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//===- ArchiveWriter.cpp - ar File Format implementation --------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the writeArchive function.
#include "llvm/Object/ArchiveWriter.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/Magic.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Object/SymbolicFile.h"
#include "llvm/Support/EndianStream.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/ToolOutputFile.h"
#include "llvm/Support/raw_ostream.h"
#include <map>
#if !defined(_MSC_VER) && !defined(__MINGW32__)
#include <unistd.h>
#include <io.h>
using namespace llvm;
NewArchiveMember::NewArchiveMember(MemoryBufferRef BufRef)
: Buf(MemoryBuffer::getMemBuffer(BufRef, false)),
MemberName(BufRef.getBufferIdentifier()) {}
NewArchiveMember::getOldMember(const object::Archive::Child &OldMember,
bool Deterministic) {
Expected<llvm::MemoryBufferRef> BufOrErr = OldMember.getMemoryBufferRef();
if (!BufOrErr)
return BufOrErr.takeError();
NewArchiveMember M;
M.Buf = MemoryBuffer::getMemBuffer(*BufOrErr, false);
M.MemberName = M.Buf->getBufferIdentifier();
if (!Deterministic) {
auto ModTimeOrErr = OldMember.getLastModified();
if (!ModTimeOrErr)
return ModTimeOrErr.takeError();
M.ModTime = ModTimeOrErr.get();
Expected<unsigned> UIDOrErr = OldMember.getUID();
if (!UIDOrErr)
return UIDOrErr.takeError();
M.UID = UIDOrErr.get();
Expected<unsigned> GIDOrErr = OldMember.getGID();
if (!GIDOrErr)
return GIDOrErr.takeError();
M.GID = GIDOrErr.get();
Expected<sys::fs::perms> AccessModeOrErr = OldMember.getAccessMode();
if (!AccessModeOrErr)
return AccessModeOrErr.takeError();
M.Perms = AccessModeOrErr.get();
return std::move(M);
Expected<NewArchiveMember> NewArchiveMember::getFile(StringRef FileName,
bool Deterministic) {
sys::fs::file_status Status;
int FD;
if (auto EC = sys::fs::openFileForRead(FileName, FD))
return errorCodeToError(EC);
assert(FD != -1);
if (auto EC = sys::fs::status(FD, Status))
return errorCodeToError(EC);
// Opening a directory doesn't make sense. Let it fail.
// Linux cannot open directories with open(2), although
// cygwin and *bsd can.
if (Status.type() == sys::fs::file_type::directory_file)
return errorCodeToError(make_error_code(errc::is_a_directory));
ErrorOr<std::unique_ptr<MemoryBuffer>> MemberBufferOrErr =
MemoryBuffer::getOpenFile(FD, FileName, Status.getSize(), false);
if (!MemberBufferOrErr)
return errorCodeToError(MemberBufferOrErr.getError());
if (close(FD) != 0)
return errorCodeToError(std::error_code(errno, std::generic_category()));
NewArchiveMember M;
M.Buf = std::move(*MemberBufferOrErr);
M.MemberName = M.Buf->getBufferIdentifier();
if (!Deterministic) {
M.ModTime = std::chrono::time_point_cast<std::chrono::seconds>(
M.UID = Status.getUser();
M.GID = Status.getGroup();
M.Perms = Status.permissions();
return std::move(M);
template <typename T>
static void printWithSpacePadding(raw_ostream &OS, T Data, unsigned Size) {
uint64_t OldPos = OS.tell();
OS << Data;
unsigned SizeSoFar = OS.tell() - OldPos;
assert(SizeSoFar <= Size && "Data doesn't fit in Size");
OS.indent(Size - SizeSoFar);
static bool isDarwin(object::Archive::Kind Kind) {
return Kind == object::Archive::K_DARWIN ||
Kind == object::Archive::K_DARWIN64;
static bool isBSDLike(object::Archive::Kind Kind) {
switch (Kind) {
case object::Archive::K_GNU:
case object::Archive::K_GNU64:
return false;
case object::Archive::K_BSD:
case object::Archive::K_DARWIN:
case object::Archive::K_DARWIN64:
return true;
case object::Archive::K_COFF:
llvm_unreachable("not supported for writting");
template <class T>
static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val) {
support::endian::write(Out, Val,
isBSDLike(Kind) ? support::little : support::big);
static void printRestOfMemberHeader(
raw_ostream &Out, const sys::TimePoint<std::chrono::seconds> &ModTime,
unsigned UID, unsigned GID, unsigned Perms, unsigned Size) {
printWithSpacePadding(Out, sys::toTimeT(ModTime), 12);
// The format has only 6 chars for uid and gid. Truncate if the provided
// values don't fit.
