arch/Kconfig

# SPDX-License-Identifier: GPL-2.0
#
# General architecture dependent options
#

#
# Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can
# override the default values in this file.
#
source "arch/$(SRCARCH)/Kconfig"

menu "General architecture-dependent options"

config CRASH_CORE
	bool

config KEXEC_CORE
	select CRASH_CORE
	bool

config KEXEC_ELF
	bool

config HAVE_IMA_KEXEC
	bool

config SET_FS
	bool

config HOTPLUG_SMT
	bool

config GENERIC_ENTRY
       bool

config OPROFILE
	tristate "OProfile system profiling"
	depends on PROFILING
	depends on HAVE_OPROFILE
	select RING_BUFFER
	select RING_BUFFER_ALLOW_SWAP
	help
	  OProfile is a profiling system capable of profiling the
	  whole system, include the kernel, kernel modules, libraries,
	  and applications.

	  If unsure, say N.

config OPROFILE_EVENT_MULTIPLEX
	bool "OProfile multiplexing support (EXPERIMENTAL)"
	default n
	depends on OPROFILE && X86
	help
	  The number of hardware counters is limited. The multiplexing
	  feature enables OProfile to gather more events than counters
	  are provided by the hardware. This is realized by switching
	  between events at a user specified time interval.

	  If unsure, say N.

config HAVE_OPROFILE
	bool

config OPROFILE_NMI_TIMER
	def_bool y
	depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64

config KPROBES
	bool "Kprobes"
	depends on MODULES
	depends on HAVE_KPROBES
	select KALLSYMS
	help
	  Kprobes allows you to trap at almost any kernel address and
	  execute a callback function.  register_kprobe() establishes
	  a probepoint and specifies the callback.  Kprobes is useful
	  for kernel debugging, non-intrusive instrumentation and testing.
	  If in doubt, say "N".

config JUMP_LABEL
	bool "Optimize very unlikely/likely branches"
	depends on HAVE_ARCH_JUMP_LABEL
	depends on CC_HAS_ASM_GOTO
	help
	 This option enables a transparent branch optimization that
	 makes certain almost-always-true or almost-always-false branch
	 conditions even cheaper to execute within the kernel.

	 Certain performance-sensitive kernel code, such as trace points,
	 scheduler functionality, networking code and KVM have such
	 branches and include support for this optimization technique.

	 If it is detected that the compiler has support for "asm goto",
	 the kernel will compile such branches with just a nop
	 instruction. When the condition flag is toggled to true, the
	 nop will be converted to a jump instruction to execute the
	 conditional block of instructions.

	 This technique lowers overhead and stress on the branch prediction
	 of the processor and generally makes the kernel faster. The update
	 of the condition is slower, but those are always very rare.

	 ( On 32-bit x86, the necessary options added to the compiler
	   flags may increase the size of the kernel slightly. )

config STATIC_KEYS_SELFTEST
	bool "Static key selftest"
	depends on JUMP_LABEL
	help
	  Boot time self-test of the branch patching code.

config STATIC_CALL_SELFTEST
	bool "Static call selftest"
	depends on HAVE_STATIC_CALL
	help
	  Boot time self-test of the call patching code.

config OPTPROBES
	def_bool y
	depends on KPROBES && HAVE_OPTPROBES
	select TASKS_RCU if PREEMPTION

config KPROBES_ON_FTRACE
	def_bool y
	depends on KPROBES && HAVE_KPROBES_ON_FTRACE
	depends on DYNAMIC_FTRACE_WITH_REGS
	help
	 If function tracer is enabled and the arch supports full
	 passing of pt_regs to function tracing, then kprobes can
	 optimize on top of function tracing.

config UPROBES
	def_bool n
	depends on ARCH_SUPPORTS_UPROBES
	help
	  Uprobes is the user-space counterpart to kprobes: they
	  enable instrumentation applications (such as 'perf probe')
	  to establish unintrusive probes in user-space binaries and
	  libraries, by executing handler functions when the probes
	  are hit by user-space applications.

	  ( These probes come in the form of single-byte breakpoints,
	    managed by the kernel and kept transparent to the probed
	    application. )

config HAVE_64BIT_ALIGNED_ACCESS
	def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
	help
	  Some architectures require 64 bit accesses to be 64 bit
	  aligned, which also requires structs containing 64 bit values
	  to be 64 bit aligned too. This includes some 32 bit
	  architectures which can do 64 bit accesses, as well as 64 bit
	  architectures without unaligned access.

	  This symbol should be selected by an architecture if 64 bit
	  accesses are required to be 64 bit aligned in this way even
	  though it is not a 64 bit architecture.

