1 # SPDX-License-Identifier: GPL-2.0
3 # General architecture dependent options
7 # Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can
8 # override the default values in this file.
10 source "arch/$(SRCARCH)/Kconfig"
12 menu "General architecture-dependent options"
36 depends on HAVE_KPROBES
39 Kprobes allows you to trap at almost any kernel address and
40 execute a callback function. register_kprobe() establishes
41 a probepoint and specifies the callback. Kprobes is useful
42 for kernel debugging, non-intrusive instrumentation and testing.
46 bool "Optimize very unlikely/likely branches"
47 depends on HAVE_ARCH_JUMP_LABEL
48 depends on CC_HAS_ASM_GOTO
50 This option enables a transparent branch optimization that
51 makes certain almost-always-true or almost-always-false branch
52 conditions even cheaper to execute within the kernel.
54 Certain performance-sensitive kernel code, such as trace points,
55 scheduler functionality, networking code and KVM have such
56 branches and include support for this optimization technique.
58 If it is detected that the compiler has support for "asm goto",
59 the kernel will compile such branches with just a nop
60 instruction. When the condition flag is toggled to true, the
61 nop will be converted to a jump instruction to execute the
62 conditional block of instructions.
64 This technique lowers overhead and stress on the branch prediction
65 of the processor and generally makes the kernel faster. The update
66 of the condition is slower, but those are always very rare.
68 ( On 32-bit x86, the necessary options added to the compiler
69 flags may increase the size of the kernel slightly. )
71 config STATIC_KEYS_SELFTEST
72 bool "Static key selftest"
75 Boot time self-test of the branch patching code.
77 config STATIC_CALL_SELFTEST
78 bool "Static call selftest"
79 depends on HAVE_STATIC_CALL
81 Boot time self-test of the call patching code.
85 depends on KPROBES && HAVE_OPTPROBES
86 select TASKS_RCU if PREEMPTION
88 config KPROBES_ON_FTRACE
90 depends on KPROBES && HAVE_KPROBES_ON_FTRACE
91 depends on DYNAMIC_FTRACE_WITH_REGS
93 If function tracer is enabled and the arch supports full
94 passing of pt_regs to function tracing, then kprobes can
95 optimize on top of function tracing.
99 depends on ARCH_SUPPORTS_UPROBES
101 Uprobes is the user-space counterpart to kprobes: they
102 enable instrumentation applications (such as 'perf probe')
103 to establish unintrusive probes in user-space binaries and
104 libraries, by executing handler functions when the probes
105 are hit by user-space applications.
107 ( These probes come in the form of single-byte breakpoints,
108 managed by the kernel and kept transparent to the probed
111 config HAVE_64BIT_ALIGNED_ACCESS
112 def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
114 Some architectures require 64 bit accesses to be 64 bit
115 aligned, which also requires structs containing 64 bit values
116 to be 64 bit aligned too. This includes some 32 bit
117 architectures which can do 64 bit accesses, as well as 64 bit
118 architectures without unaligned access.
120 This symbol should be selected by an architecture if 64 bit
121 accesses are required to be 64 bit aligned in this way even
122 though it is not a 64 bit architecture.
124 See Documentation/core-api/unaligned-memory-access.rst for
125 more information on the topic of unaligned memory accesses.
127 config HAVE_EFFICIENT_UNALIGNED_ACCESS
130 Some architectures are unable to perform unaligned accesses
131 without the use of get_unaligned/put_unaligned. Others are
132 unable to perform such accesses efficiently (e.g. trap on
133 unaligned access and require fixing it up in the exception
136 This symbol should be selected by an architecture if it can
137 perform unaligned accesses efficiently to allow different
138 code paths to be selected for these cases. Some network
139 drivers, for example, could opt to not fix up alignment
140 problems with received packets if doing so would not help
143 See Documentation/core-api/unaligned-memory-access.rst for more
144 information on the topic of unaligned memory accesses.
146 config ARCH_USE_BUILTIN_BSWAP
149 Modern versions of GCC (since 4.4) have builtin functions
150 for handling byte-swapping. Using these, instead of the old
151 inline assembler that the architecture code provides in the
152 __arch_bswapXX() macros, allows the compiler to see what's
153 happening and offers more opportunity for optimisation. In
154 particular, the compiler will be able to combine the byteswap
155 with a nearby load or store and use load-and-swap or
156 store-and-swap instructions if the architecture has them. It
157 should almost *never* result in code which is worse than the
158 hand-coded assembler in <asm/swab.h>. But just in case it
159 does, the use of the builtins is optional.
161 Any architecture with load-and-swap or store-and-swap
162 instructions should set this. And it shouldn't hurt to set it
163 on architectures that don't have such instructions.
