RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-11-25 20:23:11 +01:00
Code Issues Projects Releases Wiki Activity
fbb246b9e8
llvm-mirror/tools/llvm-cxxdump/llvm-cxxdump.cpp
Chandler Carruth ae65e281f3 Update the file headers across all of the LLVM projects in the monorepo 
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636
2019-01-19 08:50:56 +00:00

553 lines
21 KiB
C++
Raw Blame History

//===- llvm-cxxdump.cpp - Dump C++ data in an Object File -------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Dumps C++ data resident in object files and archives.
//
//===----------------------------------------------------------------------===//
#include "llvm-cxxdump.h"
#include "Error.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Object/SymbolSize.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/InitLLVM.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/WithColor.h"
#include "llvm/Support/raw_ostream.h"
#include <map>
#include <string>
#include <system_error>
using namespace llvm;
using namespace llvm::object;
using namespace llvm::support;
namespace opts {
cl::list<std::string> InputFilenames(cl::Positional,
cl::desc("<input object files>"),
cl::ZeroOrMore);
} // namespace opts
namespace llvm {
static void error(std::error_code EC) {
if (!EC)
return;
WithColor::error(outs(), "") << "reading file: " << EC.message() << ".\n";
outs().flush();
exit(1);
}
static void error(Error Err) {
if (!Err)
return;
logAllUnhandledErrors(std::move(Err), WithColor::error(outs()),
"reading file: ");
outs().flush();
exit(1);
}
} // namespace llvm
static void reportError(StringRef Input, StringRef Message) {
if (Input == "-")
Input = "<stdin>";
WithColor::error(errs(), Input) << Message << "\n";
errs().flush();
exit(1);
}
static void reportError(StringRef Input, std::error_code EC) {
reportError(Input, EC.message());
}
static std::map<SectionRef, SmallVector<SectionRef, 1>> SectionRelocMap;
static void collectRelocatedSymbols(const ObjectFile *Obj,
const SectionRef &Sec, uint64_t SecAddress,
uint64_t SymAddress, uint64_t SymSize,
StringRef *I, StringRef *E) {
uint64_t SymOffset = SymAddress - SecAddress;
uint64_t SymEnd = SymOffset + SymSize;
for (const SectionRef &SR : SectionRelocMap[Sec]) {
for (const object::RelocationRef &Reloc : SR.relocations()) {
if (I == E)
break;
const object::symbol_iterator RelocSymI = Reloc.getSymbol();
if (RelocSymI == Obj->symbol_end())
continue;
Expected<StringRef> RelocSymName = RelocSymI->getName();
error(errorToErrorCode(RelocSymName.takeError()));
uint64_t Offset = Reloc.getOffset();
if (Offset >= SymOffset && Offset < SymEnd) {
*I = *RelocSymName;
++I;
}
}
}
}
static void collectRelocationOffsets(
const ObjectFile *Obj, const SectionRef &Sec, uint64_t SecAddress,
uint64_t SymAddress, uint64_t SymSize, StringRef SymName,
std::map<std::pair<StringRef, uint64_t>, StringRef> &Collection) {
uint64_t SymOffset = SymAddress - SecAddress;
uint64_t SymEnd = SymOffset + SymSize;
for (const SectionRef &SR : SectionRelocMap[Sec]) {
for (const object::RelocationRef &Reloc : SR.relocations()) {
const object::symbol_iterator RelocSymI = Reloc.getSymbol();
if (RelocSymI == Obj->symbol_end())
continue;
Expected<StringRef> RelocSymName = RelocSymI->getName();
error(errorToErrorCode(RelocSymName.takeError()));
uint64_t Offset = Reloc.getOffset();
if (Offset >= SymOffset && Offset < SymEnd)
Collection[std::make_pair(SymName, Offset - SymOffset)] = *RelocSymName;
