Re: PATCH: Extend gdb remote protocol for AVX

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, Sep 18, 2008 at 12:38 PM, Daniel Jacobowitz <drow@false.org> wrote:
> On Thu, Sep 18, 2008 at 12:03:11PM -0700, H.J. Lu wrote:
>> On Thu, Sep 18, 2008 at 11:34 AM, Daniel Jacobowitz
>> <dan@codesourcery.com> wrote:
>> > On Thu, Sep 18, 2008 at 10:27:28AM -0700, H.J. Lu wrote:
>> >>    b. If remote target supports AVX:
>> >>       i. Don't send xmlarch.
>> >>       ii. Replace 128bit xmm registers with 256bit ymm registers in
>> >>         the g/G packet.
>> >>       iii. Gdb will auto-detect SSE unit on remote target, based on the
>> >>          the g/G packet size.
>> >
>> > Just a general note: I would much prefer you use the XML mechanism for
>> > this, either by an architecture name or a property or an explicit
>> > register description, than add more guesses to the g/G packet checks;
>> > they're a heuristic for existing remote targets.
>> >
>>
>> I tried adding xmlarch to regformats files. But I don't want to add new
>> xmlarch entry for AVX since I had to create a new arch entry in BFD for it. It
>> isn't necessary for this purpose. If I use the existing xmlarch, like
>> i386:x86-64, it will match regformats/reg-x86-64.dat. Using
>> the g/G packet size allows me not to add a new arch entry in BFD.
>> Is there a way to do it with XML without changing BFD?
>
> Yes, either of the other two options I described.  MIPS uses both of
> them; search for PROPERTY_GP32 or tdesc_has_registers.
>

I took a similar approach for remote AVX debug.  MIPS uses the
size of g/G packet to set PROPERTY_GPXX:

static void
mips_register_g_packet_guesses (struct gdbarch *gdbarch)
{
  /* If the size matches the set of 32-bit or 64-bit integer registers,
     assume that's what we've got.  */
  register_remote_g_packet_guess (gdbarch, 38 * 4, mips_tdesc_gp32);
  register_remote_g_packet_guess (gdbarch, 38 * 8, mips_tdesc_gp64);

  /* If the size matches the full set of registers GDB traditionally
     knows about, including floating point, for either 32-bit or
     64-bit, assume that's what we've got.  */
  register_remote_g_packet_guess (gdbarch, 90 * 4, mips_tdesc_gp32);
  register_remote_g_packet_guess (gdbarch, 90 * 8, mips_tdesc_gp64);

  /* Otherwise we don't have a useful guess.  */
}

AVX uses:

void
i386_register_g_packet_guesses (struct gdbarch *gdbarch,
                                int sse_unit_bytes,
                                int avx_unit_bytes)
{
  /* If the size matches the set of SSE registers, we are talking to
     an SSE remote target.  */
  register_remote_g_packet_guess (gdbarch,
                                  sse_unit_bytes,
                                  i386_tdesc_sse);

  /* If the size matches the set of AVX registers, we are talking to
     an AVX remote target.  */
  register_remote_g_packet_guess (gdbarch,
                                  avx_unit_bytes,
                                  i386_tdesc_avx);
}

Did I miss something?



-- 
H.J.