Re: [PATCH] gdb/microblaze-tdep.c: Check whether less than zero in conditional expression

[Michael Eager <eager@eagerm.com>]

On 07/23/14 18:58, Chen Gang wrote:
>
>
> On 07/24/2014 06:20 AM, Chen Gang wrote:
>> On 07/24/2014 06:17 AM, Michael Eager wrote:
>>> On 07/23/14 15:06, Chen Gang wrote:
>>>> On 07/24/2014 04:04 AM, Michael Eager wrote:
>>>>> On 07/20/14 07:03, Chen Gang wrote:
>>>>>> Use typecast 'size_t' on 'reg', not only avoid the related warning, but
>>>>>> also check whether less than zero -- for 'reg' is type 'int', and sizeof
>>>>>> (dwarf2_to_reg_map) is less than 0x7fff.
>>>>>>
>>>>>> It is quoted in gdb_assert(), so need check 'reg' whether less than zero.
>>>>>> And the related warning (with '-W'):
>>>>>>
>>>>>>      ../../binutils-gdb/gdb/microblaze-tdep.c:667:3: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>>>>>>
>>>>>> ChangeLog:
>>>>>>
>>>>>>     * microblaze-tdep.c (microblaze_dwarf2_reg_to_regnum): Check whether
>>>>>>     less tha zero in conditional expression.
>>>>>>
>>>>>>
>>>>>> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
>>>>>> ---
>>>>>>     gdb/microblaze-tdep.c | 2 +-
>>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/gdb/microblaze-tdep.c b/gdb/microblaze-tdep.c
>>>>>> index 7e89241..9bec260 100644
>>>>>> --- a/gdb/microblaze-tdep.c
>>>>>> +++ b/gdb/microblaze-tdep.c
>>>>>> @@ -664,7 +664,7 @@ static int dwarf2_to_reg_map[78] =
>>>>>>     static int
>>>>>>     microblaze_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int reg)
>>>>>>     {
>>>>>> -  gdb_assert (reg < sizeof (dwarf2_to_reg_map));
>>>>>> +  gdb_assert ((size_t) reg < sizeof (dwarf2_to_reg_map));
>>>>>>       return dwarf2_to_reg_map[reg];
>>>>>>     }
>>>>>
>>>>> I don't see anything in the patch which does what you describe,
>>>>> checking whether reg is less than zero.  Converting a signed
>>>>> integer to an unsigned integer is not a way to check whether
>>>>> it is less than zero.  This is better:
>>>>>
>>>>> + gdb_assert (reg >= 0 && (size_t) reg < sizeof (dwarf2_to_reg_map));
>>>>>
>>>>
>>>> Yeah, it is common statement. It is also OK to me, although after type
>>>> cast, 'reg >=0' can be omited (it can let code simpler, but let code
>>>> not quit easy understanding).
>>>
>>> No, if you want to verify that the value is greater than zero,
>>> this cannot be omitted.  A negative value would converted to
>>> a positive value by the cast.  There no reason to believe that
>>> this would cause the other half of the test to fail.
>>>
>>
>> When an 'int' negative value converted to a positive value, it will be
>> larger than 0x7fff which must be larget than 'sizeof (dwarf2_to_reg_map)'.
>>
>
> If what I said is correct, your idea/suggestions is still OK to me: easy
> understanding has higher priority than keeping source code simple.

Yes, you are correct.  Took me a moment to think through.

I left your patch as is.

Committed a52b4d3e2.


-- 
Michael Eager	 eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306  650-325-8077