diff --git a/tests/libs/Android.bp b/tests/libs/Android.bp
index 06ee132..f640552 100644
--- a/tests/libs/Android.bp
+++ b/tests/libs/Android.bp
@@ -123,6 +123,39 @@
     ],
 }
 
+cc_test_library {
+    name: "libtest_elftls_dynamic_filler_4",
+    defaults: ["bionic_testlib_defaults"],
+    srcs: ["elftls_dynamic_filler.cpp"],
+    cflags: [
+        "-DTLS_FILLER=400",
+    ],
+}
+
+cc_test_library {
+    name: "libtest_elftls_dynamic_filler_5",
+    defaults: ["bionic_testlib_defaults"],
+    srcs: ["elftls_dynamic_filler.cpp"],
+    cflags: [
+        "-DTLS_FILLER=500",
+    ],
+}
+
+cc_test {
+    name: "elftls_dtv_resize_helper",
+    defaults: [
+        "bionic_testlib_defaults",
+        "bionic_targets_only",
+    ],
+    srcs: ["elftls_dtv_resize_helper.cpp"],
+    include_dirs: [
+        "bionic/libc",
+    ],
+    static_libs: [
+        "libbase",
+    ],
+}
+
 // -----------------------------------------------------------------------------
 // Library to test gnu-styled hash
 // -----------------------------------------------------------------------------
diff --git a/tests/libs/elftls_dtv_resize_helper.cpp b/tests/libs/elftls_dtv_resize_helper.cpp
new file mode 100644
index 0000000..125f8e8
--- /dev/null
+++ b/tests/libs/elftls_dtv_resize_helper.cpp
@@ -0,0 +1,224 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <dlfcn.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <functional>
+#include <iostream>
+
+#include <android-base/test_utils.h>
+
+#include "bionic/pthread_internal.h"
+
+constexpr bool kDumpModulesForDebugging = false;
+
+// The old external/libcxx doesn't have operator<< for nullptr.
+// TODO(b/175635923): Remove this hack after upgrading libc++.
+template <class T>
+T fix_nullptr(T&& arg) {
+  return arg;
+}
+void* fix_nullptr(nullptr_t arg) {
+  return static_cast<void*>(arg);
+}
+
+template <class Val1, class Val2, class Compare>
+void check(int line, const char* val1_expr, Val1&& val1, const char* val2_expr, Val2&& val2,
+           Compare compare) {
+  if (!compare(val1, val2)) {
+    std::cerr << __FILE__ << ":" << line << ": assertion failed: LHS(" << val1_expr << ") is "
+              << fix_nullptr(val1) << ", RHS(" << val2_expr << ") is " << fix_nullptr(val2) << "\n"
+              << std::flush;
+    abort();
+  }
+}
+
+#define ASSERT_EQ(val1, val2) check(__LINE__, #val1, val1, #val2, val2, std::equal_to())
+#define ASSERT_NE(val1, val2) check(__LINE__, #val1, val1, #val2, val2, std::not_equal_to())
+#define ASSERT_LT(val1, val2) check(__LINE__, #val1, val1, #val2, val2, std::less())
+#define ASSERT_LE(val1, val2) check(__LINE__, #val1, val1, #val2, val2, std::less_equal())
+
+static size_t highest_loaded_modid() {
+  size_t result = 0;
+  auto update_result = [](struct dl_phdr_info* info, size_t size __unused, void* data) {
+    size_t& result = *reinterpret_cast<size_t*>(data);
+    if (kDumpModulesForDebugging) {
+      fprintf(stderr, "module %s: TLS modid %zu\n", info->dlpi_name, info->dlpi_tls_modid);
+    }
+    result = std::max(result, info->dlpi_tls_modid);
+    return 0;
+  };
+  dl_iterate_phdr(update_result, &result);
+  return result;
+}
+
+static TlsDtv* dtv() {
+  return __get_tcb_dtv(__get_bionic_tcb());
+}
+
+static size_t highest_modid_in_dtv() {
+  TlsDtv* current_dtv = dtv();
+  size_t result = 0;
+  for (size_t i = 0; i < current_dtv->count; ++i) {
+    if (current_dtv->modules[i] != nullptr) {
+      result = __tls_module_idx_to_id(i);
+    }
+  }
+  return result;
+}
+
+// Unused, but ensures that the test executable has a TLS segment. With a
+// new-enough libc++_static.a, the test executable will tend to has a TLS
+// segment to hold the libc++ EH globals pointer.
+__thread int g_tls_var_placeholder = 42;
+
+int main() {
+  // Prevent this TLS variable from being optimized away.
+  ASSERT_EQ(42, g_tls_var_placeholder);
+
+  auto load_lib = [](const char* soname) {
+    void* lib = dlopen(soname, RTLD_LOCAL | RTLD_NOW);
+    ASSERT_NE(nullptr, lib);
+    auto func = reinterpret_cast<int (*)()>(dlsym(lib, "bump"));
+    ASSERT_NE(nullptr, func);
+    return func;
+  };
+
+  static_assert(sizeof(TlsDtv) == 3 * sizeof(void*),
+                "This test assumes that the Dtv has a 3-word header");
+
+  // Initially there are 2-4 modules:
+  //  - 1: test executable
+  //  - 2: libc
+  //  - 3: libc++ (when using a new-enough libc++)
+  //  - 4: libclang_rt.hwasan (when running with HWASan)
+  size_t first_filler_modid = highest_loaded_modid() + 1;
+  ASSERT_LE(2, highest_loaded_modid());
+  ASSERT_LE(highest_loaded_modid(), 4);
+
+  // The initial DTV is an empty DTV with no generation and a size of 0.