	  See Documentation/unaligned-memory-access.txt for more
	  information on the topic of unaligned memory accesses.

config HAVE_EFFICIENT_UNALIGNED_ACCESS
	bool
	help
	  Some architectures are unable to perform unaligned accesses
	  without the use of get_unaligned/put_unaligned. Others are
	  unable to perform such accesses efficiently (e.g. trap on
	  unaligned access and require fixing it up in the exception
	  handler.)

	  This symbol should be selected by an architecture if it can
	  perform unaligned accesses efficiently to allow different
	  code paths to be selected for these cases. Some network
	  drivers, for example, could opt to not fix up alignment
	  problems with received packets if doing so would not help
	  much.

	  See Documentation/core-api/unaligned-memory-access.rst for more
	  information on the topic of unaligned memory accesses.

config ARCH_USE_BUILTIN_BSWAP
	bool
	help
	 Modern versions of GCC (since 4.4) have builtin functions
	 for handling byte-swapping. Using these, instead of the old
	 inline assembler that the architecture code provides in the
	 __arch_bswapXX() macros, allows the compiler to see what's
	 happening and offers more opportunity for optimisation. In
	 particular, the compiler will be able to combine the byteswap
	 with a nearby load or store and use load-and-swap or
	 store-and-swap instructions if the architecture has them. It
	 should almost *never* result in code which is worse than the
	 hand-coded assembler in <asm/swab.h>.  But just in case it
	 does, the use of the builtins is optional.

	 Any architecture with load-and-swap or store-and-swap
	 instructions should set this. And it shouldn't hurt to set it
	 on architectures that don't have such instructions.

config KRETPROBES
	def_bool y
	depends on KPROBES && HAVE_KRETPROBES

config USER_RETURN_NOTIFIER
	bool
	depends on HAVE_USER_RETURN_NOTIFIER
	help
	  Provide a kernel-internal notification when a cpu is about to
	  switch to user mode.

config HAVE_IOREMAP_PROT
	bool

config HAVE_KPROBES
	bool

config HAVE_KRETPROBES
	bool

config HAVE_OPTPROBES
	bool

config HAVE_KPROBES_ON_FTRACE
	bool

config HAVE_FUNCTION_ERROR_INJECTION
	bool

config HAVE_NMI
	bool

#
# An arch should select this if it provides all these things:
#
#	task_pt_regs()		in asm/processor.h or asm/ptrace.h
#	arch_has_single_step()	if there is hardware single-step support
#	arch_has_block_step()	if there is hardware block-step support
#	asm/syscall.h		supplying asm-generic/syscall.h interface
#	linux/regset.h		user_regset interfaces
#	CORE_DUMP_USE_REGSET	#define'd in linux/elf.h
#	TIF_SYSCALL_TRACE	calls tracehook_report_syscall_{entry,exit}
#	TIF_NOTIFY_RESUME	calls tracehook_notify_resume()
#	signal delivery		calls tracehook_signal_handler()
#
config HAVE_ARCH_TRACEHOOK
	bool

config HAVE_DMA_CONTIGUOUS
	bool

config GENERIC_SMP_IDLE_THREAD
	bool

config GENERIC_IDLE_POLL_SETUP
	bool

config ARCH_HAS_FORTIFY_SOURCE
	bool
	help
	  An architecture should select this when it can successfully
	  build and run with CONFIG_FORTIFY_SOURCE.

#
# Select if the arch provides a historic keepinit alias for the retain_initrd
# command line option
#
config ARCH_HAS_KEEPINITRD
	bool

# Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
config ARCH_HAS_SET_MEMORY
	bool

# Select if arch has all set_direct_map_invalid/default() functions
config ARCH_HAS_SET_DIRECT_MAP
	bool

#
# Select if the architecture provides the arch_dma_set_uncached symbol to
# either provide an uncached segement alias for a DMA allocation, or
# to remap the page tables in place.
#
config ARCH_HAS_DMA_SET_UNCACHED
	bool

#
# Select if the architectures provides the arch_dma_clear_uncached symbol
# to undo an in-place page table remap for uncached access.
#
config ARCH_HAS_DMA_CLEAR_UNCACHED
	bool

# Select if arch init_task must go in the __init_task_data section
config ARCH_TASK_STRUCT_ON_STACK
	bool

# Select if arch has its private alloc_task_struct() function
config ARCH_TASK_STRUCT_ALLOCATOR
	bool

config HAVE_ARCH_THREAD_STRUCT_WHITELIST
	bool
	depends on !ARCH_TASK_STRUCT_ALLOCATOR
	help
	  An architecture should select this to provide hardened usercopy
	  knowledge about what region of the thread_struct should be
	  whitelisted for copying to userspace. Normally this is only the
	  FPU registers. Specifically, arch_thread_struct_whitelist()
	  should be implemented. Without this, the entire thread_struct
	  field in task_struct will be left whitelisted.

