Re: [PATCH 1/1] add support to set KBUILD_BUILD_TIMESTAMP for custom kernels

[Jan Kiszka <jan.kiszka@siemens.com>]

On 21.03.22 15:40, Felix Moessbauer wrote:
> This patch adds the infrastructure to overwrite the
> KBUILD_BUILD_TIMESTAMP environment variable for custom kernel
> builds. By that, we improve the support for reproducible
> kernel builds.
> 

Agreed.

> Setting this to a fixed string further helps to profit from
> ccache caching on repeated builds.

Hmm, but the practical impact of this variable should have been limited
/wrt ccache. I was seeing significant build-time reduction before the
commit already.

> 
> Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
> ---
>  meta/recipes-kernel/linux/files/debian/isar/build.tmpl  | 1 +
>  meta/recipes-kernel/linux/files/debian/isar/common.tmpl | 2 ++
>  meta/recipes-kernel/linux/linux-custom.inc              | 3 +++
>  3 files changed, 6 insertions(+)
> 
> diff --git a/meta/recipes-kernel/linux/files/debian/isar/build.tmpl b/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
> index b7749cec..32d2eb23 100644
> --- a/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
> +++ b/meta/recipes-kernel/linux/files/debian/isar/build.tmpl
> @@ -34,6 +34,7 @@ print_settings() {
>  # ---------------
>  # ARCH=${ARCH}
>  # CROSS_COMPILE=${CROSS_COMPILE}
> +# KBUILD_BUILD_TIMESTAMP=${KBUILD_BUILD_TIMESTAMP}
>  EOF
>  }
>  
> diff --git a/meta/recipes-kernel/linux/files/debian/isar/common.tmpl b/meta/recipes-kernel/linux/files/debian/isar/common.tmpl
> index b7752fb6..ffe84745 100644
> --- a/meta/recipes-kernel/linux/files/debian/isar/common.tmpl
> +++ b/meta/recipes-kernel/linux/files/debian/isar/common.tmpl
> @@ -7,6 +7,7 @@ ARCH=${KERNEL_ARCH}
>  KERNEL_PKG_IMAGE=linux-image-${KERNEL_NAME_PROVIDED}
>  KERNEL_PKG_KERN_HEADERS=linux-headers-${KERNEL_NAME_PROVIDED}
>  KERNEL_PKG_LIBC_HEADERS=linux-libc-dev
> +KBUILD_BUILD_TIMESTAMP="${KBUILD_BUILD_TIMESTAMP}"
>  
>  # Constants
>  KCONF=.config
> @@ -36,6 +37,7 @@ main() {
>  
>      # variables to be exported
>      export ARCH
> +    export KBUILD_BUILD_TIMESTAMP
>  
>      # are we cross-compiling?
>      BUILD_ARCH=$(dpkg-architecture -qDEB_BUILD_ARCH)
> diff --git a/meta/recipes-kernel/linux/linux-custom.inc b/meta/recipes-kernel/linux/linux-custom.inc
> index 8a5dbf82..f8e87453 100644
> --- a/meta/recipes-kernel/linux/linux-custom.inc
> +++ b/meta/recipes-kernel/linux/linux-custom.inc
> @@ -33,6 +33,8 @@ KERNEL_HEADERS_DEBIAN_DEPENDS ?= "libc6, \
>  
>  KERNEL_LIBC_DEV_DEPLOY ?= "0"
>  
> +KBUILD_BUILD_TIMESTAMP ??= "LANG=C $(date)"

Can't we use SOURCE_DATE_EPOCH like the rest?

> +
>  # Settings that may be changed on a per distro, machine or layer basis
>  # --------------------------------------------------------------------
>  
> @@ -73,6 +75,7 @@ TEMPLATE_VARS += "                \
>      LINUX_VERSION_EXTENSION       \
>      KERNEL_NAME_PROVIDED          \
>      KERNEL_CONFIG_FRAGMENTS       \
> +    KBUILD_BUILD_TIMESTAMP        \
>  "
>  
>  inherit dpkg

Jan

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