newlib: force including IDF locks implementation

components/newlib/CMakeLists.txt

@@ -25,6 +25,10 @@ if(GCC_NOT_5_2_0)
         set(COMPONENT_ADD_LDFRAGMENTS esp32-spiram-rom-functions-c.lf)
     endif()
 
+    # Forces the linker to include locks.o from this component, which
+    # replaces weak locking functions defined in libc.a:locks.o
+    set(EXTRA_LINK_FLAGS "-u newlib_include_locks_impl")
+
 else()
     # Remove this section when GCC 5.2.0 is no longer supported
     # 'include' and 'lib' directories should also be removed.
@@ -58,3 +62,7 @@ endif()
 target_link_libraries(${COMPONENT_TARGET} ${LIBC} ${LIBM})
 
 set_source_files_properties(syscalls.c PROPERTIES COMPILE_FLAGS -fno-builtin)
+
+if(EXTRA_LINK_FLAGS)
+    target_link_libraries(${COMPONENT_TARGET} "${EXTRA_LINK_FLAGS}")
+endif()

components/newlib/component.mk

@@ -14,6 +14,10 @@ ifdef CONFIG_SPIRAM_CACHE_WORKAROUND
 COMPONENT_ADD_LDFRAGMENTS := esp32-spiram-rom-functions-c.lf
 endif
 
+# Forces the linker to include locks.o from this component, which
+# replaces weak locking functions defined in libc.a:locks.o
+COMPONENT_ADD_LDFLAGS += -u newlib_include_locks_impl
+
 else # GCC_NOT_5_2_0
 # Remove this section when GCC 5.2.0 is no longer supported
 

components/newlib/locks.c

@@ -216,3 +216,10 @@ void IRAM_ATTR _lock_release(_lock_t *lock) {
 void IRAM_ATTR _lock_release_recursive(_lock_t *lock) {
     lock_release_generic(lock, queueQUEUE_TYPE_RECURSIVE_MUTEX);
 }
+
+/* No-op function, used to force linking this file,
+   instead of the dummy locks implementation from newlib.
+ */
+void newlib_include_locks_impl()
+{
+}