linux-kernel - Re: [PATCH 3/5] gcov: disable for COMPILE

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Message-ID: <56C1DF57.50601@linux.vnet.ibm.com>
Date:	Mon, 15 Feb 2016 15:23:19 +0100
From:	Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
To:	Arnd Bergmann <arnd@...db.de>, Michal Marek <mmarek@...e.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] gcov: disable for COMPILE_TEST

On 12.02.2016 17:06, Arnd Bergmann wrote:
> Enabling gcov is counterproductive to compile testing: it significantly
> increases the kernel image size, compile time, and it produces lots
> of false positive "may be used uninitialized" warnings as the result
> of missed optimizations.
> 
> This is in line with how UBSAN_SANITIZE_ALL and PROFILE_ALL_BRANCHES
> work, both of which have similar problems.
> 
> With an ARM allmodconfig kernel, I see the build time drop from
> 283 minutes CPU time to 225 minutes, and the vmlinux size drops
> from 43MB to 26MB.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Agreed that COMPILE_TEST + GCOV_PROFILE_ALL is a very exotic combination
with little added use.

Acked-by: Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>

> ---
>  kernel/gcov/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig
> index c92e44855ddd..1276aabaab55 100644
> --- a/kernel/gcov/Kconfig
> +++ b/kernel/gcov/Kconfig
> @@ -37,6 +37,7 @@ config ARCH_HAS_GCOV_PROFILE_ALL
> 
>  config GCOV_PROFILE_ALL
>  	bool "Profile entire Kernel"
> +	depends on !COMPILE_TEST
>  	depends on GCOV_KERNEL
>  	depends on ARCH_HAS_GCOV_PROFILE_ALL
>  	default n
> 


-- 
Peter Oberparleiter
Linux on z Systems Development - IBM Germany