Re: [PATCH v2] gdb/i387-tdep.c: Avoid warning for "-Werror=strict-overflow"

[Chen Gang <gang dot chen dot 5i5j at gmail dot com>]

On 10/12/14 22:13, Iain Buclaw wrote:
> On 12 October 2014 14:28, Chen Gang <gang.chen.5i5j@gmail.com> wrote:
>> gdb requires "-Werror", and I387_ST0_REGNUM (tdep) is 'variable', then
>> compiler can think that I387_ST0_REGNUM (tdep) may be a large number,
>> which may cause issue, so report warning.
>>
>> Need fix this warning, and still keep the code clear enough for readers.
>> The related warning under Darwin with gnu built gcc:
>>
> 
> I had noted the same on GCC 5.0.0 development, found that the line
> number in the warning was wrong and raised a bug
> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63510), just didn't get
> round to submitting a patch for gdb.
> 

But for me, what compiler has done is correct: "-Werror=strict-overflow"
need include "(X + c) >= X" for signed overflow. And our case matches
this case:

  int st0_regnum;
  
  void i387_supply_fsave ()
  {
    int i;
    for (i = st0_regnum; i < st0_regnum + 16;)
      {
      }
  }

> 
>>
>> 2014-10-13  Chen Gang  <gang.chen.5i5j@gmail.com>
>>
>>         * i387-tdep.c (i387_supply_fsave): Avoid warning for
>>         "-Werror=strict-overflow"
>> ---
>>  gdb/i387-tdep.c | 10 ++++++----
>>  1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/gdb/i387-tdep.c b/gdb/i387-tdep.c
>> index d66ac6a..609b5be 100644
>> --- a/gdb/i387-tdep.c
>> +++ b/gdb/i387-tdep.c
>> @@ -450,11 +450,12 @@ i387_supply_fsave (struct regcache *regcache, int regnum, const void *fsave)
>>    struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
>>    enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
>>    const gdb_byte *regs = fsave;
>> -  int i;
>> +  int i, end;
>>
> 
> Also changing from int -> unsigned int fixes the warning.
> 
> -- Iain.
> 

-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed