Posted on January 15, 2017 at 21:27I am working with a Nucleo L031K6 board and my application showed strange behaviour that I could finally track down as two C variables sharing the same memory location....
Not being a specialist in neither C nor the ST family, my question is: What am I doing wrong? or is this a bug in the compiler?
Below my stripped C source and the disassembly listing from the debugging session. Of course this application does not do anything at all anymore, but it still demonstrates the fault.
The variable 'secs' shares his address with variable 'txt[1][0]'
/* Includes ------------------------------------------------------------------*/
&sharpinclude 'main.h'
&sharpinclude 'stm32l0xx_hal.h'
int32_t tel;
uint32_t Klokstat;
uint8_t txt[1][5];
uint8_t secs;
/* Private function prototypes -----------------------------------------------*/
void Error_Handler(void);
int main(void)
{
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
tel=0;
secs = 58;
Klokstat=33;
txt[1][0]=67;
while (1) {
}
} // END MAIN
void Error_Handler(void)
{
/* USER CODE BEGIN Error_Handler */
/* User can add his own implementation to report the HAL error return state */
while(1)
{
}
/* USER CODE END Error_Handler */
}
&sharpifdef USE_FULL_ASSERT
void assert_failed(uint8_t* file, uint32_t line)
{
}
&sharpendif
/******************************************************************************/
/* Cortex-M0+ Processor Interruption and Exception Handlers */
/******************************************************************************/
void SysTick_Handler(void)
{
/* USER CODE BEGIN SysTick_IRQn 0 */
/* USER CODE END SysTick_IRQn 0 */
HAL_IncTick();
HAL_SYSTICK_IRQHandler();
/* USER CODE BEGIN SysTick_IRQn 1 */
/* USER CODE END SysTick_IRQn 1 */
}
void TIM21_IRQHandler(void)
{
}
The disassembly listing shows that 'secs' is stored at 0x2000 0451 and that the byte array 'txt' starts at 0x2000 044c
Accessing txt[1][0] gives an offset of 5 and also accesses location 0x2000 0451 !
main:
08000239: 0x0000b500 push {r7, lr}
0800023b: 0x0000af00 add r7, sp, &sharp0
54 HAL_Init();
0800023c: 0x00f0b8f8 bl 0x80003b0 <HAL_Init>
57 tel=0;
08000240: 0x0000064b ldr r3, [pc, &sharp24] ; (0x800025c <main+36>)
08000242: 0x00000022 movs r2, &sharp0
08000244: 0x00001a60 str r2, [r3, &sharp0]
60 secs = 58;
08000246: 0x0000064b ldr r3, [pc, &sharp24] ; (0x8000260 <main+40>)
08000248: 0x00003a22 movs r2, &sharp58 ; 0x3a
0800024a: 0x00001a70 strb r2, [r3, &sharp0]
63 Klokstat=33;
0800024c: 0x0000054b ldr r3, [pc, &sharp20] ; (0x8000264 <main+44>)
0800024e: 0x00002122 movs r2, &sharp33 ; 0x21
08000250: 0x00001a60 str r2, [r3, &sharp0]
65 txt[1][0]=67;
08000252: 0x0000054b ldr r3, [pc, &sharp20] ; (0x8000268 <main+48>)
08000254: 0x00004322 movs r2, &sharp67 ; 0x43
08000256: 0x00005a71 strb r2, [r3, &sharp5]
73 } // end while(1)
08000258: 0x0000fee7 b.n 0x8000258 <main+32>
0800025a: 0x0000c046 nop ; (mov r8, r8)
0800025c: 0x00005404 lsls r4, r2, &sharp17
0800025e: 0x00000020 movs r0, &sharp0
08000260: 0x00005104 lsls r1, r2, &sharp17
08000262: 0x00000020 movs r0, &sharp0
08000264: 0x00005804 lsls r0, r3, &sharp17
08000266: 0x00000020 movs r0, &sharp0
08000268: 0x00004c04 lsls r4, r1, &sharp17
0800026a: 0x00000020 movs r0, &sharp0
#nucleo #stm32l031 #compiler #variables #bug #gcc
