Re: [PATCH] x86/config: Make the x86 defconfigs a bit more usable

Ingo Molnar
2022-09-04T09:48:13Z

* Masahiro Yamada <masahiroy@kernel.org> wrote:

> > Unfortunately, even without the ARCH=i386 'make savedefconfig' doesn't
> > seem to be doing the right thing & is dropping the '# CONFIG_64BIT is
> > not set' line:
>
>
> Oh, really?
>
> Without ARCH=i386, it works correctly for me.
>
>
>
> masahiro@zoe:~/ref/linux$ make i386_defconfig savedefconfig
> #
> # No change to .config
> #
> masahiro@zoe:~/ref/linux$ grep CONFIG_64BIT defconfig
> # CONFIG_64BIT is not set

Yeah, so why do these two seemingly identical commands produce two
different .config's:

$ make ARCH=i386 defconfig
*** Default configuration is based on 'i386_defconfig'

$ make i386_defconfig

?

Basically the canonical way to generate a defconfig is to provide an ARCH,
then use the common 'defconfig' target:

make ARCH=i386 defconfig
make ARCH=x86 defconfig
make ARCH=arm defconfig
make ARCH=arm64 defconfig
make ARCH=powerpc defconfig
make ARCH=s390 defconfig
make ARCH=sparc defconfig
make ARCH=sparc64 defconfig
...

This is what my build test scripts are using to quick-test cross-arch
builds. It's a straightforward way to generate defconfigs without knowing
the details of the myriads of random defconfig targets some architectures
have, such as:

kepler:~/tip> ls arch/arm/configs/
am200epdkit_defconfig gemini_defconfig multi_v5_defconfig s5pv210_defconfig
aspeed_g4_defconfig h3600_defconfig multi_v7_defconfig sama5_defconfig
aspeed_g5_defconfig h5000_defconfig mv78xx0_defconfig sama7_defconfig
assabet_defconfig hackkit_defconfig mvebu_v5_defconfig shannon_defconfig
at91_dt_defconfig hisi_defconfig mvebu_v7_defconfig shmobile_defconfig
axm55xx_defconfig imxrt_defconfig mxs_defconfig simpad_defconfig
badge4_defconfig imx_v4_v5_defconfig neponset_defconfig socfpga_defconfig
bcm2835_defconfig imx_v6_v7_defconfig netwinder_defconfig sp7021_defconfig
cerfcube_defconfig integrator_defconfig nhk8815_defconfig spear13xx_defconfig
clps711x_defconfig iop32x_defconfig omap1_defconfig spear3xx_defconfig
cm_x300_defconfig ixp4xx_defconfig omap2plus_defconfig spear6xx_defconfig
cns3420vb_defconfig jornada720_defconfig orion5x_defconfig spitz_defconfig
colibri_pxa270_defconfig keystone_defconfig oxnas_v6_defconfig stm32_defconfig
colibri_pxa300_defconfig lart_defconfig palmz72_defconfig sunxi_defconfig
collie_defconfig lpc18xx_defconfig pcm027_defconfig tct_hammer_defconfig
corgi_defconfig lpc32xx_defconfig pleb_defconfig tegra_defconfig
davinci_all_defconfig lpd270_defconfig pxa168_defconfig trizeps4_defconfig
dove_defconfig lubbock_defconfig pxa255-idp_defconfig u8500_defconfig
dram_0x00000000.config magician_defconfig pxa3xx_defconfig versatile_defconfig
dram_0xc0000000.config mainstone_defconfig pxa910_defconfig vexpress_defconfig
dram_0xd0000000.config milbeaut_m10v_defconfig pxa_defconfig vf610m4_defconfig
ep93xx_defconfig mini2440_defconfig qcom_defconfig viper_defconfig
eseries_pxa_defconfig mmp2_defconfig realview_defconfig vt8500_v6_v7_defconfig
exynos_defconfig moxart_defconfig rpc_defconfig xcep_defconfig
ezx_defconfig mps2_defconfig s3c2410_defconfig zeus_defconfig
footbridge_defconfig multi_v4t_defconfig s3c6400_defconfig

But this doesn't seem to be working reliably on i386:

kepler:~/tip> make i386_defconfig
#
# configuration written to .config
#
kepler:~/tip> /bin/cp .config .config.i386_defconfig.1

kepler:~/tip> make ARCH=i386 defconfig
*** Default configuration is based on 'i386_defconfig'
#
# configuration written to .config
#
kepler:~/tip> /bin/cp .config .config.i386_defconfig.2

kepler:~/tip> diff -up .config.i386_defconfig.1 .config.i386_defconfig.2
--- .config.i386_defconfig.1 2022-09-04 11:34:48.253202205 +0200
+++ .config.i386_defconfig.2 2022-09-04 11:35:04.268758331 +0200
@@ -1,6 +1,6 @@
#
# Automatically generated file; DO NOT EDIT.
-# Linux/x86 6.0.0-rc3 Kernel Configuration
+# Linux/i386 6.0.0-rc3 Kernel Configuration
#
CONFIG_CC_VERSION_TEXT="gcc (Ubuntu 12-20220319-1ubuntu1) 12.0.1 20220319 (experimental) [master r12-7719-g8ca61ad148f]"
CONFIG_CC_IS_GCC=y
@@ -261,7 +261,6 @@ CONFIG_PROFILING=y
CONFIG_TRACEPOINTS=y
# end of General setup

-# CONFIG_64BIT is not set
CONFIG_X86_32=y
CONFIG_X86=y
CONFIG_INSTRUCTION_DECODER=y

Note how in the ARCH=i386 case the build system claims to use i386_defconfig:

*** Default configuration is based on 'i386_defconfig'

But that doesn't seem to be identical with when we specify i386_defconfig
directly as a target...

What am I missing?

Thanks,

Ingo