arch/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0
   2 #
   3 # General architecture dependent options
   4 #
   5
   6 #
   7 # Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can
   8 # override the default values in this file.
   9 #
  10 source "arch/$(SRCARCH)/Kconfig"
  11
  12 menu "General architecture-dependent options"
  13
  14 config CRASH_CORE
  15         bool
  16
  17 config KEXEC_CORE
  18         select CRASH_CORE
  19         bool
  20
  21 config KEXEC_ELF
  22         bool
  23
  24 config HAVE_IMA_KEXEC
  25         bool
  26
  27 config SET_FS
  28         bool
  29
  30 config HOTPLUG_SMT
  31         bool
  32
  33 config GENERIC_ENTRY
  34        bool
  35
  36 config OPROFILE
  37         tristate "OProfile system profiling"
  38         depends on PROFILING
  39         depends on HAVE_OPROFILE
  40         select RING_BUFFER
  41         select RING_BUFFER_ALLOW_SWAP
  42         help
  43           OProfile is a profiling system capable of profiling the
  44           whole system, include the kernel, kernel modules, libraries,
  45           and applications.
  46
  47           If unsure, say N.
  48
  49 config OPROFILE_EVENT_MULTIPLEX
  50         bool "OProfile multiplexing support (EXPERIMENTAL)"
  51         default n
  52         depends on OPROFILE && X86
  53         help
  54           The number of hardware counters is limited. The multiplexing
  55           feature enables OProfile to gather more events than counters
  56           are provided by the hardware. This is realized by switching
  57           between events at a user specified time interval.
  58
  59           If unsure, say N.
  60
  61 config HAVE_OPROFILE
  62         bool
  63
  64 config OPROFILE_NMI_TIMER
  65         def_bool y
  66         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  67
  68 config KPROBES
  69         bool "Kprobes"
  70         depends on MODULES
  71         depends on HAVE_KPROBES
  72         select KALLSYMS
  73         help
  74           Kprobes allows you to trap at almost any kernel address and
  75           execute a callback function.  register_kprobe() establishes
  76           a probepoint and specifies the callback.  Kprobes is useful
  77           for kernel debugging, non-intrusive instrumentation and testing.
  78           If in doubt, say "N".
  79
  80 config JUMP_LABEL
  81         bool "Optimize very unlikely/likely branches"
  82         depends on HAVE_ARCH_JUMP_LABEL
  83         depends on CC_HAS_ASM_GOTO
  84         help
  85          This option enables a transparent branch optimization that
  86          makes certain almost-always-true or almost-always-false branch
  87          conditions even cheaper to execute within the kernel.
  88
  89          Certain performance-sensitive kernel code, such as trace points,
  90          scheduler functionality, networking code and KVM have such
  91          branches and include support for this optimization technique.
  92
  93          If it is detected that the compiler has support for "asm goto",
  94          the kernel will compile such branches with just a nop
  95          instruction. When the condition flag is toggled to true, the
  96          nop will be converted to a jump instruction to execute the
  97          conditional block of instructions.
  98
  99          This technique lowers overhead and stress on the branch prediction
 100          of the processor and generally makes the kernel faster. The update
 101          of the condition is slower, but those are always very rare.
 102
 103          ( On 32-bit x86, the necessary options added to the compiler
 104            flags may increase the size of the kernel slightly. )
 105
 106 config STATIC_KEYS_SELFTEST
 107         bool "Static key selftest"
 108         depends on JUMP_LABEL
 109         help
 110           Boot time self-test of the branch patching code.
 111
 112 config STATIC_CALL_SELFTEST
 113         bool "Static call selftest"
 114         depends on HAVE_STATIC_CALL
 115         help
 116           Boot time self-test of the call patching code.
 117
 118 config OPTPROBES
 119         def_bool y
 120         depends on KPROBES && HAVE_OPTPROBES
 121         select TASKS_RCU if PREEMPTION
 122
 123 config KPROBES_ON_FTRACE
 124         def_bool y
 125         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
 126         depends on DYNAMIC_FTRACE_WITH_REGS
 127         help
 128          If function tracer is enabled and the arch supports full
 129          passing of pt_regs to function tracing, then kprobes can
 130          optimize on top of function tracing.
 131
 132 config UPROBES
 133         def_bool n
 134         depends on ARCH_SUPPORTS_UPROBES
 135         help
 136           Uprobes is the user-space counterpart to kprobes: they
 137           enable instrumentation applications (such as 'perf probe')
 138           to establish unintrusive probes in user-space binaries and
 139           libraries, by executing handler functions when the probes
 140           are hit by user-space applications.
