Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

tools/relocation_packer/src/delta_encoder.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 "delta_encoder.h"
+
+#include <vector>
+
+#include "debug.h"
+#include "elf_traits.h"
+
+namespace relocation_packer {
+
+// Encode relative relocations with addends into a delta encoded (packed)
+// representation.  Represented as simple r_offset and r_addend delta pairs,
+// with an implicit neutral element at the start.
+void RelocationDeltaCodec::Encode(const std::vector<ELF::Rela>& relocations,
+                                  std::vector<ELF::Sxword>* packed) {
+  // One relocation is sufficient for delta encoding.
+  if (relocations.size() < 1)
+    return;
+
+  // Start with the element count, then append the delta pairs.
+  packed->push_back(relocations.size());
+
+  ELF::Addr offset = 0;
+  ELF::Sxword addend = 0;
+
+  for (size_t i = 0; i < relocations.size(); ++i) {
+    const ELF::Rela* relocation = &relocations[i];
+    CHECK(ELF_R_TYPE(relocation->r_info) == ELF::kRelativeRelocationCode);
+
+    packed->push_back(relocation->r_offset - offset);
+    offset = relocation->r_offset;
+    packed->push_back(relocation->r_addend - addend);
+    addend = relocation->r_addend;
+  }
+}
+
+// Decode relative relocations with addends from a delta encoded (packed)
+// representation.
+void RelocationDeltaCodec::Decode(const std::vector<ELF::Sxword>& packed,
+                                  std::vector<ELF::Rela>* relocations) {
+  // We need at least one packed pair after the packed pair count to be
+  // able to unpack.
+  if (packed.size() < 3)
+    return;
+
+  // Ensure that the packed data offers enough pairs.  There may be zero
+  // padding on it that we ignore.
+  CHECK(static_cast<size_t>(packed[0]) <= (packed.size() - 1) >> 1);
+
+  ELF::Addr offset = 0;
+  ELF::Sxword addend = 0;
+
+  // The first packed vector element is the pairs count.  Start uncondensing
+  // pairs at the second, and finish at the end of the pairs data.
+  const size_t pairs_count = packed[0];
+  for (size_t i = 1; i < 1 + (pairs_count << 1); i += 2) {
+    offset += packed[i];
+    addend += packed[i + 1];
+
+    // Generate a relocation for this offset and addend pair.
+    ELF::Rela relocation;
+    relocation.r_offset = offset;
+    relocation.r_info = ELF_R_INFO(0, ELF::kRelativeRelocationCode);
+    relocation.r_addend = addend;
+    relocations->push_back(relocation);
+  }
+}
+
+}  // namespace relocation_packer