Initialize TLS before any application code is run.

Since e19d702b8e33, dlsym and friends use recursive mutexes that
require the current thread id, which is not available before the libc
constructor. This prevents us from using dlsym() in .preinit_array.

This change moves TLS initialization from libc constructor to the earliest
possible point - immediately after linker itself is relocated. As a result,
pthread_internal_t for the initial thread is available from the start.

As a bonus, values stored in TLS in .preinit_array are not lost when libc is
initialized.

Change-Id: Iee5a710ee000173bff63e924adeb4a4c600c1e2d

libc/bionic/libc_init_common.c

@@ -52,12 +52,19 @@ unsigned int __page_shift = PAGE_SHIFT;
 
 int __system_properties_init(void);
 
-void __libc_init_common(uintptr_t *elfdata)
+/* Init TLS for the initial thread. Called by the linker _before_ libc is mapped
+ * in memory. Beware: all writes to libc globals from this function will
+ * apply to linker-private copies and will not be visible from libc later on.
+ *
+ * Note: this function creates a pthread_internal_t for the initial thread and
+ * stores the pointer in TLS, but does not add it to pthread's gThreadList. This
+ * has to be done later from libc itself (see __libc_init_common).
+ *
+ * This function also stores elfdata argument in a specific TLS slot to be later
+ * picked up by the libc constructor.
+ */
+void __libc_init_tls(unsigned** elfdata)
 {
-    int     argc = *elfdata;
-    char**  argv = (char**)(elfdata + 1);
-    char**  envp = argv + argc + 1;
-
     pthread_attr_t             thread_attr;
     static pthread_internal_t  thread;
     static void*               tls_area[BIONIC_TLS_SLOTS];
@@ -72,7 +79,19 @@ void __libc_init_common(uintptr_t *elfdata)
     _init_thread(&thread, gettid(), &thread_attr, (void*)stackbottom);
     __init_tls(tls_area, &thread);
 
-    /* clear errno - requires TLS area */
+    tls_area[TLS_SLOT_BIONIC_PREINIT] = elfdata;
+}
+
+void __libc_init_common(uintptr_t *elfdata)
+{
+    int     argc = *elfdata;
+    char**  argv = (char**)(elfdata + 1);
+    char**  envp = argv + argc + 1;
+
+    /* get the initial thread from TLS and add it to gThreadList */
+    _pthread_internal_add(__get_thread());
+
+    /* clear errno */
     errno = 0;
 
     /* set program name */

libc/bionic/libc_init_static.c

@@ -65,6 +65,11 @@ __noreturn void __libc_init(uintptr_t *elfdata,
     int  argc;
     char **argv, **envp;
 
+    __libc_init_tls(NULL);
+
+    /* get the initial thread from TLS and add it to gThreadList */
+    _pthread_internal_add(__get_thread());
+
     /* Initialize the C runtime environment */
     __libc_init_common(elfdata);
 

libc/bionic/pthread.c

@@ -145,7 +145,7 @@ _pthread_internal_remove( pthread_internal_t*  thread )
     pthread_mutex_unlock(&gThreadListLock);
 }
 
-static void
+__LIBC_ABI_PRIVATE__ void
 _pthread_internal_add( pthread_internal_t*  thread )
 {
     pthread_mutex_lock(&gThreadListLock);
@@ -157,7 +157,7 @@ _pthread_internal_add( pthread_internal_t*  thread )
     pthread_mutex_unlock(&gThreadListLock);
 }
 
-pthread_internal_t*
+__LIBC_ABI_PRIVATE__ pthread_internal_t*
 __get_thread(void)
 {
     void**  tls = (void**)__get_tls();
@@ -217,6 +217,7 @@ void __thread_entry(int (*func)(void*), void *arg, void **tls)
     pthread_exit( (void*)func(arg) );
 }
 
+__LIBC_ABI_PRIVATE__
 void _init_thread(pthread_internal_t * thread, pid_t kernel_id, pthread_attr_t * attr, void * stack_base)
 {
     if (attr == NULL) {
@@ -238,8 +239,6 @@ void _init_thread(pthread_internal_t * thread, pid_t kernel_id, pthread_attr_t *
     thread->join_count = 0;
 
     thread->cleanup_stack = NULL;
-
-    _pthread_internal_add(thread);
 }
 
 
@@ -371,6 +370,8 @@ int pthread_create(pthread_t *thread_out, pthread_attr_t const * attr,
 
     _init_thread(thread, tid, (pthread_attr_t*)attr, stack);
 
+    _pthread_internal_add(thread);
+
     if (!madestack)
         thread->attr.flags |= PTHREAD_ATTR_FLAG_USER_STACK;
 

libc/bionic/pthread_internal.h

@@ -47,6 +47,8 @@ typedef struct pthread_internal_t
 } pthread_internal_t;
 
 extern void _init_thread(pthread_internal_t * thread, pid_t kernel_id, pthread_attr_t * attr, void * stack_base);
+void _pthread_internal_add( pthread_internal_t*  thread );
+pthread_internal_t* __get_thread(void);
 
 /* needed by posix-timers.c */
 

libc/private/bionic_tls.h

@@ -134,6 +134,9 @@ extern void*  __get_tls( void );
 /* return the stack base and size, used by our malloc debugger */
 extern void*  __get_stack_base(int  *p_stack_size);
 
+/* Initialize the TLS. */
+extern void __libc_init_tls(unsigned** elfdata);
+
 __END_DECLS
 
 #endif /* _SYS_TLS_H */

linker/linker.c

@@ -2054,10 +2054,6 @@ static void parse_preloads(const char *path, char *delim)
     }
 }
 
-#define ANDROID_TLS_SLOTS  BIONIC_TLS_SLOTS
-
-static void * __tls_area[ANDROID_TLS_SLOTS];
-
 /*
  * This code is called after the linker has linked itself and
  * fixed it's own GOT. It is safe to make references to externs
@@ -2076,18 +2072,6 @@ static unsigned __linker_init_post_relocation(unsigned **elfdata)
     const char *ldpath_env = NULL;
     const char *ldpreload_env = NULL;
 
-    /* Setup a temporary TLS area that is used to get a working
-     * errno for system calls.
-     */
-    __set_tls(__tls_area);
-
-    pid = getpid();
-
-#if TIMING
-    struct timeval t0, t1;
-    gettimeofday(&t0, 0);
-#endif
-
     /* NOTE: we store the elfdata pointer on a special location
      *       of the temporary TLS area in order to pass it to
      *       the C Library's runtime initializer.
@@ -2096,7 +2080,14 @@ static unsigned __linker_init_post_relocation(unsigned **elfdata)
      *       to point to a different location to ensure that no other
      *       shared library constructor can access it.
      */
-    __tls_area[TLS_SLOT_BIONIC_PREINIT] = elfdata;
+    __libc_init_tls(elfdata);
+
+    pid = getpid();
+
+#if TIMING
+    struct timeval t0, t1;
+    gettimeofday(&t0, 0);
+#endif
 
     /* Initialize environment functions, and get to the ELF aux vectors table */
     vecs = linker_env_init(vecs);