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//===-- clang-offload-wrapper/ClangOffloadWrapper.cpp -----------*- 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
/// \file
/// Implementation of the offload wrapper tool. It takes offload target binaries
/// as input and creates wrapper bitcode file containing target binaries
/// packaged as data. Wrapper bitcode also includes initialization code which
/// registers target binaries in offloading runtime at program startup.
#include "clang/Basic/Version.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/Triple.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/Bitcode/BitcodeWriter.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/EndianStream.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/Program.h"
#include "llvm/Support/Signals.h"
#include "llvm/Support/ToolOutputFile.h"
#include "llvm/Support/VCSRevision.h"
#include "llvm/Support/WithColor.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
#include <cassert>
#include <cstdint>
using namespace llvm;
using namespace llvm::object;
static cl::opt<bool> Help("h", cl::desc("Alias for -help"), cl::Hidden);
// Mark all our options with this category, everything else (except for -version
// and -help) will be hidden.
static cl::OptionCategory
ClangOffloadWrapperCategory("clang-offload-wrapper options");
static cl::opt<std::string> Output("o", cl::Required,
cl::desc("Output filename"),
static cl::list<std::string> Inputs(cl::Positional, cl::OneOrMore,
cl::desc("<input files>"),
static cl::opt<std::string>
Target("target", cl::Required,
cl::desc("Target triple for the output module"),
cl::value_desc("triple"), cl::cat(ClangOffloadWrapperCategory));
static cl::opt<bool> SaveTemps(
cl::desc("Save temporary files that may be produced by the tool. "
"This option forces print-out of the temporary files' names."),
static cl::opt<bool> AddOpenMPOffloadNotes(
cl::desc("Add LLVMOMPOFFLOAD ELF notes to ELF device images."), cl::Hidden);
namespace {
class BinaryWrapper {
LLVMContext C;
Module M;
StructType *EntryTy = nullptr;
StructType *ImageTy = nullptr;
StructType *DescTy = nullptr;
std::string ToolName;
std::string ObjcopyPath;
// Temporary file names that may be created during adding notes
// to ELF offload images. Use -save-temps to keep them and also
// see their names. A temporary file's name includes the name
// of the original input ELF image, so you can easily match
// them, if you have multiple inputs.
std::vector<std::string> TempFiles;
IntegerType *getSizeTTy() {
switch (M.getDataLayout().getPointerTypeSize(Type::getInt8PtrTy(C))) {
case 4u:
return Type::getInt32Ty(C);
case 8u:
return Type::getInt64Ty(C);
llvm_unreachable("unsupported pointer type size");
// struct __tgt_offload_entry {
// void *addr;
// char *name;
// size_t size;
// int32_t flags;
// int32_t reserved;
// };
StructType *getEntryTy() {
if (!EntryTy)
EntryTy = StructType::create("__tgt_offload_entry", Type::getInt8PtrTy(C),
Type::getInt8PtrTy(C), getSizeTTy(),
Type::getInt32Ty(C), Type::getInt32Ty(C));
return EntryTy;
PointerType *getEntryPtrTy() { return PointerType::getUnqual(getEntryTy()); }
// struct __tgt_device_image {
// void *ImageStart;
// void *ImageEnd;
// __tgt_offload_entry *EntriesBegin;
// __tgt_offload_entry *EntriesEnd;
// };
StructType *getDeviceImageTy() {
if (!ImageTy)
ImageTy = StructType::create("__tgt_device_image", Type::getInt8PtrTy(C),
Type::getInt8PtrTy(C), getEntryPtrTy(),
return ImageTy;
PointerType *getDeviceImagePtrTy() {
return PointerType::getUnqual(getDeviceImageTy());
// struct __tgt_bin_desc {
// int32_t NumDeviceImages;
// __tgt_device_image *DeviceImages;
// __tgt_offload_entry *HostEntriesBegin;
// __tgt_offload_entry *HostEntriesEnd;
// };
StructType *getBinDescTy() {
if (!DescTy)
DescTy = StructType::create("__tgt_bin_desc", Type::getInt32Ty(C),
getDeviceImagePtrTy(), getEntryPtrTy(),
return DescTy;
PointerType *getBinDescPtrTy() {
return PointerType::getUnqual(getBinDescTy());
/// Creates binary descriptor for the given device images. Binary descriptor
/// is an object that is passed to the offloading runtime at program startup
/// and it describes all device images available in the executable or shared
/// library. It is defined as follows
/// __attribute__((visibility("hidden")))
/// extern __tgt_offload_entry *__start_omp_offloading_entries;
/// __attribute__((visibility("hidden")))
/// extern __tgt_offload_entry *__stop_omp_offloading_entries;
/// static const char Image0[] = { <Bufs.front() contents> };
/// ...
