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 Clang's Shadow
600 Call Stack and implements runtime support for shadow stack
603 config SHADOW_CALL_STACK
604 bool "Clang Shadow Call Stack"
605 depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK
606 depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
608 This option enables Clang's Shadow Call Stack, which uses a
609 shadow stack to protect function return addresses from being
610 overwritten by an attacker. More information can be found in
611 Clang's documentation:
613 https://clang.llvm.org/docs/ShadowCallStack.html
615 Note that security guarantees in the kernel differ from the
616 ones documented for user space. The kernel must store addresses
617 of shadow stacks in memory, which means an attacker capable of
618 reading and writing arbitrary memory may be able to locate them
619 and hijack control flow by modifying the stacks.
624 Selected if the kernel will be built using the compiler's LTO feature.
630 Selected if the kernel will be built using Clang's LTO feature.
632 config ARCH_SUPPORTS_LTO_CLANG
635 An architecture should select this option if it supports:
636 - compiling with Clang,
637 - compiling inline assembly with Clang's integrated assembler,
638 - and linking with LLD.
640 config ARCH_SUPPORTS_LTO_CLANG_THIN
643 An architecture should select this option if it can support Clang's
648 depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM
649 depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
650 depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
651 depends on ARCH_SUPPORTS_LTO_CLANG
652 depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
653 depends on !KASAN || KASAN_HW_TAGS
654 depends on !GCOV_KERNEL
656 The compiler and Kconfig options support building with Clang's
660 prompt "Link Time Optimization (LTO)"
663 This option enables Link Time Optimization (LTO), which allows the
664 compiler to optimize binaries globally.
666 If unsure, select LTO_NONE. Note that LTO is very resource-intensive
667 so it's disabled by default.
672 Build the kernel normally, without Link Time Optimization (LTO).
674 config LTO_CLANG_FULL
675 bool "Clang Full LTO (EXPERIMENTAL)"
676 depends on HAS_LTO_CLANG
677 depends on !COMPILE_TEST
680 This option enables Clang's full Link Time Optimization (LTO), which
681 allows the compiler to optimize the kernel globally. If you enable
682 this option, the compiler generates LLVM bitcode instead of ELF
683 object files, and the actual compilation from bitcode happens at
684 the LTO link step, which may take several minutes depending on the
685 kernel configuration. More information can be found from LLVM's
688 https://llvm.org/docs/LinkTimeOptimization.html
690 During link time, this option can use a large amount of RAM, and
691 may take much longer than the ThinLTO option.
693 config LTO_CLANG_THIN
694 bool "Clang ThinLTO (EXPERIMENTAL)"
695 depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
698 This option enables Clang's ThinLTO, which allows for parallel
699 optimization and faster incremental compiles compared to the
700 CONFIG_LTO_CLANG_FULL option. More information can be found
701 from Clang's documentation:
703 https://clang.llvm.org/docs/ThinLTO.html
708 config ARCH_SUPPORTS_CFI_CLANG
711 An architecture should select this option if it can support Clang's
712 Control-Flow Integrity (CFI) checking.
715 bool "Use Clang's Control Flow Integrity (CFI)"
716 depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG
718 # - https://bugs.llvm.org/show_bug.cgi?id=46258
719 # - https://bugs.llvm.org/show_bug.cgi?id=47479
720 depends on CLANG_VERSION >= 120000
723 This option enables Clang’s forward-edge Control Flow Integrity
724 (CFI) checking, where the compiler injects a runtime check to each
725 indirect function call to ensure the target is a valid function with
726 the correct static type. This restricts possible call targets and
727 makes it more difficult for an attacker to exploit bugs that allow
728 the modification of stored function pointers. More information can be
729 found from Clang's documentation:
731 https://clang.llvm.org/docs/ControlFlowIntegrity.html
733 config CFI_CLANG_SHADOW
734 bool "Use CFI shadow to speed up cross-module checks"
736 depends on CFI_CLANG && MODULES
738 If you select this option, the kernel builds a fast look-up table of
739 CFI check functions in loaded modules to reduce performance overhead.
743 config CFI_PERMISSIVE
744 bool "Use CFI in permissive mode"
747 When selected, Control Flow Integrity (CFI) violations result in a
748 warning instead of a kernel panic. This option should only be used
749 for finding indirect call type mismatches during development.