# Select if arch has its private alloc_thread_stack() function
config ARCH_THREAD_STACK_ALLOCATOR
	bool

# Select if arch wants to size task_struct dynamically via arch_task_struct_size:
config ARCH_WANTS_DYNAMIC_TASK_STRUCT
	bool

config ARCH_32BIT_OFF_T
	bool
	depends on !64BIT
	help
	  All new 32-bit architectures should have 64-bit off_t type on
	  userspace side which corresponds to the loff_t kernel type. This
	  is the requirement for modern ABIs. Some existing architectures
	  still support 32-bit off_t. This option is enabled for all such
	  architectures explicitly.

config HAVE_ASM_MODVERSIONS
	bool
	help
	  This symbol should be selected by an architecure if it provides
	  <asm/asm-prototypes.h> to support the module versioning for symbols
	  exported from assembly code.

config HAVE_REGS_AND_STACK_ACCESS_API
	bool
	help
	  This symbol should be selected by an architecure if it supports
	  the API needed to access registers and stack entries from pt_regs,
	  declared in asm/ptrace.h
	  For example the kprobes-based event tracer needs this API.

config HAVE_RSEQ
	bool
	depends on HAVE_REGS_AND_STACK_ACCESS_API
	help
	  This symbol should be selected by an architecture if it
	  supports an implementation of restartable sequences.

config HAVE_FUNCTION_ARG_ACCESS_API
	bool
	help
	  This symbol should be selected by an architecure if it supports
	  the API needed to access function arguments from pt_regs,
	  declared in asm/ptrace.h

config HAVE_HW_BREAKPOINT
	bool
	depends on PERF_EVENTS

config HAVE_MIXED_BREAKPOINTS_REGS
	bool
	depends on HAVE_HW_BREAKPOINT
	help
	  Depending on the arch implementation of hardware breakpoints,
	  some of them have separate registers for data and instruction
	  breakpoints addresses, others have mixed registers to store
	  them but define the access type in a control register.
	  Select this option if your arch implements breakpoints under the
	  latter fashion.

config HAVE_USER_RETURN_NOTIFIER
	bool

config HAVE_PERF_EVENTS_NMI
	bool
	help
	  System hardware can generate an NMI using the perf event
	  subsystem.  Also has support for calculating CPU cycle events
	  to determine how many clock cycles in a given period.

config HAVE_HARDLOCKUP_DETECTOR_PERF
	bool
	depends on HAVE_PERF_EVENTS_NMI
	help
	  The arch chooses to use the generic perf-NMI-based hardlockup
	  detector. Must define HAVE_PERF_EVENTS_NMI.

config HAVE_NMI_WATCHDOG
	depends on HAVE_NMI
	bool
	help
	  The arch provides a low level NMI watchdog. It provides
	  asm/nmi.h, and defines its own arch_touch_nmi_watchdog().

config HAVE_HARDLOCKUP_DETECTOR_ARCH
	bool
	select HAVE_NMI_WATCHDOG
	help
	  The arch chooses to provide its own hardlockup detector, which is
	  a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
	  interfaces and parameters provided by hardlockup detector subsystem.

config HAVE_PERF_REGS
	bool
	help
	  Support selective register dumps for perf events. This includes
	  bit-mapping of each registers and a unique architecture id.

config HAVE_PERF_USER_STACK_DUMP
	bool
	help
	  Support user stack dumps for perf event samples. This needs
	  access to the user stack pointer which is not unified across
	  architectures.

config HAVE_ARCH_JUMP_LABEL
	bool

config HAVE_ARCH_JUMP_LABEL_RELATIVE
	bool

config MMU_GATHER_TABLE_FREE
	bool

config MMU_GATHER_RCU_TABLE_FREE
	bool
	select MMU_GATHER_TABLE_FREE

config MMU_GATHER_PAGE_SIZE
	bool

config MMU_GATHER_NO_RANGE
	bool

config MMU_GATHER_NO_GATHER
	bool
	depends on MMU_GATHER_TABLE_FREE

config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
	bool
	help
	  Temporary select until all architectures can be converted to have
	  irqs disabled over activate_mm. Architectures that do IPI based TLB
	  shootdowns should enable this.

