mode processor mode switch

Pedro Alves
Thu Jan 16 18:52:00 GMT 2020

On 1/16/20 2:51 PM, Luis Machado wrote:
> Hi,
> On 1/14/20 8:58 AM, Jirka Koutný wrote:
>> Hello,
>> I have a 32-bit elf executable which at some point switches to long mode
>> (kernel is 64-bit). Is there a way to tell gdb about the .code32/64
>> directives? Because expectedly the switch messes up disassembly and
>> stepping.
>> Thank you
>> Jirka
> Unfortunately i don't think there is a good way to achieve this with the current implementation.
> You could teach GDB about the quirks in the architecture, but it sounds better to have a more general solution.
> I'm working on making this more flexible though, since i have a need to make the architecture information per-thread, at least the target description with the registers and types.

For x86-64 in particular, I think the ideal solution would be for
the remote target to always report the widest mode it supports,
which would be 64-bit, and then do the 32-bit/16-bit modes
presentation all on the gdb side (i.e., user-visible 32-bit on
top of 64-bit description).  Mode switching would not change the remote
target description.  This is unlike the current architecture where a
remote server reports a 32-bit description for a 32-bit process even
if the remote server is actually running on a 64-bit machine.

Pedro Alves

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