printWithSpacePadding(Out, UID % 1000000, 6);
printWithSpacePadding(Out, GID % 1000000, 6);
printWithSpacePadding(Out, format("%o", Perms), 8);
printWithSpacePadding(Out, Size, 10);
Out << "`\n";
static void
printGNUSmallMemberHeader(raw_ostream &Out, StringRef Name,
const sys::TimePoint<std::chrono::seconds> &ModTime,
unsigned UID, unsigned GID, unsigned Perms,
unsigned Size) {
printWithSpacePadding(Out, Twine(Name) + "/", 16);
printRestOfMemberHeader(Out, ModTime, UID, GID, Perms, Size);
static void
printBSDMemberHeader(raw_ostream &Out, uint64_t Pos, StringRef Name,
const sys::TimePoint<std::chrono::seconds> &ModTime,
unsigned UID, unsigned GID, unsigned Perms,
unsigned Size) {
uint64_t PosAfterHeader = Pos + 60 + Name.size();
// Pad so that even 64 bit object files are aligned.
unsigned Pad = OffsetToAlignment(PosAfterHeader, 8);
unsigned NameWithPadding = Name.size() + Pad;
printWithSpacePadding(Out, Twine("#1/") + Twine(NameWithPadding), 16);
printRestOfMemberHeader(Out, ModTime, UID, GID, Perms,
NameWithPadding + Size);
Out << Name;
while (Pad--)
static bool useStringTable(bool Thin, StringRef Name) {
return Thin || Name.size() >= 16 || Name.contains('/');
static bool is64BitKind(object::Archive::Kind Kind) {
switch (Kind) {
case object::Archive::K_GNU:
case object::Archive::K_BSD:
case object::Archive::K_DARWIN:
case object::Archive::K_COFF:
return false;
case object::Archive::K_DARWIN64:
case object::Archive::K_GNU64:
return true;
llvm_unreachable("not supported for writting");
static void
printMemberHeader(raw_ostream &Out, uint64_t Pos, raw_ostream &StringTable,
StringMap<uint64_t> &MemberNames, object::Archive::Kind Kind,
bool Thin, const NewArchiveMember &M,
sys::TimePoint<std::chrono::seconds> ModTime, unsigned Size) {
if (isBSDLike(Kind))
return printBSDMemberHeader(Out, Pos, M.MemberName, ModTime, M.UID, M.GID,
M.Perms, Size);
if (!useStringTable(Thin, M.MemberName))
return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID,
M.Perms, Size);
Out << '/';
uint64_t NamePos;
if (Thin) {
NamePos = StringTable.tell();
StringTable << M.MemberName << "/\n";
} else {
auto Insertion = MemberNames.insert({M.MemberName, uint64_t(0)});
if (Insertion.second) {
Insertion.first->second = StringTable.tell();
StringTable << M.MemberName << "/\n";
NamePos = Insertion.first->second;
printWithSpacePadding(Out, NamePos, 15);
printRestOfMemberHeader(Out, ModTime, M.UID, M.GID, M.Perms, Size);
namespace {
struct MemberData {
std::vector<unsigned> Symbols;
std::string Header;
StringRef Data;
StringRef Padding;
} // namespace
static MemberData computeStringTable(StringRef Names) {
unsigned Size = Names.size();
unsigned Pad = OffsetToAlignment(Size, 2);
std::string Header;
raw_string_ostream Out(Header);
printWithSpacePadding(Out, "//", 48);
printWithSpacePadding(Out, Size + Pad, 10);
Out << "`\n";
return {{}, std::move(Header), Names, Pad ? "\n" : ""};
static sys::TimePoint<std::chrono::seconds> now(bool Deterministic) {
using namespace std::chrono;
if (!Deterministic)
return time_point_cast<seconds>(system_clock::now());
return sys::TimePoint<seconds>();
static bool isArchiveSymbol(const object::BasicSymbolRef &S) {
uint32_t Symflags = S.getFlags();
if (Symflags & object::SymbolRef::SF_FormatSpecific)
return false;
if (!(Symflags & object::SymbolRef::SF_Global))
return false;
if (Symflags & object::SymbolRef::SF_Undefined)
return false;
return true;
static void printNBits(raw_ostream &Out, object::Archive::Kind Kind,
uint64_t Val) {
if (is64BitKind(Kind))
print<uint64_t>(Out, Kind, Val);
print<uint32_t>(Out, Kind, Val);
static void writeSymbolTable(raw_ostream &Out, object::Archive::Kind Kind,
bool Deterministic, ArrayRef<MemberData> Members,
StringRef StringTable) {
// We don't write a symbol table on an archive with no members -- except on
// Darwin, where the linker will abort unless the archive has a symbol table.