167 depends on KPROBES && HAVE_KRETPROBES
169 config USER_RETURN_NOTIFIER
171 depends on HAVE_USER_RETURN_NOTIFIER
173 Provide a kernel-internal notification when a cpu is about to
176 config HAVE_IOREMAP_PROT
182 config HAVE_KRETPROBES
185 config HAVE_OPTPROBES
188 config HAVE_KPROBES_ON_FTRACE
191 config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
194 Since kretprobes modifies return address on the stack, the
195 stacktrace may see the kretprobe trampoline address instead
196 of correct one. If the architecture stacktrace code and
197 unwinder can adjust such entries, select this configuration.
199 config HAVE_FUNCTION_ERROR_INJECTION
205 config TRACE_IRQFLAGS_SUPPORT
209 # An arch should select this if it provides all these things:
211 # task_pt_regs() in asm/processor.h or asm/ptrace.h
212 # arch_has_single_step() if there is hardware single-step support
213 # arch_has_block_step() if there is hardware block-step support
214 # asm/syscall.h supplying asm-generic/syscall.h interface
215 # linux/regset.h user_regset interfaces
216 # CORE_DUMP_USE_REGSET #define'd in linux/elf.h
217 # TIF_SYSCALL_TRACE calls tracehook_report_syscall_{entry,exit}
218 # TIF_NOTIFY_RESUME calls tracehook_notify_resume()
219 # signal delivery calls tracehook_signal_handler()
221 config HAVE_ARCH_TRACEHOOK
224 config HAVE_DMA_CONTIGUOUS
227 config GENERIC_SMP_IDLE_THREAD
230 config GENERIC_IDLE_POLL_SETUP
233 config ARCH_HAS_FORTIFY_SOURCE
236 An architecture should select this when it can successfully
237 build and run with CONFIG_FORTIFY_SOURCE.
240 # Select if the arch provides a historic keepinit alias for the retain_initrd
241 # command line option
243 config ARCH_HAS_KEEPINITRD
246 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
247 config ARCH_HAS_SET_MEMORY
250 # Select if arch has all set_direct_map_invalid/default() functions
251 config ARCH_HAS_SET_DIRECT_MAP
255 # Select if the architecture provides the arch_dma_set_uncached symbol to
256 # either provide an uncached segment alias for a DMA allocation, or
257 # to remap the page tables in place.
259 config ARCH_HAS_DMA_SET_UNCACHED
263 # Select if the architectures provides the arch_dma_clear_uncached symbol
264 # to undo an in-place page table remap for uncached access.
266 config ARCH_HAS_DMA_CLEAR_UNCACHED
269 # Select if arch init_task must go in the __init_task_data section
270 config ARCH_TASK_STRUCT_ON_STACK
273 # Select if arch has its private alloc_task_struct() function
274 config ARCH_TASK_STRUCT_ALLOCATOR
277 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
279 depends on !ARCH_TASK_STRUCT_ALLOCATOR
281 An architecture should select this to provide hardened usercopy
282 knowledge about what region of the thread_struct should be
283 whitelisted for copying to userspace. Normally this is only the
284 FPU registers. Specifically, arch_thread_struct_whitelist()
285 should be implemented. Without this, the entire thread_struct
286 field in task_struct will be left whitelisted.
288 # Select if arch has its private alloc_thread_stack() function
289 config ARCH_THREAD_STACK_ALLOCATOR
292 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
293 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
296 config ARCH_WANTS_NO_INSTR
299 An architecture should select this if the noinstr macro is being used on
300 functions to denote that the toolchain should avoid instrumenting such
301 functions and is required for correctness.
303 config ARCH_32BIT_OFF_T
307 All new 32-bit architectures should have 64-bit off_t type on
308 userspace side which corresponds to the loff_t kernel type. This
309 is the requirement for modern ABIs. Some existing architectures
310 still support 32-bit off_t. This option is enabled for all such
311 architectures explicitly.
313 # Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
314 config ARCH_32BIT_USTAT_F_TINODE
317 config HAVE_ASM_MODVERSIONS
320 This symbol should be selected by an architecture if it provides
321 <asm/asm-prototypes.h> to support the module versioning for symbols
322 exported from assembly code.
324 config HAVE_REGS_AND_STACK_ACCESS_API
327 This symbol should be selected by an architecture if it supports
328 the API needed to access registers and stack entries from pt_regs,
329 declared in asm/ptrace.h
330 For example the kprobes-based event tracer needs this API.
334 depends on HAVE_REGS_AND_STACK_ACCESS_API
336 This symbol should be selected by an architecture if it
337 supports an implementation of restartable sequences.
339 config HAVE_FUNCTION_ARG_ACCESS_API
342 This symbol should be selected by an architecture if it supports
343 the API needed to access function arguments from pt_regs,
344 declared in asm/ptrace.h
346 config HAVE_HW_BREAKPOINT
348 depends on PERF_EVENTS
350 config HAVE_MIXED_BREAKPOINTS_REGS
352 depends on HAVE_HW_BREAKPOINT
354 Depending on the arch implementation of hardware breakpoints,
355 some of them have separate registers for data and instruction
356 breakpoints addresses, others have mixed registers to store
357 them but define the access type in a control register.