config ARCH_HAVE_NMI_SAFE_CMPXCHG
	bool

config HAVE_ALIGNED_STRUCT_PAGE
	bool
	help
	  This makes sure that struct pages are double word aligned and that
	  e.g. the SLUB allocator can perform double word atomic operations
	  on a struct page for better performance. However selecting this
	  might increase the size of a struct page by a word.

config HAVE_CMPXCHG_LOCAL
	bool

config HAVE_CMPXCHG_DOUBLE
	bool

config ARCH_WEAK_RELEASE_ACQUIRE
	bool

config ARCH_WANT_IPC_PARSE_VERSION
	bool

config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
	bool

config ARCH_WANT_OLD_COMPAT_IPC
	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
	bool

config HAVE_ARCH_SECCOMP
	bool
	help
	  An arch should select this symbol to support seccomp mode 1 (the fixed
	  syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
	  and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
	  - __NR_seccomp_read_32
	  - __NR_seccomp_write_32
	  - __NR_seccomp_exit_32
	  - __NR_seccomp_sigreturn_32

config HAVE_ARCH_SECCOMP_FILTER
	bool
	select HAVE_ARCH_SECCOMP
	help
	  An arch should select this symbol if it provides all of these things:
	  - all the requirements for HAVE_ARCH_SECCOMP
	  - syscall_get_arch()
	  - syscall_get_arguments()
	  - syscall_rollback()
	  - syscall_set_return_value()
	  - SIGSYS siginfo_t support
	  - secure_computing is called from a ptrace_event()-safe context
	  - secure_computing return value is checked and a return value of -1
	    results in the system call being skipped immediately.
	  - seccomp syscall wired up

config SECCOMP
	prompt "Enable seccomp to safely execute untrusted bytecode"
	def_bool y
	depends on HAVE_ARCH_SECCOMP
	help
	  This kernel feature is useful for number crunching applications
	  that may need to handle untrusted bytecode during their
	  execution. By using pipes or other transports made available
	  to the process as file descriptors supporting the read/write
	  syscalls, it's possible to isolate those applications in their
	  own address space using seccomp. Once seccomp is enabled via
	  prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
	  disabled and the task is only allowed to execute a few safe
	  syscalls defined by each seccomp mode.

	  If unsure, say Y.

config SECCOMP_FILTER
	def_bool y
	depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
	help
	  Enable tasks to build secure computing environments defined
	  in terms of Berkeley Packet Filter programs which implement
	  task-defined system call filtering polices.

	  See Documentation/userspace-api/seccomp_filter.rst for details.

config HAVE_ARCH_STACKLEAK
	bool
	help
	  An architecture should select this if it has the code which
	  fills the used part of the kernel stack with the STACKLEAK_POISON
	  value before returning from system calls.

config HAVE_STACKPROTECTOR
	bool
	help
	  An arch should select this symbol if:
	  - it has implemented a stack canary (e.g. __stack_chk_guard)

config STACKPROTECTOR
	bool "Stack Protector buffer overflow detection"
	depends on HAVE_STACKPROTECTOR
	depends on $(cc-option,-fstack-protector)
	default y
	help
	  This option turns on the "stack-protector" GCC feature. This
	  feature puts, at the beginning of functions, a canary value on
	  the stack just before the return address, and validates
	  the value just before actually returning.  Stack based buffer
	  overflows (that need to overwrite this return address) now also
	  overwrite the canary, which gets detected and the attack is then
	  neutralized via a kernel panic.

	  Functions will have the stack-protector canary logic added if they
	  have an 8-byte or larger character array on the stack.

	  This feature requires gcc version 4.2 or above, or a distribution
	  gcc with the feature backported ("-fstack-protector").

	  On an x86 "defconfig" build, this feature adds canary checks to
	  about 3% of all kernel functions, which increases kernel code size
	  by about 0.3%.

config STACKPROTECTOR_STRONG
	bool "Strong Stack Protector"
	depends on STACKPROTECTOR
	depends on $(cc-option,-fstack-protector-strong)
	default y
	help
	  Functions will have the stack-protector canary logic added in any
	  of the following conditions:

	  - local variable's address used as part of the right hand side of an
	    assignment or function argument
	  - local variable is an array (or union containing an array),
	    regardless of array type or length
	  - uses register local variables

	  This feature requires gcc version 4.9 or above, or a distribution
	  gcc with the feature backported ("-fstack-protector-strong").

