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" if EXPERT
 368         depends on GCC_PLUGINS
 369         depends on !COMPILE_TEST
 370         help
 371           The complexity M of a function's control flow graph is defined as:
 372            M = E - N + 2P
 373           where
 374
 375           E = the number of edges
 376           N = the number of nodes
 377           P = the number of connected components (exit nodes).
 378
 379           Enabling this plugin reports the complexity to stderr during the
 380           build. It mainly serves as a simple example of how to create a
 381           gcc plugin for the kernel.
 382
 383 config GCC_PLUGIN_SANCOV
 384         bool
 385         depends on GCC_PLUGINS
 386         help
 387           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 388           basic blocks. It supports all gcc versions with plugin support (from
 389           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 390           by Dmitry Vyukov <dvyukov@google.com>.
 391
 392 config GCC_PLUGIN_LATENT_ENTROPY
 393         bool "Generate some entropy during boot and runtime"
 394         depends on GCC_PLUGINS
 395         help
 396           By saying Y here the kernel will instrument some kernel code to
 397           extract some entropy from both original and artificially created
 398           program state.  This will help especially embedded systems where
 399           there is little 'natural' source of entropy normally.  The cost
 400           is some slowdown of the boot process (about 0.5%) and fork and
 401           irq processing.
 402
 403           Note that entropy extracted this way is not cryptographically
 404           secure!
 405
 406           This plugin was ported from grsecurity/PaX. More information at:
 407            * https://grsecurity.net/
 408            * https://pax.grsecurity.net/
 409
 410 config HAVE_CC_STACKPROTECTOR
 411         bool
 412         help
 413           An arch should select this symbol if:
 414           - its compiler supports the -fstack-protector option
 415           - it has implemented a stack canary (e.g. __stack_chk_guard)
 416
 417 config CC_STACKPROTECTOR
 418         def_bool n
 419         help
 420           Set when a stack-protector mode is enabled, so that the build
 421           can enable kernel-side support for the GCC feature.
 422
 423 choice
 424         prompt "Stack Protector buffer overflow detection"
 425         depends on HAVE_CC_STACKPROTECTOR
 426         default CC_STACKPROTECTOR_NONE
 427         help
 428           This option turns on the "stack-protector" GCC feature. This
 429           feature puts, at the beginning of functions, a canary value on
 430           the stack just before the return address, and validates
 431           the value just before actually returning.  Stack based buffer
 432           overflows (that need to overwrite this return address) now also
 433           overwrite the canary, which gets detected and the attack is then
 434           neutralized via a kernel panic.
 435
 436 config CC_STACKPROTECTOR_NONE
 437         bool "None"
 438         help
 439           Disable "stack-protector" GCC feature.
 440
 441 config CC_STACKPROTECTOR_REGULAR
 442         bool "Regular"
 443         select CC_STACKPROTECTOR
 444         help
 445           Functions will have the stack-protector canary logic added if they
 446           have an 8-byte or larger character array on the stack.
 447
 448           This feature requires gcc version 4.2 or above, or a distribution
 449           gcc with the feature backported ("-fstack-protector").
 450
 451           On an x86 "defconfig" build, this feature adds canary checks to
 452           about 3% of all kernel functions, which increases kernel code size
 453           by about 0.3%.
 454
 455 config CC_STACKPROTECTOR_STRONG
 456         bool "Strong"
 457         select CC_STACKPROTECTOR
 458         help
 459           Functions will have the stack-protector canary logic added in any
 460           of the following conditions:
 461
 462           - local variable's address used as part of the right hand side of an
 463             assignment or function argument
 464           - local variable is an array (or union containing an array),
 465             regardless of array type or length
 466           - uses register local variables
 467
 468           This feature requires gcc version 4.9 or above, or a distribution
 469           gcc with the feature backported ("-fstack-protector-strong").
 470
 471           On an x86 "defconfig" build, this feature adds canary checks to
 472           about 20% of all kernel functions, which increases the kernel code
 473           size by about 2%.
 474
 475 endchoice
 476
 477 config THIN_ARCHIVES
 478         bool
 479         help
 480           Select this if the architecture wants to use thin archives
 481           instead of ld -r to create the built-in.o files.
 482
 483 config LD_DEAD_CODE_DATA_ELIMINATION
 484         bool
 485         help
 486           Select this if the architecture wants to do dead code and
 487           data elimination with the linker by compiling with
 488           -ffunction-sections -fdata-sections and linking with
 489           --gc-sections.
