Re: [PATCH] x86/mm/mem_encrypt_identity : fix error useage to sizeof

[Juergen Gross <jgross@suse.com>]

On 15/01/2019 11:13, Thomas Gleixner wrote:
> On Mon, 7 Jan 2019, peng.hao2@zte.com.cn wrote:
> 
>>>> Fix error usage to sizeof. It should not use sizeof to pointer.
>>>
>>> .... because?
>>>
>>> The commit message needs to explain what the potential issue could be
>>> and why it doesn't matter in this case.
>> I see the definition of pte_t may be more than sizeof(unsigned long).
>> So I think sizeof(pte_t) is safer.
> 
> What exactly is the difference between:
> 
> 	pte_t	*p;
> 
> 	sizeof(*p)
> 
> and
> 
> 	sizeof(pte_t)
> 
> and what is safer about the latter?

Please note that the current code is using sizeof(p) instead of sizeof(*p).

And this is really different for X86_32 PAE.


Juergen

> 
> Answer: No difference and nothing is safer because it's exactly the same.
> 
> In general we use sizeof(*p) simply because when the data type of p changes
> you don't have to update the code, it just works and stays correct.
> 
> Thanks,
> 
> 	tglx
>