arch/Kconfig

   1 # SPDX-License-Identifier: GPL-2.0
   2 #
   3 # General architecture dependent options
   4 #
   5
   6 config CRASH_CORE
   7         bool
   8
   9 config KEXEC_CORE
  10         select CRASH_CORE
  11         bool
  12
  13 config HAVE_IMA_KEXEC
  14         bool
  15
  16 config OPROFILE
  17         tristate "OProfile system profiling"
  18         depends on PROFILING
  19         depends on HAVE_OPROFILE
  20         select RING_BUFFER
  21         select RING_BUFFER_ALLOW_SWAP
  22         help
  23           OProfile is a profiling system capable of profiling the
  24           whole system, include the kernel, kernel modules, libraries,
  25           and applications.
  26
  27           If unsure, say N.
  28
  29 config OPROFILE_EVENT_MULTIPLEX
  30         bool "OProfile multiplexing support (EXPERIMENTAL)"
  31         default n
  32         depends on OPROFILE && X86
  33         help
  34           The number of hardware counters is limited. The multiplexing
  35           feature enables OProfile to gather more events than counters
  36           are provided by the hardware. This is realized by switching
  37           between events at a user specified time interval.
  38
  39           If unsure, say N.
  40
  41 config HAVE_OPROFILE
  42         bool
  43
  44 config OPROFILE_NMI_TIMER
  45         def_bool y
  46         depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
  47
  48 config KPROBES
  49         bool "Kprobes"
  50         depends on MODULES
  51         depends on HAVE_KPROBES
  52         select KALLSYMS
  53         help
  54           Kprobes allows you to trap at almost any kernel address and
  55           execute a callback function.  register_kprobe() establishes
  56           a probepoint and specifies the callback.  Kprobes is useful
  57           for kernel debugging, non-intrusive instrumentation and testing.
  58           If in doubt, say "N".
  59
  60 config JUMP_LABEL
  61        bool "Optimize very unlikely/likely branches"
  62        depends on HAVE_ARCH_JUMP_LABEL
  63        help
  64          This option enables a transparent branch optimization that
  65          makes certain almost-always-true or almost-always-false branch
  66          conditions even cheaper to execute within the kernel.
  67
  68          Certain performance-sensitive kernel code, such as trace points,
  69          scheduler functionality, networking code and KVM have such
  70          branches and include support for this optimization technique.
  71
  72          If it is detected that the compiler has support for "asm goto",
  73          the kernel will compile such branches with just a nop
  74          instruction. When the condition flag is toggled to true, the
  75          nop will be converted to a jump instruction to execute the
  76          conditional block of instructions.
  77
  78          This technique lowers overhead and stress on the branch prediction
  79          of the processor and generally makes the kernel faster. The update
  80          of the condition is slower, but those are always very rare.
  81
  82          ( On 32-bit x86, the necessary options added to the compiler
  83            flags may increase the size of the kernel slightly. )
  84
  85 config STATIC_KEYS_SELFTEST
  86         bool "Static key selftest"
  87         depends on JUMP_LABEL
  88         help
  89           Boot time self-test of the branch patching code.
  90
  91 config OPTPROBES
  92         def_bool y
  93         depends on KPROBES && HAVE_OPTPROBES
  94         select TASKS_RCU if PREEMPT
  95
  96 config KPROBES_ON_FTRACE
  97         def_bool y
  98         depends on KPROBES && HAVE_KPROBES_ON_FTRACE
  99         depends on DYNAMIC_FTRACE_WITH_REGS
 100         help
 101          If function tracer is enabled and the arch supports full
 102          passing of pt_regs to function tracing, then kprobes can
 103          optimize on top of function tracing.
 104
 105 config UPROBES
 106         def_bool n
 107         depends on ARCH_SUPPORTS_UPROBES
 108         help
 109           Uprobes is the user-space counterpart to kprobes: they
 110           enable instrumentation applications (such as 'perf probe')
 111           to establish unintrusive probes in user-space binaries and
 112           libraries, by executing handler functions when the probes
 113           are hit by user-space applications.
 114
 115           ( These probes come in the form of single-byte breakpoints,
 116             managed by the kernel and kept transparent to the probed
 117             application. )
 118
 119 config HAVE_64BIT_ALIGNED_ACCESS
 120         def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
 121         help
 122           Some architectures require 64 bit accesses to be 64 bit
 123           aligned, which also requires structs containing 64 bit values
 124           to be 64 bit aligned too. This includes some 32 bit
 125           architectures which can do 64 bit accesses, as well as 64 bit
 126           architectures without unaligned access.
