Import relocation packer from chromium repo
Bug: 18051137
Change-Id: Ia67fa11da8247e3f86f70a8ce99e6695f2c05423
diff --git a/tools/relocation_packer/src/delta_encoder.cc b/tools/relocation_packer/src/delta_encoder.cc
new file mode 100644
index 0000000..69cc91a
--- /dev/null
+++ b/tools/relocation_packer/src/delta_encoder.cc
@@ -0,0 +1,72 @@
+// 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