Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

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 "run_length_encoder.h"
+#include "sleb128.h"
+
+namespace relocation_packer {
+
+// Pack relative relocations into a run-length encoded packed
+// representation.
+void RelocationPacker::PackRelativeRelocations(
+    const std::vector<ELF::Rel>& relocations,
+    std::vector<uint8_t>* packed) {
+  // Run-length encode.
+  std::vector<ELF::Xword> packed_words;
+  RelocationRunLengthCodec codec;
+  codec.Encode(relocations, &packed_words);
+
+  // If insufficient data to run-length encode, do nothing.
+  if (packed_words.empty())
+    return;
+
+  // LEB128 encode, with "APR1" prefix.
+  Leb128Encoder encoder;
+  encoder.Enqueue('A');
+  encoder.Enqueue('P');
+  encoder.Enqueue('R');
+  encoder.Enqueue('1');
+  encoder.EnqueueAll(packed_words);
+
+  encoder.GetEncoding(packed);
+
+  // Pad packed to a whole number of words.  This padding will decode as
+  // LEB128 zeroes.  Run-length decoding ignores it because encoding
+  // embeds the pairs count in the stream itself.
+  while (packed->size() % sizeof(ELF::Word))
+    packed->push_back(0);
+}
+
+// Unpack relative relocations from a run-length encoded packed
+// representation.
+void RelocationPacker::UnpackRelativeRelocations(
+    const std::vector<uint8_t>& packed,
+    std::vector<ELF::Rel>* relocations) {
+  // LEB128 decode, after checking and stripping "APR1" prefix.
+  std::vector<ELF::Xword> packed_words;
+  Leb128Decoder decoder(packed);
+  CHECK(decoder.Dequeue() == 'A' &&
+        decoder.Dequeue() == 'P' &&
+        decoder.Dequeue() == 'R' &&
+        decoder.Dequeue() == '1');
+  decoder.DequeueAll(&packed_words);
+
+  // Run-length decode.
+  RelocationRunLengthCodec codec;
+  codec.Decode(packed_words, relocations);
+}
+
+// Pack relative relocations with addends into a delta encoded packed
+// representation.
+void RelocationPacker::PackRelativeRelocations(
+    const std::vector<ELF::Rela>& relocations,
+    std::vector<uint8_t>* packed) {
+  // Delta encode.
+  std::vector<ELF::Sxword> packed_words;
+  RelocationDeltaCodec codec;
+  codec.Encode(relocations, &packed_words);
+
+  // If insufficient data to delta encode, do nothing.
+  if (packed_words.empty())
+    return;
+
+  // Signed LEB128 encode, with "APA1" prefix.  ASCII does not encode as
+  // itself under signed LEB128, so we have to treat it specially.
+  Sleb128Encoder encoder;
+  encoder.EnqueueAll(packed_words);
+  std::vector<uint8_t> encoded;
+  encoder.GetEncoding(&encoded);
+
+  packed->push_back('A');
+  packed->push_back('P');
+  packed->push_back('A');
+  packed->push_back('1');
+  packed->insert(packed->end(), encoded.begin(), encoded.end());
+
+  // Pad packed to a whole number of words.  This padding will decode as
+  // signed LEB128 zeroes.  Delta decoding ignores it because encoding
+  // embeds the pairs count in the stream itself.
+  while (packed->size() % sizeof(ELF::Word))
+    packed->push_back(0);
+}
+
+// Unpack relative relocations with addends from a delta encoded
+// packed representation.
+void RelocationPacker::UnpackRelativeRelocations(
+    const std::vector<uint8_t>& packed,
+    std::vector<ELF::Rela>* relocations) {
+  // Check "APA1" prefix.
+  CHECK(packed.at(0) == 'A' &&
+        packed.at(1) == 'P' &&
+        packed.at(2) == 'A' &&
+        packed.at(3) == '1');
+
+  // Signed LEB128 decode, after stripping "APA1" prefix.
+  std::vector<ELF::Sxword> packed_words;
+  std::vector<uint8_t> stripped(packed.begin() + 4, packed.end());
+  Sleb128Decoder decoder(stripped);
+  decoder.DequeueAll(&packed_words);
+
+  // Delta decode.
+  RelocationDeltaCodec codec;
+  codec.Decode(packed_words, relocations);
+}
+
+}  // namespace relocation_packer