diff --git a/libc/bionic/grp_pwd.cpp b/libc/bionic/grp_pwd.cpp
index bd5c27d..d37fadd 100644
--- a/libc/bionic/grp_pwd.cpp
+++ b/libc/bionic/grp_pwd.cpp
@@ -26,6 +26,8 @@
  * SUCH DAMAGE.
  */
 
+#include "private/grp_pwd.h"
+
 #include <android/api-level.h>
 #include <ctype.h>
 #include <errno.h>
@@ -37,12 +39,12 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/system_properties.h>
+#include <sys/types.h>
 #include <unistd.h>
 
+#include "private/ErrnoRestorer.h"
 #include "private/android_filesystem_config.h"
 #include "private/bionic_macros.h"
-#include "private/grp_pwd.h"
-#include "private/ErrnoRestorer.h"
 
 // Generated android_ids array
 #include "generated_android_ids.h"
@@ -127,10 +129,17 @@
 // These are a list of the reserved app ranges, and should never contain anything below
 // AID_APP_START.  They exist per user, so a given uid/gid modulo AID_USER_OFFSET will map
 // to these ranges.
-static constexpr struct {
-  uid_t start;
-  uid_t end;
-} user_ranges[] = {
+struct IdRange {
+  id_t start;
+  id_t end;
+};
+
+static constexpr IdRange user_ranges[] = {
+  { AID_APP_START, AID_APP_END },
+  { AID_ISOLATED_START, AID_ISOLATED_END },
+};
+
+static constexpr IdRange group_ranges[] = {
   { AID_APP_START, AID_APP_END },
   { AID_CACHE_GID_START, AID_CACHE_GID_END },
   { AID_EXT_GID_START, AID_EXT_GID_END },
@@ -139,22 +148,40 @@
   { AID_ISOLATED_START, AID_ISOLATED_END },
 };
 
-static constexpr bool verify_user_ranges_ascending() {
-  auto array_size = arraysize(user_ranges);
+template <class T, size_t N>
+static constexpr bool verify_user_ranges_ascending(T (&ranges)[N]) {
+  auto array_size = N;
   if (array_size < 2) return false;
 
-  if (user_ranges[0].start > user_ranges[0].end) return false;
+  if (ranges[0].start > ranges[0].end) return false;
 
   for (size_t i = 1; i < array_size; ++i) {
-    if (user_ranges[i].start > user_ranges[i].end) return false;
-    if (user_ranges[i - 1].end > user_ranges[i].start) return false;
+    if (ranges[i].start > ranges[i].end) return false;
+    if (ranges[i - 1].end > ranges[i].start) return false;
   }
   return true;
 }
 
-static_assert(verify_user_ranges_ascending(), "user_ranges must have ascending ranges");
+static_assert(verify_user_ranges_ascending(user_ranges), "user_ranges must have ascending ranges");
+static_assert(verify_user_ranges_ascending(group_ranges), "user_ranges must have ascending ranges");
 
-static bool is_valid_app_id(id_t id) {
+// This list comes from PackageManagerService.java, where platform AIDs are added to list of valid
+// AIDs for packages via addSharedUserLPw().
+static constexpr const id_t secondary_user_platform_ids[] = {
+  AID_SYSTEM, AID_RADIO,          AID_LOG,           AID_NFC, AID_BLUETOOTH,
+  AID_SHELL,  AID_SECURE_ELEMENT, AID_NETWORK_STACK,
+};
+
+static bool platform_id_secondary_user_allowed(id_t id) {
+  for (const auto& allowed_id : secondary_user_platform_ids) {
+    if (allowed_id == id) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool is_valid_app_id(id_t id, bool is_group) {
   id_t appid = id % AID_USER_OFFSET;
 
   // AID_OVERFLOWUID is never a valid app id, so we explicitly return false to ensure this.
@@ -163,15 +190,23 @@
     return false;
   }
 
-  // If we've resolved to something before app_start, we have already checked against
-  // android_ids, so no need to check again.
-  if (appid < user_ranges[0].start) {
+  auto ranges_size = is_group ? arraysize(group_ranges) : arraysize(user_ranges);
+  auto ranges = is_group ? group_ranges : user_ranges;
+
+  // If we're checking an appid that resolves below the user range, then it's a platform AID for a
+  // seconary user. We only allow a reduced set of these, so we must check that it is allowed.
+  if (appid < ranges[0].start && platform_id_secondary_user_allowed(appid)) {
     return true;
   }
 
