sparse problem with duplicate __iomem?

sparse problem with duplicate __iomem?

[Randy Dunlap]

Hi,

On kernel 5.9-rc1, either i386 or x86_64 builds, I am seeing these
sparse warnings:

../drivers/gpu/drm/ast/ast_cursor.c:256:26: CK: warning: duplicate [noderef]
../drivers/gpu/drm/ast/ast_cursor.c:256:26: CK: error: multiple address space given: __iomem & __iomem

for this source line:

	u8 __iomem *dst, __iomem *sig;


Should one of those __iomem-s be removed?
I.e., does "__iomem" apply to everything after it, up to the ending ';',
or just up to the next comma ','? 


thanks.
-- 
~Randy

Re: sparse problem with duplicate __iomem?

[Luc Van Oostenryck]

On Tue, Aug 18, 2020 at 11:09:52AM -0700, Randy Dunlap wrote:
> Hi,
> 
> On kernel 5.9-rc1, either i386 or x86_64 builds, I am seeing these
> sparse warnings:
> 
> ../drivers/gpu/drm/ast/ast_cursor.c:256:26: CK: warning: duplicate [noderef]
> ../drivers/gpu/drm/ast/ast_cursor.c:256:26: CK: error: multiple address space given: __iomem & __iomem
> 
> for this source line:
> 
> 	u8 __iomem *dst, __iomem *sig;
> 
> 
> Should one of those __iomem-s be removed?

I think so. It's a bit like writing
	int const *a, const *b;
or
	int unsigned *a, unsigned *b;

> I.e., does "__iomem" apply to everything after it, up to the ending ';',
> or just up to the next comma ','? 

The (simplified) syntax for declarations is:
	declaration:
		declaration-specifiers [init-declarator-list] ;
	init-declarator-list:
		init-declarator
		init-declarator-list , init-declarator
	init-declarator
		declarator
		declarator = initializer
	declarator:
		[pointer] direct-declarator
	pointer:
		* [type-qualifier-list]
		* [type-qualifier-list] pointer
	direct-declarator:
		identifier
		...

Essentially, attributes are type modifiers, some acting like
qualifiers and others are more like specifiers. But qualifiers
and specifiers are never allowed directly after the comma because
they appertain to the declaration-specifier part of the declaration.
So, yes, the first __iomem applies to the whole declaration and
the second one should be removed.

But maybe it's not 100% clear and the best should be to use a
separate declaration for each variable?

Best regards,
-- Luc

Re: sparse problem with duplicate __iomem?

[Randy Dunlap]

On 8/18/20 12:23 PM, Luc Van Oostenryck wrote:
> On Tue, Aug 18, 2020 at 11:09:52AM -0700, Randy Dunlap wrote:
>> Hi,
>>
>> On kernel 5.9-rc1, either i386 or x86_64 builds, I am seeing these
>> sparse warnings:
>>
>> ../drivers/gpu/drm/ast/ast_cursor.c:256:26: CK: warning: duplicate [noderef]
>> ../drivers/gpu/drm/ast/ast_cursor.c:256:26: CK: error: multiple address space given: __iomem & __iomem
>>
>> for this source line:
>>
>> 	u8 __iomem *dst, __iomem *sig;
>>
>>
>> Should one of those __iomem-s be removed?
> 
> I think so. It's a bit like writing
> 	int const *a, const *b;
> or
> 	int unsigned *a, unsigned *b;
> 
>> I.e., does "__iomem" apply to everything after it, up to the ending ';',
>> or just up to the next comma ','? 
> 
> The (simplified) syntax for declarations is:
> 	declaration:
> 		declaration-specifiers [init-declarator-list] ;
> 	init-declarator-list:
> 		init-declarator
> 		init-declarator-list , init-declarator
> 	init-declarator
> 		declarator
> 		declarator = initializer
> 	declarator:
> 		[pointer] direct-declarator
> 	pointer:
> 		* [type-qualifier-list]
> 		* [type-qualifier-list] pointer
> 	direct-declarator:
> 		identifier
> 		...
> 
> Essentially, attributes are type modifiers, some acting like
> qualifiers and others are more like specifiers. But qualifiers
> and specifiers are never allowed directly after the comma because
> they appertain to the declaration-specifier part of the declaration.
> So, yes, the first __iomem applies to the whole declaration and
> the second one should be removed.
> 
> But maybe it's not 100% clear and the best should be to use a
> separate declaration for each variable?

Yes, that was my patch plan. :)

Thanks for the explanation.

-- 
~Randy