 141
 142           ( These probes come in the form of single-byte breakpoints,
 143             managed by the kernel and kept transparent to the probed
 144             application. )
 145
 146 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 147         bool
 148         help
 149           Some architectures are unable to perform unaligned accesses
 150           without the use of get_unaligned/put_unaligned. Others are
 151           unable to perform such accesses efficiently (e.g. trap on
 152           unaligned access and require fixing it up in the exception
 153           handler.)
 154
 155           This symbol should be selected by an architecture if it can
 156           perform unaligned accesses efficiently to allow different
 157           code paths to be selected for these cases. Some network
 158           drivers, for example, could opt to not fix up alignment
 159           problems with received packets if doing so would not help
 160           much.
 161
 162           See Documentation/core-api/unaligned-memory-access.rst for more
 163           information on the topic of unaligned memory accesses.
 164
 165 config ARCH_USE_BUILTIN_BSWAP
 166         bool
 167         help
 168          Modern versions of GCC (since 4.4) have builtin functions
 169          for handling byte-swapping. Using these, instead of the old
 170          inline assembler that the architecture code provides in the
 171          __arch_bswapXX() macros, allows the compiler to see what's
 172          happening and offers more opportunity for optimisation. In
 173          particular, the compiler will be able to combine the byteswap
 174          with a nearby load or store and use load-and-swap or
 175          store-and-swap instructions if the architecture has them. It
 176          should almost *never* result in code which is worse than the
 177          hand-coded assembler in <asm/swab.h>.  But just in case it
 178          does, the use of the builtins is optional.
 179
 180          Any architecture with load-and-swap or store-and-swap
 181          instructions should set this. And it shouldn't hurt to set it
 182          on architectures that don't have such instructions.
 183
 184 config KRETPROBES
 185         def_bool y
 186         depends on KPROBES && HAVE_KRETPROBES
 187
 188 config USER_RETURN_NOTIFIER
 189         bool
 190         depends on HAVE_USER_RETURN_NOTIFIER
 191         help
 192           Provide a kernel-internal notification when a cpu is about to
 193           switch to user mode.
 194
 195 config HAVE_IOREMAP_PROT
 196         bool
 197
 198 config HAVE_KPROBES
 199         bool
 200
 201 config HAVE_KRETPROBES
 202         bool
 203
 204 config HAVE_OPTPROBES
 205         bool
 206
 207 config HAVE_KPROBES_ON_FTRACE
 208         bool
 209
 210 config HAVE_FUNCTION_ERROR_INJECTION
 211         bool
 212
 213 config HAVE_NMI
 214         bool
 215
 216 #
 217 # An arch should select this if it provides all these things:
 218 #
 219 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 220 #       arch_has_single_step()  if there is hardware single-step support
 221 #       arch_has_block_step()   if there is hardware block-step support
 222 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 223 #       linux/regset.h          user_regset interfaces
 224 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 225 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 226 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 227 #       signal delivery         calls tracehook_signal_handler()
 228 #
 229 config HAVE_ARCH_TRACEHOOK
 230         bool
 231
 232 config HAVE_DMA_CONTIGUOUS
 233         bool
 234
 235 config GENERIC_SMP_IDLE_THREAD
 236         bool
 237
 238 config GENERIC_IDLE_POLL_SETUP
 239         bool
 240
 241 config ARCH_HAS_FORTIFY_SOURCE
 242         bool
 243         help
 244           An architecture should select this when it can successfully
 245           build and run with CONFIG_FORTIFY_SOURCE.
 246
 247 #
 248 # Select if the arch provides a historic keepinit alias for the retain_initrd
 249 # command line option
 250 #
 251 config ARCH_HAS_KEEPINITRD
 252         bool
 253
 254 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 255 config ARCH_HAS_SET_MEMORY
 256         bool
 257
 258 # Select if arch has all set_direct_map_invalid/default() functions
 259 config ARCH_HAS_SET_DIRECT_MAP
 260         bool
 261
 262 #
 263 # Select if the architecture provides the arch_dma_set_uncached symbol to
 264 # either provide an uncached segment alias for a DMA allocation, or
 265 # to remap the page tables in place.
 266 #
 267 config ARCH_HAS_DMA_SET_UNCACHED
 268         bool
 269
 270 #
 271 # Select if the architectures provides the arch_dma_clear_uncached symbol
 272 # to undo an in-place page table remap for uncached access.
