[aarch64] Add TPIDR2 register support for Linux

With the AArch64 Scalable Matrix Extension we have a new TPIDR2 register, and
it will be added to the existing NT_ARM_TLS register set. Kernel patches are
being reviewed here:

https://lore.kernel.org/linux-arm-kernel/20220818170111.351889-1-broonie@kernel.org/

From GDB's perspective, we handle it in a similar way to the existing TPIDR
register. But we need to consider cases of systems that only have TPIDR and
systems that have both TPIDR and TPIDR2.

With that in mind, the following patch adds the required code to support
TPIDR2 and turns the org.gnu.gdb.aarch64.tls feature into a
dynamically-generated target description as opposed to a static target
description containing only TPIDR.

That means we can remove the gdb/features/aarch64-tls.xml file and replace the
existing gdb/features/aarch64-tls.c auto-generated file with a new file that
dynamically generates the target description containing either TPIDR alone or
TPIDR and TPIDR2.

In the future, when *BSD's start to support this register, they can just
enable it as is being done for the AArch64 Linux target.

The core file read/write code has been updated to support TPIDR2 as well.

On GDBserver's side, there is a small change to the find_regno function to
expose a non-throwing version of it.

It always seemed strange to me how find_regno causes the whole operation to
abort if it doesn't find a particular register name. The patch moves code
from find_regno into find_regno_no_throw and makes find_regno call
find_regno_no_throw instead.

This allows us to do register name lookups to find a particular register
number without risking erroring out if nothing is found.

The patch also adjusts the feature detection code for aarch64-fbsd, since
the infrastructure is shared amongst all aarch64 targets. I haven't added
code to support TPIDR2 in aarch64-fbsd though, as I'm not sure when/if
that will happen.

3 files changed, 32 insertions, 15 deletions

diff --git a/gdb/features/Makefile b/gdb/features/Makefile
index c3e0780..f260849 100644
--- a/gdb/features/Makefile
+++ b/gdb/features/Makefile
@@ -202,7 +202,6 @@ FEATURE_XMLFILES = aarch64-core.xml \
 	aarch64-fpu.xml \
 	aarch64-pauth.xml \
 	aarch64-mte.xml \
-	aarch64-tls.xml \
 	arc/v1-core.xml \
 	arc/v1-aux.xml \
 	arc/v2-core.xml \
diff --git a/gdb/features/aarch64-tls.c b/gdb/features/aarch64-tls.c
index 30d730d..8a59d26 100644
--- a/gdb/features/aarch64-tls.c
+++ b/gdb/features/aarch64-tls.c
@@ -1,14 +1,43 @@
-/* THIS FILE IS GENERATED.  -*- buffer-read-only: t -*- vi:set ro:
-  Original: aarch64-tls.xml */
+/* Copyright (C) 2022 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/tdesc.h"
 
+/* This function is NOT auto generated from xml.
+
+   Create the aarch64 description containing the TLS registers.  TPIDR is
+   always available, but TPIDR2 is only available on some systems.
+
+   COUNT is the number of registers in this set.  The minimum is 1.  */
+
 static int
-create_feature_aarch64_tls (struct target_desc *result, long regnum)
+create_feature_aarch64_tls (struct target_desc *result, long regnum, int count)
 {
+  /* TPIDR is always present.  */
+  gdb_assert (count >= 1);
+
   struct tdesc_feature *feature;
 
   feature = tdesc_create_feature (result, "org.gnu.gdb.aarch64.tls");
   tdesc_create_reg (feature, "tpidr", regnum++, 1, NULL, 64, "data_ptr");
+
+  /* Add TPIDR2.  */
+  if (count > 1)
+    tdesc_create_reg (feature, "tpidr2", regnum++, 1, NULL, 64, "data_ptr");
+
   return regnum;
 }
diff --git a/gdb/features/aarch64-tls.xml b/gdb/features/aarch64-tls.xml
deleted file mode 100644
index f643778..0000000
--- a/gdb/features/aarch64-tls.xml
+++ /dev/null
@@ -1,11 +0,0 @@
-<?xml version="1.0"?>
-<!-- Copyright (C) 2022 Free Software Foundation, Inc.
-
-     Copying and distribution of this file, with or without modification,
-     are permitted in any medium without royalty provided the copyright
-     notice and this notice are preserved.  -->
-
-<!DOCTYPE feature SYSTEM "gdb-target.dtd">
-<feature name="org.gnu.gdb.aarch64.tls">
-  <reg name="tpidr" bitsize="64" type="data_ptr"/>
-</feature>