 127
 128           This symbol should be selected by an architecture if 64 bit
 129           accesses are required to be 64 bit aligned in this way even
 130           though it is not a 64 bit architecture.
 131
 132           See Documentation/unaligned-memory-access.txt for more
 133           information on the topic of unaligned memory accesses.
 134
 135 config HAVE_EFFICIENT_UNALIGNED_ACCESS
 136         bool
 137         help
 138           Some architectures are unable to perform unaligned accesses
 139           without the use of get_unaligned/put_unaligned. Others are
 140           unable to perform such accesses efficiently (e.g. trap on
 141           unaligned access and require fixing it up in the exception
 142           handler.)
 143
 144           This symbol should be selected by an architecture if it can
 145           perform unaligned accesses efficiently to allow different
 146           code paths to be selected for these cases. Some network
 147           drivers, for example, could opt to not fix up alignment
 148           problems with received packets if doing so would not help
 149           much.
 150
 151           See Documentation/unaligned-memory-access.txt for more
 152           information on the topic of unaligned memory accesses.
 153
 154 config ARCH_USE_BUILTIN_BSWAP
 155        bool
 156        help
 157          Modern versions of GCC (since 4.4) have builtin functions
 158          for handling byte-swapping. Using these, instead of the old
 159          inline assembler that the architecture code provides in the
 160          __arch_bswapXX() macros, allows the compiler to see what's
 161          happening and offers more opportunity for optimisation. In
 162          particular, the compiler will be able to combine the byteswap
 163          with a nearby load or store and use load-and-swap or
 164          store-and-swap instructions if the architecture has them. It
 165          should almost *never* result in code which is worse than the
 166          hand-coded assembler in <asm/swab.h>.  But just in case it
 167          does, the use of the builtins is optional.
 168
 169          Any architecture with load-and-swap or store-and-swap
 170          instructions should set this. And it shouldn't hurt to set it
 171          on architectures that don't have such instructions.
 172
 173 config KRETPROBES
 174         def_bool y
 175         depends on KPROBES && HAVE_KRETPROBES
 176
 177 config USER_RETURN_NOTIFIER
 178         bool
 179         depends on HAVE_USER_RETURN_NOTIFIER
 180         help
 181           Provide a kernel-internal notification when a cpu is about to
 182           switch to user mode.
 183
 184 config HAVE_IOREMAP_PROT
 185         bool
 186
 187 config HAVE_KPROBES
 188         bool
 189
 190 config HAVE_KRETPROBES
 191         bool
 192
 193 config HAVE_OPTPROBES
 194         bool
 195
 196 config HAVE_KPROBES_ON_FTRACE
 197         bool
 198
 199 config HAVE_NMI
 200         bool
 201
 202 #
 203 # An arch should select this if it provides all these things:
 204 #
 205 #       task_pt_regs()          in asm/processor.h or asm/ptrace.h
 206 #       arch_has_single_step()  if there is hardware single-step support
 207 #       arch_has_block_step()   if there is hardware block-step support
 208 #       asm/syscall.h           supplying asm-generic/syscall.h interface
 209 #       linux/regset.h          user_regset interfaces
 210 #       CORE_DUMP_USE_REGSET    #define'd in linux/elf.h
 211 #       TIF_SYSCALL_TRACE       calls tracehook_report_syscall_{entry,exit}
 212 #       TIF_NOTIFY_RESUME       calls tracehook_notify_resume()
 213 #       signal delivery         calls tracehook_signal_handler()
 214 #
 215 config HAVE_ARCH_TRACEHOOK
 216         bool
 217
 218 config HAVE_DMA_CONTIGUOUS
 219         bool
 220
 221 config GENERIC_SMP_IDLE_THREAD
 222        bool
 223
 224 config GENERIC_IDLE_POLL_SETUP
 225        bool
 226
 227 config ARCH_HAS_FORTIFY_SOURCE
 228         bool
 229         help
 230           An architecture should select this when it can successfully
 231           build and run with CONFIG_FORTIFY_SOURCE.
