crazy linker: Disable crbug/448968 fix for all KitKat and earlier.

Disable the fix for crbug/448968 for all KitKat and earlier.

LD_PRELOADS and lookup-in-main-executable behaviour now:
  SDK earlier than L:
    nothing
  SDK L:
    load preloads, on lookup search preloads then search main
  SDK L-MR1 and later:
    on lookup search main

BUG=479220

Review URL: https://codereview.chromium.org/1100343002

Cr-Commit-Position: refs/heads/master@{#326576}

third_party/android_crazy_linker/README.chromium

@@ -72,3 +72,5 @@ Local Modifications:
 
 - Add basic LD_PRELOAD handling, for crbug/448968.
 
+- Speculative fix for crbug/479220.
+

third_party/android_crazy_linker/src/src/crazy_linker_globals.h

@@ -16,6 +16,9 @@
 
 namespace crazy {
 
+// From android.os.Build.VERSION_CODES.LOLLIPOP.
+static const int SDK_VERSION_CODE_LOLLIPOP = 21;
+
 class Globals {
  public:
   Globals();

third_party/android_crazy_linker/src/src/crazy_linker_library_list.cpp

@@ -21,9 +21,6 @@ namespace crazy {
 
 namespace {
 
-// From android.os.Build.VERSION_CODES.LOLLIPOP.
-static const int SDK_VERSION_CODE_LOLLIPOP = 21;
-
 // Page size for alignment in a zip file.
 const size_t kZipAlignmentPageSize = 4096;
 COMPILE_ASSERT(kZipAlignmentPageSize % PAGE_SIZE == 0,
@@ -64,8 +61,8 @@ struct SymbolLookupState {
 LibraryList::LibraryList() : head_(0), has_error_(false) {
   const int sdk_build_version = *Globals::GetSDKBuildVersion();
 
-  // If SDK version is Lollipop or earlier, we need to load anything
-  // listed in LD_PRELOAD explicitly, because dlsym() on the main executable
+  // If SDK version is Lollipop, we need to load anything listed in
+  // LD_PRELOAD explicitly, because dlsym() on the main executable
   // fails to lookup in preloads on those releases. Also, when doing our
   // symbol resolution we need to explicity search preloads *before* we
   // search the main executable, to ensure that preloads override symbols
@@ -79,9 +76,15 @@ LibraryList::LibraryList() : head_(0), has_error_(false) {
   // of them for us, and so by not loading preloads here our preloads list
   // remains empty, so that searching it for name lookups is a no-op.
   //
+  // If SDK version is earlier than Lollipop then we also do nothing.
+  // Pre-Lollipop platforms arguably have the same dlsym() issue, but for
+  // now we disable the dlsym() workround in order to try and address
+  // crbug/479220.
+  //
   // For more, see:
   //   https://code.google.com/p/android/issues/detail?id=74255
-  if (sdk_build_version <= SDK_VERSION_CODE_LOLLIPOP)
+  //   https://code.google.com/p/chromium/issues/detail?id=479220
+  if (sdk_build_version == SDK_VERSION_CODE_LOLLIPOP)
     LoadPreloads();
 }
 

third_party/android_crazy_linker/src/src/crazy_linker_shared_library.cpp

@@ -101,6 +101,7 @@ class SharedLibraryResolver : public ElfRelocations::SymbolResolver {
                         Vector<LibraryView*>* preloads,
                         Vector<LibraryView*>* dependencies)
       : main_program_handle_(::dlopen(NULL, RTLD_NOW)),
+        sdk_build_version_(*Globals::GetSDKBuildVersion()),
         lib_(lib), preloads_(preloads), dependencies_(dependencies) {}
 
   virtual void* Lookup(const char* symbol_name) {
@@ -116,30 +117,50 @@ class SharedLibraryResolver : public ElfRelocations::SymbolResolver {
     if (address)
       return address;
 
-    // Then look inside the preloads.
+    // Make sure that we do nothing here for non-Lollipop platforms.
+    // In practice, preloads_ will be empty (because we ignore LD_PRELOAD
+    // when not Lollipop) and searching in the main executable should be
+    // benign. But crbug/479220 is weird enough that we want to take all
+    // possible precautions.
     //
-    // Note that searching preloads *before* the main executable is opposite
-    // to the search ordering used by the system linker, but it is required
-    // to work round a dlsym() bug in some Android releases (on releases
-    // without this dlsym() bug preloads_ will be empty, making this preloads
-    // search a no-op).
+    // For more, see:
+    //   https://code.google.com/p/chromium/issues/detail?id=479220
+    if (sdk_build_version_ == SDK_VERSION_CODE_LOLLIPOP) {
+      // Then look inside the preloads.
+      //
+      // Note that searching preloads *before* the main executable is opposite
+      // to the search ordering used by the system linker, but it is required
+      // to work round a dlsym() bug in some Android releases (on releases
+      // without this dlsym() bug preloads_ will be empty, making this preloads
+      // search a no-op).
+      //
+      // For more, see commentary in LibraryList(), and
+      //   https://code.google.com/p/android/issues/detail?id=74255
+      for (size_t n = 0; n < preloads_->GetCount(); ++n) {
+        LibraryView* wrap = (*preloads_)[n];
+        // LOG("%s: Looking into preload %p (%s)\n", __FUNCTION__, wrap,
+        // wrap->GetName());
+        address = LookupInWrap(symbol_name, wrap);
+        if (address)
+          return address;
+      }
+    }
+
+    // Do not lookup inside the main executable for pre-Lollipop, for
+    // crbug/479220. We do however want to do it for Lollipop and
+    // later, because in Lollipop-mr1 the dlsym() bug is fixed, so that
+    // we don't explicitly handle LD_PRELOADS but instead rely on dlsym
+    // correctly searching preloads via the main executable.
     //
-    // For more, see commentary in LibraryList(), and
-    //   https://code.google.com/p/android/issues/detail?id=74255
-    for (size_t n = 0; n < preloads_->GetCount(); ++n) {
-      LibraryView* wrap = (*preloads_)[n];
-      // LOG("%s: Looking into preload %p (%s)\n", __FUNCTION__, wrap,
-      // wrap->GetName());
-      address = LookupInWrap(symbol_name, wrap);
+    // For more, see:
+    //   https://code.google.com/p/chromium/issues/detail?id=479220
+    if (sdk_build_version_ >= SDK_VERSION_CODE_LOLLIPOP) {
+      // Then look inside the main executable.
+      address = ::dlsym(main_program_handle_, symbol_name);
       if (address)
         return address;
     }
 
-    // Then lookup inside the main executable.
-    address = ::dlsym(main_program_handle_, symbol_name);
-    if (address)
-      return address;
-
     // Then look inside the dependencies.
     for (size_t n = 0; n < dependencies_->GetCount(); ++n) {
       LibraryView* wrap = (*dependencies_)[n];
@@ -188,6 +209,7 @@ class SharedLibraryResolver : public ElfRelocations::SymbolResolver {
     return NULL;
   }
 
+  const int sdk_build_version_;
   void* main_program_handle_;
   SharedLibrary* lib_;
   Vector<LibraryView*>* preloads_;