Using GDB stub

• Add #include <GDBStub.h> to the sketch
• Upload the sketch
• Redirect serial port to TCP port:

    tcp_serial_redirect.py -p /dev/tty.SLAB_USBtoUART -b 115200 --spy -P 9980 --rts=0 --dtr=0

Change port and baud rate as necessary. This command requires python and pyserial.

• Observe serial output:

    nc localhost 9980

• When crash happens, Trap %d: pc=%p va=%p line will appear in serial output.
• Close nc and start gdb:

    xtensa-lx106-elf-gdb /path/to/Sketch.cpp.elf -ex "target remote :9980"

• Use gdb to inspect program state at the point of an exception.

Tips and tricks

• To halt the target when software WDT fires, add

    ((int*)0) = 0;

at the top of __wrap_system_restart_local in core_esp8266_postmortem.c.

License

GDB Server stub by Marko Mikulicic was taken from Cesanta's smart.js

https://github.com/cesanta/smart.js

Copyright (c) 2013-2014 Cesanta Software Limited All rights reserved

This software is dual-licensed: you can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation. For the terms of this license, see http://www.gnu.org/licenses.

You are free to use this software under the terms of the GNU General Public License, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

Alternatively, you can license this software under a commercial license, as set out in https://www.cesanta.com/license.