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 ARCH_HAS_SUBPAGE_FAULTS
  28         bool
  29         help
  30           Select if the architecture can check permissions at sub-page
  31           granularity (e.g. arm64 MTE). The probe_user_*() functions
  32           must be implemented.
  33
  34 config HOTPLUG_SMT
  35         bool
  36
  37 config GENERIC_ENTRY
  38         bool
  39
  40 config KPROBES
  41         bool "Kprobes"
  42         depends on MODULES
  43         depends on HAVE_KPROBES
  44         select KALLSYMS
  45         select TASKS_RCU if PREEMPTION
  46         help
  47           Kprobes allows you to trap at almost any kernel address and
  48           execute a callback function.  register_kprobe() establishes
  49           a probepoint and specifies the callback.  Kprobes is useful
  50           for kernel debugging, non-intrusive instrumentation and testing.
  51           If in doubt, say "N".
  52
  53 config JUMP_LABEL
  54         bool "Optimize very unlikely/likely branches"
  55         depends on HAVE_ARCH_JUMP_LABEL
  56         select OBJTOOL if HAVE_JUMP_LABEL_HACK
  57         help
  58           This option enables a transparent branch optimization that
  59           makes certain almost-always-true or almost-always-false branch
  60           conditions even cheaper to execute within the kernel.
  61
  62           Certain performance-sensitive kernel code, such as trace points,
  63           scheduler functionality, networking code and KVM have such
  64           branches and include support for this optimization technique.
  65
  66           If it is detected that the compiler has support for "asm goto",
  67           the kernel will compile such branches with just a nop
  68           instruction. When the condition flag is toggled to true, the
  69           nop will be converted to a jump instruction to execute the
  70           conditional block of instructions.
  71
  72           This technique lowers overhead and stress on the branch prediction
  73           of the processor and generally makes the kernel faster. The update
  74           of the condition is slower, but those are always very rare.
  75
  76           ( On 32-bit x86, the necessary options added to the compiler
  77             flags may increase the size of the kernel slightly. )
  78
  79 config STATIC_KEYS_SELFTEST
  80         bool "Static key selftest"
  81         depends on JUMP_LABEL
  82         help
  83           Boot time self-test of the branch patching code.
  84
  85 config STATIC_CALL_SELFTEST
  86         bool "Static call selftest"
  87         depends on HAVE_STATIC_CALL
  88         help
  89           Boot time self-test of the call patching code.
  90
  91 config OPTPROBES
  92         def_bool y
  93         depends on KPROBES && HAVE_OPTPROBES
  94         select TASKS_RCU if PREEMPTION
  95
  96 config KPROBES_ON_FTRACE
  97         def_bool y
  98         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
  99         depends on DYNAMIC_FTRACE_WITH_REGS
 100         help
 101           If function tracer is enabled and the arch supports full
 102           passing of pt_regs to function tracing, then kprobes can
 103           optimize on top of function tracing.
 104
 105 config UPROBES
 106         def_bool n
 107         depends on ARCH_SUPPORTS_UPROBES
 108         help
 109           Uprobes is the user-space counterpart to kprobes: they
 110           enable instrumentation applications (such as 'perf probe')
 111           to establish unintrusive probes in user-space binaries and
 112           libraries, by executing handler functions when the probes
 113           are hit by user-space applications.
 114
 115           ( These probes come in the form of single-byte breakpoints,
 116             managed by the kernel and kept transparent to the probed
 117             application. )
 118
 119 config HAVE_64BIT_ALIGNED_ACCESS
 120         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 121         help
 122           Some architectures require 64 bit accesses to be 64 bit
 123           aligned, which also requires structs containing 64 bit values
 124           to be 64 bit aligned too. This includes some 32 bit
 125           architectures which can do 64 bit accesses, as well as 64 bit
 126           architectures without unaligned access.
 127
 128           This symbol should be selected by an architecture if 64 bit
 129           accesses are required to be 64 bit aligned in this way even
 130           though it is not a 64 bit architecture.
 131
 132           See Documentation/core-api/unaligned-memory-access.rst for
 133           more information on the topic of unaligned memory accesses.
 134
 135 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 136         bool
 137         help
 138           Some architectures are unable to perform unaligned accesses
 139           without the use of get_unaligned/put_unaligned. Others are
 140           unable to perform such accesses efficiently (e.g. trap on
 141           unaligned access and require fixing it up in the exception
 142           handler.)
 143
 144           This symbol should be selected by an architecture if it can
 145           perform unaligned accesses efficiently to allow different
 146           code paths to be selected for these cases. Some network
 147           drivers, for example, could opt to not fix up alignment
 148           problems with received packets if doing so would not help
 149           much.
 150
 151           See Documentation/core-api/unaligned-memory-access.rst for more
 152           information on the topic of unaligned memory accesses.
 153
 154 config ARCH_USE_BUILTIN_BSWAP
 155         bool
 156         help
 157           Modern versions of GCC (since 4.4) have builtin functions
 158           for handling byte-swapping. Using these, instead of the old
 159           inline assembler that the architecture code provides in the
 160           __arch_bswapXX() macros, allows the compiler to see what's
 161           happening and offers more opportunity for optimisation. In
 162           particular, the compiler will be able to combine the byteswap
 163           with a nearby load or store and use load-and-swap or
 164           store-and-swap instructions if the architecture has them. It
 165           should almost *never* result in code which is worse than the
 166           hand-coded assembler in <asm/swab.h>.  But just in case it
 167           does, the use of the builtins is optional.
 168
 169           Any architecture with load-and-swap or store-and-swap
 170           instructions should set this. And it shouldn't hurt to set it
 171           on architectures that don't have such instructions.
 172
 173 config KRETPROBES
 174         def_bool y
 175         depends on KPROBES && (HAVE_KRETPROBES || HAVE_RETHOOK)
 176
 177 config KRETPROBE_ON_RETHOOK
 178         def_bool y
 179         depends on HAVE_RETHOOK
 180         depends on KRETPROBES
 181         select RETHOOK
 182
 183 config USER_RETURN_NOTIFIER
 184         bool
 185         depends on HAVE_USER_RETURN_NOTIFIER
 186         help
 187           Provide a kernel-internal notification when a cpu is about to
 188           switch to user mode.