 232
 233 # Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
 234 config ARCH_HAS_SET_MEMORY
 235         bool
 236
 237 # Select if arch init_task initializer is different to init/init_task.c
 238 config ARCH_INIT_TASK
 239        bool
 240
 241 # Select if arch has its private alloc_task_struct() function
 242 config ARCH_TASK_STRUCT_ALLOCATOR
 243         bool
 244
 245 # Select if arch has its private alloc_thread_stack() function
 246 config ARCH_THREAD_STACK_ALLOCATOR
 247         bool
 248
 249 # Select if arch wants to size task_struct dynamically via arch_task_struct_size:
 250 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 251         bool
 252
 253 config HAVE_REGS_AND_STACK_ACCESS_API
 254         bool
 255         help
 256           This symbol should be selected by an architecure if it supports
 257           the API needed to access registers and stack entries from pt_regs,
 258           declared in asm/ptrace.h
 259           For example the kprobes-based event tracer needs this API.
 260
 261 config HAVE_CLK
 262         bool
 263         help
 264           The <linux/clk.h> calls support software clock gating and
 265           thus are a key power management tool on many systems.
 266
 267 config HAVE_DMA_API_DEBUG
 268         bool
 269
 270 config HAVE_HW_BREAKPOINT
 271         bool
 272         depends on PERF_EVENTS
 273
 274 config HAVE_MIXED_BREAKPOINTS_REGS
 275         bool
 276         depends on HAVE_HW_BREAKPOINT
 277         help
 278           Depending on the arch implementation of hardware breakpoints,
 279           some of them have separate registers for data and instruction
 280           breakpoints addresses, others have mixed registers to store
 281           them but define the access type in a control register.
 282           Select this option if your arch implements breakpoints under the
 283           latter fashion.
 284
 285 config HAVE_USER_RETURN_NOTIFIER
 286         bool
 287
 288 config HAVE_PERF_EVENTS_NMI
 289         bool
 290         help
 291           System hardware can generate an NMI using the perf event
 292           subsystem.  Also has support for calculating CPU cycle events
 293           to determine how many clock cycles in a given period.
 294
 295 config HAVE_HARDLOCKUP_DETECTOR_PERF
 296         bool
 297         depends on HAVE_PERF_EVENTS_NMI
 298         help
 299           The arch chooses to use the generic perf-NMI-based hardlockup
 300           detector. Must define HAVE_PERF_EVENTS_NMI.
 301
 302 config HAVE_NMI_WATCHDOG
 303         depends on HAVE_NMI
 304         bool
 305         help
 306           The arch provides a low level NMI watchdog. It provides
 307           asm/nmi.h, and defines its own arch_touch_nmi_watchdog().
 308
 309 config HAVE_HARDLOCKUP_DETECTOR_ARCH
 310         bool
 311         select HAVE_NMI_WATCHDOG
 312         help
 313           The arch chooses to provide its own hardlockup detector, which is
 314           a superset of the HAVE_NMI_WATCHDOG. It also conforms to config
 315           interfaces and parameters provided by hardlockup detector subsystem.
 316
 317 config HAVE_PERF_REGS
 318         bool
 319         help
 320           Support selective register dumps for perf events. This includes
 321           bit-mapping of each registers and a unique architecture id.
 322
 323 config HAVE_PERF_USER_STACK_DUMP
 324         bool
 325         help
 326           Support user stack dumps for perf event samples. This needs
 327           access to the user stack pointer which is not unified across
 328           architectures.
 329
 330 config HAVE_ARCH_JUMP_LABEL
 331         bool
 332
 333 config HAVE_RCU_TABLE_FREE
 334         bool
 335
 336 config ARCH_HAVE_NMI_SAFE_CMPXCHG
 337         bool
 338
 339 config HAVE_ALIGNED_STRUCT_PAGE
 340         bool
 341         help
 342           This makes sure that struct pages are double word aligned and that
 343           e.g. the SLUB allocator can perform double word atomic operations
 344           on a struct page for better performance. However selecting this
 345           might increase the size of a struct page by a word.
 346
 347 config HAVE_CMPXCHG_LOCAL
 348         bool
 349
 350 config HAVE_CMPXCHG_DOUBLE
 351         bool
 352
 353 config ARCH_WEAK_RELEASE_ACQUIRE
 354         bool
 355
 356 config ARCH_WANT_IPC_PARSE_VERSION
 357         bool
 358
 359 config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 360         bool
 361
 362 config ARCH_WANT_OLD_COMPAT_IPC
 363         select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 364         bool
 365
 366 config HAVE_ARCH_SECCOMP_FILTER
 367         bool
 368         help
 369           An arch should select this symbol if it provides all of these things:
 370           - syscall_get_arch()
 371           - syscall_get_arguments()
 372           - syscall_rollback()
 373           - syscall_set_return_value()
 374           - SIGSYS siginfo_t support
 375           - secure_computing is called from a ptrace_event()-safe context
 376           - secure_computing return value is checked and a return value of -1
 377             results in the system call being skipped immediately.
