[Buildroot] [PATCH 1/1] arm: -march for Cortex A7, A12 and A15 is armv7ve

Yann E. MORIN yann.morin.1998 at free.fr
Sun Sep 28 09:46:30 UTC 2014


Eddy, All,

On 2014-09-28 04:10 +0300, Eddy Petrisor spake thusly:
> From: Eddy Petrișor <eddy.petrisor at gmail.com>
> 
> For Cortex A7, A12 and A15 setting -march=armv7-a will generate this
> type of warning by default:
> 
> warning: switch -mcpu=cortex-a15 conflicts with -march=armv7-a switch
> 
> This is because these cores have an instruction set which is based on
> the armv7-a set, but adds some extensions on top of them. This new set
> is called 'armv7ve' and is the default for A7, A12 and A15:
> 
> http://gcc.gnu.org/viewcvs?rev=207237&root=gcc&view=rev
> 
> With this patch we make sure we don't force the warning anymore.

We have an on-going discussion about dropping -march altogether, and
only keep the -mcpu option. But the situation is not quite simple.

See the thread starting there:
    http://lists.busybox.net/pipermail/buildroot/2014-September/106214.html

and especially the comments on patch 3 of that series:
    http://lists.busybox.net/pipermail/buildroot/2014-September/106218.html

The status so far is:

  - some combinations of -march, -mcpu, -mtune are not valid, some are
    just a warning;

  - -mcpu is not always enough to fully specify the actual CPU;

  - gcc-5 will no longer accept some combinations of -march, -mcpu, -mtune
    (not sure exactly which will still be valid.)

So, we'd like to go one of those routes (first is the preferred one):

  - drop -march and -mtune, only keep -mcpu;

  - conditionally set either  (-mcpu)  or  (-march and -mtune) .

So, there is a status-quo for now on this issue. I guess we'll be
discussing this at the upcoming Developpers Days in Düsseldorf:
    http://elinux.org/Buildroot:DeveloperDaysELCE2014

Regards,
Yann E. MORIN.

> Signed-off-by: Eddy Petrișor <eddy.petrisor at gmail.com>
> ---
>  arch/Config.in.arm                     | 6 +++---
>  toolchain/toolchain-external/Config.in | 6 +++---
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/Config.in.arm b/arch/Config.in.arm
> index 201ff1d..2988ac0 100644
> --- a/arch/Config.in.arm
> +++ b/arch/Config.in.arm
> @@ -369,11 +369,11 @@ config BR2_GCC_TARGET_ARCH
>  	default "armv6zk"	if BR2_arm1176jz_s
>  	default "armv6zk"	if BR2_arm1176jzf_s
>  	default "armv7-a"	if BR2_cortex_a5
> -	default "armv7-a"	if BR2_cortex_a7
> +	default "armv7ve"	if BR2_cortex_a7
>  	default "armv7-a"	if BR2_cortex_a8
>  	default "armv7-a"	if BR2_cortex_a9
> -	default "armv7-a"	if BR2_cortex_a12
> -	default "armv7-a"	if BR2_cortex_a15
> +	default "armv7ve"	if BR2_cortex_a12
> +	default "armv7ve"	if BR2_cortex_a15
>  	default "armv4"		if BR2_fa526
>  	default "armv7-a"	if BR2_pj4
>  	default "armv4"		if BR2_strongarm
> diff --git a/toolchain/toolchain-external/Config.in b/toolchain/toolchain-external/Config.in
> index 67ad450..a7b965b 100644
> --- a/toolchain/toolchain-external/Config.in
> +++ b/toolchain/toolchain-external/Config.in
> @@ -9,7 +9,7 @@ comment "(e)glibc toolchains only available with shared lib support"
>  config BR2_TOOLCHAIN_EXTERNAL_LINARO_ARM
>  	bool "Linaro ARM 2014.08"
>  	depends on BR2_arm
> -	depends on BR2_GCC_TARGET_ARCH = "armv7-a"
> +	depends on BR2_GCC_TARGET_ARCH = "armv7-a" || BR2_GCC_TARGET_ARCH = "armv7ve"
>  	depends on BR2_HOSTARCH = "x86_64" || BR2_HOSTARCH = "x86"
>  	depends on BR2_ARM_EABIHF
>  	depends on !BR2_PREFER_STATIC_LIB
> @@ -29,13 +29,13 @@ config BR2_TOOLCHAIN_EXTERNAL_LINARO_ARM
>  
>  comment "Linaro toolchains available for Cortex-A + EABIhf"
>  	depends on BR2_arm
> -	depends on BR2_GCC_TARGET_ARCH != "armv7-a" || !BR2_ARM_EABIHF
> +	depends on (BR2_GCC_TARGET_ARCH != "armv7-a" && BR2_GCC_TARGET_ARCH != "armv7ve") || !BR2_ARM_EABIHF
>  	depends on !BR2_PREFER_STATIC_LIB
>  
>  config BR2_TOOLCHAIN_EXTERNAL_LINARO_ARMEB
>  	bool "Linaro armeb 2014.08"
>  	depends on BR2_armeb
> -	depends on BR2_GCC_TARGET_ARCH = "armv7-a"
> +	depends on BR2_GCC_TARGET_ARCH = "armv7-a" || BR2_GCC_TARGET_ARCH = "armv7ve"
>  	depends on BR2_HOSTARCH = "x86_64" || BR2_HOSTARCH = "x86"
>  	depends on BR2_ARM_EABIHF
>  	depends on !BR2_PREFER_STATIC_LIB
> -- 
> 1.9.2.459.g68773ac
> 
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