Re: kernel/workqueue.c:4435:61: sparse: expression using sizeof bool

[Fengguang Wu]

On Fri, Jun 07, 2013 at 03:03:51PM -0700, Tejun Heo wrote:
> On Fri, Jun 07, 2013 at 02:15:21PM -0700, Andrew Morton wrote:
> > > 4434 /* copy worker description */
> > > > 4435 probe_kernel_read(&desc_valid, &worker->desc_valid, sizeof(desc_valid));
> >
> > I don't understand the rationale for the sparse test, really. This
> > code seems unproblematic.
>
> Yeah, I've gotten that warning a couple times now and am just ignoring
> it at this point. Maybe the standard says bool isn't a proper
> integeral type and its size isn't precisely defined or something? I
> don't know.

Hmm, I'd better disable the warnings that are normally ignored anyway..

Thanks,
Fengguang
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[Fengguang Wu]

// CC sparse people.

On Fri, Jun 07, 2013 at 07:05:49PM -0700, Tejun Heo wrote:
> Hello, Andrew.
>
> On Fri, Jun 07, 2013 at 06:46:14PM -0700, Andrew Morton wrote:
> > I believe sizeof(bool) can vary between compilers (on gcc it's 1) but
> > that doesn't matter here.
>
> Looking at the warning, I originally suspected that maybe the standard
> was crazy enough to allow mixed usages of different sizes for bool as
> the compiler sees fit. Just scanned the spec, nothing that insane.
> It's a proper integeral type, so I'm now more puzzled why sparse is
> warning about sizeof(bool).
>
> > sizeof(enum) can vary between compilers as well. In fact I've seen a
> > compiler which used 2 if the enumerated values were 0..65535, and 4
> > otherwise. So warning about sizeof(enum) would be a bit more useful
> > than about sizeof(bool).
>
> Oh yeah, gcc does that too. If the enum definition contains a number
> larger than 32bit, it'll grow it to 64bit.
>
> #include <stdio.h>
>
> enum { ENUM_A = 1LU };
> enum { ENUM_B = 1LU << 31 };
> enum { ENUM_C = 1LU << 32 };
>
> int main(void)
> {
> printf("%zu %zu %zu\n", sizeof(ENUM_A), sizeof(ENUM_B), sizeof(ENUM_C));
> return 0;
> }
>
> $ ./a.out
> 4 4 8
>
> Whether sparse should trigger a warning on it, I don't know.
>
> Thanks.
>
> --
> tejun