arch/Kconfig

   1 #
   2 # General architecture dependent options
   3 #
   4
   5 config KEXEC_CORE
   6         bool
   7
   8 config OPROFILE
   9         tristate "OProfile system profiling"
  10         depends on PROFILING
  11         depends on HAVE_OPROFILE
  12         select RING_BUFFER
  13         select RING_BUFFER_ALLOW_SWAP
  14         help
  15           OProfile is a profiling system capable of profiling the
  16           whole system, include the kernel, kernel modules, libraries,
  17           and applications.
  18
  19           If unsure, say N.
  20
  21 config OPROFILE_EVENT_MULTIPLEX
  22         bool "OProfile multiplexing support (EXPERIMENTAL)"
  23         default n
  24         depends on OPROFILE && X86
  25         help
  26           The number of hardware counters is limited. The multiplexing
  27           feature enables OProfile to gather more events than counters
  28           are provided by the hardware. This is realized by switching
  29           between events at an user specified time interval.
  30
  31           If unsure, say N.
  32
  33 config HAVE_OPROFILE
  34         bool
  35
  36 config OPROFILE_NMI_TIMER
  37         def_bool y
  38         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  39
  40 config KPROBES
  41         bool "Kprobes"
  42         depends on MODULES
  43         depends on HAVE_KPROBES
  44         select KALLSYMS
  45         help
  46           Kprobes allows you to trap at almost any kernel address and
  47           execute a callback function.  register_kprobe() establishes
  48           a probepoint and specifies the callback.  Kprobes is useful
  49           for kernel debugging, non-intrusive instrumentation and testing.
  50           If in doubt, say "N".
  51
  52 config JUMP_LABEL
  53        bool "Optimize very unlikely/likely branches"
  54        depends on HAVE_ARCH_JUMP_LABEL
  55        help
  56          This option enables a transparent branch optimization that
  57          makes certain almost-always-true or almost-always-false branch
  58          conditions even cheaper to execute within the kernel.
  59
  60          Certain performance-sensitive kernel code, such as trace points,
  61          scheduler functionality, networking code and KVM have such
  62          branches and include support for this optimization technique.
  63
  64          If it is detected that the compiler has support for "asm goto",
  65          the kernel will compile such branches with just a nop
  66          instruction. When the condition flag is toggled to true, the
  67          nop will be converted to a jump instruction to execute the
  68          conditional block of instructions.
  69
  70          This technique lowers overhead and stress on the branch prediction
  71          of the processor and generally makes the kernel faster. The update
  72          of the condition is slower, but those are always very rare.
  73
  74          ( On 32-bit x86, the necessary options added to the compiler
  75            flags may increase the size of the kernel slightly. )
  76
  77 config STATIC_KEYS_SELFTEST
  78         bool "Static key selftest"
  79         depends on JUMP_LABEL
  80         help
  81           Boot time self-test of the branch patching code.
  82
  83 config OPTPROBES
  84         def_bool y
  85         depends on KPROBES && HAVE_OPTPROBES
  86         depends on !PREEMPT
  87
  88 config KPROBES_ON_FTRACE
  89         def_bool y
  90         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
  91         depends on DYNAMIC_FTRACE_WITH_REGS
  92         help
  93          If function tracer is enabled and the arch supports full
  94          passing of pt_regs to function tracing, then kprobes can
  95          optimize on top of function tracing.
  96
  97 config UPROBES
  98         def_bool n
  99         depends on ARCH_SUPPORTS_UPROBES
 100         help
 101           Uprobes is the user-space counterpart to kprobes: they
 102           enable instrumentation applications (such as 'perf probe')
 103           to establish unintrusive probes in user-space binaries and
 104           libraries, by executing handler functions when the probes
 105           are hit by user-space applications.
 106
 107           ( These probes come in the form of single-byte breakpoints,
 108             managed by the kernel and kept transparent to the probed
 109             application. )
 110
 111 config HAVE_64BIT_ALIGNED_ACCESS
 112         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 113         help
 114           Some architectures require 64 bit accesses to be 64 bit
 115           aligned, which also requires structs containing 64 bit values
 116           to be 64 bit aligned too. This includes some 32 bit
 117           architectures which can do 64 bit accesses, as well as 64 bit
 118           architectures without unaligned access.
 119
 120           This symbol should be selected by an architecture if 64 bit
 121           accesses are required to be 64 bit aligned in this way even
 122           though it is not a 64 bit architecture.
