linux-kernel - Re: [PATCH] x86/platform/uv: make const pointer dots a static const array

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Message-ID: <d642a431-41f9-fef5-0c7f-c4cf133c945e@redhat.com>
Date:   Thu, 2 Dec 2021 10:10:55 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Steve Wahl <steve.wahl@....com>, Joe Perches <joe@...ches.com>
Cc:     Colin Ian King <colin.i.king@...glemail.com>,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>,
        platform-driver-x86@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/platform/uv: make const pointer dots a static const
 array

Hi,

On 12/1/21 22:39, Steve Wahl wrote:
> On Tue, Nov 30, 2021 at 04:26:39PM -0800, Joe Perches wrote:
>> On Tue, 2021-11-30 at 13:34 -0600, Steve Wahl wrote:
>>> On Sat, Nov 27, 2021 at 05:03:20PM +0000, Colin Ian King wrote:
>>>> Don't populate the const array dots on the stack
>> []
>>> Examination of the disassembly shows that the compiler actually
>>> eliminates the creation of the pointer "dots" on the stack and just
>>> passes the address of the string constant to the printk function.
>>>
>>> So this change should not have any actual effect (I don't know where
>>> you got the "shrinks object code" from), and in my humble opinion
>>> makes the code less clear.
>>
>> Probably shrinks an allmodconfig where the symbols are referenced.
>> It probably doesn't do anything to a defconfig.
> 
> OK, I looked. Under allmodconfig, the new code is one byte smaller.
> 
> Defconfig doesn't include CONFIG_X86_UV and this file doesn't get
> compiled.
> 
> Using defconfig plus CONFIG_X86_UV and prerequisites, the new code is
> 24 bytes larger, probably because of alignment added.
> 
> allmodconfig:
> 
>    text	   data	    bss	    dec	    hex	filename
>   30827	  18358	   1472	  50657	   c5e1	uv_nmi.o
>   30828	  18358	   1472	  50658	   c5e2	uv_nmi.orig.o
> 
> default config + CONFIG_X86_UV:
> 
>    text	   data	    bss	    dec	    hex	filename
>    9918	    216	    160	  10294	   2836	uv_nmi.o
>    9894	    216	    160	  10270	   281e	uv_nmi.orig.o
> 
> So I still don't think this patch makes sense.

I agree, so I've dropped this patch from the queue.

Regards,

Hans