef Name) {
StringRef GroupName;
if (const MCSymbol *Group = Section->getGroup())
GroupName = Group->getName();
unsigned UniqueID = Section->getUniqueID();
ELFUniquingMap.erase(
ELFSectionKey{Section->getSectionName(), GroupName, UniqueID});
auto I = ELFUniquingMap.insert(std::make_pair(
ELFSectionKey{Name, GroupName, UniqueID},
Section))
.first;
StringRef CachedName = I->first.SectionName;
const_cast<MCSectionELF *>(Section)->setSectionName(CachedName);
}
MCSectionELF *MCContext::createELFSectionImpl(StringRef Section, unsigned Type,
unsigned Flags, SectionKind K,
unsigned EntrySize,
const MCSymbolELF *Group,
unsigned UniqueID,
const MCSectionELF *Associated) {
MCSymbolELF *R;
MCSymbol *&Sym = Symbols[Section];
if (Sym && Sym->isUndefined()) {
R = cast<MCSymbolELF>(Sym);
} else {
auto NameIter = UsedNames.insert(std::make_pair(Section, false)).first;
R = new (&*NameIter, *this) MCSymbolELF(&*NameIter, /*isTemporary*/ false);
if (!Sym)
Sym = R;
}
R->setBinding(ELF::STB_LOCAL);
R->setType(ELF::STT_SECTION);
R->setRedefinable(true);
auto *Ret = new (ELFAllocator.Allocate()) MCSectionELF(
Section, Type, Flags, K, EntrySize, Group, UniqueID, R, Associated);
auto *F = new MCDataFragment();
Ret->getFragmentList().insert(Ret->begin(), F);
F->setParent(Ret);
R->setFragment(F);
return Ret;
}
MCSectionELF *MCContext::createELFRelSection(const Twine &Name, unsigned Type,
unsigned Flags, unsigned EntrySize,
const MCSymbolELF *Group,
const MCSectionELF *Associated) {
StringMap<bool>::iterator I;
bool Inserted;
std::tie(I, Inserted) =
ELFRelSecNames.insert(std::make_pair(Name.str(), true));
return createELFSectionImpl(I->getKey(), Type, Flags,
SectionKind::getReadOnly(), EntrySize, Group,
true, Associated);
}
MCSectionELF *MCContext::getELFNamedSection(const Twine &Prefix,
const Twine &Suffix, unsigned Type,
unsigned Flags,
unsigned EntrySize) {
return getELFSection(Prefix + "." + Suffix, Type, Flags, EntrySize, Suffix);
}
MCSectionELF *MCContext::getELFSection(const Twine &Section, unsigned Type,
unsigned Flags, unsigned EntrySize,
const Twine &Group, unsigned UniqueID) {
MCSymbolELF *GroupSym = nullptr;
if (!Group.isTriviallyEmpty() && !Group.str().empty())
GroupSym = cast<MCSymbolELF>(getOrCreateSymbol(Group));
return getELFSection(Section, Type, Flags, EntrySize, GroupSym, UniqueID,
nullptr);
}
MCSectionELF *MCContext::getELFSection(const Twine &Section, unsigned Type,
unsigned Flags, unsigned EntrySize,
const MCSymbolELF *GroupSym,
unsigned UniqueID,
const MCSectionELF *Associated) {
StringRef Group = "";
if (GroupSym)
Group = GroupSym->getName();
// Do the lookup, if we have a hit, return it.
auto IterBool = ELFUniquingMap.insert(
std::make_pair(ELFSectionKey{Section.str(), Group, UniqueID}, nullptr));
auto &Entry = *IterBool.first;
if (!IterBool.second)
return Entry.second;
StringRef CachedName = Entry.first.SectionName;
SectionKind Kind;
if (Flags & ELF::SHF_ARM_PURECODE)
Kind = SectionKind::getExecuteOnly();
else if (Flags & ELF::SHF_EXECINSTR)
Kind = SectionKind::getText();
else
Kind = SectionKind::getReadOnly();
MCSectionELF *Result = createELFSectionImpl(
CachedName, Type, Flags, Kind, EntrySize, GroupSym, UniqueID, Associated);
Entry.second = Result;
return Result;
}
MCSectionELF *MCContext::createELFGroupSection(const MCSymbolELF *Group) {
return createELFSectionImpl(".group", ELF::SHT_GROUP, 0,
SectionKind::getReadOnly(), 4, Group, ~0,
nullptr);
}
MCSectionCOFF *MCContext::getCOFFSection(StringRef Section,
unsigned Characteristics,
SectionKind Kind,
StringRef COMDATSymName, int Selection,
unsigned UniqueID,
const char *BeginSymName) {
MCSymbol *COMDATSymbol = nullptr;
if (!COMDATSymName.empty()) {
COMDATSymbol = getOrCreateSymbol(COMDATSymName);
COMDATSymName = COMDATSymbol->getName();
}
// Do the lookup, if we have a hit, return it.
