Extend "x" and "print" commands to support memory tagging

Extend the "x" and "print" commands to make use of memory tagging
functionality, if supported by the architecture.

The "print" command will point out any possible tag mismatches it finds
when dealing with pointers, in case such a pointer is tagged.  No additional
modifiers are needed.

Suppose we have a pointer "p" with value 0x1234 (logical tag 0x0) and that we
have an allocation tag of 0x1 for that particular area of memory. This is the
expected output:

(gdb) p/x p
Logical tag (0x0) does not match the allocation tag (0x1).
$1 = 0x1234

The "x" command has a new 'm' modifier that will enable displaying of
allocation tags alongside the data dump.  It will display one allocation
tag per line.

AArch64 has a tag granule of 16 bytes, which means we can have one tag for
every 16 bytes of memory. In this case, this is what the "x" command will
display with the new 'm' modifier:

(gdb) x/32bxm p
<Allocation Tag 0x1 for range [0x1230,0x1240)>
0x1234:	0x01	0x02	0x00	0x00	0x00	0x00	0x00	0x00
0x123c:	0x00	0x00	0x00	0x00	0x00	0x00	0x00	0x00
<Allocation Tag 0x1 for range [0x1240,0x1250)>
0x1244:	0x00	0x00	0x00	0x00	0x00	0x00	0x00	0x00
0x124c:	0x00	0x00	0x00	0x00	0x00	0x00	0x00	0x00

(gdb) x/4gxm a
<Allocation Tag 0x1 for range [0x1230,0x1240)>
0x1234:	0x0000000000000201	0x0000000000000000
<Allocation Tag 0x1 for range [0x1240,0x1250)>
0x1244:	0x0000000000000000	0x0000000000000000

gdb/ChangeLog:

2021-03-24  Luis Machado  <luis.machado@linaro.org>

	* printcmd.c (decode_format): Handle the 'm' modifier.
	(do_examine): Display allocation tags when required/supported.
	(should_validate_memtags): New function.
	(print_command_1): Display memory tag mismatches.
	* valprint.c (show_memory_tag_violations): New function.
	(value_print_option_defs): Add new option "memory-tag-violations".
	(user_print_options) <memory_tag_violations>: Initialize to 1.
	* valprint.h (struct format_data) <print_tags>: New field.
	(value_print_options) <memory_tag_violations>: New field.

gdb/testsuite/ChangeLog:

2021-03-24  Luis Machado  <luis.machado@linaro.org>

	* gdb.base/options.exp: Adjust for new print options.
	* gdb.base/with.exp: Likewise.

7 files changed, 147 insertions, 2 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 189884b..5d7069a 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,17 @@
 2021-03-24  Luis Machado  <luis.machado@linaro.org>
 
+	* printcmd.c (decode_format): Handle the 'm' modifier.
+	(do_examine): Display allocation tags when required/supported.
+	(should_validate_memtags): New function.
+	(print_command_1): Display memory tag mismatches.
+	* valprint.c (show_memory_tag_violations): New function.
+	(value_print_option_defs): Add new option "memory-tag-violations".
+	(user_print_options) <memory_tag_violations>: Initialize to 1.
+	* valprint.h (struct format_data) <print_tags>: New field.
+	(value_print_options) <memory_tag_violations>: New field.
+
+2021-03-24  Luis Machado  <luis.machado@linaro.org>
+
 	* printcmd.c: Include gdbsupport/rsp-low.h.
 	(memory_tag_list): New static global.
 	(process_print_command_args): Factored out of
diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index 9200e66..c82f709 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -72,6 +72,10 @@ static char last_size = 'w';
 
 static int last_count;
 
+/* Last specified tag-printing option.  */
+
+static bool last_print_tags = false;
+
 /* Default address to examine next, and associated architecture.  */
 
 static struct gdbarch *next_gdbarch;
@@ -193,6 +197,7 @@ decode_format (const char **string_ptr, int oformat, int osize)
   val.size = '?';
   val.count = 1;
   val.raw = 0;
+  val.print_tags = false;
 
   if (*p == '-')
     {
@@ -215,6 +220,11 @@ decode_format (const char **string_ptr, int oformat, int osize)
 	  val.raw = 1;
 	  p++;
 	}
+      else if (*p == 'm')
+	{
+	  val.print_tags = true;
+	  p++;
+	}
       else if (*p >= 'a' && *p <= 'z')
 	val.format = *p++;
       else
@@ -1100,12 +1110,50 @@ do_examine (struct format_data fmt, struct gdbarch *gdbarch, CORE_ADDR addr)
       need_to_update_next_address = 1;
     }
 
