Extend relocation packing to cover arm64.

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 ARM relative relocations into a run-length encoded packed
+// 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 ARM relative relocations from a run-length encoded packed
+// 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);
+  encoder.GetEncoding(packed);
+
+  std::vector<uint8_t> identifier;
+  identifier.push_back('A');
+  identifier.push_back('P');
+  identifier.push_back('A');
+  identifier.push_back('1');
+  packed->insert(packed->begin(), identifier.begin(), identifier.end());

[rmcilroy, 2014/07/28 10:08:44]

nit - can you insert the identifier before  sleb128 encoding the relocations?

[simonb (inactive), 2014/07/28 12:20:56]

Done.

+
+  // 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