Re: [PATCH 4/5] sparse, i386: Fix boolean bit size

[Pekka Enberg <penberg@kernel.org>]

On Fri, Aug 26, 2011 at 6:59 AM, Christopher Li <sparse@chrisli.org> wrote:
> On Mon, Aug 22, 2011 at 6:57 AM, Pekka Enberg <penberg@kernel.org> wrote:
>> The value of 'ctype->bit_size' is set to 1 for booleans which confuses the i386
>> backend:
>>
>>  ./compile allocate.c
>>  compile: compile-i386.c:1406: emit_binop: Assertion `0' failed.
>>  Aborted
>>
>> Looking at the code, we assume that "bit_size / 8" gives a sane result on
>> various places. This patch fixes the problem by bumping bit_size to 8 for
>> booleans. This also makes sizeof(_Bool) return 1 which is consistent with what
>> GCC 4.4.3, for example, does.
>>
>> diff --git a/target.c b/target.c
>> index 17b228a..6a535bc 100644
>> --- a/target.c
>> +++ b/target.c
>> @@ -14,7 +14,7 @@ int max_alignment = 16;
>>  /*
>>  * Integer data types
>>  */
>> -int bits_in_bool = 1;
>> +int bits_in_bool = 8;
>
> I object this part. I consider the sizeof(_Bool) == 1 as external behaviour.
> But internally we should know that the real useful part of bool is in just one
> bit, not any bit of that  1 byte storage.

You missed the most important part of my reasoning: sparse code
already expects "bit_size / 8" to return a non-zero number and it's
not just compile-i386.c! So while I don't disagree with you that we
should internally know that a bool is just one bit, I don't consider
that to be relevant for this particular patch.

                        Pekka
--
To unsubscribe from this list: send the line "unsubscribe linux-sparse" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html