Kernel Debug Howto

[Benjamin Kaduk]

On Sat, 25 Jul 2015, Kristof Provost wrote:

>
> > On 25 Jul 2015, at 10:54, HeTak <hetakcoder at gmail.com> wrote:
> > I have recently started some developments on FreeBSD net section.
> Great!
>
> > But I am kinda new to this field. My base interest is to first understand the
> > implementation structure via tracing the code and so.
> >
> > I have three major questions:
> > 1-  how to debug changes made to FreeBSD kernel?
> > (You know, till some levels, I can even use uprintf or so, but, for example
> > inside radix.c (where I wanna understand how a route is checked to be
> > unique and then inserted to the tree) I can't do such checks..)
> dtrace can be quite useful to understand flows. You can grab stack traces
> (i.e. figure out where things are called from), get function arguments, …

Remote kgdb over a serial line can also be useful for stepping through
execution in cases where that is appropriate, and of course kgdb on
coredumps when the kernel panics.

> > 3- what is the fastest way to apply changes to FreeBSD kernel?
> > (For now, I just follow the normal build & install kernel & reboot.)
> I pretty much do that. Depending on what you’re working on it might be easier to run it in a VM.
> My work lately has been on the network code, so a VM is very convenient.
> It’s not so useful if you’re working on drivers, of course.

To speed up the build stage, you can 'make -DKERNFAST kernel' if you have
only made "normal" code changes.

-Ben