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linux/arch/x86/Kconfig.cpu
Ingo Molnar 8b793a92d8 x86/cpu: Remove M486/M486SX/ELAN support 
In the x86 architecture we have various complicated hardware emulation
facilities on x86-32 to support ancient 32-bit CPUs that very very few
people are using with modern kernels. This compatibility glue is sometimes
even causing problems that people spend time to resolve, which time could
be spent on other things.

As Linus recently remarked:

 > I really get the feeling that it's time to leave i486 support behind.
 > There's zero real reason for anybody to waste one second of
 > development effort on this kind of issue.

Implement the first step and remove M486/M486SX/ELAN support:

  CONFIG_M486SX
  CONFIG_M486
  CONFIG_MELAN

[ There's no recent M486=y kernel package for any mainstream x86
  32-bit distribution available that I've been able to find, so
  actual users should not be impacted, and any legacy users can
  keep using older kernels. ]

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ahmed S. Darwish <darwi@linutronix.de>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20251214084710.3606385-2-mingo@kernel.org
2026-03-30 11:39:42 +02:00

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# SPDX-License-Identifier: GPL-2.0
# Put here option for CPU selection and depending optimization
choice
prompt "x86-32 Processor family"
depends on X86_32
default M686
help
This is the processor type of your CPU. This information is
used for optimizing purposes. In order to compile a kernel
that can run on all supported x86 CPU types (albeit not
optimally fast), you can specify "586" here.
Note that the 386 and 486 is no longer supported, this includes
AMD/Cyrix/Intel 386DX/DXL/SL/SLC/SX, Cyrix/TI 486DLC/DLC2,
UMC 486SX-S and the NexGen Nx586, AMD ELAN and all 486 based
CPUs.
The kernel will not necessarily run on earlier architectures than
the one you have chosen, e.g. a Pentium optimized kernel will run on
a PPro, but not necessarily on a i486.
Here are the settings recommended for greatest speed:
- "586" for generic Pentium CPUs lacking the TSC
(time stamp counter) register.
- "Pentium-Classic" for the Intel Pentium.
- "Pentium-MMX" for the Intel Pentium MMX.
- "Pentium-Pro" for the Intel Pentium Pro.
- "Pentium-II" for the Intel Pentium II or pre-Coppermine Celeron.
- "Pentium-III" for the Intel Pentium III or Coppermine Celeron.
- "Pentium-4" for the Intel Pentium 4 or P4-based Celeron.
- "K6" for the AMD K6, K6-II and K6-III (aka K6-3D).
- "Athlon" for the AMD K7 family (Athlon/Duron/Thunderbird).
- "Crusoe" for the Transmeta Crusoe series.
- "Efficeon" for the Transmeta Efficeon series.
- "Winchip-C6" for original IDT Winchip.
- "Winchip-2" for IDT Winchips with 3dNow! capabilities.
- "AMD Elan" for the 32-bit AMD Elan embedded CPU.
- "GeodeGX1" for Geode GX1 (Cyrix MediaGX).
- "Geode GX/LX" For AMD Geode GX and LX processors.
- "CyrixIII/VIA C3" for VIA Cyrix III or VIA C3.
- "VIA C3-2" for VIA C3-2 "Nehemiah" (model 9 and above).
- "VIA C7" for VIA C7.
- "Intel Atom" for the Atom-microarchitecture CPUs.
See each option's help text for additional details. If you don't know
what to do, choose "Pentium-Pro".
config M586
bool "586/K5/5x86/6x86/6x86MX"
depends on X86_32
help
Select this for an 586 or 686 series processor such as the AMD K5,
the Cyrix 5x86, 6x86 and 6x86MX. This choice does not
assume the RDTSC (Read Time Stamp Counter) instruction.
config M586TSC
bool "Pentium-Classic"
depends on X86_32
help
Select this for a Pentium Classic processor with the RDTSC (Read
Time Stamp Counter) instruction for benchmarking.
config M586MMX
bool "Pentium-MMX"
depends on X86_32
help
Select this for a Pentium with the MMX graphics/multimedia
extended instructions.
config M686
