arch/Kconfig

   1 #
   2 # General architecture dependent options
   3 #
   4
   5 config KEXEC_CORE
   6         bool
   7
   8 config HAVE_IMA_KEXEC
   9         bool
  10
  11 config OPROFILE
  12         tristate "OProfile system profiling"
  13         depends on PROFILING
  14         depends on HAVE_OPROFILE
  15         select RING_BUFFER
  16         select RING_BUFFER_ALLOW_SWAP
  17         help
  18           OProfile is a profiling system capable of profiling the
  19           whole system, include the kernel, kernel modules, libraries,
  20           and applications.
  21
  22           If unsure, say N.
  23
  24 config OPROFILE_EVENT_MULTIPLEX
  25         bool "OProfile multiplexing support (EXPERIMENTAL)"
  26         default n
  27         depends on OPROFILE && X86
  28         help
  29           The number of hardware counters is limited. The multiplexing
  30           feature enables OProfile to gather more events than counters
  31           are provided by the hardware. This is realized by switching
  32           between events at an user specified time interval.
  33
  34           If unsure, say N.
  35
  36 config HAVE_OPROFILE
  37         bool
  38
  39 config OPROFILE_NMI_TIMER
  40         def_bool y
  41         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  42
  43 config KPROBES
  44         bool "Kprobes"
  45         depends on MODULES
  46         depends on HAVE_KPROBES
  47         select KALLSYMS
  48         help
  49           Kprobes allows you to trap at almost any kernel address and
  50           execute a callback function.  register_kprobe() establishes
  51           a probepoint and specifies the callback.  Kprobes is useful
  52           for kernel debugging, non-intrusive instrumentation and testing.
  53           If in doubt, say "N".
  54
  55 config JUMP_LABEL
  56        bool "Optimize very unlikely/likely branches"
  57        depends on HAVE_ARCH_JUMP_LABEL
  58        help
  59          This option enables a transparent branch optimization that
  60          makes certain almost-always-true or almost-always-false branch
  61          conditions even cheaper to execute within the kernel.
  62
  63          Certain performance-sensitive kernel code, such as trace points,
  64          scheduler functionality, networking code and KVM have such
  65          branches and include support for this optimization technique.
  66
  67          If it is detected that the compiler has support for "asm goto",
  68          the kernel will compile such branches with just a nop
  69          instruction. When the condition flag is toggled to true, the
  70          nop will be converted to a jump instruction to execute the
  71          conditional block of instructions.
  72
  73          This technique lowers overhead and stress on the branch prediction
  74          of the processor and generally makes the kernel faster. The update
  75          of the condition is slower, but those are always very rare.
  76
  77          ( On 32-bit x86, the necessary options added to the compiler
  78            flags may increase the size of the kernel slightly. )
  79
  80 config STATIC_KEYS_SELFTEST
  81         bool "Static key selftest"
  82         depends on JUMP_LABEL
  83         help
  84           Boot time self-test of the branch patching code.
  85
  86 config OPTPROBES
  87         def_bool y
  88         depends on KPROBES && HAVE_OPTPROBES
  89         depends on !PREEMPT
  90
  91 config KPROBES_ON_FTRACE
  92         def_bool y
  93         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
  94         depends on DYNAMIC_FTRACE_WITH_REGS
  95         help
  96          If function tracer is enabled and the arch supports full
  97          passing of pt_regs to function tracing, then kprobes can
  98          optimize on top of function tracing.
  99
 100 config UPROBES
 101         def_bool n
 102         depends on ARCH_SUPPORTS_UPROBES
 103         help
 104           Uprobes is the user-space counterpart to kprobes: they
 105           enable instrumentation applications (such as 'perf probe')
 106           to establish unintrusive probes in user-space binaries and
 107           libraries, by executing handler functions when the probes
 108           are hit by user-space applications.
 109
 110           ( These probes come in the form of single-byte breakpoints,
 111             managed by the kernel and kept transparent to the probed
 112             application. )
 113
 114 config HAVE_64BIT_ALIGNED_ACCESS
 115         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 116         help
 117           Some architectures require 64 bit accesses to be 64 bit
 118           aligned, which also requires structs containing 64 bit values
 119           to be 64 bit aligned too. This includes some 32 bit
 120           architectures which can do 64 bit accesses, as well as 64 bit
 121           architectures without unaligned access.
 122
 123           This symbol should be selected by an architecture if 64 bit
 124           accesses are required to be 64 bit aligned in this way even
 125           though it is not a 64 bit architecture.