 273 #
 274 config ARCH_HAS_DMA_CLEAR_UNCACHED
 275         bool
 276
 277 # Select if arch init_task must go in the __init_task_data section
 278 config ARCH_TASK_STRUCT_ON_STACK
 279         bool
 280
 281 # Select if arch has its private alloc_task_struct() function
 282 config ARCH_TASK_STRUCT_ALLOCATOR
 283         bool
 284
 285 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 286         bool
 287         depends on !ARCH_TASK_STRUCT_ALLOCATOR
 288         help
 289           An architecture should select this to provide hardened usercopy
 290           knowledge about what region of the thread_struct should be
 291           whitelisted for copying to userspace. Normally this is only the
 292           FPU registers. Specifically, arch_thread_struct_whitelist()
 293           should be implemented. Without this, the entire thread_struct
 294           field in task_struct will be left whitelisted.
 295
 296 # Select if arch has its private alloc_thread_stack() function
 297 config ARCH_THREAD_STACK_ALLOCATOR
 298         bool
 299
 300 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 301 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 302         bool
 303
 304 config ARCH_32BIT_OFF_T
 305         bool
 306         depends on !64BIT
 307         help
 308           All new 32-bit architectures should have 64-bit off_t type on
 309           userspace side which corresponds to the loff_t kernel type. This
 310           is the requirement for modern ABIs. Some existing architectures
 311           still support 32-bit off_t. This option is enabled for all such
 312           architectures explicitly.
 313
 314 config HAVE_ASM_MODVERSIONS
 315         bool
 316         help
 317           This symbol should be selected by an architecture if it provides
 318           <asm/asm-prototypes.h> to support the module versioning for symbols
 319           exported from assembly code.
 320
 321 config HAVE_REGS_AND_STACK_ACCESS_API
 322         bool
 323         help
 324           This symbol should be selected by an architecture if it supports
 325           the API needed to access registers and stack entries from pt_regs,
 326           declared in asm/ptrace.h
 327           For example the kprobes-based event tracer needs this API.
 328
 329 config HAVE_RSEQ
 330         bool
 331         depends on HAVE_REGS_AND_STACK_ACCESS_API
 332         help
 333           This symbol should be selected by an architecture if it
 334           supports an implementation of restartable sequences.
 335
 336 config HAVE_FUNCTION_ARG_ACCESS_API
 337         bool
 338         help
 339           This symbol should be selected by an architecture if it supports
 340           the API needed to access function arguments from pt_regs,
 341           declared in asm/ptrace.h
 342
 343 config HAVE_HW_BREAKPOINT
 344         bool
 345         depends on PERF_EVENTS
 346
 347 config HAVE_MIXED_BREAKPOINTS_REGS
 348         bool
 349         depends on HAVE_HW_BREAKPOINT
 350         help
 351           Depending on the arch implementation of hardware breakpoints,
 352           some of them have separate registers for data and instruction
 353           breakpoints addresses, others have mixed registers to store
 354           them but define the access type in a control register.
 355           Select this option if your arch implements breakpoints under the
 356           latter fashion.
 357
 358 config HAVE_USER_RETURN_NOTIFIER
 359         bool
 360
 361 config HAVE_PERF_EVENTS_NMI
 362         bool
 363         help
 364           System hardware can generate an NMI using the perf event
 365           subsystem.  Also has support for calculating CPU cycle events
 366           to determine how many clock cycles in a given period.
 367
 368 config HAVE_HARDLOCKUP_DETECTOR_PERF
 369         bool
 370         depends on HAVE_PERF_EVENTS_NMI
 371         help
 372           The arch chooses to use the generic perf-NMI-based hardlockup
 373           detector. Must define HAVE_PERF_EVENTS_NMI.
 374
 375 config HAVE_NMI_WATCHDOG
 376         depends on HAVE_NMI
 377         bool
 378         help
 379           The arch provides a low level NMI watchdog. It provides
 380           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 381
 382 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 383         bool
 384         select HAVE_NMI_WATCHDOG
 385         help
 386           The arch chooses to provide its own hardlockup detector, which is
 387           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 388           interfaces and parameters provided by hardlockup detector subsystem.
 389
 390 config HAVE_PERF_REGS
 391         bool
 392         help
 393           Support selective register dumps for perf events. This includes
 394           bit-mapping of each registers and a unique architecture id.
 395
 396 config HAVE_PERF_USER_STACK_DUMP
 397         bool
 398         help
 399           Support user stack dumps for perf event samples. This needs
 400           access to the user stack pointer which is not unified across
 401           architectures.
 402
 403 config HAVE_ARCH_JUMP_LABEL
 404         bool
 405
 406 config HAVE_ARCH_JUMP_LABEL_RELATIVE
 407         bool
 408
 409 config MMU_GATHER_TABLE_FREE
 410         bool
 411
 412 config MMU_GATHER_RCU_TABLE_FREE
 413         bool
 414         select MMU_GATHER_TABLE_FREE
 415
 416 config MMU_GATHER_PAGE_SIZE
 417         bool
 418
 419 config MMU_GATHER_NO_RANGE
 420         bool
 421
 422 config MMU_GATHER_NO_GATHER
 423         bool
 424         depends on MMU_GATHER_TABLE_FREE
 425
 426 config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
 427         bool
 428         help
 429           Temporary select until all architectures can be converted to have
 430           irqs disabled over activate_mm. Architectures that do IPI based TLB
 431           shootdowns should enable this.
 432
 433 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 434         bool
 435
 436 config HAVE_ALIGNED_STRUCT_PAGE
 437         bool
 438         help
 439           This makes sure that struct pages are double word aligned and that
 440           e.g. the SLUB allocator can perform double word atomic operations
 441           on a struct page for better performance. However selecting this
 442           might increase the size of a struct page by a word.
 443
 444 config HAVE_CMPXCHG_LOCAL
 445         bool
 446
 447 config HAVE_CMPXCHG_DOUBLE
 448         bool
 449
 450 config ARCH_WEAK_RELEASE_ACQUIRE
 451         bool
 452
 453 config ARCH_WANT_IPC_PARSE_VERSION
 454         bool
 455
 456 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 457         bool
 458
 459 config ARCH_WANT_OLD_COMPAT_IPC
 460         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 461         bool
 462
 463 config HAVE_ARCH_SECCOMP
 464         bool
 465         help
 466           An arch should select this symbol to support seccomp mode 1 (the fixed
 467           syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
 468           and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
 469           - __NR_seccomp_read_32
 470           - __NR_seccomp_write_32
 471           - __NR_seccomp_exit_32
 472           - __NR_seccomp_sigreturn_32
 473
 474 config HAVE_ARCH_SECCOMP_FILTER
 475         bool
 476         select HAVE_ARCH_SECCOMP
 477         help
 478           An arch should select this symbol if it provides all of these things:
 479           - all the requirements for HAVE_ARCH_SECCOMP
 480           - syscall_get_arch()
 481           - syscall_get_arguments()
 482           - syscall_rollback()
 483           - syscall_set_return_value()
 484           - SIGSYS siginfo_t support
 485           - secure_computing is called from a ptrace_event()-safe context
 486           - secure_computing return value is checked and a return value of -1
 487             results in the system call being skipped immediately.
 488           - seccomp syscall wired up
 489           - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
 490             SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
 491             COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
 492
 493 config SECCOMP
 494         prompt "Enable seccomp to safely execute untrusted bytecode"
 495         def_bool y
 496         depends on HAVE_ARCH_SECCOMP
 497         help
 498           This kernel feature is useful for number crunching applications
 499           that may need to handle untrusted bytecode during their
 500           execution. By using pipes or other transports made available
 501           to the process as file descriptors supporting the read/write
 502           syscalls, it's possible to isolate those applications in their
 503           own address space using seccomp. Once seccomp is enabled via
 504           prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
 505           disabled and the task is only allowed to execute a few safe
 506           syscalls defined by each seccomp mode.
 507
 508           If unsure, say Y.
 509
 510 config SECCOMP_FILTER
 511         def_bool y
 512         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 513         help
 514           Enable tasks to build secure computing environments defined
 515           in terms of Berkeley Packet Filter programs which implement
 516           task-defined system call filtering polices.
 517
 518           See Documentation/userspace-api/seccomp_filter.rst for details.
 519
 520 config SECCOMP_CACHE_DEBUG
 521         bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
 522         depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
 523         depends on PROC_FS
 524         help
 525           This enables the /proc/pid/seccomp_cache interface to monitor
 526           seccomp cache data. The file format is subject to change. Reading
 527           the file requires CAP_SYS_ADMIN.
 528
 529           This option is for debugging only. Enabling presents the risk that
 530           an adversary may be able to infer the seccomp filter logic.
 531
 532           If unsure, say N.
 533
 534 config HAVE_ARCH_STACKLEAK
 535         bool
 536         help
 537           An architecture should select this if it has the code which
 538           fills the used part of the kernel stack with the STACKLEAK_POISON
 539           value before returning from system calls.
 540
 541 config HAVE_STACKPROTECTOR
 542         bool
 543         help
 544           An arch should select this symbol if:
 545           - it has implemented a stack canary (e.g. __stack_chk_guard)
 546
 547 config STACKPROTECTOR
 548         bool "Stack Protector buffer overflow detection"
 549         depends on HAVE_STACKPROTECTOR
 550         depends on $(cc-option,-fstack-protector)
 551         default y
 552         help
 553           This option turns on the "stack-protector" GCC feature. This
 554           feature puts, at the beginning of functions, a canary value on
 555           the stack just before the return address, and validates
 556           the value just before actually returning.  Stack based buffer
 557           overflows (that need to overwrite this return address) now also
 558           overwrite the canary, which gets detected and the attack is then
 559           neutralized via a kernel panic.