bool "Pentium-Pro"
depends on X86_32
help
Select this for Intel Pentium Pro chips. This enables the use of
Pentium Pro extended instructions, and disables the init-time guard
against the f00f bug found in earlier Pentiums.
config MPENTIUMII
bool "Pentium-II/Celeron(pre-Coppermine)"
depends on X86_32
help
Select this for Intel chips based on the Pentium-II and
pre-Coppermine Celeron core. This option enables an unaligned
copy optimization, compiles the kernel with optimization flags
tailored for the chip, and applies any applicable Pentium Pro
optimizations.
config MPENTIUMIII
bool "Pentium-III/Celeron(Coppermine)/Pentium-III Xeon"
depends on X86_32
help
Select this for Intel chips based on the Pentium-III and
Celeron-Coppermine core. This option enables use of some
extended prefetch instructions in addition to the Pentium II
extensions.
config MPENTIUMM
bool "Pentium M/Pentium Dual Core/Core Solo/Core Duo"
depends on X86_32
help
Select this for Intel Pentium M (not Pentium-4 M)
"Merom" Core Solo/Duo notebook chips
config MPENTIUM4
bool "Pentium-4/Celeron(P4-based)/Pentium-4 M/older Xeon"
depends on X86_32
help
Select this for Intel Pentium 4 chips. This includes the
Pentium 4, Pentium D, P4-based Celeron and Xeon, and
Pentium-4 M (not Pentium M) chips. This option enables compile
flags optimized for the chip, uses the correct cache line size, and
applies any applicable optimizations.
CPUIDs: F[0-6][1-A] (in /proc/cpuinfo show = cpu family : 15 )
Select this for:
Pentiums (Pentium 4, Pentium D, Celeron, Celeron D) corename:
-Willamette
-Northwood
-Mobile Pentium 4
-Mobile Pentium 4 M
-Extreme Edition (Gallatin)
Xeons (Intel Xeon, Xeon MP, Xeon LV, Xeon MV) corename:
-Foster
-Prestonia
-Gallatin
config MK6
bool "K6/K6-II/K6-III"
depends on X86_32
help
Select this for an AMD K6-family processor. Enables use of
some extended instructions, and passes appropriate optimization
flags to GCC.
config MK7
bool "Athlon/Duron/K7"
depends on X86_32
help
Select this for an AMD Athlon K7-family processor. Enables use of
some extended instructions, and passes appropriate optimization
flags to GCC.
config MCRUSOE
bool "Crusoe"
depends on X86_32
help
Select this for a Transmeta Crusoe processor. Treats the processor
like a 586 with TSC, and sets some GCC optimization flags (like a
Pentium Pro with no alignment requirements).
config MEFFICEON
bool "Efficeon"
depends on X86_32
help
Select this for a Transmeta Efficeon processor.
config MWINCHIPC6
bool "Winchip-C6"
depends on X86_32
help
Select this for an IDT Winchip C6 chip. Linux and GCC
treat this chip as a 586TSC with some extended instructions
and alignment requirements.
config MWINCHIP3D
bool "Winchip-2/Winchip-2A/Winchip-3"
depends on X86_32
help
Select this for an IDT Winchip-2, 2A or 3. Linux and GCC
treat this chip as a 586TSC with some extended instructions
and alignment requirements. Also enable out of order memory
stores for this CPU, which can increase performance of some
operations.
config MGEODEGX1
bool "GeodeGX1"
depends on X86_32
help
Select this for a Geode GX1 (Cyrix MediaGX) chip.
config MGEODE_LX
bool "Geode GX/LX"
depends on X86_32
help
Select this for AMD Geode GX and LX processors.
config MCYRIXIII
bool "CyrixIII/VIA-C3"
depends on X86_32
help
Select this for a Cyrix III or C3 chip. Presently Linux and GCC
treat this chip as a generic 586. Whilst the CPU is 686 class,
it lacks the cmov extension which gcc assumes is present when
generating 686 code.
Note that Nehemiah (Model 9) and above will not boot with this
kernel due to them lacking the 3DNow! instructions used in earlier
incarnations of the CPU.
config MVIAC3_2
bool "VIA C3-2 (Nehemiah)"
depends on X86_32
help
Select this for a VIA C3 "Nehemiah". Selecting this enables usage
of SSE and tells gcc to treat the CPU as a 686.