if (StringTable.empty() && !isDarwin(Kind))
unsigned NumSyms = 0;
for (const MemberData &M : Members)
NumSyms += M.Symbols.size();
unsigned Size = 0;
unsigned OffsetSize = is64BitKind(Kind) ? sizeof(uint64_t) : sizeof(uint32_t);
Size += OffsetSize; // Number of entries
if (isBSDLike(Kind))
Size += NumSyms * OffsetSize * 2; // Table
Size += NumSyms * OffsetSize; // Table
if (isBSDLike(Kind))
Size += OffsetSize; // byte count
Size += StringTable.size();
// ld64 expects the members to be 8-byte aligned for 64-bit content and at
// least 4-byte aligned for 32-bit content. Opt for the larger encoding
// uniformly.
// We do this for all bsd formats because it simplifies aligning members.
unsigned Alignment = isBSDLike(Kind) ? 8 : 2;
unsigned Pad = OffsetToAlignment(Size, Alignment);
Size += Pad;
if (isBSDLike(Kind)) {
const char *Name = is64BitKind(Kind) ? "__.SYMDEF_64" : "__.SYMDEF";
printBSDMemberHeader(Out, Out.tell(), Name, now(Deterministic), 0, 0, 0,
} else {
const char *Name = is64BitKind(Kind) ? "/SYM64" : "";
printGNUSmallMemberHeader(Out, Name, now(Deterministic), 0, 0, 0, Size);
uint64_t Pos = Out.tell() + Size;
if (isBSDLike(Kind))
printNBits(Out, Kind, NumSyms * 2 * OffsetSize);
printNBits(Out, Kind, NumSyms);
for (const MemberData &M : Members) {
for (unsigned StringOffset : M.Symbols) {
if (isBSDLike(Kind))
printNBits(Out, Kind, StringOffset);
printNBits(Out, Kind, Pos); // member offset
Pos += M.Header.size() + M.Data.size() + M.Padding.size();
if (isBSDLike(Kind))
// byte count of the string table
printNBits(Out, Kind, StringTable.size());
Out << StringTable;
while (Pad--)
static Expected<std::vector<unsigned>>
getSymbols(MemoryBufferRef Buf, raw_ostream &SymNames, bool &HasObject) {
std::vector<unsigned> Ret;
// In the scenario when LLVMContext is populated SymbolicFile will contain a
// reference to it, thus SymbolicFile should be destroyed first.
LLVMContext Context;
std::unique_ptr<object::SymbolicFile> Obj;
if (identify_magic(Buf.getBuffer()) == file_magic::bitcode) {
auto ObjOrErr = object::SymbolicFile::createSymbolicFile(
Buf, file_magic::bitcode, &Context);
if (!ObjOrErr) {
// FIXME: check only for "not an object file" errors.
return Ret;
Obj = std::move(*ObjOrErr);
} else {
auto ObjOrErr = object::SymbolicFile::createSymbolicFile(Buf);
if (!ObjOrErr) {
// FIXME: check only for "not an object file" errors.
return Ret;
Obj = std::move(*ObjOrErr);
HasObject = true;
for (const object::BasicSymbolRef &S : Obj->symbols()) {
if (!isArchiveSymbol(S))
if (auto EC = S.printName(SymNames))
return errorCodeToError(EC);
SymNames << '\0';
return Ret;
static Expected<std::vector<MemberData>>
computeMemberData(raw_ostream &StringTable, raw_ostream &SymNames,
object::Archive::Kind Kind, bool Thin, bool Deterministic,
ArrayRef<NewArchiveMember> NewMembers) {
static char PaddingData[8] = {'\n', '\n', '\n', '\n', '\n', '\n', '\n', '\n'};
// This ignores the symbol table, but we only need the value mod 8 and the
// symbol table is aligned to be a multiple of 8 bytes
uint64_t Pos = 0;
std::vector<MemberData> Ret;
bool HasObject = false;
// Deduplicate long member names in the string table and reuse earlier name
// offsets. This especially saves space for COFF Import libraries where all
// members have the same name.
