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llvm-project/lld/COFF/Librarian.cpp

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//===- Librarian.cpp ------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains functions for the Librarian. The librarian creates and
// manages libraries of the Common Object File Format (COFF) object files. It
// primarily is used for creating static libraries and import libraries.
//
//===----------------------------------------------------------------------===//
#include "Config.h"
#include "Driver.h"
#include "Error.h"
#include "Symbols.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/ArchiveWriter.h"
#include "llvm/Object/COFF.h"
#include "llvm/Support/Path.h"
#include <vector>
using namespace lld::coff;
using namespace llvm::COFF;
using namespace llvm::object;
using namespace llvm;
static bool is32bit() {
switch (Config->Machine) {
default:
llvm_unreachable("unsupported machine");
case IMAGE_FILE_MACHINE_AMD64:
return false;
case IMAGE_FILE_MACHINE_ARMNT:
case IMAGE_FILE_MACHINE_I386:
return true;
}
}
static uint16_t getImgRelRelocation() {
switch (Config->Machine) {
default:
llvm_unreachable("unsupported machine");
case IMAGE_FILE_MACHINE_AMD64:
return IMAGE_REL_AMD64_ADDR32NB;
case IMAGE_FILE_MACHINE_ARMNT:
return IMAGE_REL_ARM_ADDR32NB;
case IMAGE_FILE_MACHINE_I386:
return IMAGE_REL_I386_DIR32NB;
}
}
template <class T> static void append(std::vector<uint8_t> &B, const T &Data) {
size_t S = B.size();
B.resize(S + sizeof(T));
memcpy(&B[S], &Data, sizeof(T));
}
static void writeStringTable(std::vector<uint8_t> &B,
ArrayRef<const std::string> Strings) {
// The COFF string table consists of a 4-byte value which is the size of the
// table, including the length field itself. This value is followed by the
// string content itself, which is an array of null-terminated C-style
// strings. The termination is important as they are referenced to by offset
// by the symbol entity in the file format.
std::vector<uint8_t>::size_type Pos = B.size();
std::vector<uint8_t>::size_type Offset = B.size();
// Skip over the length field, we will fill it in later as we will have
// computed the length while emitting the string content itself.
Pos += sizeof(uint32_t);
for (const auto &S : Strings) {
B.resize(Pos + S.length() + 1);
strcpy(reinterpret_cast<char *>(&B[Pos]), S.c_str());
Pos += S.length() + 1;
}
// Backfill the length of the table now that it has been computed.
support::ulittle32_t Length(B.size() - Offset);
memcpy(&B[Offset], &Length, sizeof(Length));
}
static std::string getImplibPath() {
if (!Config->Implib.empty())
return Config->Implib;
SmallString<128> Out = StringRef(Config->OutputFile);
sys::path::replace_extension(Out, ".lib");
return Out.str();
}
static ImportNameType getNameType(StringRef Sym, StringRef ExtName) {
if (Sym != ExtName)
return IMPORT_NAME_UNDECORATE;
if (Config->Machine == I386 && Sym.startswith("_"))
return IMPORT_NAME_NOPREFIX;
return IMPORT_NAME;
}
static std::string replace(StringRef S, StringRef From, StringRef To) {
size_t Pos = S.find(From);
assert(Pos != StringRef::npos);
return (Twine(S.substr(0, Pos)) + To + S.substr(Pos + From.size())).str();
}
static const std::string NullImportDescriptorSymbolName =
"__NULL_IMPORT_DESCRIPTOR";
namespace {
// This class constructs various small object files necessary to support linking
// symbols imported from a DLL. The contents are pretty strictly defined and
// nearly entirely static. The details of the structures files are defined in
// WINNT.h and the PE/COFF specification.
class ObjectFactory {
using u16 = support::ulittle16_t;
using u32 = support::ulittle32_t;
BumpPtrAllocator Alloc;
StringRef DLLName;
StringRef Library;
std::string ImportDescriptorSymbolName;
std::string NullThunkSymbolName;
public:
ObjectFactory(StringRef S)
: DLLName(S), Library(S.drop_back(4)),
ImportDescriptorSymbolName(("__IMPORT_DESCRIPTOR_" + Library).str()),
NullThunkSymbolName(("\x7f" + Library + "_NULL_THUNK_DATA").str()) {}
// Creates an Import Descriptor. This is a small object file which contains a
// reference to the terminators and contains the library name (entry) for the
// import name table. It will force the linker to construct the necessary
// structure to import symbols from the DLL.
