gdb/x86: move have_ptrace_getfpxregs global into gdb/nat directory

The have_ptrace_getfpxregs global tracks whether GDB or gdbserver is
running on a kernel that supports the GETFPXREGS ptrace request.

Currently this global is declared twice (once in GDB and once in
gdbserver), I think it makes sense to move this global into the nat/
directory, and have a single declaration and definition.

While moving this variable I have converted it to a tribool, as that
was what it really was, if even used the same numbering as the tribool
enum (-1, 0, 1).  Where have_ptrace_getfpxregs was used I have updated
in the obvious way.

However, while making this change I noticed what I think is a bug in
x86_linux_nat_target::read_description and x86_linux_read_description,
both of these functions can be called multiple times, but in both
cases we only end up calling i386_linux_read_description the first
time through in the event that PTRACE_GETFPXREGS is not supported.
This is because initially have_ptrace_getfpxregs will be
TRIBOOL_UNKNOWN, but after the ptrace call fails we set
have_ptrace_getfpxregs to TRIBOOL_FALSE.  The next time we attempt to
read the target description we'll skip the ptrace call, and so skip
the call to i386_linux_read_description.

I've not tried to address this preexisting bug in this commit, this is
purely a refactor, there should be no user visible changes after this
commit.  In later commits I'll merge the gdbserver and GDB code
together into the nat/ directory, and after that I'll try to address
this bug.

Reviewed-By: Felix Willgerodt <felix.willgerodt@intel.com>

2 files changed, 66 insertions, 0 deletions

diff --git a/gdb/nat/i386-linux.c b/gdb/nat/i386-linux.c
new file mode 100644
index 0000000..64605be
--- /dev/null
+++ b/gdb/nat/i386-linux.c
@@ -0,0 +1,29 @@
+/* Native-dependent code for GNU/Linux i386.
+
+   Copyright (C) 2024 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 "nat/i386-linux.h"
+
+/* See nat/i386-linux.h.  */
+tribool have_ptrace_getfpxregs =
+#ifdef HAVE_PTRACE_GETFPXREGS
+  TRIBOOL_UNKNOWN
+#else
+  TRIBOOL_FALSE
+#endif
+;
diff --git a/gdb/nat/i386-linux.h b/gdb/nat/i386-linux.h
new file mode 100644
index 0000000..c93626b
--- /dev/null
+++ b/gdb/nat/i386-linux.h
@@ -0,0 +1,37 @@
+/* Native-dependent code for GNU/Linux i386.
+
+   Copyright (C) 2024 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_I386_LINUX_H
+#define NAT_I386_LINUX_H
+
+/* Does the current host support the GETFPXREGS request?  The system header
+   file may or may not define it, but even if it is defined, the kernel
+   will return EIO if it's running on a pre-SSE processor.
+
+   Initially this will be TRIBOOL_UNKNOWN and should be changed to
+   TRIBOOL_FALSE if the ptrace call is attempted and fails or changed to
+   TRIBOOL_TRUE if the ptrace call is attempted and succeeds.
+
+   My instinct is to attach this to some architecture- or target-specific
+   data structure, but really, a particular GDB process can only run on top
+   of one kernel at a time.  So it's okay - for this to be a global
+   variable.  */
+extern tribool have_ptrace_getfpxregs;
+
+#endif /* NAT_I386_LINUX_H */