+  // The shared GID range is only valid for the first user.
+  if (appid >= AID_SHARED_GID_START && appid <= AID_SHARED_GID_END && appid != id) {
+    return false;
+  }
+
   // Otherwise check that the appid is in one of the reserved ranges.
-  for (size_t i = 0; i < arraysize(user_ranges); ++i) {
-    if (appid >= user_ranges[i].start && appid <= user_ranges[i].end) {
+  for (size_t i = 0; i < ranges_size; ++i) {
+    if (appid >= ranges[i].start && appid <= ranges[i].end) {
       return true;
     }
   }
@@ -180,26 +215,29 @@
 }
 
 // This provides an iterater for app_ids within the first user's app id's.
-static uid_t get_next_app_id(uid_t current_id) {
-  // If current_id is below the first of the user_ranges, then we're uninitialized, and return the
-  // first valid id.
-  if (current_id < user_ranges[0].start) {
-    return user_ranges[0].start;
+static id_t get_next_app_id(id_t current_id, bool is_group) {
+  auto ranges_size = is_group ? arraysize(group_ranges) : arraysize(user_ranges);
+  auto ranges = is_group ? group_ranges : user_ranges;
+
+  // If current_id is below the first of the ranges, then we're uninitialized, and return the first
+  // valid id.
+  if (current_id < ranges[0].start) {
+    return ranges[0].start;
   }
 
-  uid_t incremented_id = current_id + 1;
+  id_t incremented_id = current_id + 1;
 
   // Check to see if our incremented_id is between two ranges, and if so, return the beginning of
   // the next valid range.
-  for (size_t i = 1; i < arraysize(user_ranges); ++i) {
-    if (incremented_id > user_ranges[i - 1].end && incremented_id < user_ranges[i].start) {
-      return user_ranges[i].start;
+  for (size_t i = 1; i < ranges_size; ++i) {
+    if (incremented_id > ranges[i - 1].end && incremented_id < ranges[i].start) {
+      return ranges[i].start;
     }
   }
 
   // Check to see if our incremented_id is above final range, and return -1 to indicate that we've
   // completed if so.
-  if (incremented_id > user_ranges[arraysize(user_ranges) - 1].end) {
+  if (incremented_id > ranges[ranges_size - 1].end) {
     return -1;
   }
 
@@ -209,6 +247,8 @@
 
 // Translate a user/group name to the corresponding user/group id.
 // all_a1234 -> 0 * AID_USER_OFFSET + AID_SHARED_GID_START + 1234 (group name only)
+// u0_a1234_ext_cache -> 0 * AID_USER_OFFSET + AID_EXT_CACHE_GID_START + 1234 (group name only)
+// u0_a1234_ext -> 0 * AID_USER_OFFSET + AID_EXT_GID_START + 1234 (group name only)
 // u0_a1234_cache -> 0 * AID_USER_OFFSET + AID_CACHE_GID_START + 1234 (group name only)
 // u0_a1234 -> 0 * AID_USER_OFFSET + AID_APP_START + 1234
 // u2_i1000 -> 2 * AID_USER_OFFSET + AID_ISOLATED_START + 1000
@@ -247,9 +287,19 @@
     } else {
       // end will point to \0 if the strtoul below succeeds.
       appid = strtoul(end+2, &end, 10);
-      if (is_group && !strcmp(end, "_cache")) {
-        end += 6;
-        appid += AID_CACHE_GID_START;
+      if (is_group) {
+        if (!strcmp(end, "_ext_cache")) {
+          end += 10;
+          appid += AID_EXT_CACHE_GID_START;
+        } else if (!strcmp(end, "_ext")) {
+          end += 4;
+          appid += AID_EXT_GID_START;
+        } else if (!strcmp(end, "_cache")) {
+          end += 6;
+          appid += AID_CACHE_GID_START;
+        } else {
+          appid += AID_APP_START;
+        }
       } else {
         appid += AID_APP_START;
       }
@@ -260,6 +310,10 @@
   } else if (auto* android_id_info = find_android_id_info(end + 1); android_id_info != nullptr) {
     appid = android_id_info->aid;
     end += strlen(android_id_info->name) + 1;
+    if (!platform_id_secondary_user_allowed(appid)) {
+      errno = ENOENT;
+      return 0;
+    }
   }
 
