threads: optimize single threaded applications

Revert the removal of the weak pthread functions and
guarantee a link order so that single threaded applications
doesn't link in all the pthread functions they don't use.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Tested-by: Waldemar Brodkorb <wbx@uclibc-ng.org>

libc/misc/internals/Makefile.in

@@ -25,7 +25,9 @@ libc-shared-y += $(MISC_INTERNALS_OUT)/__uClibc_main.oS
 else
 libc-shared-y += $(MISC_INTERNALS_OUT)/__uClibc_main.os
 endif
-libc-static-y += $(MISC_INTERNALS_OUT)/__uClibc_main.o
+# link order is important to not pull in pthread functions, when
+# a single threaded application is statically linked
+libc-static-y := $(MISC_INTERNALS_OUT)/__uClibc_main.o $(libc-static-y)
 libc-static-$(UCLIBC_FORMAT_FLAT_SEP_DATA) += \
   $(MISC_INTERNALS_OUT)/shared_flat_initfini.o \
   $(MISC_INTERNALS_OUT)/shared_flat_add_library.o

libc/misc/internals/__uClibc_main.c

@@ -68,6 +68,43 @@ uintptr_t __stack_chk_guard attribute_relro;
 
 void internal_function _dl_aux_init (ElfW(auxv_t) *av);
 
+#ifdef __UCLIBC_HAS_THREADS__
+/*
+ * uClibc internal locking requires that we have weak aliases
+ * for dummy functions in case a single threaded application is linked.
+ * This needs to be in compilation unit that is pulled always
+ * in or linker will disregard these weaks.
+ */
+
+static int __pthread_return_0 (pthread_mutex_t *unused) { return 0; }
+weak_alias (__pthread_return_0, __pthread_mutex_lock)
+weak_alias (__pthread_return_0, __pthread_mutex_trylock)
+weak_alias (__pthread_return_0, __pthread_mutex_unlock)
+
+int weak_function
+__pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *attr)
+{
+        return 0;
+}
+
+void weak_function
+_pthread_cleanup_push_defer(struct _pthread_cleanup_buffer *__buffer,
+                            void (*__routine) (void *), void *__arg)
+{
+        __buffer->__routine = __routine;
+        __buffer->__arg = __arg;
+}
+
+void weak_function
+_pthread_cleanup_pop_restore(struct _pthread_cleanup_buffer *__buffer,
+                             int __execute)
+{
+        if (__execute)
+                __buffer->__routine(__buffer->__arg);
+}
+
+#endif /* __UCLIBC_HAS_THREADS__ */
+
 #endif /* !SHARED */
 
 /* Defeat compiler optimization which assumes function addresses are never NULL */