Re: [Buildroot] [PATCH 3/4] core: introduce BR2_KERNEL_ARCH_OVERRIDE

[Romain Naour <romain.naour@smile.fr>]

Hello Thomas,

Le 18/05/2021 à 13:36, Thomas De Schampheleire a écrit :
> From: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
> 
> There are cases where a 64-bit architecture is running a 64-bit kernel but
> 32-bit userspace. Examples include:
>     * aarch64 architecture, with aarch64 kernel and 32-bit (ARM) userspace
>     * x86_64 architecture, with x86_64 kernel and 32-bit (i386) userspace

Can you provide a new qemu defconfig that cover this use case?
This is for gitlab-ci runtime testing.

Best regards,
Romain

PS: (This email doesn't count as a review of this series :))

> 
> In Buildroot, the ARCH/BR2_ARCH and NORMALIZED_ARCH variables will refer to
> the 32-bit architecture, but the kernel needs to be built with the 64-bit
> architecture.
> 
> Make it possible to define the correct architecture to be used for the
> kernel, in a new config option 'BR2_KERNEL_ARCH_OVERRIDE'. The user is
> expected to know the valid values.
> 
> Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
> ---
>  Makefile       |  4 ++++
>  arch/Config.in | 15 +++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index c5399e9a35..d09cf7c958 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -434,7 +434,11 @@ QUIET := $(if $(findstring s,$(filter-out --%,$(MAKEFLAGS))),-q)
>  # Strip off the annoying quoting
>  ARCH := $(call qstrip,$(BR2_ARCH))
>  NORMALIZED_ARCH := $(call qstrip,$(BR2_KERNEL_ARCH))
> +ifeq ($(call qstrip,$(BR2_KERNEL_ARCH_OVERRIDE)),)
>  KERNEL_ARCH := $(call qstrip,$(BR2_KERNEL_ARCH))
> +else
> +KERNEL_ARCH := $(call qstrip,$(BR2_KERNEL_ARCH_OVERRIDE))
> +endif
>  
>  ZCAT := $(call qstrip,$(BR2_ZCAT))
>  BZCAT := $(call qstrip,$(BR2_BZCAT))
> diff --git a/arch/Config.in b/arch/Config.in
> index 7575acf48c..c82100f541 100644
> --- a/arch/Config.in
> +++ b/arch/Config.in
> @@ -329,6 +329,21 @@ config BR2_ARCH
>  config BR2_KERNEL_ARCH
>  	string
>  
> +config BR2_KERNEL_ARCH_OVERRIDE
> +	string "Kernel architecture override"
> +	help
> +	  Normally, the correct kernel architecture value is derived
> +	  from the selected architecture, and you should keep this
> +	  option empty.
> +	  However, there are cases where you may want to enter a custom
> +	  value, for example when using a 64-bit architecture but
> +	  running userspace in 32-bit mode.
> +	  As an example, in case of an x86_64 processor where you want
> +	  32-bit userspace, BR2_ARCH will be 'i386'/'i486'/'i686' and
> +	  BR2_KERNEL_ARCH_OVERRIDE should be set to 'x86_64'. Note that
> +	  in this example you will also need a multilib toolchain and
> +	  pass '-m32' via BR2_TARGET_OPTIMIZATION.
> +
>  config BR2_ENDIAN
>  	string
>  
> 

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