COFFSectionKey T{Section, COMDATSymName, Selection, UniqueID};
auto IterBool = COFFUniquingMap.insert(std::make_pair(T, nullptr));
auto Iter = IterBool.first;
if (!IterBool.second)
return Iter->second;
MCSymbol *Begin = nullptr;
if (BeginSymName)
Begin = createTempSymbol(BeginSymName, false);
StringRef CachedName = Iter->first.SectionName;
MCSectionCOFF *Result = new (COFFAllocator.Allocate()) MCSectionCOFF(
CachedName, Characteristics, COMDATSymbol, Selection, Kind, Begin);
Iter->second = Result;
return Result;
}
MCSectionCOFF *MCContext::getCOFFSection(StringRef Section,
unsigned Characteristics,
SectionKind Kind,
const char *BeginSymName) {
return getCOFFSection(Section, Characteristics, Kind, "", 0, GenericSectionID,
BeginSymName);
}
MCSectionCOFF *MCContext::getCOFFSection(StringRef Section) {
COFFSectionKey T{Section, "", 0, GenericSectionID};
auto Iter = COFFUniquingMap.find(T);
if (Iter == COFFUniquingMap.end())
return nullptr;
return Iter->second;
}
MCSectionCOFF *MCContext::getAssociativeCOFFSection(MCSectionCOFF *Sec,
const MCSymbol *KeySym,
unsigned UniqueID) {
// Return the normal section if we don't have to be associative or unique.
if (!KeySym && UniqueID == GenericSectionID)
return Sec;
// If we have a key symbol, make an associative section with the same name and
// kind as the normal section.
unsigned Characteristics = Sec->getCharacteristics();
if (KeySym) {
Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
return getCOFFSection(Sec->getSectionName(), Characteristics,
Sec->getKind(), KeySym->getName(),
COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID);
}
return getCOFFSection(Sec->getSectionName(), Characteristics, Sec->getKind(),
"", 0, UniqueID);
}
MCSubtargetInfo &MCContext::getSubtargetCopy(const MCSubtargetInfo &STI) {
return *new (MCSubtargetAllocator.Allocate()) MCSubtargetInfo(STI);
}
//===----------------------------------------------------------------------===//
// Dwarf Management
//===----------------------------------------------------------------------===//
/// getDwarfFile - takes a file name an number to place in the dwarf file and
/// directory tables. If the file number has already been allocated it is an
/// error and zero is returned and the client reports the error, else the
/// allocated file number is returned. The file numbers may be in any order.
unsigned MCContext::getDwarfFile(StringRef Directory, StringRef FileName,
unsigned FileNumber, unsigned CUID) {
MCDwarfLineTable &Table = MCDwarfLineTablesCUMap[CUID];
return Table.getFile(Directory, FileName, FileNumber);
}
/// isValidDwarfFileNumber - takes a dwarf file number and returns true if it
/// currently is assigned and false otherwise.
bool MCContext::isValidDwarfFileNumber(unsigned FileNumber, unsigned CUID) {
const SmallVectorImpl<MCDwarfFile> &MCDwarfFiles = getMCDwarfFiles(CUID);
if (FileNumber == 0 || FileNumber >= MCDwarfFiles.size())
return false;
return !MCDwarfFiles[FileNumber].Name.empty();
}
/// Remove empty sections from SectionStartEndSyms, to avoid generating
/// useless debug info for them.
void MCContext::finalizeDwarfSections(MCStreamer &MCOS) {
SectionsForRanges.remove_if(
[&](MCSection *Sec) { return !MCOS.mayHaveInstructions(*Sec); });
}
CodeViewContext &MCContext::getCVContext() {
if (!CVContext.get())
CVContext.reset(new CodeViewContext);
return *CVContext.get();
}
//===----------------------------------------------------------------------===//
// Error Reporting
//===----------------------------------------------------------------------===//
void MCContext::reportError(SMLoc Loc, const Twine &Msg) {
HadError = true;
// If we have a source manager use it. Otherwise just use the generic
// report_fatal_error().
if (!SrcMgr)
report_fatal_error(Msg, false);
// Use the source manager to print the message.
SrcMgr->PrintMessage(Loc, SourceMgr::DK_Error, Msg);
}
void MCContext::reportFatalError(SMLoc Loc, const Twine &Msg) {
reportError(Loc, Msg);
// If we reached here, we are failing ungracefully. Run the interrupt handlers
// to make sure any special cleanups get done, in particular that we remove
// files registered with RemoveFileOnSignal.
sys::RunInterruptHandlers();
exit(1);
}
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