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From: Pedro Alves <pedro@codesourcery.com>
To: gdb-patches@sourceware.org
Subject: Re: PATCH: gdbserver: Clear regcache if buf is NULL
Date: Sat, 16 Oct 2010 20:49:00 -0000
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Cc: "H.J. Lu" <hjl.tools@gmail.com>
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On Saturday 16 October 2010 21:16:37, H.J. Lu wrote:
> >
> > Thanks, and sorry as for not coming back to this promptly.
> > Hmm, I don't think I have a way to trigger that.
> > So is the registers' value really zero, or should gdb
> > ideally present them as not available (and zero is just a
> > hack)?
> >
>=20
> You will see it only on machines with XSAVE and enabled in OS.
> Please see
>=20
> 13.6 XSAVE/XRSTOR AND PROCESSOR EXTENDED STATE
> MANAGEMENT
>=20
> in
>=20
> Intel=AE 64 and IA-32 Architectures Software Developer=92s Manual
> Volume 3A: System Programming Guide, Part 1
>=20
> Basically values in vector registers may not be valid, depending
> on vector state.

Okay, thanks.  The changes I'm working on would make gdb print
for such registers:

 (gdb) info registers
 ...
 foo-register             *value not available*
 ...

rather than:

 (gdb) info registers
 ...
 foo-register             0x0    0
 ...

Trying to print the register's value will show something
like "$1 =3D <unavailable>", and using it's value in expression
evaluation to determine a computed expression value, an error
will be reported.

Does that sound good?  Or do you think keep using 0 would
be better in this case?

--=20
Pedro Alves