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Always use signed leb128 encoding

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According to runs on /system/lib there using
 unsigned leb128 does not save us any additional
 space. In order to keep packing as simple as
 possible switch to using signed leb128 for
 everything.

Bug: http://b/18051137
Change-Id: I1a47cb9eb2175895b3c3f7c13b4c6b1060de86c0
This commit is contained in:
Dmitriy Ivanov 2015-04-21 15:03:04 -07:00
parent 913fe559f6
commit f15ceeb784
11 changed files with 50 additions and 317 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
tools/relocation_packer/Android.mk
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@ -26,7 +26,6 @@ LOCAL_SRC_FILES := \
src/debug.cc \
src/delta_encoder.cc \
src/elf_file.cc \
src/leb128.cc \
src/packer.cc \
src/sleb128.cc \
@ -67,7 +66,6 @@ LOCAL_SRC_FILES := \
src/debug_unittest.cc \
src/delta_encoder_unittest.cc \
src/elf_file_unittest.cc \
src/leb128_unittest.cc \
src/sleb128_unittest.cc \
src/packer_unittest.cc \

16
tools/relocation_packer/src/elf_file.cc
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@ -190,6 +190,7 @@ bool ElfFile<ELF>::Load() {
// these; both is unsupported.
bool has_rel_relocations = false;
bool has_rela_relocations = false;
bool has_android_relocations = false;
Elf_Scn* section = NULL;
while ((section = elf_nextscn(elf, section)) != nullptr) {
@ -209,6 +210,11 @@ bool ElfFile<ELF>::Load() {
if ((name == ".rel.dyn" || name == ".rela.dyn") &&
section_header->sh_size > 0) {
found_relocations_section = section;
// Note if relocation section is already packed
has_android_relocations =
section_header->sh_type == SHT_ANDROID_REL ||
section_header->sh_type == SHT_ANDROID_RELA;
}
if (section_header->sh_offset == dynamic_program_header->p_offset) {
@ -250,6 +256,7 @@ bool ElfFile<ELF>::Load() {
relocations_section_ = found_relocations_section;
dynamic_section_ = found_dynamic_section;
relocations_type_ = has_rel_relocations ? REL : RELA;
has_android_relocations_ = has_android_relocations;
return true;
}
@ -610,10 +617,15 @@ template <typename ELF>
bool ElfFile<ELF>::PackTypedRelocations(std::vector<typename ELF::Rela>* relocations) {
typedef typename ELF::Rela Rela;
if (has_android_relocations_) {
LOG(ERROR) << "Relocation table is already packed";
return false;
}
// If no relocations then we have nothing packable. Perhaps
// the shared object has already been packed?
if (relocations->empty()) {
LOG(ERROR) << "No relocations found (already packed?)";
LOG(ERROR) << "No relocations found";
return false;
}
@ -737,7 +749,7 @@ bool ElfFile<ELF>::UnpackRelocations() {
packed.size() > 3 &&
packed[0] == 'A' &&
packed[1] == 'P' &&
(packed[2] == 'U' || packed[2] == 'S') &&
packed[2] == 'S' &&
packed[3] == '2') {
LOG(INFO) << "Relocations : " << (relocations_type_ == REL ? "REL" : "RELA");
} else {

5
tools/relocation_packer/src/elf_file.h
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@ -36,7 +36,7 @@ class ElfFile {
explicit ElfFile(int fd)
: fd_(fd), is_padding_relocations_(false), elf_(NULL),
relocations_section_(NULL), dynamic_section_(NULL),
relocations_type_(NONE) {}
relocations_type_(NONE), has_android_relocations_(false) {}
~ElfFile() {}
// Set padding mode. When padding, PackRelocations() will not shrink
@ -111,6 +111,9 @@ class ElfFile {
// Relocation type found, assigned by Load().
relocations_type_t relocations_type_;
// Elf-file has android relocations section
bool has_android_relocations_;
};
} // namespace relocation_packer

10
tools/relocation_packer/src/elf_file_unittest.cc
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@ -175,13 +175,19 @@ static void RunPackRelocationsTestFor(const std::string& arch) {
namespace relocation_packer {
TEST(ElfFile, PackRelocations) {
TEST(ElfFile, PackRelocationsArm32) {
RunPackRelocationsTestFor("arm32");
}
TEST(ElfFile, PackRelocationsArm64) {
RunPackRelocationsTestFor("arm64");
}
TEST(ElfFile, UnpackRelocations) {
TEST(ElfFile, UnpackRelocationsArm32) {
RunUnpackRelocationsTestFor("arm32");
}
TEST(ElfFile, UnpackRelocationsArm64) {
RunUnpackRelocationsTestFor("arm64");
}