NewArchiveMember createImportDescriptor(std::vector<uint8_t> &Buffer);
// Creates a NULL import descriptor. This is a small object file whcih
// contains a NULL import descriptor. It is used to terminate the imports
// from a specific DLL.
NewArchiveMember createNullImportDescriptor(std::vector<uint8_t> &Buffer);
// Create a NULL Thunk Entry. This is a small object file which contains a
// NULL Import Address Table entry and a NULL Import Lookup Table Entry. It
// is used to terminate the IAT and ILT.
NewArchiveMember createNullThunk(std::vector<uint8_t> &Buffer);
// Create a short import file which is described in PE/COFF spec 7. Import
// Library Format.
NewArchiveMember createShortImport(StringRef Sym, uint16_t Ordinal,
ImportNameType NameType, bool isData);
};
}
NewArchiveMember
ObjectFactory::createImportDescriptor(std::vector<uint8_t> &Buffer) {
static const uint32_t NumberOfSections = 2;
static const uint32_t NumberOfSymbols = 7;
static const uint32_t NumberOfRelocations = 3;
// COFF Header
coff_file_header Header{
u16(Config->Machine), u16(NumberOfSections), u32(0),
u32(sizeof(Header) + (NumberOfSections * sizeof(coff_section)) +
// .idata$2
sizeof(coff_import_directory_table_entry) +
NumberOfRelocations * sizeof(coff_relocation) +
// .idata$4
(DLLName.size() + 1)),
u32(NumberOfSymbols), u16(0),
u16(is32bit() ? IMAGE_FILE_32BIT_MACHINE : 0),
};
append(Buffer, Header);
// Section Header Table
static const coff_section SectionTable[NumberOfSections] = {
{{'.', 'i', 'd', 'a', 't', 'a', '$', '2'},
u32(0),
u32(0),
u32(sizeof(coff_import_directory_table_entry)),
u32(sizeof(coff_file_header) + NumberOfSections * sizeof(coff_section)),
u32(sizeof(coff_file_header) + NumberOfSections * sizeof(coff_section) +
sizeof(coff_import_directory_table_entry)),
u32(0),
u16(NumberOfRelocations),
u16(0),
u32(IMAGE_SCN_ALIGN_4BYTES | IMAGE_SCN_CNT_INITIALIZED_DATA |
IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE)},
{{'.', 'i', 'd', 'a', 't', 'a', '$', '6'},
u32(0),
u32(0),
u32(DLLName.size() + 1),
u32(sizeof(coff_file_header) + NumberOfSections * sizeof(coff_section) +
sizeof(coff_import_directory_table_entry) +
NumberOfRelocations * sizeof(coff_relocation)),
u32(0),
u32(0),
u16(0),
u16(0),
u32(IMAGE_SCN_ALIGN_2BYTES | IMAGE_SCN_CNT_INITIALIZED_DATA |
IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE)},
};
append(Buffer, SectionTable);
// .idata$2
static const coff_import_directory_table_entry ImportDescriptor{
u32(0), u32(0), u32(0), u32(0), u32(0),
};
append(Buffer, ImportDescriptor);
static const coff_relocation RelocationTable[NumberOfRelocations] = {
{u32(offsetof(coff_import_directory_table_entry, NameRVA)), u32(2),
u16(getImgRelRelocation())},
{u32(offsetof(coff_import_directory_table_entry, ImportLookupTableRVA)),
u32(3), u16(getImgRelRelocation())},
{u32(offsetof(coff_import_directory_table_entry, ImportAddressTableRVA)),
u32(4), u16(getImgRelRelocation())},
};
append(Buffer, RelocationTable);
// .idata$6
auto S = Buffer.size();
Buffer.resize(S + DLLName.size() + 1);
memcpy(&Buffer[S], DLLName.data(), DLLName.size());
Buffer[S + DLLName.size()] = '\0';
// Symbol Table
coff_symbol16 SymbolTable[NumberOfSymbols] = {
{{{0, 0, 0, 0, 0, 0, 0, 0}},
u32(0),
u16(1),
u16(0),
IMAGE_SYM_CLASS_EXTERNAL,
0},
{{{'.', 'i', 'd', 'a', 't', 'a', '$', '2'}},
u32(0),
u16(1),
u16(0),