/// static const char ImageN[] = { <Bufs.back() contents> };
/// static const __tgt_device_image Images[] = {
/// {
/// Image0, /*ImageStart*/
/// Image0 + sizeof(Image0), /*ImageEnd*/
/// __start_omp_offloading_entries, /*EntriesBegin*/
/// __stop_omp_offloading_entries /*EntriesEnd*/
/// },
/// ...
/// {
/// ImageN, /*ImageStart*/
/// ImageN + sizeof(ImageN), /*ImageEnd*/
/// __start_omp_offloading_entries, /*EntriesBegin*/
/// __stop_omp_offloading_entries /*EntriesEnd*/
/// }
/// };
/// static const __tgt_bin_desc BinDesc = {
/// sizeof(Images) / sizeof(Images[0]), /*NumDeviceImages*/
/// Images, /*DeviceImages*/
/// __start_omp_offloading_entries, /*HostEntriesBegin*/
/// __stop_omp_offloading_entries /*HostEntriesEnd*/
/// };
/// Global variable that represents BinDesc is returned.
GlobalVariable *createBinDesc(ArrayRef<ArrayRef<char>> Bufs) {
// Create external begin/end symbols for the offload entries table.
auto *EntriesB = new GlobalVariable(
M, getEntryTy(), /*isConstant*/ true, GlobalValue::ExternalLinkage,
/*Initializer*/ nullptr, "__start_omp_offloading_entries");
auto *EntriesE = new GlobalVariable(
M, getEntryTy(), /*isConstant*/ true, GlobalValue::ExternalLinkage,
/*Initializer*/ nullptr, "__stop_omp_offloading_entries");
// We assume that external begin/end symbols that we have created above will
// be defined by the linker. But linker will do that only if linker inputs
// have section with "omp_offloading_entries" name which is not guaranteed.
// So, we just create dummy zero sized object in the offload entries section
// to force linker to define those symbols.
auto *DummyInit =
ConstantAggregateZero::get(ArrayType::get(getEntryTy(), 0u));
auto *DummyEntry = new GlobalVariable(
M, DummyInit->getType(), true, GlobalVariable::ExternalLinkage,
DummyInit, "__dummy.omp_offloading.entry");
auto *Zero = ConstantInt::get(getSizeTTy(), 0u);
Constant *ZeroZero[] = {Zero, Zero};
// Create initializer for the images array.
SmallVector<Constant *, 4u> ImagesInits;
for (ArrayRef<char> Buf : Bufs) {
auto *Data = ConstantDataArray::get(C, Buf);
auto *Image = new GlobalVariable(M, Data->getType(), /*isConstant*/ true,
GlobalVariable::InternalLinkage, Data,
auto *Size = ConstantInt::get(getSizeTTy(), Buf.size());
Constant *ZeroSize[] = {Zero, Size};
auto *ImageB = ConstantExpr::getGetElementPtr(Image->getValueType(),
Image, ZeroZero);
auto *ImageE = ConstantExpr::getGetElementPtr(Image->getValueType(),
Image, ZeroSize);
ImagesInits.push_back(ConstantStruct::get(getDeviceImageTy(), ImageB,
ImageE, EntriesB, EntriesE));
// Then create images array.
auto *ImagesData = ConstantArray::get(
ArrayType::get(getDeviceImageTy(), ImagesInits.size()), ImagesInits);
auto *Images =
new GlobalVariable(M, ImagesData->getType(), /*isConstant*/ true,
GlobalValue::InternalLinkage, ImagesData,
auto *ImagesB = ConstantExpr::getGetElementPtr(Images->getValueType(),
Images, ZeroZero);
// And finally create the binary descriptor object.
