[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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