}
}
}
static void dumpCXXData(const ObjectFile *Obj) {
struct CompleteObjectLocator {
StringRef Symbols[2];
ArrayRef<little32_t> Data;
};
struct ClassHierarchyDescriptor {
StringRef Symbols[1];
ArrayRef<little32_t> Data;
};
struct BaseClassDescriptor {
StringRef Symbols[2];
ArrayRef<little32_t> Data;
};
struct TypeDescriptor {
StringRef Symbols[1];
uint64_t AlwaysZero;
StringRef MangledName;
};
struct ThrowInfo {
uint32_t Flags;
};
struct CatchableTypeArray {
uint32_t NumEntries;
};
struct CatchableType {
uint32_t Flags;
uint32_t NonVirtualBaseAdjustmentOffset;
int32_t VirtualBasePointerOffset;
uint32_t VirtualBaseAdjustmentOffset;
uint32_t Size;
StringRef Symbols[2];
};
std::map<std::pair<StringRef, uint64_t>, StringRef> VFTableEntries;
std::map<std::pair<StringRef, uint64_t>, StringRef> TIEntries;
std::map<std::pair<StringRef, uint64_t>, StringRef> CTAEntries;
std::map<StringRef, ArrayRef<little32_t>> VBTables;
std::map<StringRef, CompleteObjectLocator> COLs;
std::map<StringRef, ClassHierarchyDescriptor> CHDs;
std::map<std::pair<StringRef, uint64_t>, StringRef> BCAEntries;
std::map<StringRef, BaseClassDescriptor> BCDs;
std::map<StringRef, TypeDescriptor> TDs;
std::map<StringRef, ThrowInfo> TIs;
std::map<StringRef, CatchableTypeArray> CTAs;
std::map<StringRef, CatchableType> CTs;
std::map<std::pair<StringRef, uint64_t>, StringRef> VTableSymEntries;
std::map<std::pair<StringRef, uint64_t>, int64_t> VTableDataEntries;
std::map<std::pair<StringRef, uint64_t>, StringRef> VTTEntries;
std::map<StringRef, StringRef> TINames;
SectionRelocMap.clear();
for (const SectionRef &Section : Obj->sections()) {
section_iterator Sec2 = Section.getRelocatedSection();
if (Sec2 != Obj->section_end())
SectionRelocMap[*Sec2].push_back(Section);
}
uint8_t BytesInAddress = Obj->getBytesInAddress();
std::vector<std::pair<SymbolRef, uint64_t>> SymAddr =
object::computeSymbolSizes(*Obj);
for (auto &P : SymAddr) {
object::SymbolRef Sym = P.first;
uint64_t SymSize = P.second;
Expected<StringRef> SymNameOrErr = Sym.getName();
error(errorToErrorCode(SymNameOrErr.takeError()));
StringRef SymName = *SymNameOrErr;
Expected<object::section_iterator> SecIOrErr = Sym.getSection();
error(errorToErrorCode(SecIOrErr.takeError()));
object::section_iterator SecI = *SecIOrErr;
// Skip external symbols.
if (SecI == Obj->section_end())
continue;
const SectionRef &Sec = *SecI;
// Skip virtual or BSS sections.
if (Sec.isBSS() || Sec.isVirtual())
continue;
StringRef SecContents;
error(Sec.getContents(SecContents));
Expected<uint64_t> SymAddressOrErr = Sym.getAddress();
error(errorToErrorCode(SymAddressOrErr.takeError()));
uint64_t SymAddress = *SymAddressOrErr;
uint64_t SecAddress = Sec.getAddress();
uint64_t SecSize = Sec.getSize();
uint64_t SymOffset = SymAddress - SecAddress;
StringRef SymContents = SecContents.substr(SymOffset, SymSize);
// VFTables in the MS-ABI start with '??_7' and are contained within their
// own COMDAT section. We then determine the contents of the VFTable by
// looking at each relocation in the section.
if (SymName.startswith("??_7")) {
// Each relocation either names a virtual method or a thunk. We note the
// offset into the section and the symbol used for the relocation.
collectRelocationOffsets(Obj, Sec, SecAddress, SecAddress, SecSize,
SymName, VFTableEntries);
}
// VBTables in the MS-ABI start with '??_8' and are filled with 32-bit
// offsets of virtual bases.