753 config HAVE_ARCH_WITHIN_STACK_FRAMES
756 An architecture should select this if it can walk the kernel stack
757 frames to determine if an object is part of either the arguments
758 or local variables (i.e. that it excludes saved return addresses,
759 and similar) by implementing an inline arch_within_stack_frames(),
760 which is used by CONFIG_HARDENED_USERCOPY.
762 config HAVE_CONTEXT_TRACKING
765 Provide kernel/user boundaries probes necessary for subsystems
766 that need it, such as userspace RCU extended quiescent state.
767 Syscalls need to be wrapped inside user_exit()-user_enter(), either
768 optimized behind static key or through the slow path using TIF_NOHZ
769 flag. Exceptions handlers must be wrapped as well. Irqs are already
770 protected inside rcu_irq_enter/rcu_irq_exit() but preemption or signal
771 handling on irq exit still need to be protected.
773 config HAVE_CONTEXT_TRACKING_OFFSTACK
776 Architecture neither relies on exception_enter()/exception_exit()
777 nor on schedule_user(). Also preempt_schedule_notrace() and
778 preempt_schedule_irq() can't be called in a preemptible section
779 while context tracking is CONTEXT_USER. This feature reflects a sane
780 entry implementation where the following requirements are met on
781 critical entry code, ie: before user_exit() or after user_enter():
783 - Critical entry code isn't preemptible (or better yet:
785 - No use of RCU read side critical sections, unless rcu_nmi_enter()
787 - No use of instrumentation, unless instrumentation_begin() got
793 Arch relies on TIF_NOHZ and syscall slow path to implement context
794 tracking calls to user_enter()/user_exit().
796 config HAVE_VIRT_CPU_ACCOUNTING
799 config HAVE_VIRT_CPU_ACCOUNTING_IDLE
802 Architecture has its own way to account idle CPU time and therefore
803 doesn't implement vtime_account_idle().
805 config ARCH_HAS_SCALED_CPUTIME
808 config HAVE_VIRT_CPU_ACCOUNTING_GEN
812 With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
813 Before enabling this option, arch code must be audited
814 to ensure there are no races in concurrent read/write of
815 cputime_t. For example, reading/writing 64-bit cputime_t on
816 some 32-bit arches may require multiple accesses, so proper
817 locking is needed to protect against concurrent accesses.
819 config HAVE_IRQ_TIME_ACCOUNTING
822 Archs need to ensure they use a high enough resolution clock to
823 support irq time accounting and then call enable_sched_clock_irqtime().
828 Architectures that select this are able to move page tables at the
829 PUD level. If there are only 3 page table levels, the move effectively
830 happens at the PGD level.
835 Archs that select this are able to move page tables at the PMD level.
837 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
840 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
843 config HAVE_ARCH_HUGE_VMAP
847 # Archs that select this would be capable of PMD-sized vmaps (i.e.,
848 # arch_vmap_pmd_supported() returns true), and they must make no assumptions
849 # that vmalloc memory is mapped with PAGE_SIZE ptes. The VM_NO_HUGE_VMAP flag
850 # can be used to prohibit arch-specific allocations from using hugepages to
851 # help with this (e.g., modules may require it).
853 config HAVE_ARCH_HUGE_VMALLOC
854 depends on HAVE_ARCH_HUGE_VMAP
857 config ARCH_WANT_HUGE_PMD_SHARE
860 config HAVE_ARCH_SOFT_DIRTY
863 config HAVE_MOD_ARCH_SPECIFIC
866 The arch uses struct mod_arch_specific to store data. Many arches
867 just need a simple module loader without arch specific data - those
868 should not enable this.
870 config MODULES_USE_ELF_RELA
873 Modules only use ELF RELA relocations. Modules with ELF REL
874 relocations will give an error.
876 config MODULES_USE_ELF_REL
879 Modules only use ELF REL relocations. Modules with ELF RELA
880 relocations will give an error.
882 config HAVE_IRQ_EXIT_ON_IRQ_STACK
885 Architecture doesn't only execute the irq handler on the irq stack
886 but also irq_exit(). This way we can process softirqs on this irq
887 stack instead of switching to a new one when we call __do_softirq()
888 in the end of an hardirq.
