1# 2# General architecture dependent options 3# 4 5config KEXEC_CORE 6 bool 7 8config HAVE_IMA_KEXEC 9 bool 10 11config 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 24config 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 36config HAVE_OPROFILE 37 bool 38 39config OPROFILE_NMI_TIMER 40 def_bool y 41 depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64 42 43config 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 55config 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 80config 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 86config OPTPROBES 87 def_bool y 88 depends on KPROBES && HAVE_OPTPROBES 89 depends on !PREEMPT 90 91config 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 100config 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 114config 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 130config 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 149config 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 168config KRETPROBES 169 def_bool y 170 depends on KPROBES && HAVE_KRETPROBES 171 172config 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 179config HAVE_IOREMAP_PROT 180 bool 181 182config HAVE_KPROBES 183 bool 184 185config HAVE_KRETPROBES 186 bool 187 188config HAVE_OPTPROBES 189 bool 190 191config HAVE_KPROBES_ON_FTRACE 192 bool 193 194config HAVE_NMI 195 bool 196 197config 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# 213config HAVE_ARCH_TRACEHOOK 214 bool 215 216config HAVE_DMA_CONTIGUOUS 217 bool 218 219config GENERIC_SMP_IDLE_THREAD 220 bool 221 222config GENERIC_IDLE_POLL_SETUP 223 bool 224 225# Select if arch init_task initializer is different to init/init_task.c 226config ARCH_INIT_TASK 227 bool 228 229# Select if arch has its private alloc_task_struct() function 230config ARCH_TASK_STRUCT_ALLOCATOR 231 bool 232 233# Select if arch has its private alloc_thread_stack() function 234config ARCH_THREAD_STACK_ALLOCATOR 235 bool 236 237# Select if arch wants to size task_struct dynamically via arch_task_struct_size: 238config ARCH_WANTS_DYNAMIC_TASK_STRUCT 239 bool 240 241config 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 249config 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 255config HAVE_DMA_API_DEBUG 256 bool 257 258config HAVE_HW_BREAKPOINT 259 bool 260 depends on PERF_EVENTS 261 262config 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 273config HAVE_USER_RETURN_NOTIFIER 274 bool 275 276config 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 283config 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 289config 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 296config HAVE_ARCH_JUMP_LABEL 297 bool 298 299config HAVE_RCU_TABLE_FREE 300 bool 301 302config ARCH_HAVE_NMI_SAFE_CMPXCHG 303 bool 304 305config 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 313config HAVE_CMPXCHG_LOCAL 314 bool 315 316config HAVE_CMPXCHG_DOUBLE 317 bool 318 319config ARCH_WANT_IPC_PARSE_VERSION 320 bool 321 322config ARCH_WANT_COMPAT_IPC_PARSE_VERSION 323 bool 324 325config ARCH_WANT_OLD_COMPAT_IPC 326 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION 327 bool 328 329config 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 343config 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 353config HAVE_GCC_PLUGINS 354 bool 355 help 356 An arch should select this symbol if it supports building with 357 GCC plugins. 358 359menuconfig 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 369config 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 386config 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 395config 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 413config 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 420config 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 426choice 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 439config CC_STACKPROTECTOR_NONE 440 bool "None" 441 help 442 Disable "stack-protector" GCC feature. 443 444config 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 458config 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 478endchoice 479 480config 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 486config 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 501config 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 510config 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 521config HAVE_VIRT_CPU_ACCOUNTING 522 bool 523 524config ARCH_HAS_SCALED_CPUTIME 525 bool 526 527config 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 539config 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 545config HAVE_ARCH_TRANSPARENT_HUGEPAGE 546 bool 547 548config HAVE_ARCH_HUGE_VMAP 549 bool 550 551config HAVE_ARCH_SOFT_DIRTY 552 bool 553 554config 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 561config 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 567config 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 573config 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 579config 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 589config PGTABLE_LEVELS 590 int 591 default 2 592 593config 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 601config 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 610config HAVE_EXIT_THREAD 611 bool 612 help 613 An architecture implements exit_thread. 614 615config ARCH_MMAP_RND_BITS_MIN 616 int 617 618config ARCH_MMAP_RND_BITS_MAX 619 int 620 621config ARCH_MMAP_RND_BITS_DEFAULT 622 int 623 624config 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 639config 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 649config ARCH_MMAP_RND_COMPAT_BITS_MIN 650 int 651 652config ARCH_MMAP_RND_COMPAT_BITS_MAX 653 int 654 655config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT 656 int 657 658config 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 674config 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 681config 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 687config 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 695config ISA_BUS_API 696 def_bool ISA 697 698# 699# ABI hall of shame 700# 701config CLONE_BACKWARDS 702 bool 703 help 704 Architecture has tls passed as the 4th argument of clone(2), 705 not the 5th one. 706 707config CLONE_BACKWARDS2 708 bool 709 help 710 Architecture has the first two arguments of clone(2) swapped. 711 712config CLONE_BACKWARDS3 713 bool 714 help 715 Architecture has tls passed as the 3rd argument of clone(2), 716 not the 5th one. 717 718config ODD_RT_SIGACTION 719 bool 720 help 721 Architecture has unusual rt_sigaction(2) arguments 722 723config OLD_SIGSUSPEND 724 bool 725 help 726 Architecture has old sigsuspend(2) syscall, of one-argument variety 727 728config OLD_SIGSUSPEND3 729 bool 730 help 731 Even weirder antique ABI - three-argument sigsuspend(2) 732 733config 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 741config COMPAT_OLD_SIGACTION 742 bool 743 744config ARCH_NO_COHERENT_DMA_MMAP 745 bool 746 747config CPU_NO_EFFICIENT_FFS 748 def_bool n 749 750config 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 770config 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 784source "kernel/gcov/Kconfig" 785