358 Select this option if your arch implements breakpoints under the
361 config HAVE_USER_RETURN_NOTIFIER
364 config HAVE_PERF_EVENTS_NMI
367 System hardware can generate an NMI using the perf event
368 subsystem. Also has support for calculating CPU cycle events
369 to determine how many clock cycles in a given period.
371 config HAVE_HARDLOCKUP_DETECTOR_PERF
373 depends on HAVE_PERF_EVENTS_NMI
375 The arch chooses to use the generic perf-NMI-based hardlockup
376 detector. Must define HAVE_PERF_EVENTS_NMI.
378 config HAVE_NMI_WATCHDOG
382 The arch provides a low level NMI watchdog. It provides
383 asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
385 config HAVE_HARDLOCKUP_DETECTOR_ARCH
387 select HAVE_NMI_WATCHDOG
389 The arch chooses to provide its own hardlockup detector, which is
390 a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
391 interfaces and parameters provided by hardlockup detector subsystem.
393 config HAVE_PERF_REGS
396 Support selective register dumps for perf events. This includes
397 bit-mapping of each registers and a unique architecture id.
399 config HAVE_PERF_USER_STACK_DUMP
402 Support user stack dumps for perf event samples. This needs
403 access to the user stack pointer which is not unified across
406 config HAVE_ARCH_JUMP_LABEL
409 config HAVE_ARCH_JUMP_LABEL_RELATIVE
412 config MMU_GATHER_TABLE_FREE
415 config MMU_GATHER_RCU_TABLE_FREE
417 select MMU_GATHER_TABLE_FREE
419 config MMU_GATHER_PAGE_SIZE
422 config MMU_GATHER_NO_RANGE
425 config MMU_GATHER_NO_GATHER
427 depends on MMU_GATHER_TABLE_FREE
429 config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
432 Temporary select until all architectures can be converted to have
433 irqs disabled over activate_mm. Architectures that do IPI based TLB
434 shootdowns should enable this.
436 config ARCH_HAVE_NMI_SAFE_CMPXCHG
439 config HAVE_ALIGNED_STRUCT_PAGE
442 This makes sure that struct pages are double word aligned and that
443 e.g. the SLUB allocator can perform double word atomic operations
444 on a struct page for better performance. However selecting this
445 might increase the size of a struct page by a word.
447 config HAVE_CMPXCHG_LOCAL
450 config HAVE_CMPXCHG_DOUBLE
453 config ARCH_WEAK_RELEASE_ACQUIRE
456 config ARCH_WANT_IPC_PARSE_VERSION
459 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
462 config ARCH_WANT_OLD_COMPAT_IPC
463 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
466 config HAVE_ARCH_SECCOMP
469 An arch should select this symbol to support seccomp mode 1 (the fixed
470 syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
471 and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
472 - __NR_seccomp_read_32
473 - __NR_seccomp_write_32
474 - __NR_seccomp_exit_32
475 - __NR_seccomp_sigreturn_32
477 config HAVE_ARCH_SECCOMP_FILTER
479 select HAVE_ARCH_SECCOMP
481 An arch should select this symbol if it provides all of these things:
482 - all the requirements for HAVE_ARCH_SECCOMP
484 - syscall_get_arguments()
486 - syscall_set_return_value()
487 - SIGSYS siginfo_t support
488 - secure_computing is called from a ptrace_event()-safe context
489 - secure_computing return value is checked and a return value of -1
490 results in the system call being skipped immediately.
491 - seccomp syscall wired up
492 - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
493 SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
494 COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
497 prompt "Enable seccomp to safely execute untrusted bytecode"
499 depends on HAVE_ARCH_SECCOMP
501 This kernel feature is useful for number crunching applications
502 that may need to handle untrusted bytecode during their
503 execution. By using pipes or other transports made available
504 to the process as file descriptors supporting the read/write
505 syscalls, it's possible to isolate those applications in their
506 own address space using seccomp. Once seccomp is enabled via
507 prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
508 disabled and the task is only allowed to execute a few safe
509 syscalls defined by each seccomp mode.
513 config SECCOMP_FILTER
515 depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
517 Enable tasks to build secure computing environments defined
518 in terms of Berkeley Packet Filter programs which implement
519 task-defined system call filtering polices.
521 See Documentation/userspace-api/seccomp_filter.rst for details.
523 config SECCOMP_CACHE_DEBUG
524 bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
525 depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
528 This enables the /proc/pid/seccomp_cache interface to monitor
529 seccomp cache data. The file format is subject to change. Reading
530 the file requires CAP_SYS_ADMIN.
532 This option is for debugging only. Enabling presents the risk that
533 an adversary may be able to infer the seccomp filter logic.
537 config HAVE_ARCH_STACKLEAK
540 An architecture should select this if it has the code which
541 fills the used part of the kernel stack with the STACKLEAK_POISON
542 value before returning from system calls.