889 This spares a stack switch and improves cache usage on softirq
892 config HAVE_SOFTIRQ_ON_OWN_STACK
895 Architecture provides a function to run __do_softirq() on a
898 config ALTERNATE_USER_ADDRESS_SPACE
901 Architectures set this when the CPU uses separate address
902 spaces for kernel and user space pointers. In this case, the
903 access_ok() check on a __user pointer is skipped.
905 config PGTABLE_LEVELS
909 config ARCH_HAS_ELF_RANDOMIZE
912 An architecture supports choosing randomized locations for
913 stack, mmap, brk, and ET_DYN. Defined functions:
915 - arch_randomize_brk()
917 config HAVE_ARCH_MMAP_RND_BITS
920 An arch should select this symbol if it supports setting a variable
921 number of bits for use in establishing the base address for mmap
922 allocations, has MMU enabled and provides values for both:
923 - ARCH_MMAP_RND_BITS_MIN
924 - ARCH_MMAP_RND_BITS_MAX
926 config HAVE_EXIT_THREAD
929 An architecture implements exit_thread.
931 config ARCH_MMAP_RND_BITS_MIN
934 config ARCH_MMAP_RND_BITS_MAX
937 config ARCH_MMAP_RND_BITS_DEFAULT
940 config ARCH_MMAP_RND_BITS
941 int "Number of bits to use for ASLR of mmap base address" if EXPERT
942 range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
943 default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
944 default ARCH_MMAP_RND_BITS_MIN
945 depends on HAVE_ARCH_MMAP_RND_BITS
947 This value can be used to select the number of bits to use to
948 determine the random offset to the base address of vma regions
949 resulting from mmap allocations. This value will be bounded
950 by the architecture's minimum and maximum supported values.
952 This value can be changed after boot using the
953 /proc/sys/vm/mmap_rnd_bits tunable
955 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
958 An arch should select this symbol if it supports running applications
959 in compatibility mode, supports setting a variable number of bits for
960 use in establishing the base address for mmap allocations, has MMU
961 enabled and provides values for both:
962 - ARCH_MMAP_RND_COMPAT_BITS_MIN
963 - ARCH_MMAP_RND_COMPAT_BITS_MAX
965 config ARCH_MMAP_RND_COMPAT_BITS_MIN
968 config ARCH_MMAP_RND_COMPAT_BITS_MAX
971 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
974 config ARCH_MMAP_RND_COMPAT_BITS
975 int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
976 range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
977 default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
978 default ARCH_MMAP_RND_COMPAT_BITS_MIN
979 depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
981 This value can be used to select the number of bits to use to
982 determine the random offset to the base address of vma regions
983 resulting from mmap allocations for compatible applications This
984 value will be bounded by the architecture's minimum and maximum
987 This value can be changed after boot using the
988 /proc/sys/vm/mmap_rnd_compat_bits tunable
990 config HAVE_ARCH_COMPAT_MMAP_BASES
993 This allows 64bit applications to invoke 32-bit mmap() syscall
994 and vice-versa 32-bit applications to call 64-bit mmap().
995 Required for applications doing different bitness syscalls.
997 config PAGE_SIZE_LESS_THAN_64KB
999 depends on !ARM64_64K_PAGES
1000 depends on !IA64_PAGE_SIZE_64KB
1001 depends on !PAGE_SIZE_64KB
1002 depends on !PARISC_PAGE_SIZE_64KB
1003 depends on !PPC_64K_PAGES
1004 depends on PAGE_SIZE_LESS_THAN_256KB
1006 config PAGE_SIZE_LESS_THAN_256KB
1008 depends on !PPC_256K_PAGES
1009 depends on !PAGE_SIZE_256KB
1011 # This allows to use a set of generic functions to determine mmap base
1012 # address by giving priority to top-down scheme only if the process
1013 # is not in legacy mode (compat task, unlimited stack size or
1014 # sysctl_legacy_va_layout).
1015 # Architecture that selects this option can provide its own version of:
1017 config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
1020 select ARCH_HAS_ELF_RANDOMIZE
1022 config HAVE_STACK_VALIDATION
1025 Architecture supports the 'objtool check' host tool command, which
1026 performs compile-time stack metadata validation.
