Revert "Revert "Pull the pthread_key_t functions out of pthread.c.""

This reverts commit 6260553d48f6fd87ca220270bea8bafdde5726ec

(Removing the accidental libm/Android.mk change.)

Change-Id: I6cddd9857c31facc05636e8221505b3d2344cb75

4 files changed, 294 insertions, 307 deletions

diff --git a/libc/bionic/pthread.c b/libc/bionic/pthread.c
index 88a972d..e1ace7d 100644
--- a/libc/bionic/pthread.c
+++ b/libc/bionic/pthread.c
@@ -101,8 +101,8 @@ static const pthread_attr_t gDefaultPthreadAttr = {
     .sched_priority = 0
 };
 
-static pthread_internal_t* gThreadList = NULL;
-static pthread_mutex_t gThreadListLock = PTHREAD_MUTEX_INITIALIZER;
+__LIBC_HIDDEN__ pthread_internal_t* gThreadList = NULL;
+__LIBC_HIDDEN__ pthread_mutex_t gThreadListLock = PTHREAD_MUTEX_INITIALIZER;
 static pthread_mutex_t gDebuggerNotificationLock = PTHREAD_MUTEX_INITIALIZER;
 
 static void _pthread_internal_remove_locked(pthread_internal_t* thread) {
@@ -550,9 +550,6 @@ void __pthread_cleanup_pop( __pthread_cleanup_t*  c, int  execute )
         c->__cleanup_routine(c->__cleanup_arg);
 }
 
-/* used by pthread_exit() to clean all TLS keys of the current thread */
-static void pthread_key_clean_all(void);
-
 void pthread_exit(void * retval)
 {
     pthread_internal_t*  thread     = __get_thread();
@@ -1780,303 +1777,6 @@ int pthread_cond_timeout_np(pthread_cond_t *cond,
 }
 