auto *DescInit = ConstantStruct::get(
ConstantInt::get(Type::getInt32Ty(C), ImagesInits.size()), ImagesB,
EntriesB, EntriesE);
return new GlobalVariable(M, DescInit->getType(), /*isConstant*/ true,
GlobalValue::InternalLinkage, DescInit,
void createRegisterFunction(GlobalVariable *BinDesc) {
auto *FuncTy = FunctionType::get(Type::getVoidTy(C), /*isVarArg*/ false);
auto *Func = Function::Create(FuncTy, GlobalValue::InternalLinkage,
".omp_offloading.descriptor_reg", &M);
// Get __tgt_register_lib function declaration.
auto *RegFuncTy = FunctionType::get(Type::getVoidTy(C), getBinDescPtrTy(),
/*isVarArg*/ false);
FunctionCallee RegFuncC =
M.getOrInsertFunction("__tgt_register_lib", RegFuncTy);
// Construct function body
IRBuilder<> Builder(BasicBlock::Create(C, "entry", Func));
Builder.CreateCall(RegFuncC, BinDesc);
// Add this function to constructors.
// Set priority to 1 so that __tgt_register_lib is executed AFTER
// __tgt_register_requires (we want to know what requirements have been
// asked for before we load a libomptarget plugin so that by the time the
// plugin is loaded it can report how many devices there are which can
// satisfy these requirements).
appendToGlobalCtors(M, Func, /*Priority*/ 1);
void createUnregisterFunction(GlobalVariable *BinDesc) {
auto *FuncTy = FunctionType::get(Type::getVoidTy(C), /*isVarArg*/ false);
auto *Func = Function::Create(FuncTy, GlobalValue::InternalLinkage,
".omp_offloading.descriptor_unreg", &M);
// Get __tgt_unregister_lib function declaration.
auto *UnRegFuncTy = FunctionType::get(Type::getVoidTy(C), getBinDescPtrTy(),
/*isVarArg*/ false);
FunctionCallee UnRegFuncC =
M.getOrInsertFunction("__tgt_unregister_lib", UnRegFuncTy);
// Construct function body
IRBuilder<> Builder(BasicBlock::Create(C, "entry", Func));
Builder.CreateCall(UnRegFuncC, BinDesc);
// Add this function to global destructors.
// Match priority of __tgt_register_lib
appendToGlobalDtors(M, Func, /*Priority*/ 1);
BinaryWrapper(StringRef Target, StringRef ToolName)
: M("offload.wrapper.object", C), ToolName(ToolName) {
// Look for llvm-objcopy in the same directory, from which
// clang-offload-wrapper is invoked. This helps OpenMP offload
// LIT tests.
// This just needs to be some symbol in the binary; C++ doesn't
// allow taking the address of ::main however.
void *P = (void *)(intptr_t)&Help;
std::string COWPath = sys::fs::getMainExecutable(ToolName.str().c_str(), P);
if (!COWPath.empty()) {
auto COWDir = sys::path::parent_path(COWPath);
ErrorOr<std::string> ObjcopyPathOrErr =
sys::findProgramByName("llvm-objcopy", {COWDir});
if (ObjcopyPathOrErr) {
ObjcopyPath = *ObjcopyPathOrErr;
// Otherwise, look through PATH environment.
ErrorOr<std::string> ObjcopyPathOrErr =
if (!ObjcopyPathOrErr) {
WithColor::warning(errs(), ToolName)
<< "cannot find llvm-objcopy[.exe] in PATH; ELF notes cannot be "
ObjcopyPath = *ObjcopyPathOrErr;
~BinaryWrapper() {
if (TempFiles.empty())
StringRef ToolNameRef(ToolName);
auto warningOS = [ToolNameRef]() -> raw_ostream & {
return WithColor::warning(errs(), ToolNameRef);
for (auto &F : TempFiles) {
if (SaveTemps) {
warningOS() << "keeping temporary file " << F << "\n";
auto EC = sys::fs::remove(F, false);
if (EC)
warningOS() << "cannot remove temporary file " << F << ": "
<< EC.message().c_str() << "\n";
const Module &wrapBinaries(ArrayRef<ArrayRef<char>> Binaries) {
GlobalVariable *Desc = createBinDesc(Binaries);
assert(Desc && "no binary descriptor");
return M;
std::unique_ptr<MemoryBuffer> addELFNotes(std::unique_ptr<MemoryBuffer> Buf,
StringRef OriginalFileName) {
// Cannot add notes, if llvm-objcopy is not available.