 123
 124           See Documentation/unaligned-memory-access.txt for more
 125           information on the topic of unaligned memory accesses.
 126
 127 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 128         bool
 129         help
 130           Some architectures are unable to perform unaligned accesses
 131           without the use of get_unaligned/put_unaligned. Others are
 132           unable to perform such accesses efficiently (e.g. trap on
 133           unaligned access and require fixing it up in the exception
 134           handler.)
 135
 136           This symbol should be selected by an architecture if it can
 137           perform unaligned accesses efficiently to allow different
 138           code paths to be selected for these cases. Some network
 139           drivers, for example, could opt to not fix up alignment
 140           problems with received packets if doing so would not help
 141           much.
 142
 143           See Documentation/unaligned-memory-access.txt for more
 144           information on the topic of unaligned memory accesses.
 145
 146 config ARCH_USE_BUILTIN_BSWAP
 147        bool
 148        help
 149          Modern versions of GCC (since 4.4) have builtin functions
 150          for handling byte-swapping. Using these, instead of the old
 151          inline assembler that the architecture code provides in the
 152          __arch_bswapXX() macros, allows the compiler to see what's
 153          happening and offers more opportunity for optimisation. In
 154          particular, the compiler will be able to combine the byteswap
 155          with a nearby load or store and use load-and-swap or
 156          store-and-swap instructions if the architecture has them. It
 157          should almost *never* result in code which is worse than the
 158          hand-coded assembler in <asm/swab.h>.  But just in case it
 159          does, the use of the builtins is optional.
 160
 161          Any architecture with load-and-swap or store-and-swap
 162          instructions should set this. And it shouldn't hurt to set it
 163          on architectures that don't have such instructions.
 164
 165 config KRETPROBES
 166         def_bool y
 167         depends on KPROBES && HAVE_KRETPROBES
 168
 169 config USER_RETURN_NOTIFIER
 170         bool
 171         depends on HAVE_USER_RETURN_NOTIFIER
 172         help
 173           Provide a kernel-internal notification when a cpu is about to
 174           switch to user mode.
 175
 176 config HAVE_IOREMAP_PROT
 177         bool
 178
 179 config HAVE_KPROBES
 180         bool
 181
 182 config HAVE_KRETPROBES
 183         bool
 184
 185 config HAVE_OPTPROBES
 186         bool
 187
 188 config HAVE_KPROBES_ON_FTRACE
 189         bool
 190
 191 config HAVE_NMI
 192         bool
 193
 194 config HAVE_NMI_WATCHDOG
 195         depends on HAVE_NMI
 196         bool
 197 #
 198 # An arch should select this if it provides all these things:
 199 #
 200 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 201 #       arch_has_single_step()  if there is hardware single-step support
 202 #       arch_has_block_step()   if there is hardware block-step support
 203 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 204 #       linux/regset.h          user_regset interfaces
 205 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 206 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 207 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 208 #       signal delivery         calls tracehook_signal_handler()
 209 #
 210 config HAVE_ARCH_TRACEHOOK
 211         bool
 212
 213 config HAVE_DMA_CONTIGUOUS
 214         bool
 215
 216 config GENERIC_SMP_IDLE_THREAD
 217        bool
 218
 219 config GENERIC_IDLE_POLL_SETUP
 220        bool
 221
 222 # Select if arch init_task initializer is different to init/init_task.c
 223 config ARCH_INIT_TASK
 224        bool
 225
 226 # Select if arch has its private alloc_task_struct() function
 227 config ARCH_TASK_STRUCT_ALLOCATOR
 228         bool
 229
 230 # Select if arch has its private alloc_thread_stack() function
 231 config ARCH_THREAD_STACK_ALLOCATOR
 232         bool
 233
 234 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 235 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 236         bool
 237
 238 config HAVE_REGS_AND_STACK_ACCESS_API
 239         bool
 240         help
 241           This symbol should be selected by an architecure if it supports
 242           the API needed to access registers and stack entries from pt_regs,
 243           declared in asm/ptrace.h
 244           For example the kprobes-based event tracer needs this API.
 245
 246 config HAVE_CLK
 247         bool
 248         help
 249           The <linux/clk.h> calls support software clock gating and
 250           thus are a key power management tool on many systems.