 126
 127           See Documentation/unaligned-memory-access.txt for more
 128           information on the topic of unaligned memory accesses.
 129
 130 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 131         bool
 132         help
 133           Some architectures are unable to perform unaligned accesses
 134           without the use of get_unaligned/put_unaligned. Others are
 135           unable to perform such accesses efficiently (e.g. trap on
 136           unaligned access and require fixing it up in the exception
 137           handler.)
 138
 139           This symbol should be selected by an architecture if it can
 140           perform unaligned accesses efficiently to allow different
 141           code paths to be selected for these cases. Some network
 142           drivers, for example, could opt to not fix up alignment
 143           problems with received packets if doing so would not help
 144           much.
 145
 146           See Documentation/unaligned-memory-access.txt for more
 147           information on the topic of unaligned memory accesses.
 148
 149 config ARCH_USE_BUILTIN_BSWAP
 150        bool
 151        help
 152          Modern versions of GCC (since 4.4) have builtin functions
 153          for handling byte-swapping. Using these, instead of the old
 154          inline assembler that the architecture code provides in the
 155          __arch_bswapXX() macros, allows the compiler to see what's
 156          happening and offers more opportunity for optimisation. In
 157          particular, the compiler will be able to combine the byteswap
 158          with a nearby load or store and use load-and-swap or
 159          store-and-swap instructions if the architecture has them. It
 160          should almost *never* result in code which is worse than the
 161          hand-coded assembler in <asm/swab.h>.  But just in case it
 162          does, the use of the builtins is optional.
 163
 164          Any architecture with load-and-swap or store-and-swap
 165          instructions should set this. And it shouldn't hurt to set it
 166          on architectures that don't have such instructions.
 167
 168 config KRETPROBES
 169         def_bool y
 170         depends on KPROBES && HAVE_KRETPROBES
 171
 172 config USER_RETURN_NOTIFIER
 173         bool
 174         depends on HAVE_USER_RETURN_NOTIFIER
 175         help
 176           Provide a kernel-internal notification when a cpu is about to
 177           switch to user mode.
 178
 179 config HAVE_IOREMAP_PROT
 180         bool
 181
 182 config HAVE_KPROBES
 183         bool
 184
 185 config HAVE_KRETPROBES
 186         bool
 187
 188 config HAVE_OPTPROBES
 189         bool
 190
 191 config HAVE_KPROBES_ON_FTRACE
 192         bool
 193
 194 config HAVE_NMI
 195         bool
 196
 197 config HAVE_NMI_WATCHDOG
 198         depends on HAVE_NMI
 199         bool
 200 #
 201 # An arch should select this if it provides all these things:
 202 #
 203 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 204 #       arch_has_single_step()  if there is hardware single-step support
 205 #       arch_has_block_step()   if there is hardware block-step support
 206 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 207 #       linux/regset.h          user_regset interfaces
 208 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 209 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 210 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 211 #       signal delivery         calls tracehook_signal_handler()
 212 #
 213 config HAVE_ARCH_TRACEHOOK
 214         bool
 215
 216 config HAVE_DMA_CONTIGUOUS
 217         bool
 218
 219 config GENERIC_SMP_IDLE_THREAD
 220        bool
 221
 222 config GENERIC_IDLE_POLL_SETUP
 223        bool
 224
 225 # Select if arch init_task initializer is different to init/init_task.c
 226 config ARCH_INIT_TASK
 227        bool
 228
 229 # Select if arch has its private alloc_task_struct() function
 230 config ARCH_TASK_STRUCT_ALLOCATOR
 231         bool
 232
 233 # Select if arch has its private alloc_thread_stack() function
 234 config ARCH_THREAD_STACK_ALLOCATOR
 235         bool
 236
 237 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 238 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 239         bool
 240
 241 config HAVE_REGS_AND_STACK_ACCESS_API
 242         bool
 243         help
 244           This symbol should be selected by an architecure if it supports
 245           the API needed to access registers and stack entries from pt_regs,
 246           declared in asm/ptrace.h
 247           For example the kprobes-based event tracer needs this API.
 248
 249 config HAVE_CLK
 250         bool
 251         help
 252           The <linux/clk.h> calls support software clock gating and
 253           thus are a key power management tool on many systems.