 378           - seccomp syscall wired up
 379
 380 config SECCOMP_FILTER
 381         def_bool y
 382         depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
 383         help
 384           Enable tasks to build secure computing environments defined
 385           in terms of Berkeley Packet Filter programs which implement
 386           task-defined system call filtering polices.
 387
 388           See Documentation/prctl/seccomp_filter.txt for details.
 389
 390 config HAVE_GCC_PLUGINS
 391         bool
 392         help
 393           An arch should select this symbol if it supports building with
 394           GCC plugins.
 395
 396 menuconfig GCC_PLUGINS
 397         bool "GCC plugins"
 398         depends on HAVE_GCC_PLUGINS
 399         depends on !COMPILE_TEST
 400         help
 401           GCC plugins are loadable modules that provide extra features to the
 402           compiler. They are useful for runtime instrumentation and static analysis.
 403
 404           See Documentation/gcc-plugins.txt for details.
 405
 406 config GCC_PLUGIN_CYC_COMPLEXITY
 407         bool "Compute the cyclomatic complexity of a function" if EXPERT
 408         depends on GCC_PLUGINS
 409         depends on !COMPILE_TEST
 410         help
 411           The complexity M of a function's control flow graph is defined as:
 412            M = E - N + 2P
 413           where
 414
 415           E = the number of edges
 416           N = the number of nodes
 417           P = the number of connected components (exit nodes).
 418
 419           Enabling this plugin reports the complexity to stderr during the
 420           build. It mainly serves as a simple example of how to create a
 421           gcc plugin for the kernel.
 422
 423 config GCC_PLUGIN_SANCOV
 424         bool
 425         depends on GCC_PLUGINS
 426         help
 427           This plugin inserts a __sanitizer_cov_trace_pc() call at the start of
 428           basic blocks. It supports all gcc versions with plugin support (from
 429           gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 430           by Dmitry Vyukov <dvyukov@google.com>.
 431
 432 config GCC_PLUGIN_LATENT_ENTROPY
 433         bool "Generate some entropy during boot and runtime"
 434         depends on GCC_PLUGINS
 435         help
 436           By saying Y here the kernel will instrument some kernel code to
 437           extract some entropy from both original and artificially created
 438           program state.  This will help especially embedded systems where
 439           there is little 'natural' source of entropy normally.  The cost
 440           is some slowdown of the boot process (about 0.5%) and fork and
 441           irq processing.
 442
 443           Note that entropy extracted this way is not cryptographically
 444           secure!
 445
 446           This plugin was ported from grsecurity/PaX. More information at:
 447            * https://grsecurity.net/
 448            * https://pax.grsecurity.net/
 449
 450 config GCC_PLUGIN_STRUCTLEAK
 451         bool "Force initialization of variables containing userspace addresses"
 452         depends on GCC_PLUGINS
 453         help
 454           This plugin zero-initializes any structures containing a
 455           __user attribute. This can prevent some classes of information
 456           exposures.
 457
 458           This plugin was ported from grsecurity/PaX. More information at:
 459            * https://grsecurity.net/
 460            * https://pax.grsecurity.net/
 461
 462 config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
 463         bool "Force initialize all struct type variables passed by reference"
 464         depends on GCC_PLUGIN_STRUCTLEAK
 465         help
 466           Zero initialize any struct type local variable that may be passed by
 467           reference without having been initialized.
 468
 469 config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 470         bool "Report forcefully initialized variables"
 471         depends on GCC_PLUGIN_STRUCTLEAK
 472         depends on !COMPILE_TEST
 473         help
 474           This option will cause a warning to be printed each time the
 475           structleak plugin finds a variable it thinks needs to be
 476           initialized. Since not all existing initializers are detected
 477           by the plugin, this can produce false positive warnings.