IMAGE_SYM_CLASS_SECTION,
0},
{{{'.', 'i', 'd', 'a', 't', 'a', '$', '6'}},
u32(0),
u16(2),
u16(0),
IMAGE_SYM_CLASS_STATIC,
0},
{{{'.', 'i', 'd', 'a', 't', 'a', '$', '4'}},
u32(0),
u16(0),
u16(0),
IMAGE_SYM_CLASS_SECTION,
0},
{{{'.', 'i', 'd', 'a', 't', 'a', '$', '5'}},
u32(0),
u16(0),
u16(0),
IMAGE_SYM_CLASS_SECTION,
0},
{{{0, 0, 0, 0, 0, 0, 0, 0}},
u32(0),
u16(0),
u16(0),
IMAGE_SYM_CLASS_EXTERNAL,
0},
{{{0, 0, 0, 0, 0, 0, 0, 0}},
u32(0),
u16(0),
u16(0),
IMAGE_SYM_CLASS_EXTERNAL,
0},
};
reinterpret_cast<StringTableOffset &>(SymbolTable[0].Name).Offset =
sizeof(uint32_t);
reinterpret_cast<StringTableOffset &>(SymbolTable[5].Name).Offset =
sizeof(uint32_t) + ImportDescriptorSymbolName.length() + 1;
reinterpret_cast<StringTableOffset &>(SymbolTable[6].Name).Offset =
sizeof(uint32_t) + ImportDescriptorSymbolName.length() + 1 +
NullImportDescriptorSymbolName.length() + 1;
append(Buffer, SymbolTable);
// String Table
writeStringTable(Buffer,
{ImportDescriptorSymbolName, NullImportDescriptorSymbolName,
NullThunkSymbolName});
StringRef F{reinterpret_cast<const char *>(Buffer.data()), Buffer.size()};
return {MemoryBufferRef(F, DLLName)};
}
NewArchiveMember
ObjectFactory::createNullImportDescriptor(std::vector<uint8_t> &Buffer) {
static const uint32_t NumberOfSections = 1;
static const uint32_t NumberOfSymbols = 1;
// COFF Header
coff_file_header Header{
u16(Config->Machine), u16(NumberOfSections), u32(0),
u32(sizeof(Header) + (NumberOfSections * sizeof(coff_section)) +
// .idata$3
sizeof(coff_import_directory_table_entry)),
u32(NumberOfSymbols), u16(0),
u16(is32bit() ? IMAGE_FILE_32BIT_MACHINE : 0),
};
append(Buffer, Header);
// Section Header Table
static const coff_section SectionTable[NumberOfSections] = {
{{'.', 'i', 'd', 'a', 't', 'a', '$', '3'},
u32(0),
u32(0),
u32(sizeof(coff_import_directory_table_entry)),
u32(sizeof(coff_file_header) +
(NumberOfSections * sizeof(coff_section))),
u32(0),
u32(0),
u16(0),
u16(0),
u32(IMAGE_SCN_ALIGN_4BYTES | IMAGE_SCN_CNT_INITIALIZED_DATA |
IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE)},
};
append(Buffer, SectionTable);
// .idata$3
static const coff_import_directory_table_entry ImportDescriptor{
u32(0), u32(0), u32(0), u32(0), u32(0),
};
append(Buffer, ImportDescriptor);
// Symbol Table
coff_symbol16 SymbolTable[NumberOfSymbols] = {
{{{0, 0, 0, 0, 0, 0, 0, 0}},
u32(0),
u16(1),
u16(0),
IMAGE_SYM_CLASS_EXTERNAL,
0},
};
reinterpret_cast<StringTableOffset &>(SymbolTable[0].Name).Offset =
sizeof(uint32_t);
append(Buffer, SymbolTable);
// String Table
writeStringTable(Buffer, {NullImportDescriptorSymbolName});
StringRef F{reinterpret_cast<const char *>(Buffer.data()), Buffer.size()};
return {MemoryBufferRef(F, DLLName)};
}
NewArchiveMember ObjectFactory::createNullThunk(std::vector<uint8_t> &Buffer) {
static const uint32_t NumberOfSections = 2;
static const uint32_t NumberOfSymbols = 1;
uint32_t VASize = is32bit() ? 4 : 8;
// COFF Header
coff_file_header Header{
u16(Config->Machine), u16(NumberOfSections), u32(0),
u32(sizeof(Header) + (NumberOfSections * sizeof(coff_section)) +
// .idata$5
VASize +
// .idata$4
VASize),
u32(NumberOfSymbols), u16(0),
u16(is32bit() ? IMAGE_FILE_32BIT_MACHINE : 0),
};
append(Buffer, Header);
// Section Header Table
static const coff_section SectionTable[NumberOfSections] = {
{{'.', 'i', 'd', 'a', 't', 'a', '$', '5'},