 560
 561           Functions will have the stack-protector canary logic added if they
 562           have an 8-byte or larger character array on the stack.
 563
 564           This feature requires gcc version 4.2 or above, or a distribution
 565           gcc with the feature backported ("-fstack-protector").
 566
 567           On an x86 "defconfig" build, this feature adds canary checks to
 568           about 3% of all kernel functions, which increases kernel code size
 569           by about 0.3%.
 570
 571 config STACKPROTECTOR_STRONG
 572         bool "Strong Stack Protector"
 573         depends on STACKPROTECTOR
 574         depends on $(cc-option,-fstack-protector-strong)
 575         default y
 576         help
 577           Functions will have the stack-protector canary logic added in any
 578           of the following conditions:
 579
 580           - local variable's address used as part of the right hand side of an
 581             assignment or function argument
 582           - local variable is an array (or union containing an array),
 583             regardless of array type or length
 584           - uses register local variables
 585
 586           This feature requires gcc version 4.9 or above, or a distribution
 587           gcc with the feature backported ("-fstack-protector-strong").
 588
 589           On an x86 "defconfig" build, this feature adds canary checks to
 590           about 20% of all kernel functions, which increases the kernel code
 591           size by about 2%.
 592
 593 config ARCH_SUPPORTS_SHADOW_CALL_STACK
 594         bool
 595         help
 596           An architecture should select this if it supports Clang's Shadow
 597           Call Stack and implements runtime support for shadow stack
 598           switching.
 599
 600 config SHADOW_CALL_STACK
 601         bool "Clang Shadow Call Stack"
 602         depends on CC_IS_CLANG && ARCH_SUPPORTS_SHADOW_CALL_STACK
 603         depends on DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
 604         help
 605           This option enables Clang's Shadow Call Stack, which uses a
 606           shadow stack to protect function return addresses from being
 607           overwritten by an attacker. More information can be found in
 608           Clang's documentation:
 609
 610             https://clang.llvm.org/docs/ShadowCallStack.html
 611
 612           Note that security guarantees in the kernel differ from the
 613           ones documented for user space. The kernel must store addresses
 614           of shadow stacks in memory, which means an attacker capable of
 615           reading and writing arbitrary memory may be able to locate them
 616           and hijack control flow by modifying the stacks.
 617
 618 config HAVE_ARCH_WITHIN_STACK_FRAMES
 619         bool
 620         help
 621           An architecture should select this if it can walk the kernel stack
 622           frames to determine if an object is part of either the arguments
 623           or local variables (i.e. that it excludes saved return addresses,
 624           and similar) by implementing an inline arch_within_stack_frames(),
 625           which is used by CONFIG_HARDENED_USERCOPY.
 626
 627 config HAVE_CONTEXT_TRACKING
 628         bool
 629         help
 630           Provide kernel/user boundaries probes necessary for subsystems
 631           that need it, such as userspace RCU extended quiescent state.
 632           Syscalls need to be wrapped inside user_exit()-user_enter(), either
 633           optimized behind static key or through the slow path using TIF_NOHZ
 634           flag. Exceptions handlers must be wrapped as well. Irqs are already
 635           protected inside rcu_irq_enter/rcu_irq_exit() but preemption or signal
 636           handling on irq exit still need to be protected.
 637
 638 config HAVE_CONTEXT_TRACKING_OFFSTACK
 639         bool
 640         help
 641           Architecture neither relies on exception_enter()/exception_exit()
 642           nor on schedule_user(). Also preempt_schedule_notrace() and
 643           preempt_schedule_irq() can't be called in a preemptible section
 644           while context tracking is CONTEXT_USER. This feature reflects a sane
 645           entry implementation where the following requirements are met on
 646           critical entry code, ie: before user_exit() or after user_enter():
 647
 648           - Critical entry code isn't preemptible (or better yet:
 649             not interruptible).
 650           - No use of RCU read side critical sections, unless rcu_nmi_enter()
 651             got called.
 652           - No use of instrumentation, unless instrumentation_begin() got
 653             called.
 654
 655 config HAVE_TIF_NOHZ
 656         bool
 657         help
 658           Arch relies on TIF_NOHZ and syscall slow path to implement context
 659           tracking calls to user_enter()/user_exit().
 660
 661 config HAVE_VIRT_CPU_ACCOUNTING
 662         bool
 663
 664 config HAVE_VIRT_CPU_ACCOUNTING_IDLE
 665         bool
 666         help
 667           Architecture has its own way to account idle CPU time and therefore
 668           doesn't implement vtime_account_idle().
