On 12 November 2014 16:22, Christopher Li <[email protected]> wrote:
> On Wed, Nov 12, 2014 at 9:35 PM, Matt Fleming <[email protected]> wrote:
>> (Pulling sparse list in)
>>
>> On Wed, 2014-11-12 at 11:31 +0100, Ard Biesheuvel wrote:
>>> > tree: git://git.kernel.org/pub/scm/linux/kernel/git/mfleming/efi.git
>>> > next
>>> >>> arch/x86/boot/compressed/eboot.c:26:16: sparse: incorrect type in
>>> >>> return expression (different modifiers)
>>> > arch/x86/boot/compressed/eboot.c:26:16: expected struct efi_config
>>> > const [pure] *
>>> > arch/x86/boot/compressed/eboot.c:26:16: got struct efi_config
>>> > *static [toplevel] efi_early
>>> >
>>>
>>> This smells like a sparse bug: __pure applies to functions only, so
>>> there is no way we could ever return something with the __pure
>>> modifier attached.
>
> That make sense.
>
>>
>> Yes, that warning does look a little strange.
>>
>> Christopher, Fengguang, what do you guys think?
>>
>
> Do you get me a small test function that reproduce the error with sparse?
>
> We can even add a test case for it.
>
Well, I spent some time playing around with this:
This one is accepted:
static __attribute__((__pure__)) int pure1(void)
{
int i = 0;
return i;
}
This one is not accepted:
static __attribute__((__pure__)) void *pure2(void)
{
void *i = (void *)0;
return i;
}
and produces
pure.c:11:16: warning: incorrect type in return expression (different modifiers)
pure.c:11:16: expected void [pure] *
pure.c:11:16: got void *i
I also noticed that the following triggers a warning as well:
static void*(*f)(void) = pure2;
(using the definition of pure2 as above)
pure.c:14:26: warning: incorrect type in initializer (different modifiers)
pure.c:14:26: expected void *( *static [toplevel] f )( ... )
pure.c:14:26: got void [pure] *( static [toplevel] *<noident> )( ... )
i.e., you are not allowed to assign a pointer to a pure function to a
non-pure function pointer, which is quite ok. The opposite should be
an error, though.
This patch
diff --git a/evaluate.c b/evaluate.c
index a5a830978bda..2e9ad8b7b31d 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -1375,7 +1375,7 @@ static int compatible_assignment_types(struct
expression *expr, struct symbol *t
goto Cast;
}
/* It's OK if the target is more volatile or const
than the source */
- typediff = type_difference(&t->ctype, &s->ctype, 0, mod1);
+ typediff = type_difference(&t->ctype, &s->ctype, 0,
mod1 | MOD_PURE);
if (typediff)
goto Err;
return 1;
fixes the first issue, but I am not sure if it is an appropriate fix or not.
--
Ard.
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