544 config HAVE_STACKPROTECTOR
547 An arch should select this symbol if:
548 - it has implemented a stack canary (e.g. __stack_chk_guard)
550 config STACKPROTECTOR
551 bool "Stack Protector buffer overflow detection"
552 depends on HAVE_STACKPROTECTOR
553 depends on $(cc-option,-fstack-protector)
556 This option turns on the "stack-protector" GCC feature. This
557 feature puts, at the beginning of functions, a canary value on
558 the stack just before the return address, and validates
559 the value just before actually returning. Stack based buffer
560 overflows (that need to overwrite this return address) now also
561 overwrite the canary, which gets detected and the attack is then
562 neutralized via a kernel panic.
564 Functions will have the stack-protector canary logic added if they
565 have an 8-byte or larger character array on the stack.
567 This feature requires gcc version 4.2 or above, or a distribution
568 gcc with the feature backported ("-fstack-protector").
570 On an x86 "defconfig" build, this feature adds canary checks to
571 about 3% of all kernel functions, which increases kernel code size
574 config STACKPROTECTOR_STRONG
575 bool "Strong Stack Protector"
576 depends on STACKPROTECTOR
577 depends on $(cc-option,-fstack-protector-strong)
580 Functions will have the stack-protector canary logic added in any
581 of the following conditions:
583 - local variable's address used as part of the right hand side of an
584 assignment or function argument
585 - local variable is an array (or union containing an array),
586 regardless of array type or length
587 - uses register local variables
589 This feature requires gcc version 4.9 or above, or a distribution
590 gcc with the feature backported ("-fstack-protector-strong").
592 On an x86 "defconfig" build, this feature adds canary checks to
593 about 20% of all kernel functions, which increases the kernel code
596 config ARCH_SUPPORTS_SHADOW_CALL_STACK
599 An architecture should select this if it supports the compiler's
600 Shadow Call Stack and implements runtime support for shadow stack
603 config SHADOW_CALL_STACK
604 bool "Shadow Call Stack"
605 depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
606 depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
608 This option enables the compiler's Shadow Call Stack, which
609 uses a shadow stack to protect function return addresses from
610 being overwritten by an attacker. More information can be found
611 in the compiler's documentation:
613 - Clang: https://clang.llvm.org/docs/ShadowCallStack.html
614 - GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options
616 Note that security guarantees in the kernel differ from the
617 ones documented for user space. The kernel must store addresses
618 of shadow stacks in memory, which means an attacker capable of
619 reading and writing arbitrary memory may be able to locate them
620 and hijack control flow by modifying the stacks.
625 Selected if the kernel will be built using the compiler's LTO feature.
631 Selected if the kernel will be built using Clang's LTO feature.
633 config ARCH_SUPPORTS_LTO_CLANG
636 An architecture should select this option if it supports:
637 - compiling with Clang,
638 - compiling inline assembly with Clang's integrated assembler,
639 - and linking with LLD.
641 config ARCH_SUPPORTS_LTO_CLANG_THIN
644 An architecture should select this option if it can support Clang's
649 depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM
650 depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
651 depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
652 depends on ARCH_SUPPORTS_LTO_CLANG
653 depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
654 depends on !KASAN || KASAN_HW_TAGS
655 depends on !GCOV_KERNEL
657 The compiler and Kconfig options support building with Clang's
661 prompt "Link Time Optimization (LTO)"
664 This option enables Link Time Optimization (LTO), which allows the
665 compiler to optimize binaries globally.
667 If unsure, select LTO_NONE. Note that LTO is very resource-intensive
668 so it's disabled by default.
673 Build the kernel normally, without Link Time Optimization (LTO).
675 config LTO_CLANG_FULL
676 bool "Clang Full LTO (EXPERIMENTAL)"
677 depends on HAS_LTO_CLANG
678 depends on !COMPILE_TEST
681 This option enables Clang's full Link Time Optimization (LTO), which
682 allows the compiler to optimize the kernel globally. If you enable
683 this option, the compiler generates LLVM bitcode instead of ELF
684 object files, and the actual compilation from bitcode happens at
685 the LTO link step, which may take several minutes depending on the
686 kernel configuration. More information can be found from LLVM's
689 https://llvm.org/docs/LinkTimeOptimization.html
691 During link time, this option can use a large amount of RAM, and
692 may take much longer than the ThinLTO option.
