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 HAVE_IMA_KEXEC
  22         bool
  23
  24 config HOTPLUG_SMT
  25         bool
  26
  27 config OPROFILE
  28         tristate "OProfile system profiling"
  29         depends on PROFILING
  30         depends on HAVE_OPROFILE
  31         select RING_BUFFER
  32         select RING_BUFFER_ALLOW_SWAP
  33         help
  34           OProfile is a profiling system capable of profiling the
  35           whole system, include the kernel, kernel modules, libraries,
  36           and applications.
  37
  38           If unsure, say N.
  39
  40 config OPROFILE_EVENT_MULTIPLEX
  41         bool "OProfile multiplexing support (EXPERIMENTAL)"
  42         default n
  43         depends on OPROFILE && X86
  44         help
  45           The number of hardware counters is limited. The multiplexing
  46           feature enables OProfile to gather more events than counters
  47           are provided by the hardware. This is realized by switching
  48           between events at a user specified time interval.
  49
  50           If unsure, say N.
  51
  52 config HAVE_OPROFILE
  53         bool
  54
  55 config OPROFILE_NMI_TIMER
  56         def_bool y
  57         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  58
  59 config KPROBES
  60         bool "Kprobes"
  61         depends on MODULES
  62         depends on HAVE_KPROBES
  63         select KALLSYMS
  64         help
  65           Kprobes allows you to trap at almost any kernel address and
  66           execute a callback function.  register_kprobe() establishes
  67           a probepoint and specifies the callback.  Kprobes is useful
  68           for kernel debugging, non-intrusive instrumentation and testing.
  69           If in doubt, say "N".
  70
  71 config JUMP_LABEL
  72        bool "Optimize very unlikely/likely branches"
  73        depends on HAVE_ARCH_JUMP_LABEL
  74        help
  75          This option enables a transparent branch optimization that
  76          makes certain almost-always-true or almost-always-false branch
  77          conditions even cheaper to execute within the kernel.
  78
  79          Certain performance-sensitive kernel code, such as trace points,
  80          scheduler functionality, networking code and KVM have such
  81          branches and include support for this optimization technique.
  82
  83          If it is detected that the compiler has support for "asm goto",
  84          the kernel will compile such branches with just a nop
  85          instruction. When the condition flag is toggled to true, the
  86          nop will be converted to a jump instruction to execute the
  87          conditional block of instructions.
  88
  89          This technique lowers overhead and stress on the branch prediction
  90          of the processor and generally makes the kernel faster. The update
  91          of the condition is slower, but those are always very rare.
  92
  93          ( On 32-bit x86, the necessary options added to the compiler
  94            flags may increase the size of the kernel slightly. )
  95
  96 config STATIC_KEYS_SELFTEST
  97         bool "Static key selftest"
  98         depends on JUMP_LABEL
  99         help
 100           Boot time self-test of the branch patching code.
 101
 102 config OPTPROBES
 103         def_bool y
 104         depends on KPROBES && HAVE_OPTPROBES
 105         select TASKS_RCU if PREEMPT
 106
 107 config KPROBES_ON_FTRACE
 108         def_bool y
 109         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
 110         depends on DYNAMIC_FTRACE_WITH_REGS
 111         help
 112          If function tracer is enabled and the arch supports full
 113          passing of pt_regs to function tracing, then kprobes can
 114          optimize on top of function tracing.
 115
 116 config UPROBES
 117         def_bool n
 118         depends on ARCH_SUPPORTS_UPROBES
 119         help
 120           Uprobes is the user-space counterpart to kprobes: they
 121           enable instrumentation applications (such as 'perf probe')
 122           to establish unintrusive probes in user-space binaries and
 123           libraries, by executing handler functions when the probes
 124           are hit by user-space applications.
 125
 126           ( These probes come in the form of single-byte breakpoints,
 127             managed by the kernel and kept transparent to the probed
 128             application. )
 129
 130 config HAVE_64BIT_ALIGNED_ACCESS
 131         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 132         help
 133           Some architectures require 64 bit accesses to be 64 bit
 134           aligned, which also requires structs containing 64 bit values
 135           to be 64 bit aligned too. This includes some 32 bit
 136           architectures which can do 64 bit accesses, as well as 64 bit
 137           architectures without unaligned access.
