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384 lines
10 KiB
ReStructuredText
384 lines
10 KiB
ReStructuredText
Using GDB to Debug Applications
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===============================
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ESP applications can be debugged using GDB, the GNU debugger, which is
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included with the standard IDE installation. This note will only discuss
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the ESP specific steps, so please refer to the
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`main GNU GDB documentation
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<//sourceware.org/gdb/download/onlinedocs/gdb/index.html>`__.
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Note that as of 2.5.0, the toolchain moved from the ESPRESSIF patched,
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closed-source version of GDB to the main GNU version. The debugging
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formats are different, so please be sure to use only the latest Arduino
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toolchain GDB executable.
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CLI and IDE Note
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----------------
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Because the Arduino IDE doesn't support interactive debugging, the following
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sections describe debugging using the command line. Other IDEs which use
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GDB in their debug backends should work identically, but you may need to
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edit their configuration files or options to enable the remote serial
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debugging required and to set the standard options. PRs are happily
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accepted for updates to this document with additional IDEs!
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Preparing your application for GDB
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----------------------------------
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Applications need to be changed to enable GDB debugging support. This
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change will add 2-3KB of flash and around 700 bytes of IRAM usage, but
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should not affect operation of the application.
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In your main ``sketch.ino`` file, add the following line to the top of
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the application:
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.. code:: cpp
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#include <GDBStub.h>
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And in the ``void setup()`` function ensure the serial port is initialized
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and call ``gdbstub_init()``:
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.. code:: cpp
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Serial.begin(115200);
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gdbstub_init();
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Rebuild and reupload your application and it should run exactly as before.
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Starting a Debug Session
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------------------------
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Once your application is running, the process to attach a debugger is
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quite simple:
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. Close the Arduino Serial Monitor
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. Locate Application.ino.elf File
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. Open a Command Prompt and Start GDB
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. Apply the GDB configurations
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. Attach the Debugger
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. Debug Away!
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Close the Arduino Serial Monitor
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Because GDB needs full control of the serial port, you will need to close
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any Arduino Serial Monitor windows you may have open. Otherwise GDB will
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report an error while attempting to debug.
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Locate Application.ino.elf File
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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In order for GDB to debug your application, you need to locate the compiled
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ELF format version of it (which includes needed debug symbols).
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Under Linux these files are stored in ``/tmp/arduino_build_*`` and the following command will help locate the right file for your app:
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.. code:: bash
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find /tmp -name "*.elf" -print
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Under Windows these files are stored in ``%userprofile%\AppData\Local\Temp\arduino_build_*`` and the following command will help locate the right file for your app:
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.. code:: bash
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dir %userprofile%\appdata\*.elf /s/b
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Note the full path of ELF file that corresponds to your sketch name, it will
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be needed later once GDB is started.
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Open a Command Prompt and Start GDB
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Open a terminal or ``CMD`` prompt and navigate to the proper ESP8266 toolchain
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directory.
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Linux
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.. code:: bash
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~/.arduino15/packages/esp8266/hardware/xtensa-lx106-elf/bin/xtensa-lx106-elf-gdb
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Windows (Using Board Manager version)
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.. code:: bash
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%userprofile%\AppData\Local\Arduino15\packages\esp8266\tools\xtensa-lx106-elf-gcc\2.5.0-3-20ed2b9\bin\xtensa-lx106-elf-gdb.exe
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Windows (Using Git version)
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.. code:: bash
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%userprofile%\Documents\Arduino\hardware\esp8266com\esp8266\tools\xtensa-lx106-elf\bin\xtensa-lx106-elf-gdb.exe
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Please note the proper GDB name is "xtensa-lx106-elf-gdb". If you accidentally
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run "gdb" you may start your own operating system's GDB, which will not know how
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to talk to the ESP8266.
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Apply the GDB Configurations
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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At the ``(gdb)`` prompt, enter the following options to configure GDB for the
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ESP8266 memory map and configuration:
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.. code:: bash
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set remote hardware-breakpoint-limit 1
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set remote hardware-watchpoint-limit 1
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set remote interrupt-on-connect on
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set remote kill-packet off
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set remote symbol-lookup-packet off
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set remote verbose-resume-packet off
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mem 0x20000000 0x3fefffff ro cache
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mem 0x3ff00000 0x3fffffff rw
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mem 0x40000000 0x400fffff ro cache
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mem 0x40100000 0x4013ffff rw cache
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mem 0x40140000 0x5fffffff ro cache
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mem 0x60000000 0x60001fff rw
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set serial baud 115200
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Now tell GDB where your compiled ELF file is located:
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.. code:: bash
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file /tmp/arduino_build_257110/sketch_dec26a.ino.elf
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Attach the Debugger
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~~~~~~~~~~~~~~~~~~~
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Once GDB has been configured properly and loaded your debugging symbols, connect
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it to the ESP with the command (replace the ttyUSB0 or COM9 with your ESP's serial
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port):
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.. code:: bash
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target remote /dev/ttyUSB0
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or
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.. code:: bash
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target remote \\.\COM9
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At this point GDB will send a stop the application on the ESP8266 and you can
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begin setting a breakpoint (``break loop``) or any other debugging operation.
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Example Debugging Session
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-------------------------
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Create a new sketch and paste the following code into it:
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.. code:: cpp
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#include <GDBStub.h>
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void setup() {
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Serial.begin(115200);
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gdbstub_init();
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Serial.printf("Starting...\n");
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}
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void loop() {
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static uint32_t cnt = 0;
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Serial.printf("%d\n", cnt++);
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delay(100);
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}
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Save it and then build and upload to your ESP8266. On the Serial monitor you
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should see something like
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.. code:: bash
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1
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2
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3
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....