694 config LTO_CLANG_THIN
695 bool "Clang ThinLTO (EXPERIMENTAL)"
696 depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
699 This option enables Clang's ThinLTO, which allows for parallel
700 optimization and faster incremental compiles compared to the
701 CONFIG_LTO_CLANG_FULL option. More information can be found
702 from Clang's documentation:
704 https://clang.llvm.org/docs/ThinLTO.html
709 config ARCH_SUPPORTS_CFI_CLANG
712 An architecture should select this option if it can support Clang's
713 Control-Flow Integrity (CFI) checking.
716 bool "Use Clang's Control Flow Integrity (CFI)"
717 depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG
719 # - https://bugs.llvm.org/show_bug.cgi?id=46258
720 # - https://bugs.llvm.org/show_bug.cgi?id=47479
721 depends on CLANG_VERSION >= 120000
724 This option enables Clang’s forward-edge Control Flow Integrity
725 (CFI) checking, where the compiler injects a runtime check to each
726 indirect function call to ensure the target is a valid function with
727 the correct static type. This restricts possible call targets and
728 makes it more difficult for an attacker to exploit bugs that allow
729 the modification of stored function pointers. More information can be
730 found from Clang's documentation:
732 https://clang.llvm.org/docs/ControlFlowIntegrity.html
734 config CFI_CLANG_SHADOW
735 bool "Use CFI shadow to speed up cross-module checks"
737 depends on CFI_CLANG && MODULES
739 If you select this option, the kernel builds a fast look-up table of
740 CFI check functions in loaded modules to reduce performance overhead.
744 config CFI_PERMISSIVE
745 bool "Use CFI in permissive mode"
748 When selected, Control Flow Integrity (CFI) violations result in a
749 warning instead of a kernel panic. This option should only be used
750 for finding indirect call type mismatches during development.
754 config HAVE_ARCH_WITHIN_STACK_FRAMES
757 An architecture should select this if it can walk the kernel stack
758 frames to determine if an object is part of either the arguments
759 or local variables (i.e. that it excludes saved return addresses,
760 and similar) by implementing an inline arch_within_stack_frames(),
761 which is used by CONFIG_HARDENED_USERCOPY.
763 config HAVE_CONTEXT_TRACKING
766 Provide kernel/user boundaries probes necessary for subsystems
767 that need it, such as userspace RCU extended quiescent state.
768 Syscalls need to be wrapped inside user_exit()-user_enter(), either
769 optimized behind static key or through the slow path using TIF_NOHZ
770 flag. Exceptions handlers must be wrapped as well. Irqs are already
771 protected inside rcu_irq_enter/rcu_irq_exit() but preemption or signal
772 handling on irq exit still need to be protected.
774 config HAVE_CONTEXT_TRACKING_OFFSTACK
777 Architecture neither relies on exception_enter()/exception_exit()
778 nor on schedule_user(). Also preempt_schedule_notrace() and
779 preempt_schedule_irq() can't be called in a preemptible section
780 while context tracking is CONTEXT_USER. This feature reflects a sane
781 entry implementation where the following requirements are met on
782 critical entry code, ie: before user_exit() or after user_enter():
784 - Critical entry code isn't preemptible (or better yet:
786 - No use of RCU read side critical sections, unless rcu_nmi_enter()
788 - No use of instrumentation, unless instrumentation_begin() got
794 Arch relies on TIF_NOHZ and syscall slow path to implement context
795 tracking calls to user_enter()/user_exit().
797 config HAVE_VIRT_CPU_ACCOUNTING
800 config HAVE_VIRT_CPU_ACCOUNTING_IDLE
803 Architecture has its own way to account idle CPU time and therefore
804 doesn't implement vtime_account_idle().
806 config ARCH_HAS_SCALED_CPUTIME
809 config HAVE_VIRT_CPU_ACCOUNTING_GEN
813 With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
814 Before enabling this option, arch code must be audited
815 to ensure there are no races in concurrent read/write of
816 cputime_t. For example, reading/writing 64-bit cputime_t on
817 some 32-bit arches may require multiple accesses, so proper
818 locking is needed to protect against concurrent accesses.
820 config HAVE_IRQ_TIME_ACCOUNTING
823 Archs need to ensure they use a high enough resolution clock to
824 support irq time accounting and then call enable_sched_clock_irqtime().
829 Architectures that select this are able to move page tables at the
830 PUD level. If there are only 3 page table levels, the move effectively
831 happens at the PGD level.
836 Archs that select this are able to move page tables at the PMD level.
838 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
841 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
844 config HAVE_ARCH_HUGE_VMAP
848 # Archs that select this would be capable of PMD-sized vmaps (i.e.,
849 # arch_vmap_pmd_supported() returns true), and they must make no assumptions
850 # that vmalloc memory is mapped with PAGE_SIZE ptes. The VM_NO_HUGE_VMAP flag
851 # can be used to prohibit arch-specific allocations from using hugepages to
852 # help with this (e.g., modules may require it).
854 config HAVE_ARCH_HUGE_VMALLOC
855 depends on HAVE_ARCH_HUGE_VMAP
858 config ARCH_WANT_HUGE_PMD_SHARE
861 config HAVE_ARCH_SOFT_DIRTY
864 config HAVE_MOD_ARCH_SPECIFIC
867 The arch uses struct mod_arch_specific to store data. Many arches
868 just need a simple module loader without arch specific data - those
869 should not enable this.
