[PATCH v4 04/13] x86 nat: Add helper functions to save the XSAVE layout for the host.

[John Baldwin <jhb@FreeBSD.org>]

x86_xsave_length returns the total length of the XSAVE state area
standard format as queried from CPUID.

x86_fetch_xsave_layout uses CPUID to query the offsets of XSAVE
extended regions from the running host.  The total length of the XSAVE
state area can either be supplied the caller if known (e.g. from
FreeBSD's PT_GETXSTATEINFO) or it can be queried from the running host
using x86_xsave_length.
---
 gdb/nat/x86-xstate.c | 65 ++++++++++++++++++++++++++++++++++++++++++++
 gdb/nat/x86-xstate.h | 35 ++++++++++++++++++++++++
 2 files changed, 100 insertions(+)
 create mode 100644 gdb/nat/x86-xstate.c
 create mode 100644 gdb/nat/x86-xstate.h

diff --git a/gdb/nat/x86-xstate.c b/gdb/nat/x86-xstate.c
new file mode 100644
index 00000000000..7b42efe1266
--- /dev/null
+++ b/gdb/nat/x86-xstate.c
@@ -0,0 +1,65 @@
+/* x86 XSAVE extended state functions.
+
+   Copyright (C) 2022-2023 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 "gdbsupport/x86-xstate.h"
+#include "nat/x86-cpuid.h"
+#include "nat/x86-xstate.h"
+
+/* Fetch the offset of a specific XSAVE extended region.  */
+
+static int
+xsave_feature_offset (uint64_t xcr0, int feature)
+{
+  uint32_t ebx;
+
+  if ((xcr0 & (1ULL << feature)) == 0)
+    return 0;
+
+  if (!x86_cpuid_count (0xd, feature, nullptr, &ebx, nullptr, nullptr))
+    return 0;
+  return ebx;
+}
+
+/* See x86-xstate.h.  */
+
+int
+x86_xsave_length ()
+{
+  uint32_t ecx;
+
+  if (!x86_cpuid_count (0xd, 0, nullptr, nullptr, &ecx, nullptr))
+    return 0;
+  return ecx;
+}
+
+/* See x86-xstate.h.  */
+
+void
+x86_fetch_xsave_layout (uint64_t xcr0, int len, x86_xsave_layout &layout)
+{
+  layout.sizeof_xsave = len;
+  layout.avx_offset = xsave_feature_offset(xcr0, X86_XSTATE_AVX_ID);
+  layout.bndregs_offset = xsave_feature_offset(xcr0, X86_XSTATE_BNDREGS_ID);
+  layout.bndcfg_offset = xsave_feature_offset(xcr0, X86_XSTATE_BNDCFG_ID);
+  layout.k_offset = xsave_feature_offset(xcr0, X86_XSTATE_K_ID);
+  layout.zmm_h_offset = xsave_feature_offset(xcr0, X86_XSTATE_ZMM_H_ID);
+  layout.zmm_offset = xsave_feature_offset(xcr0, X86_XSTATE_ZMM_ID);
+  layout.pkru_offset = xsave_feature_offset(xcr0, X86_XSTATE_PKRU_ID);
+}
diff --git a/gdb/nat/x86-xstate.h b/gdb/nat/x86-xstate.h
new file mode 100644
index 00000000000..e9f5fb57e3a
--- /dev/null
+++ b/gdb/nat/x86-xstate.h
@@ -0,0 +1,35 @@
+/* x86 XSAVE extended state functions.
+
+   Copyright (C) 2022-2023 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/>.  */
+
+#ifndef NAT_X86_XSTATE_H
+#define NAT_X86_XSTATE_H
+
+#include "gdbsupport/x86-xstate.h"
+
+/* Return the size of the XSAVE extended state fetched via CPUID.  */
+
+int x86_xsave_length ();
+
+/* Save the size and offsets of the XSAVE extended regions for the
+   running host in LAYOUT.  Offsets of each of the enabled regions in
+   XCR0 are fetched via CPUID.  */
+
+void x86_fetch_xsave_layout (uint64_t xcr0, int len, x86_xsave_layout &layout);
+
+#endif /* NAT_X86_XSTATE_H */
-- 
2.39.1