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Duncan Mac Leod
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Joined: 02 May 2004
Posts: 251
Location: Germany

PostPosted: Wed May 31, 2017 12:34 pm    Post subject: Question about /usr/src/linux/.config Reply with quote

Can I use (copy) my .config file (/usr/src/linux/.config) from my 64bit kernel to another box running a 32bit kernel without modification?

I don't want to go through every part in menuconfig again.

To be more specific - is anything stored in .config which is x64 / x86 specific ? Ok - I should select the specific CPU config, but are all other things the same?
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depontius
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Joined: 05 May 2004
Posts: 3384

PostPosted: Wed May 31, 2017 12:59 pm    Post subject: Re: Question about /usr/src/linux/.config Reply with quote

Duncan Mac Leod wrote:
Can I use (copy) my .config file (/usr/src/linux/.config) from my 64bit kernel to another box running a 32bit kernel without modification?

I don't want to go through every part in menuconfig again.

To be more specific - is anything stored in .config which is x64 / x86 specific ? Ok - I should select the specific CPU config, but are all other things the same?


Can't do, at least not as simply as you say:
Quote:
$ grep 64 .config
CONFIG_64BIT=y
CONFIG_X86_64=y
CONFIG_OUTPUT_FORMAT="elf64-x86-64"
CONFIG_ARCH_DEFCONFIG="arch/x86/configs/x86_64_defconfig"
CONFIG_X86_64_SMP=y
# CONFIG_HAVE_64BIT_ALIGNED_ACCESS is not set
CONFIG_X86_CMPXCHG64=y
CONFIG_X86_MINIMUM_CPU_FAMILY=64
CONFIG_X86_ESPFIX64=y
CONFIG_ARCH_PHYS_ADDR_T_64BIT=y
CONFIG_ARCH_DMA_ADDR_T_64BIT=y
CONFIG_PHYS_ADDR_T_64BIT=y
CONFIG_X86_RESERVE_LOW=64
CONFIG_PCI_BUS_ADDR_T_64BIT=y
CONFIG_COMPAT_FOR_U64_ALIGNMENT=y
CONFIG_IP6_NF_MATCH_EUI64=m
# CONFIG_PATA_CMD64X is not set
# CONFIG_PATA_CMD640_PCI is not set
# CONFIG_KEYBOARD_TCA6416 is not set
# CONFIG_R3964 is not set
# CONFIG_SENSORS_MAX6642 is not set
# CONFIG_SENSORS_MAX16064 is not set
# CONFIG_USB_ZR364XX is not set
CONFIG_AGP_AMD64=y
# CONFIG_DRM_I2C_SIL164 is not set
# CONFIG_SND_LX6464ES is not set
CONFIG_SND_HDA_PREALLOC_SIZE=64
# CONFIG_SND_SOC_INTEL_BYTCR_RT5640_MACH is not set
# CONFIG_SND_SOC_AK4642 is not set
# CONFIG_LEDS_LM3642 is not set
# CONFIG_INTEL_IDMA64 is not set
# CONFIG_NLS_CODEPAGE_864 is not set
# CONFIG_ATOMIC64_SELFTEST is not set
# CONFIG_CRYPTO_POLY1305_X86_64 is not set
CONFIG_CRYPTO_AES_X86_64=m
CONFIG_CRYPTO_BLOWFISH_X86_64=m
CONFIG_CRYPTO_CAMELLIA_X86_64=m
CONFIG_CRYPTO_CAMELLIA_AESNI_AVX_X86_64=m
CONFIG_CRYPTO_CAMELLIA_AESNI_AVX2_X86_64=m
CONFIG_CRYPTO_CAST5_AVX_X86_64=m
CONFIG_CRYPTO_CAST6_AVX_X86_64=m
# CONFIG_CRYPTO_DES3_EDE_X86_64 is not set
# CONFIG_CRYPTO_SALSA20_X86_64 is not set
# CONFIG_CRYPTO_CHACHA20_X86_64 is not set
CONFIG_CRYPTO_SERPENT_SSE2_X86_64=m
CONFIG_CRYPTO_SERPENT_AVX_X86_64=m
CONFIG_CRYPTO_SERPENT_AVX2_X86_64=m
CONFIG_CRYPTO_TWOFISH_X86_64=m
CONFIG_CRYPTO_TWOFISH_X86_64_3WAY=m
CONFIG_CRYPTO_TWOFISH_AVX_X86_64=m
CONFIG_XZ_DEC_IA64=y


As you can see, a fair number of these are specific to 64-bit architecture. What you might be able to do is copy this to a 32-bit machine, then start tweaking to turn it back to 32-bit. I got to my 64-bit .config files by starting with old 32-bit, then doing the 64-bit tweaks. Looking at what I've just posted, I see a number of places to possibly tweak, myself. I need to read the help text before simply turning things on or off, though. After all, there is a lot of ancient history in this file, some of which may be sub-optimal.
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krinn
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Joined: 02 May 2003
Posts: 7071

PostPosted: Thu Jun 01, 2017 12:15 pm    Post subject: Reply with quote

kernel options use dependencies, that's why you must enable something sometimes to enable another thing.
and i'm 99% sure that just disable 64bits to enable 32bits will disable every options a 32bits kernel couldn't use, it will also enable 32bits options that your current 64bits config couldn't select (i only have one in mind, the memory selection).

So for me as easy as going in the menu and just uncheck 64bits kernel option should be enough.
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