New target methods for memory tagging support

This patch starts adding some of the generic pieces to accomodate memory
tagging.

We have three new target methods:

- supports_memory_tagging: Checks if the target supports memory tagging. This
  defaults to false for targets that don't support memory tagging.

- fetch_memtags: Fetches the allocation tags associated with a particular
  memory range [address, address + length).

  The default is to return 0 without returning any tags. This should only
  be called if memory tagging is supported.

- store_memtags: Stores a set of allocation tags for a particular memory
  range [address, address + length).

  The default is to return 0. This should only
  be called if memory tagging is supported.

It also adds a control option for enabling/disabling memory tagging
manually: set memory-tagging on/off.

The default is "on", with GDB making its use conditional to the
architecture supporting memory tagging.

gdb/ChangeLog:

YYYY-MM-DD  Luis Machado  <luis.machado@linaro.org>

	* printcmd.c (memtag): New static global.
	(show_memtag): New function.
	(_initialize_printcmd): Add set/show memory-tagging command.
	* remote.c (remote_target) <supports_memory_tagging>: New method
	override.
	<fetch_memtags>: New method override.
	<store_memtags>: New method override.
	(remote_target::supports_memory_tagging): New method.
	(remote_target::fetch_memtags): New method.
	(remote_target::store_memtags): New method.
	* target-delegates.c
	(dummy_target) <supports_memory_tagging>: New method override.
	<fetch_memtags>: New method override.
	<store_memtags>: New method override.
	(debug_target) <supports_memory_tagging>: New method override.
	<fetch_memtags>: New method override.
	<store_memtags>: New method override.
	(target_ops::supports_memory_tagging): New method.
	(target_ops::fetch_memtags): New method.
	(target_ops::store_memtags): New method.
	(dummy_target::supports_memory_tagging): New method.
	(dummy_target::fetch_memtags): New method.
	(dummy_target::store_memtags): New method.
	(debug_target::supports_memory_tagging): New method.
	(debug_target::fetch_memtags): New method.
	(debug_target::store_memtags): New method.
	* target.h (struct target_ops) <supports_memory_tagging>: New virtual
	method.
	<fetch_memtags: New virtual method.
	<store_memtags>: New virtual method.
	(target_supports_memory_tagging): Define.
	(target_fetch_memtags): Define.
	(target_store_memtags): Define.

gdb/printcmd.c

@@ -84,6 +84,24 @@ static CORE_ADDR last_examine_address;
 
 static value_ref_ptr last_examine_value;
 
+/* If TRUE (default), and the architecture supports it, GDB will attempt to use
+   the memory tagging infrastructure to validate certain memory accesses.  It
+   will also report memory tag violations alongside a SIGSEGV signal.
+
+   If FALSE, GDB will not use memory tagging in any way, and debugging will work
+   in the standard way.  */
+static bool memtag = true;
+
+static void
+show_memtag (struct ui_file *file, int from_tty,
+	     struct cmd_list_element *c,
+	     const char *value)
+{
+  fprintf_filtered (file,
+		    _("Use of memory tagging infrastructure is \"%s\".\n"),
+		    value);
+}
+
 /* Largest offset between a symbolic value and an address, that will be
    printed as `0x1234 <symbol+offset>'.  */
 
@@ -2882,4 +2900,14 @@ Construct a GDB command and then evaluate it.\n\
 Usage: eval \"format string\", ARG1, ARG2, ARG3, ..., ARGN\n\
 Convert the arguments to a string as \"printf\" would, but then\n\
 treat this string as a command line, and evaluate it."));
+
+  add_setshow_boolean_cmd ("memory-tagging", class_support,
+			   &memtag, _("\
+Set whether the debugger should use memory tagging infrastructure."), _("\
+Show whether the debugger should use memory tagging infrastructure."), _("\
+If on, gdb will attempt to validate memory tags and will warn the user if\n\
+certain operations have illegal tags."),
+			    NULL,
+			    show_memtag,
+			    &setlist, &showlist);
 }

gdb/remote.c

@@ -685,6 +685,16 @@ public:
   int remove_exec_catchpoint (int) override;
   enum exec_direction_kind execution_direction () override;
 
+  bool supports_memory_tagging () override;
+
+  /* Read memory tags via the qMemTags packet  */
+  int fetch_memtags (CORE_ADDR address, size_t len,
+		     gdb::byte_vector &tags) override;
+
+  /* Write allocation tags via the QMemTags packet.  */
+  int store_memtags (CORE_ADDR address, size_t len,
+		     const gdb::byte_vector &tags) override;
+
 public: /* Remote specific methods.  */
 
   void remote_download_command_source (int num, ULONGEST addr,
@@ -14378,6 +14388,32 @@ set_range_stepping (const char *ignore_args, int from_tty,
     }
 }
 
