[Bug server/31526] New: GDBServer crashes with an internal error cannot find "ymm0h"

["wmessmer at microsoft dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31526

            Bug ID: 31526
           Summary: GDBServer crashes with an internal error cannot find
                    "ymm0h"
           Product: gdb
           Version: 14.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: server
          Assignee: unassigned at sourceware dot org
          Reporter: wmessmer at microsoft dot com
  Target Milestone: ---

WinDbg recently added support for connecting to and debugging Linux processes
via gdbserver.  On gdbserver 12.1, the connection works fine.  On gdbserver
14.x, the initial connection results in an immediate internal error in
gdbserver claiming that it cannot find "ymm0h"

Looking through things, it appears that this is caused by the WinDbg plug-in
which provides this functionality inadvertently sending a "qSupported:" packet
without "xmlRegisters=..." after having sent one with
"xmlRegisters=aarch64,i386".

On 12.1, this clears x86_xcr0 of the AVX flag and causes utilization of a
target description without AVX registers (which largely works fine).  On 14.x,
this does NOT clear x86_xcr0 of the AVX flag but still causes utilization of a
target description without AVX registers.  The next time the plug-in sends a
packet across the RSP which involves register state read, gdbserver attempts to
read AVX registers and faults with the internal error because the target
description does not contain them.

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