[PATCH v5 22/25] Extend "x" and "print" commands to support memory tagging

Luis Machado via Gdb-patches
2021-01-27T20:22:01Z

Updates on v5:

- Add -memory-tag-violations print option to control whether GDB should print
a warning when a logical tag from a pointer doesn't match the allocation tag
contained in memory.
- Remove checks for a removed memory_tagging global variable.
- Update tests listing print options.

Updates on v4:

- Updated function names.
- Removed useless include of infrun.h

--

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:

YYYY-MM-DD 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:

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

* gdb.base/options.exp: Adjust for new print options.
* gdb.base/with.exp: Likewise.
---
gdb/printcmd.c | 82 +++++++++++++++++++++++++++++-
gdb/testsuite/gdb.base/options.exp | 1 +
gdb/testsuite/gdb.base/with.exp | 2 +-
gdb/valprint.c | 22 ++++++++
gdb/valprint.h | 4 ++
5 files changed, 109 insertions(+), 2 deletions(-)

diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index 78acda4e37..322ad16eed 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -193,6 +193,7 @@ 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 +216,11 @@ 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 +1106,47 @@ 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))
+ {
+ std::string atag = gdbarch_memtag_to_string (gdbarch, v_addr,
+ tag_allocation);
+
+ 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 +1177,11 @@ 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 +1254,26 @@ 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 && value_type (value));
+
+ 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 +1312,21 @@ 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))
+ {
+ std::string ltag = gdbarch_memtag_to_string (target_gdbarch (),
+ val, tag_logical);
+ std::string atag = gdbarch_memtag_to_string (target_gdbarch (),
+ val, tag_allocation);
+ 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
diff --git a/gdb/testsuite/gdb.base/options.exp b/gdb/testsuite/gdb.base/options.exp
index 44c773c3fa..78ec54502c 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 0e83ad4898..0d53dbebba 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 2c3541e668..95f2930adf 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
@@ -3023,6 +3035,16 @@ will be replaced with either '{...}' or '(...)' depending on the language.\n\
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_("When logical tags in pointers do not match the allocation tags in\n\
+memory, issue a warning."),
+ },
+
boolean_option_def {
"null-stop",
[] (value_print_options *opt) { return &opt->stop_print_at_null; },
diff --git a/gdb/valprint.h b/gdb/valprint.h
index ca8ad6aa71..e1dae2cc8f 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. */
--
2.25.1