Init fork handler after __libc_init_malloc.

pthread_atfork may call malloc() during its once-init. This causes
problems with allocators (GWP-ASan) that require explicit initialisation
before calls to malloc().

Bug: 135634846
Test: atest bionic
Change-Id: I1810a00465db99d5aa34fa6f74dea5908a628d3a

libc/bionic/libc_init_common.cpp

@@ -101,13 +101,15 @@ void __libc_init_common() {
 
   __libc_add_main_thread();
 
-  // Register atfork handlers to take and release the arc4random lock.
-  pthread_atfork(arc4random_fork_handler, _thread_arc4_unlock, _thread_arc4_unlock);
-
   __system_properties_init(); // Requires 'environ'.
   __libc_init_fdsan(); // Requires system properties (for debug.fdsan).
 }
 
+void __libc_init_fork_handler() {
+  // Register atfork handlers to take and release the arc4random lock.
+  pthread_atfork(arc4random_fork_handler, _thread_arc4_unlock, _thread_arc4_unlock);
+}
+
 __noreturn static void __early_abort(int line) {
   // We can't write to stdout or stderr because we're aborting before we've checked that
   // it's safe for us to use those file descriptors. We probably can't strace either, so

libc/bionic/libc_init_common.h

@@ -56,4 +56,8 @@ __LIBC_HIDDEN__ void __libc_init_common();
 
 __LIBC_HIDDEN__ void __libc_init_AT_SECURE(char** envp);
 
+// The fork handler must be initialised after __libc_init_malloc, as
+// pthread_atfork may call malloc() during its once-init.
+__LIBC_HIDDEN__ void __libc_init_fork_handler();
+
 #endif

libc/bionic/libc_init_dynamic.cpp

@@ -99,6 +99,8 @@ static void __libc_preinit_impl() {
   // Hooks for various libraries to let them know that we're starting up.
   __libc_globals.mutate(__libc_init_malloc);
 
+  __libc_init_fork_handler();
+
 #if __has_feature(hwaddress_sanitizer)
   // Notify the HWASan runtime library whenever a library is loaded or unloaded
   // so that it can update its shadow memory.

libc/bionic/libc_init_static.cpp

@@ -181,6 +181,7 @@ __noreturn static void __real_libc_init(void *raw_args,
   layout_static_tls(args);
   __libc_init_main_thread_final();
   __libc_init_common();
+  __libc_init_fork_handler();
 
   call_ifunc_resolvers();
   apply_gnu_relro();