 478
 479 config GCC_PLUGIN_RANDSTRUCT
 480         bool "Randomize layout of sensitive kernel structures"
 481         depends on GCC_PLUGINS
 482         select MODVERSIONS if MODULES
 483         help
 484           If you say Y here, the layouts of structures that are entirely
 485           function pointers (and have not been manually annotated with
 486           __no_randomize_layout), or structures that have been explicitly
 487           marked with __randomize_layout, will be randomized at compile-time.
 488           This can introduce the requirement of an additional information
 489           exposure vulnerability for exploits targeting these structure
 490           types.
 491
 492           Enabling this feature will introduce some performance impact,
 493           slightly increase memory usage, and prevent the use of forensic
 494           tools like Volatility against the system (unless the kernel
 495           source tree isn't cleaned after kernel installation).
 496
 497           The seed used for compilation is located at
 498           scripts/gcc-plgins/randomize_layout_seed.h.  It remains after
 499           a make clean to allow for external modules to be compiled with
 500           the existing seed and will be removed by a make mrproper or
 501           make distclean.
 502
 503           Note that the implementation requires gcc 4.7 or newer.
 504
 505           This plugin was ported from grsecurity/PaX. More information at:
 506            * https://grsecurity.net/
 507            * https://pax.grsecurity.net/
 508
 509 config GCC_PLUGIN_RANDSTRUCT_PERFORMANCE
 510         bool "Use cacheline-aware structure randomization"
 511         depends on GCC_PLUGIN_RANDSTRUCT
 512         depends on !COMPILE_TEST
 513         help
 514           If you say Y here, the RANDSTRUCT randomization will make a
 515           best effort at restricting randomization to cacheline-sized
 516           groups of elements.  It will further not randomize bitfields
 517           in structures.  This reduces the performance hit of RANDSTRUCT
 518           at the cost of weakened randomization.
 519
 520 config HAVE_CC_STACKPROTECTOR
 521         bool
 522         help
 523           An arch should select this symbol if:
 524           - its compiler supports the -fstack-protector option
 525           - it has implemented a stack canary (e.g. __stack_chk_guard)
 526
 527 config CC_STACKPROTECTOR
 528         def_bool n
 529         help
 530           Set when a stack-protector mode is enabled, so that the build
 531           can enable kernel-side support for the GCC feature.
 532
 533 choice
 534         prompt "Stack Protector buffer overflow detection"
 535         depends on HAVE_CC_STACKPROTECTOR
 536         default CC_STACKPROTECTOR_NONE
 537         help
 538           This option turns on the "stack-protector" GCC feature. This
 539           feature puts, at the beginning of functions, a canary value on
 540           the stack just before the return address, and validates
 541           the value just before actually returning.  Stack based buffer
 542           overflows (that need to overwrite this return address) now also
 543           overwrite the canary, which gets detected and the attack is then
 544           neutralized via a kernel panic.
 545
 546 config CC_STACKPROTECTOR_NONE
 547         bool "None"
 548         help
 549           Disable "stack-protector" GCC feature.
 550
 551 config CC_STACKPROTECTOR_REGULAR
 552         bool "Regular"
 553         select CC_STACKPROTECTOR
 554         help
 555           Functions will have the stack-protector canary logic added if they
 556           have an 8-byte or larger character array on the stack.
 557
 558           This feature requires gcc version 4.2 or above, or a distribution
 559           gcc with the feature backported ("-fstack-protector").
 560
 561           On an x86 "defconfig" build, this feature adds canary checks to
 562           about 3% of all kernel functions, which increases kernel code size
 563           by about 0.3%.
 564
 565 config CC_STACKPROTECTOR_STRONG
 566         bool "Strong"
 567         select CC_STACKPROTECTOR
 568         help
 569           Functions will have the stack-protector canary logic added in any
 570           of the following conditions:
 571
 572           - local variable's address used as part of the right hand side of an
 573             assignment or function argument
 574           - local variable is an array (or union containing an array),
 575             regardless of array type or length
 576           - uses register local variables
 577
 578           This feature requires gcc version 4.9 or above, or a distribution
 579           gcc with the feature backported ("-fstack-protector-strong").
 580
 581           On an x86 "defconfig" build, this feature adds canary checks to
 582           about 20% of all kernel functions, which increases the kernel code
 583           size by about 2%.
 584
 585 endchoice
 586
 587 config THIN_ARCHIVES
 588         def_bool y
 589         help
 590           Select this if the architecture wants to use thin archives
 591           instead of ld -r to create the built-in.o files.