 138
 139           This symbol should be selected by an architecture if 64 bit
 140           accesses are required to be 64 bit aligned in this way even
 141           though it is not a 64 bit architecture.
 142
 143           See Documentation/unaligned-memory-access.txt for more
 144           information on the topic of unaligned memory accesses.
 145
 146 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 147         bool
 148         help
 149           Some architectures are unable to perform unaligned accesses
 150           without the use of get_unaligned/put_unaligned. Others are
 151           unable to perform such accesses efficiently (e.g. trap on
 152           unaligned access and require fixing it up in the exception
 153           handler.)
 154
 155           This symbol should be selected by an architecture if it can
 156           perform unaligned accesses efficiently to allow different
 157           code paths to be selected for these cases. Some network
 158           drivers, for example, could opt to not fix up alignment
 159           problems with received packets if doing so would not help
 160           much.
 161
 162           See Documentation/unaligned-memory-access.txt for more
 163           information on the topic of unaligned memory accesses.
 164
 165 config ARCH_USE_BUILTIN_BSWAP
 166        bool
 167        help
 168          Modern versions of GCC (since 4.4) have builtin functions
 169          for handling byte-swapping. Using these, instead of the old
 170          inline assembler that the architecture code provides in the
 171          __arch_bswapXX() macros, allows the compiler to see what's
 172          happening and offers more opportunity for optimisation. In
 173          particular, the compiler will be able to combine the byteswap
 174          with a nearby load or store and use load-and-swap or
 175          store-and-swap instructions if the architecture has them. It
 176          should almost *never* result in code which is worse than the
 177          hand-coded assembler in <asm/swab.h>.  But just in case it
 178          does, the use of the builtins is optional.
 179
 180          Any architecture with load-and-swap or store-and-swap
 181          instructions should set this. And it shouldn't hurt to set it
 182          on architectures that don't have such instructions.
 183
 184 config KRETPROBES
 185         def_bool y
 186         depends on KPROBES && HAVE_KRETPROBES
 187
 188 config USER_RETURN_NOTIFIER
 189         bool
 190         depends on HAVE_USER_RETURN_NOTIFIER
 191         help
 192           Provide a kernel-internal notification when a cpu is about to
 193           switch to user mode.
 194
 195 config HAVE_IOREMAP_PROT
 196         bool
 197
 198 config HAVE_KPROBES
 199         bool
 200
 201 config HAVE_KRETPROBES
 202         bool
 203
 204 config HAVE_OPTPROBES
 205         bool
 206
 207 config HAVE_KPROBES_ON_FTRACE
 208         bool
 209
 210 config HAVE_FUNCTION_ERROR_INJECTION
 211         bool
 212
 213 config HAVE_NMI
 214         bool
 215
 216 #
 217 # An arch should select this if it provides all these things:
 218 #
 219 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 220 #       arch_has_single_step()  if there is hardware single-step support
 221 #       arch_has_block_step()   if there is hardware block-step support
 222 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 223 #       linux/regset.h          user_regset interfaces
 224 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 225 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 226 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 227 #       signal delivery         calls tracehook_signal_handler()
 228 #
 229 config HAVE_ARCH_TRACEHOOK
 230         bool
 231
 232 config HAVE_DMA_CONTIGUOUS
 233         bool
 234
 235 config GENERIC_SMP_IDLE_THREAD
 236        bool
 237
 238 config GENERIC_IDLE_POLL_SETUP
 239        bool
 240
 241 config ARCH_HAS_FORTIFY_SOURCE
 242         bool
 243         help
 244           An architecture should select this when it can successfully
 245           build and run with CONFIG_FORTIFY_SOURCE.
 246
 247 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 248 config ARCH_HAS_SET_MEMORY
 249         bool
 250
 251 # Select if arch init_task must go in the __init_task_data section
 252 config ARCH_TASK_STRUCT_ON_STACK
 253        bool
 254
 255 # Select if arch has its private alloc_task_struct() function
 256 config ARCH_TASK_STRUCT_ALLOCATOR
 257         bool
 258
 259 config HAVE_ARCH_THREAD_STRUCT_WHITELIST
 260         bool
 261         depends on !ARCH_TASK_STRUCT_ALLOCATOR
 262         help
 263           An architecture should select this to provide hardened usercopy
 264           knowledge about what region of the thread_struct should be
 265           whitelisted for copying to userspace. Normally this is only the
 266           FPU registers. Specifically, arch_thread_struct_whitelist()
 267           should be implemented. Without this, the entire thread_struct
 268           field in task_struct will be left whitelisted.
 269
 270 # Select if arch has its private alloc_thread_stack() function
 271 config ARCH_THREAD_STACK_ALLOCATOR
 272         bool
 273
 274 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 275 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 276         bool
 277
 278 config HAVE_REGS_AND_STACK_ACCESS_API
 279         bool
 280         help
 281           This symbol should be selected by an architecure if it supports
 282           the API needed to access registers and stack entries from pt_regs,
 283           declared in asm/ptrace.h
 284           For example the kprobes-based event tracer needs this API.
 285
 286 config HAVE_RSEQ
 287         bool
 288         depends on HAVE_REGS_AND_STACK_ACCESS_API
 289         help
 290           This symbol should be selected by an architecture if it
 291           supports an implementation of restartable sequences.
 292
 293 config HAVE_FUNCTION_ARG_ACCESS_API
 294         bool
 295         help
 296           This symbol should be selected by an architecure if it supports
 297           the API needed to access function arguments from pt_regs,
 298           declared in asm/ptrace.h
 299
 300 config HAVE_CLK
 301         bool
 302         help
 303           The <linux/clk.h> calls support software clock gating and
 304           thus are a key power management tool on many systems.
 305
 306 config HAVE_HW_BREAKPOINT
 307         bool
 308         depends on PERF_EVENTS
 309
 310 config HAVE_MIXED_BREAKPOINTS_REGS
 311         bool
 312         depends on HAVE_HW_BREAKPOINT
 313         help
 314           Depending on the arch implementation of hardware breakpoints,
 315           some of them have separate registers for data and instruction
 316           breakpoints addresses, others have mixed registers to store
 317           them but define the access type in a control register.
 318           Select this option if your arch implements breakpoints under the
 319           latter fashion.
 320
 321 config HAVE_USER_RETURN_NOTIFIER
 322         bool
 323
 324 config HAVE_PERF_EVENTS_NMI
 325         bool
 326         help
 327           System hardware can generate an NMI using the perf event
 328           subsystem.  Also has support for calculating CPU cycle events
 329           to determine how many clock cycles in a given period.
 330
 331 config HAVE_HARDLOCKUP_DETECTOR_PERF
 332         bool
 333         depends on HAVE_PERF_EVENTS_NMI
 334         help
 335           The arch chooses to use the generic perf-NMI-based hardlockup
 336           detector. Must define HAVE_PERF_EVENTS_NMI.
 337
 338 config HAVE_NMI_WATCHDOG
 339         depends on HAVE_NMI
 340         bool
 341         help
 342           The arch provides a low level NMI watchdog. It provides
 343           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 344
 345 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 346         bool
 347         select HAVE_NMI_WATCHDOG
 348         help
 349           The arch chooses to provide its own hardlockup detector, which is
 350           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 351           interfaces and parameters provided by hardlockup detector subsystem.
 352
 353 config HAVE_PERF_REGS
 354         bool
 355         help
 356           Support selective register dumps for perf events. This includes
 357           bit-mapping of each registers and a unique architecture id.
 358
 359 config HAVE_PERF_USER_STACK_DUMP
 360         bool
 361         help
 362           Support user stack dumps for perf event samples. This needs
 363           access to the user stack pointer which is not unified across
 364           architectures.
 365
 366 config HAVE_ARCH_JUMP_LABEL
 367         bool
 368
 369 config HAVE_ARCH_JUMP_LABEL_RELATIVE
 370         bool
 371
 372 config HAVE_RCU_TABLE_FREE
 373         bool
 374
 375 config HAVE_RCU_TABLE_INVALIDATE
 376         bool
 377
 378 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 379         bool
 380
 381 config HAVE_ALIGNED_STRUCT_PAGE
 382         bool
 383         help
 384           This makes sure that struct pages are double word aligned and that
 385           e.g. the SLUB allocator can perform double word atomic operations
 386           on a struct page for better performance. However selecting this
 387           might increase the size of a struct page by a word.
