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

[Michael Eager <eager@eagercon.com>]

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.

>> I do not see this error message in my build which uses -Wall.
>> What is your build environment?  Which version of GCC?
>>
>
> Originally, I use "CFLAGS=-W -g -O2" pass to configure. And '-W' is
> different from '-Wall'.  '-W' reports real 'all' warnings which can be
> found by compiler, but '-Wall' reports most valuable warnings.

OK


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