   // Check that the entire string was consumed by one of the 3 cases above.
@@ -304,6 +358,10 @@
     snprintf(buffer, bufferlen, "u%u_i%u", userid, appid - AID_ISOLATED_START);
   } else if (userid == 0 && appid >= AID_SHARED_GID_START && appid <= AID_SHARED_GID_END) {
     snprintf(buffer, bufferlen, "all_a%u", appid - AID_SHARED_GID_START);
+  } else if (appid >= AID_EXT_CACHE_GID_START && appid <= AID_EXT_CACHE_GID_END) {
+    snprintf(buffer, bufferlen, "u%u_a%u_ext_cache", userid, appid - AID_EXT_CACHE_GID_START);
+  } else if (appid >= AID_EXT_GID_START && appid <= AID_EXT_GID_END) {
+    snprintf(buffer, bufferlen, "u%u_a%u_ext", userid, appid - AID_EXT_GID_START);
   } else if (appid >= AID_CACHE_GID_START && appid <= AID_CACHE_GID_END) {
     snprintf(buffer, bufferlen, "u%u_a%u_cache", userid, appid - AID_CACHE_GID_START);
   } else if (appid < AID_APP_START) {
@@ -405,7 +463,7 @@
 // AID_USER_OFFSET+                        -> u1_radio, u1_a1234, u2_i1234, etc.
 // returns a passwd structure (sets errno to ENOENT on failure).
 static passwd* app_id_to_passwd(uid_t uid, passwd_state_t* state) {
-  if (uid < AID_APP_START || !is_valid_app_id(uid)) {
+  if (uid < AID_APP_START || !is_valid_app_id(uid, false)) {
     errno = ENOENT;
     return nullptr;
   }
@@ -430,7 +488,7 @@
 // Translate a gid into the corresponding app_<gid>
 // group structure (sets errno to ENOENT on failure).
 static group* app_id_to_group(gid_t gid, group_state_t* state) {
-  if (gid < AID_APP_START || !is_valid_app_id(gid)) {
+  if (gid < AID_APP_START || !is_valid_app_id(gid, true)) {
     errno = ENOENT;
     return nullptr;
   }
@@ -575,7 +633,7 @@
         state->getpwent_idx++ - start + AID_OEM_RESERVED_2_START, state);
   }
 
-  state->getpwent_idx = get_next_app_id(state->getpwent_idx);
+  state->getpwent_idx = get_next_app_id(state->getpwent_idx, false);
 
   if (state->getpwent_idx != -1) {
     return app_id_to_passwd(state->getpwent_idx, state);
@@ -698,7 +756,7 @@
   start = end;
   end += AID_USER_OFFSET - AID_APP_START; // Do not expose higher groups
 
-  state->getgrent_idx = get_next_app_id(state->getgrent_idx);
+  state->getgrent_idx = get_next_app_id(state->getgrent_idx, true);
 
   if (state->getgrent_idx != -1) {
     return app_id_to_group(state->getgrent_idx, state);
diff --git a/tests/grp_pwd_test.cpp b/tests/grp_pwd_test.cpp
index ebc357c..5b6eed8 100644
--- a/tests/grp_pwd_test.cpp
+++ b/tests/grp_pwd_test.cpp
@@ -46,6 +46,8 @@
 using android::base::Split;
 using android::base::StartsWith;
 
+using namespace std::literals;
+
 enum uid_type_t {
   TYPE_APP,
   TYPE_SYSTEM,
@@ -130,12 +132,41 @@
 
 static void check_get_passwd(const char* username, uid_t uid, uid_type_t uid_type,
                              bool check_username = true) {
+  SCOPED_TRACE("username '"s + username + "'");
   check_getpwuid(username, uid, uid_type, check_username);
   check_getpwnam(username, uid, uid_type, check_username);
   check_getpwuid_r(username, uid, uid_type, check_username);
   check_getpwnam_r(username, uid, uid_type, check_username);
 }
 
