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llvm-mirror/tools/llvm-objcopy/MachO/MachOLayoutBuilder.cpp
Fangrui Song 37f389b2f8 [llvm-objcopy][MachO] Support LC_LINKER_OPTIMIZATION_HINT load command 
The load command is currently specific to arm64 and holds information
for instruction rewriting, e.g.  converting a GOT load to an ADR to
compute a local address.
(On ELF the information is usually conveyed by relocations, e.g.
R_X86_64_REX_GOTPCRELX, R_PPC64_TOC16_HA)

Reviewed By: alexander-shaposhnikov

Differential Revision: https://reviews.llvm.org/D104968
2021-06-29 18:47:55 -07:00

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//===- MachOLayoutBuilder.cpp -----------------------------------*- 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
//
//===----------------------------------------------------------------------===//
#include "MachOLayoutBuilder.h"
#include "llvm/Support/Alignment.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/ErrorHandling.h"
using namespace llvm;
using namespace llvm::objcopy::macho;
StringTableBuilder::Kind
MachOLayoutBuilder::getStringTableBuilderKind(const Object &O, bool Is64Bit) {
if (O.Header.FileType == MachO::HeaderFileType::MH_OBJECT)
return Is64Bit ? StringTableBuilder::MachO64 : StringTableBuilder::MachO;
return Is64Bit ? StringTableBuilder::MachO64Linked
: StringTableBuilder::MachOLinked;
}
uint32_t MachOLayoutBuilder::computeSizeOfCmds() const {
uint32_t Size = 0;
for (const LoadCommand &LC : O.LoadCommands) {
const MachO::macho_load_command &MLC = LC.MachOLoadCommand;
auto cmd = MLC.load_command_data.cmd;
switch (cmd) {
case MachO::LC_SEGMENT:
Size += sizeof(MachO::segment_command) +
sizeof(MachO::section) * LC.Sections.size();
continue;
case MachO::LC_SEGMENT_64:
Size += sizeof(MachO::segment_command_64) +
sizeof(MachO::section_64) * LC.Sections.size();
continue;
}
switch (cmd) {
#define HANDLE_LOAD_COMMAND(LCName, LCValue, LCStruct) \
case MachO::LCName: \
Size += sizeof(MachO::LCStruct) + LC.Payload.size(); \
break;
#include "llvm/BinaryFormat/MachO.def"
#undef HANDLE_LOAD_COMMAND
}
}
return Size;
}
void MachOLayoutBuilder::constructStringTable() {
for (std::unique_ptr<SymbolEntry> &Sym : O.SymTable.Symbols)
StrTableBuilder.add(Sym->Name);
StrTableBuilder.finalize();
}
void MachOLayoutBuilder::updateSymbolIndexes() {
uint32_t Index = 0;
for (auto &Symbol : O.SymTable.Symbols)
Symbol->Index = Index++;
}
// Updates the index and the number of local/external/undefined symbols.
void MachOLayoutBuilder::updateDySymTab(MachO::macho_load_command &MLC) {
assert(MLC.load_command_data.cmd == MachO::LC_DYSYMTAB);
// Make sure that nlist entries in the symbol table are sorted by the those
// types. The order is: local < defined external < undefined external.
assert(llvm::is_sorted(O.SymTable.Symbols,
[](const std::unique_ptr<SymbolEntry> &A,
const std::unique_ptr<SymbolEntry> &B) {
bool AL = A->isLocalSymbol(),
BL = B->isLocalSymbol();
if (AL != BL)
return AL;
return !AL && !A->isUndefinedSymbol() &&
B->isUndefinedSymbol();
}) &&
"Symbols are not sorted by their types.");
uint32_t NumLocalSymbols = 0;
auto Iter = O.SymTable.Symbols.begin();
auto End = O.SymTable.Symbols.end();
for (; Iter != End; ++Iter) {
if ((*Iter)->isExternalSymbol())
break;
++NumLocalSymbols;
}
uint32_t NumExtDefSymbols = 0;
for (; Iter != End; ++Iter) {
if ((*Iter)->isUndefinedSymbol())
break;
++NumExtDefSymbols;
}
MLC.dysymtab_command_data.ilocalsym = 0;
MLC.dysymtab_command_data.nlocalsym = NumLocalSymbols;
MLC.dysymtab_command_data.iextdefsym = NumLocalSymbols;
MLC.dysymtab_command_data.nextdefsym = NumExtDefSymbols;
MLC.dysymtab_command_data.iundefsym = NumLocalSymbols + NumExtDefSymbols;
MLC.dysymtab_command_data.nundefsym =
O.SymTable.Symbols.size() - (NumLocalSymbols + NumExtDefSymbols);
}
// Recomputes and updates offset and size fields in load commands and sections
// since they could be modified.