 189
 190 config HAVE_IOREMAP_PROT
 191         bool
 192
 193 config HAVE_KPROBES
 194         bool
 195
 196 config HAVE_KRETPROBES
 197         bool
 198
 199 config HAVE_OPTPROBES
 200         bool
 201
 202 config HAVE_KPROBES_ON_FTRACE
 203         bool
 204
 205 config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
 206         bool
 207         help
 208           Since kretprobes modifies return address on the stack, the
 209           stacktrace may see the kretprobe trampoline address instead
 210           of correct one. If the architecture stacktrace code and
 211           unwinder can adjust such entries, select this configuration.
 212
 213 config HAVE_FUNCTION_ERROR_INJECTION
 214         bool
 215
 216 config HAVE_NMI
 217         bool
 218
 219 config HAVE_FUNCTION_DESCRIPTORS
 220         bool
 221
 222 config TRACE_IRQFLAGS_SUPPORT
 223         bool
 224
 225 config TRACE_IRQFLAGS_NMI_SUPPORT
 226         bool
 227
 228 #
 229 # An arch should select this if it provides all these things:
 230 #
 231 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 232 #       arch_has_single_step()  if there is hardware single-step support
 233 #       arch_has_block_step()   if there is hardware block-step support
 234 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 235 #       linux/regset.h          user_regset interfaces
 236 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 237 #       TIF_SYSCALL_TRACE       calls ptrace_report_syscall_{entry,exit}
 238 #       TIF_NOTIFY_RESUME       calls resume_user_mode_work()
 239 #
 240 config HAVE_ARCH_TRACEHOOK
 241         bool
 242
 243 config HAVE_DMA_CONTIGUOUS
 244         bool
 245
 246 config GENERIC_SMP_IDLE_THREAD
 247         bool
 248
 249 config GENERIC_IDLE_POLL_SETUP
 250         bool
 251
 252 config ARCH_HAS_FORTIFY_SOURCE
 253         bool
 254         help
 255           An architecture should select this when it can successfully
 256           build and run with CONFIG_FORTIFY_SOURCE.
 257
 258 #
 259 # Select if the arch provides a historic keepinit alias for the retain_initrd
 260 # command line option
 261 #
 262 config ARCH_HAS_KEEPINITRD
 263         bool
 264
 265 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 266 config ARCH_HAS_SET_MEMORY
 267         bool
 268
 269 # Select if arch has all set_direct_map_invalid/default() functions
 270 config ARCH_HAS_SET_DIRECT_MAP
 271         bool
 272
 273 #
 274 # Select if the architecture provides the arch_dma_set_uncached symbol to
 275 # either provide an uncached segment alias for a DMA allocation, or
 276 # to remap the page tables in place.
 277 #
 278 config ARCH_HAS_DMA_SET_UNCACHED
 279         bool
 280
 281 #
 282 # Select if the architectures provides the arch_dma_clear_uncached symbol
 283 # to undo an in-place page table remap for uncached access.
 284 #
 285 config ARCH_HAS_DMA_CLEAR_UNCACHED
 286         bool
 287
 288 # Select if arch init_task must go in the __init_task_data section
 289 config ARCH_TASK_STRUCT_ON_STACK
 290         bool
 291
 292 # Select if arch has its private alloc_task_struct() function
 293 config ARCH_TASK_STRUCT_ALLOCATOR
 294         bool
 295
 296 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 297         bool
 298         depends on !ARCH_TASK_STRUCT_ALLOCATOR
 299         help
 300           An architecture should select this to provide hardened usercopy
 301           knowledge about what region of the thread_struct should be
 302           whitelisted for copying to userspace. Normally this is only the
 303           FPU registers. Specifically, arch_thread_struct_whitelist()
 304           should be implemented. Without this, the entire thread_struct
 305           field in task_struct will be left whitelisted.
 306
 307 # Select if arch has its private alloc_thread_stack() function
 308 config ARCH_THREAD_STACK_ALLOCATOR
 309         bool
 310
 311 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 312 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 313         bool
 314
 315 config ARCH_WANTS_NO_INSTR
 316         bool
 317         help
 318           An architecture should select this if the noinstr macro is being used on
 319           functions to denote that the toolchain should avoid instrumenting such
 320           functions and is required for correctness.
 321
 322 config ARCH_32BIT_OFF_T
 323         bool
 324         depends on !64BIT
 325         help
 326           All new 32-bit architectures should have 64-bit off_t type on
 327           userspace side which corresponds to the loff_t kernel type. This
 328           is the requirement for modern ABIs. Some existing architectures
 329           still support 32-bit off_t. This option is enabled for all such
 330           architectures explicitly.
 331
 332 # Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
 333 config ARCH_32BIT_USTAT_F_TINODE
 334         bool
 335
 336 config HAVE_ASM_MODVERSIONS
 337         bool
 338         help
 339           This symbol should be selected by an architecture if it provides
 340           <asm/asm-prototypes.h> to support the module versioning for symbols
 341           exported from assembly code.
 342
 343 config HAVE_REGS_AND_STACK_ACCESS_API
 344         bool
 345         help
 346           This symbol should be selected by an architecture if it supports
 347           the API needed to access registers and stack entries from pt_regs,
 348           declared in asm/ptrace.h
 349           For example the kprobes-based event tracer needs this API.
 350
 351 config HAVE_RSEQ
 352         bool
 353         depends on HAVE_REGS_AND_STACK_ACCESS_API
 354         help
 355           This symbol should be selected by an architecture if it
 356           supports an implementation of restartable sequences.
 357
 358 config HAVE_RUST
 359         bool
 360         help
 361           This symbol should be selected by an architecture if it
 362           supports Rust.
 363
 364 config HAVE_FUNCTION_ARG_ACCESS_API
 365         bool
 366         help
 367           This symbol should be selected by an architecture if it supports
 368           the API needed to access function arguments from pt_regs,
 369           declared in asm/ptrace.h
 370
 371 config HAVE_HW_BREAKPOINT
 372         bool
 373         depends on PERF_EVENTS
 374
 375 config HAVE_MIXED_BREAKPOINTS_REGS
 376         bool
 377         depends on HAVE_HW_BREAKPOINT
 378         help
 379           Depending on the arch implementation of hardware breakpoints,
 380           some of them have separate registers for data and instruction
 381           breakpoints addresses, others have mixed registers to store
 382           them but define the access type in a control register.
 383           Select this option if your arch implements breakpoints under the
 384           latter fashion.
 385
 386 config HAVE_USER_RETURN_NOTIFIER
 387         bool
 388
 389 config HAVE_PERF_EVENTS_NMI
 390         bool
 391         help
 392           System hardware can generate an NMI using the perf event
 393           subsystem.  Also has support for calculating CPU cycle events
 394           to determine how many clock cycles in a given period.
