ARM组装 - 监控堆栈指针

Question

I am trying to monitor the stack pointer in C on an embedded ARM MCU. As the project grows, I'd like to know how much space is left and map more if necessary.

I already know the start and top address of the stack from the map file generated when compiled.

I would like to get the address the sp is pointing to so I can do some basic math and monitor the stack on a percentage used basis, but I am new to ARM and don't understand why my assembly is not working.

This is what I am doing:

int stackptr;
asm
{                
    LDR r0, =stackptr  // put address of C variable stackptr in r0
    MOV r1, sp         // move value of sp to r1
    STR r1, [r0]       // put value of r1 in address contained in r0 (stackptr)
}

// math using stackptr...

If I look at the address stored in stackptr, its right at the start of the stack and its not changing (I am calling this every 100ms). I expected this to be bouncing around somewhere in the middle of my stack.

Also, if I try to get the address of the stack base and limit (using the same method but with sb and sl), I just get 0's. I am not as concerned about this since from my research it seems they are not always used.

Thanks for the help

Answer 1

Try making stackptr volatile , since compiler can think it is not getting updated and use stale copy in a register or completely optimize away access to it.

Another approach to your problem might be to ask compiler to calculate possible stack usage and create a report. For example with GCC you can use -fstack-usage and -Wstack-usage flags. -fstack-usage creates a .su file with the same name, reporting stack usage of each function. -Wstack-usage=X warns if a function requires more stack than what's passed in. Of course this is static analysis so compiler can't handle all the cases (but generate warnings if so). I would also expect any commercial compiler to have such functionality if you are not using GCC.