On Fri, 27 Aug 2021 at 15:49, Changbin Du <changbin...@gmail.com> wrote: > > On Tue, Aug 24, 2021 at 10:11:14AM +0100, Peter Maydell wrote: > > On Tue, 24 Aug 2021 at 00:05, Changbin Du <changbin...@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?
I think that you need to start by talking to the gdb folks about how debugging a dynamic endianness target should work. Fixing this probably goes something like: * agree on design for how dynamic endianness, 32-64 mode changes, etc, should be handled by gdb * make gdb changes * document required gdbstub protocol enhancements (ie how the stub tells gdb about endianness changes, whether this changes how we send register information, memory data, etc) * implement those changes in QEMU You seem to be trying to start with the final step, not the first one :-) -- PMM
