Re: [PATCH v4 12/13] gdbserver: Read offsets of the XSAVE extended region via CPUID

[John Baldwin <jhb@FreeBSD.org>]

On 4/12/23 12:11 PM, Simon Marchi wrote:
> On 3/17/23 21:09, John Baldwin wrote:
>> From: Aleksandar Paunovic <aleksandar.paunovic@intel.com>
> Finally, do you think this class could eventually be shared with GDB,
> and could help simplify the implementation there?  The i387_xsave could
> take a reference to an existing x86_xsave_layout object to take the
> offsets from, rather than referring to the global instance as it does
> currently.

What I would really like to do (and planned to try as a followup after
this series) is try to use regcache_map_entry arrays to describe the
various XSAVE regions.  Those arrays could be shared between GDB and
gdbserver (might need to make some of the regcache_map_entry stuff
be shared instead of GDB-only).  I want to do this for eventual FreeBSD
support in gdbserver as well where I want to share the regcache maps
used in the foo-fbsd-tdep.c files with the equivalent low.cc file over
in gdbserver to describe the register sets available via ptrace.

But using regcache_map_entry would mean you would do something like this
for the AVX region:

/* The AVX region includes the YMMH registers.  */
const struct regcache_map_entry xsave_avx_regmap[] =
{
   { 16, 0, 16 },  /* ymmh0 ... ymmh15 */
};

const struct regset xsave_avx_regset =
{
   xsave_avx_regmap,
   regcache_collect_regset, regcache_supply_regset
};

Similar to how aarch64_fbsd_tls_regset is handled in aarch64-fbsd-tdep.c,
but using I387_YMMH0_REGNUM (tdep) instead of tdep->tls_base_regnum as
the base register number.

Just as in the case of aarch64-fbsd I share the same regset for TLS between
both the tdep.c and nat.c, the regsets for XSAVE regions could be shared
between GDB and gdbserver.

The gdbserver patches here I have only modified lightly from Aleksandar's
original work.  I can work on them further, but I think if I want to unify
them (probably using regcache maps) I'd like to do that as a followup series.

-- 
John Baldwin