 395
 396 config HAVE_HARDLOCKUP_DETECTOR_PERF
 397         bool
 398         depends on HAVE_PERF_EVENTS_NMI
 399         help
 400           The arch chooses to use the generic perf-NMI-based hardlockup
 401           detector. Must define HAVE_PERF_EVENTS_NMI.
 402
 403 config HAVE_NMI_WATCHDOG
 404         depends on HAVE_NMI
 405         bool
 406         help
 407           The arch provides a low level NMI watchdog. It provides
 408           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 409
 410 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 411         bool
 412         select HAVE_NMI_WATCHDOG
 413         help
 414           The arch chooses to provide its own hardlockup detector, which is
 415           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 416           interfaces and parameters provided by hardlockup detector subsystem.
 417
 418 config HAVE_PERF_REGS
 419         bool
 420         help
 421           Support selective register dumps for perf events. This includes
 422           bit-mapping of each registers and a unique architecture id.
 423
 424 config HAVE_PERF_USER_STACK_DUMP
 425         bool
 426         help
 427           Support user stack dumps for perf event samples. This needs
 428           access to the user stack pointer which is not unified across
 429           architectures.
 430
 431 config HAVE_ARCH_JUMP_LABEL
 432         bool
 433
 434 config HAVE_ARCH_JUMP_LABEL_RELATIVE
 435         bool
 436
 437 config MMU_GATHER_TABLE_FREE
 438         bool
 439
 440 config MMU_GATHER_RCU_TABLE_FREE
 441         bool
 442         select MMU_GATHER_TABLE_FREE
 443
 444 config MMU_GATHER_PAGE_SIZE
 445         bool
 446
 447 config MMU_GATHER_NO_RANGE
 448         bool
 449         select MMU_GATHER_MERGE_VMAS
 450
 451 config MMU_GATHER_NO_FLUSH_CACHE
 452         bool
 453
 454 config MMU_GATHER_MERGE_VMAS
 455         bool
 456
 457 config MMU_GATHER_NO_GATHER
 458         bool
 459         depends on MMU_GATHER_TABLE_FREE
 460
 461 config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
 462         bool
 463         help
 464           Temporary select until all architectures can be converted to have
 465           irqs disabled over activate_mm. Architectures that do IPI based TLB
 466           shootdowns should enable this.
 467
 468 # Use normal mm refcounting for MMU_LAZY_TLB kernel thread references.
 469 # MMU_LAZY_TLB_REFCOUNT=n can improve the scalability of context switching
 470 # to/from kernel threads when the same mm is running on a lot of CPUs (a large
 471 # multi-threaded application), by reducing contention on the mm refcount.
 472 #
 473 # This can be disabled if the architecture ensures no CPUs are using an mm as a
 474 # "lazy tlb" beyond its final refcount (i.e., by the time __mmdrop frees the mm
 475 # or its kernel page tables). This could be arranged by arch_exit_mmap(), or
 476 # final exit(2) TLB flush, for example.
 477 #
 478 # To implement this, an arch *must*:
 479 # Ensure the _lazy_tlb variants of mmgrab/mmdrop are used when manipulating
 480 # the lazy tlb reference of a kthread's ->active_mm (non-arch code has been
 481 # converted already).
 482 config MMU_LAZY_TLB_REFCOUNT
 483         def_bool y
 484         depends on !MMU_LAZY_TLB_SHOOTDOWN
 485
 486 # This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an
 487 # mm as a lazy tlb beyond its last reference count, by shooting down these
 488 # users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may
 489 # be using the mm as a lazy tlb, so that they may switch themselves to using
 490 # init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs
 491 # may be using mm as a lazy tlb mm.
 492 #
 493 # To implement this, an arch *must*:
 494 # - At the time of the final mmdrop of the mm, ensure mm_cpumask(mm) contains
 495 #   at least all possible CPUs in which the mm is lazy.
 496 # - It must meet the requirements for MMU_LAZY_TLB_REFCOUNT=n (see above).
 497 config MMU_LAZY_TLB_SHOOTDOWN
 498         bool
 499
 500 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 501         bool
 502
 503 config ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 504         bool
 505
 506 config HAVE_ALIGNED_STRUCT_PAGE
 507         bool
 508         help
 509           This makes sure that struct pages are double word aligned and that
 510           e.g. the SLUB allocator can perform double word atomic operations
 511           on a struct page for better performance. However selecting this
 512           might increase the size of a struct page by a word.
 513
 514 config HAVE_CMPXCHG_LOCAL
 515         bool
 516
 517 config HAVE_CMPXCHG_DOUBLE
 518         bool
 519
 520 config ARCH_WEAK_RELEASE_ACQUIRE
 521         bool
 522
 523 config ARCH_WANT_IPC_PARSE_VERSION
 524         bool
 525
 526 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 527         bool
 528
 529 config ARCH_WANT_OLD_COMPAT_IPC
 530         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 531         bool
 532
 533 config HAVE_ARCH_SECCOMP
 534         bool
 535         help
 536           An arch should select this symbol to support seccomp mode 1 (the fixed
 537           syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
 538           and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
 539           - __NR_seccomp_read_32
 540           - __NR_seccomp_write_32
 541           - __NR_seccomp_exit_32
 542           - __NR_seccomp_sigreturn_32
 543
 544 config HAVE_ARCH_SECCOMP_FILTER
 545         bool
 546         select HAVE_ARCH_SECCOMP
 547         help
 548           An arch should select this symbol if it provides all of these things:
 549           - all the requirements for HAVE_ARCH_SECCOMP
 550           - syscall_get_arch()
 551           - syscall_get_arguments()
 552           - syscall_rollback()
 553           - syscall_set_return_value()
 554           - SIGSYS siginfo_t support
 555           - secure_computing is called from a ptrace_event()-safe context
 556           - secure_computing return value is checked and a return value of -1
 557             results in the system call being skipped immediately.
 558           - seccomp syscall wired up
 559           - if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
 560             SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
 561             COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
 562
 563 config SECCOMP
 564         prompt "Enable seccomp to safely execute untrusted bytecode"
 565         def_bool y
 566         depends on HAVE_ARCH_SECCOMP
 567         help
 568           This kernel feature is useful for number crunching applications
 569           that may need to handle untrusted bytecode during their
 570           execution. By using pipes or other transports made available
 571           to the process as file descriptors supporting the read/write
 572           syscalls, it's possible to isolate those applications in their
 573           own address space using seccomp. Once seccomp is enabled via
 574           prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
 575           disabled and the task is only allowed to execute a few safe
 576           syscalls defined by each seccomp mode.