 251
 252 config HAVE_DMA_API_DEBUG
 253         bool
 254
 255 config HAVE_HW_BREAKPOINT
 256         bool
 257         depends on PERF_EVENTS
 258
 259 config HAVE_MIXED_BREAKPOINTS_REGS
 260         bool
 261         depends on HAVE_HW_BREAKPOINT
 262         help
 263           Depending on the arch implementation of hardware breakpoints,
 264           some of them have separate registers for data and instruction
 265           breakpoints addresses, others have mixed registers to store
 266           them but define the access type in a control register.
 267           Select this option if your arch implements breakpoints under the
 268           latter fashion.
 269
 270 config HAVE_USER_RETURN_NOTIFIER
 271         bool
 272
 273 config HAVE_PERF_EVENTS_NMI
 274         bool
 275         help
 276           System hardware can generate an NMI using the perf event
 277           subsystem.  Also has support for calculating CPU cycle events
 278           to determine how many clock cycles in a given period.
 279
 280 config HAVE_PERF_REGS
 281         bool
 282         help
 283           Support selective register dumps for perf events. This includes
 284           bit-mapping of each registers and a unique architecture id.
 285
 286 config HAVE_PERF_USER_STACK_DUMP
 287         bool
 288         help
 289           Support user stack dumps for perf event samples. This needs
 290           access to the user stack pointer which is not unified across
 291           architectures.
 292
 293 config HAVE_ARCH_JUMP_LABEL
 294         bool
 295
 296 config HAVE_RCU_TABLE_FREE
 297         bool
 298
 299 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 300         bool
 301
 302 config HAVE_ALIGNED_STRUCT_PAGE
 303         bool
 304         help
 305           This makes sure that struct pages are double word aligned and that
 306           e.g. the SLUB allocator can perform double word atomic operations
 307           on a struct page for better performance. However selecting this
 308           might increase the size of a struct page by a word.
 309
 310 config HAVE_CMPXCHG_LOCAL
 311         bool
 312
 313 config HAVE_CMPXCHG_DOUBLE
 314         bool
 315
 316 config ARCH_WANT_IPC_PARSE_VERSION
 317         bool
 318
 319 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 320         bool
 321
 322 config ARCH_WANT_OLD_COMPAT_IPC
 323         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 324         bool
 325
 326 config HAVE_ARCH_SECCOMP_FILTER
 327         bool
 328         help
 329           An arch should select this symbol if it provides all of these things:
 330           - syscall_get_arch()
 331           - syscall_get_arguments()
 332           - syscall_rollback()
 333           - syscall_set_return_value()
 334           - SIGSYS siginfo_t support
 335           - secure_computing is called from a ptrace_event()-safe context
 336           - secure_computing return value is checked and a return value of -1
 337             results in the system call being skipped immediately.
 338           - seccomp syscall wired up
 339
 340 config SECCOMP_FILTER
 341         def_bool y
 342         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 343         help
 344           Enable tasks to build secure computing environments defined
 345           in terms of Berkeley Packet Filter programs which implement
 346           task-defined system call filtering polices.
 347
 348           See Documentation/prctl/seccomp_filter.txt for details.
 349
 350 config HAVE_GCC_PLUGINS
 351         bool
 352         help
 353           An arch should select this symbol if it supports building with
 354           GCC plugins.
 355
 356 menuconfig GCC_PLUGINS
 357         bool "GCC plugins"
 358         depends on HAVE_GCC_PLUGINS
 359         depends on !COMPILE_TEST
 360         help
 361           GCC plugins are loadable modules that provide extra features to the
 362           compiler. They are useful for runtime instrumentation and static analysis.
 363
 364           See Documentation/gcc-plugins.txt for details.
 365
 366 config GCC_PLUGIN_CYC_COMPLEXITY
 367         bool "Compute the cyclomatic complexity of a function"
 368         depends on GCC_PLUGINS
 369         help
 370           The complexity M of a function's control flow graph is defined as:
 371            M = E - N + 2P
 372           where
 373
 374           E = the number of edges
 375           N = the number of nodes
 376           P = the number of connected components (exit nodes).
 377
 378 config GCC_PLUGIN_SANCOV
 379         bool
 380         depends on GCC_PLUGINS
 381         help
 382           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 383           basic blocks. It supports all gcc versions with plugin support (from
 384           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 385           by Dmitry Vyukov <dvyukov@google.com>.