 669
 670 config ARCH_HAS_SCALED_CPUTIME
 671         bool
 672
 673 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 674         bool
 675         default y if 64BIT
 676         help
 677           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 678           Before enabling this option, arch code must be audited
 679           to ensure there are no races in concurrent read/write of
 680           cputime_t. For example, reading/writing 64-bit cputime_t on
 681           some 32-bit arches may require multiple accesses, so proper
 682           locking is needed to protect against concurrent accesses.
 683
 684 config HAVE_IRQ_TIME_ACCOUNTING
 685         bool
 686         help
 687           Archs need to ensure they use a high enough resolution clock to
 688           support irq time accounting and then call enable_sched_clock_irqtime().
 689
 690 config HAVE_MOVE_PUD
 691         bool
 692         help
 693           Architectures that select this are able to move page tables at the
 694           PUD level. If there are only 3 page table levels, the move effectively
 695           happens at the PGD level.
 696
 697 config HAVE_MOVE_PMD
 698         bool
 699         help
 700           Archs that select this are able to move page tables at the PMD level.
 701
 702 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 703         bool
 704
 705 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 706         bool
 707
 708 config HAVE_ARCH_HUGE_VMAP
 709         bool
 710
 711 config ARCH_WANT_HUGE_PMD_SHARE
 712         bool
 713
 714 config HAVE_ARCH_SOFT_DIRTY
 715         bool
 716
 717 config HAVE_MOD_ARCH_SPECIFIC
 718         bool
 719         help
 720           The arch uses struct mod_arch_specific to store data.  Many arches
 721           just need a simple module loader without arch specific data - those
 722           should not enable this.
 723
 724 config MODULES_USE_ELF_RELA
 725         bool
 726         help
 727           Modules only use ELF RELA relocations.  Modules with ELF REL
 728           relocations will give an error.
 729
 730 config MODULES_USE_ELF_REL
 731         bool
 732         help
 733           Modules only use ELF REL relocations.  Modules with ELF RELA
 734           relocations will give an error.
 735
 736 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 737         bool
 738         help
 739           Architecture doesn't only execute the irq handler on the irq stack
 740           but also irq_exit(). This way we can process softirqs on this irq
 741           stack instead of switching to a new one when we call __do_softirq()
 742           in the end of an hardirq.
 743           This spares a stack switch and improves cache usage on softirq
 744           processing.
 745
 746 config PGTABLE_LEVELS
 747         int
 748         default 2
 749
 750 config ARCH_HAS_ELF_RANDOMIZE
 751         bool
 752         help
 753           An architecture supports choosing randomized locations for
 754           stack, mmap, brk, and ET_DYN. Defined functions:
 755           - arch_mmap_rnd()
 756           - arch_randomize_brk()
 757
 758 config HAVE_ARCH_MMAP_RND_BITS
 759         bool
 760         help
 761           An arch should select this symbol if it supports setting a variable
 762           number of bits for use in establishing the base address for mmap
 763           allocations, has MMU enabled and provides values for both:
 764           - ARCH_MMAP_RND_BITS_MIN
 765           - ARCH_MMAP_RND_BITS_MAX
 766
 767 config HAVE_EXIT_THREAD
 768         bool
 769         help
 770           An architecture implements exit_thread.
 771
 772 config ARCH_MMAP_RND_BITS_MIN
 773         int
 774
 775 config ARCH_MMAP_RND_BITS_MAX
 776         int
 777
 778 config ARCH_MMAP_RND_BITS_DEFAULT
 779         int
 780
 781 config ARCH_MMAP_RND_BITS
 782         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 783         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 784         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 785         default ARCH_MMAP_RND_BITS_MIN
 786         depends on HAVE_ARCH_MMAP_RND_BITS
 787         help
 788           This value can be used to select the number of bits to use to
 789           determine the random offset to the base address of vma regions
 790           resulting from mmap allocations. This value will be bounded
 791           by the architecture's minimum and maximum supported values.
 792
 793           This value can be changed after boot using the
 794           /proc/sys/vm/mmap_rnd_bits tunable
 795
 796 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 797         bool
 798         help
 799           An arch should select this symbol if it supports running applications
 800           in compatibility mode, supports setting a variable number of bits for
 801           use in establishing the base address for mmap allocations, has MMU
 802           enabled and provides values for both:
 803           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 804           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 805
 806 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 807         int
 808
 809 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 810         int
 811
 812 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 813         int
 814
 815 config ARCH_MMAP_RND_COMPAT_BITS
 816         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 817         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 818         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 819         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 820         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 821         help
 822           This value can be used to select the number of bits to use to
 823           determine the random offset to the base address of vma regions
 824           resulting from mmap allocations for compatible applications This
 825           value will be bounded by the architecture's minimum and maximum
 826           supported values.