 577
 578           If unsure, say Y.
 579
 580 config SECCOMP_FILTER
 581         def_bool y
 582         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 583         help
 584           Enable tasks to build secure computing environments defined
 585           in terms of Berkeley Packet Filter programs which implement
 586           task-defined system call filtering polices.
 587
 588           See Documentation/userspace-api/seccomp_filter.rst for details.
 589
 590 config SECCOMP_CACHE_DEBUG
 591         bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
 592         depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
 593         depends on PROC_FS
 594         help
 595           This enables the /proc/pid/seccomp_cache interface to monitor
 596           seccomp cache data. The file format is subject to change. Reading
 597           the file requires CAP_SYS_ADMIN.
 598
 599           This option is for debugging only. Enabling presents the risk that
 600           an adversary may be able to infer the seccomp filter logic.
 601
 602           If unsure, say N.
 603
 604 config HAVE_ARCH_STACKLEAK
 605         bool
 606         help
 607           An architecture should select this if it has the code which
 608           fills the used part of the kernel stack with the STACKLEAK_POISON
 609           value before returning from system calls.
 610
 611 config HAVE_STACKPROTECTOR
 612         bool
 613         help
 614           An arch should select this symbol if:
 615           - it has implemented a stack canary (e.g. __stack_chk_guard)
 616
 617 config STACKPROTECTOR
 618         bool "Stack Protector buffer overflow detection"
 619         depends on HAVE_STACKPROTECTOR
 620         depends on $(cc-option,-fstack-protector)
 621         default y
 622         help
 623           This option turns on the "stack-protector" GCC feature. This
 624           feature puts, at the beginning of functions, a canary value on
 625           the stack just before the return address, and validates
 626           the value just before actually returning.  Stack based buffer
 627           overflows (that need to overwrite this return address) now also
 628           overwrite the canary, which gets detected and the attack is then
 629           neutralized via a kernel panic.
 630
 631           Functions will have the stack-protector canary logic added if they
 632           have an 8-byte or larger character array on the stack.
 633
 634           This feature requires gcc version 4.2 or above, or a distribution
 635           gcc with the feature backported ("-fstack-protector").
 636
 637           On an x86 "defconfig" build, this feature adds canary checks to
 638           about 3% of all kernel functions, which increases kernel code size
 639           by about 0.3%.
 640
 641 config STACKPROTECTOR_STRONG
 642         bool "Strong Stack Protector"
 643         depends on STACKPROTECTOR
 644         depends on $(cc-option,-fstack-protector-strong)
 645         default y
 646         help
 647           Functions will have the stack-protector canary logic added in any
 648           of the following conditions:
 649
 650           - local variable's address used as part of the right hand side of an
 651             assignment or function argument
 652           - local variable is an array (or union containing an array),
 653             regardless of array type or length
 654           - uses register local variables
 655
 656           This feature requires gcc version 4.9 or above, or a distribution
 657           gcc with the feature backported ("-fstack-protector-strong").
 658
 659           On an x86 "defconfig" build, this feature adds canary checks to
 660           about 20% of all kernel functions, which increases the kernel code
 661           size by about 2%.
 662
 663 config ARCH_SUPPORTS_SHADOW_CALL_STACK
 664         bool
 665         help
 666           An architecture should select this if it supports the compiler's
 667           Shadow Call Stack and implements runtime support for shadow stack
 668           switching.
 669
 670 config SHADOW_CALL_STACK
 671         bool "Shadow Call Stack"
 672         depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
 673         depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
 674         help
 675           This option enables the compiler's Shadow Call Stack, which
 676           uses a shadow stack to protect function return addresses from
 677           being overwritten by an attacker. More information can be found
 678           in the compiler's documentation:
 679
 680           - Clang: https://clang.llvm.org/docs/ShadowCallStack.html
 681           - GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options
 682
 683           Note that security guarantees in the kernel differ from the
 684           ones documented for user space. The kernel must store addresses
 685           of shadow stacks in memory, which means an attacker capable of
 686           reading and writing arbitrary memory may be able to locate them
 687           and hijack control flow by modifying the stacks.
 688
 689 config DYNAMIC_SCS
 690         bool
 691         help
 692           Set by the arch code if it relies on code patching to insert the
 693           shadow call stack push and pop instructions rather than on the
 694           compiler.
 695
 696 config LTO
 697         bool
 698         help
 699           Selected if the kernel will be built using the compiler's LTO feature.
 700
 701 config LTO_CLANG
 702         bool
 703         select LTO
 704         help
 705           Selected if the kernel will be built using Clang's LTO feature.
 706
 707 config ARCH_SUPPORTS_LTO_CLANG
 708         bool
 709         help
 710           An architecture should select this option if it supports:
 711           - compiling with Clang,
 712           - compiling inline assembly with Clang's integrated assembler,
 713           - and linking with LLD.
 714
 715 config ARCH_SUPPORTS_LTO_CLANG_THIN
 716         bool
 717         help
 718           An architecture should select this option if it can support Clang's
 719           ThinLTO mode.
 720
 721 config HAS_LTO_CLANG
 722         def_bool y
 723         depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM
 724         depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
 725         depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
 726         depends on ARCH_SUPPORTS_LTO_CLANG
 727         depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
 728         depends on !KASAN || KASAN_HW_TAGS
 729         depends on !GCOV_KERNEL
 730         help
 731           The compiler and Kconfig options support building with Clang's
 732           LTO.
 733
 734 choice
 735         prompt "Link Time Optimization (LTO)"
 736         default LTO_NONE
 737         help
 738           This option enables Link Time Optimization (LTO), which allows the
 739           compiler to optimize binaries globally.
 740
 741           If unsure, select LTO_NONE. Note that LTO is very resource-intensive
 742           so it's disabled by default.
 743
 744 config LTO_NONE
 745         bool "None"
 746         help
 747           Build the kernel normally, without Link Time Optimization (LTO).
 748
 749 config LTO_CLANG_FULL
 750         bool "Clang Full LTO (EXPERIMENTAL)"
 751         depends on HAS_LTO_CLANG
 752         depends on !COMPILE_TEST
 753         select LTO_CLANG
 754         help
 755           This option enables Clang's full Link Time Optimization (LTO), which
 756           allows the compiler to optimize the kernel globally. If you enable
 757           this option, the compiler generates LLVM bitcode instead of ELF
 758           object files, and the actual compilation from bitcode happens at
 759           the LTO link step, which may take several minutes depending on the
 760           kernel configuration. More information can be found from LLVM's
 761           documentation:
 762
 763             https://llvm.org/docs/LinkTimeOptimization.html
 764
 765           During link time, this option can use a large amount of RAM, and
 766           may take much longer than the ThinLTO option.