 592
 593 config LD_DEAD_CODE_DATA_ELIMINATION
 594         bool
 595         help
 596           Select this if the architecture wants to do dead code and
 597           data elimination with the linker by compiling with
 598           -ffunction-sections -fdata-sections and linking with
 599           --gc-sections.
 600
 601           This requires that the arch annotates or otherwise protects
 602           its external entry points from being discarded. Linker scripts
 603           must also merge .text.*, .data.*, and .bss.* correctly into
 604           output sections. Care must be taken not to pull in unrelated
 605           sections (e.g., '.text.init'). Typically '.' in section names
 606           is used to distinguish them from label names / C identifiers.
 607
 608 config HAVE_ARCH_WITHIN_STACK_FRAMES
 609         bool
 610         help
 611           An architecture should select this if it can walk the kernel stack
 612           frames to determine if an object is part of either the arguments
 613           or local variables (i.e. that it excludes saved return addresses,
 614           and similar) by implementing an inline arch_within_stack_frames(),
 615           which is used by CONFIG_HARDENED_USERCOPY.
 616
 617 config HAVE_CONTEXT_TRACKING
 618         bool
 619         help
 620           Provide kernel/user boundaries probes necessary for subsystems
 621           that need it, such as userspace RCU extended quiescent state.
 622           Syscalls need to be wrapped inside user_exit()-user_enter() through
 623           the slow path using TIF_NOHZ flag. Exceptions handlers must be
 624           wrapped as well. Irqs are already protected inside
 625           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
 626           irq exit still need to be protected.
 627
 628 config HAVE_VIRT_CPU_ACCOUNTING
 629         bool
 630
 631 config ARCH_HAS_SCALED_CPUTIME
 632         bool
 633
 634 config HAVE_VIRT_CPU_ACCOUNTING_GEN
 635         bool
 636         default y if 64BIT
 637         help
 638           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
 639           Before enabling this option, arch code must be audited
 640           to ensure there are no races in concurrent read/write of
 641           cputime_t. For example, reading/writing 64-bit cputime_t on
 642           some 32-bit arches may require multiple accesses, so proper
 643           locking is needed to protect against concurrent accesses.
 644
 645
 646 config HAVE_IRQ_TIME_ACCOUNTING
 647         bool
 648         help
 649           Archs need to ensure they use a high enough resolution clock to
 650           support irq time accounting and then call enable_sched_clock_irqtime().
 651
 652 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 653         bool
 654
 655 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 656         bool
 657
 658 config HAVE_ARCH_HUGE_VMAP
 659         bool
 660
 661 config HAVE_ARCH_SOFT_DIRTY
 662         bool
 663
 664 config HAVE_MOD_ARCH_SPECIFIC
 665         bool
 666         help
 667           The arch uses struct mod_arch_specific to store data.  Many arches
 668           just need a simple module loader without arch specific data - those
 669           should not enable this.
 670
 671 config MODULES_USE_ELF_RELA
 672         bool
 673         help
 674           Modules only use ELF RELA relocations.  Modules with ELF REL
 675           relocations will give an error.
 676
 677 config MODULES_USE_ELF_REL
 678         bool
 679         help
 680           Modules only use ELF REL relocations.  Modules with ELF RELA
 681           relocations will give an error.
 682
 683 config HAVE_UNDERSCORE_SYMBOL_PREFIX
 684         bool
 685         help
 686           Some architectures generate an _ in front of C symbols; things like
 687           module loading and assembly files need to know about this.
 688
 689 config HAVE_IRQ_EXIT_ON_IRQ_STACK
 690         bool
 691         help
 692           Architecture doesn't only execute the irq handler on the irq stack
 693           but also irq_exit(). This way we can process softirqs on this irq
 694           stack instead of switching to a new one when we call __do_softirq()
 695           in the end of an hardirq.
 696           This spares a stack switch and improves cache usage on softirq
 697           processing.