// I did not find a clean way to add a new notes section into an existing
// ELF file. llvm-objcopy seems to recreate a new ELF from scratch,
// and we just try to use llvm-objcopy here.
if (ObjcopyPath.empty())
return Buf;
StringRef ToolNameRef(ToolName);
// Helpers to emit warnings.
auto warningOS = [ToolNameRef]() -> raw_ostream & {
return WithColor::warning(errs(), ToolNameRef);
auto handleErrorAsWarning = [&warningOS](Error E) {
logAllUnhandledErrors(std::move(E), warningOS());
Expected<std::unique_ptr<ObjectFile>> BinOrErr =
if (Error E = BinOrErr.takeError()) {
// This warning is questionable, but let it be here,
// assuming that most OpenMP offload models use ELF offload images.
warningOS() << OriginalFileName
<< " is not an ELF image, so notes cannot be added to it.\n";
return Buf;
// If we fail to add the note section, we just pass through the original
// ELF image for wrapping. At some point we should enforce the note section
// and start emitting errors vs warnings.
support::endianness Endianness;
if (isa<ELF64LEObjectFile>(BinOrErr->get()) ||
isa<ELF32LEObjectFile>(BinOrErr->get())) {
Endianness = support::little;
} else if (isa<ELF64BEObjectFile>(BinOrErr->get()) ||
isa<ELF32BEObjectFile>(BinOrErr->get())) {
Endianness = support::big;
} else {
warningOS() << OriginalFileName
<< " is an ELF image of unrecognized format.\n";
return Buf;
// Create temporary file for the data of a new SHT_NOTE section.
// We fill it in with data and then pass to llvm-objcopy invocation
// for reading.
Twine NotesFileModel = OriginalFileName + Twine(".elfnotes.%%%%%%%.tmp");
Expected<sys::fs::TempFile> NotesTemp =
if (Error E = NotesTemp.takeError()) {
handleErrorAsWarning(createFileError(NotesFileModel, std::move(E)));
return Buf;
// Create temporary file for the updated ELF image.
// This is an empty file that we pass to llvm-objcopy invocation
// for writing.
Twine ELFFileModel = OriginalFileName + Twine(".elfwithnotes.%%%%%%%.tmp");
Expected<sys::fs::TempFile> ELFTemp =
if (Error E = ELFTemp.takeError()) {
handleErrorAsWarning(createFileError(ELFFileModel, std::move(E)));
return Buf;
// Keep the new ELF image file to reserve the name for the future
// llvm-objcopy invocation.
std::string ELFTmpFileName = ELFTemp->TmpName;
if (Error E = ELFTemp->keep(ELFTmpFileName)) {
handleErrorAsWarning(createFileError(ELFTmpFileName, std::move(E)));
return Buf;
// Write notes to the *elfnotes*.tmp file.
raw_fd_ostream NotesOS(NotesTemp->FD, false);
struct NoteTy {
// Note name is a null-terminated "LLVMOMPOFFLOAD".
std::string Name;
// Note type defined in llvm/include/llvm/BinaryFormat/ELF.h.
uint32_t Type = 0;
// Each note has type-specific associated data.
std::string Desc;
NoteTy(std::string &&Name, uint32_t Type, std::string &&Desc)
: Name(std::move(Name)), Type(Type), Desc(std::move(Desc)) {}
// So far we emit just three notes.
SmallVector<NoteTy, 3> Notes;
// Version of the offload image identifying the structure of the ELF image.
// Version 1.0 does not have any specific requirements.
// We may come up with some structure that has to be honored by all
// offload implementations in future (e.g. to let libomptarget
// get some information from the offload image).
// This is a producer identification string. We are LLVM!
// This is a producer version. Use the same format that is used
// by clang to report the LLVM version.