871 config MODULES_USE_ELF_RELA
874 Modules only use ELF RELA relocations. Modules with ELF REL
875 relocations will give an error.
877 config MODULES_USE_ELF_REL
880 Modules only use ELF REL relocations. Modules with ELF RELA
881 relocations will give an error.
883 config HAVE_IRQ_EXIT_ON_IRQ_STACK
886 Architecture doesn't only execute the irq handler on the irq stack
887 but also irq_exit(). This way we can process softirqs on this irq
888 stack instead of switching to a new one when we call __do_softirq()
889 in the end of an hardirq.
890 This spares a stack switch and improves cache usage on softirq
893 config HAVE_SOFTIRQ_ON_OWN_STACK
896 Architecture provides a function to run __do_softirq() on a
899 config ALTERNATE_USER_ADDRESS_SPACE
902 Architectures set this when the CPU uses separate address
903 spaces for kernel and user space pointers. In this case, the
904 access_ok() check on a __user pointer is skipped.
906 config PGTABLE_LEVELS
910 config ARCH_HAS_ELF_RANDOMIZE
913 An architecture supports choosing randomized locations for
914 stack, mmap, brk, and ET_DYN. Defined functions:
916 - arch_randomize_brk()
918 config HAVE_ARCH_MMAP_RND_BITS
921 An arch should select this symbol if it supports setting a variable
922 number of bits for use in establishing the base address for mmap
923 allocations, has MMU enabled and provides values for both:
924 - ARCH_MMAP_RND_BITS_MIN
925 - ARCH_MMAP_RND_BITS_MAX
927 config HAVE_EXIT_THREAD
930 An architecture implements exit_thread.
932 config ARCH_MMAP_RND_BITS_MIN
935 config ARCH_MMAP_RND_BITS_MAX
938 config ARCH_MMAP_RND_BITS_DEFAULT
941 config ARCH_MMAP_RND_BITS
942 int "Number of bits to use for ASLR of mmap base address" if EXPERT
943 range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
944 default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
945 default ARCH_MMAP_RND_BITS_MIN
946 depends on HAVE_ARCH_MMAP_RND_BITS
948 This value can be used to select the number of bits to use to
949 determine the random offset to the base address of vma regions
950 resulting from mmap allocations. This value will be bounded
951 by the architecture's minimum and maximum supported values.
953 This value can be changed after boot using the
954 /proc/sys/vm/mmap_rnd_bits tunable
956 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
959 An arch should select this symbol if it supports running applications
960 in compatibility mode, supports setting a variable number of bits for
961 use in establishing the base address for mmap allocations, has MMU
962 enabled and provides values for both:
963 - ARCH_MMAP_RND_COMPAT_BITS_MIN
964 - ARCH_MMAP_RND_COMPAT_BITS_MAX
966 config ARCH_MMAP_RND_COMPAT_BITS_MIN
969 config ARCH_MMAP_RND_COMPAT_BITS_MAX
972 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
975 config ARCH_MMAP_RND_COMPAT_BITS
976 int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
977 range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
978 default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
979 default ARCH_MMAP_RND_COMPAT_BITS_MIN
980 depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
982 This value can be used to select the number of bits to use to
983 determine the random offset to the base address of vma regions
984 resulting from mmap allocations for compatible applications This
985 value will be bounded by the architecture's minimum and maximum
988 This value can be changed after boot using the
989 /proc/sys/vm/mmap_rnd_compat_bits tunable
991 config HAVE_ARCH_COMPAT_MMAP_BASES
994 This allows 64bit applications to invoke 32-bit mmap() syscall
995 and vice-versa 32-bit applications to call 64-bit mmap().
996 Required for applications doing different bitness syscalls.
998 config PAGE_SIZE_LESS_THAN_64KB
1000 depends on !ARM64_64K_PAGES
1001 depends on !IA64_PAGE_SIZE_64KB
1002 depends on !PAGE_SIZE_64KB
1003 depends on !PARISC_PAGE_SIZE_64KB
1004 depends on !PPC_64K_PAGES
1005 depends on PAGE_SIZE_LESS_THAN_256KB
1007 config PAGE_SIZE_LESS_THAN_256KB
1009 depends on !PPC_256K_PAGES
1010 depends on !PAGE_SIZE_256KB
1012 # This allows to use a set of generic functions to determine mmap base
1013 # address by giving priority to top-down scheme only if the process
1014 # is not in legacy mode (compat task, unlimited stack size or
1015 # sysctl_legacy_va_layout).
1016 # Architecture that selects this option can provide its own version of:
1018 config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
1021 select ARCH_HAS_ELF_RANDOMIZE
1023 config HAVE_STACK_VALIDATION
1026 Architecture supports the 'objtool check' host tool command, which
1027 performs compile-time stack metadata validation.
