STM32F4 executable stack?

Question

Is the stack executable on the STM32F4 MCU? I want to do this:

 unsigned int buffer[3];
 buffer[0] = 0x10000FA5; //Address: 0x10000FA0
 buffer[1] = 0xA0E1; //Address: 0x10000FA4 NOP
 buffer[2] = 0xA0E1; //Address> 0x10000FA8 NOP
 __asm __volatile__
 (
   "movw R1, #0x0fa0\n"  
   "movt R1, #0x1000\n" 
   "ldr pc, [r1, #0]\n" 
 );

In the assembly code, I fetch the content at address 0x10000fa0 (buffer[0]) to get my new program counter. The new program counter is 0x10000FA5, which is the address of the content of buffer[1]. In buffer[1] there is now an instruction (NOP) saved. Is this possible to execute?

Edit: I tried it out with GDB but I am getting following exception: prvGetRegistersFromStack (pulFaultStackAddress=0x10000f78 ) from FreeRTOS

Answer 1

The stm32 can happily execute from RAM, so yes, this is possible. Depending on which variant of STM32F4 you have different sections of SRAM are attached to the I-bus, this is detailed in the reference manual for your part.

Why do you want to do this? What problem are you trying to solve?

If you are trying to execute code from RAM there are well defined ways to achieve this with the linker.

Answer 2

I think this should work. But keep in mind that you probably can't just do a BL from RAM to FLASH or vice versa because the distance is too large (much larger than the maximum distance within RAM or FLASH).

I have used something similar to this to write a timed delay loop (on LPC2148 IIRC) because RAM timing is much more predicatble than FLASH timing (due to wait states, read buffering, alignment, etc.)

Answer 3

It is possible to protect the stack against execution using the Memory Protection Unit (MPU) of the Cortex-M4, but this is rarely done. So yes, it should generally be possible to execute code on the stack.