[PATCH v2 6/8] Windows gdb: Get available XState features

Also prepares the thread context for the additional registers.
---
v2:
  - Remove PKRU from the implemented features mask
---
 gdb/nat/windows-nat.c | 54 ++++++++++++++++++++++++++++++++++++++++++-
 gdb/nat/windows-nat.h |  5 ++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index cd1f9e7bc64..28678b9f1a7 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -20,6 +20,7 @@
 #include "gdbsupport/common-debug.h"
 #include "gdbsupport/gdb_signals.h"
 #include "gdbsupport/gdb_wait.h"
+#include "gdbsupport/x86-xstate.h"
 #include "target/target.h"
 
 #undef GetModuleFileNameEx
@@ -84,6 +85,8 @@ RtlGetExtendedFeaturesMask_ftype *RtlGetExtendedFeaturesMask;
 RtlSetExtendedFeaturesMask_ftype *RtlSetExtendedFeaturesMask;
 RtlLocateExtendedFeature_ftype *RtlLocateExtendedFeature;
 #endif
+
+DWORD64 xstate_features;
 #endif
 
 /* Note that 'debug_events' must be locally defined in the relevant
@@ -308,12 +311,38 @@ windows_process_info::pid_to_exec_file (int pid)
 
 void windows_process_info::initialize_context (windows_thread_info *th)
 {
+#if defined __i386__ || defined __x86_64__
+  if (xstate_features != 0)
+    {
+      DWORD context_flags = with_context (nullptr, [] (auto *context)
+	{
+	  return WindowsContext<decltype(context)>::all;
+	});
+      context_flags |= CONTEXT_XSTATE_FLAG;
+      DWORD xstate_size = 0;
+      InitializeContext (NULL, context_flags, NULL, &xstate_size);
+      th->context_buffer.reset (xmalloc (xstate_size));
+      CONTEXT *context = nullptr;
+      if (!InitializeContext (th->context_buffer.get (),
+			      context_flags, &context, &xstate_size))
+	error ("InitializeContext failure %lu\n", GetLastError ());
 #ifdef __x86_64__
-  if (wow64_process)
+      /* InitializeContext actually initializes a WOW64_CONTEXT when
+	 context_flags contains a WOW64_CONTEXT_* value, so a cast is needed.
+	 */
+      if (wow64_process)
+	th->wow64_context = (WOW64_CONTEXT *) context;
+      else
+#endif
+	th->context = context;
+    }
+#ifdef __x86_64__
+  else if (wow64_process)
     {
       th->context_buffer.reset (xmalloc (sizeof (WOW64_CONTEXT)));
       th->wow64_context = (WOW64_CONTEXT *) th->context_buffer.get ();
     }
+#endif
   else
 #endif
     {
@@ -1289,6 +1318,29 @@ initialize_loadable ()
 
 #undef GPA
 
+#if defined __i386__ || defined __x86_64__
+  if (GetEnabledXStateFeatures != nullptr
+      && InitializeContext != nullptr
+      && GetXStateFeaturesMask != nullptr
+      && SetXStateFeaturesMask != nullptr
+      && LocateXStateFeature != nullptr
+#ifdef __x86_64__
+      && RtlGetExtendedFeaturesMask != nullptr
+      && RtlSetExtendedFeaturesMask != nullptr
+      && RtlLocateExtendedFeature != nullptr
+#endif
+  )
+    {
+      /* Available XState features masked with implemented features.  */
+      xstate_features = GetEnabledXStateFeatures ()
+	& (X86_XSTATE_AVX_AVX512_MASK | X86_XSTATE_CET_U);
+      /* The extended XState functions are only needed if the available
+	 features exceed SSE.  */
+      if ((xstate_features & ~X86_XSTATE_SSE_MASK) == 0)
+	xstate_features = 0;
+    }
+#endif
+
   return result;
 }
 
diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index a344b0a966f..8fcf5e339cb 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -760,6 +760,11 @@ locate_xstate_feature (WOW64_CONTEXT *context, DWORD feature, DWORD *length)
 }
 #endif
 
+#if defined __i386__ || defined __x86_64__
+/* Available XState features.  */
+extern DWORD64 xstate_features;
+#endif
+
 /* This is available starting with Windows 10.  */
 #ifndef DBG_REPLY_LATER
 # define DBG_REPLY_LATER 0x40010001L
-- 
2.54.0