[AArch64] MTE corefile support

Teach GDB how to dump memory tags for AArch64 when using the gcore command
and how to read memory tag data back from a core file generated by GDB
(via gcore) or by the Linux kernel.

The format is documented in the Linux Kernel documentation [1].

Each tagged memory range (listed in /proc/<pid>/smaps) gets dumped to its
own PT_AARCH64_MEMTAG_MTE segment. A section named ".memtag" is created for each
of those segments when reading the core file back.

To save a little bit of space, given MTE tags only take 4 bits, the memory tags
are stored packed as 2 tags per byte.

When reading the data back, the tags are unpacked.

I've added a new testcase to exercise the feature.

Build-tested with --enable-targets=all and regression tested on aarch64-linux
Ubuntu 20.04.

[1] Documentation/arm64/memory-tagging-extension.rst (Core Dump Support)

1 files changed, 50 insertions, 0 deletions

diff --git a/gdb/memtag.h b/gdb/memtag.h
new file mode 100644
index 0000000..fe908c1
--- /dev/null
+++ b/gdb/memtag.h
@@ -0,0 +1,50 @@
+/* GDB generic memory tagging definitions.
+   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/>.  */
+
+#ifndef MEMTAG_H
+#define MEMTAG_H
+
+#include "bfd.h"
+
+struct memtag_section_info
+{
+  /* The start address of the tagged memory range.  */
+  CORE_ADDR start_address;
+  /* The final address of the tagged memory range.  */
+  CORE_ADDR end_address;
+  /* The section containing tags for the memory range
+     [start_address, end_address).  */
+  asection *memtag_section;
+};
+
+/* Helper function to walk through memory tag sections in a core file.
+
+   Return TRUE if there is a "memtag" section containing ADDRESS.  Return FALSE
+   otherwise.
+
+   If SECTION is provided, search from that section onwards. If SECTION is
+   nullptr, then start a new search.
+
+   If a "memtag" section containing ADDRESS is found, fill INFO with data
+   about such section.  Otherwise leave it unchanged.  */
+
+bool get_next_core_memtag_section (bfd *abfd, asection *section,
+				   CORE_ADDR address,
+				   memtag_section_info &info);
+
+#endif /* MEMTAG_H */