1029 config HAVE_RELIABLE_STACKTRACE
1032 Architecture has either save_stack_trace_tsk_reliable() or
1033 arch_stack_walk_reliable() function which only returns a stack trace
1034 if it can guarantee the trace is reliable.
1036 config HAVE_ARCH_HASH
1040 If this is set, the architecture provides an <asm/hash.h>
1041 file which provides platform-specific implementations of some
1042 functions in <linux/hash.h> or fs/namei.c.
1044 config HAVE_ARCH_NVRAM_OPS
1053 config CLONE_BACKWARDS
1056 Architecture has tls passed as the 4th argument of clone(2),
1059 config CLONE_BACKWARDS2
1062 Architecture has the first two arguments of clone(2) swapped.
1064 config CLONE_BACKWARDS3
1067 Architecture has tls passed as the 3rd argument of clone(2),
1070 config ODD_RT_SIGACTION
1073 Architecture has unusual rt_sigaction(2) arguments
1075 config OLD_SIGSUSPEND
1078 Architecture has old sigsuspend(2) syscall, of one-argument variety
1080 config OLD_SIGSUSPEND3
1083 Even weirder antique ABI - three-argument sigsuspend(2)
1085 config OLD_SIGACTION
1088 Architecture has old sigaction(2) syscall. Nope, not the same
1089 as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
1090 but fairly different variant of sigaction(2), thanks to OSF/1
1093 config COMPAT_OLD_SIGACTION
1096 config COMPAT_32BIT_TIME
1097 bool "Provide system calls for 32-bit time_t"
1098 default !64BIT || COMPAT
1100 This enables 32 bit time_t support in addition to 64 bit time_t support.
1101 This is relevant on all 32-bit architectures, and 64-bit architectures
1102 as part of compat syscall handling.
1104 config ARCH_NO_PREEMPT
1107 config ARCH_EPHEMERAL_INODES
1110 An arch should select this symbol if it doesn't keep track of inode
1111 instances on its own, but instead relies on something else (e.g. the
1112 host kernel for an UML kernel).
1114 config ARCH_SUPPORTS_RT
1117 config CPU_NO_EFFICIENT_FFS
1120 config HAVE_ARCH_VMAP_STACK
1123 An arch should select this symbol if it can support kernel stacks
1124 in vmalloc space. This means:
1126 - vmalloc space must be large enough to hold many kernel stacks.
1127 This may rule out many 32-bit architectures.
1129 - Stacks in vmalloc space need to work reliably. For example, if
1130 vmap page tables are created on demand, either this mechanism
1131 needs to work while the stack points to a virtual address with
1132 unpopulated page tables or arch code (switch_to() and switch_mm(),
1133 most likely) needs to ensure that the stack's page table entries
1134 are populated before running on a possibly unpopulated stack.
1136 - If the stack overflows into a guard page, something reasonable
1137 should happen. The definition of "reasonable" is flexible, but
1138 instantly rebooting without logging anything would be unfriendly.
1142 bool "Use a virtually-mapped stack"
1143 depends on HAVE_ARCH_VMAP_STACK
1144 depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
1146 Enable this if you want the use virtually-mapped kernel stacks
1147 with guard pages. This causes kernel stack overflows to be
1148 caught immediately rather than causing difficult-to-diagnose
1151 To use this with software KASAN modes, the architecture must support
1152 backing virtual mappings with real shadow memory, and KASAN_VMALLOC
1155 config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1158 An arch should select this symbol if it can support kernel stack
1159 offset randomization with calls to add_random_kstack_offset()
1160 during syscall entry and choose_random_kstack_offset() during
1161 syscall exit. Careful removal of -fstack-protector-strong and
1162 -fstack-protector should also be applied to the entry code and
1163 closely examined, as the artificial stack bump looks like an array
1164 to the compiler, so it will attempt to add canary checks regardless
1165 of the static branch state.
1167 config RANDOMIZE_KSTACK_OFFSET
1168 bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT
1170 depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1171 depends on INIT_STACK_NONE || !CC_IS_CLANG || CLANG_VERSION >= 140000
1173 The kernel stack offset can be randomized (after pt_regs) by
1174 roughly 5 bits of entropy, frustrating memory corruption
1175 attacks that depend on stack address determinism or
1176 cross-syscall address exposures.
1178 The feature is controlled via the "randomize_kstack_offset=on/off"
1179 kernel boot param, and if turned off has zero overhead due to its use
1180 of static branches (see JUMP_LABEL).
