Re: [PATCH 0/3] gdbstub: add support for switchable endianness

[Changbin Du]

On Tue, Aug 24, 2021 at 10:11:14AM +0100, Peter Maydell wrote:
> On Tue, 24 Aug 2021 at 00:05, Changbin Du <changbin.du@gmail.com> wrote:
> >
> > On Mon, Aug 23, 2021 at 04:30:05PM +0100, Peter Maydell wrote:
> > > changes to be more capable of handling dynamic target changes
> > > (this would also help with eg debugging across 32<->64 bit switches);
> > > as I understand it that gdb work would be pretty significant,
> > > and at least for aarch64 pretty much nobody cares about
> > > big-endian, so nobody's got round to doing it yet.
> > >
> > Mostly we do not care dynamic target changes because nearly all OS will 
> > setup
> > endianness mode by its first instruction. And dynamic changes for gdb is 
> > hard
> > since the byte order of debugging info in elf is fixed. And currently the 
> > GDB
> > remote protocol does not support querying endianness info from remote.
> >
> > So usually we needn't change byte order during a debug session, but we just 
> > want
> > the qemu gdbstub can send data in and handle data it received in right byte 
> > order.
> > This patch does this work with the help of users via the option 
> > 'endianness='.
> 
> I'm not a huge fan of putting in workarounds that deal with the
> problem for specific cases and require users to tweak options settings,
> rather than solving the problem in a more general way that would
> let it all Just Work for all cases.
>
Probably we can add a new callback 'gdb_get_endianness' for CPUClass, and use
this callback to determine if bswap is needed every time we read/write cpu
registers. What's your thought?

> -- PMM

-- 
Cheers,
Changbin Du