Port Android relocation packer to chromium build

third_party/android_platform/bionic/tools/relocation_packer/src/packer.cc

+// 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 "packer.h"
+
+#include <vector>
+
+#include "debug.h"
+#include "delta_encoder.h"
+#include "elf_traits.h"
+#include "leb128.h"
+#include "sleb128.h"
+
+namespace relocation_packer {
+
+// Pack relocations into a group encoded packed representation.
+template <typename ELF>
+void RelocationPacker<ELF>::PackRelocations(const std::vector<typename ELF::Rela>& relocations,
+                                            std::vector<uint8_t>* packed) {
+  // Run-length encode.
+  std::vector<typename ELF::Addr> packed_words;
+  RelocationDeltaCodec<ELF> codec;
+  codec.Encode(relocations, &packed_words);
+
+  // If insufficient data do nothing.
+  if (packed_words.empty())
+    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
+// representation.
+template <typename ELF>
+void RelocationPacker<ELF>::UnpackRelocations(
+    const std::vector<uint8_t>& packed,
+    std::vector<typename ELF::Rela>* relocations) {
+
+  std::vector<typename ELF::Addr> packed_words;
+  CHECK(packed.size() > 4 &&
+        packed[0] == 'A' &&
+        packed[1] == 'P' &&
+        (packed[2] == 'U' || 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);
+}
+
+template class RelocationPacker<ELF32_traits>;
+template class RelocationPacker<ELF64_traits>;
+
+}  // namespace relocation_packer