 698
 699 config PGTABLE_LEVELS
 700         int
 701         default 2
 702
 703 config ARCH_HAS_ELF_RANDOMIZE
 704         bool
 705         help
 706           An architecture supports choosing randomized locations for
 707           stack, mmap, brk, and ET_DYN. Defined functions:
 708           - arch_mmap_rnd()
 709           - arch_randomize_brk()
 710
 711 config HAVE_ARCH_MMAP_RND_BITS
 712         bool
 713         help
 714           An arch should select this symbol if it supports setting a variable
 715           number of bits for use in establishing the base address for mmap
 716           allocations, has MMU enabled and provides values for both:
 717           - ARCH_MMAP_RND_BITS_MIN
 718           - ARCH_MMAP_RND_BITS_MAX
 719
 720 config HAVE_EXIT_THREAD
 721         bool
 722         help
 723           An architecture implements exit_thread.
 724
 725 config ARCH_MMAP_RND_BITS_MIN
 726         int
 727
 728 config ARCH_MMAP_RND_BITS_MAX
 729         int
 730
 731 config ARCH_MMAP_RND_BITS_DEFAULT
 732         int
 733
 734 config ARCH_MMAP_RND_BITS
 735         int "Number of bits to use for ASLR of mmap base address" if EXPERT
 736         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
 737         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
 738         default ARCH_MMAP_RND_BITS_MIN
 739         depends on HAVE_ARCH_MMAP_RND_BITS
 740         help
 741           This value can be used to select the number of bits to use to
 742           determine the random offset to the base address of vma regions
 743           resulting from mmap allocations. This value will be bounded
 744           by the architecture's minimum and maximum supported values.
 745
 746           This value can be changed after boot using the
 747           /proc/sys/vm/mmap_rnd_bits tunable
 748
 749 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
 750         bool
 751         help
 752           An arch should select this symbol if it supports running applications
 753           in compatibility mode, supports setting a variable number of bits for
 754           use in establishing the base address for mmap allocations, has MMU
 755           enabled and provides values for both:
 756           - ARCH_MMAP_RND_COMPAT_BITS_MIN
 757           - ARCH_MMAP_RND_COMPAT_BITS_MAX
 758
 759 config ARCH_MMAP_RND_COMPAT_BITS_MIN
 760         int
 761
 762 config ARCH_MMAP_RND_COMPAT_BITS_MAX
 763         int
 764
 765 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 766         int
 767
 768 config ARCH_MMAP_RND_COMPAT_BITS
 769         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
 770         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
 771         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
 772         default ARCH_MMAP_RND_COMPAT_BITS_MIN
 773         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
 774         help
 775           This value can be used to select the number of bits to use to
 776           determine the random offset to the base address of vma regions
 777           resulting from mmap allocations for compatible applications This
 778           value will be bounded by the architecture's minimum and maximum
 779           supported values.
 780
 781           This value can be changed after boot using the
 782           /proc/sys/vm/mmap_rnd_compat_bits tunable
 783
 784 config HAVE_ARCH_COMPAT_MMAP_BASES
 785         bool
 786         help
 787           This allows 64bit applications to invoke 32-bit mmap() syscall
 788           and vice-versa 32-bit applications to call 64-bit mmap().
 789           Required for applications doing different bitness syscalls.
 790
 791 config HAVE_COPY_THREAD_TLS
 792         bool
 793         help
 794           Architecture provides copy_thread_tls to accept tls argument via
 795           normal C parameter passing, rather than extracting the syscall
 796           argument from pt_regs.
 797
 798 config HAVE_STACK_VALIDATION
 799         bool
 800         help
 801           Architecture supports the 'objtool check' host tool command, which
 802           performs compile-time stack metadata validation.
 803
 804 config HAVE_RELIABLE_STACKTRACE
 805         bool
 806         help
 807           Architecture has a save_stack_trace_tsk_reliable() function which
 808           only returns a stack trace if it can guarantee the trace is reliable.
 809
 810 config HAVE_ARCH_HASH
 811         bool
 812         default n
 813         help
 814           If this is set, the architecture provides an <asm/hash.h>
 815           file which provides platform-specific implementations of some
 816           functions in <linux/hash.h> or fs/namei.c.
 817
 818 config ISA_BUS_API
 819         def_bool ISA
 820
 821 #
 822 # ABI hall of shame
 823 #
 824 config CLONE_BACKWARDS
 825         bool
 826         help
 827           Architecture has tls passed as the 4th argument of clone(2),
 828           not the 5th one.
 829
 830 config CLONE_BACKWARDS2
 831         bool
 832         help
 833           Architecture has the first two arguments of clone(2) swapped.
 834
 835 config CLONE_BACKWARDS3
 836         bool
 837         help
 838           Architecture has tls passed as the 3rd argument of clone(2),
 839           not the 5th one.