StringMap<uint64_t> MemberNames;
// UniqueTimestamps is a special case to improve debugging on Darwin:
// The Darwin linker does not link debug info into the final
// binary. Instead, it emits entries of type N_OSO in in the output
// binary's symbol table, containing references to the linked-in
// object files. Using that reference, the debugger can read the
// debug data directly from the object files. Alternatively, an
// invocation of 'dsymutil' will link the debug data from the object
// files into a dSYM bundle, which can be loaded by the debugger,
// instead of the object files.
// For an object file, the N_OSO entries contain the absolute path
// path to the file, and the file's timestamp. For an object
// included in an archive, the path is formatted like
// "/absolute/path/to/archive.a(member.o)", and the timestamp is the
// archive member's timestamp, rather than the archive's timestamp.
// However, this doesn't always uniquely identify an object within
// an archive -- an archive file can have multiple entries with the
// same filename. (This will happen commonly if the original object
// files started in different directories.) The only way they get
// distinguished, then, is via the timestamp. But this process is
// unable to find the correct object file in the archive when there
// are two files of the same name and timestamp.
// Additionally, timestamp==0 is treated specially, and causes the
// timestamp to be ignored as a match criteria.
// That will "usually" work out okay when creating an archive not in
// deterministic timestamp mode, because the objects will probably
// have been created at different timestamps.
// To ameliorate this problem, in deterministic archive mode (which
// is the default), on Darwin we will emit a unique non-zero
// timestamp for each entry with a duplicated name. This is still
// deterministic: the only thing affecting that timestamp is the
// order of the files in the resultant archive.
// See also the functions that handle the lookup:
// in lldb: ObjectContainerBSDArchive::Archive::FindObject()
// in llvm/tools/dsymutil: BinaryHolder::GetArchiveMemberBuffers().
bool UniqueTimestamps = Deterministic && isDarwin(Kind);
std::map<StringRef, unsigned> FilenameCount;
if (UniqueTimestamps) {
for (const NewArchiveMember &M : NewMembers)
for (auto &Entry : FilenameCount)
Entry.second = Entry.second > 1 ? 1 : 0;
for (const NewArchiveMember &M : NewMembers) {
std::string Header;
raw_string_ostream Out(Header);
MemoryBufferRef Buf = M.Buf->getMemBufferRef();
StringRef Data = Thin ? "" : Buf.getBuffer();
// ld64 expects the members to be 8-byte aligned for 64-bit content and at
// least 4-byte aligned for 32-bit content. Opt for the larger encoding
// uniformly. This matches the behaviour with cctools and ensures that ld64
// is happy with archives that we generate.
unsigned MemberPadding =
isDarwin(Kind) ? OffsetToAlignment(Data.size(), 8) : 0;
unsigned TailPadding = OffsetToAlignment(Data.size() + MemberPadding, 2);
StringRef Padding = StringRef(PaddingData, MemberPadding + TailPadding);
sys::TimePoint<std::chrono::seconds> ModTime;
if (UniqueTimestamps)
// Increment timestamp for each file of a given name.
ModTime = sys::toTimePoint(FilenameCount[M.MemberName]++);
ModTime = M.ModTime;
printMemberHeader(Out, Pos, StringTable, MemberNames, Kind, Thin, M,
ModTime, Buf.getBufferSize() + MemberPadding);
Expected<std::vector<unsigned>> Symbols =
getSymbols(Buf, SymNames, HasObject);
if (auto E = Symbols.takeError())
return std::move(E);
Pos += Header.size() + Data.size() + Padding.size();
Ret.push_back({std::move(*Symbols), std::move(Header), Data, Padding});
// If there are no symbols, emit an empty symbol table, to satisfy Solaris
// tools, older versions of which expect a symbol table in a non-empty
// archive, regardless of whether there are any symbols in it.
if (HasObject && SymNames.tell() == 0)
SymNames << '\0' << '\0' << '\0';
return Ret;
namespace llvm {
// Compute the relative path from From to To.