else if (SymName.startswith("??_8")) {
ArrayRef<little32_t> VBTableData(
reinterpret_cast<const little32_t *>(SymContents.data()),
SymContents.size() / sizeof(little32_t));
VBTables[SymName] = VBTableData;
}
// Complete object locators in the MS-ABI start with '??_R4'
else if (SymName.startswith("??_R4")) {
CompleteObjectLocator COL;
COL.Data = makeArrayRef(
reinterpret_cast<const little32_t *>(SymContents.data()), 3);
StringRef *I = std::begin(COL.Symbols), *E = std::end(COL.Symbols);
collectRelocatedSymbols(Obj, Sec, SecAddress, SymAddress, SymSize, I, E);
COLs[SymName] = COL;
}
// Class hierarchy descriptors in the MS-ABI start with '??_R3'
else if (SymName.startswith("??_R3")) {
ClassHierarchyDescriptor CHD;
CHD.Data = makeArrayRef(
reinterpret_cast<const little32_t *>(SymContents.data()), 3);
StringRef *I = std::begin(CHD.Symbols), *E = std::end(CHD.Symbols);
collectRelocatedSymbols(Obj, Sec, SecAddress, SymAddress, SymSize, I, E);
CHDs[SymName] = CHD;
}
// Class hierarchy descriptors in the MS-ABI start with '??_R2'
else if (SymName.startswith("??_R2")) {
// Each relocation names a base class descriptor. We note the offset into
// the section and the symbol used for the relocation.
collectRelocationOffsets(Obj, Sec, SecAddress, SymAddress, SymSize,
SymName, BCAEntries);
}
// Base class descriptors in the MS-ABI start with '??_R1'
else if (SymName.startswith("??_R1")) {
BaseClassDescriptor BCD;
BCD.Data = makeArrayRef(
reinterpret_cast<const little32_t *>(SymContents.data()) + 1, 5);
StringRef *I = std::begin(BCD.Symbols), *E = std::end(BCD.Symbols);
collectRelocatedSymbols(Obj, Sec, SecAddress, SymAddress, SymSize, I, E);
BCDs[SymName] = BCD;
}
// Type descriptors in the MS-ABI start with '??_R0'
else if (SymName.startswith("??_R0")) {
const char *DataPtr = SymContents.drop_front(BytesInAddress).data();
TypeDescriptor TD;
if (BytesInAddress == 8)
TD.AlwaysZero = *reinterpret_cast<const little64_t *>(DataPtr);
else
TD.AlwaysZero = *reinterpret_cast<const little32_t *>(DataPtr);
TD.MangledName = SymContents.drop_front(BytesInAddress * 2);
StringRef *I = std::begin(TD.Symbols), *E = std::end(TD.Symbols);
collectRelocatedSymbols(Obj, Sec, SecAddress, SymAddress, SymSize, I, E);
TDs[SymName] = TD;
}
// Throw descriptors in the MS-ABI start with '_TI'
else if (SymName.startswith("_TI") || SymName.startswith("__TI")) {
ThrowInfo TI;
TI.Flags = *reinterpret_cast<const little32_t *>(SymContents.data());
collectRelocationOffsets(Obj, Sec, SecAddress, SymAddress, SymSize,
SymName, TIEntries);
TIs[SymName] = TI;
}
// Catchable type arrays in the MS-ABI start with _CTA or __CTA.
else if (SymName.startswith("_CTA") || SymName.startswith("__CTA")) {
CatchableTypeArray CTA;
CTA.NumEntries =
*reinterpret_cast<const little32_t *>(SymContents.data());
collectRelocationOffsets(Obj, Sec, SecAddress, SymAddress, SymSize,
SymName, CTAEntries);
CTAs[SymName] = CTA;
}
// Catchable types in the MS-ABI start with _CT or __CT.
