[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, 10 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 4d6de31..d2efe2a 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,16 @@
 
 *** Changes since GDB 12
 
+* GDB now supports dumping memory tag data for AArch64 MTE.  It also supports
+  reading memory tag data for AArch64 MTE from core files generated by
+  the gcore command or the Linux kernel.
+
+  When a process uses memory-mapped pages protected by memory tags (for
+  example, AArch64 MTE), this additional information will be recorded in
+  the core file in the event of a crash or if GDB generates a core file
+  from the current process state.  GDB will show this additional information
+  automatically, or through one of the memory-tag subcommands.
+
 * "info breakpoints" now displays enabled breakpoint locations of
   disabled breakpoints as in the "y-" state.  For example: