netdev - Re: [PATCH] net/sch_generic.h: use sizeof_member() and get rid of unused variable

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Date:   Wed, 20 May 2020 23:25:38 +0200
From:   Antonio Quartulli <a@...table.cc>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, cake@...ts.bufferbloat.net, toke@...e.dk,
        jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        stephen@...workplumber.org
Subject: Re: [PATCH] net/sch_generic.h: use sizeof_member() and get rid of
 unused variable

On 20/05/2020 20:17, David Miller wrote:
> From: Antonio Quartulli <a@...table.cc>
> Date: Wed, 20 May 2020 10:39:33 +0200
> 
>> I don't think it's BUILD_BUG_ON()'s fault, because qcb->data is passed
>> to sizeof() first.
>>
>> My best guess is that gcc is somewhat optimizing the sizeof(gcb->data)
>> and thus leaving the gcb variable unused.
> 
> If you remove the argument from the function but leave the BUILD_BUG_ON()
> calls the same, the compilation will fail.
> 
> Any such optimization is therefore unreasonable.
> 
> The variable is used otherwise compilation would not fail when you
> remove it right?

You're correct.
I guess this should be reported to gcc then.


Regards,

-- 
Antonio Quartulli