 767
 768 config LTO_CLANG_THIN
 769         bool "Clang ThinLTO (EXPERIMENTAL)"
 770         depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
 771         select LTO_CLANG
 772         help
 773           This option enables Clang's ThinLTO, which allows for parallel
 774           optimization and faster incremental compiles compared to the
 775           CONFIG_LTO_CLANG_FULL option. More information can be found
 776           from Clang's documentation:
 777
 778             https://clang.llvm.org/docs/ThinLTO.html
 779
 780           If unsure, say Y.
 781 endchoice
 782
 783 config ARCH_SUPPORTS_CFI_CLANG
 784         bool
 785         help
 786           An architecture should select this option if it can support Clang's
 787           Control-Flow Integrity (CFI) checking.
 788
 789 config ARCH_USES_CFI_TRAPS
 790         bool
 791
 792 config CFI_CLANG
 793         bool "Use Clang's Control Flow Integrity (CFI)"
 794         depends on ARCH_SUPPORTS_CFI_CLANG
 795         depends on $(cc-option,-fsanitize=kcfi)
 796         help
 797           This option enables Clang’s forward-edge Control Flow Integrity
 798           (CFI) checking, where the compiler injects a runtime check to each
 799           indirect function call to ensure the target is a valid function with
 800           the correct static type. This restricts possible call targets and
 801           makes it more difficult for an attacker to exploit bugs that allow
 802           the modification of stored function pointers. More information can be
 803           found from Clang's documentation:
 804
 805             https://clang.llvm.org/docs/ControlFlowIntegrity.html
 806
 807 config CFI_PERMISSIVE
 808         bool "Use CFI in permissive mode"
 809         depends on CFI_CLANG
 810         help
 811           When selected, Control Flow Integrity (CFI) violations result in a
 812           warning instead of a kernel panic. This option should only be used
 813           for finding indirect call type mismatches during development.
 814
 815           If unsure, say N.
 816
 817 config HAVE_ARCH_WITHIN_STACK_FRAMES
 818         bool
 819         help
 820           An architecture should select this if it can walk the kernel stack
 821           frames to determine if an object is part of either the arguments
 822           or local variables (i.e. that it excludes saved return addresses,
 823           and similar) by implementing an inline arch_within_stack_frames(),
 824           which is used by CONFIG_HARDENED_USERCOPY.
 825
 826 config HAVE_CONTEXT_TRACKING_USER
 827         bool
 828         help
 829           Provide kernel/user boundaries probes necessary for subsystems
 830           that need it, such as userspace RCU extended quiescent state.
 831           Syscalls need to be wrapped inside user_exit()-user_enter(), either
 832           optimized behind static key or through the slow path using TIF_NOHZ
 833           flag. Exceptions handlers must be wrapped as well. Irqs are already
 834           protected inside ct_irq_enter/ct_irq_exit() but preemption or signal
 835           handling on irq exit still need to be protected.
 836
 837 config HAVE_CONTEXT_TRACKING_USER_OFFSTACK
 838         bool
 839         help
 840           Architecture neither relies on exception_enter()/exception_exit()
 841           nor on schedule_user(). Also preempt_schedule_notrace() and
 842           preempt_schedule_irq() can't be called in a preemptible section
 843           while context tracking is CONTEXT_USER. This feature reflects a sane
 844           entry implementation where the following requirements are met on
 845           critical entry code, ie: before user_exit() or after user_enter():
 846
 847           - Critical entry code isn't preemptible (or better yet:
 848             not interruptible).
 849           - No use of RCU read side critical sections, unless ct_nmi_enter()
 850             got called.
 851           - No use of instrumentation, unless instrumentation_begin() got
 852             called.
 853
 854 config HAVE_TIF_NOHZ
 855         bool
 856         help
 857           Arch relies on TIF_NOHZ and syscall slow path to implement context
 858           tracking calls to user_enter()/user_exit().
 859
 860 config HAVE_VIRT_CPU_ACCOUNTING
 861         bool
 862
 863 config HAVE_VIRT_CPU_ACCOUNTING_IDLE
 864         bool
 865         help
 866           Architecture has its own way to account idle CPU time and therefore
 867           doesn't implement vtime_account_idle().
 868
 869 config ARCH_HAS_SCALED_CPUTIME
 870         bool
 871
 872 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 873         bool
 874         default y if 64BIT
 875         help
 876           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 877           Before enabling this option, arch code must be audited
 878           to ensure there are no races in concurrent read/write of
 879           cputime_t. For example, reading/writing 64-bit cputime_t on
 880           some 32-bit arches may require multiple accesses, so proper
 881           locking is needed to protect against concurrent accesses.
 882
 883 config HAVE_IRQ_TIME_ACCOUNTING
 884         bool
 885         help
 886           Archs need to ensure they use a high enough resolution clock to
 887           support irq time accounting and then call enable_sched_clock_irqtime().
 888
 889 config HAVE_MOVE_PUD
 890         bool
 891         help
 892           Architectures that select this are able to move page tables at the
 893           PUD level. If there are only 3 page table levels, the move effectively
 894           happens at the PGD level.
 895
 896 config HAVE_MOVE_PMD
 897         bool
 898         help
 899           Archs that select this are able to move page tables at the PMD level.
 900
 901 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 902         bool
 903
 904 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 905         bool
 906
 907 config HAVE_ARCH_HUGE_VMAP
 908         bool
 909
 910 #
 911 #  Archs that select this would be capable of PMD-sized vmaps (i.e.,
 912 #  arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag
 913 #  must be used to enable allocations to use hugepages.
 914 #
 915 config HAVE_ARCH_HUGE_VMALLOC
 916         depends on HAVE_ARCH_HUGE_VMAP
 917         bool
 918
 919 config ARCH_WANT_HUGE_PMD_SHARE
 920         bool
 921
 922 config HAVE_ARCH_SOFT_DIRTY
 923         bool
 924
 925 config HAVE_MOD_ARCH_SPECIFIC
 926         bool
 927         help
 928           The arch uses struct mod_arch_specific to store data.  Many arches
 929           just need a simple module loader without arch specific data - those
 930           should not enable this.
 931
 932 config MODULES_USE_ELF_RELA
 933         bool
 934         help
 935           Modules only use ELF RELA relocations.  Modules with ELF REL
 936           relocations will give an error.