+  /* Whether we need to print the memory tag information for the current
+     address range.  */
+  bool print_range_tag = true;
+  uint32_t gsize = gdbarch_memtag_granule_size (gdbarch);
+
   /* Print as many objects as specified in COUNT, at most maxelts per line,
      with the address of the next one at the start of each line.  */
 
   while (count > 0)
     {
       QUIT;
+
+      CORE_ADDR tag_laddr = 0, tag_haddr = 0;
+
+      /* Print the memory tag information if requested.  */
+      if (fmt.print_tags && print_range_tag
+	  && target_supports_memory_tagging ())
+	{
+	  tag_laddr = align_down (next_address, gsize);
+	  tag_haddr = align_down (next_address + gsize, gsize);
+
+	  struct value *v_addr
+	    = value_from_ulongest (builtin_type (gdbarch)->builtin_data_ptr,
+				   tag_laddr);
+
+	  if (gdbarch_tagged_address_p (target_gdbarch (), v_addr))
+	    {
+	      /* Fetch the allocation tag.  */
+	      struct value *tag
+		= gdbarch_get_memtag (gdbarch, v_addr, memtag_type::allocation);
+	      std::string atag
+		= gdbarch_memtag_to_string (gdbarch, tag);
+
+	      if (!atag.empty ())
+		{
+		  printf_filtered (_("<Allocation Tag %s for range [%s,%s)>\n"),
+				   atag.c_str (),
+				   paddress (gdbarch, tag_laddr),
+				   paddress (gdbarch, tag_haddr));
+		}
+	    }
+	  print_range_tag = false;
+	}
+
       if (format == 'i')
 	fputs_filtered (pc_prefix (next_address), gdb_stdout);
       print_address (next_gdbarch, next_address, gdb_stdout);
@@ -1136,6 +1184,11 @@ do_examine (struct format_data fmt, struct gdbarch *gdbarch, CORE_ADDR addr)
 	  /* Display any branch delay slots following the final insn.  */
 	  if (format == 'i' && count == 1)
 	    count += branch_delay_insns;
+
+	  /* Update the tag range based on the current address being
+	     processed.  */
+	  if (tag_haddr <= next_address)
+	      print_range_tag = true;
 	}
       printf_filtered ("\n");
     }
@@ -1208,6 +1261,26 @@ print_value (value *val, const value_print_options &opts)
   annotate_value_history_end ();
 }
 
+/* Returns true if memory tags should be validated.  False otherwise.  */
+
+static bool
+should_validate_memtags (struct value *value)
+{
+  if (target_supports_memory_tagging ()
+      && gdbarch_tagged_address_p (target_gdbarch (), value))
+    {
+      gdb_assert (value != nullptr && value_type (value) != nullptr);
+
+      enum type_code code = value_type (value)->code ();
+
+      return (code == TYPE_CODE_PTR
+	      || code == TYPE_CODE_REF
+	      || code == TYPE_CODE_METHODPTR
+	      || code == TYPE_CODE_MEMBERPTR);
+    }
+  return false;
+}
+
 /* Helper for parsing arguments for print_command_1.  */
 
 static struct value *
@@ -1246,7 +1319,30 @@ print_command_1 (const char *args, int voidprint)
 
   if (voidprint || (val && value_type (val) &&
 		    value_type (val)->code () != TYPE_CODE_VOID))
-    print_value (val, print_opts);
+    {
+      /* If memory tagging validation is on, check if the tag is valid.  */
+      if (print_opts.memory_tag_violations && should_validate_memtags (val)
+	  && !gdbarch_memtag_matches_p (target_gdbarch (), val))
+	{
+	  /* Fetch the logical tag.  */
+	  struct value *tag
+	    = gdbarch_get_memtag (target_gdbarch (), val,
+				  memtag_type::logical);
+	  std::string ltag
+	    = gdbarch_memtag_to_string (target_gdbarch (), tag);
+
+	  /* Fetch the allocation tag.  */
+	  tag = gdbarch_get_memtag (target_gdbarch (), val,
+				    memtag_type::allocation);
+	  std::string atag
+	    = gdbarch_memtag_to_string (target_gdbarch (), tag);
+
+	  printf_filtered (_("Logical tag (%s) does not match the "
+			     "allocation tag (%s).\n"),
+			   ltag.c_str (), atag.c_str ());
+	}
+      print_value (val, print_opts);
+    }
 }
 