else if (SymName.startswith("_CT") || SymName.startswith("__CT")) {
const little32_t *DataPtr =
reinterpret_cast<const little32_t *>(SymContents.data());
CatchableType CT;
CT.Flags = DataPtr[0];
CT.NonVirtualBaseAdjustmentOffset = DataPtr[2];
CT.VirtualBasePointerOffset = DataPtr[3];
CT.VirtualBaseAdjustmentOffset = DataPtr[4];
CT.Size = DataPtr[5];
StringRef *I = std::begin(CT.Symbols), *E = std::end(CT.Symbols);
collectRelocatedSymbols(Obj, Sec, SecAddress, SymAddress, SymSize, I, E);
CTs[SymName] = CT;
}
// Construction vtables in the Itanium ABI start with '_ZTT' or '__ZTT'.
else if (SymName.startswith("_ZTT") || SymName.startswith("__ZTT")) {
collectRelocationOffsets(Obj, Sec, SecAddress, SymAddress, SymSize,
SymName, VTTEntries);
}
// Typeinfo names in the Itanium ABI start with '_ZTS' or '__ZTS'.
else if (SymName.startswith("_ZTS") || SymName.startswith("__ZTS")) {
TINames[SymName] = SymContents.slice(0, SymContents.find('\0'));
}
// Vtables in the Itanium ABI start with '_ZTV' or '__ZTV'.
else if (SymName.startswith("_ZTV") || SymName.startswith("__ZTV")) {
collectRelocationOffsets(Obj, Sec, SecAddress, SymAddress, SymSize,
SymName, VTableSymEntries);
for (uint64_t SymOffI = 0; SymOffI < SymSize; SymOffI += BytesInAddress) {
auto Key = std::make_pair(SymName, SymOffI);
if (VTableSymEntries.count(Key))
continue;
const char *DataPtr =
SymContents.substr(SymOffI, BytesInAddress).data();
int64_t VData;
if (BytesInAddress == 8)
VData = *reinterpret_cast<const little64_t *>(DataPtr);
else
VData = *reinterpret_cast<const little32_t *>(DataPtr);
VTableDataEntries[Key] = VData;
}
}
// Typeinfo structures in the Itanium ABI start with '_ZTI' or '__ZTI'.
else if (SymName.startswith("_ZTI") || SymName.startswith("__ZTI")) {
// FIXME: Do something with these!
}
}
for (const auto &VFTableEntry : VFTableEntries) {
StringRef VFTableName = VFTableEntry.first.first;
uint64_t Offset = VFTableEntry.first.second;
StringRef SymName = VFTableEntry.second;
outs() << VFTableName << '[' << Offset << "]: " << SymName << '\n';
}
for (const auto &VBTable : VBTables) {
StringRef VBTableName = VBTable.first;
uint32_t Idx = 0;
for (little32_t Offset : VBTable.second) {
outs() << VBTableName << '[' << Idx << "]: " << Offset << '\n';
Idx += sizeof(Offset);
}
}
for (const auto &COLPair : COLs) {
StringRef COLName = COLPair.first;
const CompleteObjectLocator &COL = COLPair.second;
outs() << COLName << "[IsImageRelative]: " << COL.Data[0] << '\n';
outs() << COLName << "[OffsetToTop]: " << COL.Data[1] << '\n';
outs() << COLName << "[VFPtrOffset]: " << COL.Data[2] << '\n';
outs() << COLName << "[TypeDescriptor]: " << COL.Symbols[0] << '\n';
outs() << COLName << "[ClassHierarchyDescriptor]: " << COL.Symbols[1]
<< '\n';
}
for (const auto &CHDPair : CHDs) {
StringRef CHDName = CHDPair.first;
const ClassHierarchyDescriptor &CHD = CHDPair.second;
outs() << CHDName << "[AlwaysZero]: " << CHD.Data[0] << '\n';
outs() << CHDName << "[Flags]: " << CHD.Data[1] << '\n';
outs() << CHDName << "[NumClasses]: " << CHD.Data[2] << '\n';
outs() << CHDName << "[BaseClassArray]: " << CHD.Symbols[0] << '\n';
}
for (const auto &BCAEntry : BCAEntries) {
