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// Copyright (C) 2016 The Android Open Source Project
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include "update_engine/payload_generator/xz.h"
#include <elf.h>
#include <endian.h>
#include <algorithm>
#include <7zCrc.h>
#include <Xz.h>
#include <XzEnc.h>
#include <base/logging.h>
namespace {
bool xz_initialized = false;
// An ISeqInStream implementation that reads all the data from the passed Blob.
struct BlobReaderStream : public ISeqInStream {
explicit BlobReaderStream(const brillo::Blob& data) : data_(data) {
Read = &BlobReaderStream::ReadStatic;
static SRes ReadStatic(const ISeqInStream* p, void* buf, size_t* size) {
auto* self = static_cast<BlobReaderStream*>(const_cast<ISeqInStream*>(p));
*size = std::min(*size, self->data_.size() - self->pos_);
memcpy(buf, self-> + self->pos_, *size);
self->pos_ += *size;
return SZ_OK;
const brillo::Blob& data_;
// The current reader position.
size_t pos_ = 0;
// An ISeqOutStream implementation that writes all the data to the passed Blob.
struct BlobWriterStream : public ISeqOutStream {
explicit BlobWriterStream(brillo::Blob* data) : data_(data) {
Write = &BlobWriterStream::WriteStatic;
static size_t WriteStatic(const ISeqOutStream* p,
const void* buf,
size_t size) {
auto* self = static_cast<const BlobWriterStream*>(p);
const uint8_t* buffer = reinterpret_cast<const uint8_t*>(buf);
self->data_->reserve(self->data_->size() + size);
self->data_->insert(self->data_->end(), buffer, buffer + size);
return size;
brillo::Blob* data_;
// Returns the filter id to be used to compress |data|.
// Only BCJ filter for x86 and ARM ELF file are supported, returns 0 otherwise.
int GetFilterID(const brillo::Blob& data) {
if (data.size() < sizeof(Elf32_Ehdr) ||
memcmp(, ELFMAG, SELFMAG) != 0)
return 0;
const Elf32_Ehdr* header = reinterpret_cast<const Elf32_Ehdr*>(;
// Only little-endian is supported.
if (header->e_ident[EI_DATA] != ELFDATA2LSB)
return 0;
switch (le16toh(header->e_machine)) {
case EM_386:
case EM_X86_64:
return XZ_ID_X86;
case EM_ARM:
// Both ARM and ARM Thumb instructions could be found in the same ARM ELF
// file. We choose to use the ARM Thumb filter here because testing shows
// that it usually works better than the ARM filter.
return XZ_ID_ARMT;
#ifdef EM_AARCH64
case EM_AARCH64:
// Neither the ARM nor the ARM Thumb filter works well with AArch64.
return 0;
return 0;
} // namespace
namespace chromeos_update_engine {
void XzCompressInit() {
if (xz_initialized)
xz_initialized = true;
// Although we don't include a CRC32 for the stream, the xz file header has
// a CRC32 of the header itself, which required the CRC table to be
// initialized.
bool XzCompress(const brillo::Blob& in, brillo::Blob* out) {
CHECK(xz_initialized) << "Initialize XzCompress first";
if (in.empty())
return true;
// Xz compression properties.
CXzProps props;
// No checksum in the xz stream. xz-embedded (used by the decompressor) only
// supports CRC32, but we already check the sha-1 of the whole blob during
// payload application.
props.checkId = XZ_CHECK_NO;
// LZMA2 compression properties.
CLzma2EncProps lzma2Props;
// LZMA compression "level 6" requires 9 MB of RAM to decompress in the worst
// case.
lzma2Props.lzmaProps.level = 6;
lzma2Props.lzmaProps.numThreads = 1;
// The input size data is used to reduce the dictionary size if possible.
lzma2Props.lzmaProps.reduceSize = in.size();
props.lzma2Props = lzma2Props; = GetFilterID(in);
BlobWriterStream out_writer(out);
BlobReaderStream in_reader(in);
SRes res = Xz_Encode(&out_writer, &in_reader, &props, nullptr /* progress */);
return res == SZ_OK;
} // namespace chromeos_update_engine