 388
 389 config HAVE_CMPXCHG_LOCAL
 390         bool
 391
 392 config HAVE_CMPXCHG_DOUBLE
 393         bool
 394
 395 config ARCH_WEAK_RELEASE_ACQUIRE
 396         bool
 397
 398 config ARCH_WANT_IPC_PARSE_VERSION
 399         bool
 400
 401 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 402         bool
 403
 404 config ARCH_WANT_OLD_COMPAT_IPC
 405         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 406         bool
 407
 408 config HAVE_ARCH_SECCOMP_FILTER
 409         bool
 410         help
 411           An arch should select this symbol if it provides all of these things:
 412           - syscall_get_arch()
 413           - syscall_get_arguments()
 414           - syscall_rollback()
 415           - syscall_set_return_value()
 416           - SIGSYS siginfo_t support
 417           - secure_computing is called from a ptrace_event()-safe context
 418           - secure_computing return value is checked and a return value of -1
 419             results in the system call being skipped immediately.
 420           - seccomp syscall wired up
 421
 422 config SECCOMP_FILTER
 423         def_bool y
 424         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 425         help
 426           Enable tasks to build secure computing environments defined
 427           in terms of Berkeley Packet Filter programs which implement
 428           task-defined system call filtering polices.
 429
 430           See Documentation/userspace-api/seccomp_filter.rst for details.
 431
 432 config HAVE_ARCH_STACKLEAK
 433         bool
 434         help
 435           An architecture should select this if it has the code which
 436           fills the used part of the kernel stack with the STACKLEAK_POISON
 437           value before returning from system calls.
 438
 439 config HAVE_STACKPROTECTOR
 440         bool
 441         help
 442           An arch should select this symbol if:
 443           - it has implemented a stack canary (e.g. __stack_chk_guard)
 444
 445 config CC_HAS_STACKPROTECTOR_NONE
 446         def_bool $(cc-option,-fno-stack-protector)
 447
 448 config STACKPROTECTOR
 449         bool "Stack Protector buffer overflow detection"
 450         depends on HAVE_STACKPROTECTOR
 451         depends on $(cc-option,-fstack-protector)
 452         default y
 453         help
 454           This option turns on the "stack-protector" GCC feature. This
 455           feature puts, at the beginning of functions, a canary value on
 456           the stack just before the return address, and validates
 457           the value just before actually returning.  Stack based buffer
 458           overflows (that need to overwrite this return address) now also
 459           overwrite the canary, which gets detected and the attack is then
 460           neutralized via a kernel panic.
 461
 462           Functions will have the stack-protector canary logic added if they
 463           have an 8-byte or larger character array on the stack.
 464
 465           This feature requires gcc version 4.2 or above, or a distribution
 466           gcc with the feature backported ("-fstack-protector").
 467
 468           On an x86 "defconfig" build, this feature adds canary checks to
 469           about 3% of all kernel functions, which increases kernel code size
 470           by about 0.3%.
 471
 472 config STACKPROTECTOR_STRONG
 473         bool "Strong Stack Protector"
 474         depends on STACKPROTECTOR
 475         depends on $(cc-option,-fstack-protector-strong)
 476         default y
 477         help
 478           Functions will have the stack-protector canary logic added in any
 479           of the following conditions:
 480
 481           - local variable's address used as part of the right hand side of an
 482             assignment or function argument
 483           - local variable is an array (or union containing an array),
 484             regardless of array type or length
 485           - uses register local variables
 486
 487           This feature requires gcc version 4.9 or above, or a distribution
 488           gcc with the feature backported ("-fstack-protector-strong").
 489
 490           On an x86 "defconfig" build, this feature adds canary checks to
 491           about 20% of all kernel functions, which increases the kernel code
 492           size by about 2%.
 493
 494 config HAVE_ARCH_WITHIN_STACK_FRAMES
 495         bool
 496         help
 497           An architecture should select this if it can walk the kernel stack
 498           frames to determine if an object is part of either the arguments
 499           or local variables (i.e. that it excludes saved return addresses,
 500           and similar) by implementing an inline arch_within_stack_frames(),
 501           which is used by CONFIG_HARDENED_USERCOPY.
