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Tasks backtrace switcher/viewer snippet for debugger (gcc, gdb, ARM Cortex-M3 MPU port, Eclipse support)

Artem Pisarenko

March 30, 2013 15:30

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This solution allows switch to any task from almost any context while debugging via GNU GDB debugger (even in Eclipse IDE !).

Supported ports:
- ARM Cortex-M3
- ARM Cortex-M3 MPU
(Switching from system exceptions (first 15 vectors) IS NOT supported.)

Supported compiler: gcc

Archive contains .gdbinit script with commands and port-dependent source file (contains alternative context-switcher and debug-interface variables).

1. add corresponding source file to your project (freertos port folder is good location for placing)
2. add following replacement macro in FreeRTOSConfig.h:
   #define xPortPendSVHandler xPortPendSVHandler_native // any valid c identifier name

   Macro name must match PendSV vector name in startup file. Startup file should NOT #include FreeRTOSConfig.h (either directly, or indirectly through freertos headers and other headers). Example provided for CMSIS-based project.

3. execute .gdbinit script file at start of debug session (source -v <script file>)

While debugging you can stop execution at almost any place (manually or via breakpoint hits) and use following commands in debug console:

• freertos_show_threads

  Shows tasks table: handle(xTaskHandle) and name

• freertos_switch_to_task handle
  Switches debugging context to specified task. Argument: task handle taken from freertos_show_threads output.

  You can switch to any task many times as desired to view their context. BUT don't step/execute anything from switched state because you will break freertos state machine and following program execution will be unpredictable (for example, task may be in blocked state waiting to receive item from a queue).

• freertos_restore_running_context
  Restores current running context. This command will return you to initial state and you can resume execution !

 

Tested with:

- Yagarto GNU ARM toolchain (windows build yagarto-bu-2.23.1_gcc-4.7.2-c-c++_nl-1.20.0_gdb-7.5.1_eabi_20121222.exe), FreeRTOS V7.4.0;

- GCC ARM Embedded toolchain (windows build gnu_tools_arm_embedded_4.7 2013q1), , FreeRTOS V7.4.2.

 

Guidelines for Eclipse (Indigo SR2, Juno SR2)

 

Go to debug configuration (GDB Hardware Debugging) -> Startup tab -> add following line to Initialization commands:

source -v <absolute path to .gdbinit file>

(make sure there are no trailing spaces and empty lines in textbox !)

Example: source -v C:\Users\Artem\Documents\test\.gdbinit-FreeRTOS-helpers

While debugging select gdb leaf ("arm-none-eabi-gdb.exe" in my case) in Debug view and use Console to execute commands.

 

Known issues:

1. Backtrace looks broken in some situations (i.e. tasks switched out in vTaskDelay()). I described problem here:
   http://stackoverflow.com/questions/15701074/cortex-m3-gdb-shows-broken-backtrace-when-stopped-in-the-middle-of-function-epi
   Question isn't answered yet. Current workaround is show_broken_backtrace command, but it's very specific for case I personally faced with. It may not work in your situation and may damage execution context (or even cause crash after you continue debugging).

2. Sometimes (rarely) one instruction may be executed during switch.
3. Sometimes Eclipse shows errors in Variables view. These variables are ok and may be inspected with any other method (but I don't know how to change their values, maybe via console only).

Enjoy !

UPDATED (13 june 2013):
- added ARM Cortex-M3 port (non-MPU);
- fixed critical error with integer size mismatching (might cause hard fault).

UPDATED (04 april 2013):
- added support for switching from exception context (except system exceptions);
- fixed case when interrupts globally disabled (PRIMASK set to 1 or context is within __disable_irq()/__enable_irq() section);
- fixed case when pending context switch (requested from interrupt) was lost;
- added validating of running context before trying to switch;
- added "RUNNING" label to task table;
- fixed error with nameless tasks output;
- added early checking for freertos_switch_to_task argument (before it fails in the middle of command execution);
- "freertos_restore_running_task" command renamed to "freertos_restore_running_context".

