On 14/02/17 22:51, Luc Van Oostenryck wrote:
> On Tue, Feb 14, 2017 at 09:36:40PM +0000, Edward Cree wrote:
>> I'm given to understand that bitwise types consider 0 'special', in that
>> sparse will allow, say:
>> typedef __u32 __bitwise __be32;
>> __be32 value = 0;
>> However, it appears that if I try to cast a constant 0 to a bitwise type,
>> static inline void ip6_fill_mask(__be32 *mask)
>> {
>> mask[0] = mask[1] = mask[2] = mask[3] = ~(__be32)0;
>> }
>> sparse complains "warning: cast to restricted __be32".
> I can't reproduce this with the current head.
> Wich version of sparse are you using? Can you retry with sparse's head?
I was using v0.5.0, which appears to be the most recent tag.
With latest HEAD (9208e04972f2) I still reproduce.
*However*, on either version I can only reproduce it 'in situ' in my code, it
turns out that the synthetic example I gave above does _not_ reproduce it.
sparse only gives the warning if the function is _used_; if I comment out the
calls to the function in my 'real' code, the warning goes away. The calls
are passing a __be32[4] as the mask argument.
(The actual code that is hitting this is drivers/net/ethernet/sfc/ethtool.c
in recent Linux trees.)
>From this I was able to create a new synthetic example, which *does*
reproduce the warning:
typedef unsigned int __attribute__((bitwise)) __be32;
static inline void ip6_fill_mask(__be32 *mask)
{
mask[0] = mask[1] = mask[2] = mask[3] = ~(__be32)0;
}
static void f(void)
{
__be32 mask[4];
ip6_fill_mask(mask);
}
Feeding the above program to sparse yields the output
"test.c:5:51: warning: cast to restricted __be32"
In fact the example can be reduced even further:
typedef unsigned int __attribute__((bitwise)) __be32;
static __be32 foo = (__be32)0;
yields "test.c:3:22: warning: cast to restricted __be32"
My apologies for previously providing an incorrect example; I should have
tested it rather than assuming, as I did, that a static inline that was
never called would still be type-checked.
-Ed
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