 937
 938 config MODULES_USE_ELF_REL
 939         bool
 940         help
 941           Modules only use ELF REL relocations.  Modules with ELF RELA
 942           relocations will give an error.
 943
 944 config ARCH_WANTS_MODULES_DATA_IN_VMALLOC
 945         bool
 946         help
 947           For architectures like powerpc/32 which have constraints on module
 948           allocation and need to allocate module data outside of module area.
 949
 950 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 951         bool
 952         help
 953           Architecture doesn't only execute the irq handler on the irq stack
 954           but also irq_exit(). This way we can process softirqs on this irq
 955           stack instead of switching to a new one when we call __do_softirq()
 956           in the end of an hardirq.
 957           This spares a stack switch and improves cache usage on softirq
 958           processing.
 959
 960 config HAVE_SOFTIRQ_ON_OWN_STACK
 961         bool
 962         help
 963           Architecture provides a function to run __do_softirq() on a
 964           separate stack.
 965
 966 config SOFTIRQ_ON_OWN_STACK
 967         def_bool HAVE_SOFTIRQ_ON_OWN_STACK && !PREEMPT_RT
 968
 969 config ALTERNATE_USER_ADDRESS_SPACE
 970         bool
 971         help
 972           Architectures set this when the CPU uses separate address
 973           spaces for kernel and user space pointers. In this case, the
 974           access_ok() check on a __user pointer is skipped.
 975
 976 config PGTABLE_LEVELS
 977         int
 978         default 2
 979
 980 config ARCH_HAS_ELF_RANDOMIZE
 981         bool
 982         help
 983           An architecture supports choosing randomized locations for
 984           stack, mmap, brk, and ET_DYN. Defined functions:
 985           - arch_mmap_rnd()
 986           - arch_randomize_brk()
 987
 988 config HAVE_ARCH_MMAP_RND_BITS
 989         bool
 990         help
 991           An arch should select this symbol if it supports setting a variable
 992           number of bits for use in establishing the base address for mmap
 993           allocations, has MMU enabled and provides values for both:
 994           - ARCH_MMAP_RND_BITS_MIN
 995           - ARCH_MMAP_RND_BITS_MAX
 996
 997 config HAVE_EXIT_THREAD
 998         bool
 999         help
1000           An architecture implements exit_thread.
1001
1002 config ARCH_MMAP_RND_BITS_MIN
1003         int
1004
1005 config ARCH_MMAP_RND_BITS_MAX
1006         int
1007
1008 config ARCH_MMAP_RND_BITS_DEFAULT
1009         int
1010
1011 config ARCH_MMAP_RND_BITS
1012         int "Number of bits to use for ASLR of mmap base address" if EXPERT
1013         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
1014         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
1015         default ARCH_MMAP_RND_BITS_MIN
1016         depends on HAVE_ARCH_MMAP_RND_BITS
1017         help
1018           This value can be used to select the number of bits to use to
1019           determine the random offset to the base address of vma regions
1020           resulting from mmap allocations. This value will be bounded
1021           by the architecture's minimum and maximum supported values.
1022
1023           This value can be changed after boot using the
1024           /proc/sys/vm/mmap_rnd_bits tunable
1025
1026 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
1027         bool
1028         help
1029           An arch should select this symbol if it supports running applications
1030           in compatibility mode, supports setting a variable number of bits for
1031           use in establishing the base address for mmap allocations, has MMU
1032           enabled and provides values for both:
1033           - ARCH_MMAP_RND_COMPAT_BITS_MIN
1034           - ARCH_MMAP_RND_COMPAT_BITS_MAX
1035
1036 config ARCH_MMAP_RND_COMPAT_BITS_MIN
1037         int
1038
1039 config ARCH_MMAP_RND_COMPAT_BITS_MAX
1040         int
1041
1042 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
1043         int
1044
1045 config ARCH_MMAP_RND_COMPAT_BITS
1046         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
1047         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
1048         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
1049         default ARCH_MMAP_RND_COMPAT_BITS_MIN
1050         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
1051         help
1052           This value can be used to select the number of bits to use to
1053           determine the random offset to the base address of vma regions
1054           resulting from mmap allocations for compatible applications This
1055           value will be bounded by the architecture's minimum and maximum
1056           supported values.
1057
1058           This value can be changed after boot using the
1059           /proc/sys/vm/mmap_rnd_compat_bits tunable
1060
1061 config HAVE_ARCH_COMPAT_MMAP_BASES
1062         bool
1063         help
1064           This allows 64bit applications to invoke 32-bit mmap() syscall
1065           and vice-versa 32-bit applications to call 64-bit mmap().
1066           Required for applications doing different bitness syscalls.
1067
1068 config PAGE_SIZE_LESS_THAN_64KB
1069         def_bool y
1070         depends on !ARM64_64K_PAGES
1071         depends on !IA64_PAGE_SIZE_64KB
1072         depends on !PAGE_SIZE_64KB
1073         depends on !PARISC_PAGE_SIZE_64KB
1074         depends on PAGE_SIZE_LESS_THAN_256KB
1075
1076 config PAGE_SIZE_LESS_THAN_256KB
1077         def_bool y
1078         depends on !PAGE_SIZE_256KB
1079
1080 # This allows to use a set of generic functions to determine mmap base
1081 # address by giving priority to top-down scheme only if the process
1082 # is not in legacy mode (compat task, unlimited stack size or
1083 # sysctl_legacy_va_layout).
1084 # Architecture that selects this option can provide its own version of:
1085 # - STACK_RND_MASK
1086 config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
1087         bool
1088         depends on MMU
1089         select ARCH_HAS_ELF_RANDOMIZE
1090
1091 config HAVE_OBJTOOL
1092         bool
1093
1094 config HAVE_JUMP_LABEL_HACK
1095         bool
1096
1097 config HAVE_NOINSTR_HACK
1098         bool
1099
1100 config HAVE_NOINSTR_VALIDATION
1101         bool
1102
1103 config HAVE_UACCESS_VALIDATION
1104         bool
1105         select OBJTOOL
1106
1107 config HAVE_STACK_VALIDATION
1108         bool
1109         help
1110           Architecture supports objtool compile-time frame pointer rule
1111           validation.
1112
1113 config HAVE_RELIABLE_STACKTRACE
1114         bool
1115         help
1116           Architecture has either save_stack_trace_tsk_reliable() or
1117           arch_stack_walk_reliable() function which only returns a stack trace
1118           if it can guarantee the trace is reliable.
