diff --git a/boards/native/Makefile.include b/boards/native/Makefile.include
index 10dab68a1d..48474fb055 100644
--- a/boards/native/Makefile.include
+++ b/boards/native/Makefile.include
@@ -20,9 +20,17 @@ export CGANNOTATE ?= cg_annotate
 export GPROF ?= gprof
 
 # basic cflags:
-CFLAGS += -Wall -Wextra -pedantic $(CFLAGS_DBG)
+CFLAGS += -Wall -Wextra -pedantic $(CFLAGS_DBG) $(CFLAGS_OPT)
+CFLAGS += -U_FORTIFY_SOURCE
 CFLAGS_DBG ?= -g3
 
+ifneq (,$(filter backtrace,$(USEMODULE)))
+  $(warning module backtrace is used, do not omit frame pointers)
+  CFLAGS_OPT ?= -Og -fno-omit-frame-pointer
+else
+  CFLAGS_OPT ?= -Og
+endif
+
 # default std set to gnu11 if not overwritten by user
 ifeq (,$(filter -std=%, $(CFLAGS)))
   CFLAGS += -std=gnu11
diff --git a/examples/filesystem/main.c b/examples/filesystem/main.c
index 759d61c4ab..add2dda4ec 100644
--- a/examples/filesystem/main.c
+++ b/examples/filesystem/main.c
@@ -287,7 +287,7 @@ static int _tee(int argc, char **argv)
     }
     fclose(f);
 #else
-    int fd = open(argv[1], O_RDWR | O_CREAT);
+    int fd = open(argv[1], O_RDWR | O_CREAT, 00777);
     if (fd < 0) {
         printf("error while trying to create %s\n", argv[1]);
         return 1;
diff --git a/pkg/qcbor/Makefile b/pkg/qcbor/Makefile
index a995413d6a..41f7bf5817 100644
--- a/pkg/qcbor/Makefile
+++ b/pkg/qcbor/Makefile
@@ -5,5 +5,11 @@ PKG_LICENSE = BSD-3-Clause
 
 include $(RIOTBASE)/pkg/pkg.mk
 
+# some variable seem uninitialized to gcc with -Og but are not
+# https://gcc.gnu.org/bugzilla/buglist.cgi?quicksearch=may%20be%20used%20uninitialized
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42145
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90710#c1
+CFLAGS += -Wno-maybe-uninitialized
+
 all:
 	"$(MAKE)" -C $(PKG_SOURCE_DIR)/src -f $(RIOTBASE)/Makefile.base MODULE=$(PKG_NAME)
diff --git a/pkg/wakaama/Makefile b/pkg/wakaama/Makefile
index 0238324760..5cea8c9bae 100644
--- a/pkg/wakaama/Makefile
+++ b/pkg/wakaama/Makefile
@@ -5,6 +5,12 @@ PKG_LICENSE=EDL-1.0,EPL-1.0
 
 include $(RIOTBASE)/pkg/pkg.mk
 
+# some variable seem uninitialized to gcc with -Og but are not
+# https://gcc.gnu.org/bugzilla/buglist.cgi?quicksearch=may%20be%20used%20uninitialized
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42145
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90710#c1
+CFLAGS += -Wno-maybe-uninitialized
+
 all:
 	"$(MAKE)" -C $(PKG_SOURCE_DIR)/core -f $(RIOTBASE)/Makefile.base MODULE=wakaama_core
 	"$(MAKE)" -C $(PKG_SOURCE_DIR)/core/er-coap-13 -f $(RIOTBASE)/Makefile.base MODULE=wakaama_core_coap13
diff --git a/pkg/wolfssl/Makefile b/pkg/wolfssl/Makefile
index 109e9de4b4..4e57baab62 100644
--- a/pkg/wolfssl/Makefile
+++ b/pkg/wolfssl/Makefile
@@ -5,6 +5,12 @@ PKG_LICENSE=GPLv2
 
 include $(RIOTBASE)/pkg/pkg.mk
 
+# some variable seem uninitialized to gcc with -Og but are not
+# https://gcc.gnu.org/bugzilla/buglist.cgi?quicksearch=may%20be%20used%20uninitialized
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42145
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90710#c1
+CFLAGS += -Wno-maybe-uninitialized
+
 .PHONY: wolfcrypt%
 
 all: $(filter wolfcrypt wolfcrypt-test wolfcrypt-benchmark,$(USEMODULE))
diff --git a/tests/unittests/tests-ieee802154/tests-ieee802154.c b/tests/unittests/tests-ieee802154/tests-ieee802154.c
index b966cb8ad1..ee202466a5 100644
--- a/tests/unittests/tests-ieee802154/tests-ieee802154.c
+++ b/tests/unittests/tests-ieee802154/tests-ieee802154.c
@@ -44,10 +44,10 @@ static void test_ieee802154_set_frame_hdr_flags0_non_beacon_non_ack(void)
     const le_uint16_t src_pan = byteorder_htols(0);
     const le_uint16_t dst_pan = byteorder_htols(0);
     const uint8_t flags = IEEE802154_FCF_TYPE_DATA;
-    uint8_t res;
+    uint8_t res[2];
 
     TEST_ASSERT_EQUAL_INT(0,
-                          ieee802154_set_frame_hdr(&res, NULL, 0,
+                          ieee802154_set_frame_hdr(res, NULL, 0,
                                                    NULL, 0,
                                                    src_pan, dst_pan,
                                                    flags, TEST_UINT8));