	  On an x86 "defconfig" build, this feature adds canary checks to
	  about 20% of all kernel functions, which increases the kernel code
	  size by about 2%.

config ARCH_SUPPORTS_SHADOW_CALL_STACK
	bool
	help
	  An architecture should select this if it supports Clang's Shadow
	  Call Stack and implements runtime support for shadow stack
	  switching.

config SHADOW_CALL_STACK
	bool "Clang Shadow Call Stack"
	depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK
	depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
	help
	  This option enables Clang's Shadow Call Stack, which uses a
	  shadow stack to protect function return addresses from being
	  overwritten by an attacker. More information can be found in
	  Clang's documentation:

	    https://clang.llvm.org/docs/ShadowCallStack.html

	  Note that security guarantees in the kernel differ from the
	  ones documented for user space. The kernel must store addresses
	  of shadow stacks in memory, which means an attacker capable of
	  reading and writing arbitrary memory may be able to locate them
	  and hijack control flow by modifying the stacks.

config LTO
	bool
	help
	  Selected if the kernel will be built using the compiler's LTO feature.

config LTO_CLANG
	bool
	select LTO
	help
	  Selected if the kernel will be built using Clang's LTO feature.

config ARCH_SUPPORTS_LTO_CLANG
	bool
	help
	  An architecture should select this option if it supports:
	  - compiling with Clang,
	  - compiling inline assembly with Clang's integrated assembler,
	  - and linking with LLD.

config ARCH_SUPPORTS_LTO_CLANG_THIN
	bool
	help
	  An architecture should select this option if it can support Clang's
	  ThinLTO mode.

config HAS_LTO_CLANG
	def_bool y
	# Clang >= 11: https://github.com/ClangBuiltLinux/linux/issues/510
	depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD && AS_IS_LLVM
	depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
	depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
	depends on ARCH_SUPPORTS_LTO_CLANG
	depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
	depends on !KASAN || KASAN_HW_TAGS
	depends on !GCOV_KERNEL
	help
	  The compiler and Kconfig options support building with Clang's
	  LTO.

choice
	prompt "Link Time Optimization (LTO)"
	default LTO_NONE
	help
	  This option enables Link Time Optimization (LTO), which allows the
	  compiler to optimize binaries globally.

	  If unsure, select LTO_NONE. Note that LTO is very resource-intensive
	  so it's disabled by default.

config LTO_NONE
	bool "None"
	help
	  Build the kernel normally, without Link Time Optimization (LTO).

config LTO_CLANG_FULL
	bool "Clang Full LTO (EXPERIMENTAL)"
	depends on HAS_LTO_CLANG
	depends on !COMPILE_TEST
	select LTO_CLANG
	help
          This option enables Clang's full Link Time Optimization (LTO), which
          allows the compiler to optimize the kernel globally. If you enable
          this option, the compiler generates LLVM bitcode instead of ELF
          object files, and the actual compilation from bitcode happens at
          the LTO link step, which may take several minutes depending on the
          kernel configuration. More information can be found from LLVM's
          documentation:

	    https://llvm.org/docs/LinkTimeOptimization.html

	  During link time, this option can use a large amount of RAM, and
	  may take much longer than the ThinLTO option.

config LTO_CLANG_THIN
	bool "Clang ThinLTO (EXPERIMENTAL)"
	depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
	select LTO_CLANG
	help
	  This option enables Clang's ThinLTO, which allows for parallel
	  optimization and faster incremental compiles compared to the
	  CONFIG_LTO_CLANG_FULL option. More information can be found
	  from Clang's documentation:

	    https://clang.llvm.org/docs/ThinLTO.html

	  If unsure, say Y.
endchoice

config CFI_CLANG
	bool "Use Clang's Control Flow Integrity (CFI)"
	depends on LTO_CLANG && KALLSYMS
	help
	  This option enables Clang's Control Flow Integrity (CFI), which adds
	  runtime checking for indirect function calls.

config CFI_CLANG_SHADOW
	bool "Use CFI shadow to speed up cross-module checks"
	default y
	depends on CFI_CLANG && MODULES
	help
	  If you select this option, the kernel builds a fast look-up table of
	  CFI check functions in loaded modules to reduce overhead.

config CFI_PERMISSIVE
	bool "Use CFI in permissive mode"
	depends on CFI_CLANG
	help
	  When selected, Control Flow Integrity (CFI) violations result in a
	  warning instead of a kernel panic. This option is useful for finding
	  CFI violations during development.

config HAVE_ARCH_WITHIN_STACK_FRAMES
	bool
	help
	  An architecture should select this if it can walk the kernel stack
	  frames to determine if an object is part of either the arguments
	  or local variables (i.e. that it excludes saved return addresses,
	  and similar) by implementing an inline arch_within_stack_frames(),
	  which is used by CONFIG_HARDENED_USERCOPY.