1028 config HAVE_RELIABLE_STACKTRACE
1031 Architecture has either save_stack_trace_tsk_reliable() or
1032 arch_stack_walk_reliable() function which only returns a stack trace
1033 if it can guarantee the trace is reliable.
1035 config HAVE_ARCH_HASH
1039 If this is set, the architecture provides an <asm/hash.h>
1040 file which provides platform-specific implementations of some
1041 functions in <linux/hash.h> or fs/namei.c.
1043 config HAVE_ARCH_NVRAM_OPS
1052 config CLONE_BACKWARDS
1055 Architecture has tls passed as the 4th argument of clone(2),
1058 config CLONE_BACKWARDS2
1061 Architecture has the first two arguments of clone(2) swapped.
1063 config CLONE_BACKWARDS3
1066 Architecture has tls passed as the 3rd argument of clone(2),
1069 config ODD_RT_SIGACTION
1072 Architecture has unusual rt_sigaction(2) arguments
1074 config OLD_SIGSUSPEND
1077 Architecture has old sigsuspend(2) syscall, of one-argument variety
1079 config OLD_SIGSUSPEND3
1082 Even weirder antique ABI - three-argument sigsuspend(2)
1084 config OLD_SIGACTION
1087 Architecture has old sigaction(2) syscall. Nope, not the same
1088 as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
1089 but fairly different variant of sigaction(2), thanks to OSF/1
1092 config COMPAT_OLD_SIGACTION
1095 config COMPAT_32BIT_TIME
1096 bool "Provide system calls for 32-bit time_t"
1097 default !64BIT || COMPAT
1099 This enables 32 bit time_t support in addition to 64 bit time_t support.
1100 This is relevant on all 32-bit architectures, and 64-bit architectures
1101 as part of compat syscall handling.
1103 config ARCH_NO_PREEMPT
1106 config ARCH_EPHEMERAL_INODES
1109 An arch should select this symbol if it doesn't keep track of inode
1110 instances on its own, but instead relies on something else (e.g. the
1111 host kernel for an UML kernel).
1113 config ARCH_SUPPORTS_RT
1116 config CPU_NO_EFFICIENT_FFS
1119 config HAVE_ARCH_VMAP_STACK
1122 An arch should select this symbol if it can support kernel stacks
1123 in vmalloc space. This means:
1125 - vmalloc space must be large enough to hold many kernel stacks.
1126 This may rule out many 32-bit architectures.
1128 - Stacks in vmalloc space need to work reliably. For example, if
1129 vmap page tables are created on demand, either this mechanism
1130 needs to work while the stack points to a virtual address with
1131 unpopulated page tables or arch code (switch_to() and switch_mm(),
1132 most likely) needs to ensure that the stack's page table entries
1133 are populated before running on a possibly unpopulated stack.
1135 - If the stack overflows into a guard page, something reasonable
1136 should happen. The definition of "reasonable" is flexible, but
1137 instantly rebooting without logging anything would be unfriendly.
1141 bool "Use a virtually-mapped stack"
1142 depends on HAVE_ARCH_VMAP_STACK
1143 depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
1145 Enable this if you want the use virtually-mapped kernel stacks
1146 with guard pages. This causes kernel stack overflows to be
1147 caught immediately rather than causing difficult-to-diagnose
1150 To use this with software KASAN modes, the architecture must support
1151 backing virtual mappings with real shadow memory, and KASAN_VMALLOC
1154 config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1157 An arch should select this symbol if it can support kernel stack
1158 offset randomization with calls to add_random_kstack_offset()
1159 during syscall entry and choose_random_kstack_offset() during
1160 syscall exit. Careful removal of -fstack-protector-strong and
1161 -fstack-protector should also be applied to the entry code and
1162 closely examined, as the artificial stack bump looks like an array
1163 to the compiler, so it will attempt to add canary checks regardless
1164 of the static branch state.
1166 config RANDOMIZE_KSTACK_OFFSET_DEFAULT
1167 bool "Randomize kernel stack offset on syscall entry"
1168 depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1170 The kernel stack offset can be randomized (after pt_regs) by
1171 roughly 5 bits of entropy, frustrating memory corruption
1172 attacks that depend on stack address determinism or
1173 cross-syscall address exposures. This feature is controlled
1174 by kernel boot param "randomize_kstack_offset=on/off", and this
1175 config chooses the default boot state.