 /* Called from command completion function to skip over /FMT
@@ -1741,6 +1837,7 @@ x_command (const char *exp, int from_tty)
   struct value *val;
 
   fmt.format = last_format ? last_format : 'x';
+  fmt.print_tags = last_print_tags;
   fmt.size = last_size;
   fmt.count = 1;
   fmt.raw = 0;
@@ -1797,6 +1894,9 @@ x_command (const char *exp, int from_tty)
     last_size = fmt.size;
   last_format = fmt.format;
 
+  /* Remember tag-printing setting.  */
+  last_print_tags = fmt.print_tags;
+
   /* Set a couple of internal variables if appropriate.  */
   if (last_examine_value != nullptr)
     {
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 848e089..8513f32 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2021-03-24  Luis Machado  <luis.machado@linaro.org>
+
+	* gdb.base/options.exp: Adjust for new print options.
+	* gdb.base/with.exp: Likewise.
+
 2021-03-22  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* gdb.dwarf2/dw2-missing-cu-tag.c: New file.
diff --git a/gdb/testsuite/gdb.base/options.exp b/gdb/testsuite/gdb.base/options.exp
index 44c773c..78ec545 100644
--- a/gdb/testsuite/gdb.base/options.exp
+++ b/gdb/testsuite/gdb.base/options.exp
@@ -165,6 +165,7 @@ proc_with_prefix test-print {{prefix ""}} {
 	"-array-indexes"
 	"-elements"
 	"-max-depth"
+	"-memory-tag-violations"
 	"-null-stop"
 	"-object"
 	"-pretty"
diff --git a/gdb/testsuite/gdb.base/with.exp b/gdb/testsuite/gdb.base/with.exp
index 0e83ad4..0d53dbe 100644
--- a/gdb/testsuite/gdb.base/with.exp
+++ b/gdb/testsuite/gdb.base/with.exp
@@ -238,7 +238,7 @@ with_test_prefix "errors" {
     gdb_test "with w" \
 	"Ambiguous set command \"w\": watchdog, width, write\\."
     gdb_test "with print m" \
-	"Ambiguous set print command \"m\": max-depth, max-symbolic-offset\\."
+	"Ambiguous set print command \"m\": max-depth, max-symbolic-offset, memory-tag-violations\\."
 
     gdb_test "with variable xxx=1" \
 	"Cannot use this setting with the \"with\" command"
diff --git a/gdb/valprint.c b/gdb/valprint.c
index 340a329..c089ee2 100644
--- a/gdb/valprint.c
+++ b/gdb/valprint.c
@@ -110,6 +110,7 @@ struct value_print_options user_print_options =
   10,				/* repeat_count_threshold */
   0,				/* output_format */
   0,				/* format */
+  1,				/* memory_tag_violations */
   0,				/* stop_print_at_null */
   0,				/* print_array_indexes */
   0,				/* deref_ref */
@@ -203,6 +204,17 @@ show_repeat_count_threshold (struct ui_file *file, int from_tty,
 		    value);
 }
 
+/* If nonzero, prints memory tag violations for pointers.  */
+
+static void
+show_memory_tag_violations (struct ui_file *file, int from_tty,
+			    struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file,
+		    _("Printing of memory tag violations is %s.\n"),
+		    value);
+}
+
 /* If nonzero, stops printing of char arrays at first null.  */
 
 static void
@@ -3024,6 +3036,17 @@ Use \"unlimited\" to print the complete structure.")
   },
 
   boolean_option_def {
+    "memory-tag-violations",
+    [] (value_print_options *opt) { return &opt->memory_tag_violations; },
+    show_memory_tag_violations, /* show_cmd_cb */
+    N_("Set printing of memory tag violations for pointers."),
+    N_("Show printing of memory tag violations for pointers."),
+    N_("Issue a warning when the printed value is a pointer\n\
+whose logical tag doesn't match the allocation tag of the memory\n\
+location it points to."),
+  },
+
+  boolean_option_def {
     "null-stop",
     [] (value_print_options *opt) { return &opt->stop_print_at_null; },
     show_stop_print_at_null, /* show_cmd_cb */
diff --git a/gdb/valprint.h b/gdb/valprint.h
index ca8ad6a..e1dae2c 100644
--- a/gdb/valprint.h
+++ b/gdb/valprint.h
@@ -65,6 +65,9 @@ struct value_print_options
      e.g. when the user passes a format to "print".  */
   int format;
 
+  /* Print memory tag violations for pointers.  */
+  bool memory_tag_violations;
+
   /* Stop printing at null character?  */
   bool stop_print_at_null;
 
@@ -252,6 +255,7 @@ struct format_data
     int count;
     char format;
     char size;
+    bool print_tags;
 
     /* True if the value should be printed raw -- that is, bypassing
        python-based formatters.  */