Re: can target code change architecture setting?

[Doug Evans <dje@google.com>]

On Tue, Oct 11, 2016 at 7:29 AM, Duane Ellis <duane@duaneellis.com> wrote:
>>
>>> Question #2 - How should the remote debugger respond to GDB?
>>>
>>>      I don't think there is an "architecture change" packet.
>>>
>>
>> Such packet is not needed, because GDB has to determine the gdbarch
>> of each when unwinding.
>
> I think you are making the assumption that GDB always has access to full debug (i.e.: dwarf) information.
>
> In bare metal - You don’t always have this, you might have *labels* only (function name vrs address) but no source, no dwarf information.
>
> The only solution is to *ask* the target “what is your *current* arch.
>
> Or the target needs to send a “target-arch-change-indication” in some way.

Agreed.

Consider booting some x86 kernel on qemu (e.g., passing -s -S to qemu).
At the start $pc is at the x86 reset location and the architecture is 16-bit.

(gdb) tar ext :1234
Remote debugging using :1234
0x000000000000fff0 in ?? ()

At some later point the o/s will switch to 32 or 64-bit mode but until
then gdb isn't as useful as one might want it to be.