pthread: force linking pthread implementation from IDF

Force linking pthread implementation from IDF, instead of the weak
functions provided by gthread library. Previously this would either
work or not depending on the linking order.

Thanks @bpietsch for suggesting the fix.

Closes #3709

components/pthread/CMakeLists.txt

@@ -3,6 +3,16 @@ idf_component_register(SRCS "pthread.c"
                             "pthread_local_storage.c"
                     INCLUDE_DIRS include)
 
+if(GCC_NOT_5_2_0)
+    set(extra_link_flags "-u pthread_include_pthread_impl")
+    list(APPEND extra_link_flags "-u pthread_include_pthread_cond_impl")
+    list(APPEND extra_link_flags "-u pthread_include_pthread_local_storage_impl")
+endif()
+
 if(CONFIG_FREERTOS_ENABLE_STATIC_TASK_CLEAN_UP)
     target_link_libraries(${COMPONENT_LIB} "-Wl,--wrap=vPortCleanUpTCB")
 endif()
+
+if(extra_link_flags)
+    target_link_libraries(${COMPONENT_LIB} INTERFACE "${extra_link_flags}")
+endif()

components/pthread/component.mk

@@ -11,3 +11,11 @@ COMPONENT_ADD_LDFLAGS := -lpthread
 ifdef CONFIG_FREERTOS_ENABLE_STATIC_TASK_CLEAN_UP
 COMPONENT_ADD_LDFLAGS += -Wl,--wrap=vPortCleanUpTCB
 endif
+
+ifeq ($(GCC_NOT_5_2_0), 1)
+# Forces the linker to include pthread implementation from this component,
+# instead of the weak implementations provided by libgcc.
+COMPONENT_ADD_LDFLAGS += -u pthread_include_pthread_impl
+COMPONENT_ADD_LDFLAGS += -u pthread_include_pthread_cond_impl
+COMPONENT_ADD_LDFLAGS += -u pthread_include_pthread_local_storage_impl
+endif  # GCC_NOT_5_2_0

components/pthread/pthread.c

@@ -820,3 +820,8 @@ int pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate)
     }
     return EINVAL;
 }
+
+/* Hook function to force linking this file */
+void pthread_include_pthread_impl()
+{
+}

components/pthread/pthread_cond_var.c

@@ -198,3 +198,8 @@ int pthread_cond_destroy(pthread_cond_t *cv)
 
     return ret;
 }
+
+/* Hook function to force linking this file */
+void pthread_include_pthread_cond_var_impl()
+{
+}

components/pthread/pthread_local_storage.c

@@ -255,3 +255,8 @@ int pthread_setspecific(pthread_key_t key, const void *value)
 
     return 0;
 }
+
+/* Hook function to force linking this file */
+void pthread_include_pthread_local_storage_impl()
+{
+}