1184 config RANDOMIZE_KSTACK_OFFSET_DEFAULT
1185 bool "Default state of kernel stack offset randomization"
1186 depends on RANDOMIZE_KSTACK_OFFSET
1188 Kernel stack offset randomization is controlled by kernel boot param
1189 "randomize_kstack_offset=on/off", and this config chooses the default
1192 config ARCH_OPTIONAL_KERNEL_RWX
1195 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1198 config ARCH_HAS_STRICT_KERNEL_RWX
1201 config STRICT_KERNEL_RWX
1202 bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
1203 depends on ARCH_HAS_STRICT_KERNEL_RWX
1204 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1206 If this is set, kernel text and rodata memory will be made read-only,
1207 and non-text memory will be made non-executable. This provides
1208 protection against certain security exploits (e.g. executing the heap
1211 These features are considered standard security practice these days.
1212 You should say Y here in almost all cases.
1214 config ARCH_HAS_STRICT_MODULE_RWX
1217 config STRICT_MODULE_RWX
1218 bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1219 depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1220 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1222 If this is set, module text and rodata memory will be made read-only,
1223 and non-text memory will be made non-executable. This provides
1224 protection against certain security exploits (e.g. writing to text)
1226 # select if the architecture provides an asm/dma-direct.h header
1227 config ARCH_HAS_PHYS_TO_DMA
1230 config HAVE_ARCH_COMPILER_H
1233 An architecture can select this if it provides an
1234 asm/compiler.h header that should be included after
1235 linux/compiler-*.h in order to override macro definitions that those
1236 headers generally provide.
1238 config HAVE_ARCH_PREL32_RELOCATIONS
1241 May be selected by an architecture if it supports place-relative
1242 32-bit relocations, both in the toolchain and in the module loader,
1243 in which case relative references can be used in special sections
1244 for PCI fixup, initcalls etc which are only half the size on 64 bit
1245 architectures, and don't require runtime relocation on relocatable
1248 config ARCH_USE_MEMREMAP_PROT
1251 config LOCK_EVENT_COUNTS
1252 bool "Locking event counts collection"
1255 Enable light-weight counting of various locking related events
1256 in the system with minimal performance impact. This reduces
1257 the chance of application behavior change because of timing
1258 differences. The counts are reported via debugfs.
1260 # Select if the architecture has support for applying RELR relocations.
1261 config ARCH_HAS_RELR
1265 bool "Use RELR relocation packing"
1266 depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1269 Store the kernel's dynamic relocations in the RELR relocation packing
1270 format. Requires a compatible linker (LLD supports this feature), as
1271 well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1274 config ARCH_HAS_MEM_ENCRYPT
1277 config ARCH_HAS_CC_PLATFORM
1280 config HAVE_SPARSE_SYSCALL_NR
1283 An architecture should select this if its syscall numbering is sparse
1284 to save space. For example, MIPS architecture has a syscall array with
1285 entries at 4000, 5000 and 6000 locations. This option turns on syscall
1286 related optimizations for a given architecture.
1288 config ARCH_HAS_VDSO_DATA
1291 config HAVE_STATIC_CALL
1294 config HAVE_STATIC_CALL_INLINE
1296 depends on HAVE_STATIC_CALL
1298 config HAVE_PREEMPT_DYNAMIC
1301 config HAVE_PREEMPT_DYNAMIC_CALL
1303 depends on HAVE_STATIC_CALL
1304 select HAVE_PREEMPT_DYNAMIC
1306 An architecture should select this if it can handle the preemption
1307 model being selected at boot time using static calls.
1309 Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
1310 preemption function will be patched directly.
1312 Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
1313 call to a preemption function will go through a trampoline, and the
1314 trampoline will be patched.
1316 It is strongly advised to support inline static call to avoid any
1319 config HAVE_PREEMPT_DYNAMIC_KEY
1321 depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO
1322 select HAVE_PREEMPT_DYNAMIC
1324 An architecture should select this if it can handle the preemption
1325 model being selected at boot time using static keys.
1327 Each preemption function will be given an early return based on a
1328 static key. This should have slightly lower overhead than non-inline
1329 static calls, as this effectively inlines each trampoline into the
1330 start of its callee. This may avoid redundant work, and may
1331 integrate better with CFI schemes.
1333 This will have greater overhead than using inline static calls as
1334 the call to the preemption function cannot be entirely elided.
1336 config ARCH_WANT_LD_ORPHAN_WARN
1339 An arch should select this symbol once all linker sections are explicitly
1340 included, size-asserted, or discarded in the linker scripts. This is
1341 important because we never want expected sections to be placed heuristically
1342 by the linker, since the locations of such sections can change between linker
1345 config HAVE_ARCH_PFN_VALID
1348 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1351 config ARCH_SUPPORTS_PAGE_TABLE_CHECK
1354 config ARCH_SPLIT_ARG64
1357 If a 32-bit architecture requires 64-bit arguments to be split into
1358 pairs of 32-bit arguments, select this option.
1360 config ARCH_HAS_ELFCORE_COMPAT
1363 config ARCH_HAS_PARANOID_L1D_FLUSH
1366 config DYNAMIC_SIGFRAME
1369 # Select, if arch has a named attribute group bound to NUMA device nodes.
1370 config HAVE_ARCH_NODE_DEV_GROUP
1373 source "kernel/gcov/Kconfig"
1375 source "scripts/gcc-plugins/Kconfig"