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

Hi Hannes, 

This is on my list for review. However, I likely won't be able to complete it before next week, as I need to spend some time experimenting with Windows and familiarizing myself with the environment.

Please also note that my review will be focused on the x86-related parts.

Christina


> -----Original Message-----
> From: Hannes Domani <[email protected]>
> Sent: Montag, 10. August 2026 19:25
> To: [email protected]; Joos, Christina <[email protected]>
> Subject: Re: [PATCH v2 7/8] Windows gdb: Implement XState (Intel AVX)
> support
> 
> Ping for this series.
> 
> 
> Am Montag, 27. Juli 2026 um 19:47:52 MESZ hat Hannes Domani
> <[email protected]> Folgendes geschrieben:
> 
> > This adds support for the Intel AVX and AVX-512 registers on Windows.
> > It enables accessing registers $ymm0 - $ymm31, $zmm0 - $zmm31, and
> > $k0 - $k7 where they are available.
> >
> > It also enables reading the shadow stack pointer register $pl3_ssp
> > (for executables marked compatible with CET shadow stack [1]), but
> > modifying it seems to be restricted restricted by windows.
> >
> > After this patch the tests gdb.arch/i386-avx.exp and
> > gdb.arch/i386-avx512.exp pass on windows.
> >
> > [1] https://learn.microsoft.com/en-us/cpp/build/reference/cetcompat
> > ---
> > v2:
> >   - Extended commit message and NEWS entry
> >   - Remove PKRU support
> >   - Fixed context offset of $pl3_ssp
> > ---
> > gdb/NEWS              |  6 +++
> > gdb/x86-windows-nat.c | 108
> ++++++++++++++++++++++++++++++++++++++++--
> > 2 files changed, 111 insertions(+), 3 deletions(-)
> >
> > diff --git a/gdb/NEWS b/gdb/NEWS
> > index 8f40ca5cb11..71ff5508d6d 100644
> > --- a/gdb/NEWS
> > +++ b/gdb/NEWS
> > @@ -116,6 +116,12 @@
> >   intent to remove it in a future release.
> >   The s390 64-bit target (s390x-*) remains supported.
> >
> > +* Support for Intel AVX registers on Windows.
> > +  Support displaying and modifying Intel AVX registers $ymm0 - $ymm31.
> > +  Support displaying and modifying Intel AVX-512 registers $zmm0 -
> > +$zmm31
> > +  and $k0 - $k7.
> > +  Support displaying the shadow stack pointer register $pl3_ssp.
> > +
> > * Configure changes
> >
> > ** --with-babeltrace has been removed.  The babeltrace library was
> > diff --git a/gdb/x86-windows-nat.c b/gdb/x86-windows-nat.c index
> > 3af5ef4dae0..270f9eae8e7 100644
> > --- a/gdb/x86-windows-nat.c
> > +++ b/gdb/x86-windows-nat.c
> > @@ -27,6 +27,9 @@
> >
> > #include "i386-tdep.h"
> > #include "i387-tdep.h"
> > +#ifdef __x86_64__
> > +#include "amd64-tdep.h"
> > +#endif
> >
> > using namespace windows_nat;
> >
> > @@ -70,6 +73,8 @@ struct x86_windows_nat_target final : public
> >x86_nat_target<windows_nat_target>
> >               windows_thread_info *th, int r) override;
> >
> >   bool is_sw_breakpoint (const EXCEPTION_RECORD *er) const override;
> > +
> > +  const struct target_desc *read_description () override;
> > };
> >
> > /* The current process.  */
> > @@ -109,7 +114,31 @@ x86_windows_per_inferior::fill_thread_context
> >(windows_thread_info *th)
> >       if (context->ContextFlags == 0)
> >     {
> >       context->ContextFlags = WindowsContext<decltype(context)>::all;
> > +      if (xstate_features != 0)
> > +        {
> > +          context->ContextFlags |= CONTEXT_XSTATE_FLAG;
> > +          set_xstate_features_mask (context, xstate_features);
> > +        }
> >       CHECK (get_thread_context (th->h, context));
> > +
> > +      if (xstate_features != 0)
> > +        {
> > +          DWORD64 features = 0;
> > +          CHECK (get_xstate_features_mask (context, &features));
> > +          DWORD64 zeroed_features = xstate_features & ~features;
> > +
> > +          for (int f = X86_XSTATE_AVX_ID; f <= X86_XSTATE_CET_U_ID;
> > +f++)
> > +        {
> > +          DWORD64 flag = 1ULL << f;
> > +          if ((zeroed_features & flag) != 0)
> > +            {
> > +              DWORD size = 0;
> > +              void *loc = locate_xstate_feature (context, f, &size);
> > +              if (loc != nullptr && size > 0)
> > +            memset (loc, 0, size);
> > +            }
> > +        }
> > +        }
> >     }
> >     });
> > }
> > @@ -198,6 +227,14 @@
> x86_windows_nat_target::thread_context_continue
> >(windows_thread_info *th,
> >       if (GetExitCodeThread (th->h, &ec)
> >           && ec == STILL_ACTIVE)
> >         {
> > +          DWORD debug_registers =
> > +WindowsContext<decltype(context)>::debug;
> > +          if (xstate_features != 0
> > +          && (context->ContextFlags & ~debug_registers) != 0)
> > +        {
> > +          context->ContextFlags |= CONTEXT_XSTATE_FLAG;
