Add ANDROID_DLEXT_FORCE_LOAD flag

This flag allows to force loading of the library
  in the case when for some reason multiple ELF files
  share the same filename (because the already-loaded
  library has been removed and overwritten, for example).

Change-Id: I798d44409ee13d63eaa75d685e99c4d028d2b0c1

libc/include/android/dlext.h

@@ -59,16 +59,28 @@ enum {
   /* If opening a library using library_fd read it starting at library_fd_offset.
    * This flag is only valid when ANDROID_DLEXT_USE_LIBRARY_FD is set.
    */
-
   ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET    = 0x20,
 
+  /* When set, do not check if the library has already been loaded by file stat(2)s.
+   *
+   * This flag allows forced loading of the library in the case when for some
+   * reason multiple ELF files share the same filename (because the already-loaded
+   * library has been removed and overwritten, for example).
+   *
+   * Note that if the library has the same dt_soname as an old one and some other
+   * library has the soname in DT_NEEDED list, the first one will be used to resolve any
+   * dependencies.
+   */
+  ANDROID_DLEXT_FORCE_LOAD = 0x40,
+
   /* Mask of valid bits */
   ANDROID_DLEXT_VALID_FLAG_BITS       = ANDROID_DLEXT_RESERVED_ADDRESS |
                                         ANDROID_DLEXT_RESERVED_ADDRESS_HINT |
                                         ANDROID_DLEXT_WRITE_RELRO |
                                         ANDROID_DLEXT_USE_RELRO |
                                         ANDROID_DLEXT_USE_LIBRARY_FD |
-                                        ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET,
+                                        ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET |
+                                        ANDROID_DLEXT_FORCE_LOAD,
 };
 
 typedef struct {

linker/linker.cpp

@@ -1014,16 +1014,18 @@ static soinfo* load_library(LoadTaskList& load_tasks,
   }
 
   // Check for symlink and other situations where
-  // file can have different names.
+  // file can have different names, unless ANDROID_DLEXT_FORCE_LOAD is set
-  for (soinfo* si = solist; si != nullptr; si = si->next) {
+  if (extinfo == nullptr || (extinfo->flags & ANDROID_DLEXT_FORCE_LOAD) == 0) {
-    if (si->get_st_dev() != 0 &&
+    for (soinfo* si = solist; si != nullptr; si = si->next) {
-        si->get_st_ino() != 0 &&
+      if (si->get_st_dev() != 0 &&
-        si->get_st_dev() == file_stat.st_dev &&
+          si->get_st_ino() != 0 &&
-        si->get_st_ino() == file_stat.st_ino &&
+          si->get_st_dev() == file_stat.st_dev &&
-        si->get_file_offset() == file_offset) {
+          si->get_st_ino() == file_stat.st_ino &&
-      TRACE("library \"%s\" is already loaded under different name/path \"%s\" - "
+          si->get_file_offset() == file_offset) {
-          "will return existing soinfo", name, si->name);
+        TRACE("library \"%s\" is already loaded under different name/path \"%s\" - "
-      return si;
+            "will return existing soinfo", name, si->name);
+        return si;
+      }
     }
   }
 

tests/dlext_test.cpp

@@ -173,6 +173,40 @@ TEST_F(DlExtTest, ExtInfoUseOffsetWihtoutFd) {
   ASSERT_STREQ("dlopen failed: invalid extended flag combination (ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET without ANDROID_DLEXT_USE_LIBRARY_FD): 0x20", dlerror());
 }
 
+TEST(dlext, android_dlopen_ext_force_load_smoke) {
+  // 1. Open actual file
+  void* handle = dlopen("libdlext_test.so", RTLD_NOW);
+  ASSERT_DL_NOTNULL(handle);
+  // 2. Open link with force_load flag set
+  android_dlextinfo extinfo;
+  extinfo.flags = ANDROID_DLEXT_FORCE_LOAD;
+  void* handle2 = android_dlopen_ext("libdlext_test_v2.so", RTLD_NOW, &extinfo);
+  ASSERT_DL_NOTNULL(handle2);
+  ASSERT_TRUE(handle != handle2);
+
+  dlclose(handle2);
+  dlclose(handle);
+}
+
+TEST(dlext, android_dlopen_ext_force_load_soname_exception) {
+  // Check if soname lookup still returns already loaded library
+  // when ANDROID_DLEXT_FORCE_LOAD flag is specified.
+  void* handle = dlopen("libdlext_test_v2.so", RTLD_NOW);
+  ASSERT_DL_NOTNULL(handle);
+
+  android_dlextinfo extinfo;
+  extinfo.flags = ANDROID_DLEXT_FORCE_LOAD;
+
+  // Note that 'libdlext_test.so' is dt_soname for libdlext_test_v2.so
+  void* handle2 = android_dlopen_ext("libdlext_test.so", RTLD_NOW, &extinfo);
+
+  ASSERT_DL_NOTNULL(handle2);
+  ASSERT_TRUE(handle == handle2);
+
+  dlclose(handle2);
+  dlclose(handle);
+}
+
 TEST(dlfcn, dlopen_from_zip_absolute_path) {
   const std::string lib_path = std::string(getenv("ANDROID_DATA")) + LIBZIPPATH;