 254
 255 config HAVE_DMA_API_DEBUG
 256         bool
 257
 258 config HAVE_HW_BREAKPOINT
 259         bool
 260         depends on PERF_EVENTS
 261
 262 config HAVE_MIXED_BREAKPOINTS_REGS
 263         bool
 264         depends on HAVE_HW_BREAKPOINT
 265         help
 266           Depending on the arch implementation of hardware breakpoints,
 267           some of them have separate registers for data and instruction
 268           breakpoints addresses, others have mixed registers to store
 269           them but define the access type in a control register.
 270           Select this option if your arch implements breakpoints under the
 271           latter fashion.
 272
 273 config HAVE_USER_RETURN_NOTIFIER
 274         bool
 275
 276 config HAVE_PERF_EVENTS_NMI
 277         bool
 278         help
 279           System hardware can generate an NMI using the perf event
 280           subsystem.  Also has support for calculating CPU cycle events
 281           to determine how many clock cycles in a given period.
 282
 283 config HAVE_PERF_REGS
 284         bool
 285         help
 286           Support selective register dumps for perf events. This includes
 287           bit-mapping of each registers and a unique architecture id.
 288
 289 config HAVE_PERF_USER_STACK_DUMP
 290         bool
 291         help
 292           Support user stack dumps for perf event samples. This needs
 293           access to the user stack pointer which is not unified across
 294           architectures.
 295
 296 config HAVE_ARCH_JUMP_LABEL
 297         bool
 298
 299 config HAVE_RCU_TABLE_FREE
 300         bool
 301
 302 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 303         bool
 304
 305 config HAVE_ALIGNED_STRUCT_PAGE
 306         bool
 307         help
 308           This makes sure that struct pages are double word aligned and that
 309           e.g. the SLUB allocator can perform double word atomic operations
 310           on a struct page for better performance. However selecting this
 311           might increase the size of a struct page by a word.
 312
 313 config HAVE_CMPXCHG_LOCAL
 314         bool
 315
 316 config HAVE_CMPXCHG_DOUBLE
 317         bool
 318
 319 config ARCH_WANT_IPC_PARSE_VERSION
 320         bool
 321
 322 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 323         bool
 324
 325 config ARCH_WANT_OLD_COMPAT_IPC
 326         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 327         bool
 328
 329 config HAVE_ARCH_SECCOMP_FILTER
 330         bool
 331         help
 332           An arch should select this symbol if it provides all of these things:
 333           - syscall_get_arch()
 334           - syscall_get_arguments()
 335           - syscall_rollback()
 336           - syscall_set_return_value()
 337           - SIGSYS siginfo_t support
 338           - secure_computing is called from a ptrace_event()-safe context
 339           - secure_computing return value is checked and a return value of -1
 340             results in the system call being skipped immediately.
 341           - seccomp syscall wired up
 342
 343 config SECCOMP_FILTER
 344         def_bool y
 345         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 346         help
 347           Enable tasks to build secure computing environments defined
 348           in terms of Berkeley Packet Filter programs which implement
 349           task-defined system call filtering polices.
 350
 351           See Documentation/prctl/seccomp_filter.txt for details.
 352
 353 config HAVE_GCC_PLUGINS
 354         bool
 355         help
 356           An arch should select this symbol if it supports building with
 357           GCC plugins.
 358
 359 menuconfig GCC_PLUGINS
 360         bool "GCC plugins"
 361         depends on HAVE_GCC_PLUGINS
 362         depends on !COMPILE_TEST
 363         help
 364           GCC plugins are loadable modules that provide extra features to the
 365           compiler. They are useful for runtime instrumentation and static analysis.
 366
 367           See Documentation/gcc-plugins.txt for details.
 368
 369 config GCC_PLUGIN_CYC_COMPLEXITY
 370         bool "Compute the cyclomatic complexity of a function" if EXPERT
 371         depends on GCC_PLUGINS
 372         depends on !COMPILE_TEST
 373         help
 374           The complexity M of a function's control flow graph is defined as:
 375            M = E - N + 2P
 376           where
 377
 378           E = the number of edges
 379           N = the number of nodes
 380           P = the number of connected components (exit nodes).
 381
 382           Enabling this plugin reports the complexity to stderr during the
 383           build. It mainly serves as a simple example of how to create a
 384           gcc plugin for the kernel.
 385
 386 config GCC_PLUGIN_SANCOV
 387         bool
 388         depends on GCC_PLUGINS
 389         help
 390           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 391           basic blocks. It supports all gcc versions with plugin support (from
 392           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 393           by Dmitry Vyukov <dvyukov@google.com>.