uint64_t MachOLayoutBuilder::layoutSegments() {
auto HeaderSize =
Is64Bit ? sizeof(MachO::mach_header_64) : sizeof(MachO::mach_header);
const bool IsObjectFile =
O.Header.FileType == MachO::HeaderFileType::MH_OBJECT;
uint64_t Offset = IsObjectFile ? (HeaderSize + O.Header.SizeOfCmds) : 0;
for (LoadCommand &LC : O.LoadCommands) {
auto &MLC = LC.MachOLoadCommand;
StringRef Segname;
uint64_t SegmentVmAddr;
uint64_t SegmentVmSize;
switch (MLC.load_command_data.cmd) {
case MachO::LC_SEGMENT:
SegmentVmAddr = MLC.segment_command_data.vmaddr;
SegmentVmSize = MLC.segment_command_data.vmsize;
Segname = StringRef(MLC.segment_command_data.segname,
strnlen(MLC.segment_command_data.segname,
sizeof(MLC.segment_command_data.segname)));
break;
case MachO::LC_SEGMENT_64:
SegmentVmAddr = MLC.segment_command_64_data.vmaddr;
SegmentVmSize = MLC.segment_command_64_data.vmsize;
Segname = StringRef(MLC.segment_command_64_data.segname,
strnlen(MLC.segment_command_64_data.segname,
sizeof(MLC.segment_command_64_data.segname)));
break;
default:
continue;
}
if (Segname == "__LINKEDIT") {
// We update the __LINKEDIT segment later (in layoutTail).
assert(LC.Sections.empty() && "__LINKEDIT segment has sections");
LinkEditLoadCommand = &MLC;
continue;
}
// Update file offsets and sizes of sections.
uint64_t SegOffset = Offset;
uint64_t SegFileSize = 0;
uint64_t VMSize = 0;
for (std::unique_ptr<Section> &Sec : LC.Sections) {
assert(SegmentVmAddr <= Sec->Addr &&
"Section's address cannot be smaller than Segment's one");
uint32_t SectOffset = Sec->Addr - SegmentVmAddr;
if (IsObjectFile) {
if (!Sec->hasValidOffset()) {
Sec->Offset = 0;
} else {
uint64_t PaddingSize =
offsetToAlignment(SegFileSize, Align(1ull << Sec->Align));
Sec->Offset = SegOffset + SegFileSize + PaddingSize;
Sec->Size = Sec->Content.size();
SegFileSize += PaddingSize + Sec->Size;
}
} else {
if (!Sec->hasValidOffset()) {
Sec->Offset = 0;
} else {
Sec->Offset = SegOffset + SectOffset;
Sec->Size = Sec->Content.size();
SegFileSize = std::max(SegFileSize, SectOffset + Sec->Size);
}
}
VMSize = std::max(VMSize, SectOffset + Sec->Size);
}
if (IsObjectFile) {
Offset += SegFileSize;
} else {
Offset = alignTo(Offset + SegFileSize, PageSize);
SegFileSize = alignTo(SegFileSize, PageSize);
// Use the original vmsize if the segment is __PAGEZERO.
VMSize =
Segname == "__PAGEZERO" ? SegmentVmSize : alignTo(VMSize, PageSize);
}
switch (MLC.load_command_data.cmd) {
case MachO::LC_SEGMENT:
MLC.segment_command_data.cmdsize =
sizeof(MachO::segment_command) +
sizeof(MachO::section) * LC.Sections.size();
MLC.segment_command_data.nsects = LC.Sections.size();
MLC.segment_command_data.fileoff = SegOffset;
MLC.segment_command_data.vmsize = VMSize;
MLC.segment_command_data.filesize = SegFileSize;
break;
case MachO::LC_SEGMENT_64:
MLC.segment_command_64_data.cmdsize =
sizeof(MachO::segment_command_64) +
sizeof(MachO::section_64) * LC.Sections.size();
MLC.segment_command_64_data.nsects = LC.Sections.size();
MLC.segment_command_64_data.fileoff = SegOffset;
MLC.segment_command_64_data.vmsize = VMSize;
MLC.segment_command_64_data.filesize = SegFileSize;
break;
}
}
return Offset;
}
uint64_t MachOLayoutBuilder::layoutRelocations(uint64_t Offset) {
for (LoadCommand &LC : O.LoadCommands)
for (std::unique_ptr<Section> &Sec : LC.Sections) {
Sec->RelOff = Sec->Relocations.empty() ? 0 : Offset;
Sec->NReloc = Sec->Relocations.size();
Offset += sizeof(MachO::any_relocation_info) * Sec->NReloc;
}
return Offset;
}
Error MachOLayoutBuilder::layoutTail(uint64_t Offset) {
// If we are building the layout of an executable or dynamic library
// which does not have any segments other than __LINKEDIT,
// the Offset can be equal to zero by this time. It happens because of the
// convention that in such cases the file offsets specified by LC_SEGMENT
// start with zero (unlike the case of a relocatable object file).