std::string computeArchiveRelativePath(StringRef From, StringRef To) {
if (sys::path::is_absolute(From) || sys::path::is_absolute(To))
return To;
StringRef DirFrom = sys::path::parent_path(From);
auto FromI = sys::path::begin(DirFrom);
auto ToI = sys::path::begin(To);
while (*FromI == *ToI) {
SmallString<128> Relative;
for (auto FromE = sys::path::end(DirFrom); FromI != FromE; ++FromI)
sys::path::append(Relative, "..");
for (auto ToE = sys::path::end(To); ToI != ToE; ++ToI)
sys::path::append(Relative, *ToI);
#ifdef _WIN32
// Replace backslashes with slashes so that the path is portable between *nix
// and Windows.
std::replace(Relative.begin(), Relative.end(), '\\', '/');
return Relative.str();
Error writeArchive(StringRef ArcName, ArrayRef<NewArchiveMember> NewMembers,
bool WriteSymtab, object::Archive::Kind Kind,
bool Deterministic, bool Thin,
std::unique_ptr<MemoryBuffer> OldArchiveBuf) {
assert((!Thin || !isBSDLike(Kind)) && "Only the gnu format has a thin mode");
SmallString<0> SymNamesBuf;
raw_svector_ostream SymNames(SymNamesBuf);
SmallString<0> StringTableBuf;
raw_svector_ostream StringTable(StringTableBuf);
Expected<std::vector<MemberData>> DataOrErr = computeMemberData(
StringTable, SymNames, Kind, Thin, Deterministic, NewMembers);
if (Error E = DataOrErr.takeError())
return E;
std::vector<MemberData> &Data = *DataOrErr;
if (!StringTableBuf.empty())
Data.insert(Data.begin(), computeStringTable(StringTableBuf));
// We would like to detect if we need to switch to a 64-bit symbol table.
if (WriteSymtab) {
uint64_t MaxOffset = 0;
uint64_t LastOffset = MaxOffset;
for (const auto &M : Data) {
// Record the start of the member's offset
LastOffset = MaxOffset;
// Account for the size of each part associated with the member.
MaxOffset += M.Header.size() + M.Data.size() + M.Padding.size();
// We assume 32-bit symbols to see if 32-bit symbols are possible or not.
MaxOffset += M.Symbols.size() * 4;
// The SYM64 format is used when an archive's member offsets are larger than
// 32-bits can hold. The need for this shift in format is detected by
// writeArchive. To test this we need to generate a file with a member that
// has an offset larger than 32-bits but this demands a very slow test. To
// speed the test up we use this environment variable to pretend like the
// cutoff happens before 32-bits and instead happens at some much smaller
// value.
const char *Sym64Env = std::getenv("SYM64_THRESHOLD");
int Sym64Threshold = 32;
if (Sym64Env)
StringRef(Sym64Env).getAsInteger(10, Sym64Threshold);
// If LastOffset isn't going to fit in a 32-bit varible we need to switch
// to 64-bit. Note that the file can be larger than 4GB as long as the last
// member starts before the 4GB offset.
if (LastOffset >= (1ULL << Sym64Threshold)) {
if (Kind == object::Archive::K_DARWIN)
Kind = object::Archive::K_DARWIN64;
Kind = object::Archive::K_GNU64;
Expected<sys::fs::TempFile> Temp =
sys::fs::TempFile::create(ArcName + ".temp-archive-%%%%%%%.a");
if (!Temp)
return Temp.takeError();
raw_fd_ostream Out(Temp->FD, false);
if (Thin)
Out << "!<thin>\n";
Out << "!<arch>\n";
if (WriteSymtab)
writeSymbolTable(Out, Kind, Deterministic, Data, SymNamesBuf);
for (const MemberData &M : Data)
Out << M.Header << M.Data << M.Padding;
// At this point, we no longer need whatever backing memory
// was used to generate the NewMembers. On Windows, this buffer
// could be a mapped view of the file we want to replace (if
// we're updating an existing archive, say). In that case, the
// rename would still succeed, but it would leave behind a
// temporary file (actually the original file renamed) because
// a file cannot be deleted while there's a handle open on it,
// only renamed. So by freeing this buffer, this ensures that
// the last open handle on the destination file, if any, is
// closed before we attempt to rename.
return Temp->keep(ArcName);
} // namespace llvm