Re: [PATCH 7/16] Let void have sizeof 1

["Alexey Zaytsev" <alexey.zaytsev@gmail.com>]

On Thu, Dec 25, 2008 at 02:10, Christopher Li <sparse@chrisli.org> wrote:
> On Wed, Dec 24, 2008 at 1:59 PM, David Given <dg@cowlark.com> wrote:
>> The thing is, sizeof(void) is *not* 1. sizeof(void) is *illegal*. It
>> just happens that gcc, as a platform-specific extension, treats
>> sizeof(void) as 1 by default.
>
> Exactly. I am unhappy about that patch as well.
> Sparse internally use symbol->bit_size == 0 to determine uncompleted type.
> Thanks this change. Now is_byte_type() will return true for void type as well.

I can only agree here. I made my patch that way only because of my poor
understanding of the sparse internals (which I stated in my first email).

>> As a linter, sparse really ought not to be encouraging non-portable
>> behaviour. Admittedly, there's so much stuff in the kernel source that's
>> gcc-specific that it's probably not going to be possible to make it
>> build on anything else, but it should still warn people about it unless
>> specifically told otherwise --- it's bad practice, and may be indicative
>> of further problems elsewhere, and as such is worth a diagnostic.
>
> I don't see the kernel directly use sizeof(void). Most of the place is
> using (void*) pointer + offset. It is not portable. But it is probably not
> worthy while to fix. Convert the void* to char*, add offset, convert it back
> to void* is pretty annoying as well. If we really want to make it clean, maybe
> we can use a macro or inline functions. Again, probably not worth the effort.
>
> But legitimize sizeof(void) == 1 is a different story. That I feel is just
> plain wrong.

Of course explicit sizeof(void) itself is just plain wrong, but also
it's something
that nobody would ever use. So, if you warn here, I of course have no
objections.