1119
1120 config HAVE_ARCH_HASH
1121         bool
1122         default n
1123         help
1124           If this is set, the architecture provides an <asm/hash.h>
1125           file which provides platform-specific implementations of some
1126           functions in <linux/hash.h> or fs/namei.c.
1127
1128 config HAVE_ARCH_NVRAM_OPS
1129         bool
1130
1131 config ISA_BUS_API
1132         def_bool ISA
1133
1134 #
1135 # ABI hall of shame
1136 #
1137 config CLONE_BACKWARDS
1138         bool
1139         help
1140           Architecture has tls passed as the 4th argument of clone(2),
1141           not the 5th one.
1142
1143 config CLONE_BACKWARDS2
1144         bool
1145         help
1146           Architecture has the first two arguments of clone(2) swapped.
1147
1148 config CLONE_BACKWARDS3
1149         bool
1150         help
1151           Architecture has tls passed as the 3rd argument of clone(2),
1152           not the 5th one.
1153
1154 config ODD_RT_SIGACTION
1155         bool
1156         help
1157           Architecture has unusual rt_sigaction(2) arguments
1158
1159 config OLD_SIGSUSPEND
1160         bool
1161         help
1162           Architecture has old sigsuspend(2) syscall, of one-argument variety
1163
1164 config OLD_SIGSUSPEND3
1165         bool
1166         help
1167           Even weirder antique ABI - three-argument sigsuspend(2)
1168
1169 config OLD_SIGACTION
1170         bool
1171         help
1172           Architecture has old sigaction(2) syscall.  Nope, not the same
1173           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
1174           but fairly different variant of sigaction(2), thanks to OSF/1
1175           compatibility...
1176
1177 config COMPAT_OLD_SIGACTION
1178         bool
1179
1180 config COMPAT_32BIT_TIME
1181         bool "Provide system calls for 32-bit time_t"
1182         default !64BIT || COMPAT
1183         help
1184           This enables 32 bit time_t support in addition to 64 bit time_t support.
1185           This is relevant on all 32-bit architectures, and 64-bit architectures
1186           as part of compat syscall handling.
1187
1188 config ARCH_NO_PREEMPT
1189         bool
1190
1191 config ARCH_EPHEMERAL_INODES
1192         def_bool n
1193         help
1194           An arch should select this symbol if it doesn't keep track of inode
1195           instances on its own, but instead relies on something else (e.g. the
1196           host kernel for an UML kernel).
1197
1198 config ARCH_SUPPORTS_RT
1199         bool
1200
1201 config CPU_NO_EFFICIENT_FFS
1202         def_bool n
1203
1204 config HAVE_ARCH_VMAP_STACK
1205         def_bool n
1206         help
1207           An arch should select this symbol if it can support kernel stacks
1208           in vmalloc space.  This means:
1209
1210           - vmalloc space must be large enough to hold many kernel stacks.
1211             This may rule out many 32-bit architectures.
1212
1213           - Stacks in vmalloc space need to work reliably.  For example, if
1214             vmap page tables are created on demand, either this mechanism
1215             needs to work while the stack points to a virtual address with
1216             unpopulated page tables or arch code (switch_to() and switch_mm(),
1217             most likely) needs to ensure that the stack's page table entries
1218             are populated before running on a possibly unpopulated stack.
1219
1220           - If the stack overflows into a guard page, something reasonable
1221             should happen.  The definition of "reasonable" is flexible, but
1222             instantly rebooting without logging anything would be unfriendly.
1223
1224 config VMAP_STACK
1225         default y
1226         bool "Use a virtually-mapped stack"
1227         depends on HAVE_ARCH_VMAP_STACK
1228         depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
1229         help
1230           Enable this if you want the use virtually-mapped kernel stacks
1231           with guard pages.  This causes kernel stack overflows to be
1232           caught immediately rather than causing difficult-to-diagnose
1233           corruption.
1234
1235           To use this with software KASAN modes, the architecture must support
1236           backing virtual mappings with real shadow memory, and KASAN_VMALLOC
1237           must be enabled.
1238
1239 config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1240         def_bool n
1241         help
1242           An arch should select this symbol if it can support kernel stack
1243           offset randomization with calls to add_random_kstack_offset()
1244           during syscall entry and choose_random_kstack_offset() during
1245           syscall exit. Careful removal of -fstack-protector-strong and
1246           -fstack-protector should also be applied to the entry code and
1247           closely examined, as the artificial stack bump looks like an array
1248           to the compiler, so it will attempt to add canary checks regardless
1249           of the static branch state.
1250
1251 config RANDOMIZE_KSTACK_OFFSET
1252         bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT
1253         default y
1254         depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
1255         depends on INIT_STACK_NONE || !CC_IS_CLANG || CLANG_VERSION >= 140000
1256         help
1257           The kernel stack offset can be randomized (after pt_regs) by
1258           roughly 5 bits of entropy, frustrating memory corruption
1259           attacks that depend on stack address determinism or
1260           cross-syscall address exposures.
1261
1262           The feature is controlled via the "randomize_kstack_offset=on/off"
1263           kernel boot param, and if turned off has zero overhead due to its use
1264           of static branches (see JUMP_LABEL).
1265
1266           If unsure, say Y.
1267
1268 config RANDOMIZE_KSTACK_OFFSET_DEFAULT
1269         bool "Default state of kernel stack offset randomization"
1270         depends on RANDOMIZE_KSTACK_OFFSET
1271         help
1272           Kernel stack offset randomization is controlled by kernel boot param
1273           "randomize_kstack_offset=on/off", and this config chooses the default
1274           boot state.
1275
1276 config ARCH_OPTIONAL_KERNEL_RWX
1277         def_bool n
1278
1279 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1280         def_bool n
1281
1282 config ARCH_HAS_STRICT_KERNEL_RWX
1283         def_bool n
1284
1285 config STRICT_KERNEL_RWX
1286         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
1287         depends on ARCH_HAS_STRICT_KERNEL_RWX
1288         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1289         help
1290           If this is set, kernel text and rodata memory will be made read-only,
1291           and non-text memory will be made non-executable. This provides
1292           protection against certain security exploits (e.g. executing the heap
1293           or modifying text)
1294
1295           These features are considered standard security practice these days.
1296           You should say Y here in almost all cases.
1297
1298 config ARCH_HAS_STRICT_MODULE_RWX
1299         def_bool n
1300
1301 config STRICT_MODULE_RWX
1302         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
1303         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
1304         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
1305         help
1306           If this is set, module text and rodata memory will be made read-only,
1307           and non-text memory will be made non-executable. This provides
1308           protection against certain security exploits (e.g. writing to text)
1309
1310 # select if the architecture provides an asm/dma-direct.h header
1311 config ARCH_HAS_PHYS_TO_DMA
1312         bool
1313
1314 config HAVE_ARCH_COMPILER_H
1315         bool
1316         help
1317           An architecture can select this if it provides an
1318           asm/compiler.h header that should be included after
1319           linux/compiler-*.h in order to override macro definitions that those
1320           headers generally provide.