 840
 841 config ODD_RT_SIGACTION
 842         bool
 843         help
 844           Architecture has unusual rt_sigaction(2) arguments
 845
 846 config OLD_SIGSUSPEND
 847         bool
 848         help
 849           Architecture has old sigsuspend(2) syscall, of one-argument variety
 850
 851 config OLD_SIGSUSPEND3
 852         bool
 853         help
 854           Even weirder antique ABI - three-argument sigsuspend(2)
 855
 856 config OLD_SIGACTION
 857         bool
 858         help
 859           Architecture has old sigaction(2) syscall.  Nope, not the same
 860           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
 861           but fairly different variant of sigaction(2), thanks to OSF/1
 862           compatibility...
 863
 864 config COMPAT_OLD_SIGACTION
 865         bool
 866
 867 config ARCH_NO_COHERENT_DMA_MMAP
 868         bool
 869
 870 config CPU_NO_EFFICIENT_FFS
 871         def_bool n
 872
 873 config HAVE_ARCH_VMAP_STACK
 874         def_bool n
 875         help
 876           An arch should select this symbol if it can support kernel stacks
 877           in vmalloc space.  This means:
 878
 879           - vmalloc space must be large enough to hold many kernel stacks.
 880             This may rule out many 32-bit architectures.
 881
 882           - Stacks in vmalloc space need to work reliably.  For example, if
 883             vmap page tables are created on demand, either this mechanism
 884             needs to work while the stack points to a virtual address with
 885             unpopulated page tables or arch code (switch_to() and switch_mm(),
 886             most likely) needs to ensure that the stack's page table entries
 887             are populated before running on a possibly unpopulated stack.
 888
 889           - If the stack overflows into a guard page, something reasonable
 890             should happen.  The definition of "reasonable" is flexible, but
 891             instantly rebooting without logging anything would be unfriendly.
 892
 893 config VMAP_STACK
 894         default y
 895         bool "Use a virtually-mapped stack"
 896         depends on HAVE_ARCH_VMAP_STACK && !KASAN
 897         ---help---
 898           Enable this if you want the use virtually-mapped kernel stacks
 899           with guard pages.  This causes kernel stack overflows to be
 900           caught immediately rather than causing difficult-to-diagnose
 901           corruption.
 902
 903           This is presently incompatible with KASAN because KASAN expects
 904           the stack to map directly to the KASAN shadow map using a formula
 905           that is incorrect if the stack is in vmalloc space.
 906
 907 config ARCH_OPTIONAL_KERNEL_RWX
 908         def_bool n
 909
 910 config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 911         def_bool n
 912
 913 config ARCH_HAS_STRICT_KERNEL_RWX
 914         def_bool n
 915
 916 config STRICT_KERNEL_RWX
 917         bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
 918         depends on ARCH_HAS_STRICT_KERNEL_RWX
 919         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 920         help
 921           If this is set, kernel text and rodata memory will be made read-only,
 922           and non-text memory will be made non-executable. This provides
 923           protection against certain security exploits (e.g. executing the heap
 924           or modifying text)
 925
 926           These features are considered standard security practice these days.
 927           You should say Y here in almost all cases.
 928
 929 config ARCH_HAS_STRICT_MODULE_RWX
 930         def_bool n
 931
 932 config STRICT_MODULE_RWX
 933         bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
 934         depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
 935         default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 936         help
 937           If this is set, module text and rodata memory will be made read-only,
 938           and non-text memory will be made non-executable. This provides
 939           protection against certain security exploits (e.g. writing to text)
 940
 941 config ARCH_HAS_REFCOUNT
 942         bool
 943         help
 944           An architecture selects this when it has implemented refcount_t
 945           using open coded assembly primitives that provide an optimized
 946           refcount_t implementation, possibly at the expense of some full
 947           refcount state checks of CONFIG_REFCOUNT_FULL=y.
 948
 949           The refcount overflow check behavior, however, must be retained.
 950           Catching overflows is the primary security concern for protecting
 951           against bugs in reference counts.
 952
 953 config REFCOUNT_FULL
 954         bool "Perform full reference count validation at the expense of speed"
 955         help
 956           Enabling this switches the refcounting infrastructure from a fast
 957           unchecked atomic_t implementation to a fully state checked
 958           implementation, which can be (slightly) slower but provides protections
 959           against various use-after-free conditions that can be used in
 960           security flaw exploits.
 961
 962 source "kernel/gcov/Kconfig"