[Ovmsdev] Debugging

Stephen Casner casner at acm.org
Thu Nov 23 06:03:36 HKT 2017

On Wed, 22 Nov 2017, Geir ?yvind V?lidalo wrote:

> I see some of your are talking about gdb-stub, but I have never used
> gbd and need some help.
> How do I debug? What options do I have?

Happy to help with that.  To use the gdb-stub you change the parameter
in menuconfig / Component Config / ESP32-specific / Panic handler
behavior / Invoke GDBStub.

When the crash occurs, you'll be presented with a "gdb>" command
prompt.  You can find references for "gdb commands" online.  Here is
one:  http://www.yolinux.com/TUTORIALS/GDB-Commands.html

The first command I would expect you will want is "bt" which displays
a stack backtrace telling in which function each call is made,
including the source line number.  The frames on the stack are
numbered; you can give the command "frame N" where N is a frame number
to change to the context of that frame, since the lowest one might not
be the place where things started to go wrong.

When you're at the right frame, you can use the "print" command to
look at the value of variables.  If variable foo is a pointer, you can
say "print *foo" to display the contents of the object foo points to.
In many cases this will be enough to figure out the problem.  I also
use the "x" command to examine memory by address in various ways.

You can also use the "list" command to see a few lines of source code
around the point in the code referenced by that stack frame.  Usually
I just look at my source in a separate window.

When using gdb on a real computer you can set breakpoints before
starting the program, but I have not learned whether that is possible
to do with the ESP32.

As I mentioned in one of the emails, if you are running on a Mac you
should use the gdb binary that I made which references the newer
libiconv library in order to avoid gdb getting stuck in an infinite
loop.  If so, let me know and I'll send the binary and library to you.
If you are running on a different platform, you should check to see
what version of libiconv DLL (Windows) or shared library (Linux) is
referenced.  On my Mac the new one is 9.0.0 vs. 7.0.0.  The old one is
usable, but you have to be careful not to give any command that might
result in gdb tryinging to display a variable value that has non-ASCII

                                                        -- Steve

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