+static void expect_no_passwd_id(uid_t uid) {
+  SCOPED_TRACE("uid '" + std::to_string(uid) + "'");
+  errno = 0;
+  passwd* passwd = nullptr;
+  passwd = getpwuid(uid);
+  EXPECT_EQ(nullptr, passwd) << "name = '" << passwd->pw_name << "'";
+  EXPECT_EQ(ENOENT, errno);
+
+  struct passwd passwd_storage;
+  char buf[512];
+  EXPECT_EQ(ENOENT, getpwuid_r(uid, &passwd_storage, buf, sizeof(buf), &passwd));
+  EXPECT_EQ(nullptr, passwd) << "name = '" << passwd->pw_name << "'";
+}
+
+static void expect_no_passwd_name(const char* username) {
+  SCOPED_TRACE("username '"s + username + "'");
+  errno = 0;
+  passwd* passwd = nullptr;
+  passwd = getpwnam(username);
+  EXPECT_EQ(nullptr, passwd) << "name = '" << passwd->pw_name << "'";
+  EXPECT_EQ(ENOENT, errno);
+
+  struct passwd passwd_storage;
+  char buf[512];
+  EXPECT_EQ(ENOENT, getpwnam_r(username, &passwd_storage, buf, sizeof(buf), &passwd));
+  EXPECT_EQ(nullptr, passwd) << "name = '" << passwd->pw_name << "'";
+}
+
 #else // !defined(__BIONIC__)
 
 static void check_get_passwd(const char* /* username */, uid_t /* uid */, uid_type_t /* uid_type */,
@@ -147,75 +178,124 @@
   GTEST_SKIP() << "bionic-only test";
 }
 
+static void expect_no_passwd_id(uid_t /* uid */) {
+  GTEST_SKIP() << "bionic-only test";
+}
+
+static void expect_no_passwd_name(const char* /* username */) {
+  GTEST_SKIP() << "bionic-only test";
+}
+
 #endif
 
-TEST(pwd, getpwnam_system_id_root) {
+TEST(pwd, getpwnam_platform_ids) {
   check_get_passwd("root", 0, TYPE_SYSTEM);
-}
+  check_get_passwd("daemon", 1, TYPE_SYSTEM);
+  check_get_passwd("bin", 2, TYPE_SYSTEM);
 
-TEST(pwd, getpwnam_system_id_system) {
   check_get_passwd("system", 1000, TYPE_SYSTEM);
-}
-
-TEST(pwd, getpwnam_app_id_radio) {
   check_get_passwd("radio", 1001, TYPE_SYSTEM);
-}
 
-TEST(pwd, getpwnam_oem_id_5000) {
-  check_get_passwd("oem_5000", 5000, TYPE_VENDOR, false);
-}
+  check_get_passwd("shell", 2000, TYPE_SYSTEM);
 
-TEST(pwd, getpwnam_oem_id_5999) {
-  check_get_passwd("oem_5999", 5999, TYPE_VENDOR, false);
-}
-
-TEST(pwd, getpwnam_oem_id_2900) {
-  check_get_passwd("oem_2900", 2900, TYPE_VENDOR, false);
-}
-
-TEST(pwd, getpwnam_oem_id_2999) {
-  check_get_passwd("oem_2999", 2999, TYPE_VENDOR, false);
-}
-
-TEST(pwd, getpwnam_app_id_nobody) {
   check_get_passwd("nobody", 9999, TYPE_SYSTEM);
 }
 