 490
 491           This requires that the arch annotates or otherwise protects
 492           its external entry points from being discarded. Linker scripts
 493           must also merge .text.*, .data.*, and .bss.* correctly into
 494           output sections. Care must be taken not to pull in unrelated
 495           sections (e.g., '.text.init'). Typically '.' in section names
 496           is used to distinguish them from label names / C identifiers.
 497
 498 config HAVE_ARCH_WITHIN_STACK_FRAMES
 499         bool
 500         help
 501           An architecture should select this if it can walk the kernel stack
 502           frames to determine if an object is part of either the arguments
 503           or local variables (i.e. that it excludes saved return addresses,
 504           and similar) by implementing an inline arch_within_stack_frames(),
 505           which is used by CONFIG_HARDENED_USERCOPY.
 506
 507 config HAVE_CONTEXT_TRACKING
 508         bool
 509         help
 510           Provide kernel/user boundaries probes necessary for subsystems
 511           that need it, such as userspace RCU extended quiescent state.
 512           Syscalls need to be wrapped inside user_exit()-user_enter() through
 513           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 514           wrapped as well. Irqs are already protected inside
 515           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 516           irq exit still need to be protected.
 517
 518 config HAVE_VIRT_CPU_ACCOUNTING
 519         bool
 520
 521 config ARCH_HAS_SCALED_CPUTIME
 522         bool
 523
 524 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 525         bool
 526         default y if 64BIT
 527         help
 528           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 529           Before enabling this option, arch code must be audited
 530           to ensure there are no races in concurrent read/write of
 531           cputime_t. For example, reading/writing 64-bit cputime_t on
 532           some 32-bit arches may require multiple accesses, so proper
 533           locking is needed to protect against concurrent accesses.
 534
 535
 536 config HAVE_IRQ_TIME_ACCOUNTING
 537         bool
 538         help
 539           Archs need to ensure they use a high enough resolution clock to
 540           support irq time accounting and then call enable_sched_clock_irqtime().
 541
 542 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 543         bool
 544
 545 config HAVE_ARCH_HUGE_VMAP
 546         bool
 547
 548 config HAVE_ARCH_SOFT_DIRTY
 549         bool
 550
 551 config HAVE_MOD_ARCH_SPECIFIC
 552         bool
 553         help
 554           The arch uses struct mod_arch_specific to store data.  Many arches
 555           just need a simple module loader without arch specific data - those
 556           should not enable this.
 557
 558 config MODULES_USE_ELF_RELA
 559         bool
 560         help
 561           Modules only use ELF RELA relocations.  Modules with ELF REL
 562           relocations will give an error.
 563
 564 config MODULES_USE_ELF_REL
 565         bool
 566         help
 567           Modules only use ELF REL relocations.  Modules with ELF RELA
 568           relocations will give an error.
 569
 570 config HAVE_UNDERSCORE_SYMBOL_PREFIX
 571         bool
 572         help
 573           Some architectures generate an _ in front of C symbols; things like
 574           module loading and assembly files need to know about this.
 575
 576 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 577         bool
 578         help
 579           Architecture doesn't only execute the irq handler on the irq stack
 580           but also irq_exit(). This way we can process softirqs on this irq
 581           stack instead of switching to a new one when we call __do_softirq()
 582           in the end of an hardirq.
 583           This spares a stack switch and improves cache usage on softirq
 584           processing.
 585
 586 config PGTABLE_LEVELS
 587         int
 588         default 2
 589
 590 config ARCH_HAS_ELF_RANDOMIZE
 591         bool
 592         help
 593           An architecture supports choosing randomized locations for
 594           stack, mmap, brk, and ET_DYN. Defined functions:
 595           - arch_mmap_rnd()
 596           - arch_randomize_brk()
 597
 598 config HAVE_ARCH_MMAP_RND_BITS
 599         bool
 600         help
 601           An arch should select this symbol if it supports setting a variable
 602           number of bits for use in establishing the base address for mmap
 603           allocations, has MMU enabled and provides values for both:
 604           - ARCH_MMAP_RND_BITS_MIN
 605           - ARCH_MMAP_RND_BITS_MAX
 606
 607 config HAVE_EXIT_THREAD
 608         bool
 609         help
 610           An architecture implements exit_thread.
 611
 612 config ARCH_MMAP_RND_BITS_MIN
 613         int
 614
 615 config ARCH_MMAP_RND_BITS_MAX
 616         int
 617
 618 config ARCH_MMAP_RND_BITS_DEFAULT
 619         int
 620
 621 config ARCH_MMAP_RND_BITS
 622         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 623         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 624         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 625         default ARCH_MMAP_RND_BITS_MIN
 626         depends on HAVE_ARCH_MMAP_RND_BITS
 627         help
 628           This value can be used to select the number of bits to use to
 629           determine the random offset to the base address of vma regions
 630           resulting from mmap allocations. This value will be bounded
 631           by the architecture's minimum and maximum supported values.
