netdev - Re: [PATCH] rt2x00: make const array glrt

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Message-ID: <ff540218-a260-98ac-b1d1-d4b9f3317a9f@canonical.com>
Date:   Wed, 12 Jul 2017 08:04:40 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Stanislaw Gruszka <sgruszka@...hat.com>
Cc:     Helmut Schaa <helmut.schaa@...glemail.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org, kernel-janitors@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] rt2x00: make const array glrt_table static

On 12/07/17 07:49, Stanislaw Gruszka wrote:
> On Tue, Jul 11, 2017 at 12:47:33PM +0100, Colin King wrote:
>> From: Colin Ian King <colin.king@...onical.com>
>>
>> Don't populate array glrt_table on the stack but make it static.
>> Makes the object code a smaller by over 670 bytes:
>>
>> Before:
>>    text	   data	    bss	    dec	    hex	filename
>>  131772	   4733	      0	 136505	  21539	rt2800lib.o
>>
>> After:
>>    text	   data	    bss	    dec	    hex	filename
>>  131043	   4789	      0	 135832	  21298	rt2800lib.o
>>
>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> 
> Acked-by: Stanislaw Gruszka <sgruszka@...hat.com>
> 
> I wonder why compiler do not optimize by itself since array is
> const, but patch is ok.

Afraid marking it as const does not guarantee that at all. The const
qualifier just announces that the value will not be changed [1]. So one
requires static const to ensure it's not populated on the stack and also
marked as non-modifiable.

[1] Section A4.4, The C programming Language, page 196

Colin

> 
> Stanislaw 
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