ESP32 Forum

Posted: **Wed Jan 26, 2022 6:02 am**

I'm looking into an issue where the system hangs and would trigger task watchdog if enabled. Backtrace reported by WDT looks like the following:

: backtrace.png (136.27 KiB) Viewed 2164 times

Seems the hang happens inside a call to __log2(), which is itself a simple function:

Code: [Select all] [Expand/Collapse]

__uint32_t
__log2(num)
    __uint32_t num;
{
    __uint32_t i, limit;
 
    limit = 1;
    for (i = 0; limit < num; limit = limit << 1, i++);
    return (i);
}

GeSHi © Codebox Plus Extension

So I attached gdb to a running (hanging) instance and examined the assembly listing as running on the core:

: assembly.png (50.68 KiB) Viewed 2164 times

Here is the weird part: the jump address for instruction at <__log2+17> is nowhere inside the valid range (not a start address of an instruction), right? What could be wrong?

Thanks for your help!

Posted: **Wed Jan 26, 2022 9:52 am**

Further digging indicates the hang is related to -1 being passed to __log2() and the way this function is implemented (left shift and compare). However, I'm still curious about the jump address not being the start address of any instruction. Is this a feature of Xtensa architecture?

ESP32 Forum

Task WDT triggered in __log2() and weird program behavior

Task WDT triggered in __log2() and weird program behavior

Re: Task WDT triggered in __log2() and weird program behavior