 
-
-/* A technical note regarding our thread-local-storage (TLS) implementation:
- *
- * There can be up to TLSMAP_SIZE independent TLS keys in a given process,
- * though the first TLSMAP_START keys are reserved for Bionic to hold
- * special thread-specific variables like errno or a pointer to
- * the current thread's descriptor.
- *
- * while stored in the TLS area, these entries cannot be accessed through
- * pthread_getspecific() / pthread_setspecific() and pthread_key_delete()
- *
- * also, some entries in the key table are pre-allocated (see tlsmap_lock)
- * to greatly simplify and speedup some OpenGL-related operations. though the
- * initialy value will be NULL on all threads.
- *
- * you can use pthread_getspecific()/setspecific() on these, and in theory
- * you could also call pthread_key_delete() as well, though this would
- * probably break some apps.
- *
- * The 'tlsmap_t' type defined below implements a shared global map of
- * currently created/allocated TLS keys and the destructors associated
- * with them. You should use tlsmap_lock/unlock to access it to avoid
- * any race condition.
- *
- * the global TLS map simply contains a bitmap of allocated keys, and
- * an array of destructors.
- *
- * each thread has a TLS area that is a simple array of TLSMAP_SIZE void*
- * pointers. the TLS area of the main thread is stack-allocated in
- * __libc_init_common, while the TLS area of other threads is placed at
- * the top of their stack in pthread_create.
- *
- * when pthread_key_create() is called, it finds the first free key in the
- * bitmap, then set it to 1, saving the destructor altogether
- *
- * when pthread_key_delete() is called. it will erase the key's bitmap bit
- * and its destructor, and will also clear the key data in the TLS area of
- * all created threads. As mandated by Posix, it is the responsability of
- * the caller of pthread_key_delete() to properly reclaim the objects that
- * were pointed to by these data fields (either before or after the call).
- *
- */
-
-/* TLS Map implementation
- */
-
-#define TLSMAP_START      (TLS_SLOT_MAX_WELL_KNOWN+1)
-#define TLSMAP_SIZE       BIONIC_TLS_SLOTS
-#define TLSMAP_BITS       32
-#define TLSMAP_WORDS      ((TLSMAP_SIZE+TLSMAP_BITS-1)/TLSMAP_BITS)
-#define TLSMAP_WORD(m,k)  (m)->map[(k)/TLSMAP_BITS]
-#define TLSMAP_MASK(k)    (1U << ((k)&(TLSMAP_BITS-1)))
-
-/* this macro is used to quickly check that a key belongs to a reasonable range */
-#define TLSMAP_VALIDATE_KEY(key)  \
-    ((key) >= TLSMAP_START && (key) < TLSMAP_SIZE)
-
-/* the type of tls key destructor functions */
-typedef void (*tls_dtor_t)(void*);
-
-typedef struct {
-    int         init;                  /* see comment in tlsmap_lock() */
-    uint32_t    map[TLSMAP_WORDS];     /* bitmap of allocated keys */
-    tls_dtor_t  dtors[TLSMAP_SIZE];    /* key destructors */
-} tlsmap_t;
-
-static pthread_mutex_t  _tlsmap_lock = PTHREAD_MUTEX_INITIALIZER;
-static tlsmap_t         _tlsmap;
-
-/* lock the global TLS map lock and return a handle to it */
-static __inline__ tlsmap_t* tlsmap_lock(void)
-{
-    tlsmap_t*   m = &_tlsmap;
-
-    pthread_mutex_lock(&_tlsmap_lock);
-    /* we need to initialize the first entry of the 'map' array
-     * with the value TLS_DEFAULT_ALLOC_MAP. doing it statically
-     * when declaring _tlsmap is a bit awkward and is going to
-     * produce warnings, so do it the first time we use the map
-     * instead
-     */
-    if (__unlikely(!m->init)) {
-        TLSMAP_WORD(m,0) = TLS_DEFAULT_ALLOC_MAP;
-        m->init          = 1;
-    }
-    return m;
-}
-
-/* unlock the global TLS map */
-static __inline__ void tlsmap_unlock(tlsmap_t*  m)
-{
-    pthread_mutex_unlock(&_tlsmap_lock);
-    (void)m;  /* a good compiler is a happy compiler */
-}
-
-/* test to see wether a key is allocated */
-static __inline__ int tlsmap_test(tlsmap_t*  m, int  key)
-{
-    return (TLSMAP_WORD(m,key) & TLSMAP_MASK(key)) != 0;
-}
-
-/* set the destructor and bit flag on a newly allocated key */
-static __inline__ void tlsmap_set(tlsmap_t*  m, int  key, tls_dtor_t  dtor)
-{
-    TLSMAP_WORD(m,key) |= TLSMAP_MASK(key);
-    m->dtors[key]       = dtor;
-}
-
-/* clear the destructor and bit flag on an existing key */
-static __inline__ void  tlsmap_clear(tlsmap_t*  m, int  key)
-{
-    TLSMAP_WORD(m,key) &= ~TLSMAP_MASK(key);
-    m->dtors[key]       = NULL;
-}
-
-/* allocate a new TLS key, return -1 if no room left */
-static int tlsmap_alloc(tlsmap_t*  m, tls_dtor_t  dtor)
-{
-    int  key;
-
-    for ( key = TLSMAP_START; key < TLSMAP_SIZE; key++ ) {
-        if ( !tlsmap_test(m, key) ) {
-            tlsmap_set(m, key, dtor);
-            return key;
-        }
-    }
-    return -1;
-}
-
-
-int pthread_key_create(pthread_key_t *key, void (*destructor_function)(void *))
-{
-    uint32_t   err = ENOMEM;
-    tlsmap_t*  map = tlsmap_lock();
-    int        k   = tlsmap_alloc(map, destructor_function);
-
-    if (k >= 0) {
-        *key = k;
-        err  = 0;
-    }
-    tlsmap_unlock(map);
-    return err;
-}
-
-
-/* This deletes a pthread_key_t. note that the standard mandates that this does
- * not call the destructor of non-NULL key values. Instead, it is the
- * responsibility of the caller to properly dispose of the corresponding data
- * and resources, using any means it finds suitable.
- *
- * On the other hand, this function will clear the corresponding key data
- * values in all known threads. this prevents later (invalid) calls to
- * pthread_getspecific() to receive invalid/stale values.
- */
-int pthread_key_delete(pthread_key_t key)
-{
-    uint32_t             err;
-    pthread_internal_t*  thr;
-    tlsmap_t*            map;
-
-    if (!TLSMAP_VALIDATE_KEY(key)) {
-        return EINVAL;
-    }
-
-    map = tlsmap_lock();
-
-    if (!tlsmap_test(map, key)) {
-        err = EINVAL;
-        goto err1;
-    }
-
-    /* clear value in all threads */
-    pthread_mutex_lock(&gThreadListLock);
-    for ( thr = gThreadList; thr != NULL; thr = thr->next ) {
-        /* avoid zombie threads with a negative 'join_count'. these are really
-         * already dead and don't have a TLS area anymore.
-         *
-         * similarly, it is possible to have thr->tls == NULL for threads that
-         * were just recently created through pthread_create() but whose
-         * startup trampoline (__thread_entry) hasn't been run yet by the
-         * scheduler. thr->tls will also be NULL after it's stack has been
-         * unmapped but before the ongoing pthread_join() is finished.
-         * so check for this too.
-         */
-        if (thr->join_count < 0 || !thr->tls)
-            continue;
-
-        thr->tls[key] = NULL;
-    }
-    tlsmap_clear(map, key);
-
-    pthread_mutex_unlock(&gThreadListLock);
-    err = 0;
-
-err1:
-    tlsmap_unlock(map);
-    return err;
-}
-
-
-int pthread_setspecific(pthread_key_t key, const void *ptr)
-{
-    int        err = EINVAL;
-    tlsmap_t*  map;
-
-    if (TLSMAP_VALIDATE_KEY(key)) {
-        /* check that we're trying to set data for an allocated key */
-        map = tlsmap_lock();
-        if (tlsmap_test(map, key)) {
-            ((uint32_t *)__get_tls())[key] = (uint32_t)ptr;
-            err = 0;
-        }
-        tlsmap_unlock(map);
-    }
-    return err;
-}
-
-void * pthread_getspecific(pthread_key_t key)
-{
-    if (!TLSMAP_VALIDATE_KEY(key)) {
-        return NULL;
-    }
-
-    /* for performance reason, we do not lock/unlock the global TLS map
-     * to check that the key is properly allocated. if the key was not
-     * allocated, the value read from the TLS should always be NULL
-     * due to pthread_key_delete() clearing the values for all threads.
-     */
-    return (void *)(((unsigned *)__get_tls())[key]);
-}
-
-/* Posix mandates that this be defined in <limits.h> but we don't have
- * it just yet.
- */
-#ifndef PTHREAD_DESTRUCTOR_ITERATIONS
-#  define PTHREAD_DESTRUCTOR_ITERATIONS  4
-#endif
-
-/* this function is called from pthread_exit() to remove all TLS key data
- * from this thread's TLS area. this must call the destructor of all keys
- * that have a non-NULL data value (and a non-NULL destructor).
- *
- * because destructors can do funky things like deleting/creating other
- * keys, we need to implement this in a loop
- */
-static void pthread_key_clean_all(void)
-{
-    tlsmap_t*    map;
-    void**       tls = (void**)__get_tls();
-    int          rounds = PTHREAD_DESTRUCTOR_ITERATIONS;
-
-    map = tlsmap_lock();
-
-    for (rounds = PTHREAD_DESTRUCTOR_ITERATIONS; rounds > 0; rounds--)
-    {
-        int  kk, count = 0;
-
-        for (kk = TLSMAP_START; kk < TLSMAP_SIZE; kk++) {
-            if ( tlsmap_test(map, kk) )
-            {
-                void*       data = tls[kk];
-                tls_dtor_t  dtor = map->dtors[kk];
-
-                if (data != NULL && dtor != NULL)
-                {
-                   /* we need to clear the key data now, this will prevent the
-                    * destructor (or a later one) from seeing the old value if
-                    * it calls pthread_getspecific() for some odd reason
-                    *
-                    * we do not do this if 'dtor == NULL' just in case another
-                    * destructor function might be responsible for manually
-                    * releasing the corresponding data.
-                    */
-                    tls[kk] = NULL;
-
-                   /* because the destructor is free to call pthread_key_create
-                    * and/or pthread_key_delete, we need to temporarily unlock
-                    * the TLS map
-                    */
-                    tlsmap_unlock(map);
-                    (*dtor)(data);
-                    map = tlsmap_lock();
-
-                    count += 1;
-                }
-            }
-        }
-
-        /* if we didn't call any destructor, there is no need to check the
-         * TLS data again
-         */
-        if (count == 0)
-            break;
-    }
-    tlsmap_unlock(map);
-}
-
 // man says this should be in <linux/unistd.h>, but it isn't
 extern int tgkill(int tgid, int tid, int sig);
 
diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h
index bc68291..24b420c 100644
--- a/libc/bionic/pthread_internal.h
+++ b/libc/bionic/pthread_internal.h
@@ -60,6 +60,11 @@ int _init_thread(pthread_internal_t* thread, pid_t kernel_id, const pthread_attr
 void _pthread_internal_add( pthread_internal_t*  thread );
 pthread_internal_t* __get_thread(void);
 
+__LIBC_HIDDEN__ void pthread_key_clean_all(void);
+
+extern pthread_internal_t* gThreadList;
+extern pthread_mutex_t gThreadListLock;
+
 /* needed by posix-timers.c */
 
 static __inline__ void timespec_add( struct timespec*  a, const struct timespec*  b )
diff --git a/libc/bionic/pthread_key.cpp b/libc/bionic/pthread_key.cpp
new file mode 100644
index 0000000..00dacba
--- /dev/null
+++ b/libc/bionic/pthread_key.cpp
@@ -0,0 +1,280 @@
+/*
+ * Copyright (C) 2008 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 <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <malloc.h>
+#include <memory.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/atomics.h>
+#include <sys/mman.h>
+#include <sys/prctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "bionic_atomic_inline.h"
+#include "bionic_futex.h"
+#include "bionic_pthread.h"
+#include "bionic_ssp.h"
+#include "bionic_tls.h"
+#include "debug_format.h"
+#include "pthread_internal.h"
+#include "thread_private.h"
+
+/* A technical note regarding our thread-local-storage (TLS) implementation:
+ *
+ * There can be up to BIONIC_TLS_SLOTS independent TLS keys in a given process,
+ * The keys below TLS_SLOT_FIRST_USER_SLOT are reserved for Bionic to hold
+ * special thread-specific variables like errno or a pointer to
+ * the current thread's descriptor. These entries cannot be accessed through
+ * pthread_getspecific() / pthread_setspecific() or pthread_key_delete()
+ *
+ * The 'tls_map_t' type defined below implements a shared global map of
+ * currently created/allocated TLS keys and the destructors associated
+ * with them.
+ *
+ * The global TLS map simply contains a bitmap of allocated keys, and
+ * an array of destructors.
+ *
+ * Each thread has a TLS area that is a simple array of BIONIC_TLS_SLOTS void*
+ * pointers. the TLS area of the main thread is stack-allocated in
+ * __libc_init_common, while the TLS area of other threads is placed at
+ * the top of their stack in pthread_create.
+ *
+ * When pthread_key_delete() is called it will erase the key's bitmap bit
+ * and its destructor, and will also clear the key data in the TLS area of
+ * all created threads. As mandated by Posix, it is the responsibility of
+ * the caller of pthread_key_delete() to properly reclaim the objects that
+ * were pointed to by these data fields (either before or after the call).
+ */
+
+#define TLSMAP_BITS       32
+#define TLSMAP_WORDS      ((BIONIC_TLS_SLOTS+TLSMAP_BITS-1)/TLSMAP_BITS)
+#define TLSMAP_WORD(m,k)  (m).map[(k)/TLSMAP_BITS]
+#define TLSMAP_MASK(k)    (1U << ((k)&(TLSMAP_BITS-1)))
+
+static inline bool IsValidUserKey(pthread_key_t key) {
+  return (key >= TLS_SLOT_FIRST_USER_SLOT && key < BIONIC_TLS_SLOTS);
+}
+
+typedef void (*key_destructor_t)(void*);
+
+struct tls_map_t {
+  bool is_initialized;
+
+  /* bitmap of allocated keys */
+  uint32_t map[TLSMAP_WORDS];
+
+  key_destructor_t key_destructors[BIONIC_TLS_SLOTS];
+};
+
+class ScopedTlsMapAccess {
+ public:
+  ScopedTlsMapAccess() {
+    Lock();
+
+    // If this is the first time the TLS map has been accessed,
+    // mark the slots belonging to well-known keys as being in use.
+    // This isn't currently necessary because the well-known keys
+    // can only be accessed directly by bionic itself, do not have
+    // destructors, and all the functions that touch the TLS map
+    // start after the maximum well-known slot.
+    if (!s_tls_map_.is_initialized) {
+      for (pthread_key_t key = 0; key < TLS_SLOT_FIRST_USER_SLOT; ++key) {
+        SetInUse(key, NULL);
+      }
+      s_tls_map_.is_initialized = true;
+    }
+  }
+
+  ~ScopedTlsMapAccess() {
+    Unlock();
+  }
+
+  int CreateKey(pthread_key_t* result, void (*key_destructor)(void*)) {
+    // Take the first unallocated key.
+    for (int key = 0; key < BIONIC_TLS_SLOTS; ++key) {
+      if (!IsInUse(key)) {
+        SetInUse(key, key_destructor);
+        *result = key;
+        return 0;
+      }
+    }
+
+    // We hit PTHREAD_KEYS_MAX. POSIX says EAGAIN for this case.
+    return EAGAIN;
+  }
+
+  void DeleteKey(pthread_key_t key) {
+    TLSMAP_WORD(s_tls_map_, key) &= ~TLSMAP_MASK(key);
+    s_tls_map_.key_destructors[key] = NULL;
+  }
+
+  bool IsInUse(pthread_key_t key) {
+    return (TLSMAP_WORD(s_tls_map_, key) & TLSMAP_MASK(key)) != 0;
+  }