const uint64_t HeaderSize =
Is64Bit ? sizeof(MachO::mach_header_64) : sizeof(MachO::mach_header);
assert((!(O.Header.FileType == MachO::HeaderFileType::MH_OBJECT) ||
Offset >= HeaderSize + O.Header.SizeOfCmds) &&
"Incorrect tail offset");
Offset = std::max(Offset, HeaderSize + O.Header.SizeOfCmds);
// The order of LINKEDIT elements is as follows:
// rebase info, binding info, weak binding info, lazy binding info, export
// trie, data-in-code, symbol table, indirect symbol table, symbol table
// strings, code signature.
uint64_t NListSize = Is64Bit ? sizeof(MachO::nlist_64) : sizeof(MachO::nlist);
uint64_t StartOfLinkEdit = Offset;
uint64_t StartOfRebaseInfo = StartOfLinkEdit;
uint64_t StartOfBindingInfo = StartOfRebaseInfo + O.Rebases.Opcodes.size();
uint64_t StartOfWeakBindingInfo = StartOfBindingInfo + O.Binds.Opcodes.size();
uint64_t StartOfLazyBindingInfo =
StartOfWeakBindingInfo + O.WeakBinds.Opcodes.size();
uint64_t StartOfExportTrie =
StartOfLazyBindingInfo + O.LazyBinds.Opcodes.size();
uint64_t StartOfFunctionStarts = StartOfExportTrie + O.Exports.Trie.size();
uint64_t StartOfDataInCode =
StartOfFunctionStarts + O.FunctionStarts.Data.size();
uint64_t StartOfLinkerOptimizationHint =
StartOfDataInCode + O.DataInCode.Data.size();
uint64_t StartOfSymbols =
StartOfLinkerOptimizationHint + O.LinkerOptimizationHint.Data.size();
uint64_t StartOfIndirectSymbols =
StartOfSymbols + NListSize * O.SymTable.Symbols.size();
uint64_t StartOfSymbolStrings =
StartOfIndirectSymbols +
sizeof(uint32_t) * O.IndirectSymTable.Symbols.size();
uint64_t StartOfCodeSignature =
StartOfSymbolStrings + StrTableBuilder.getSize();
if (O.CodeSignatureCommandIndex)
StartOfCodeSignature = alignTo(StartOfCodeSignature, 16);
uint64_t LinkEditSize =
(StartOfCodeSignature + O.CodeSignature.Data.size()) - StartOfLinkEdit;
// Now we have determined the layout of the contents of the __LINKEDIT
// segment. Update its load command.
if (LinkEditLoadCommand) {
MachO::macho_load_command *MLC = LinkEditLoadCommand;
switch (LinkEditLoadCommand->load_command_data.cmd) {
case MachO::LC_SEGMENT:
MLC->segment_command_data.cmdsize = sizeof(MachO::segment_command);
MLC->segment_command_data.fileoff = StartOfLinkEdit;
MLC->segment_command_data.vmsize = alignTo(LinkEditSize, PageSize);
MLC->segment_command_data.filesize = LinkEditSize;
break;
case MachO::LC_SEGMENT_64:
MLC->segment_command_64_data.cmdsize = sizeof(MachO::segment_command_64);
MLC->segment_command_64_data.fileoff = StartOfLinkEdit;
MLC->segment_command_64_data.vmsize = alignTo(LinkEditSize, PageSize);
MLC->segment_command_64_data.filesize = LinkEditSize;
break;
}
}
for (LoadCommand &LC : O.LoadCommands) {
auto &MLC = LC.MachOLoadCommand;
auto cmd = MLC.load_command_data.cmd;
switch (cmd) {
case MachO::LC_CODE_SIGNATURE:
MLC.linkedit_data_command_data.dataoff = StartOfCodeSignature;
MLC.linkedit_data_command_data.datasize = O.CodeSignature.Data.size();
break;
case MachO::LC_SYMTAB:
MLC.symtab_command_data.symoff = StartOfSymbols;
MLC.symtab_command_data.nsyms = O.SymTable.Symbols.size();
MLC.symtab_command_data.stroff = StartOfSymbolStrings;
MLC.symtab_command_data.strsize = StrTableBuilder.getSize();
break;
case MachO::LC_DYSYMTAB: {
if (MLC.dysymtab_command_data.ntoc != 0 ||
MLC.dysymtab_command_data.nmodtab != 0 ||
MLC.dysymtab_command_data.nextrefsyms != 0 ||
MLC.dysymtab_command_data.nlocrel != 0 ||
MLC.dysymtab_command_data.nextrel != 0)
return createStringError(llvm::errc::not_supported,
"shared library is not yet supported");
