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

> -----Original Message-----
> From: Hannes Domani <[email protected]>
> Sent: Freitag, 17. Juli 2026 18:27
> 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 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.

Yes, this should work for windows, too.
 
> > 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

I would have expected this but cannot say for sure.  And I don't know the state for
Memory Protection Keys windows support. 

> > > 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/20250821171029.1555603-1-chri
> > [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.

I don't know the state for windows but would be curious about it. :-)
At least for Kernel Mode, I could find some documentation for it.

Christina
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