-TEST(pwd, getpwnam_app_id_u0_a0) {
+TEST(pwd, getpwnam_oem_ids) {
+  check_get_passwd("oem_2900", 2900, TYPE_VENDOR, false);
+  check_get_passwd("oem_2945", 2945, TYPE_VENDOR, false);
+  check_get_passwd("oem_2999", 2999, TYPE_VENDOR, false);
+  check_get_passwd("oem_5000", 5000, TYPE_VENDOR, false);
+  check_get_passwd("oem_5454", 5454, TYPE_VENDOR, false);
+  check_get_passwd("oem_5999", 5999, TYPE_VENDOR, false);
+}
+
+TEST(pwd, getpwnam_non_exist) {
+  expect_no_passwd_id(999);   // End of the system reserved range, unallocated.
+  expect_no_passwd_id(1999);  // End of the system reserved range, unallocated.
+  expect_no_passwd_id(2899);  // End of the system reserved range, unallocated.
+
+  // These ranges are for GIDs only.
+  expect_no_passwd_id(20000);
+  expect_no_passwd_id(30000);
+  expect_no_passwd_id(40000);
+  expect_no_passwd_id(50000);
+
+  // These should not be parsed as users, only as groups.
+  expect_no_passwd_name("u0_a9999_cache");
+  expect_no_passwd_name("u0_a9999_ext");
+  expect_no_passwd_name("u0_a9999_ext_cache");
+  expect_no_passwd_name("all_a9999");
+}
+
+TEST(pwd, getpwnam_u0_app_ids) {
   check_get_passwd("u0_a0", 10000, TYPE_APP);
-}
-
-TEST(pwd, getpwnam_app_id_u0_a1234) {
   check_get_passwd("u0_a1234", 11234, TYPE_APP);
-}
+  check_get_passwd("u0_a9999", 19999, TYPE_APP);
 
-// Test the difference between uid and shared gid.
-TEST(pwd, getpwnam_app_id_u0_a49999) {
-  check_get_passwd("u0_a49999", 59999, TYPE_APP);
-}
-
-TEST(pwd, getpwnam_app_id_u0_i1) {
   check_get_passwd("u0_i1", 90001, TYPE_APP);
+  check_get_passwd("u0_i4545", 94545, TYPE_APP);
+  check_get_passwd("u0_i9999", 99999, TYPE_APP);
 }
 
-TEST(pwd, getpwnam_app_id_u1_root) {
-  check_get_passwd("u1_root", 100000, TYPE_SYSTEM);
-}
-
-TEST(pwd, getpwnam_app_id_u1_radio) {
+TEST(pwd, getpwnam_app_id_u1_ids) {
+  check_get_passwd("u1_system", 101000, TYPE_SYSTEM);
   check_get_passwd("u1_radio", 101001, TYPE_SYSTEM);
-}
 
-TEST(pwd, getpwnam_app_id_u1_a0) {
   check_get_passwd("u1_a0", 110000, TYPE_APP);
+  check_get_passwd("u1_a1234", 111234, TYPE_APP);
+  check_get_passwd("u1_a9999", 119999, TYPE_APP);
+
+  check_get_passwd("u1_i1", 190001, TYPE_APP);
+  check_get_passwd("u1_i4545", 194545, TYPE_APP);
+  check_get_passwd("u1_i9999", 199999, TYPE_APP);
 }
 
-TEST(pwd, getpwnam_app_id_u1_a40000) {
-  check_get_passwd("u1_a40000", 150000, TYPE_APP);
+TEST(pwd, getpwnam_app_id_u31_ids) {
+  check_get_passwd("u31_system", 3101000, TYPE_SYSTEM);
+  check_get_passwd("u31_radio", 3101001, TYPE_SYSTEM);
+
+  check_get_passwd("u31_a0", 3110000, TYPE_APP);
+  check_get_passwd("u31_a1234", 3111234, TYPE_APP);
+  check_get_passwd("u31_a9999", 3119999, TYPE_APP);
+
+  check_get_passwd("u31_i1", 3190001, TYPE_APP);
+  check_get_passwd("u31_i4545", 3194545, TYPE_APP);
+  check_get_passwd("u31_i9999", 3199999, TYPE_APP);
 }
 
-TEST(pwd, getpwnam_app_id_u1_i0) {
-  check_get_passwd("u1_i0", 190000, TYPE_APP);
+TEST(pwd, getpwnam_app_id_not_allowed_platform) {
+  expect_no_passwd_name("u1_root");
+  expect_no_passwd_name("u1_debuggerd");
+
+  expect_no_passwd_name("u31_root");
+  expect_no_passwd_name("u31_debuggerd");
+}
+
+TEST(pwd, getpwuid_app_id_u1_non_exist) {
+  expect_no_passwd_id(100000);  // There is no 'root' for secondary users.
+  expect_no_passwd_id(101999);  // End of the system reserved range, unallocated.
+  expect_no_passwd_id(102900);  // The OEM ranges were never allocated to secondary users.
+  expect_no_passwd_id(105000);  // The OEM ranges were never allocated to secondary users.
+
+  // These ranges are for GIDs only.
+  expect_no_passwd_id(120000);
+  expect_no_passwd_id(130000);
+  expect_no_passwd_id(140000);
+  expect_no_passwd_id(150000);
+}
+
+TEST(pwd, getpwuid_app_id_u31_non_exist) {
+  expect_no_passwd_id(3100000);  // There is no 'root' for secondary users.
+  expect_no_passwd_id(3101999);  // End of the system reserved range, unallocated.
+  expect_no_passwd_id(3102900);  // The OEM ranges were never allocated to secondary users.
+  expect_no_passwd_id(3105000);  // The OEM ranges were never allocated to secondary users.
+
+  // These ranges are for GIDs only.
+  expect_no_passwd_id(3120000);
+  expect_no_passwd_id(3130000);
+  expect_no_passwd_id(3140000);
+  expect_no_passwd_id(3150000);
 }
 
 TEST(pwd, getpwnam_r_alignment) {
@@ -302,7 +382,7 @@
 
 #if defined(__BIONIC__)
 template <typename T>
-static void expect_ids(const T& ids) {
+static void expect_ids(const T& ids, bool is_group) {
   std::set<typename T::key_type> expected_ids;
   // Ensure that all android_ids are iterated through.
   for (size_t n = 0; n < android_id_count; ++n) {
@@ -321,10 +401,12 @@
   expect_range(AID_OEM_RESERVED_START, AID_OEM_RESERVED_END);
   expect_range(AID_OEM_RESERVED_2_START, AID_OEM_RESERVED_2_END);
   expect_range(AID_APP_START, AID_APP_END);
-  expect_range(AID_CACHE_GID_START, AID_CACHE_GID_END);
-  expect_range(AID_EXT_GID_START, AID_EXT_GID_END);
-  expect_range(AID_EXT_CACHE_GID_START, AID_EXT_CACHE_GID_END);
-  expect_range(AID_SHARED_GID_START, AID_SHARED_GID_END);
+  if (is_group) {
+    expect_range(AID_CACHE_GID_START, AID_CACHE_GID_END);
+    expect_range(AID_EXT_GID_START, AID_EXT_GID_END);
+    expect_range(AID_EXT_CACHE_GID_START, AID_EXT_CACHE_GID_END);
+    expect_range(AID_SHARED_GID_START, AID_SHARED_GID_END);
+  }
   expect_range(AID_ISOLATED_START, AID_ISOLATED_END);
 
   // TODO(73062966): We still don't have a good way to create vendor AIDs in the system or other
@@ -388,7 +470,7 @@
   }
   endpwent();
 
-  expect_ids(uids);
+  expect_ids(uids, false);
 #else
   GTEST_SKIP() << "bionic-only test";
 #endif
@@ -453,12 +535,41 @@
 }
 
 static void check_get_group(const char* group_name, gid_t gid, bool check_groupname = true) {
+  SCOPED_TRACE("groupname '"s + group_name + "'");
   check_getgrgid(group_name, gid, check_groupname);
   check_getgrnam(group_name, gid, check_groupname);
   check_getgrgid_r(group_name, gid, check_groupname);
   check_getgrnam_r(group_name, gid, check_groupname);
 }
 
+static void expect_no_group_id(gid_t gid) {
+  SCOPED_TRACE("gid '" + std::to_string(gid) + "'");
+  errno = 0;
+  group* group = nullptr;
+  group = getgrgid(gid);
+  EXPECT_EQ(nullptr, group) << "name = '" << group->gr_name << "'";
+  EXPECT_EQ(ENOENT, errno);
+
+  struct group group_storage;
+  char buf[512];
+  EXPECT_EQ(ENOENT, getgrgid_r(gid, &group_storage, buf, sizeof(buf), &group));
+  EXPECT_EQ(nullptr, group) << "name = '" << group->gr_name << "'";
+}
+
+static void expect_no_group_name(const char* groupname) {
+  SCOPED_TRACE("groupname '"s + groupname + "'");
+  errno = 0;
+  group* group = nullptr;
+  group = getgrnam(groupname);
+  EXPECT_EQ(nullptr, group) << "name = '" << group->gr_name << "'";
+  EXPECT_EQ(ENOENT, errno);
+
+  struct group group_storage;
+  char buf[512];
+  EXPECT_EQ(ENOENT, getgrnam_r(groupname, &group_storage, buf, sizeof(buf), &group));
+  EXPECT_EQ(nullptr, group) << "name = '" << group->gr_name << "'";
+}
+
 #else // !defined(__BIONIC__)
 
 static void check_get_group(const char*, gid_t, bool) {
@@ -469,95 +580,144 @@
   GTEST_SKIP() << "bionic-only test";
 }
 