if (!O.IndirectSymTable.Symbols.empty()) {
MLC.dysymtab_command_data.indirectsymoff = StartOfIndirectSymbols;
MLC.dysymtab_command_data.nindirectsyms =
O.IndirectSymTable.Symbols.size();
}
updateDySymTab(MLC);
break;
}
case MachO::LC_DATA_IN_CODE:
MLC.linkedit_data_command_data.dataoff = StartOfDataInCode;
MLC.linkedit_data_command_data.datasize = O.DataInCode.Data.size();
break;
case MachO::LC_LINKER_OPTIMIZATION_HINT:
MLC.linkedit_data_command_data.dataoff = StartOfLinkerOptimizationHint;
MLC.linkedit_data_command_data.datasize =
O.LinkerOptimizationHint.Data.size();
break;
case MachO::LC_FUNCTION_STARTS:
MLC.linkedit_data_command_data.dataoff = StartOfFunctionStarts;
MLC.linkedit_data_command_data.datasize = O.FunctionStarts.Data.size();
break;
case MachO::LC_DYLD_INFO:
case MachO::LC_DYLD_INFO_ONLY:
MLC.dyld_info_command_data.rebase_off =
O.Rebases.Opcodes.empty() ? 0 : StartOfRebaseInfo;
MLC.dyld_info_command_data.rebase_size = O.Rebases.Opcodes.size();
MLC.dyld_info_command_data.bind_off =
O.Binds.Opcodes.empty() ? 0 : StartOfBindingInfo;
MLC.dyld_info_command_data.bind_size = O.Binds.Opcodes.size();
MLC.dyld_info_command_data.weak_bind_off =
O.WeakBinds.Opcodes.empty() ? 0 : StartOfWeakBindingInfo;
MLC.dyld_info_command_data.weak_bind_size = O.WeakBinds.Opcodes.size();
MLC.dyld_info_command_data.lazy_bind_off =
O.LazyBinds.Opcodes.empty() ? 0 : StartOfLazyBindingInfo;
MLC.dyld_info_command_data.lazy_bind_size = O.LazyBinds.Opcodes.size();
MLC.dyld_info_command_data.export_off =
O.Exports.Trie.empty() ? 0 : StartOfExportTrie;
MLC.dyld_info_command_data.export_size = O.Exports.Trie.size();
break;
// Note that LC_ENCRYPTION_INFO.cryptoff despite its name and the comment in
// <mach-o/loader.h> is not an offset in the binary file, instead, it is a
// relative virtual address. At the moment modification of the __TEXT
// segment of executables isn't supported anyway (e.g. data in code entries
// are not recalculated). Moreover, in general
// LC_ENCRYPT_INFO/LC_ENCRYPTION_INFO_64 are nontrivial to update because
// without making additional assumptions (e.g. that the entire __TEXT
// segment should be encrypted) we do not know how to recalculate the
// boundaries of the encrypted part. For now just copy over these load
// commands until we encounter a real world usecase where
// LC_ENCRYPT_INFO/LC_ENCRYPTION_INFO_64 need to be adjusted.
case MachO::LC_ENCRYPTION_INFO:
case MachO::LC_ENCRYPTION_INFO_64:
case MachO::LC_LOAD_DYLINKER:
case MachO::LC_MAIN:
case MachO::LC_RPATH:
case MachO::LC_SEGMENT:
case MachO::LC_SEGMENT_64:
case MachO::LC_VERSION_MIN_MACOSX:
case MachO::LC_VERSION_MIN_IPHONEOS:
case MachO::LC_VERSION_MIN_TVOS:
case MachO::LC_VERSION_MIN_WATCHOS:
case MachO::LC_BUILD_VERSION:
case MachO::LC_ID_DYLIB:
case MachO::LC_LOAD_DYLIB:
case MachO::LC_LOAD_WEAK_DYLIB:
case MachO::LC_UUID:
case MachO::LC_SOURCE_VERSION:
case MachO::LC_THREAD:
case MachO::LC_UNIXTHREAD:
// Nothing to update.
break;
default:
// Abort if it's unsupported in order to prevent corrupting the object.
return createStringError(llvm::errc::not_supported,
"unsupported load command (cmd=0x%x)", cmd);
}
}
return Error::success();
}
Error MachOLayoutBuilder::layout() {
O.Header.NCmds = O.LoadCommands.size();
O.Header.SizeOfCmds = computeSizeOfCmds();
constructStringTable();
updateSymbolIndexes();
uint64_t Offset = layoutSegments();
Offset = layoutRelocations(Offset);
return layoutTail(Offset);
}
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