Import relocation packer from chromium repo
Bug: 18051137
Change-Id: Ia67fa11da8247e3f86f70a8ce99e6695f2c05423
diff --git a/tools/relocation_packer/src/elf_file.h b/tools/relocation_packer/src/elf_file.h
new file mode 100644
index 0000000..6550274
--- /dev/null
+++ b/tools/relocation_packer/src/elf_file.h
@@ -0,0 +1,134 @@
+// 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.
+
+// ELF shared object file updates handler.
+//
+// Provides functions to remove relative relocations from the .rel.dyn
+// or .rela.dyn sections and pack into .android.rel.dyn or .android.rela.dyn,
+// and unpack to return the file to its pre-packed state.
+//
+// Files to be packed or unpacked must include an existing .android.rel.dyn
+// or android.rela.dyn section. A standard libchrome.<version>.so will not
+// contain this section, so the following can be used to add one:
+//
+// echo -n 'NULL' >/tmp/small
+// if file libchrome.<version>.so | grep -q 'ELF 32'; then
+// arm-linux-androideabi-objcopy
+// --add-section .android.rel.dyn=/tmp/small
+// libchrome.<version>.so libchrome.<version>.so.packed
+// else
+// aarch64-linux-android-objcopy
+// --add-section .android.rela.dyn=/tmp/small
+// libchrome.<version>.so libchrome.<version>.so.packed
+// fi
+// rm /tmp/small
+//
+// To use, open the file and pass the file descriptor to the constructor,
+// then pack or unpack as desired. Packing or unpacking will flush the file
+// descriptor on success. Example:
+//
+// int fd = open(..., O_RDWR);
+// ElfFile elf_file(fd);
+// bool status;
+// if (is_packing)
+// status = elf_file.PackRelocations();
+// else
+// status = elf_file.UnpackRelocations();
+// close(fd);
+//
+// SetPadding() causes PackRelocations() to pad .rel.dyn or .rela.dyn with
+// NONE-type entries rather than cutting a hole out of the shared object
+// file. This keeps all load addresses and offsets constant, and enables
+// easier debugging and testing.
+//
+// A packed shared object file has all of its relative relocations
+// removed from .rel.dyn or .rela.dyn, and replaced as packed data in
+// .android.rel.dyn or .android.rela.dyn respectively. The resulting file
+// is shorter than its non-packed original.
+//
+// Unpacking a packed file restores the file to its non-packed state, by
+// expanding the packed data in .android.rel.dyn or .android.rela.dyn,
+// combining the relative relocations with the data already in .rel.dyn
+// or .rela.dyn, and then writing back the now expanded section.
+
+#ifndef TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_
+#define TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_
+
+#include <string.h>
+#include <vector>
+
+#include "elf.h"
+#include "libelf.h"
+#include "packer.h"
+
+namespace relocation_packer {
+
+// An ElfFile reads shared objects, and shuttles relative relocations
+// between .rel.dyn or .rela.dyn and .android.rel.dyn or .android.rela.dyn
+// sections.
+class ElfFile {
+ public:
+ explicit ElfFile(int fd)
+ : fd_(fd), is_padding_relocations_(false), elf_(NULL),
+ relocations_section_(NULL), dynamic_section_(NULL),
+ android_relocations_section_(NULL), relocations_type_(NONE) {}
+ ~ElfFile() {}
+
+ // Set padding mode. When padding, PackRelocations() will not shrink
+ // the .rel.dyn or .rela.dyn section, but instead replace relative with
+ // NONE-type entries.
+ // |flag| is true to pad .rel.dyn or .rela.dyn, false to shrink it.
+ inline void SetPadding(bool flag) { is_padding_relocations_ = flag; }
+
+ // Transfer relative relocations from .rel.dyn or .rela.dyn to a packed
+ // representation in .android.rel.dyn or .android.rela.dyn. Returns true
+ // on success.
+ bool PackRelocations();
+
+ // Transfer relative relocations from a packed representation in
+ // .android.rel.dyn or .android.rela.dyn to .rel.dyn or .rela.dyn. Returns
+ // true on success.
+ bool UnpackRelocations();
+
+ private:
+ // Load a new ElfFile from a filedescriptor. If flushing, the file must
+ // be open for read/write. Returns true on successful ELF file load.
+ // |fd| is an open file descriptor for the shared object.
+ bool Load();
+
+ // Templated packer, helper for PackRelocations(). Rel type is one of
+ // ELF::Rel or ELF::Rela.
+ template <typename Rel>
+ bool PackTypedRelocations(const std::vector<Rel>& relocations);
+
+ // Templated unpacker, helper for UnpackRelocations(). Rel type is one of
+ // ELF::Rel or ELF::Rela.
+ template <typename Rel>
+ bool UnpackTypedRelocations(const std::vector<uint8_t>& packed);
+
+ // Write ELF file changes.
+ void Flush();
+
+ // File descriptor opened on the shared object.
+ int fd_;
+
+ // If set, pad rather than shrink .rel.dyn or .rela.dyn. Primarily for
+ // debugging, allows packing to be checked without affecting load addresses.
+ bool is_padding_relocations_;
+
+ // Libelf handle, assigned by Load().
+ Elf* elf_;
+
+ // Sections that we manipulate, assigned by Load().
+ Elf_Scn* relocations_section_;
+ Elf_Scn* dynamic_section_;
+ Elf_Scn* android_relocations_section_;
+
+ // Relocation type found, assigned by Load().
+ enum { NONE = 0, REL, RELA } relocations_type_;
+};
+
+} // namespace relocation_packer
+
+#endif // TOOLS_RELOCATION_PACKER_SRC_ELF_FILE_H_