Note, this kernel will not boot on older (pre model 9) C3s.
config MVIAC7
bool "VIA C7"
depends on X86_32
help
Select this for a VIA C7. Selecting this uses the correct cache
shift and tells gcc to treat the CPU as a 686.
config MATOM
bool "Intel Atom"
help
Select this for the Intel Atom platform. Intel Atom CPUs have an
in-order pipelining architecture and thus can benefit from
accordingly optimized code. Use a recent GCC with specific Atom
support in order to fully benefit from selecting this option.
endchoice
config CC_HAS_MARCH_NATIVE
# This flag might not be available in cross-compilers:
def_bool $(cc-option, -march=native)
# LLVM 18 has an easily triggered internal compiler error in core
# networking code with '-march=native' on certain systems:
# https://github.com/llvm/llvm-project/issues/72026
# LLVM 19 introduces an optimization that resolves some high stack
# usage warnings that only appear wth '-march=native'.
depends on CC_IS_GCC || CLANG_VERSION >= 190100
config X86_NATIVE_CPU
bool "Build and optimize for local/native CPU"
depends on X86_64
depends on CC_HAS_MARCH_NATIVE
help
Optimize for the current CPU used to compile the kernel.
Use this option if you intend to build the kernel for your
local machine.
Note that such a kernel might not work optimally on a
different x86 machine.
If unsure, say N.
config X86_GENERIC
bool "Generic x86 support"
depends on X86_32
help
Instead of just including optimizations for the selected
x86 variant (e.g. PII, Crusoe or Athlon), include some more
generic optimizations as well. This will make the kernel
perform better on x86 CPUs other than that selected.
This is really intended for distributors who need more
generic optimizations.
#
# Define implied options from the CPU selection here
config X86_INTERNODE_CACHE_SHIFT
int
default "12" if X86_VSMP
default X86_L1_CACHE_SHIFT
config X86_L1_CACHE_SHIFT
int
default "7" if MPENTIUM4
default "6" if MK7 || MPENTIUMM || MATOM || MVIAC7 || X86_GENERIC || X86_64
default "4" if MGEODEGX1
default "5" if MWINCHIP3D || MWINCHIPC6 || MCRUSOE || MEFFICEON || MCYRIXIII || MK6 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODE_LX
config X86_F00F_BUG
def_bool y
depends on M586MMX || M586TSC || M586
config X86_INVD_BUG
def_bool y
depends on M486SX || M486
config X86_ALIGNMENT_16
def_bool y
depends on MWINCHIP3D || MWINCHIPC6 || MCYRIXIII || MK6 || M586MMX || M586TSC || M586 || MVIAC3_2 || MGEODEGX1
config X86_INTEL_USERCOPY
def_bool y
depends on MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M586MMX || X86_GENERIC || MK7 || MEFFICEON
config X86_USE_PPRO_CHECKSUM
def_bool y
depends on MWINCHIP3D || MWINCHIPC6 || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MEFFICEON || MGEODE_LX || MATOM
config X86_TSC
def_bool y
depends on (MWINCHIP3D || MCRUSOE || MEFFICEON || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || MVIAC3_2 || MVIAC7 || MGEODEGX1 || MGEODE_LX || MATOM) || X86_64
config X86_HAVE_PAE
def_bool y
depends on MCRUSOE || MEFFICEON || MCYRIXIII || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC7 || MATOM || X86_64
config X86_CX8
def_bool y
depends on X86_HAVE_PAE || M586TSC || M586MMX || MK6 || MK7 || MGEODEGX1 || MGEODE_LX
# this should be set for all -march=.. options where the compiler
# generates cmov.
config X86_CMOV
def_bool y
depends on (MK7 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MCRUSOE || MEFFICEON || MATOM || MGEODE_LX || X86_64)
config X86_MINIMUM_CPU_FAMILY
int
default "64" if X86_64
default "6" if X86_32 && (MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MEFFICEON || MATOM || MK7)
default "5"
config X86_DEBUGCTLMSR
def_bool y
depends on !(MK6 || MWINCHIPC6 || MWINCHIP3D || MCYRIXIII || M586MMX || M586TSC || M586) && !UML
config IA32_FEAT_CTL
def_bool y
depends on CPU_SUP_INTEL || CPU_SUP_CENTAUR || CPU_SUP_ZHAOXIN
config X86_VMX_FEATURE_NAMES
def_bool y
depends on IA32_FEAT_CTL
menuconfig PROCESSOR_SELECT
bool "Supported processor vendors" if EXPERT
help
This lets you choose what x86 vendor support code your kernel
will include.
config BROADCAST_TLB_FLUSH
def_bool y
depends on CPU_SUP_AMD && 64BIT
config CPU_SUP_INTEL
default y
bool "Support Intel processors" if PROCESSOR_SELECT
help
This enables detection, tunings and quirks for Intel processors
You need this enabled if you want your kernel to run on an
Intel CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller. Disabling it on an Intel
CPU might render the kernel unbootable.
If unsure, say N.
config CPU_SUP_CYRIX_32
default y
bool "Support Cyrix processors" if PROCESSOR_SELECT
depends on M586 || M586TSC || M586MMX || (EXPERT && !64BIT)
help
This enables detection, tunings and quirks for Cyrix processors
You need this enabled if you want your kernel to run on a
Cyrix CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller. Disabling it on a Cyrix
CPU might render the kernel unbootable.
If unsure, say N.
config CPU_SUP_AMD
default y
bool "Support AMD processors" if PROCESSOR_SELECT
help
This enables detection, tunings and quirks for AMD processors
You need this enabled if you want your kernel to run on an
AMD CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller. Disabling it on an AMD
CPU might render the kernel unbootable.
If unsure, say N.
config CPU_SUP_HYGON
default y
bool "Support Hygon processors" if PROCESSOR_SELECT
select CPU_SUP_AMD
help
This enables detection, tunings and quirks for Hygon processors
You need this enabled if you want your kernel to run on an
Hygon CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller. Disabling it on an Hygon
CPU might render the kernel unbootable.
If unsure, say N.
config CPU_SUP_CENTAUR
default y
bool "Support Centaur processors" if PROCESSOR_SELECT
help
This enables detection, tunings and quirks for Centaur processors
You need this enabled if you want your kernel to run on a
Centaur CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller. Disabling it on a Centaur
CPU might render the kernel unbootable.
If unsure, say N.
config CPU_SUP_TRANSMETA_32
default y
bool "Support Transmeta processors" if PROCESSOR_SELECT
depends on !64BIT
help
This enables detection, tunings and quirks for Transmeta processors
You need this enabled if you want your kernel to run on a
Transmeta CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller. Disabling it on a Transmeta
CPU might render the kernel unbootable.
If unsure, say N.
config CPU_SUP_UMC_32
default y
bool "Support UMC processors" if PROCESSOR_SELECT
depends on M486SX || M486 || (EXPERT && !64BIT)
help
This enables detection, tunings and quirks for UMC processors
You need this enabled if you want your kernel to run on a
UMC CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller. Disabling it on a UMC
CPU might render the kernel unbootable.
If unsure, say N.
config CPU_SUP_ZHAOXIN
default y
bool "Support Zhaoxin processors" if PROCESSOR_SELECT
help
This enables detection, tunings and quirks for Zhaoxin processors
You need this enabled if you want your kernel to run on a
Zhaoxin CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller. Disabling it on a Zhaoxin
CPU might render the kernel unbootable.
If unsure, say N.
config CPU_SUP_VORTEX_32
default y
bool "Support Vortex processors" if PROCESSOR_SELECT
depends on X86_32
help
This enables detection, tunings and quirks for Vortex processors
You need this enabled if you want your kernel to run on a
Vortex CPU. Disabling this option on other types of CPUs
makes the kernel a tiny bit smaller.
If unsure, say N.
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