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