 632
 633           This value can be changed after boot using the
 634           /proc/sys/vm/mmap_rnd_bits tunable
 635
 636 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 637         bool
 638         help
 639           An arch should select this symbol if it supports running applications
 640           in compatibility mode, supports setting a variable number of bits for
 641           use in establishing the base address for mmap allocations, has MMU
 642           enabled and provides values for both:
 643           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 644           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 645
 646 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 647         int
 648
 649 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 650         int
 651
 652 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 653         int
 654
 655 config ARCH_MMAP_RND_COMPAT_BITS
 656         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 657         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 658         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 659         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 660         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 661         help
 662           This value can be used to select the number of bits to use to
 663           determine the random offset to the base address of vma regions
 664           resulting from mmap allocations for compatible applications This
 665           value will be bounded by the architecture's minimum and maximum
 666           supported values.
 667
 668           This value can be changed after boot using the
 669           /proc/sys/vm/mmap_rnd_compat_bits tunable
 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_ARCH_HASH
 685         bool
 686         default n
 687         help
 688           If this is set, the architecture provides an <asm/hash.h>
 689           file which provides platform-specific implementations of some
 690           functions in <linux/hash.h> or fs/namei.c.
 691
 692 config ISA_BUS_API
 693         def_bool ISA
 694
 695 #
 696 # ABI hall of shame
 697 #
 698 config CLONE_BACKWARDS
 699         bool
 700         help
 701           Architecture has tls passed as the 4th argument of clone(2),
 702           not the 5th one.
 703
 704 config CLONE_BACKWARDS2
 705         bool
 706         help
 707           Architecture has the first two arguments of clone(2) swapped.
 708
 709 config CLONE_BACKWARDS3
 710         bool
 711         help
 712           Architecture has tls passed as the 3rd argument of clone(2),
 713           not the 5th one.
 714
 715 config ODD_RT_SIGACTION
 716         bool
 717         help
 718           Architecture has unusual rt_sigaction(2) arguments
 719
 720 config OLD_SIGSUSPEND
 721         bool
 722         help
 723           Architecture has old sigsuspend(2) syscall, of one-argument variety
 724
 725 config OLD_SIGSUSPEND3
 726         bool
 727         help
 728           Even weirder antique ABI - three-argument sigsuspend(2)
 729
 730 config OLD_SIGACTION
 731         bool
 732         help
 733           Architecture has old sigaction(2) syscall.  Nope, not the same
 734           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 735           but fairly different variant of sigaction(2), thanks to OSF/1
 736           compatibility...
 737
 738 config COMPAT_OLD_SIGACTION
 739         bool
 740
 741 config ARCH_NO_COHERENT_DMA_MMAP
 742         bool
 743
 744 config CPU_NO_EFFICIENT_FFS
 745         def_bool n
 746
 747 config HAVE_ARCH_VMAP_STACK
 748         def_bool n
 749         help
 750           An arch should select this symbol if it can support kernel stacks
 751           in vmalloc space.  This means:
 752
 753           - vmalloc space must be large enough to hold many kernel stacks.
 754             This may rule out many 32-bit architectures.
 755
 756           - Stacks in vmalloc space need to work reliably.  For example, if
 757             vmap page tables are created on demand, either this mechanism
 758             needs to work while the stack points to a virtual address with
 759             unpopulated page tables or arch code (switch_to() and switch_mm(),
 760             most likely) needs to ensure that the stack's page table entries
 761             are populated before running on a possibly unpopulated stack.
 762
 763           - If the stack overflows into a guard page, something reasonable
 764             should happen.  The definition of "reasonable" is flexible, but
 765             instantly rebooting without logging anything would be unfriendly.
 766
 767 config VMAP_STACK
 768         default y
 769         bool "Use a virtually-mapped stack"
 770         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 771         ---help---
 772           Enable this if you want the use virtually-mapped kernel stacks
 773           with guard pages.  This causes kernel stack overflows to be
 774           caught immediately rather than causing difficult-to-diagnose
 775           corruption.
 776
 777           This is presently incompatible with KASAN because KASAN expects
 778           the stack to map directly to the KASAN shadow map using a formula
 779           that is incorrect if the stack is in vmalloc space.
 780
 781 source "kernel/gcov/Kconfig"