> William "Chops" Westfield wrote:
>
>> On Jun 23, 2011, at 8:29 PM, Harold Hallikainen wrote:
>>
>>> Is it possible to read the current stack pointer in C? If so, what
>>> would the instruction be?
>>
>> Exactly or approximately?
>>
>> void *returnsp()
>> {
>>    int a;
>>    return &a;
>> }
>>
>> Should be pretty close (on almost any processor that uses stack frames
>> for local variables.)
>
> That's probably close, but at the caller's location almost certainly off
> by an int, possibly by an int and a return address and possibly some
> stack frame overhead (if the function didn't get inlined).
>
>> Otherwise you get to look at inline assembler and/or assembler
>> subroutines.
>
> And the compiler docs and generated code for how the compiler uses the
> stack.
>


Thanks for the obvious solution that I did not think of? I kept digging
through documentation on MIPS assembly, trying to figure this out. I
messed around with locals a bit and did come up with a method of matching
the pointer to the SP as reported in the processor registers window.

What I'm doing now is writing a known pattern to the space between the
heap and the stack, running code for a while, then looking back at that
space. I can't figure out any other method on a PIC32 to determine whether
the stack and the heap have collided. The PIC24 has a stack limit
register, but apparently not the PIC32. I assume malloc returns a null
pointer when it runs out of space allocated for the heap in the linker,
but that does not keep the stack from growing down into the heap space. I
think this is what's causing my occasional bus exceptions.

Again, thanks for the solution!

Harold


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