 502
 503 config HAVE_CONTEXT_TRACKING
 504         bool
 505         help
 506           Provide kernel/user boundaries probes necessary for subsystems
 507           that need it, such as userspace RCU extended quiescent state.
 508           Syscalls need to be wrapped inside user_exit()-user_enter() through
 509           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 510           wrapped as well. Irqs are already protected inside
 511           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 512           irq exit still need to be protected.
 513
 514 config HAVE_VIRT_CPU_ACCOUNTING
 515         bool
 516
 517 config ARCH_HAS_SCALED_CPUTIME
 518         bool
 519
 520 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 521         bool
 522         default y if 64BIT
 523         help
 524           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 525           Before enabling this option, arch code must be audited
 526           to ensure there are no races in concurrent read/write of
 527           cputime_t. For example, reading/writing 64-bit cputime_t on
 528           some 32-bit arches may require multiple accesses, so proper
 529           locking is needed to protect against concurrent accesses.
 530
 531
 532 config HAVE_IRQ_TIME_ACCOUNTING
 533         bool
 534         help
 535           Archs need to ensure they use a high enough resolution clock to
 536           support irq time accounting and then call enable_sched_clock_irqtime().
 537
 538 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 539         bool
 540
 541 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 542         bool
 543
 544 config HAVE_ARCH_HUGE_VMAP
 545         bool
 546
 547 config HAVE_ARCH_SOFT_DIRTY
 548         bool
 549
 550 config HAVE_MOD_ARCH_SPECIFIC
 551         bool
 552         help
 553           The arch uses struct mod_arch_specific to store data.  Many arches
 554           just need a simple module loader without arch specific data - those
 555           should not enable this.
 556
 557 config MODULES_USE_ELF_RELA
 558         bool
 559         help
 560           Modules only use ELF RELA relocations.  Modules with ELF REL
 561           relocations will give an error.
 562
 563 config MODULES_USE_ELF_REL
 564         bool
 565         help
 566           Modules only use ELF REL relocations.  Modules with ELF RELA
 567           relocations will give an error.
 568
 569 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 570         bool
 571         help
 572           Architecture doesn't only execute the irq handler on the irq stack
 573           but also irq_exit(). This way we can process softirqs on this irq
 574           stack instead of switching to a new one when we call __do_softirq()
 575           in the end of an hardirq.
 576           This spares a stack switch and improves cache usage on softirq
 577           processing.
 578
 579 config PGTABLE_LEVELS
 580         int
 581         default 2
 582
 583 config ARCH_HAS_ELF_RANDOMIZE
 584         bool
 585         help
 586           An architecture supports choosing randomized locations for
 587           stack, mmap, brk, and ET_DYN. Defined functions:
 588           - arch_mmap_rnd()
 589           - arch_randomize_brk()
 590
 591 config HAVE_ARCH_MMAP_RND_BITS
 592         bool
 593         help
 594           An arch should select this symbol if it supports setting a variable
 595           number of bits for use in establishing the base address for mmap
 596           allocations, has MMU enabled and provides values for both:
 597           - ARCH_MMAP_RND_BITS_MIN
 598           - ARCH_MMAP_RND_BITS_MAX
 599
 600 config HAVE_EXIT_THREAD
 601         bool
 602         help
 603           An architecture implements exit_thread.
 604
 605 config ARCH_MMAP_RND_BITS_MIN
 606         int
 607
 608 config ARCH_MMAP_RND_BITS_MAX
 609         int
 610
 611 config ARCH_MMAP_RND_BITS_DEFAULT
 612         int
 613
 614 config ARCH_MMAP_RND_BITS
 615         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 616         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 617         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 618         default ARCH_MMAP_RND_BITS_MIN
 619         depends on HAVE_ARCH_MMAP_RND_BITS
 620         help
 621           This value can be used to select the number of bits to use to
 622           determine the random offset to the base address of vma regions
 623           resulting from mmap allocations. This value will be bounded
 624           by the architecture's minimum and maximum supported values.
