diff --git a/libc/private/bionic_elf_tls.h b/libc/private/bionic_elf_tls.h
new file mode 100644
index 0000000..e847669
--- /dev/null
+++ b/libc/private/bionic_elf_tls.h
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+struct StaticTlsLayout {
+  constexpr StaticTlsLayout() {}
+
+private:
+  size_t offset_ = 0;
+  size_t alignment_ = 1;
+  bool overflowed_ = false;
+
+  // Offsets to various Bionic TLS structs from the beginning of static TLS.
+  size_t offset_bionic_tcb_ = SIZE_MAX;
+  size_t offset_bionic_tls_ = SIZE_MAX;
+
+public:
+  size_t offset_bionic_tcb() const { return offset_bionic_tcb_; }
+  size_t offset_bionic_tls() const { return offset_bionic_tls_; }
+
+  size_t size() const { return offset_; }
+  size_t alignment() const { return alignment_; }
+  bool overflowed() const { return overflowed_; }
+
+  void reserve_tcb();
+  void reserve_bionic_tls();
+  void finish_layout();
+
+private:
+  size_t reserve(size_t size, size_t alignment);
+
+  template <typename T> size_t reserve_type() {
+    return reserve(sizeof(T), alignof(T));
+  }
+
+  size_t round_up_with_overflow_check(size_t value, size_t alignment);
+};