Re: [Buildroot] [RFC] Makefile: do defconfig with /dev/null instead of .defconfig

[Peter Seiderer via buildroot <buildroot@buildroot.org>]

Hello Arnout,

On Sat, 24 Oct 2026 19:08:30 +0200, Arnout Vandecappelle via buildroot <buildroot@buildroot.org> wrote:

> For `make defconfig`, we use a .defconfig file. This is inherited from
> the kernel, which has a different defconfig for each architecture. The
> kernel defconfig passes ARCH on the command line rather than in Kconfig,
> and defaults are very different for different architectures. In
> Buildroot, we don't have that, instead we have a .defconfig file which
> only has the default architecture. And it's not actually a defconfig,
> it's a very old full .config where only the first part is kept.
> 
> Since we have architecture-independent defaults, and any architecture
> specific things are expressed with "depend on" and an occasional
> "default ... if ...", we don't need this infrastructure at all. We can
> simply make .defconfig an empty file - the BR2_arch choice has a default
> and that's all we need. And we don't even need an empty file, we have
> /dev/null to do that job.
> 
> Use /dev/null for the "defconfig" target if no DEFCONFIG is given.
> Remove the now unnecessary .defconfig.
> 
> Note that this also makes one hunk of
> support/kconfig/patches/01-kconfig-kernel-to-buildroot.patch redundant.
> Let's not do the effort of removing it now, we can remove it if it
> causes issues when updating the kconfig infrastructure.
> 
> Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>
> ---
>  .defconfig | 50 --------------------------------------------------
>  Makefile   |  2 +-
>  2 files changed, 1 insertion(+), 51 deletions(-)
>  delete mode 100644 .defconfig
> 
> diff --git a/.defconfig b/.defconfig
> deleted file mode 100644
> index d25c62e104..0000000000
> --- a/.defconfig
> +++ /dev/null
> @@ -1,50 +0,0 @@
> -#
> -# Automatically generated make config: don't edit
> -# Mon Feb 18 09:11:56 2008
> -#
> -BR2_HAVE_DOT_CONFIG=y
> -# BR2_alpha is not set
> -# BR2_arm is not set
> -# BR2_armeb is not set
> -# BR2_cris is not set
> -# BR2_ia64 is not set
> -BR2_i386=y
> -# BR2_m68k is not set
> -# BR2_mips is not set
> -# BR2_mipsel is not set
> -# BR2_powerpc is not set
> -# BR2_sh is not set
> -# BR2_sparc is not set
> -# BR2_sparc64 is not set
> -# BR2_x86_64 is not set
> -# BR2_x86_i486 is not set
> -# BR2_x86_i586 is not set
> -BR2_x86_i686=y
> -# BR2_x86_pentiumpro is not set
> -# BR2_x86_pentium_mmx is not set
> -# BR2_x86_pentium_m is not set
> -# BR2_x86_pentium2 is not set
> -# BR2_x86_pentium3 is not set
> -# BR2_x86_pentium4 is not set
> -# BR2_x86_prescott is not set
> -# BR2_x86_nocona is not set
> -# BR2_x86_core2 is not set
> -# BR2_x86_k6 is not set
> -# BR2_x86_k6_2 is not set
> -# BR2_x86_athlon is not set
> -# BR2_x86_athlon_4 is not set
> -# BR2_x86_opteron is not set
> -# BR2_x86_opteron_sse3 is not set
> -# BR2_x86_barcelona is not set
> -# BR2_x86_geode is not set
> -# BR2_x86_c3 is not set
> -# BR2_x86_winchip_c6 is not set
> -# BR2_x86_winchip2 is not set
> -BR2_ARCH="i686"
> -BR2_ENDIAN="LITTLE"
> -BR2_GCC_TARGET_TUNE="i686"
> -BR2_GCC_TARGET_ARCH="i686"
> -
> -#
> -# Target options
> -#
> diff --git a/Makefile b/Makefile
> index 9b62da3e40..aa3826b5b4 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1037,7 +1037,7 @@ oldconfig syncconfig olddefconfig: $(BUILD_DIR)/buildroot-config/conf outputmake
>  	@$(COMMON_CONFIG_ENV) $< --$@ $(CONFIG_CONFIG_IN)
>  
>  defconfig: $(BUILD_DIR)/buildroot-config/conf outputmakefile
> -	@$(COMMON_CONFIG_ENV) $< --defconfig$(if $(DEFCONFIG),=$(DEFCONFIG)) $(CONFIG_CONFIG_IN)
> +	@$(COMMON_CONFIG_ENV) $< --defconfig=$(or $(DEFCONFIG),/dev/null) $(CONFIG_CONFIG_IN)
>  
>  %_defconfig: $(BUILD_DIR)/buildroot-config/conf  outputmakefile
>  	@defconfig=$(or \

The Makefile part looks very familiar:

	Makefile: always use a base config file for defconfig

	https://lore.kernel.org/buildroot/ZjyqwNLypWWS21v5@landeda/

Regards,
Peter
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