Re: [PATCH v2 7/8] Windows gdb: Implement XState (Intel AVX) support

[Hannes Domani <ssbssa@yahoo.de>]

 Am Donnerstag, 27. August 2026 um 17:17:46 MESZ hat Joos, Christina <christina.joos@intel.com> Folgendes geschrieben:

> > -----Original Message-----
> > From: Hannes Domani <ssbssa@yahoo.de>
> > Sent: Donnerstag, 27. August 2026 16:21
> > To: gdb-patches@sourceware.org; Joos, Christina <christina.joos@intel.com>
> > Subject: Re: [PATCH v2 7/8] Windows gdb: Implement XState (Intel AVX)
> > support
> >
> >  Am Donnerstag, 27. August 2026 um 12:43:04 MESZ hat Joos, Christina
> > <christina.joos@intel.com> Folgendes geschrieben:
> >
> > > > -----Original Message-----
> > > > From: Hannes Domani <ssbssa@yahoo.de>
> > > > Sent: Mittwoch, 26. August 2026 17:20
> > > > To: gdb-patches@sourceware.org; Joos, Christina
> > > > <christina.joos@intel.com>
> > > > Subject: Re: [PATCH v2 7/8] Windows gdb: Implement XState (Intel
> > > > AVX) support
> > > >
> > > >  Am Mittwoch, 26. August 2026 um 16:28:41 MESZ hat Joos, Christina
> > > ><christina.joos@intel.com> Folgendes geschrieben:
> > > >
> > > > > Hi Hannes,
> > > > >
> > > > > Thanks a lot for working on this.
> > > > >
> > > > > I did not find the time to try this out on windows myself, since I
> > > > > was not able
> > > > to work last week.
> > > > > This is my code-based review for now.
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Hannes Domani <ssbssa@yahoo.de>
> > > > > > Sent: Montag, 27. Juli 2026 19:43
> > > > > > To: gdb-patches@sourceware.org
> > > > > > Subject: [PATCH v2 7/8] Windows gdb: Implement XState (Intel
> > > > > > AVX) support
> > > > >
> > > > > The commit message header still seems somewhat misleading, as it
> > > > > references only Intel AVX, while the commit also includes changes
> > > > > related to
> > > > AVX-512 and shadow stack.
> > > > >
> > > > > I think it would be helpful if we'd adapt the commit message
> > > > > header of this patch to include AVX-512, too.
> > > > >
> > > > > For shadow stack I think it would make sense to move this to a
> > > > > separate commit and give more details on the tests that are
> > > > > passing/ not passing and the limitations we have in windows for
> > > > > shadow stack enabled
> > > > programs.
> > > >
> > > > I agree, at least shadow stack should be its own commit.
> > > >
> > > > And I wonder if, instead of splitting up into gdb/gdbserver as it is
> > > > now, maybe I should merge them, and split them again into AVX/AVX-
> > 512/shadow-stack.
> > >
> > > I think this is up to you. I usually prefer to have gdb + gdbserver together.
> > > But this also depends on how complicated/big the patches are, I guess.
> > >
> > > At the state of this patch your general NEWS comment doesn't state any
> > > specifics about gdb or gdbserver.
> > > My assumption would be that both is working. However, gdbserver only
> > > works with the next patch. So, from that perspective it would make sense to
> > merge them.
> >
> > I now also think it's better to merge them, so I'll do that.
> >
> >
> > > > > Besides reading or writing the shadow stack pointer for linux we
> > > > > had to enable
> > > > > - displaced stepping
> > > > > - the return command
> > > > > - inferior calls
> > > > > for shadow stack enabled programs, which are all covered by
> > > > > current shadow
> > > > stack tests.
> > > > >
> > > > > Based on what you said
> > > > >
> > > > > ~~~
> > > > > It turns out binutils/gcc really don't support this on windows yet.
> > > > > To enable this in the executable, at least a special marker bit
> > > > > has to be set in
> > > > the Extended DLL Characteristics [1].
> > > > > With msvc you can do that with the /CETCOMPAT linker argument [2].
> > > > >
> > > > > So I compiled amd64-shadow-stack.c with msvc and /CETCOMPAT, and
> > > > > tried
> > > > it out with my gdb build.
> > > > > Before I always got $pl3_ssp=0, and with this new exe I always get
> > > > $pl3_ssp=1.
> > > > > ~~~
> > > > > I assume you cannot execute those tests. Can you confirm?
> > > > >
> > > > > Would it make sense to add dedicated tests for windows shadow
> > > > > stack (in the shadow-stack specific patch), based on the current
> > > > > enablement you
> > > > describe above ?
> > > > >
> > > > > Or, maybe even better, can you adapt the proc allow_ssp_tests for
> > > > > window
> > > > support?
> > > > > You said:
> > > > > " It turns out binutils/gcc really don't support this on windows yet."
> > > > > Could you add a fix to make this work for windows using msvc and
> > > > /CETCOMPAT ?
> > > >
> > > > I'm not sure what you mean here.
> > > > Instead of the binutils linker, use the one from msvc?
> > >
> > > You said "So I compiled amd64-shadow-stack.c with msvc and /CETCOMPAT,
> > > and tried it out with my gdb build." Based on that I assumed it's
> > > somehow possible to enable shadow stack for a msvc compiled program in
> > windows.
> >
> > Yes.
> >
> >
> > > I also inferred that GDB was able to debug such programs and run
> > > relevant tests against them. That may have been an incorrect
> > > assumption on my part, as I'm not very familiar with the current state
> > > of support in this area. 😊
> >
> > msvc doesn't create dwarf debug info, so in my tests I was only debugging in
> > assembly mode.
> 
> Yes, this is what I expected. Can we run tests in the gdb testsuite with msvc?

I don't think it's possible with msvc directly.
But Pedro has recently made changes to the testsuite for clang configured
as x86_64-pc-windows-msvc, which could maybe be used for this as well.


Hannes