config HAVE_CONTEXT_TRACKING
	bool
	help
	  Provide kernel/user boundaries probes necessary for subsystems
	  that need it, such as userspace RCU extended quiescent state.
	  Syscalls need to be wrapped inside user_exit()-user_enter(), either
	  optimized behind static key or through the slow path using TIF_NOHZ
	  flag. Exceptions handlers must be wrapped as well. Irqs are already
	  protected inside rcu_irq_enter/rcu_irq_exit() but preemption or signal
	  handling on irq exit still need to be protected.

config HAVE_TIF_NOHZ
	bool
	help
	  Arch relies on TIF_NOHZ and syscall slow path to implement context
	  tracking calls to user_enter()/user_exit().

config HAVE_VIRT_CPU_ACCOUNTING
	bool

config ARCH_HAS_SCALED_CPUTIME
	bool

config HAVE_VIRT_CPU_ACCOUNTING_GEN
	bool
	default y if 64BIT
	help
	  With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
	  Before enabling this option, arch code must be audited
	  to ensure there are no races in concurrent read/write of
	  cputime_t. For example, reading/writing 64-bit cputime_t on
	  some 32-bit arches may require multiple accesses, so proper
	  locking is needed to protect against concurrent accesses.


config HAVE_IRQ_TIME_ACCOUNTING
	bool
	help
	  Archs need to ensure they use a high enough resolution clock to
	  support irq time accounting and then call enable_sched_clock_irqtime().

config HAVE_MOVE_PUD
	bool
	help
	  Architectures that select this are able to move page tables at the
	  PUD level. If there are only 3 page table levels, the move effectively
	  happens at the PGD level.

config HAVE_MOVE_PMD
	bool
	help
	  Archs that select this are able to move page tables at the PMD level.

config HAVE_ARCH_TRANSPARENT_HUGEPAGE
	bool

config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
	bool

config HAVE_ARCH_HUGE_VMAP
	bool

config ARCH_WANT_HUGE_PMD_SHARE
	bool

config HAVE_ARCH_SOFT_DIRTY
	bool

config HAVE_MOD_ARCH_SPECIFIC
	bool
	help
	  The arch uses struct mod_arch_specific to store data.  Many arches
	  just need a simple module loader without arch specific data - those
	  should not enable this.

config MODULES_USE_ELF_RELA
	bool
	help
	  Modules only use ELF RELA relocations.  Modules with ELF REL
	  relocations will give an error.

config MODULES_USE_ELF_REL
	bool
	help
	  Modules only use ELF REL relocations.  Modules with ELF RELA
	  relocations will give an error.

config HAVE_IRQ_EXIT_ON_IRQ_STACK
	bool
	help
	  Architecture doesn't only execute the irq handler on the irq stack
	  but also irq_exit(). This way we can process softirqs on this irq
	  stack instead of switching to a new one when we call __do_softirq()
	  in the end of an hardirq.
	  This spares a stack switch and improves cache usage on softirq
	  processing.

config PGTABLE_LEVELS
	int
	default 2

config ARCH_HAS_ELF_RANDOMIZE
	bool
	help
	  An architecture supports choosing randomized locations for
	  stack, mmap, brk, and ET_DYN. Defined functions:
	  - arch_mmap_rnd()
	  - arch_randomize_brk()

config HAVE_ARCH_MMAP_RND_BITS
	bool
	help
	  An arch should select this symbol if it supports setting a variable
	  number of bits for use in establishing the base address for mmap
	  allocations, has MMU enabled and provides values for both:
	  - ARCH_MMAP_RND_BITS_MIN
	  - ARCH_MMAP_RND_BITS_MAX

config HAVE_EXIT_THREAD
	bool
	help
	  An architecture implements exit_thread.

config ARCH_MMAP_RND_BITS_MIN
	int

config ARCH_MMAP_RND_BITS_MAX
	int

config ARCH_MMAP_RND_BITS_DEFAULT
	int

config ARCH_MMAP_RND_BITS
	int "Number of bits to use for ASLR of mmap base address" if EXPERT
	range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
	default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
	default ARCH_MMAP_RND_BITS_MIN
	depends on HAVE_ARCH_MMAP_RND_BITS
	help
	  This value can be used to select the number of bits to use to
	  determine the random offset to the base address of vma regions
	  resulting from mmap allocations. This value will be bounded
	  by the architecture's minimum and maximum supported values.