 625
 626           This value can be changed after boot using the
 627           /proc/sys/vm/mmap_rnd_bits tunable
 628
 629 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 630         bool
 631         help
 632           An arch should select this symbol if it supports running applications
 633           in compatibility mode, supports setting a variable number of bits for
 634           use in establishing the base address for mmap allocations, has MMU
 635           enabled and provides values for both:
 636           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 637           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 638
 639 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 640         int
 641
 642 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 643         int
 644
 645 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 646         int
 647
 648 config ARCH_MMAP_RND_COMPAT_BITS
 649         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 650         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 651         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 652         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 653         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 654         help
 655           This value can be used to select the number of bits to use to
 656           determine the random offset to the base address of vma regions
 657           resulting from mmap allocations for compatible applications This
 658           value will be bounded by the architecture's minimum and maximum
 659           supported values.
 660
 661           This value can be changed after boot using the
 662           /proc/sys/vm/mmap_rnd_compat_bits tunable
 663
 664 config HAVE_ARCH_COMPAT_MMAP_BASES
 665         bool
 666         help
 667           This allows 64bit applications to invoke 32-bit mmap() syscall
 668           and vice-versa 32-bit applications to call 64-bit mmap().
 669           Required for applications doing different bitness syscalls.
 670
 671 config HAVE_COPY_THREAD_TLS
 672         bool
 673         help
 674           Architecture provides copy_thread_tls to accept tls argument via
 675           normal C parameter passing, rather than extracting the syscall
 676           argument from pt_regs.
 677
 678 config HAVE_STACK_VALIDATION
 679         bool
 680         help
 681           Architecture supports the 'objtool check' host tool command, which
 682           performs compile-time stack metadata validation.
 683
 684 config HAVE_RELIABLE_STACKTRACE
 685         bool
 686         help
 687           Architecture has a save_stack_trace_tsk_reliable() function which
 688           only returns a stack trace if it can guarantee the trace is reliable.
 689
 690 config HAVE_ARCH_HASH
 691         bool
 692         default n
 693         help
 694           If this is set, the architecture provides an <asm/hash.h>
 695           file which provides platform-specific implementations of some
 696           functions in <linux/hash.h> or fs/namei.c.
 697
 698 config ISA_BUS_API
 699         def_bool ISA
 700
 701 #
 702 # ABI hall of shame
 703 #
 704 config CLONE_BACKWARDS
 705         bool
 706         help
 707           Architecture has tls passed as the 4th argument of clone(2),
 708           not the 5th one.
 709
 710 config CLONE_BACKWARDS2
 711         bool
 712         help
 713           Architecture has the first two arguments of clone(2) swapped.
 714
 715 config CLONE_BACKWARDS3
 716         bool
 717         help
 718           Architecture has tls passed as the 3rd argument of clone(2),
 719           not the 5th one.
 720
 721 config ODD_RT_SIGACTION
 722         bool
 723         help
 724           Architecture has unusual rt_sigaction(2) arguments
 725
 726 config OLD_SIGSUSPEND
 727         bool
 728         help
 729           Architecture has old sigsuspend(2) syscall, of one-argument variety
 730
 731 config OLD_SIGSUSPEND3
 732         bool
 733         help
 734           Even weirder antique ABI - three-argument sigsuspend(2)
 735
 736 config OLD_SIGACTION
 737         bool
 738         help
 739           Architecture has old sigaction(2) syscall.  Nope, not the same
 740           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 741           but fairly different variant of sigaction(2), thanks to OSF/1
 742           compatibility...
 743
 744 config COMPAT_OLD_SIGACTION
 745         bool
 746
 747 config 64BIT_TIME
 748         def_bool ARCH_HAS_64BIT_TIME
 749         help
 750           This should be selected by all architectures that need to support
 751           new system calls with a 64-bit time_t. This is relevant on all 32-bit
 752           architectures, and 64-bit architectures as part of compat syscall
 753           handling.
 754
 755 config COMPAT_32BIT_TIME
 756         def_bool (!64BIT && 64BIT_TIME) || COMPAT
 757         help
 758           This enables 32 bit time_t support in addition to 64 bit time_t support.
 759           This is relevant on all 32-bit architectures, and 64-bit architectures
 760           as part of compat syscall handling.
 761
 762 config ARCH_NO_COHERENT_DMA_MMAP
 763         bool
 764
 765 config ARCH_NO_PREEMPT
 766         bool
 767
 768 config CPU_NO_EFFICIENT_FFS
 769         def_bool n
 770
 771 config HAVE_ARCH_VMAP_STACK
 772         def_bool n
 773         help
 774           An arch should select this symbol if it can support kernel stacks
 775           in vmalloc space.  This means:
 776
 777           - vmalloc space must be large enough to hold many kernel stacks.