// Return the amount of padding required for a blob of N bytes
// to be aligned to Alignment bytes.
auto getPadAmount = [](uint32_t N, uint32_t Alignment) -> uint32_t {
uint32_t Mod = (N % Alignment);
if (Mod == 0)
return 0;
return Alignment - Mod;
auto emitPadding = [&getPadAmount](raw_ostream &OS, uint32_t Size) {
for (uint32_t I = 0; I < getPadAmount(Size, 4); ++I)
OS << '\0';
// Put notes into the file.
for (auto &N : Notes) {
assert(!N.Name.empty() && "We should not create notes with empty names.");
// Name must be null-terminated.
if (N.Name.back() != '\0')
N.Name += '\0';
uint32_t NameSz = N.Name.size();
uint32_t DescSz = N.Desc.size();
// A note starts with three 4-byte values:
// NameSz
// DescSz
// Type
// These three fields are endian-sensitive.
support::endian::write<uint32_t>(NotesOS, NameSz, Endianness);
support::endian::write<uint32_t>(NotesOS, DescSz, Endianness);
support::endian::write<uint32_t>(NotesOS, N.Type, Endianness);
// Next, we have a null-terminated Name padded to a 4-byte boundary.
NotesOS << N.Name;
emitPadding(NotesOS, NameSz);
if (DescSz == 0)
// Finally, we have a descriptor, which is an arbitrary flow of bytes.
NotesOS << N.Desc;
emitPadding(NotesOS, DescSz);
// Keep the notes file.
std::string NotesTmpFileName = NotesTemp->TmpName;
if (Error E = NotesTemp->keep(NotesTmpFileName)) {
handleErrorAsWarning(createFileError(NotesTmpFileName, std::move(E)));
return Buf;
// Run llvm-objcopy like this:
// llvm-objcopy --add-section=.note.openmp=<notes-tmp-file-name> \
// <orig-file-name> <elf-tmp-file-name>
// This will add a SHT_NOTE section on top of the original ELF.
std::vector<StringRef> Args;
std::string Option("--add-section=.note.openmp=" + NotesTmpFileName);
bool ExecutionFailed = false;
std::string ErrMsg;
(void)sys::ExecuteAndWait(ObjcopyPath, Args,
/*Env=*/llvm::None, /*Redirects=*/{},
/*MemoryLimit=*/0, &ErrMsg, &ExecutionFailed);
if (ExecutionFailed) {
warningOS() << ErrMsg << "\n";
return Buf;
// Substitute the original ELF with new one.
ErrorOr<std::unique_ptr<MemoryBuffer>> BufOrErr =
if (!BufOrErr) {
createFileError(ELFTmpFileName, BufOrErr.getError()));
return Buf;
return std::move(*BufOrErr);
} // anonymous namespace
int main(int argc, const char **argv) {
cl::SetVersionPrinter([](raw_ostream &OS) {
OS << clang::getClangToolFullVersion("clang-offload-wrapper") << '\n';
argc, argv,
"A tool to create a wrapper bitcode for offload target binaries. Takes "
"offload\ntarget binaries as input and produces bitcode file containing "
"target binaries packaged\nas data and initialization code which "
"registers target binaries in offload runtime.\n");
if (Help) {
return 0;
auto reportError = [argv](Error E) {
logAllUnhandledErrors(std::move(E), WithColor::error(errs(), argv[0]));
if (Triple(Target).getArch() == Triple::UnknownArch) {
errc::invalid_argument, "'" + Target + "': unsupported target triple"));
return 1;
BinaryWrapper Wrapper(Target, argv[0]);
// Read device binaries.
SmallVector<std::unique_ptr<MemoryBuffer>, 4u> Buffers;
SmallVector<ArrayRef<char>, 4u> Images;
for (const std::string &File : Inputs) {
ErrorOr<std::unique_ptr<MemoryBuffer>> BufOrErr =
if (!BufOrErr) {
reportError(createFileError(File, BufOrErr.getError()));
return 1;
std::unique_ptr<MemoryBuffer> Buffer(std::move(*BufOrErr));
if (File != "-" && AddOpenMPOffloadNotes) {
// Adding ELF notes for STDIN is not supported yet.
Buffer = Wrapper.addELFNotes(std::move(Buffer), File);
const std::unique_ptr<MemoryBuffer> &Buf =
Images.emplace_back(Buf->getBufferStart(), Buf->getBufferSize());
// Create the output file to write the resulting bitcode to.
std::error_code EC;
ToolOutputFile Out(Output, EC, sys::fs::OF_None);
if (EC) {
reportError(createFileError(Output, EC));
return 1;
// Create a wrapper for device binaries and write its bitcode to the file.
Wrapper.wrapBinaries(makeArrayRef(, Images.size())),
if (Out.os().has_error()) {
reportError(createFileError(Output, Out.os().error()));
return 1;
// Success.
return 0;