1177 config ARCH_OPTIONAL_KERNEL_RWX
1180 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1183 config ARCH_HAS_STRICT_KERNEL_RWX
1186 config STRICT_KERNEL_RWX
1187 bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
1188 depends on ARCH_HAS_STRICT_KERNEL_RWX
1189 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1191 If this is set, kernel text and rodata memory will be made read-only,
1192 and non-text memory will be made non-executable. This provides
1193 protection against certain security exploits (e.g. executing the heap
1196 These features are considered standard security practice these days.
1197 You should say Y here in almost all cases.
1199 config ARCH_HAS_STRICT_MODULE_RWX
1202 config STRICT_MODULE_RWX
1203 bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1204 depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1205 default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1207 If this is set, module text and rodata memory will be made read-only,
1208 and non-text memory will be made non-executable. This provides
1209 protection against certain security exploits (e.g. writing to text)
1211 # select if the architecture provides an asm/dma-direct.h header
1212 config ARCH_HAS_PHYS_TO_DMA
1215 config HAVE_ARCH_COMPILER_H
1218 An architecture can select this if it provides an
1219 asm/compiler.h header that should be included after
1220 linux/compiler-*.h in order to override macro definitions that those
1221 headers generally provide.
1223 config HAVE_ARCH_PREL32_RELOCATIONS
1226 May be selected by an architecture if it supports place-relative
1227 32-bit relocations, both in the toolchain and in the module loader,
1228 in which case relative references can be used in special sections
1229 for PCI fixup, initcalls etc which are only half the size on 64 bit
1230 architectures, and don't require runtime relocation on relocatable
1233 config ARCH_USE_MEMREMAP_PROT
1236 config LOCK_EVENT_COUNTS
1237 bool "Locking event counts collection"
1240 Enable light-weight counting of various locking related events
1241 in the system with minimal performance impact. This reduces
1242 the chance of application behavior change because of timing
1243 differences. The counts are reported via debugfs.
1245 # Select if the architecture has support for applying RELR relocations.
1246 config ARCH_HAS_RELR
1250 bool "Use RELR relocation packing"
1251 depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1254 Store the kernel's dynamic relocations in the RELR relocation packing
1255 format. Requires a compatible linker (LLD supports this feature), as
1256 well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1259 config ARCH_HAS_MEM_ENCRYPT
1262 config ARCH_HAS_CC_PLATFORM
1265 config HAVE_SPARSE_SYSCALL_NR
1268 An architecture should select this if its syscall numbering is sparse
1269 to save space. For example, MIPS architecture has a syscall array with
1270 entries at 4000, 5000 and 6000 locations. This option turns on syscall
1271 related optimizations for a given architecture.
1273 config ARCH_HAS_VDSO_DATA
1276 config HAVE_STATIC_CALL
1279 config HAVE_STATIC_CALL_INLINE
1281 depends on HAVE_STATIC_CALL
1283 config HAVE_PREEMPT_DYNAMIC
1285 depends on HAVE_STATIC_CALL
1286 depends on GENERIC_ENTRY
1288 Select this if the architecture support boot time preempt setting
1289 on top of static calls. It is strongly advised to support inline
1290 static call to avoid any overhead.
1292 config ARCH_WANT_LD_ORPHAN_WARN
1295 An arch should select this symbol once all linker sections are explicitly
1296 included, size-asserted, or discarded in the linker scripts. This is
1297 important because we never want expected sections to be placed heuristically
1298 by the linker, since the locations of such sections can change between linker
1301 config HAVE_ARCH_PFN_VALID
1304 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1307 config ARCH_SUPPORTS_PAGE_TABLE_CHECK
1310 config ARCH_SPLIT_ARG64
1313 If a 32-bit architecture requires 64-bit arguments to be split into
1314 pairs of 32-bit arguments, select this option.
1316 config ARCH_HAS_ELFCORE_COMPAT
1319 config ARCH_HAS_PARANOID_L1D_FLUSH
1322 config DYNAMIC_SIGFRAME
1325 # Select, if arch has a named attribute group bound to NUMA device nodes.
1326 config HAVE_ARCH_NODE_DEV_GROUP
1329 source "kernel/gcov/Kconfig"
1331 source "scripts/gcc-plugins/Kconfig"