	  This value can be changed after boot using the
	  /proc/sys/vm/mmap_rnd_bits tunable

config HAVE_ARCH_MMAP_RND_COMPAT_BITS
	bool
	help
	  An arch should select this symbol if it supports running applications
	  in compatibility mode, supports setting a variable number of bits for
	  use in establishing the base address for mmap allocations, has MMU
	  enabled and provides values for both:
	  - ARCH_MMAP_RND_COMPAT_BITS_MIN
	  - ARCH_MMAP_RND_COMPAT_BITS_MAX

config ARCH_MMAP_RND_COMPAT_BITS_MIN
	int

config ARCH_MMAP_RND_COMPAT_BITS_MAX
	int

config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
	int

config ARCH_MMAP_RND_COMPAT_BITS
	int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
	range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
	default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
	default ARCH_MMAP_RND_COMPAT_BITS_MIN
	depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
	help
	  This value can be used to select the number of bits to use to
	  determine the random offset to the base address of vma regions
	  resulting from mmap allocations for compatible applications This
	  value will be bounded by the architecture's minimum and maximum
	  supported values.

	  This value can be changed after boot using the
	  /proc/sys/vm/mmap_rnd_compat_bits tunable

config HAVE_ARCH_COMPAT_MMAP_BASES
	bool
	help
	  This allows 64bit applications to invoke 32-bit mmap() syscall
	  and vice-versa 32-bit applications to call 64-bit mmap().
	  Required for applications doing different bitness syscalls.

# This allows to use a set of generic functions to determine mmap base
# address by giving priority to top-down scheme only if the process
# is not in legacy mode (compat task, unlimited stack size or
# sysctl_legacy_va_layout).
# Architecture that selects this option can provide its own version of:
# - STACK_RND_MASK
config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
	bool
	depends on MMU
	select ARCH_HAS_ELF_RANDOMIZE

config HAVE_STACK_VALIDATION
	bool
	help
	  Architecture supports the 'objtool check' host tool command, which
	  performs compile-time stack metadata validation.

config HAVE_RELIABLE_STACKTRACE
	bool
	help
	  Architecture has either save_stack_trace_tsk_reliable() or
	  arch_stack_walk_reliable() function which only returns a stack trace
	  if it can guarantee the trace is reliable.

config HAVE_ARCH_HASH
	bool
	default n
	help
	  If this is set, the architecture provides an <asm/hash.h>
	  file which provides platform-specific implementations of some
	  functions in <linux/hash.h> or fs/namei.c.

config HAVE_ARCH_NVRAM_OPS
	bool

config ISA_BUS_API
	def_bool ISA

#
# ABI hall of shame
#
config CLONE_BACKWARDS
	bool
	help
	  Architecture has tls passed as the 4th argument of clone(2),
	  not the 5th one.

config CLONE_BACKWARDS2
	bool
	help
	  Architecture has the first two arguments of clone(2) swapped.

config CLONE_BACKWARDS3
	bool
	help
	  Architecture has tls passed as the 3rd argument of clone(2),
	  not the 5th one.

config ODD_RT_SIGACTION
	bool
	help
	  Architecture has unusual rt_sigaction(2) arguments

config OLD_SIGSUSPEND
	bool
	help
	  Architecture has old sigsuspend(2) syscall, of one-argument variety

config OLD_SIGSUSPEND3
	bool
	help
	  Even weirder antique ABI - three-argument sigsuspend(2)

config OLD_SIGACTION
	bool
	help
	  Architecture has old sigaction(2) syscall.  Nope, not the same
	  as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
	  but fairly different variant of sigaction(2), thanks to OSF/1
	  compatibility...

config COMPAT_OLD_SIGACTION
	bool

config COMPAT_32BIT_TIME
	bool "Provide system calls for 32-bit time_t"
	default !64BIT || COMPAT
	help
	  This enables 32 bit time_t support in addition to 64 bit time_t support.
	  This is relevant on all 32-bit architectures, and 64-bit architectures
	  as part of compat syscall handling.

config ARCH_NO_PREEMPT
	bool

config ARCH_SUPPORTS_RT
	bool

config CPU_NO_EFFICIENT_FFS
	def_bool n

config HAVE_ARCH_VMAP_STACK
	def_bool n
	help
	  An arch should select this symbol if it can support kernel stacks
	  in vmalloc space.  This means:

	  - vmalloc space must be large enough to hold many kernel stacks.
	    This may rule out many 32-bit architectures.

	  - Stacks in vmalloc space need to work reliably.  For example, if
	    vmap page tables are created on demand, either this mechanism
	    needs to work while the stack points to a virtual address with
	    unpopulated page tables or arch code (switch_to() and switch_mm(),
	    most likely) needs to ensure that the stack's page table entries
	    are populated before running on a possibly unpopulated stack.

