linux-kernel - Re: powerpc/Makefile: set -mcpu=860 flag for the 8xx

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Message-Id: <40zxgL3MdHz9s7X@ozlabs.org>
Date:   Tue,  5 Jun 2018 00:11:07 +1000 (AEST)
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: powerpc/Makefile: set -mcpu=860 flag for the 8xx

On Mon, 2018-05-28 at 06:08:34 UTC, Christophe Leroy wrote:
> When compiled with GCC 8.1, vmlinux is significantly bigger than
> with GCC 4.8.
> 
> When looking at the generated code with objdump, we notice that
> all functions and loops when a 16 bytes alignment. This significantly
> increases the size of the kernel. It is pointless and even
> counterproductive as on the 8xx 'nop' also consumes one clock cycle.
> 
> Size of vmlinux with GCC 4.8:
>    text	   data	    bss	    dec	    hex	filename
> 5801948	1626076	 457796	7885820	 7853fc	vmlinux
> 
> Size of vmlinux with GCC 8.1:
>    text	   data	    bss	    dec	    hex	filename
> 6764592	1630652	 456476	8851720	 871108	vmlinux
> 
> Size of vmlinux with GCC 8.1 and this patch:
>    text	   data	    bss	    dec	    hex	filename
> 6331544	1631756	 456476	8419776	 8079c0	vmlinux
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/1c38976334c0efce1b285369a6037f

cheers