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Now close the Serial Monitor.
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Open a command prompt and find the ELF file:
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.. code:: bash
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earle@server:~$ find /tmp -name "*.elf" -print
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/tmp/arduino_build_257110/testgdb.ino.elf
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/tmp/arduino_build_531411/listfiles.ino.elf
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/tmp/arduino_build_156712/SDWebServer.ino.elf
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In this example there are multiple ``elf`` files found, but we only care about
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the one we just built, ``testgdb.ino.elf``.
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Open up the proper ESP8266-specific GDB
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.. code:: bash
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earle@server:~$ ~/.arduino15/packages/esp8266/hardware/xtensa-lx106-elf/bin/xtensa-lx106-elf-gdb
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GNU gdb (GDB) 8.2.50.20180723-git
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Copyright (C) 2018 Free Software Foundation, Inc.
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License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
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This is free software: you are free to change and redistribute it.
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There is NO WARRANTY, to the extent permitted by law.
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Type "show copying" and "show warranty" for details.
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This GDB was configured as "--host=x86_64-linux-gnu --target=xtensa-lx106-elf".
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Type "show configuration" for configuration details.
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For bug reporting instructions, please see:
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<https://www.gnu.org/software/gdb/bugs/>.
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Find the GDB manual and other documentation resources online at:
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<https://www.gnu.org/software/gdb/documentation/>.
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For help, type "help".
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Type "apropos word" to search for commands related to "word".
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(gdb)
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We're now at the GDB prompt, but nothing has been set up for the ESP8266
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and no debug information has been loaded. Cut-and-paste the setup options:
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.. code:: bash
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(gdb) set remote hardware-breakpoint-limit 1
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(gdb) set remote hardware-watchpoint-limit 1
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(gdb) set remote interrupt-on-connect on
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(gdb) set remote kill-packet off
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(gdb) set remote symbol-lookup-packet off
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(gdb) set remote verbose-resume-packet off
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(gdb) mem 0x20000000 0x3fefffff ro cache
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(gdb) mem 0x3ff00000 0x3fffffff rw
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(gdb) mem 0x40000000 0x400fffff ro cache
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(gdb) mem 0x40100000 0x4013ffff rw cache
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(gdb) mem 0x40140000 0x5fffffff ro cache
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(gdb) mem 0x60000000 0x60001fff rw
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(gdb) set serial baud 115200
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(gdb)
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And tell GDB where the debugging info ELF file is located:
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.. code:: bash
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(gdb) file /tmp/arduino_build_257110/testgdb.ino.elf
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Reading symbols from /tmp/arduino_build_257110/testgdb.ino.elf...done.
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Now, connect to the running ESP8266:
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.. code:: bash
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(gdb) target remote /dev/ttyUSB0
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Remote debugging using /dev/ttyUSB0
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0x40000f68 in ?? ()
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(gdb)
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Don't worry that GDB doesn't know what is at our present address, we broke
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into the code at a random spot and we could be in an interrupt, in the
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ROM, or elsewhere. The important bit is that we're now connected and
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two things will now happen: we can debug, and the app's regular serial
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output will be displayed on the GDB console..
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Continue the running app to see the serial output:
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.. code:: bash
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(gdb) cont
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Continuing.
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74
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75
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76
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77
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...
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The app is back running and we can stop it at any time using ``Ctrl-C``:
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.. code:: bash
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113
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^C
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Program received signal SIGINT, Interrupt.
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0x40000f68 in ?? ()
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(gdb)
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At this point we can set a breakpoint on the main ``loop()`` and restart
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to get into our own code:
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.. code:: bash
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(gdb) break loop
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Breakpoint 1 at 0x40202e33: file /home/earle/Arduino/sketch_dec26a/sketch_dec26a.ino, line 10.
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(gdb) cont
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Continuing.
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Note: automatically using hardware breakpoints for read-only addresses.
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bcn_timout,ap_probe_send_start
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Breakpoint 1, loop () at /home/earle/Arduino/sketch_dec26a/sketch_dec26a.ino:10
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10 void loop()
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(gdb)
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Let's examine the local variable:
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.. code:: bash
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(gdb) next
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loop () at /home/earle/Arduino/sketch_dec26a/sketch_dec26a.ino:13
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13 Serial.printf("%d\n", cnt++);
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(gdb) print cnt
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$1 = 114
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(gdb)
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And change it:
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.. code:: bash
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$2 = 114
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(gdb) set cnt = 2000
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(gdb) print cnt
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$3 = 2000
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(gdb)
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And restart the app and see our changes take effect:
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.. code:: bash
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(gdb) cont
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Continuing.
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2000
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Breakpoint 1, loop () at /home/earle/Arduino/sketch_dec26a/sketch_dec26a.ino:10
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10 void loop() {
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(gdb) cont
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Continuing.
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2001
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Breakpoint 1, loop () at /home/earle/Arduino/sketch_dec26a/sketch_dec26a.ino:10
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10 void loop() {
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(gdb)
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Looks like we left the breakpoint on loop(), let's get rid of it and try again:
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.. code:: bash
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(gdb) delete
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Delete all breakpoints? (y or n) y
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(gdb) cont
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Continuing.
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2002
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2003
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2004
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2005
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2006
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....
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At this point we can exit GDB with ``quit`` or do further debugging.
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ESP8266 Hardware Debugging Limitations
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--------------------------------------
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The ESP8266 only supports a single hardware breakpoint and a single
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hardware data watchpoint. This means only one breakpoint in user code
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is allowed at any time. Consider using the ``thb`` (temporary hardware
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breakpoint) command in GDB while debugging instead of the more common
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``break`` command, since ``thb`` will remove the breakpoint once it is
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reached automatically and save you some trouble.
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