 386
 387 config GCC_PLUGIN_LATENT_ENTROPY
 388         bool "Generate some entropy during boot and runtime"
 389         depends on GCC_PLUGINS
 390         help
 391           By saying Y here the kernel will instrument some kernel code to
 392           extract some entropy from both original and artificially created
 393           program state.  This will help especially embedded systems where
 394           there is little 'natural' source of entropy normally.  The cost
 395           is some slowdown of the boot process (about 0.5%) and fork and
 396           irq processing.
 397
 398           Note that entropy extracted this way is not cryptographically
 399           secure!
 400
 401           This plugin was ported from grsecurity/PaX. More information at:
 402            * https://grsecurity.net/
 403            * https://pax.grsecurity.net/
 404
 405 config HAVE_CC_STACKPROTECTOR
 406         bool
 407         help
 408           An arch should select this symbol if:
 409           - its compiler supports the -fstack-protector option
 410           - it has implemented a stack canary (e.g. __stack_chk_guard)
 411
 412 config CC_STACKPROTECTOR
 413         def_bool n
 414         help
 415           Set when a stack-protector mode is enabled, so that the build
 416           can enable kernel-side support for the GCC feature.
 417
 418 choice
 419         prompt "Stack Protector buffer overflow detection"
 420         depends on HAVE_CC_STACKPROTECTOR
 421         default CC_STACKPROTECTOR_NONE
 422         help
 423           This option turns on the "stack-protector" GCC feature. This
 424           feature puts, at the beginning of functions, a canary value on
 425           the stack just before the return address, and validates
 426           the value just before actually returning.  Stack based buffer
 427           overflows (that need to overwrite this return address) now also
 428           overwrite the canary, which gets detected and the attack is then
 429           neutralized via a kernel panic.
 430
 431 config CC_STACKPROTECTOR_NONE
 432         bool "None"
 433         help
 434           Disable "stack-protector" GCC feature.
 435
 436 config CC_STACKPROTECTOR_REGULAR
 437         bool "Regular"
 438         select CC_STACKPROTECTOR
 439         help
 440           Functions will have the stack-protector canary logic added if they
 441           have an 8-byte or larger character array on the stack.
 442
 443           This feature requires gcc version 4.2 or above, or a distribution
 444           gcc with the feature backported ("-fstack-protector").
 445
 446           On an x86 "defconfig" build, this feature adds canary checks to
 447           about 3% of all kernel functions, which increases kernel code size
 448           by about 0.3%.
 449
 450 config CC_STACKPROTECTOR_STRONG
 451         bool "Strong"
 452         select CC_STACKPROTECTOR
 453         help
 454           Functions will have the stack-protector canary logic added in any
 455           of the following conditions:
 456
 457           - local variable's address used as part of the right hand side of an
 458             assignment or function argument
 459           - local variable is an array (or union containing an array),
 460             regardless of array type or length
 461           - uses register local variables
 462
 463           This feature requires gcc version 4.9 or above, or a distribution
 464           gcc with the feature backported ("-fstack-protector-strong").
 465
 466           On an x86 "defconfig" build, this feature adds canary checks to
 467           about 20% of all kernel functions, which increases the kernel code
 468           size by about 2%.
 469
 470 endchoice
 471
 472 config THIN_ARCHIVES
 473         bool
 474         help
 475           Select this if the architecture wants to use thin archives
 476           instead of ld -r to create the built-in.o files.
 477
 478 config LD_DEAD_CODE_DATA_ELIMINATION
 479         bool
 480         help
 481           Select this if the architecture wants to do dead code and
 482           data elimination with the linker by compiling with
 483           -ffunction-sections -fdata-sections and linking with
 484           --gc-sections.
 485
 486           This requires that the arch annotates or otherwise protects
 487           its external entry points from being discarded. Linker scripts
 488           must also merge .text.*, .data.*, and .bss.* correctly into
 489           output sections. Care must be taken not to pull in unrelated
 490           sections (e.g., '.text.init'). Typically '.' in section names
 491           is used to distinguish them from label names / C identifiers.
 492
 493 config HAVE_ARCH_WITHIN_STACK_FRAMES
 494         bool
 495         help
 496           An architecture should select this if it can walk the kernel stack
 497           frames to determine if an object is part of either the arguments
 498           or local variables (i.e. that it excludes saved return addresses,
 499           and similar) by implementing an inline arch_within_stack_frames(),
 500           which is used by CONFIG_HARDENED_USERCOPY.