 394
 395 config GCC_PLUGIN_LATENT_ENTROPY
 396         bool "Generate some entropy during boot and runtime"
 397         depends on GCC_PLUGINS
 398         help
 399           By saying Y here the kernel will instrument some kernel code to
 400           extract some entropy from both original and artificially created
 401           program state.  This will help especially embedded systems where
 402           there is little 'natural' source of entropy normally.  The cost
 403           is some slowdown of the boot process (about 0.5%) and fork and
 404           irq processing.
 405
 406           Note that entropy extracted this way is not cryptographically
 407           secure!
 408
 409           This plugin was ported from grsecurity/PaX. More information at:
 410            * https://grsecurity.net/
 411            * https://pax.grsecurity.net/
 412
 413 config HAVE_CC_STACKPROTECTOR
 414         bool
 415         help
 416           An arch should select this symbol if:
 417           - its compiler supports the -fstack-protector option
 418           - it has implemented a stack canary (e.g. __stack_chk_guard)
 419
 420 config CC_STACKPROTECTOR
 421         def_bool n
 422         help
 423           Set when a stack-protector mode is enabled, so that the build
 424           can enable kernel-side support for the GCC feature.
 425
 426 choice
 427         prompt "Stack Protector buffer overflow detection"
 428         depends on HAVE_CC_STACKPROTECTOR
 429         default CC_STACKPROTECTOR_NONE
 430         help
 431           This option turns on the "stack-protector" GCC feature. This
 432           feature puts, at the beginning of functions, a canary value on
 433           the stack just before the return address, and validates
 434           the value just before actually returning.  Stack based buffer
 435           overflows (that need to overwrite this return address) now also
 436           overwrite the canary, which gets detected and the attack is then
 437           neutralized via a kernel panic.
 438
 439 config CC_STACKPROTECTOR_NONE
 440         bool "None"
 441         help
 442           Disable "stack-protector" GCC feature.
 443
 444 config CC_STACKPROTECTOR_REGULAR
 445         bool "Regular"
 446         select CC_STACKPROTECTOR
 447         help
 448           Functions will have the stack-protector canary logic added if they
 449           have an 8-byte or larger character array on the stack.
 450
 451           This feature requires gcc version 4.2 or above, or a distribution
 452           gcc with the feature backported ("-fstack-protector").
 453
 454           On an x86 "defconfig" build, this feature adds canary checks to
 455           about 3% of all kernel functions, which increases kernel code size
 456           by about 0.3%.
 457
 458 config CC_STACKPROTECTOR_STRONG
 459         bool "Strong"
 460         select CC_STACKPROTECTOR
 461         help
 462           Functions will have the stack-protector canary logic added in any
 463           of the following conditions:
 464
 465           - local variable's address used as part of the right hand side of an
 466             assignment or function argument
 467           - local variable is an array (or union containing an array),
 468             regardless of array type or length
 469           - uses register local variables
 470
 471           This feature requires gcc version 4.9 or above, or a distribution
 472           gcc with the feature backported ("-fstack-protector-strong").
 473
 474           On an x86 "defconfig" build, this feature adds canary checks to
 475           about 20% of all kernel functions, which increases the kernel code
 476           size by about 2%.
 477
 478 endchoice
 479
 480 config THIN_ARCHIVES
 481         bool
 482         help
 483           Select this if the architecture wants to use thin archives
 484           instead of ld -r to create the built-in.o files.
 485
 486 config LD_DEAD_CODE_DATA_ELIMINATION
 487         bool
 488         help
 489           Select this if the architecture wants to do dead code and
 490           data elimination with the linker by compiling with
 491           -ffunction-sections -fdata-sections and linking with
 492           --gc-sections.
 493
 494           This requires that the arch annotates or otherwise protects
 495           its external entry points from being discarded. Linker scripts
 496           must also merge .text.*, .data.*, and .bss.* correctly into
 497           output sections. Care must be taken not to pull in unrelated
 498           sections (e.g., '.text.init'). Typically '.' in section names
 499           is used to distinguish them from label names / C identifiers.
 500
 501 config HAVE_ARCH_WITHIN_STACK_FRAMES
 502         bool
 503         help
 504           An architecture should select this if it can walk the kernel stack
 505           frames to determine if an object is part of either the arguments
 506           or local variables (i.e. that it excludes saved return addresses,
 507           and similar) by implementing an inline arch_within_stack_frames(),
 508           which is used by CONFIG_HARDENED_USERCOPY.