+
+  void SetInUse(pthread_key_t key, void (*key_destructor)(void*)) {
+    TLSMAP_WORD(s_tls_map_, key) |= TLSMAP_MASK(key);
+    s_tls_map_.key_destructors[key] = key_destructor;
+  }
+
+  // Called from pthread_exit() to remove all TLS key data
+  // from this thread's TLS area. This must call the destructor of all keys
+  // that have a non-NULL data value and a non-NULL destructor.
+  void CleanAll() {
+    void** tls = (void**)__get_tls();
+
+    // Because destructors can do funky things like deleting/creating other
+    // keys, we need to implement this in a loop.
+    for (int rounds = PTHREAD_DESTRUCTOR_ITERATIONS; rounds > 0; --rounds) {
+      size_t called_destructor_count = 0;
+      for (int key = 0; key < BIONIC_TLS_SLOTS; ++key) {
+        if (IsInUse(key)) {
+          void* data = tls[key];
+          void (*key_destructor)(void*) = s_tls_map_.key_destructors[key];
+
+          if (data != NULL && key_destructor != NULL) {
+            // we need to clear the key data now, this will prevent the
+            // destructor (or a later one) from seeing the old value if
+            // it calls pthread_getspecific() for some odd reason
+
+            // we do not do this if 'key_destructor == NULL' just in case another
+            // destructor function might be responsible for manually
+            // releasing the corresponding data.
+            tls[key] = NULL;
+
+            // because the destructor is free to call pthread_key_create
+            // and/or pthread_key_delete, we need to temporarily unlock
+            // the TLS map
+            Unlock();
+            (*key_destructor)(data);
+            Lock();
+            ++called_destructor_count;
+          }
+        }
+      }
+
+      // If we didn't call any destructors, there is no need to check the TLS data again.
+      if (called_destructor_count == 0) {
+        break;
+      }
+    }
+  }
+
+ private:
+  static tls_map_t s_tls_map_;
+  static pthread_mutex_t s_tls_map_lock_;
+
+  void Lock() {
+    pthread_mutex_lock(&s_tls_map_lock_);
+  }
+
+  void Unlock() {
+    pthread_mutex_unlock(&s_tls_map_lock_);
+  }
+};
+
+tls_map_t ScopedTlsMapAccess::s_tls_map_;
+pthread_mutex_t ScopedTlsMapAccess::s_tls_map_lock_;
+
+__LIBC_HIDDEN__ void pthread_key_clean_all() {
+  ScopedTlsMapAccess tls_map;
+  tls_map.CleanAll();
+}
+
+int pthread_key_create(pthread_key_t* key, void (*key_destructor)(void*)) {
+  ScopedTlsMapAccess tls_map;
+  return tls_map.CreateKey(key, key_destructor);
+}
+
+// Deletes a pthread_key_t. note that the standard mandates that this does
+// not call the destructors for non-NULL key values. Instead, it is the
+// responsibility of the caller to properly dispose of the corresponding data
+// and resources, using any means it finds suitable.
+int pthread_key_delete(pthread_key_t key) {
+  ScopedTlsMapAccess tls_map;
+
+  if (!IsValidUserKey(key) || !tls_map.IsInUse(key)) {
+    return EINVAL;
+  }
+
+  // Clear value in all threads.
+  pthread_mutex_lock(&gThreadListLock);
+  for (pthread_internal_t*  t = gThreadList; t != NULL; t = t->next) {
+    // Avoid zombie threads with a negative 'join_count'. These are really
+    // already dead and don't have a TLS area anymore.
+
+    // Similarly, it is possible to have t->tls == NULL for threads that
+    // were just recently created through pthread_create() but whose
+    // startup trampoline (__thread_entry) hasn't been run yet by the
+    // scheduler. t->tls will also be NULL after it's stack has been
+    // unmapped but before the ongoing pthread_join() is finished.
+    // so check for this too.
+    if (t->join_count < 0 || !t->tls) {
+      continue;
+    }
+
+    t->tls[key] = NULL;
+  }
+  tls_map.DeleteKey(key);
+
+  pthread_mutex_unlock(&gThreadListLock);
+  return 0;
+}
+
+void* pthread_getspecific(pthread_key_t key) {
+  if (!IsValidUserKey(key)) {
+    return NULL;
+  }
+
+  // For performance reasons, we do not lock/unlock the global TLS map
+  // to check that the key is properly allocated. If the key was not
+  // allocated, the value read from the TLS should always be NULL
+  // due to pthread_key_delete() clearing the values for all threads.
+  return (void *)(((unsigned *)__get_tls())[key]);
+}
+
+int pthread_setspecific(pthread_key_t key, const void* ptr) {
+  ScopedTlsMapAccess tls_map;
+
+  if (!IsValidUserKey(key) || !tls_map.IsInUse(key)) {
+    return EINVAL;
+  }
+
+  ((uint32_t *)__get_tls())[key] = (uint32_t)ptr;
+  return 0;
+}
diff --git a/libc/bionic/sysconf.cpp b/libc/bionic/sysconf.cpp
index 6555a66..f4845e1 100644
--- a/libc/bionic/sysconf.cpp
+++ b/libc/bionic/sysconf.cpp
@@ -55,7 +55,6 @@
 