87
tools/relocation_packer/src/leb128.cc
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@ -1,87 +0,0 @@
// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "leb128.h"
#include <stdint.h>
#include <vector>
#include "elf_traits.h"
namespace relocation_packer {
// Empty constructor and destructor to silence chromium-style.
template <typename uint_t>
Leb128Encoder<uint_t>::Leb128Encoder() { }
template <typename uint_t>
Leb128Encoder<uint_t>::~Leb128Encoder() { }
// Add a single value to the encoding. Values are encoded with variable
// length. The least significant 7 bits of each byte hold 7 bits of data,
// and the most significant bit is set on each byte except the last.
template <typename uint_t>
void Leb128Encoder<uint_t>::Enqueue(uint_t value) {
uint_t uvalue = static_cast<uint_t>(value);
do {
const uint8_t byte = uvalue & 127;
uvalue >>= 7;
encoding_.push_back((uvalue ? 128 : 0) | byte);
} while (uvalue);
}
// Add a vector of values to the encoding.
template <typename uint_t>
void Leb128Encoder<uint_t>::EnqueueAll(const std::vector<uint_t>& values) {
for (size_t i = 0; i < values.size(); ++i) {
Enqueue(values[i]);
}
}
// Create a new decoder for the given encoded stream.
template <typename uint_t>
Leb128Decoder<uint_t>::Leb128Decoder(const std::vector<uint8_t>& encoding, size_t start_with) {
encoding_ = encoding;
cursor_ = start_with;
}
// Empty destructor to silence chromium-style.
template <typename uint_t>
Leb128Decoder<uint_t>::~Leb128Decoder() { }
// Decode and retrieve a single value from the encoding. Read forwards until
// a byte without its most significant bit is found, then read the 7 bit
// fields of the bytes spanned to re-form the value.
template <typename uint_t>
uint_t Leb128Decoder<uint_t>::Dequeue() {
uint_t value = 0;
size_t shift = 0;
uint8_t byte;
// Loop until we reach a byte with its high order bit clear.
do {
byte = encoding_[cursor_++];
value |= static_cast<uint_t>(byte & 127) << shift;
shift += 7;
} while (byte & 128);
return value;
}
// Decode and retrieve all remaining values from the encoding.
template <typename uint_t>
void Leb128Decoder<uint_t>::DequeueAll(std::vector<uint_t>* values) {
while (cursor_ < encoding_.size()) {
values->push_back(Dequeue());
}
}
template class Leb128Encoder<uint32_t>;
template class Leb128Encoder<uint64_t>;
template class Leb128Decoder<uint32_t>;
template class Leb128Decoder<uint64_t>;
} // namespace relocation_packer

75
tools/relocation_packer/src/leb128.h
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@ -1,75 +0,0 @@
// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// LEB128 encoder and decoder for packed relative relocations.
//
// Packed relocations consist of a large number of relatively small
// integer values. Encoding these as LEB128 saves space.
//
// For more on LEB128 see http://en.wikipedia.org/wiki/LEB128.
#ifndef TOOLS_RELOCATION_PACKER_SRC_LEB128_H_
#define TOOLS_RELOCATION_PACKER_SRC_LEB128_H_
#include <stdint.h>
#include <vector>
#include "elf_traits.h"
namespace relocation_packer {
// Encode packed words as a LEB128 byte stream.
template <typename uint_t>
class Leb128Encoder {
public:
// Explicit (but empty) constructor and destructor, for chromium-style.
Leb128Encoder();
~Leb128Encoder();
// Add a value to the encoding stream.
// |value| is the unsigned int to add.
void Enqueue(uint_t value);
// Add a vector of values to the encoding stream.
// |values| is the vector of unsigned ints to add.
void EnqueueAll(const std::vector<uint_t>& values);
// Retrieve the encoded representation of the values.
// |encoding| is the returned vector of encoded data.
void GetEncoding(std::vector<uint8_t>* encoding) { *encoding = encoding_; }
private:
// Growable vector holding the encoded LEB128 stream.
std::vector<uint8_t> encoding_;
};
// Decode a LEB128 byte stream to produce packed words.
template <typename uint_t>
class Leb128Decoder {
public:
// Create a new decoder for the given encoded stream.
// |encoding| is the vector of encoded data.
explicit Leb128Decoder(const std::vector<uint8_t>& encoding, size_t start_with);
// Explicit (but empty) destructor, for chromium-style.
~Leb128Decoder();
// Retrieve the next value from the encoded stream.
uint_t Dequeue();
// Retrieve all remaining values from the encoded stream.
// |values| is the vector of decoded data.
void DequeueAll(std::vector<uint_t>* values);
private:
// Encoded LEB128 stream.
std::vector<uint8_t> encoding_;
// Cursor indicating the current stream retrieval point.
size_t cursor_;
};
} // namespace relocation_packer
#endif // TOOLS_RELOCATION_PACKER_SRC_LEB128_H_