> > +          set_xstate_features_mask (context, xstate_features);
> > +        }
> > +
> >           BOOL status = set_thread_context (th->h, context);
> >
> >           if (!killed)
> > @@ -227,7 +264,7 @@ x86_windows_nat_target::thread_context_step
> >(windows_thread_info *th,
> >
> > template<typename Context>
> > static char *
> > -get_context_reg_ptr (Context *context, int r)
> > +get_context_reg_ptr (Context *context, int r, i386_gdbarch_tdep
> > +*tdep)
> > {
> >   const int *mappings;
> >   int mappings_count;
> > @@ -247,6 +284,54 @@ get_context_reg_ptr (Context *context, int r)
> >   char *context_offset;
> >   if (r < mappings_count)
> >     context_offset = (char *) context + mappings[r];
> > +  else if (I387_ZMM0H_REGNUM (tdep) > 0 && r >=
> I387_ZMM0H_REGNUM
> > +(tdep)
> > +      && r < I387_ZMM16H_REGNUM (tdep) && r <
> I387_ZMMENDH_REGNUM
> > +(tdep))
> > +    {
> > +      context_offset = (char *) locate_xstate_feature
> > +    (context, X86_XSTATE_ZMM_H_ID, NULL);
> > +      context_offset += 32 * (r - I387_ZMM0H_REGNUM (tdep));
> > +    }
> > +  else if (I387_ZMM0H_REGNUM (tdep) > 0 && r >=
> I387_ZMM16H_REGNUM
> > +(tdep)
> > +      && r < I387_ZMMENDH_REGNUM (tdep))
> > +    {
> > +      context_offset = (char *) locate_xstate_feature
> > +    (context, X86_XSTATE_ZMM_ID, NULL);
> > +      context_offset += 32 + 64 * (r - I387_ZMM16H_REGNUM (tdep));
> > +    }
> > +  else if (I387_K0_REGNUM (tdep) > 0 && r >= I387_K0_REGNUM (tdep)
> > +      && r < I387_KEND_REGNUM (tdep))
> > +    {
> > +      context_offset = (char *) locate_xstate_feature
> > +    (context, X86_XSTATE_K_ID, NULL);
> > +      context_offset += 8 * (r - I387_K0_REGNUM (tdep));
> > +    }
> > +  else if (I387_YMM16H_REGNUM (tdep) > 0 && r >=
> I387_YMM16H_REGNUM
> > +(tdep)
> > +      && r < I387_YMMH_AVX512_END_REGNUM (tdep))
> > +    {
> > +      context_offset = (char *) locate_xstate_feature
> > +    (context, X86_XSTATE_ZMM_ID, NULL);
> > +      context_offset += 16 + 64 * (r - I387_YMM16H_REGNUM (tdep));
> > +    }
> > +  else if (I387_XMM16_REGNUM (tdep) > 0 && r >= I387_XMM16_REGNUM
> > +(tdep)
> > +      && r < I387_XMM_AVX512_END_REGNUM (tdep))
> > +    {
> > +      context_offset = (char *) locate_xstate_feature
> > +    (context, X86_XSTATE_ZMM_ID, NULL);
> > +      context_offset += 64 * (r - I387_XMM16_REGNUM (tdep));
> > +    }
> > +  else if (I387_YMM0H_REGNUM (tdep) > 0 && r >=
> I387_YMM0H_REGNUM
> > +(tdep)
> > +      && r < I387_YMMENDH_REGNUM (tdep))
> > +    {
> > +      context_offset = (char *) locate_xstate_feature
> > +    (context, X86_XSTATE_AVX_ID, NULL);
> > +      context_offset += 16 * (r - I387_YMM0H_REGNUM (tdep));
> > +    }
> > +  else if (tdep->ssp_regnum > 0 && r == tdep->ssp_regnum)
> > +    {
> > +      context_offset = (char *) locate_xstate_feature
> > +    (context, X86_XSTATE_CET_U_ID, NULL);
> > +      context_offset += 8;
> > +    }
> >   else
> >     gdb_assert_not_reached ("invalid register number %d", r);
> >
> > @@ -267,7 +352,7 @@ x86_windows_nat_target::fetch_one_register (struct
> >regcache *regcache,
> >   char *context_offset
> >     = x86_windows_process.with_context (th, [&] (auto *context)
> >     {
> > -      return get_context_reg_ptr (context, r);
> > +      return get_context_reg_ptr (context, r, tdep);
> >     });
> >
> >   gdb_assert (!gdbarch_read_pc_p (gdbarch));  @@ -333,7 +418,7 @@
> >x86_windows_nat_target::store_one_register (const struct regcache
> >*regcache,
> >     = x86_windows_process.with_context (th, [&] (auto *context)
> >     {
> >       gdb_assert (context->ContextFlags != 0);
> > -      return get_context_reg_ptr (context, r);
> > +      return get_context_reg_ptr (context, r, tdep);
> >     });
> >
> >   /* GDB treats some registers as 32-bit, where they are in fact only
> >@@ -368,6 +453,23 @@ x86_windows_nat_target::is_sw_breakpoint (const
> >EXCEPTION_RECORD *er) const
> >       || er->ExceptionCode == STATUS_WX86_BREAKPOINT);  }
> >
> > +const struct target_desc *
> > +x86_windows_nat_target::read_description () {
> > +  if (inferior_ptid == null_ptid)
> > +    return this->beneath ()->read_description ();
> > +
> > +  if (xstate_features == 0)
> > +    return nullptr;
> > +
> > +#ifdef __x86_64__
> > +  if (!x86_windows_process.wow64_process)
> > +    return amd64_target_description (xstate_features, false);
> > +  else
> > +#endif
> > +    return i386_target_description (xstate_features, false); }
> > +
> > /* Hardware watchpoint support, adapted from go32-nat.c code.  */
> >
> > /* Pass the address ADDR to the inferior in the I'th debug register.
> > --
> > 2.54.0
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