• State Not Answered
  • Locked Locked
  • Replies 2 replies
  • Subscribers 21 subscribers
  • Views 747 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Passing by address results in compiler miscalculation?

Tim Stein

When I use a local struct variable of type RCC_ClocksTypeDef (part of the ST peripheral library) and I call the RCC_GetClocksFreq() function passing the local struct as the parameter, for some reason the compiler increments the address by 4 so the data is all misaligned. However, if I use a global variable of the same type, the compiler handles this ok.

The issue only occurs with compiler optimization level of 0 or 1.

I'm using Keil MDK-Arm 4.13a and targeting the STM32F103. Using the simulator for now. I have the latest version of the ST peripheral library. My code snip in 'C' looks like:

.....

RCC_ClocksTypeDef  grcc_clocks;

int main(void)
{
   RCC_ClocksTypeDef  rcc_clocks;
   RCC_GetClocksFreq(&rcc_clocks);
         RCC_GetClocksFreq(&grcc_clocks);
}

So with the code optimization set to Level 0 or 1, where the code does not result in the expected result, here is the asm:

   106:    RCC_ClocksTypeDef  rcc_clocks;
0x0800357C B086      SUB      sp,sp,#0x18
   107:    RCC_GetClocksFreq(&rcc_clocks);
0x0800357E A801      ADD      r0,sp,#0x04
0x08003580 F7FEFCBC  BL.W     RCC_GetClocksFreq (0x08001EFC)
   108:          RCC_GetClocksFreq(&grcc_clocks);
   109:
0x08003584 4842      LDR      r0,[pc,#264]  ; @0x08003690
0x08003586 F7FEFCB9  BL.W     RCC_GetClocksFreq (0x08001EFC)

So now with the code optimized to 2 or 3, THIS code works properly:

   106:    RCC_ClocksTypeDef  rcc_clocks;
0x0800332C B086      SUB      sp,sp,#0x18
   107:    RCC_GetClocksFreq(&rcc_clocks);
0x0800332E 4668      MOV      r0,sp
0x08003330 F7FEFD88  BL.W     RCC_GetClocksFreq (0x08001E44)
   108:          RCC_GetClocksFreq(&grcc_clocks);
   109:
0x08003334 4842      LDR      r0,[pc,#264]  ; @0x08003440
0x08003336 F7FEFD85  BL.W     RCC_GetClocksFreq (0x08001E44)

So the issue seems to be this line:

0x0800357E A801      ADD      r0,sp,#0x04

Is this a compiler error?

0