topic Re: How can i find out what a local variable in the stack has been overwritten? in LPC Microcontrollers

How can i find out what a local variable in the stack has been overwritten?

basti — Thu, 04 Jan 2018 12:50:38 GMT

I am using LPC1778 controller with RTOS. A local variable in a subfunction has been overwritten by a overflow. How can i find out what a local variable in the stack has been overwritten?

Re: How can i find out what a local variable in the stack has been overwritten?

jeremyzhou — Fri, 05 Jan 2018 02:01:43 GMT

Hi Sebastian Bläsing，

Thank you for your interest in NXP Semiconductor products and 

for the opportunity to serve you.

Actually, I'm not very clear with your question, so whether you can describe the question in details and attaching corresponding codes will be better☺.

I'm looking to forward to your reply.

TIC
 
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Re: How can i find out what a local variable in the stack has been overwritten?

basti — Fri, 05 Jan 2018 07:53:54 GMT

Hi jeremyzhou,

thank you for your reply.

A local variable (in a function) is always stored in the stack, is that correct? The value of this variable I can read out via the JTAG interface via LPCXpresso, for this I use the breakpoints. I found out that the value of a local variable (integer) was overridden by another function / task. Now I want to find out which function / task overwrites this memory area.

I use the FreeRTOS V7.6 Memory Allocation implementation "heap_2".

Re: How can i find out what a local variable in the stack has been overwritten?

carstengroen — Fri, 05 Jan 2018 08:26:12 GMT

Sebastian,

depending on what tool you use for debug you can set breakpoints on memory access in Cortex processors. I use Keil, and setting a breakpoint on a overwrite, it looks like this:

You can also define memory areas etc, its just a matter of syntax. If you know an exact place (address) that is being written in the tasks stackarea, set this address as the breakpoint. The processor will then stop at the exact spot where the write (to the illegal address) occurs.