Re: [PATCH] fix expansion of constant bitfield dereference

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

On Mon, Aug 21, 2017 at 2:26 PM, Christopher Li <sparse@chrisli.org> wrote:
> On Sun, Aug 20, 2017 at 6:16 PM, Luc Van Oostenryck wrote:
>
> With this applied, sparse still have a bug at did not match the
> value to the bit field member, right? I saw on the other email
> thread said the value always pick offset zero.

I'm not sure to understand.
Have you an example?

> Should I apply this as patch format or wait for it show up in a
> git pull request later?

Wait for the pull request, please.

>> --- a/expand.c
>> +++ b/expand.c
>> @@ -644,6 +644,8 @@ static int expand_dereference(struct expression *expr)
>>                 if (value) {
>>                         /* FIXME! We should check that the size is right! */
>>                         if (value->type == EXPR_VALUE) {
>> +                               if (is_bitfield_type(value->ctype))
>> +                                       return UNSAFE;
>
> You might want to consider move this outside of the EXPR_VALUE.
> I assume there is a bug in sparse matching the value to the member
> wrong, it could happen to EXPR_FVALUE as well.

Well ..., if we have an EXPR_FVALUE which type is a bitfield, yes
for sure there would be a bug. But I have no reason to belive there
is such bug and since checking the ctype is more costly than checking
the expr->type, I think it's best so.

Note, I find this check already annoying and hackish if not worse.

-- Luc