	  - If the stack overflows into a guard page, something reasonable
	    should happen.  The definition of "reasonable" is flexible, but
	    instantly rebooting without logging anything would be unfriendly.

config VMAP_STACK
	default y
	bool "Use a virtually-mapped stack"
	depends on HAVE_ARCH_VMAP_STACK
	depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
	help
	  Enable this if you want the use virtually-mapped kernel stacks
	  with guard pages.  This causes kernel stack overflows to be
	  caught immediately rather than causing difficult-to-diagnose
	  corruption.

	  To use this with software KASAN modes, the architecture must support
	  backing virtual mappings with real shadow memory, and KASAN_VMALLOC
	  must be enabled.

config ARCH_OPTIONAL_KERNEL_RWX
	def_bool n

config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
	def_bool n

config ARCH_HAS_STRICT_KERNEL_RWX
	def_bool n

config STRICT_KERNEL_RWX
	bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
	depends on ARCH_HAS_STRICT_KERNEL_RWX
	default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
	help
	  If this is set, kernel text and rodata memory will be made read-only,
	  and non-text memory will be made non-executable. This provides
	  protection against certain security exploits (e.g. executing the heap
	  or modifying text)

	  These features are considered standard security practice these days.
	  You should say Y here in almost all cases.

config ARCH_HAS_STRICT_MODULE_RWX
	def_bool n

config STRICT_MODULE_RWX
	bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
	depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
	default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
	help
	  If this is set, module text and rodata memory will be made read-only,
	  and non-text memory will be made non-executable. This provides
	  protection against certain security exploits (e.g. writing to text)

# select if the architecture provides an asm/dma-direct.h header
config ARCH_HAS_PHYS_TO_DMA
	bool

config HAVE_ARCH_COMPILER_H
	bool
	help
	  An architecture can select this if it provides an
	  asm/compiler.h header that should be included after
	  linux/compiler-*.h in order to override macro definitions that those
	  headers generally provide.

config HAVE_ARCH_PREL32_RELOCATIONS
	bool
	help
	  May be selected by an architecture if it supports place-relative
	  32-bit relocations, both in the toolchain and in the module loader,
	  in which case relative references can be used in special sections
	  for PCI fixup, initcalls etc which are only half the size on 64 bit
	  architectures, and don't require runtime relocation on relocatable
	  kernels.

config ARCH_USE_MEMREMAP_PROT
	bool

config LOCK_EVENT_COUNTS
	bool "Locking event counts collection"
	depends on DEBUG_FS
	help
	  Enable light-weight counting of various locking related events
	  in the system with minimal performance impact. This reduces
	  the chance of application behavior change because of timing
	  differences. The counts are reported via debugfs.

# Select if the architecture has support for applying RELR relocations.
config ARCH_HAS_RELR
	bool

config RELR
	bool "Use RELR relocation packing"
	depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
	default y
	help
	  Store the kernel's dynamic relocations in the RELR relocation packing
	  format. Requires a compatible linker (LLD supports this feature), as
	  well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
	  are compatible).

config ARCH_HAS_MEM_ENCRYPT
	bool

config ARCH_HAS_CC_PLATFORM
	bool

config HAVE_SPARSE_SYSCALL_NR
       bool
       help
          An architecture should select this if its syscall numbering is sparse
	  to save space. For example, MIPS architecture has a syscall array with
	  entries at 4000, 5000 and 6000 locations. This option turns on syscall
	  related optimizations for a given architecture.

config ARCH_HAS_VDSO_DATA
	bool

config HAVE_STATIC_CALL
	bool

config HAVE_STATIC_CALL_INLINE
	bool
	depends on HAVE_STATIC_CALL

config ARCH_WANT_LD_ORPHAN_WARN
	bool
	help
	  An arch should select this symbol once all linker sections are explicitly
	  included, size-asserted, or discarded in the linker scripts. This is
	  important because we never want expected sections to be placed heuristically
	  by the linker, since the locations of such sections can change between linker
	  versions.

config ARCH_SPLIT_ARG64
	bool
	help
	   If a 32-bit architecture requires 64-bit arguments to be split into
	   pairs of 32-bit arguments, select this option.

config ARCH_HAS_NONLEAF_PMD_YOUNG
	bool
	depends on PGTABLE_LEVELS > 2
	help
	  Architectures that select this option are capable of setting the
	  accessed bit in non-leaf PMD entries when using them as part of linear
	  address translations. Page table walkers that clear the accessed bit
	  may use this capability to reduce their search space.

source "kernel/gcov/Kconfig"

source "scripts/gcc-plugins/Kconfig"

endmenu