[PATCH] gdb: fix nr_bits gdb_assert in append_flags_type_field

[PATCH] gdb: fix nr_bits gdb_assert in append_flags_type_field

[Simon Marchi]

The assertion

    gdb_assert (nr_bits >= 1 && nr_bits <= type_bitsize);

is not correct.  Well, it's correct in that we do want the number of
bits to be in the range [1, type_bitsize].  But we don't check anywhere
that the end of the specified flag is within the containing type.

The following code should generate a failed assertion, as the flag goes
past the 32 bits of the underlying type, but it's currently not caught:

    static void
    test_print_flag (gdbarch *arch)
    {
      type *flags_type = arch_flags_type (arch, "test_type", 32);
      type *field_type = builtin_type (arch)->builtin_uint32;
      append_flags_type_field (flags_type, 31, 2, field_type, "invalid");
    }

(You can test this by registering it as a selftest using
selftests::register_test_foreach_arc and running.)

Change the assertion to verify that the end bit is within the range of
the underlying type.  This implicitly verifies that nr_bits is not
too big as well, so we don't need a separate assertion for that.

Change-Id: I9be79e5fd7a5917bf25b03b598727e6274c892e8
Co-Authored-By: Tony Tye <Tony.Tye@amd.com>
---
 gdb/gdbtypes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index 1a261719422a..85c9df0e2c6d 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -5825,7 +5825,7 @@ append_flags_type_field (struct type *type, int start_bitpos, int nr_bits,
   gdb_assert (type->code () == TYPE_CODE_FLAGS);
   gdb_assert (type->num_fields () + 1 <= type_bitsize);
   gdb_assert (start_bitpos >= 0 && start_bitpos < type_bitsize);
-  gdb_assert (nr_bits >= 1 && nr_bits <= type_bitsize);
+  gdb_assert (nr_bits >= 1 && (start_bitpos + nr_bits) <= type_bitsize);
   gdb_assert (name != NULL);
 
   TYPE_FIELD_NAME (type, field_nr) = xstrdup (name);
-- 
2.32.0

Re: [PATCH] gdb: fix nr_bits gdb_assert in append_flags_type_field

[Tom Tromey]

>>>>> "Simon" == Simon Marchi via Gdb-patches <gdb-patches@sourceware.org> writes:

Simon> -  gdb_assert (nr_bits >= 1 && nr_bits <= type_bitsize);
Simon> +  gdb_assert (nr_bits >= 1 && (start_bitpos + nr_bits) <= type_bitsize);

This looks good to me.

Tom

Re: [PATCH] gdb: fix nr_bits gdb_assert in append_flags_type_field

[Simon Marchi]

On 2021-07-29 4:04 p.m., Tom Tromey wrote:
>>>>>> "Simon" == Simon Marchi via Gdb-patches <gdb-patches@sourceware.org> writes:
> 
> Simon> -  gdb_assert (nr_bits >= 1 && nr_bits <= type_bitsize);
> Simon> +  gdb_assert (nr_bits >= 1 && (start_bitpos + nr_bits) <= type_bitsize);
> 
> This looks good to me.
> 
> Tom
> 

Thanks, pushed.

Simon