Re: [PATCH 7/8] Windows gdb: Implement XState (Intel AVX) support

 Am Freitag, 17. Juli 2026 um 17:26:14 MESZ hat Schimpe, Christina <[email protected]> Folgendes geschrieben:

> > -----Original Message-----
> > From: Hannes Domani <[email protected]>
> > Sent: Freitag, 17. Juli 2026 16:50
> > To: [email protected]; Schimpe, Christina
> > <[email protected]>
> > Subject: Re: [PATCH 7/8] Windows gdb: Implement XState (Intel AVX) support
> >
> >  Am Freitag, 17. Juli 2026 um 16:16:31 MESZ hat Schimpe, Christina
> > <[email protected]> Folgendes geschrieben:
> >
> > > > -----Original Message-----
> > > > From: Hannes Domani <[email protected]>
> > > > Sent: Freitag, 17. Juli 2026 15:47
> > > > To: [email protected]; Schimpe, Christina
> > > > <[email protected]>
> > > > Subject: Re: [PATCH 7/8] Windows gdb: Implement XState (Intel AVX)
> > > > support
> > > >
> > > >  Am Freitag, 17. Juli 2026 um 14:54:59 MESZ hat Schimpe, Christina
> > > ><[email protected]> Folgendes geschrieben:
> > > >
> > > > > Hi Hannes,
> > > > >
> > > > > Thank you for working on this.
> > > > > It appears that this patch uses the same commit message header as
> > > > > patch #8. Is it intentional that these are separate commits?
> > > >
> > > > This one is the gdb part, and #8 is the gdbserver part, that is
> > > > stated in the title.
> > >
> > > Oups, I wonder how I came to that conclusion.  Sorry for that.
> > >
> > > >
> > > > > In any case, IMO, commit messages should not have identical headers.
> > > > > Also, this patch seems big enough for a commit message which is
> > > > > not header only. :)
> > >
> > > This part still stands for the commit message. Since it's not only avx
> > > registers, I believe it makes sense to share more details here.
> >
> > Yes, I will do that.
> >
> >
> > > > > Do any AVX-* specific tests pass on Windows now? If so, it would
> > > > > be helpful to mention that in the commit message as well.
> > > >
> > > > I actually planned to add that info, but forgot.
> > > >
> > > > These tests then pass on Windows:
> > > > gdb.arch/i386-avx.exp
> > > > gdb.arch/i386-avx512.exp
> > >
> > > What's the state for SSE  (gdb.arch/i386-sse.exp) ?
> >
> > i386-sse.exp works since patch #1, it was only a compile issue of the test
> > itself.
> > I will mention this in the patch as well.
> 
> Thanks.
> 
> >
> > > I also saw you introduced some code for PKRU and the shadow stack
> > pointer.
> > > We have GDB tests for those registers, too:
> > > - gdb.arch/i386-pkru.exp
> > > - gdb.arch/amd64-shadow-stack*.exp
> >
> > For these I just added the equivalent code as is done on Linux, without really
> > knowing what they are for.
> >
> > i386-pkru.exp tells me:
> >
> > (gdb) print have_pkru()
> > $1 = 0
> > (gdb) PASS: gdb.arch/i386-pkru.exp: probe PKRU support
> > UNSUPPORTED: gdb.arch/i386-pkru.exp: processor does not support
> > protection key feature.
> >
> > Do only certain CPU's have this register?
> 
> Most recent CPUs should have it. To be sure you can check if the corresponding bit
> is configured in xcr0.

I thought that's what have_pkru() does, but I might be wrong about that.


> I believe for windows this should be the mask returned by get_xstate_features_mask.

You probably mean GetEnabledXStateFeatures, but yes, it also tells me my CPU
doesn't support this.


> If your cpu does have it, I think you must look at the test in more detail to find out why it's
> unsupported. It might need some adaptions for windows.

Google tells me only not all recent CPUs have this, is mine one of them?:
11th Gen Intel(R) Core(TM) i7-11850H


> > And amd64-shadow-stack.exp:
> >
> > (gdb) print $pl3_ssp
> > $1 = (void *) 0x0
> > (gdb) FAIL: gdb.arch/amd64-shadow-stack.exp: test shadow stack support
> >
> > No idea if that should work, since Windows is supplying data for the $pl3_ssp
> > register.
> >
> >
> > Hannes
> 
> Without knowing any of the details in windows I believe adding full support for CET shadow
> stack might need some more changes. At least for linux, this was the case:
> https://inbox.sourceware.org/gdb-patches/[email protected]/
> 
> I believe it would be better to handle this in a separate patch-(series).
> This also applies for any other register that you add and whose dedicated test does not pass.
> 
> Does that make sense to you?

I was wondering if it isn't the compiler or linker on windows (or maybe windows itself?)
that doesn't support this -fcf-protection=return stuff.


Hannes