 509
 510 config HAVE_CONTEXT_TRACKING
 511         bool
 512         help
 513           Provide kernel/user boundaries probes necessary for subsystems
 514           that need it, such as userspace RCU extended quiescent state.
 515           Syscalls need to be wrapped inside user_exit()-user_enter() through
 516           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 517           wrapped as well. Irqs are already protected inside
 518           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 519           irq exit still need to be protected.
 520
 521 config HAVE_VIRT_CPU_ACCOUNTING
 522         bool
 523
 524 config ARCH_HAS_SCALED_CPUTIME
 525         bool
 526
 527 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 528         bool
 529         default y if 64BIT
 530         help
 531           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 532           Before enabling this option, arch code must be audited
 533           to ensure there are no races in concurrent read/write of
 534           cputime_t. For example, reading/writing 64-bit cputime_t on
 535           some 32-bit arches may require multiple accesses, so proper
 536           locking is needed to protect against concurrent accesses.
 537
 538
 539 config HAVE_IRQ_TIME_ACCOUNTING
 540         bool
 541         help
 542           Archs need to ensure they use a high enough resolution clock to
 543           support irq time accounting and then call enable_sched_clock_irqtime().
 544
 545 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 546         bool
 547
 548 config HAVE_ARCH_HUGE_VMAP
 549         bool
 550
 551 config HAVE_ARCH_SOFT_DIRTY
 552         bool
 553
 554 config HAVE_MOD_ARCH_SPECIFIC
 555         bool
 556         help
 557           The arch uses struct mod_arch_specific to store data.  Many arches
 558           just need a simple module loader without arch specific data - those
 559           should not enable this.
 560
 561 config MODULES_USE_ELF_RELA
 562         bool
 563         help
 564           Modules only use ELF RELA relocations.  Modules with ELF REL
 565           relocations will give an error.
 566
 567 config MODULES_USE_ELF_REL
 568         bool
 569         help
 570           Modules only use ELF REL relocations.  Modules with ELF RELA
 571           relocations will give an error.
 572
 573 config HAVE_UNDERSCORE_SYMBOL_PREFIX
 574         bool
 575         help
 576           Some architectures generate an _ in front of C symbols; things like
 577           module loading and assembly files need to know about this.
 578
 579 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 580         bool
 581         help
 582           Architecture doesn't only execute the irq handler on the irq stack
 583           but also irq_exit(). This way we can process softirqs on this irq
 584           stack instead of switching to a new one when we call __do_softirq()
 585           in the end of an hardirq.
 586           This spares a stack switch and improves cache usage on softirq
 587           processing.
 588
 589 config PGTABLE_LEVELS
 590         int
 591         default 2
 592
 593 config ARCH_HAS_ELF_RANDOMIZE
 594         bool
 595         help
 596           An architecture supports choosing randomized locations for
 597           stack, mmap, brk, and ET_DYN. Defined functions:
 598           - arch_mmap_rnd()
 599           - arch_randomize_brk()
 600
 601 config HAVE_ARCH_MMAP_RND_BITS
 602         bool
 603         help
 604           An arch should select this symbol if it supports setting a variable
 605           number of bits for use in establishing the base address for mmap
 606           allocations, has MMU enabled and provides values for both:
 607           - ARCH_MMAP_RND_BITS_MIN
 608           - ARCH_MMAP_RND_BITS_MAX
 609
 610 config HAVE_EXIT_THREAD
 611         bool
 612         help
 613           An architecture implements exit_thread.
 614
 615 config ARCH_MMAP_RND_BITS_MIN
 616         int
 617
 618 config ARCH_MMAP_RND_BITS_MAX
 619         int
 620
 621 config ARCH_MMAP_RND_BITS_DEFAULT
 622         int
 623
 624 config ARCH_MMAP_RND_BITS
 625         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 626         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 627         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 628         default ARCH_MMAP_RND_BITS_MIN
 629         depends on HAVE_ARCH_MMAP_RND_BITS
 630         help
 631           This value can be used to select the number of bits to use to
 632           determine the random offset to the base address of vma regions
 633           resulting from mmap allocations. This value will be bounded
 634           by the architecture's minimum and maximum supported values.