 827
 828           This value can be changed after boot using the
 829           /proc/sys/vm/mmap_rnd_compat_bits tunable
 830
 831 config HAVE_ARCH_COMPAT_MMAP_BASES
 832         bool
 833         help
 834           This allows 64bit applications to invoke 32-bit mmap() syscall
 835           and vice-versa 32-bit applications to call 64-bit mmap().
 836           Required for applications doing different bitness syscalls.
 837
 838 # This allows to use a set of generic functions to determine mmap base
 839 # address by giving priority to top-down scheme only if the process
 840 # is not in legacy mode (compat task, unlimited stack size or
 841 # sysctl_legacy_va_layout).
 842 # Architecture that selects this option can provide its own version of:
 843 # - STACK_RND_MASK
 844 config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 845         bool
 846         depends on MMU
 847         select ARCH_HAS_ELF_RANDOMIZE
 848
 849 config HAVE_STACK_VALIDATION
 850         bool
 851         help
 852           Architecture supports the 'objtool check' host tool command, which
 853           performs compile-time stack metadata validation.
 854
 855 config HAVE_RELIABLE_STACKTRACE
 856         bool
 857         help
 858           Architecture has either save_stack_trace_tsk_reliable() or
 859           arch_stack_walk_reliable() function which only returns a stack trace
 860           if it can guarantee the trace is reliable.
 861
 862 config HAVE_ARCH_HASH
 863         bool
 864         default n
 865         help
 866           If this is set, the architecture provides an <asm/hash.h>
 867           file which provides platform-specific implementations of some
 868           functions in <linux/hash.h> or fs/namei.c.
 869
 870 config HAVE_ARCH_NVRAM_OPS
 871         bool
 872
 873 config ISA_BUS_API
 874         def_bool ISA
 875
 876 #
 877 # ABI hall of shame
 878 #
 879 config CLONE_BACKWARDS
 880         bool
 881         help
 882           Architecture has tls passed as the 4th argument of clone(2),
 883           not the 5th one.
 884
 885 config CLONE_BACKWARDS2
 886         bool
 887         help
 888           Architecture has the first two arguments of clone(2) swapped.
 889
 890 config CLONE_BACKWARDS3
 891         bool
 892         help
 893           Architecture has tls passed as the 3rd argument of clone(2),
 894           not the 5th one.
 895
 896 config ODD_RT_SIGACTION
 897         bool
 898         help
 899           Architecture has unusual rt_sigaction(2) arguments
 900
 901 config OLD_SIGSUSPEND
 902         bool
 903         help
 904           Architecture has old sigsuspend(2) syscall, of one-argument variety
 905
 906 config OLD_SIGSUSPEND3
 907         bool
 908         help
 909           Even weirder antique ABI - three-argument sigsuspend(2)
 910
 911 config OLD_SIGACTION
 912         bool
 913         help
 914           Architecture has old sigaction(2) syscall.  Nope, not the same
 915           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 916           but fairly different variant of sigaction(2), thanks to OSF/1
 917           compatibility...
 918
 919 config COMPAT_OLD_SIGACTION
 920         bool
 921
 922 config COMPAT_32BIT_TIME
 923         bool "Provide system calls for 32-bit time_t"
 924         default !64BIT || COMPAT
 925         help
 926           This enables 32 bit time_t support in addition to 64 bit time_t support.
 927           This is relevant on all 32-bit architectures, and 64-bit architectures
 928           as part of compat syscall handling.
 929
 930 config ARCH_NO_PREEMPT
 931         bool
 932
 933 config ARCH_SUPPORTS_RT
 934         bool
 935
 936 config CPU_NO_EFFICIENT_FFS
 937         def_bool n
 938
 939 config HAVE_ARCH_VMAP_STACK
 940         def_bool n
 941         help
 942           An arch should select this symbol if it can support kernel stacks
 943           in vmalloc space.  This means:
 944
 945           - vmalloc space must be large enough to hold many kernel stacks.
 946             This may rule out many 32-bit architectures.
 947
 948           - Stacks in vmalloc space need to work reliably.  For example, if
 949             vmap page tables are created on demand, either this mechanism
 950             needs to work while the stack points to a virtual address with
 951             unpopulated page tables or arch code (switch_to() and switch_mm(),
 952             most likely) needs to ensure that the stack's page table entries
 953             are populated before running on a possibly unpopulated stack.
 954
 955           - If the stack overflows into a guard page, something reasonable
 956             should happen.  The definition of "reasonable" is flexible, but
 957             instantly rebooting without logging anything would be unfriendly.