 501
 502 config HAVE_CONTEXT_TRACKING
 503         bool
 504         help
 505           Provide kernel/user boundaries probes necessary for subsystems
 506           that need it, such as userspace RCU extended quiescent state.
 507           Syscalls need to be wrapped inside user_exit()-user_enter() through
 508           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 509           wrapped as well. Irqs are already protected inside
 510           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 511           irq exit still need to be protected.
 512
 513 config HAVE_VIRT_CPU_ACCOUNTING
 514         bool
 515
 516 config ARCH_HAS_SCALED_CPUTIME
 517         bool
 518
 519 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 520         bool
 521         default y if 64BIT
 522         help
 523           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 524           Before enabling this option, arch code must be audited
 525           to ensure there are no races in concurrent read/write of
 526           cputime_t. For example, reading/writing 64-bit cputime_t on
 527           some 32-bit arches may require multiple accesses, so proper
 528           locking is needed to protect against concurrent accesses.
 529
 530
 531 config HAVE_IRQ_TIME_ACCOUNTING
 532         bool
 533         help
 534           Archs need to ensure they use a high enough resolution clock to
 535           support irq time accounting and then call enable_sched_clock_irqtime().
 536
 537 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 538         bool
 539
 540 config HAVE_ARCH_HUGE_VMAP
 541         bool
 542
 543 config HAVE_ARCH_SOFT_DIRTY
 544         bool
 545
 546 config HAVE_MOD_ARCH_SPECIFIC
 547         bool
 548         help
 549           The arch uses struct mod_arch_specific to store data.  Many arches
 550           just need a simple module loader without arch specific data - those
 551           should not enable this.
 552
 553 config MODULES_USE_ELF_RELA
 554         bool
 555         help
 556           Modules only use ELF RELA relocations.  Modules with ELF REL
 557           relocations will give an error.
 558
 559 config MODULES_USE_ELF_REL
 560         bool
 561         help
 562           Modules only use ELF REL relocations.  Modules with ELF RELA
 563           relocations will give an error.
 564
 565 config HAVE_UNDERSCORE_SYMBOL_PREFIX
 566         bool
 567         help
 568           Some architectures generate an _ in front of C symbols; things like
 569           module loading and assembly files need to know about this.
 570
 571 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 572         bool
 573         help
 574           Architecture doesn't only execute the irq handler on the irq stack
 575           but also irq_exit(). This way we can process softirqs on this irq
 576           stack instead of switching to a new one when we call __do_softirq()
 577           in the end of an hardirq.
 578           This spares a stack switch and improves cache usage on softirq
 579           processing.
 580
 581 config PGTABLE_LEVELS
 582         int
 583         default 2
 584
 585 config ARCH_HAS_ELF_RANDOMIZE
 586         bool
 587         help
 588           An architecture supports choosing randomized locations for
 589           stack, mmap, brk, and ET_DYN. Defined functions:
 590           - arch_mmap_rnd()
 591           - arch_randomize_brk()
 592
 593 config HAVE_ARCH_MMAP_RND_BITS
 594         bool
 595         help
 596           An arch should select this symbol if it supports setting a variable
 597           number of bits for use in establishing the base address for mmap
 598           allocations, has MMU enabled and provides values for both:
 599           - ARCH_MMAP_RND_BITS_MIN
 600           - ARCH_MMAP_RND_BITS_MAX
 601
 602 config HAVE_EXIT_THREAD
 603         bool
 604         help
 605           An architecture implements exit_thread.
 606
 607 config ARCH_MMAP_RND_BITS_MIN
 608         int
 609
 610 config ARCH_MMAP_RND_BITS_MAX
 611         int
 612
 613 config ARCH_MMAP_RND_BITS_DEFAULT
 614         int
 615
 616 config ARCH_MMAP_RND_BITS
 617         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 618         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 619         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 620         default ARCH_MMAP_RND_BITS_MIN
 621         depends on HAVE_ARCH_MMAP_RND_BITS
 622         help
 623           This value can be used to select the number of bits to use to
 624           determine the random offset to the base address of vma regions
 625           resulting from mmap allocations. This value will be bounded
 626           by the architecture's minimum and maximum supported values.