 635
 636           This value can be changed after boot using the
 637           /proc/sys/vm/mmap_rnd_bits tunable
 638
 639 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 640         bool
 641         help
 642           An arch should select this symbol if it supports running applications
 643           in compatibility mode, supports setting a variable number of bits for
 644           use in establishing the base address for mmap allocations, has MMU
 645           enabled and provides values for both:
 646           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 647           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 648
 649 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 650         int
 651
 652 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 653         int
 654
 655 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 656         int
 657
 658 config ARCH_MMAP_RND_COMPAT_BITS
 659         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 660         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 661         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 662         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 663         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 664         help
 665           This value can be used to select the number of bits to use to
 666           determine the random offset to the base address of vma regions
 667           resulting from mmap allocations for compatible applications This
 668           value will be bounded by the architecture's minimum and maximum
 669           supported values.
 670
 671           This value can be changed after boot using the
 672           /proc/sys/vm/mmap_rnd_compat_bits tunable
 673
 674 config HAVE_COPY_THREAD_TLS
 675         bool
 676         help
 677           Architecture provides copy_thread_tls to accept tls argument via
 678           normal C parameter passing, rather than extracting the syscall
 679           argument from pt_regs.
 680
 681 config HAVE_STACK_VALIDATION
 682         bool
 683         help
 684           Architecture supports the 'objtool check' host tool command, which
 685           performs compile-time stack metadata validation.
 686
 687 config HAVE_ARCH_HASH
 688         bool
 689         default n
 690         help
 691           If this is set, the architecture provides an <asm/hash.h>
 692           file which provides platform-specific implementations of some
 693           functions in <linux/hash.h> or fs/namei.c.
 694
 695 config ISA_BUS_API
 696         def_bool ISA
 697
 698 #
 699 # ABI hall of shame
 700 #
 701 config CLONE_BACKWARDS
 702         bool
 703         help
 704           Architecture has tls passed as the 4th argument of clone(2),
 705           not the 5th one.
 706
 707 config CLONE_BACKWARDS2
 708         bool
 709         help
 710           Architecture has the first two arguments of clone(2) swapped.
 711
 712 config CLONE_BACKWARDS3
 713         bool
 714         help
 715           Architecture has tls passed as the 3rd argument of clone(2),
 716           not the 5th one.
 717
 718 config ODD_RT_SIGACTION
 719         bool
 720         help
 721           Architecture has unusual rt_sigaction(2) arguments
 722
 723 config OLD_SIGSUSPEND
 724         bool
 725         help
 726           Architecture has old sigsuspend(2) syscall, of one-argument variety
 727
 728 config OLD_SIGSUSPEND3
 729         bool
 730         help
 731           Even weirder antique ABI - three-argument sigsuspend(2)
 732
 733 config OLD_SIGACTION
 734         bool
 735         help
 736           Architecture has old sigaction(2) syscall.  Nope, not the same
 737           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 738           but fairly different variant of sigaction(2), thanks to OSF/1
 739           compatibility...
 740
 741 config COMPAT_OLD_SIGACTION
 742         bool
 743
 744 config ARCH_NO_COHERENT_DMA_MMAP
 745         bool
 746
 747 config CPU_NO_EFFICIENT_FFS
 748         def_bool n
 749
 750 config HAVE_ARCH_VMAP_STACK
 751         def_bool n
 752         help
 753           An arch should select this symbol if it can support kernel stacks
 754           in vmalloc space.  This means:
 755
 756           - vmalloc space must be large enough to hold many kernel stacks.
 757             This may rule out many 32-bit architectures.
 758
 759           - Stacks in vmalloc space need to work reliably.  For example, if
 760             vmap page tables are created on demand, either this mechanism
 761             needs to work while the stack points to a virtual address with
 762             unpopulated page tables or arch code (switch_to() and switch_mm(),
 763             most likely) needs to ensure that the stack's page table entries
 764             are populated before running on a possibly unpopulated stack.
 765
 766           - If the stack overflows into a guard page, something reasonable
 767             should happen.  The definition of "reasonable" is flexible, but
 768             instantly rebooting without logging anything would be unfriendly.
 769
 770 config VMAP_STACK
 771         default y
 772         bool "Use a virtually-mapped stack"
 773         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 774         ---help---
 775           Enable this if you want the use virtually-mapped kernel stacks
 776           with guard pages.  This causes kernel stack overflows to be
 777           caught immediately rather than causing difficult-to-diagnose
 778           corruption.
 779
 780           This is presently incompatible with KASAN because KASAN expects
 781           the stack to map directly to the KASAN shadow map using a formula
 782           that is incorrect if the stack is in vmalloc space.
 783
 784 source "kernel/gcov/Kconfig"