 958
 959 config VMAP_STACK
 960         default y
 961         bool "Use a virtually-mapped stack"
 962         depends on HAVE_ARCH_VMAP_STACK
 963         depends on !KASAN || KASAN_VMALLOC
 964         help
 965           Enable this if you want the use virtually-mapped kernel stacks
 966           with guard pages.  This causes kernel stack overflows to be
 967           caught immediately rather than causing difficult-to-diagnose
 968           corruption.
 969
 970           To use this with KASAN, the architecture must support backing
 971           virtual mappings with real shadow memory, and KASAN_VMALLOC must
 972           be enabled.
 973
 974 config ARCH_OPTIONAL_KERNEL_RWX
 975         def_bool n
 976
 977 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 978         def_bool n
 979
 980 config ARCH_HAS_STRICT_KERNEL_RWX
 981         def_bool n
 982
 983 config STRICT_KERNEL_RWX
 984         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 985         depends on ARCH_HAS_STRICT_KERNEL_RWX
 986         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 987         help
 988           If this is set, kernel text and rodata memory will be made read-only,
 989           and non-text memory will be made non-executable. This provides
 990           protection against certain security exploits (e.g. executing the heap
 991           or modifying text)
 992
 993           These features are considered standard security practice these days.
 994           You should say Y here in almost all cases.
 995
 996 config ARCH_HAS_STRICT_MODULE_RWX
 997         def_bool n
 998
 999 config STRICT_MODULE_RWX
1000         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1001         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1002         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1003         help
1004           If this is set, module text and rodata memory will be made read-only,
1005           and non-text memory will be made non-executable. This provides
1006           protection against certain security exploits (e.g. writing to text)
1007
1008 # select if the architecture provides an asm/dma-direct.h header
1009 config ARCH_HAS_PHYS_TO_DMA
1010         bool
1011
1012 config HAVE_ARCH_COMPILER_H
1013         bool
1014         help
1015           An architecture can select this if it provides an
1016           asm/compiler.h header that should be included after
1017           linux/compiler-*.h in order to override macro definitions that those
1018           headers generally provide.
1019
1020 config HAVE_ARCH_PREL32_RELOCATIONS
1021         bool
1022         help
1023           May be selected by an architecture if it supports place-relative
1024           32-bit relocations, both in the toolchain and in the module loader,
1025           in which case relative references can be used in special sections
1026           for PCI fixup, initcalls etc which are only half the size on 64 bit
1027           architectures, and don't require runtime relocation on relocatable
1028           kernels.
1029
1030 config ARCH_USE_MEMREMAP_PROT
1031         bool
1032
1033 config LOCK_EVENT_COUNTS
1034         bool "Locking event counts collection"
1035         depends on DEBUG_FS
1036         help
1037           Enable light-weight counting of various locking related events
1038           in the system with minimal performance impact. This reduces
1039           the chance of application behavior change because of timing
1040           differences. The counts are reported via debugfs.
1041
1042 # Select if the architecture has support for applying RELR relocations.
1043 config ARCH_HAS_RELR
1044         bool
1045
1046 config RELR
1047         bool "Use RELR relocation packing"
1048         depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1049         default y
1050         help
1051           Store the kernel's dynamic relocations in the RELR relocation packing
1052           format. Requires a compatible linker (LLD supports this feature), as
1053           well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1054           are compatible).
1055
1056 config ARCH_HAS_MEM_ENCRYPT
1057         bool
1058
1059 config HAVE_SPARSE_SYSCALL_NR
1060        bool
1061        help
1062           An architecture should select this if its syscall numbering is sparse
1063           to save space. For example, MIPS architecture has a syscall array with
1064           entries at 4000, 5000 and 6000 locations. This option turns on syscall
1065           related optimizations for a given architecture.
1066
1067 config ARCH_HAS_VDSO_DATA
1068         bool
1069
1070 config HAVE_STATIC_CALL
1071         bool
1072
1073 config HAVE_STATIC_CALL_INLINE
1074         bool
1075         depends on HAVE_STATIC_CALL
1076
1077 config ARCH_WANT_LD_ORPHAN_WARN
1078         bool
1079         help
1080           An arch should select this symbol once all linker sections are explicitly
1081           included, size-asserted, or discarded in the linker scripts. This is
1082           important because we never want expected sections to be placed heuristically
1083           by the linker, since the locations of such sections can change between linker
1084           versions.
1085
1086 config HAVE_ARCH_PFN_VALID
1087         bool
1088
1089 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1090         bool
1091
1092 source "kernel/gcov/Kconfig"
1093
1094 source "scripts/gcc-plugins/Kconfig"
1095
1096 endmenu