Split .oat_patches to multiple sections.

.oat_patches section currently contains encoded patch locations for
several other sections. Split it to several sections - one for each
of the destination sections. For example, .text.oat_patches section
contains patch locations for the .text section.

This ensures that if we strip some the sections using standard
tools, we strip the corresponding .oat_patches section as well.

It also makes the overall design simpler.
I should have done it this way in the first place.

Since ApplyOatPatches has been simplified and uses unaligned memory
access, this also fixes bug 21403573.

Bug:20556771
Bug:21403573
Change-Id: Iae7c423911507b524eec500e8d61744046fcd3ba
diff --git a/compiler/oat_writer.h b/compiler/oat_writer.h
index 6f1b4ec..82b9377 100644
--- a/compiler/oat_writer.h
+++ b/compiler/oat_writer.h
@@ -19,7 +19,6 @@
 
 #include <stdint.h>
 #include <cstddef>
-#include <map>
 #include <memory>
 
 #include "linker/relative_patcher.h"  // For linker::RelativePatcherTargetProvider.
@@ -82,8 +81,6 @@
 //
 class OatWriter {
  public:
-  typedef std::map<std::string, std::unique_ptr<std::vector<uintptr_t>>> PatchLocationsMap;
-
   OatWriter(const std::vector<const DexFile*>& dex_files,
             uint32_t image_file_location_oat_checksum,
             uintptr_t image_file_location_oat_begin,
@@ -105,19 +102,10 @@
     return bss_size_;
   }
 
-  const PatchLocationsMap& GetAbsolutePatchLocations() const {
+  const std::vector<uintptr_t>& GetAbsolutePatchLocations() const {
     return absolute_patch_locations_;
   }
 
-  std::vector<uintptr_t>* GetAbsolutePatchLocationsFor(const char* section_name) {
-    auto it = absolute_patch_locations_.emplace(
-        std::string(section_name), std::unique_ptr<std::vector<uintptr_t>>());
-    if (it.second) {  // Inserted new item.
-      it.first->second.reset(new std::vector<uintptr_t>());
-    }
-    return it.first->second.get();
-  }
-
   bool WriteRodata(OutputStream* out);
   bool WriteCode(OutputStream* out);
 
@@ -339,9 +327,8 @@
 
   std::unique_ptr<linker::RelativePatcher> relative_patcher_;
 
-  // The locations of absolute patches relative to the start of section.
-  // The map's key is the ELF's section name (including the dot).
-  PatchLocationsMap absolute_patch_locations_;
+  // The locations of absolute patches relative to the start of the executable section.
+  std::vector<uintptr_t> absolute_patch_locations_;
 
   // Map method reference to assigned offset.
   // Wrap the map in a class implementing linker::RelativePatcherTargetProvider.