 /* the following depends on our implementation */
 #define  SYSTEM_ATEXIT_MAX          65536    /* our implementation is unlimited */
-#define  SYSTEM_THREAD_KEYS_MAX     BIONIC_TLS_SLOTS
 #define  SYSTEM_THREAD_STACK_MIN    32768    /* lower values may be possible, but be conservative */
 #define  SYSTEM_THREAD_THREADS_MAX  2048     /* really unlimited */
 
@@ -302,10 +301,13 @@ int sysconf(int name) {
     // GETPW_R_SIZE_MAX ?
 
     case _SC_LOGIN_NAME_MAX:    return SYSTEM_LOGIN_NAME_MAX;
-#ifdef _POSIX_THREAD_DESTRUCTOR_ITERATIONS
-    case _SC_THREAD_DESTRUCTOR_ITERATIONS:  return _POSIX_THREAD_DESTRUCTOR_ITERATIONS;
-#endif
-    case _SC_THREAD_KEYS_MAX:     return SYSTEM_THREAD_KEYS_MAX;
+
+    case _SC_THREAD_DESTRUCTOR_ITERATIONS:
+      return _POSIX_THREAD_DESTRUCTOR_ITERATIONS;
+
+    case _SC_THREAD_KEYS_MAX:
+      return (BIONIC_TLS_SLOTS - TLS_SLOT_FIRST_USER_SLOT);
+
     case _SC_THREAD_STACK_MIN:    return SYSTEM_THREAD_STACK_MIN;
     case _SC_THREAD_THREADS_MAX:  return SYSTEM_THREAD_THREADS_MAX;
     case _SC_TTY_NAME_MAX:        return SYSTEM_TTY_NAME_MAX;