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