On Tue, Jul 04, 2023 at 05:07:17PM +0300, Dan Carpenter wrote:
> On Tue, Jul 04, 2023 at 04:38:41PM +0300, Leon Romanovsky wrote:
> > On Thu, Jun 29, 2023 at 09:07:37AM +0300, Dan Carpenter wrote:
> > > This code is trying to ensure that only the flags specified in the list
> > > are allowed. The problem is that ucmd->rx_hash_fields_mask is a u64 and
> > > the flags are an enum which is treated as a u32 in this context. That
> > > means the test doesn't check whether the highest 32 bits are zero.
> > >
> > > Fixes: 4d02ebd9bbbd ("IB/mlx4: Fix RSS hash fields restrictions")
> > > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > > ---
> > > The MLX4_IB_RX_HASH_INNER value is declared as
> > > "MLX4_IB_RX_HASH_INNER = 1ULL << 31," which suggests that it
> > > should be type ULL but that doesn't work. It will still be basically a
> > > u32. (Enum types are weird).
> >
> > Can you please elaborate more why enum left to be int? It is surprise to me.
>
> Enum types are not defined very strictly in C so it's up to the
> compiler.
>
> Clang, GCC and Sparse implement them in the same way. They default
> to u32 unless the values can't fit, then they become whatever type fits.
> So if you have a negative, it becomes an int or a big value changes the
> type to unsigned long.
>
> Since 1ULL < 31 fits in u32 the type is just u32.
Thanks for an explanation, I found the relevant sentence in the C
standard as well.
"The choice of type is implementation-defined, 128) but shall be
capable of representing the values of all the members of the enumeration."
Thanks
>
> regards,
> dan carpenter
>
> #include <stdio.h>
>
> enum example_one {
> VAL = 1ULL << 31,
> };
>
> enum example_two {
> NEGATIVE = -2,
> };
>
> enum example_three {
> BIG = 1ULL << 32,
> };
>
> int main(void)
> {
> enum example_one one = -1;
> enum example_two two = -1;
> enum example_three three = -1;
>
> printf("%lu\n", sizeof(enum example_one));
>
> if (one > 0)
> printf("one unsigned\n");
> if (two < 0)
> printf("two signed\n");
>
> printf("%lu\n", sizeof(enum example_three));
> if (three > 0)
> printf("three unsigned\n");
>
> return 0;
> }
>
>