111
tools/relocation_packer/src/leb128_unittest.cc
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@ -1,111 +0,0 @@
// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "leb128.h"
#include <vector>
#include "gtest/gtest.h"
namespace relocation_packer {
TEST(Leb128, Encoder64) {
std::vector<uint64_t> values;
values.push_back(624485);
values.push_back(0);
values.push_back(1);
values.push_back(127);
values.push_back(128);
Leb128Encoder<uint64_t> encoder;
encoder.EnqueueAll(values);
encoder.Enqueue(4294967295);
encoder.Enqueue(18446744073709551615ul);
std::vector<uint8_t> encoding;
encoder.GetEncoding(&encoding);
EXPECT_EQ(23U, encoding.size());
// 624485
EXPECT_EQ(0xe5, encoding[0]);
EXPECT_EQ(0x8e, encoding[1]);
EXPECT_EQ(0x26, encoding[2]);
// 0
EXPECT_EQ(0x00, encoding[3]);
// 1
EXPECT_EQ(0x01, encoding[4]);
// 127
EXPECT_EQ(0x7f, encoding[5]);
// 128
EXPECT_EQ(0x80, encoding[6]);
EXPECT_EQ(0x01, encoding[7]);
// 4294967295
EXPECT_EQ(0xff, encoding[8]);
EXPECT_EQ(0xff, encoding[9]);
EXPECT_EQ(0xff, encoding[10]);
EXPECT_EQ(0xff, encoding[11]);
EXPECT_EQ(0x0f, encoding[12]);
// 18446744073709551615
EXPECT_EQ(0xff, encoding[13]);
EXPECT_EQ(0xff, encoding[14]);
EXPECT_EQ(0xff, encoding[15]);
EXPECT_EQ(0xff, encoding[16]);
EXPECT_EQ(0xff, encoding[17]);
EXPECT_EQ(0xff, encoding[18]);
EXPECT_EQ(0xff, encoding[19]);
EXPECT_EQ(0xff, encoding[20]);
EXPECT_EQ(0xff, encoding[21]);
EXPECT_EQ(0x01, encoding[22]);
}
TEST(Leb128, Decoder64) {
std::vector<uint8_t> encoding;
// 624485
encoding.push_back(0xe5);
encoding.push_back(0x8e);
encoding.push_back(0x26);
// 0
encoding.push_back(0x00);
// 1
encoding.push_back(0x01);
// 127
encoding.push_back(0x7f);
// 128
encoding.push_back(0x80);
encoding.push_back(0x01);
// 4294967295
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0x0f);
// 18446744073709551615
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0xff);
encoding.push_back(0x01);
Leb128Decoder<uint64_t> decoder(encoding, 0);
EXPECT_EQ(624485U, decoder.Dequeue());
std::vector<uint64_t> dequeued;
decoder.DequeueAll(&dequeued);
EXPECT_EQ(6U, dequeued.size());
EXPECT_EQ(0U, dequeued[0]);
EXPECT_EQ(1U, dequeued[1]);
EXPECT_EQ(127U, dequeued[2]);
EXPECT_EQ(128U, dequeued[3]);
EXPECT_EQ(4294967295U, dequeued[4]);
EXPECT_EQ(18446744073709551615UL, dequeued[5]);
}
} // namespace relocation_packer

23
tools/relocation_packer/src/packer.cc
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@ -9,7 +9,6 @@
#include "debug.h"
#include "delta_encoder.h"
#include "elf_traits.h"
#include "leb128.h"
#include "sleb128.h"
namespace relocation_packer {
@ -28,32 +27,17 @@ void RelocationPacker<ELF>::PackRelocations(const std::vector<typename ELF::Rela
return;
Sleb128Encoder<typename ELF::Addr> sleb128_encoder;
Leb128Encoder<typename ELF::Addr> leb128_encoder;
std::vector<uint8_t> leb128_packed;
std::vector<uint8_t> sleb128_packed;
leb128_encoder.EnqueueAll(packed_words);
leb128_encoder.GetEncoding(&leb128_packed);
sleb128_encoder.EnqueueAll(packed_words);
sleb128_encoder.GetEncoding(&sleb128_packed);
// TODO (simonb): Estimate savings on current android system image and consider using
// one encoder for all packed relocations to reduce complexity.
if (leb128_packed.size() <= sleb128_packed.size()) {
packed->push_back('A');
packed->push_back('P');
packed->push_back('U');
packed->push_back('2');
packed->insert(packed->end(), leb128_packed.begin(), leb128_packed.end());
} else {
packed->push_back('A');
packed->push_back('P');
packed->push_back('S');
packed->push_back('2');
packed->insert(packed->end(), sleb128_packed.begin(), sleb128_packed.end());
}
}
// Unpack relative relocations from a run-length encoded packed
@ -67,16 +51,11 @@ void RelocationPacker<ELF>::UnpackRelocations(
CHECK(packed.size() > 4 &&
packed[0] == 'A' &&
packed[1] == 'P' &&
(packed[2] == 'U' || packed[2] == 'S') &&
packed[2] == 'S' &&
packed[3] == '2');
if (packed[2] == 'U') {
Leb128Decoder<typename ELF::Addr> decoder(packed, 4);
decoder.DequeueAll(&packed_words);
} else {
Sleb128Decoder<typename ELF::Addr> decoder(packed, 4);
decoder.DequeueAll(&packed_words);
}
RelocationDeltaCodec<ELF> codec;
codec.Decode(packed_words, relocations);

