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Re: The right way to port GDB to a new architecture
- From: Doug Evans <dje at google dot com>
- To: Andreas Olofsson <andreas dot d dot olofsson at gmail dot com>
- Cc: gdb at sourceware dot org
- Date: Tue, 13 Jan 2009 11:30:53 -0800
- Subject: Re: The right way to port GDB to a new architecture
- References: <email@example.com>
On Tue, Jan 13, 2009 at 7:39 AM, Andreas Olofsson
> I have been reading through the GDB documentation and I need some
> advice on the best approach to porting GDB to a new architecture
> before I dive into the porting process..
> Describing the architecture doesn't seem too bad and is well described
> in Jeremy Bennett's document "Howto: Porting the GNU debugger". How
> to actually communicate with the target looks to be more of a
> challenge and there seem to be a number of different approaches.
> Possible approaches(we already have bfd, binutils, gcc, and all the
> other stuff ported):
> 1.) Use cgen or sid to generate a gdb compliant simulator and link in
> the simulator library. Since we will need the remote debugging option
> eventually, I am thinking that integrating a cgen based simulator with
> GDB would be extra work and I would like to skip this step if
If you don't *need* a simulator, skip it. Often a simulator is
written because it's an easier vehicle for testing gcc (and gdb to
> 2.) Write a stub for the target and use remote serial protocol. The
> included stubs in the distribution are quite old? Is this no longer a
> preferred method?
What kind of architecture + o/s? Is it an embedded system? Does it
run some o/s? The stubs are mostly intended for embedded systems
where the device isn't running an o/s, per se, and the application
"owns" the device. The stub is linked into the application to be
debugged and inserts handlers for various interrupts - not something
one can typically do if running on a typical o/s. They may be old but
there's not much too them, if your system is similar they could still
be good boilerplate.
> 3.) Port gdbserver to the new architecture. Is it a requirement to
> have linux running on the target? Based on the ports I have seen in
> GDB it would seem to be the case? Why doesn't the ARM have a stub for
> example? I can't imagine you have to run linux on an arm based device
> to be able use remote GDB?
Porting gdbserver doesn't require linux, linux is just the canonical
example. gdbserver is for situations where the remote target is
running a multitasking o/s, and it serves as a proxy for gdb. A lot
of the porting work is similar to the work one must do to port gdb
You are correct, you don't need linux to debug arm based devices, but
it depends on the device. For example, if the arm based device is
running linux then a gdbserver port is a reasonable thing to have.
The arm doesn't have a stub only because I suspect no one has
contributed one to the gdb tree.
For reference sake (meaning, here's some data, use it if you get
stuck, but I suspect most of the following won't be helpful) ...
You might also look at rda, http://sourceware.org/rda/, but it's a bit
old too. There are also stubs in the libgloss part of newlib
(http://sourceware.org/newlib/). Plus ecos has some gdb stubs
(http://ecos.sourcware.org), although ecos is a big package itself and
extracting the stubs out may be problematic.
> 4.) Another approach?
> If we assume that the target is not running linux, what would be a
> good starting point to work from: m32r?
m32r is my favorite starting point, but the reasons aren't technical. :-)
I would pick an architecture that is reasonably similar to yours and
go from there.
What architecture (+ o/s if any) are you porting to?