nRF51822 gcc unknown errors.

Question

SDK: 12.3.0 
 SOFTDEVICE: s130_nrf51_2.0.1_softdevice 
 CHIP: nrf51822 AC 256K flash 32K ram 
 GCC flags: 
 # C flags common to all targets 
 CFLAGS += -DBOARD_CUSTOM 
 CFLAGS += -DSOFTDEVICE_PRESENT 
 CFLAGS += -DNRF51 
 CFLAGS += -DS130 
 CFLAGS += -DBLE_STACK_SUPPORT_REQD 
 CFLAGS += -DSWI_DISABLE0 
 CFLAGS += -DNRF51422 
 CFLAGS += -DNRF_SD_BLE_API_VERSION=2 
 CFLAGS += -mcpu=cortex-m0 
 CFLAGS += -mthumb -mabi=aapcs 
 #CFLAGS += -Wall -Werror 
 CFLAGS += -O3 -Os -g3 
 #CFLAGS += -O3 -Os -g3 
 # CFLAGS += -Wint-conversion -Wint-to-pointer-cast 
 CFLAGS += -mfloat-abi=soft 
 # keep every function in separate section, this allows linker to discard unused ones 
 CFLAGS += -ffunction-sections -fdata-sections -fno-strict-aliasing 
 CFLAGS += -fno-builtin --short-enums

CFLAGS += -DDEBUG 
 CFLAGS += -DDEBUG_NRF

Keil: 
 DEBUG_NRF DEBUG BLE_STACK_SUPPORT_REQD NRF51422 BOARD_CUSTOM NRF_SD_BLE_API_VERSION=2 S130 NRF51 SOFTDEVICE_PRESENT SWI_DISABLE0 
 
 hi, I have used both keil and gcc for nRF51822 development. 
 I found some strange situation. keil compiled product has no problem. 
 but, gcc product has some problem. 
 first, when ble connected, hardfault error occur sometimes. 
 second, In ble connected state or just after disconnect event triggered, I have called ble_advertising_start(BLE_ADV_MODE_IDLE) function for triggering idle event. 
 but, gcc code always stuck somewhere. never out ble_advertising_start function. 
 
 The more weird thing is that second problem disappear after removing CFLAGS optimization flags -O3 -Os -g3 in Makefile. 
 and I again attached CFLAGS optimization flags -O3 -Os -g3. but second problem never occur. but The first problem still occurs. 
 
 I don't understand this situation and I can not be sure of the completeness of the product. 
 
 Thank you for your advice.