 778             This may rule out many 32-bit architectures.
 779
 780           - Stacks in vmalloc space need to work reliably.  For example, if
 781             vmap page tables are created on demand, either this mechanism
 782             needs to work while the stack points to a virtual address with
 783             unpopulated page tables or arch code (switch_to() and switch_mm(),
 784             most likely) needs to ensure that the stack's page table entries
 785             are populated before running on a possibly unpopulated stack.
 786
 787           - If the stack overflows into a guard page, something reasonable
 788             should happen.  The definition of "reasonable" is flexible, but
 789             instantly rebooting without logging anything would be unfriendly.
 790
 791 config VMAP_STACK
 792         default y
 793         bool "Use a virtually-mapped stack"
 794         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 795         ---help---
 796           Enable this if you want the use virtually-mapped kernel stacks
 797           with guard pages.  This causes kernel stack overflows to be
 798           caught immediately rather than causing difficult-to-diagnose
 799           corruption.
 800
 801           This is presently incompatible with KASAN because KASAN expects
 802           the stack to map directly to the KASAN shadow map using a formula
 803           that is incorrect if the stack is in vmalloc space.
 804
 805 config ARCH_OPTIONAL_KERNEL_RWX
 806         def_bool n
 807
 808 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 809         def_bool n
 810
 811 config ARCH_HAS_STRICT_KERNEL_RWX
 812         def_bool n
 813
 814 config STRICT_KERNEL_RWX
 815         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 816         depends on ARCH_HAS_STRICT_KERNEL_RWX
 817         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 818         help
 819           If this is set, kernel text and rodata memory will be made read-only,
 820           and non-text memory will be made non-executable. This provides
 821           protection against certain security exploits (e.g. executing the heap
 822           or modifying text)
 823
 824           These features are considered standard security practice these days.
 825           You should say Y here in almost all cases.
 826
 827 config ARCH_HAS_STRICT_MODULE_RWX
 828         def_bool n
 829
 830 config STRICT_MODULE_RWX
 831         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 832         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 833         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 834         help
 835           If this is set, module text and rodata memory will be made read-only,
 836           and non-text memory will be made non-executable. This provides
 837           protection against certain security exploits (e.g. writing to text)
 838
 839 # select if the architecture provides an asm/dma-direct.h header
 840 config ARCH_HAS_PHYS_TO_DMA
 841         bool
 842
 843 config ARCH_HAS_REFCOUNT
 844         bool
 845         help
 846           An architecture selects this when it has implemented refcount_t
 847           using open coded assembly primitives that provide an optimized
 848           refcount_t implementation, possibly at the expense of some full
 849           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 850
 851           The refcount overflow check behavior, however, must be retained.
 852           Catching overflows is the primary security concern for protecting
 853           against bugs in reference counts.
 854
 855 config REFCOUNT_FULL
 856         bool "Perform full reference count validation at the expense of speed"
 857         help
 858           Enabling this switches the refcounting infrastructure from a fast
 859           unchecked atomic_t implementation to a fully state checked
 860           implementation, which can be (slightly) slower but provides protections
 861           against various use-after-free conditions that can be used in
 862           security flaw exploits.
 863
 864 config HAVE_ARCH_COMPILER_H
 865         bool
 866         help
 867           An architecture can select this if it provides an
 868           asm/compiler.h header that should be included after
 869           linux/compiler-*.h in order to override macro definitions that those
 870           headers generally provide.
 871
 872 config HAVE_ARCH_PREL32_RELOCATIONS
 873         bool
 874         help
 875           May be selected by an architecture if it supports place-relative
 876           32-bit relocations, both in the toolchain and in the module loader,
 877           in which case relative references can be used in special sections
 878           for PCI fixup, initcalls etc which are only half the size on 64 bit
 879           architectures, and don't require runtime relocation on relocatable
 880           kernels.
 881
 882 source "kernel/gcov/Kconfig"
 883
 884 source "scripts/gcc-plugins/Kconfig"
 885
 886 endmenu