StringRef BCAName = BCAEntry.first.first;
uint64_t Offset = BCAEntry.first.second;
StringRef SymName = BCAEntry.second;
outs() << BCAName << '[' << Offset << "]: " << SymName << '\n';
}
for (const auto &BCDPair : BCDs) {
StringRef BCDName = BCDPair.first;
const BaseClassDescriptor &BCD = BCDPair.second;
outs() << BCDName << "[TypeDescriptor]: " << BCD.Symbols[0] << '\n';
outs() << BCDName << "[NumBases]: " << BCD.Data[0] << '\n';
outs() << BCDName << "[OffsetInVBase]: " << BCD.Data[1] << '\n';
outs() << BCDName << "[VBPtrOffset]: " << BCD.Data[2] << '\n';
outs() << BCDName << "[OffsetInVBTable]: " << BCD.Data[3] << '\n';
outs() << BCDName << "[Flags]: " << BCD.Data[4] << '\n';
outs() << BCDName << "[ClassHierarchyDescriptor]: " << BCD.Symbols[1]
<< '\n';
}
for (const auto &TDPair : TDs) {
StringRef TDName = TDPair.first;
const TypeDescriptor &TD = TDPair.second;
outs() << TDName << "[VFPtr]: " << TD.Symbols[0] << '\n';
outs() << TDName << "[AlwaysZero]: " << TD.AlwaysZero << '\n';
outs() << TDName << "[MangledName]: ";
outs().write_escaped(TD.MangledName.rtrim(StringRef("\0", 1)),
/*UseHexEscapes=*/true)
<< '\n';
}
for (const auto &TIPair : TIs) {
StringRef TIName = TIPair.first;
const ThrowInfo &TI = TIPair.second;
auto dumpThrowInfoFlag = [&](const char *Name, uint32_t Flag) {
outs() << TIName << "[Flags." << Name
<< "]: " << (TI.Flags & Flag ? "true" : "false") << '\n';
};
auto dumpThrowInfoSymbol = [&](const char *Name, int Offset) {
outs() << TIName << '[' << Name << "]: ";
auto Entry = TIEntries.find(std::make_pair(TIName, Offset));
outs() << (Entry == TIEntries.end() ? "null" : Entry->second) << '\n';
};
outs() << TIName << "[Flags]: " << TI.Flags << '\n';
dumpThrowInfoFlag("Const", 1);
dumpThrowInfoFlag("Volatile", 2);
dumpThrowInfoSymbol("CleanupFn", 4);
dumpThrowInfoSymbol("ForwardCompat", 8);
dumpThrowInfoSymbol("CatchableTypeArray", 12);
}
for (const auto &CTAPair : CTAs) {
StringRef CTAName = CTAPair.first;
const CatchableTypeArray &CTA = CTAPair.second;
outs() << CTAName << "[NumEntries]: " << CTA.NumEntries << '\n';
unsigned Idx = 0;
for (auto I = CTAEntries.lower_bound(std::make_pair(CTAName, 0)),
E = CTAEntries.upper_bound(std::make_pair(CTAName, UINT64_MAX));
I != E; ++I)
outs() << CTAName << '[' << Idx++ << "]: " << I->second << '\n';
}
for (const auto &CTPair : CTs) {
StringRef CTName = CTPair.first;
const CatchableType &CT = CTPair.second;
auto dumpCatchableTypeFlag = [&](const char *Name, uint32_t Flag) {
outs() << CTName << "[Flags." << Name
<< "]: " << (CT.Flags & Flag ? "true" : "false") << '\n';
};
outs() << CTName << "[Flags]: " << CT.Flags << '\n';
dumpCatchableTypeFlag("ScalarType", 1);
dumpCatchableTypeFlag("VirtualInheritance", 4);
outs() << CTName << "[TypeDescriptor]: " << CT.Symbols[0] << '\n';
outs() << CTName << "[NonVirtualBaseAdjustmentOffset]: "
<< CT.NonVirtualBaseAdjustmentOffset << '\n';
outs() << CTName
<< "[VirtualBasePointerOffset]: " << CT.VirtualBasePointerOffset
<< '\n';
outs() << CTName << "[VirtualBaseAdjustmentOffset]: "
<< CT.VirtualBaseAdjustmentOffset << '\n';
outs() << CTName << "[Size]: " << CT.Size << '\n';
