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

[Michael Eager <eager at eagerm dot 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
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