+  TlsDtv* zero_dtv = dtv();
+  ASSERT_EQ(0u, zero_dtv->count);
+  ASSERT_EQ(nullptr, zero_dtv->next);
+  ASSERT_EQ(kTlsGenerationNone, zero_dtv->generation);
+
+  // Load a module. The DTV is still empty unless the TLS variable is accessed.
+  auto func1 = load_lib("libtest_elftls_dynamic_filler_1.so");
+  ASSERT_EQ(zero_dtv, dtv());
+  ASSERT_EQ(first_filler_modid, highest_loaded_modid());
+
+  // After accessing a TLS variable, the DTV should be initialized. It should be
+  // 8 words in size, with a 5-entry capacity.
+  ASSERT_EQ(101, func1());
+  TlsDtv* initial_dtv = dtv();
+  ASSERT_EQ(5u, dtv()->count);
+  ASSERT_EQ(zero_dtv, initial_dtv->next);
+  ASSERT_LT(0u, initial_dtv->generation);
+  ASSERT_EQ(first_filler_modid, highest_modid_in_dtv());
+  ASSERT_NE(nullptr, initial_dtv->modules[__tls_module_id_to_idx(first_filler_modid)]);
+
+  size_t current_generation = initial_dtv->generation;
+
+  // Fill the rest of the DTV up. (i.e. Ensure that exactly 5 modules with TLS
+  // segments are loaded.)
+  auto fill_entry = [&](size_t modid, const char* soname, int tls_var_value) {
+    if (highest_modid_in_dtv() == modid - 1) {
+      auto func = load_lib(soname);
+
+      // Loading the module doesn't affect the DTV yet.
+      ASSERT_EQ(initial_dtv, dtv());
+      ASSERT_EQ(modid, highest_loaded_modid());
+      ASSERT_EQ(modid - 1, highest_modid_in_dtv());
+      ASSERT_EQ(current_generation, initial_dtv->generation);
+
+      // Access the TLS variable, which will allocate it in the DTV.
+      ASSERT_EQ(tls_var_value, func());
+
+      // Verify allocation and a bumped generation.
+      ASSERT_EQ(initial_dtv, dtv());
+      ASSERT_EQ(modid, highest_modid_in_dtv());
+      ASSERT_LT(current_generation, initial_dtv->generation);
+      current_generation = initial_dtv->generation;
+    }
+  };
+
+  fill_entry(4u, "libtest_elftls_dynamic_filler_2.so", 201);
+  fill_entry(5u, "libtest_elftls_dynamic_filler_3.so", 301);
+  ASSERT_EQ(5u, highest_modid_in_dtv());
+
+  // Load module 6, which will require doubling the size of the DTV.
+  auto func4 = load_lib("libtest_elftls_dynamic_filler_4.so");
+  ASSERT_EQ(6u, highest_loaded_modid());
+  ASSERT_EQ(5u, highest_modid_in_dtv());
+  ASSERT_EQ(initial_dtv, dtv());
+
+  // Access a TLS variable from the first filler module.
+  ASSERT_EQ(102, func1());
+  ASSERT_EQ(5u, highest_modid_in_dtv());
+#if defined(__aarch64__)
+  // The arm64 TLSDESC resolver doesn't update the DTV if it is new enough for
+  // the given access.
+  ASSERT_EQ(initial_dtv, dtv());
+  ASSERT_EQ(5u, dtv()->count);
+  ASSERT_EQ(current_generation, dtv()->generation);
+#else
+  // __tls_get_addr updates the DTV anytime the generation counter changes, but
+  // the highest modid in the DTV is still 5, because module 6 hasn't been
+  // allocated yet.
+  ASSERT_NE(initial_dtv, dtv());
+  ASSERT_EQ(13u, dtv()->count);
+  ASSERT_LT(current_generation, dtv()->generation);
+#endif
+
+  // Accessing the TLS variable in the latest module will always expand the DTV.
+  ASSERT_EQ(401, func4());
+  TlsDtv* new_dtv = dtv();
+  ASSERT_NE(initial_dtv, new_dtv);
+  ASSERT_EQ(initial_dtv, new_dtv->next);
+  ASSERT_EQ(13u, new_dtv->count);
+  ASSERT_LT(current_generation, new_dtv->generation);
+  ASSERT_EQ(6u, highest_modid_in_dtv());
+  current_generation = new_dtv->generation;
+
+  // Load one more filler, module 7.
+  auto func5 = load_lib("libtest_elftls_dynamic_filler_5.so");
+  ASSERT_EQ(103, func1());
+  ASSERT_EQ(402, func4());
+  ASSERT_EQ(6u, highest_modid_in_dtv());
+  ASSERT_EQ(501, func5());
+  ASSERT_EQ(7u, highest_modid_in_dtv());
+
+  // Verify that no new DTV has been allocated.
+  ASSERT_EQ(new_dtv, dtv());
+  ASSERT_EQ(13u, new_dtv->count);
+  ASSERT_LT(current_generation, new_dtv->generation);
+
+  return 0;
+}