[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, 68 insertions, 0 deletions

diff --git a/gdb/memtag.c b/gdb/memtag.c
new file mode 100644
index 0000000..ca64569
--- /dev/null
+++ b/gdb/memtag.c
@@ -0,0 +1,68 @@
+/* GDB generic memory tagging functions.
+
+   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 "defs.h"
+#include "memtag.h"
+#include "bfd.h"
+
+/* See memtag.h */
+
+bool
+get_next_core_memtag_section (bfd *abfd, asection *section,
+			      CORE_ADDR address, memtag_section_info &info)
+{
+  /* If the caller provided no SECTION to start from, search from the
+     beginning.  */
+  if (section == nullptr)
+    section = bfd_get_section_by_name (abfd, "memtag");
+
+  /* Go through all the memtag sections and figure out if ADDRESS
+     falls within one of the memory ranges that contain tags.  */
+  while (section != nullptr)
+    {
+      size_t memtag_range_size = section->rawsize;
+      size_t tags_size = bfd_section_size (section);
+
+      /* Empty memory range or empty tag dump should not happen.  Warn about
+	 it but keep going through the sections.  */
+      if (memtag_range_size == 0 || tags_size == 0)
+	{
+	  warning (_("Found memtag section with empty memory "
+		     "range or empty tag dump"));
+	  continue;
+	}
+      else
+	{
+	  CORE_ADDR start_address = bfd_section_vma (section);
+	  CORE_ADDR end_address = start_address + memtag_range_size;
+
+	  /* Is the address within [start_address, end_address)?  */
+	  if (address >= start_address
+	      && address < end_address)
+	    {
+	      info.start_address = start_address;
+	      info.end_address = end_address;
+	      info.memtag_section = section;
+	      return true;
+	    }
+	}
+      section = bfd_get_next_section_by_name (abfd, section);
+    }
+  return false;
+}