Add a host tool to pack R_ARM_RELATIVE relocations in libchrome.<ver>.so.

tools/relocation_packer/src/relocation_packer_leb128.h

+// 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 R_ARM_RELATIVE relocations.
+//
+// Run-length encoded R_ARM_RELATIVE relocations consist of a large number
+// of pairs of relatively small positive integer values.  Encoding these as
+// LEB128 saves space.
+//
+// For more on LEB128 see http://en.wikipedia.org/wiki/LEB128.
+
+#ifndef RELOCATION_PACKER_LEB128_H
+#define RELOCATION_PACKER_LEB128_H
+
+#include <stdint.h>
+#include <unistd.h>
+#include <vector>
+
+namespace relocation_packer {
+
+// Encode packed words as a LEB128 byte stream.
+class Leb128Encoder {
+ public:
+  // Add a value or a vector of values to the encoding stream.
+  // |value| is the unsigned int to add.
+  void Enqueue(uint32_t value);
+  // |values| is the vector of unsigned ints to add.
+  void Enqueue(const std::vector<uint32_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_; }

[rmcilroy, 2014/06/02 15:16:35]

nit - just return the pointer rather than having an out arg.

[simonb (inactive), 2014/06/04 16:40:35]

More awkward for the current client code.

+
+ private:
+  // Growable vector holding the encoded LEB128 stream.
+  std::vector<uint8_t> encoding_;
+};
+
+// Decode a LEB128 byte stream to produce packed words.
+class Leb128Decoder {
+ public:
+  // Create a new decoder for the given encoded stream.
+  // |encoding| is the vector of encoded data.
+  Leb128Decoder(const std::vector<uint8_t>& encoding)
+      : encoding_(encoding), cursor_(0) { }
+
+  // Retrieve the next value from the encoded stream.
+  uint32_t Dequeue();
+
+  // Retrieve all remaining values from the encoded stream.
+  // |values| is the vector of decoded data.
+  void Dequeue(std::vector<uint32_t>* values);

[rmcilroy, 2014/06/02 15:16:35]

DequeueAll (and maybe EnqueueAll above) to make it clear this retrieve's all
remaining values

[simonb (inactive), 2014/06/04 16:40:35]

Done.

+
+ private:
+  // Encoded LEB128 stream.
+  std::vector<uint8_t> encoding_;
+
+  // Cursor indicating the current stream retrieval point.
+  size_t cursor_;
+};
+
+}  // namespace relocation_packer
+
+#endif  // RELOCATION_PACKER_LEB128_H