esp-gdbstub

Intro

ESP8266 debugging tool intended to be used with esp-open-rtos. Based on Espressif/esp-gdbstub.

Usage

1. Build requires premake5 and xtensa-lx106-elf toolchain. Make sure both are in your PATH.

2. Configure with premake5 gmake. The following options are supported:

   • --with-eor=/path/to/esp-open-rtos: this option is required. It should point to an actual esp-open-rtos location.

   • --with-threads: enable RTOS task debugging. As for now, there is very basic support of threads, you will be able
     to see multiple tasks when a breakpoint is hit, but GDB will most likely crash shorlty after. This option also has
     a performance impact because a lot of data will be transferred through serial connection — consider increasing
     the baudrate.

     When thread support is enabled, you need to add the following definitions to CFLAGS of your project before compiling
     FreeRTOS libs:

     EXTRA_CFLAGS+=-DportREMOVE_STATIC_QUALIFIER -DINCLUDE_pcTaskGetTaskName=1
     # The line above should go before including common.mk

     Run make clean after switching the state of this flag.

3. Run make

4. Add library to your project:

    PROGRAM=blink
    # Order is important!
    EXTRA_CFLAGS+=-I../../../esp-gdbstub/include
    EXTRA_LDFLAGS+=-L../../../esp-gdbstub/lib
    include ../../common.mk
    LIBS+=esp-gdbstub
    PROGRAM_CFLAGS+=-O0

5. Call gdbstub_init() after configuring UART speed.

Optimization, stack trace resolving and GDB

It has been observed that GDB may crash when user requests step over source in a file compiled with optimization turned on. I haven’t figured out why exactly this happens, but it has something to do with stack frame resolving. Turning optimization off for the whole project would impact performance and code size — that’s why only PROGRAM_CFLAGS is modified.

Eclipse CDT setup

To use Eclipse CDT for debugging, open Eclipse, create a new project and create a debug configuration for C/C++ Remote Application.

You need to set the following options:

1. Main → Application: Firmware ELF
2. Debugger: Uncheck “Stop on startup at: main”
3. Debugger → Main: select GDB binary and .gdbinit file provided with esp-gdbstub
4. Debugger → Connection → Type: Serial
5. Debugger → Connection → Speed: 115200

Note that upon launching the debug session gdb will send “continue” command if the target is paused at gdbstub_do_break. If you want to stop right after debug session launch, place gdbstub_do_break macro twice in your code.

Notes

• Using software breakpoints (‘br’) only works on code that’s in RAM. Code in flash can only have a hardware breakpoint (‘hbr’). If you know where you want to break before downloading the program to the target, you can use gdbstub_do_break() macro as much as you want.
• Due to hardware limitations, only one hardware breakpount and one hardware watchpoint are available.