+static void expect_no_group_id(gid_t /* gid */) {
+  GTEST_SKIP() << "bionic-only test";
+}
+
+static void expect_no_group_name(const char* /* groupname */) {
+  GTEST_SKIP() << "bionic-only test";
+}
+
 #endif
 
-TEST(grp, getgrnam_system_id_root) {
+TEST(grp, getgrnam_platform_ids) {
   check_get_group("root", 0);
-}
+  check_get_group("daemon", 1);
+  check_get_group("bin", 2);
 
-TEST(grp, getgrnam_system_id_system) {
   check_get_group("system", 1000);
-}
-
-TEST(grp, getgrnam_app_id_radio) {
   check_get_group("radio", 1001);
-}
 
-TEST(grp, getgrnam_oem_id_5000) {
-  check_get_group("oem_5000", 5000, false);
-}
+  check_get_group("shell", 2000);
 
-TEST(grp, getgrnam_oem_id_5999) {
-  check_get_group("oem_5999", 5999, false);
-}
-
-TEST(grp, getgrnam_oem_id_2900) {
-  check_get_group("oem_2900", 2900, false);
-}
-
-TEST(grp, getgrnam_oem_id_2999) {
-  check_get_group("oem_2999", 2999, false);
-}
-
-TEST(grp, getgrnam_app_id_nobody) {
   check_get_group("nobody", 9999);
 }
 
-TEST(grp, getgrnam_app_id_u0_a0) {
+TEST(grp, getgrnam_oem_ids) {
+  check_get_group("oem_2900", 2900, false);
+  check_get_group("oem_2945", 2945, false);
+  check_get_group("oem_2999", 2999, false);
+  check_get_group("oem_5000", 5000, false);
+  check_get_group("oem_5454", 5454, false);
+  check_get_group("oem_5999", 5999, false);
+}
+
+TEST(grp, getgrnam_non_exist) {
+  expect_no_passwd_id(999);   // End of the system reserved range, unallocated.
+  expect_no_passwd_id(1999);  // End of the system reserved range, unallocated.
+  expect_no_passwd_id(2899);  // End of the system reserved range, unallocated.
+}
+
+TEST(grp, getgrnam_u0_app_ids) {
   check_get_group("u0_a0", 10000);
-}
-
-TEST(grp, getgrnam_app_id_u0_a1234) {
   check_get_group("u0_a1234", 11234);
-}
-
-TEST(grp, getgrnam_app_id_u0_a9999) {
   check_get_group("u0_a9999", 19999);
-}
 
-TEST(getgrnam, app_id_u0_a0_cache) {
   check_get_group("u0_a0_cache", 20000);
-}
-
-TEST(getgrnam, app_id_u0_a1234_cache) {
   check_get_group("u0_a1234_cache", 21234);
-}
-
-TEST(getgrnam, app_id_u0_a9999_cache) {
   check_get_group("u0_a9999_cache", 29999);
-}
 
-TEST(getgrnam, app_id_u10_a1234_cache) {
-  check_get_group("u10_a1234_cache", 1021234);
-}
+  check_get_group("u0_a0_ext", 30000);
+  check_get_group("u0_a4545_ext", 34545);
+  check_get_group("u0_a9999_ext", 39999);
 
-// Test the difference between uid and shared gid.
-TEST(grp, getgrnam_app_id_all_a9999) {
+  check_get_group("u0_a0_ext_cache", 40000);
+  check_get_group("u0_a4545_ext_cache", 44545);
+  check_get_group("u0_a9999_ext_cache", 49999);
+
+  check_get_group("all_a0", 50000);
+  check_get_group("all_a4545", 54545);
   check_get_group("all_a9999", 59999);
-}
 
