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