Re: [PATCH] [Arm] Remove dead FPA code

[Pedro Alves <pedro@palves.net>]

Hi,

On 2022-10-04 9:43 a.m., Luis Machado wrote:
> 
> 
>>> -   The packet format which
>>> -   includes FPA registers should be considered deprecated for
>>> -   M-profile targets.  */
>>> -
>>> -static void
>>> -arm_register_g_packet_guesses (struct gdbarch *gdbarch)
>>> -{
>>> -  arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
>>> -
>>> -  if (tdep->is_m)
>>> -    {
>>> -      const target_desc *tdesc;
>>> -
>>> -      /* If we know from the executable this is an M-profile target,
>>> -     cater for remote targets whose register set layout is the
>>> -     same as the FPA layout.  */
>>> -      tdesc = arm_read_mprofile_description (ARM_M_TYPE_WITH_FPA);
>>> -      register_remote_g_packet_guess (gdbarch,
>>> -                      ARM_CORE_REGS_SIZE + ARM_FP_REGS_SIZE,
>>> -                      tdesc);
>>> -
>>> -      /* The regular M-profile layout.  */
>>> -      tdesc = arm_read_mprofile_description (ARM_M_TYPE_M_PROFILE);
>>> -      register_remote_g_packet_guess (gdbarch, ARM_CORE_REGS_SIZE,
>>> -                      tdesc);
>>> -
>>> -      /* M-profile plus M4F VFP.  */
>>> -      tdesc = arm_read_mprofile_description (ARM_M_TYPE_VFP_D16);
>>> -      register_remote_g_packet_guess (gdbarch,
>>> -                      ARM_CORE_REGS_SIZE + ARM_VFP2_REGS_SIZE,
>>> -                      tdesc);
>>> -      /* M-profile plus MVE.  */
>>> -      tdesc = arm_read_mprofile_description (ARM_M_TYPE_MVE);
>>> -      register_remote_g_packet_guess (gdbarch, ARM_CORE_REGS_SIZE
>>> -                      + ARM_VFP2_REGS_SIZE
>>> -                      + ARM_INT_REGISTER_SIZE, tdesc);
>>> -
>>> -      /* M-profile system (stack pointers).  */
>>> -      tdesc = arm_read_mprofile_description (ARM_M_TYPE_SYSTEM);
>>> -      register_remote_g_packet_guess (gdbarch, 2 * ARM_INT_REGISTER_SIZE, tdesc);
>>
>> And what about all these other non-FPA guesses?  Do you really mean to drop them?
>>
> 
> More recently we've added two new guesses for MVE and M-profile system registers, but it doesn't
> make sense to do so, as these features are advertised as XML already. 

What was the justification for adding them back then, then?

> So in my opinion, we should
> drop the g packet guesses completely and rely solely on XML descriptions.

Then I think that it should be proposed in a separate patch, as it has nothing to
do with dropping FPA support.

Off hand, I don't really see what you win much removing the guesses.  The code that it allows
removing isn't something that would block any redesign or big cleanup in gdb, as gdb needs to know
how to create built-in tdescs for core files, anyhow (even if not these particular tdescs),
and the tdesc generation code is even shared with gdbserver.