-TEST(grp, getgrnam_app_id_u0_i1) {
   check_get_group("u0_i1", 90001);
 }
 
-TEST(grp, getgrnam_app_id_u1_root) {
-  check_get_group("u1_root", 100000);
-}
-
-TEST(grp, getgrnam_app_id_u1_radio) {
+TEST(grp, getgrnam_u1_app_ids) {
+  check_get_group("u1_system", 101000);
   check_get_group("u1_radio", 101001);
-}
 
-TEST(grp, getgrnam_app_id_u1_a0) {
   check_get_group("u1_a0", 110000);
+  check_get_group("u1_a1234", 111234);
+  check_get_group("u1_a9999", 119999);
+
+  check_get_group("u1_a0_cache", 120000);
+  check_get_group("u1_a1234_cache", 121234);
+  check_get_group("u1_a9999_cache", 129999);
+
+  check_get_group("u1_a0_ext", 130000);
+  check_get_group("u1_a4545_ext", 134545);
+  check_get_group("u1_a9999_ext", 139999);
+
+  check_get_group("u1_a0_ext_cache", 140000);
+  check_get_group("u1_a4545_ext_cache", 144545);
+  check_get_group("u1_a9999_ext_cache", 149999);
+
+  check_get_group("u1_i1", 190001);
 }
 
-TEST(grp, getgrnam_app_id_u1_a40000) {
-  check_get_group("u1_a40000", 150000);
+TEST(grp, getgrnam_u31_app_ids) {
+  check_get_group("u31_system", 3101000);
+  check_get_group("u31_radio", 3101001);
+
+  check_get_group("u31_a0", 3110000);
+  check_get_group("u31_a1234", 3111234);
+  check_get_group("u31_a9999", 3119999);
+
+  check_get_group("u31_a0_cache", 3120000);
+  check_get_group("u31_a1234_cache", 3121234);
+  check_get_group("u31_a9999_cache", 3129999);
+
+  check_get_group("u31_a0_cache", 3120000);
+  check_get_group("u31_a1234_cache", 3121234);
+  check_get_group("u31_a9999_cache", 3129999);
+
+  check_get_group("u31_a0_ext", 3130000);
+  check_get_group("u31_a4545_ext", 3134545);
+  check_get_group("u31_a9999_ext", 3139999);
+
+  check_get_group("u31_a0_ext_cache", 3140000);
+  check_get_group("u31_a4545_ext_cache", 3144545);
+  check_get_group("u31_a9999_ext_cache", 3149999);
+
+  check_get_group("u31_i1", 3190001);
 }
 
-TEST(grp, getgrnam_app_id_u1_i0) {
-  check_get_group("u1_i0", 190000);
+TEST(grp, getpgram_app_id_not_allowed_platform) {
+  expect_no_group_name("u1_root");
+  expect_no_group_name("u1_debuggerd");
+
+  expect_no_group_name("u31_root");
+  expect_no_group_name("u31_debuggerd");
+}
+
+TEST(grp, getgrgid_app_id_u1_non_exist) {
+  expect_no_group_id(100000);  // There is no 'root' for secondary users.
+  expect_no_group_id(101999);  // End of the system reserved range, unallocated.
+  expect_no_group_id(102900);  // The OEM ranges were never allocated to secondary users.
+  expect_no_group_id(105000);  // The OEM ranges were never allocated to secondary users.
+
+  // The shared range is shared among users, and therefore doesn't exist for secondary users.
+  expect_no_group_id(150000);
+}
+
+TEST(grp, getgrgid_app_id_u31_non_exist) {
+  expect_no_group_id(3100000);  // There is no 'root' for secondary users.
+  expect_no_group_id(3101999);  // End of the system reserved range, unallocated.
+  expect_no_group_id(3102900);  // The OEM ranges were never allocated to secondary users.
+  expect_no_group_id(3105000);  // The OEM ranges were never allocated to secondary users.
+
+  // The shared range is shared among users, and therefore doesn't exist for secondary users.
+  expect_no_group_id(3150000);
 }
 
 TEST(grp, getgrnam_r_alignment) {
@@ -660,7 +820,7 @@
   }
   endgrent();
 
-  expect_ids(gids);
+  expect_ids(gids, true);
 #else
   GTEST_SKIP() << "bionic-only test";
 #endif