+/* Implement the "supports_memory_tagging" target_ops method.  */
+
+bool
+remote_target::supports_memory_tagging ()
+{
+  return false;
+}
+
+/* Implement the "fetch_memtags" target_ops method.  */
+
+int
+remote_target::fetch_memtags (CORE_ADDR address, size_t len,
+			      gdb::byte_vector &tags)
+{
+  return 0;
+}
+
+/* Implement the "store_memtags" target_ops method.  */
+
+int
+remote_target::store_memtags (CORE_ADDR address, size_t len,
+			      const gdb::byte_vector &tags)
+{
+  return 0;
+}
+
 void _initialize_remote ();
 void
 _initialize_remote ()

gdb/target-delegates.c

@@ -171,6 +171,11 @@ struct dummy_target : public target_ops
   const struct frame_unwind *get_tailcall_unwinder () override;
   void prepare_to_generate_core () override;
   void done_generating_core () override;
+  bool supports_memory_tagging () override;
+  int fetch_memtags (CORE_ADDR address, size_t len,
+		     gdb::byte_vector &tags) override;
+  int store_memtags (CORE_ADDR address, size_t len,
+		     const gdb::byte_vector &tags) override;
 };
 
 struct debug_target : public target_ops
@@ -340,6 +345,11 @@ struct debug_target : public target_ops
   const struct frame_unwind *get_tailcall_unwinder () override;
   void prepare_to_generate_core () override;
   void done_generating_core () override;
+  bool supports_memory_tagging () override;
+  int fetch_memtags (CORE_ADDR address, size_t len,
+		     gdb::byte_vector &tags) override;
+  int store_memtags (CORE_ADDR address, size_t len,
+		     const gdb::byte_vector &tags) override;
 };
 
 void
@@ -4363,3 +4373,77 @@ debug_target::done_generating_core ()
   fputs_unfiltered (")\n", gdb_stdlog);
 }
 
+bool
+target_ops::supports_memory_tagging ()
+{
+  return this->beneath ()->supports_memory_tagging ();
+}
+
+int
+target_ops::fetch_memtags (CORE_ADDR address, size_t len,
+			   gdb::byte_vector &tags)
+{
+  return this->beneath ()->fetch_memtags (address, len, tags);
+}
+
+int
+target_ops::store_memtags (CORE_ADDR address, size_t len,
+			   const gdb::byte_vector &tags)
+{
+  return this->beneath ()->store_memtags (address, len, tags);
+}
+
+bool
+dummy_target::supports_memory_tagging ()
+{
+  return false;
+}
+
+int
+dummy_target::fetch_memtags (CORE_ADDR address, size_t len,
+			     gdb::byte_vector &tags)
+{
+  return 0;
+}
+
+int
+dummy_target::store_memtags (CORE_ADDR address, size_t len,
+			     const gdb::byte_vector &tags)
+{
+  return 0;
+}
+
+bool
+debug_target::supports_memory_tagging ()
+{
+  bool result;
+  fprintf_unfiltered (gdb_stdlog, "-> %s->supports_memory_tagging (...)\n", this->beneath ()->shortname ());
+  result = this->beneath ()->supports_memory_tagging ();
+  fprintf_unfiltered (gdb_stdlog, "<- %s->supports_memory_tagging (", this->beneath ()->shortname ());
+  fputs_unfiltered (") = ", gdb_stdlog);
+  target_debug_print_bool (result);
+  fputs_unfiltered ("\n", gdb_stdlog);
+  return result;
+}
+
+int
+debug_target::fetch_memtags (CORE_ADDR address, size_t len,
+			     gdb::byte_vector &tags)
+{
+  fprintf_unfiltered (gdb_stdlog, "-> %s->fetch_memtags (...)\n", this->beneath ()->shortname ());
+  int result = this->beneath ()->fetch_memtags (address, len, tags);
+  fprintf_unfiltered (gdb_stdlog, "<- %s->fetch_memtags (", this->beneath ()->shortname ());
+  fputs_unfiltered (")\n", gdb_stdlog);
+  return result;
+}
+
+int
+debug_target::store_memtags (CORE_ADDR address, size_t len,
+			     const gdb::byte_vector &tags)
+{
+  fprintf_unfiltered (gdb_stdlog, "-> %s->store_memtags (...)\n", this->beneath ()->shortname ());
+  int result = this->beneath ()->store_memtags (address, len, tags);
+  fprintf_unfiltered (gdb_stdlog, "<- %s->store_memtags (", this->beneath ()->shortname ());
+  fputs_unfiltered (")\n", gdb_stdlog);
+  return result;
+}

gdb/target.h

@@ -1252,6 +1252,22 @@ struct target_ops
     /* Cleanup after generating a core file.  */
     virtual void done_generating_core ()
       TARGET_DEFAULT_IGNORE ();
+
+    /* Returns true if the target supports memory tagging.  */
+    virtual bool supports_memory_tagging ()
+      TARGET_DEFAULT_RETURN (false);
+
+    /* Return the allocated memory tags associated with
+       [ADDRESS, ADDRESS + LEN) in TAGS.  */
+    virtual int fetch_memtags (CORE_ADDR address, size_t len,
+			       gdb::byte_vector &tags)
+      TARGET_DEFAULT_IGNORE ();
+
+    /* Write the allocation tags contained in TAGS to the memory range
+       [ADDRESS, ADDRESS + LEN).  */
+    virtual int store_memtags (CORE_ADDR address, size_t len,
+			       const gdb::byte_vector &tags)
+      TARGET_DEFAULT_IGNORE ();
   };
 
 /* Deleter for std::unique_ptr.  See comments in
@@ -2308,6 +2324,15 @@ extern gdb::unique_xmalloc_ptr<char> target_fileio_read_stralloc
 #define target_augmented_libraries_svr4_read() \
   (current_top_target ()->augmented_libraries_svr4_read) ()
 
+#define target_supports_memory_tagging() \
+  ((current_top_target ()->supports_memory_tagging) ())
+
+#define target_fetch_memtags(address, len, tags) \
+  (current_top_target ()->fetch_memtags) ((address), (len), (tags))
+
+#define target_store_memtags(address, len, tags) \
+  (current_top_target ()->store_memtags) ((address), (len), (tags))
+
 /* Command logging facility.  */
 
 #define target_log_command(p)					\