Re: net: rnpgbe: Pass an expression directly in rnpgbe_rm_adapter()

[Markus Elfring]

Am 15.07.26 um 15:12 schrieb Uwe Kleine-König:
> On Mon, Jul 13, 2026 at 10:22:06AM +0200, Markus Elfring wrote:
>>>> The address of a data structure member was determined before
>>>> a corresponding null pointer check in the implementation of
>>>> the function “rnpgbe_rm_adapter”.
>>>>
>>>> Thus avoid the risk for undefined behaviour by omitting the variable “hw”.
>>>> Pass the required address directly to a function call.
>>>>
>>>> This issue was detected by using the Coccinelle software.
>>>>
>>>> Fixes: 2ee95ec17e97c58b65e978a08b75fa8cb6424e4e ("net: rnpgbe: Add register_netdev")
>>>
>>> There is no NULL dereference here.  It's just pointer math.
>>> No need for a Fixes tag.
>>
>> How does your view fit to information in an article like “Fun with
>> NULL pointers, part 1”(by Jonathan Corbet from 2009-07-20)?
>> https://lwn.net/Articles/342330/
> 
> It does fit, because the problematic code discussed in Jonathan Corbet's
> article is of the type:
> 
> 	int i = ptr->i;
> 
> 	if (!ptr)
> 		do_something();
> 
> while here we have:
> 
> 	int *i = &ptr->i;
> 
> 	if (!ptr)
> 		do_something();
> 
> which at least in my test[1] is relevantly different.

Jonathan Corbet provided the following information.

“…
But Herbert's patch added a line which dereferences the pointer prior to the check. That, of course, is a bug.
…”


>                                                       Note, I didn't
> study the C standard

I hope that clarification approaches can evolve further according to this information source.


>                      if the compiler is free to optimize out
> do_something() also in the 2nd case, but at least today gcc doesn't.

Can development interests grow also according to another clarification approach?

Does &((struct name *)NULL -> b) cause undefined behaviour in C11?
https://stackoverflow.com/questions/26906621/does-struct-name-null-b-cause-undefined-behaviour-in-c11



Would you prefer to omit a “sanity check” in the discussed function implementation?

Regards,
Markus