 627
 628           This value can be changed after boot using the
 629           /proc/sys/vm/mmap_rnd_bits tunable
 630
 631 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 632         bool
 633         help
 634           An arch should select this symbol if it supports running applications
 635           in compatibility mode, supports setting a variable number of bits for
 636           use in establishing the base address for mmap allocations, has MMU
 637           enabled and provides values for both:
 638           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 639           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 640
 641 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 642         int
 643
 644 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 645         int
 646
 647 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 648         int
 649
 650 config ARCH_MMAP_RND_COMPAT_BITS
 651         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 652         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 653         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 654         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 655         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 656         help
 657           This value can be used to select the number of bits to use to
 658           determine the random offset to the base address of vma regions
 659           resulting from mmap allocations for compatible applications This
 660           value will be bounded by the architecture's minimum and maximum
 661           supported values.
 662
 663           This value can be changed after boot using the
 664           /proc/sys/vm/mmap_rnd_compat_bits tunable
 665
 666 config HAVE_COPY_THREAD_TLS
 667         bool
 668         help
 669           Architecture provides copy_thread_tls to accept tls argument via
 670           normal C parameter passing, rather than extracting the syscall
 671           argument from pt_regs.
 672
 673 config HAVE_STACK_VALIDATION
 674         bool
 675         help
 676           Architecture supports the 'objtool check' host tool command, which
 677           performs compile-time stack metadata validation.
 678
 679 config HAVE_ARCH_HASH
 680         bool
 681         default n
 682         help
 683           If this is set, the architecture provides an <asm/hash.h>
 684           file which provides platform-specific implementations of some
 685           functions in <linux/hash.h> or fs/namei.c.
 686
 687 config ISA_BUS_API
 688         def_bool ISA
 689
 690 #
 691 # ABI hall of shame
 692 #
 693 config CLONE_BACKWARDS
 694         bool
 695         help
 696           Architecture has tls passed as the 4th argument of clone(2),
 697           not the 5th one.
 698
 699 config CLONE_BACKWARDS2
 700         bool
 701         help
 702           Architecture has the first two arguments of clone(2) swapped.
 703
 704 config CLONE_BACKWARDS3
 705         bool
 706         help
 707           Architecture has tls passed as the 3rd argument of clone(2),
 708           not the 5th one.
 709
 710 config ODD_RT_SIGACTION
 711         bool
 712         help
 713           Architecture has unusual rt_sigaction(2) arguments
 714
 715 config OLD_SIGSUSPEND
 716         bool
 717         help
 718           Architecture has old sigsuspend(2) syscall, of one-argument variety
 719
 720 config OLD_SIGSUSPEND3
 721         bool
 722         help
 723           Even weirder antique ABI - three-argument sigsuspend(2)
 724
 725 config OLD_SIGACTION
 726         bool
 727         help
 728           Architecture has old sigaction(2) syscall.  Nope, not the same
 729           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 730           but fairly different variant of sigaction(2), thanks to OSF/1
 731           compatibility...
 732
 733 config COMPAT_OLD_SIGACTION
 734         bool
 735
 736 config ARCH_NO_COHERENT_DMA_MMAP
 737         bool
 738
 739 config CPU_NO_EFFICIENT_FFS
 740         def_bool n
 741
 742 config HAVE_ARCH_VMAP_STACK
 743         def_bool n
 744         help
 745           An arch should select this symbol if it can support kernel stacks
 746           in vmalloc space.  This means:
 747
 748           - vmalloc space must be large enough to hold many kernel stacks.
 749             This may rule out many 32-bit architectures.
 750
 751           - Stacks in vmalloc space need to work reliably.  For example, if
 752             vmap page tables are created on demand, either this mechanism
 753             needs to work while the stack points to a virtual address with
 754             unpopulated page tables or arch code (switch_to() and switch_mm(),
 755             most likely) needs to ensure that the stack's page table entries
 756             are populated before running on a possibly unpopulated stack.
 757
 758           - If the stack overflows into a guard page, something reasonable
 759             should happen.  The definition of "reasonable" is flexible, but
 760             instantly rebooting without logging anything would be unfriendly.
 761
 762 config VMAP_STACK
 763         default y
 764         bool "Use a virtually-mapped stack"
 765         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 766         ---help---
 767           Enable this if you want the use virtually-mapped kernel stacks
 768           with guard pages.  This causes kernel stack overflows to be
 769           caught immediately rather than causing difficult-to-diagnose
 770           corruption.
 771
 772           This is presently incompatible with KASAN because KASAN expects
 773           the stack to map directly to the KASAN shadow map using a formula
 774           that is incorrect if the stack is in vmalloc space.
 775
 776 source "kernel/gcov/Kconfig"