1321
1322 config HAVE_ARCH_PREL32_RELOCATIONS
1323         bool
1324         help
1325           May be selected by an architecture if it supports place-relative
1326           32-bit relocations, both in the toolchain and in the module loader,
1327           in which case relative references can be used in special sections
1328           for PCI fixup, initcalls etc which are only half the size on 64 bit
1329           architectures, and don't require runtime relocation on relocatable
1330           kernels.
1331
1332 config ARCH_USE_MEMREMAP_PROT
1333         bool
1334
1335 config LOCK_EVENT_COUNTS
1336         bool "Locking event counts collection"
1337         depends on DEBUG_FS
1338         help
1339           Enable light-weight counting of various locking related events
1340           in the system with minimal performance impact. This reduces
1341           the chance of application behavior change because of timing
1342           differences. The counts are reported via debugfs.
1343
1344 # Select if the architecture has support for applying RELR relocations.
1345 config ARCH_HAS_RELR
1346         bool
1347
1348 config RELR
1349         bool "Use RELR relocation packing"
1350         depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
1351         default y
1352         help
1353           Store the kernel's dynamic relocations in the RELR relocation packing
1354           format. Requires a compatible linker (LLD supports this feature), as
1355           well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
1356           are compatible).
1357
1358 config ARCH_HAS_MEM_ENCRYPT
1359         bool
1360
1361 config ARCH_HAS_CC_PLATFORM
1362         bool
1363
1364 config HAVE_SPARSE_SYSCALL_NR
1365         bool
1366         help
1367           An architecture should select this if its syscall numbering is sparse
1368           to save space. For example, MIPS architecture has a syscall array with
1369           entries at 4000, 5000 and 6000 locations. This option turns on syscall
1370           related optimizations for a given architecture.
1371
1372 config ARCH_HAS_VDSO_DATA
1373         bool
1374
1375 config HAVE_STATIC_CALL
1376         bool
1377
1378 config HAVE_STATIC_CALL_INLINE
1379         bool
1380         depends on HAVE_STATIC_CALL
1381         select OBJTOOL
1382
1383 config HAVE_PREEMPT_DYNAMIC
1384         bool
1385
1386 config HAVE_PREEMPT_DYNAMIC_CALL
1387         bool
1388         depends on HAVE_STATIC_CALL
1389         select HAVE_PREEMPT_DYNAMIC
1390         help
1391           An architecture should select this if it can handle the preemption
1392           model being selected at boot time using static calls.
1393
1394           Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
1395           preemption function will be patched directly.
1396
1397           Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
1398           call to a preemption function will go through a trampoline, and the
1399           trampoline will be patched.
1400
1401           It is strongly advised to support inline static call to avoid any
1402           overhead.
1403
1404 config HAVE_PREEMPT_DYNAMIC_KEY
1405         bool
1406         depends on HAVE_ARCH_JUMP_LABEL
1407         select HAVE_PREEMPT_DYNAMIC
1408         help
1409           An architecture should select this if it can handle the preemption
1410           model being selected at boot time using static keys.
1411
1412           Each preemption function will be given an early return based on a
1413           static key. This should have slightly lower overhead than non-inline
1414           static calls, as this effectively inlines each trampoline into the
1415           start of its callee. This may avoid redundant work, and may
1416           integrate better with CFI schemes.
1417
1418           This will have greater overhead than using inline static calls as
1419           the call to the preemption function cannot be entirely elided.
1420
1421 config ARCH_WANT_LD_ORPHAN_WARN
1422         bool
1423         help
1424           An arch should select this symbol once all linker sections are explicitly
1425           included, size-asserted, or discarded in the linker scripts. This is
1426           important because we never want expected sections to be placed heuristically
1427           by the linker, since the locations of such sections can change between linker
1428           versions.
1429
1430 config HAVE_ARCH_PFN_VALID
1431         bool
1432
1433 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
1434         bool
1435
1436 config ARCH_SUPPORTS_PAGE_TABLE_CHECK
1437         bool
1438
1439 config ARCH_SPLIT_ARG64
1440         bool
1441         help
1442           If a 32-bit architecture requires 64-bit arguments to be split into
1443           pairs of 32-bit arguments, select this option.
1444
1445 config ARCH_HAS_ELFCORE_COMPAT
1446         bool
1447
1448 config ARCH_HAS_PARANOID_L1D_FLUSH
1449         bool
1450
1451 config ARCH_HAVE_TRACE_MMIO_ACCESS
1452         bool
1453
1454 config DYNAMIC_SIGFRAME
1455         bool
1456
1457 # Select, if arch has a named attribute group bound to NUMA device nodes.
1458 config HAVE_ARCH_NODE_DEV_GROUP
1459         bool
1460
1461 config ARCH_HAS_NONLEAF_PMD_YOUNG
1462         bool
1463         help
1464           Architectures that select this option are capable of setting the
1465           accessed bit in non-leaf PMD entries when using them as part of linear
1466           address translations. Page table walkers that clear the accessed bit
1467           may use this capability to reduce their search space.
1468
1469 source "kernel/gcov/Kconfig"
1470
1471 source "scripts/gcc-plugins/Kconfig"
1472
1473 config FUNCTION_ALIGNMENT_4B
1474         bool
1475
1476 config FUNCTION_ALIGNMENT_8B
1477         bool
1478
1479 config FUNCTION_ALIGNMENT_16B
1480         bool
1481
1482 config FUNCTION_ALIGNMENT_32B
1483         bool
1484
1485 config FUNCTION_ALIGNMENT_64B
1486         bool
1487
1488 config FUNCTION_ALIGNMENT
1489         int
1490         default 64 if FUNCTION_ALIGNMENT_64B
1491         default 32 if FUNCTION_ALIGNMENT_32B
1492         default 16 if FUNCTION_ALIGNMENT_16B
1493         default 8 if FUNCTION_ALIGNMENT_8B
1494         default 4 if FUNCTION_ALIGNMENT_4B
1495         default 0
1496
1497 endmenu