[RFC,06/13] nat/x86-cpuid: Add a function to build the contents of a NT_X86_CPUID note

diff --git a/gdb/nat/x86-cpuid.c b/gdb/nat/x86-cpuid.c
new file mode 100644
index 00000000000..a0fc9c2b192
--- /dev/null
+++ b/gdb/nat/x86-cpuid.c
@@ -0,0 +1,91 @@ 
+/* x86 CPUID functions.
+
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "gdbsupport/common-defs.h"
+#include "nat/x86-cpuid.h"
+
+/* Data stored in the note for a single CPUID leaf.  */
+
+struct cpuid_leaf
+{
+  uint32_t leaf;
+  uint32_t subleaf;
+  uint32_t eax;
+  uint32_t ebx;
+  uint32_t ecx;
+  uint32_t edx;
+};
+
+/* Append a single CPUID leaf.  */
+
+static void
+append_cpuid_note (gdb::unique_xmalloc_ptr<gdb_byte> &buf, size_t &len,
+		   uint32_t leaf, uint32_t subleaf)
+{
+  struct cpuid_leaf data;
+  if (!x86_cpuid_count (leaf, subleaf, &data.eax, &data.ebx, &data.ecx,
+			&data.edx))
+    return;
+
+  data.leaf = leaf;
+  data.subleaf = subleaf;
+
+  buf.reset ((gdb_byte *) xrealloc (buf.release (), len + sizeof (data)));
+  memcpy (buf.get() + len, &data, sizeof (data));
+  len += sizeof (data);
+}
+
+/* See x86-cpuid.h.  */
+
+void
+x86_cpuid_note (gdb::unique_xmalloc_ptr<gdb_byte> &buf, size_t &len)
+{
+  buf.reset (nullptr);
+  len = 0;
+
+  /* Include 0xd sub-leaves that describe the XSAVE extended state.  */
+  uint32_t eax, edx;
+  if (x86_cpuid_count (0xd, 0, &eax, nullptr, nullptr, &edx)
+      && (eax != 0 || edx != 0))
+    {
+      /* Main leaf and sub-leaf 1. */
+      append_cpuid_note (buf, len, 0xd, 0);
+      append_cpuid_note (buf, len, 0xd, 1);
+
+      /* Sub-leaves for each enabled feature.  */
+      eax >>= 2;
+      uint32_t i = 2;
+      while (eax != 0)
+	{
+	  if ((eax & 1) == 1)
+	    append_cpuid_note (buf, len, 0xd, i);
+	  eax >>= 1;
+	  i++;
+	}
+
+      i = 0;
+      while (edx != 0)
+	{
+	  if ((edx & 1) == 1)
+	    append_cpuid_note (buf, len, 0xd, i + 32);
+	  edx >>= 1;
+	  i++;
+	}
+    }
+}
diff --git a/gdb/nat/x86-cpuid.h b/gdb/nat/x86-cpuid.h
index 9401705c44d..6b0561dfcf4 100644
--- a/gdb/nat/x86-cpuid.h
+++ b/gdb/nat/x86-cpuid.h
@@ -82,4 +82,11 @@  x86_cpuid_count (unsigned int __level, unsigned int __sublevel,
 #undef nullptr
 #endif
 
+#ifdef __cplusplus
+/* Store data for the NT_X86_CPUID core dump note in BUF for the current
+   host.  The size of the data is stored in LEN.  */
+
+void x86_cpuid_note (gdb::unique_xmalloc_ptr<gdb_byte> &buf, size_t &len);
+#endif
+
 #endif /* NAT_X86_CPUID_H */