Re: How to configure GDB for software single-stepping on an ARM remote stub

[Jonas Zaddach <zaddach@eurecom.fr>]

Thank you, that is exactly what I wanted :) I felt a bit stupid since
I thought that there must be some configuration file for it ...
A good way to make this configurable in my opinion would be to allow
the remote stub to reply with an error to the step command, or query
stepping support with a qStepping command, and then switch on software
stepping when needed ... If you think other people are interested in
that I can do a patch.

On Thu, May 31, 2012 at 12:27 PM, Pedro Alves <palves@redhat.com> wrote:
> On 05/31/2012 11:02 AM, Jonas Zaddach wrote:
>
>> Hi,
>>
>> I have written a remote stub for some ARM hardware that supports just
>> memory breakpoints (the device does not have a hardware debugging
>> unit). I figured out that I need single-stepping to go around
>> breakpoints,
>
>
> Or more fundamentally, for all stepping, right?
>
>> and that there is support for software single-stepping in
>> the code ... but I have no idea on how to tell GDB that I want
>> software single-stepping on my target. Can you give me a hint how to
>> do it or where to look for documentation?
>
>
> Unfortunately, GDB is not smart enough to figure out the target can't
> single-step, and that it needs to do it itself with software
> single-stepping.
> The current way is that GDB hardcodes knowledge of when does the target
> need it; it depends on architecture, for example, on ARM and MIPS, gdb
> assumes the target can step, and then knows that if the target is running
> Linux, it needs software stepping.  On other archs, knowing that no chip
> was or will be built with hardware debugging smarts, GDB always uses
> software stepping.  The simplest is to use a hack like below to force your
> GDB to assume software stepping is necessary.  The best would be to make
> GDB smarter.
>
>  gdb/arm-tdep.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
> index df5dea7..829cb5c 100644
> --- a/gdb/arm-tdep.c
> +++ b/gdb/arm-tdep.c
> @@ -10122,6 +10122,8 @@ arm_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>                      _("arm_gdbarch_init: bad byte order for float format"));
>     }
>
> +  set_gdbarch_software_single_step (gdbarch, arm_software_single_step);
> +
>   /* On ARM targets char defaults to unsigned.  */
>   set_gdbarch_char_signed (gdbarch, 0);
>