 

freertos_tasks_switcher_support__gdb__armcm3.zip

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8 comments

• 0
  
  Geoffrey Wossum September 30, 2014 14:49

  Artem,

  This is a great module!  However, could you clarify the license this code is provided under (e.g. BSD, MIT, etc.)?

  Thanks!

• 0
  
  Artem Pisarenko October 01, 2014 12:07

  Thank you for your feedback ! Glad to hear you like it.
  As far as I remember, this code falls under the terms of this forum. At least, I do not restrict any usage/modification/distribution of this code.
• 0
  
  Prasanna November 08, 2014 21:53

  Hi Artem,

   I have a Cortex-M3 non MPU port for Atmel SAM3X (Although the Micro does have a MPU!). I tried compiling in the file "cm3_debug_gdb_helper.c" and changed FreeRTOSConfig.h as you mentioned. With these changes, my board doesn't seem to boot up all the way. I am using arm-none-gnueabi- 4.7.2013q3 under windows/eclipse.

   Attached is the PendSVHandler for my port, which looks a little bit different than your implementation (apart from the task switching and debug hooks). Please see if any change is needed to your file to make it work.

   This would be a very useful feature to have, and I would really like to get this to work.

• 0
  
  Artem Pisarenko November 12, 2014 08:43

  Hi Prasanna,
  
  Actually, my implementation is modified implementation from standard Cortex-M3 port. There are no atmel port (i.e. it's microcontroller-independent). I compared it with your implementation and found no differences. Provided that you use standard unmodified port, there are should be no issues.
  
  Check that your startup file uses exactly same vector name as you defined in FreeRTOSConfig (i.e. "xPortPendSVHandler"). Also, I forgot to mention in my first post, that startup file should NOT #include freertos headers (either directly, or indirectly through other #includes).
  
  It might also be that FreeRTOS version you use is incompatible with my snippet anymore (because snippet depends on internal freertos implementation, which may be changed at any time).
• 0
  
  Geoffrey Wossum November 12, 2014 16:05

  Hi Prasanna,

  I had the same problem trying to use this out of the box on an Atmel ATSAM4E16E.  I have attached a modified version that works on the ATSAM4E16E, which is a Cortex-M4.  The PendSVHandler between the SAM4 and the non-Cortex-M4 is nearly identical, so this might work for you out of the box.  Otherwise, there's only a couple of minor differences between the two Atmel ports which you should be able to apply to this.

  Couple of notes:

  1. The file to build into your project is now sam4_debug_gdb_helper.c. 
  2. The macro to define in your FreeRTOSConfig.h is now PendSV_Handler.

  Good luck!

• 0
  
  Element Green June 02, 2016 20:02

  I was getting the error "Argument to arithmetic operation not a number or boolean." when attempting to use the freertos_switch_to_task GDB command.  I was able to fix this by changing the following line in the .gdbinit-FreeRTOS-helpers file:

  From:

  set $current_IPSR_val = $xpsr & 0xFF

  To:

  set $current_IPSR_val = $xPSR & 0xFF

  Seems the reference to the xPSR register is case sensitive.  Probably relates to the version of GDB I'm using, which is 7.10.

  Hope that helps someone!

• 0
  
  L29Ah July 20, 2016 02:22

  Somehow my gdb won't see the global variables declared in that file. I.e.

  (gdb) p dbgFreeRTOSConfig_suspend_value
  No symbol "dbgFreeRTOSConfig_suspend_value" in current context.
  
  

  Although it clearly linked in and i can grep the name out of the elf, it doesn't get included in the symbol table.

• 0
  
  Artem Pisarenko July 21, 2016 19:02

  Sorry to hear that. I'm too busy right now. I'll update snippet to be compatible with latest FreeRTOS/GDB/Eclipse as soon as I'll have enough time to test it...