24
tools/relocation_packer/src/packer_unittest.cc
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@ -39,6 +39,7 @@ template <typename ELF>
static void DoPackNoAddend() {
std::vector<typename ELF::Rela> relocations;
std::vector<uint8_t> packed;
bool is_32 = sizeof(typename ELF::Addr) == 4;
// Initial relocation.
AddRelocation<ELF>(0xd1ce0000, 0x11, 0, &relocations);
// Two more relocations, 4 byte deltas.
@ -59,16 +60,16 @@ static void DoPackNoAddend() {
size_t ndx = 0;
EXPECT_EQ('A', packed[ndx++]);
EXPECT_EQ('P', packed[ndx++]);
EXPECT_EQ('U', packed[ndx++]);
EXPECT_EQ('S', packed[ndx++]);
EXPECT_EQ('2', packed[ndx++]);
// relocation count
EXPECT_EQ(6, packed[ndx++]);
// base relocation = 0xd1cdfffc -> fc, ff, b7, 8e, 0d
// base relocation = 0xd1cdfffc -> fc, ff, b7, 8e, 7d/0d (32/64bit)
EXPECT_EQ(0xfc, packed[ndx++]);
EXPECT_EQ(0xff, packed[ndx++]);
EXPECT_EQ(0xb7, packed[ndx++]);
EXPECT_EQ(0x8e, packed[ndx++]);
EXPECT_EQ(0x0d, packed[ndx++]);
EXPECT_EQ(is_32 ? 0x7d : 0x0d, packed[ndx++]);
// first group
EXPECT_EQ(3, packed[ndx++]); // size
EXPECT_EQ(3, packed[ndx++]); // flags
@ -83,8 +84,11 @@ static void DoPackNoAddend() {
EXPECT_EQ(ndx, packed.size());
}
TEST(Packer, PackNoAddend) {
TEST(Packer, PackNoAddend32) {
DoPackNoAddend<ELF32_traits>();
}
TEST(Packer, PackNoAddend64) {
DoPackNoAddend<ELF64_traits>();
}
@ -92,18 +96,19 @@ template <typename ELF>
static void DoUnpackNoAddend() {
std::vector<typename ELF::Rela> relocations;
std::vector<uint8_t> packed;
bool is_32 = sizeof(typename ELF::Addr) == 4;
packed.push_back('A');
packed.push_back('P');
packed.push_back('U');
packed.push_back('S');
packed.push_back('2');
// relocation count
packed.push_back(6);
// base relocation = 0xd1cdfffc -> fc, ff, b7, 8e, 0d
// base relocation = 0xd1cdfffc -> fc, ff, b7, 8e, 7d/0d (32/64bit)
packed.push_back(0xfc);
packed.push_back(0xff);
packed.push_back(0xb7);
packed.push_back(0x8e);
packed.push_back(0x0d);
packed.push_back(is_32 ? 0x7d : 0x0d);
// first group
packed.push_back(3); // size
packed.push_back(3); // flags
@ -131,8 +136,11 @@ static void DoUnpackNoAddend() {
EXPECT_EQ(ndx, relocations.size());
}
TEST(Packer, UnpackNoAddend) {
TEST(Packer, UnpackNoAddend32) {
DoUnpackNoAddend<ELF32_traits>();
}
TEST(Packer, UnpackNoAddend64) {
DoUnpackNoAddend<ELF64_traits>();
}

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tools/relocation_packer/test_data/elf_file_unittest_relocs_arm32_packed.so
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tools/relocation_packer/test_data/elf_file_unittest_relocs_arm64_packed.so
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