u32(0),
u32(0),
u32(VASize),
u32(sizeof(coff_file_header) + NumberOfSections * sizeof(coff_section)),
u32(0),
u32(0),
u16(0),
u16(0),
u32((is32bit() ? IMAGE_SCN_ALIGN_4BYTES : IMAGE_SCN_ALIGN_8BYTES) |
IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ |
IMAGE_SCN_MEM_WRITE)},
{{'.', 'i', 'd', 'a', 't', 'a', '$', '4'},
u32(0),
u32(0),
u32(VASize),
u32(sizeof(coff_file_header) + NumberOfSections * sizeof(coff_section) +
VASize),
u32(0),
u32(0),
u16(0),
u16(0),
u32((is32bit() ? IMAGE_SCN_ALIGN_4BYTES : IMAGE_SCN_ALIGN_8BYTES) |
IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ |
IMAGE_SCN_MEM_WRITE)},
};
append(Buffer, SectionTable);
// .idata$5, ILT
append(Buffer, u32(0));
if (!is32bit())
append(Buffer, u32(0));
// .idata$4, IAT
append(Buffer, u32(0));
if (!is32bit())
append(Buffer, u32(0));
// Symbol Table
coff_symbol16 SymbolTable[NumberOfSymbols] = {
{{{0, 0, 0, 0, 0, 0, 0, 0}},
u32(0),
u16(1),
u16(0),
IMAGE_SYM_CLASS_EXTERNAL,
0},
};
reinterpret_cast<StringTableOffset &>(SymbolTable[0].Name).Offset =
sizeof(uint32_t);
append(Buffer, SymbolTable);
// String Table
writeStringTable(Buffer, {NullThunkSymbolName});
StringRef F{reinterpret_cast<const char *>(Buffer.data()), Buffer.size()};
return {MemoryBufferRef{F, DLLName}};
}
NewArchiveMember ObjectFactory::createShortImport(StringRef Sym,
uint16_t Ordinal,
ImportNameType NameType,
bool isData) {
size_t ImpSize = DLLName.size() + Sym.size() + 2; // +2 for NULs
size_t Size = sizeof(coff_import_header) + ImpSize;
char *Buf = Alloc.Allocate<char>(Size);
memset(Buf, 0, Size);
char *P = Buf;
// Write short import library.
auto *Imp = reinterpret_cast<coff_import_header *>(P);
P += sizeof(*Imp);
Imp->Sig2 = 0xFFFF;
Imp->Machine = Config->Machine;
Imp->SizeOfData = ImpSize;
if (Ordinal > 0)
Imp->OrdinalHint = Ordinal;
Imp->TypeInfo = (isData ? IMPORT_DATA : IMPORT_CODE);
Imp->TypeInfo |= NameType << 2;
// Write symbol name and DLL name.
memcpy(P, Sym.data(), Sym.size());
P += Sym.size() + 1;
memcpy(P, DLLName.data(), DLLName.size());
return {MemoryBufferRef(StringRef(Buf, Size), DLLName)};
}
// Creates an import library for a DLL. In this function, we first
// create an empty import library using lib.exe and then adds short
// import files to that file.
void lld::coff::writeImportLibrary() {
std::vector<NewArchiveMember> Members;
std::string Path = getImplibPath();
std::string DLLName = sys::path::filename(Config->OutputFile);
ObjectFactory OF(DLLName);
std::vector<uint8_t> ImportDescriptor;
Members.push_back(OF.createImportDescriptor(ImportDescriptor));
std::vector<uint8_t> NullImportDescriptor;
Members.push_back(OF.createNullImportDescriptor(NullImportDescriptor));
std::vector<uint8_t> NullThunk;
Members.push_back(OF.createNullThunk(NullThunk));
for (Export &E : Config->Exports) {
if (E.Private)
continue;
ImportNameType Type = getNameType(E.SymbolName, E.Name);
std::string Name = E.ExtName.empty()
? std::string(E.SymbolName)
: replace(E.SymbolName, E.Name, E.ExtName);
Members.push_back(OF.createShortImport(Name, E.Ordinal, Type, E.Data));
}
std::pair<StringRef, std::error_code> Result =
writeArchive(Path, Members, /*WriteSymtab*/ true, object::Archive::K_GNU,
/*Deterministic*/ true, /*Thin*/ false);
if (auto EC = Result.second)
fatal(EC, "failed to write " + Path);
}
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