outs() << CTName
<< "[CopyCtor]: " << (CT.Symbols[1].empty() ? "null" : CT.Symbols[1])
<< '\n';
}
for (const auto &VTTPair : VTTEntries) {
StringRef VTTName = VTTPair.first.first;
uint64_t VTTOffset = VTTPair.first.second;
StringRef VTTEntry = VTTPair.second;
outs() << VTTName << '[' << VTTOffset << "]: " << VTTEntry << '\n';
}
for (const auto &TIPair : TINames) {
StringRef TIName = TIPair.first;
outs() << TIName << ": " << TIPair.second << '\n';
}
auto VTableSymI = VTableSymEntries.begin();
auto VTableSymE = VTableSymEntries.end();
auto VTableDataI = VTableDataEntries.begin();
auto VTableDataE = VTableDataEntries.end();
for (;;) {
bool SymDone = VTableSymI == VTableSymE;
bool DataDone = VTableDataI == VTableDataE;
if (SymDone && DataDone)
break;
if (!SymDone && (DataDone || VTableSymI->first < VTableDataI->first)) {
StringRef VTableName = VTableSymI->first.first;
uint64_t Offset = VTableSymI->first.second;
StringRef VTableEntry = VTableSymI->second;
outs() << VTableName << '[' << Offset << "]: ";
outs() << VTableEntry;
outs() << '\n';
++VTableSymI;
continue;
}
if (!DataDone && (SymDone || VTableDataI->first < VTableSymI->first)) {
StringRef VTableName = VTableDataI->first.first;
uint64_t Offset = VTableDataI->first.second;
int64_t VTableEntry = VTableDataI->second;
outs() << VTableName << '[' << Offset << "]: ";
outs() << VTableEntry;
outs() << '\n';
++VTableDataI;
continue;
}
}
}
static void dumpArchive(const Archive *Arc) {
Error Err = Error::success();
for (auto &ArcC : Arc->children(Err)) {
Expected<std::unique_ptr<Binary>> ChildOrErr = ArcC.getAsBinary();
if (!ChildOrErr) {
// Ignore non-object files.
if (auto E = isNotObjectErrorInvalidFileType(ChildOrErr.takeError())) {
std::string Buf;
raw_string_ostream OS(Buf);
logAllUnhandledErrors(std::move(E), OS);
OS.flush();
reportError(Arc->getFileName(), Buf);
}
consumeError(ChildOrErr.takeError());
continue;
}
if (ObjectFile *Obj = dyn_cast<ObjectFile>(&*ChildOrErr.get()))
dumpCXXData(Obj);
else
reportError(Arc->getFileName(), cxxdump_error::unrecognized_file_format);
}
error(std::move(Err));
}
static void dumpInput(StringRef File) {
// Attempt to open the binary.
Expected<OwningBinary<Binary>> BinaryOrErr = createBinary(File);
if (!BinaryOrErr) {
auto EC = errorToErrorCode(BinaryOrErr.takeError());
reportError(File, EC);
return;
}
Binary &Binary = *BinaryOrErr.get().getBinary();
if (Archive *Arc = dyn_cast<Archive>(&Binary))
dumpArchive(Arc);
else if (ObjectFile *Obj = dyn_cast<ObjectFile>(&Binary))
dumpCXXData(Obj);
else
reportError(File, cxxdump_error::unrecognized_file_format);
}
int main(int argc, const char *argv[]) {
InitLLVM X(argc, argv);
// Initialize targets.
llvm::InitializeAllTargetInfos();
// Register the target printer for --version.
cl::AddExtraVersionPrinter(TargetRegistry::printRegisteredTargetsForVersion);
cl::ParseCommandLineOptions(argc, argv, "LLVM C++ ABI Data Dumper\n");
// Default to stdin if no filename is specified.
if (opts::InputFilenames.size() == 0)
opts::InputFilenames.push_back("-");
llvm::for_each(opts::InputFilenames, dumpInput);
return EXIT_SUCCESS;
}
Reference in New Issue View Git Blame Copy Permalink