Extend relocation packing to cover arm64.

tools/relocation_packer/src/elf_file.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.
 
 // ELF shared object file updates handler.
 //
-// Provides functions to remove ARM relative relocations from the .rel.dyn
-// section and pack them in .android.rel.dyn, and unpack to return the file
-// to its pre-packed state.
+// 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
-// section.  A standard libchrome.<version>.so will not contain this section,
-// so the following can be used to add one:
+// 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
-//   arm-linux-gnueabi-objcopy
-//       --add-section .android.rel.dyn=/tmp/small
-//       libchrome.<version>.so libchrome.<version>.so.packed
+//   if file libchrome.<version>.so | grep -q 'ELF 32'; then
+//     arm-linux-gnueabi-objcopy
+//         --add-section .android.rel.dyn=/tmp/small
+//         libchrome.<version>.so libchrome.<version>.so.packed
+//   else
+//     arm-linux-gnueabi-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 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.
+// 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 ARM relative relocations
-// removed from .rel.dyn, and replaced as packed data in .android.rel.dyn.
-// The resulting file is shorter than its non-packed original.
+// 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, combining the ARM relative
-// relocations with the data already in .rel.dyn, and then writing back the
-// now expanded .rel.dyn section.
+// 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 ARM relative relocations
-// between .rel.dyn and .android.rel.dyn sections.
+// 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) { memset(this, 0, sizeof(*this)); fd_ = fd; }
   ~ElfFile() {}
 
   // Set padding mode.  When padding, PackRelocations() will not shrink
-  // the .rel.dyn section, but instead replace ARM relative with
+  // the .rel.dyn or .rela.dyn section, but instead replace relative with
   // NONE-type entries.
-  // |flag| is true to pad .rel.dyn, false to shrink it.
-  inline void SetPadding(bool flag) { is_padding_rel_dyn_ = flag; }
+  // |flag| is true to pad .rel.dyn or .rela.dyn, false to shrink it.
+  inline void SetPadding(bool flag) { is_padding_relocations_ = flag; }
 
-  // Transfer ARM relative relocations from .rel.dyn to a packed
-  // representation in .android.rel.dyn.  Returns true on success.
+  // 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 ARM relative relocations from a packed representation in
-  // .android.rel.dyn to .rel.dyn.  Returns true on success.
+  // 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,
+                            Elf_Data* data);
+
+  // 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,
+                              Elf_Data* data);
+
   // Write ELF file changes.
   void Flush();
 
-  // If set, pad rather than shrink .rel.dyn.  Primarily for debugging,
-  // allows packing to be checked without affecting load addresses.
-  bool is_padding_rel_dyn_;
+  // 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_;
 
   // File descriptor opened on the shared object.
   int fd_;
 
   // Libelf handle, assigned by Load().
   Elf* elf_;
 
   // Sections that we manipulate, assigned by Load().
-  Elf_Scn* rel_dyn_section_;
+  Elf_Scn* relocations_section_;
   Elf_Scn* dynamic_section_;
-  Elf_Scn* android_rel_dyn_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_