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Linux/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 GCC_PLUGIN_LATENT_ENTROPY
387         bool "Generate some entropy during boot and runtime"
388         depends on GCC_PLUGINS
389         help
390           By saying Y here the kernel will instrument some kernel code to
391           extract some entropy from both original and artificially created
392           program state.  This will help especially embedded systems where
393           there is little 'natural' source of entropy normally.  The cost
394           is some slowdown of the boot process (about 0.5%) and fork and
395           irq processing.
396 
397           Note that entropy extracted this way is not cryptographically
398           secure!
399 
400           This plugin was ported from grsecurity/PaX. More information at:
401            * https://grsecurity.net/
402            * https://pax.grsecurity.net/
403 
404 config HAVE_CC_STACKPROTECTOR
405         bool
406         help
407           An arch should select this symbol if:
408           - its compiler supports the -fstack-protector option
409           - it has implemented a stack canary (e.g. __stack_chk_guard)
410 
411 config CC_STACKPROTECTOR
412         def_bool n
413         help
414           Set when a stack-protector mode is enabled, so that the build
415           can enable kernel-side support for the GCC feature.
416 
417 choice
418         prompt "Stack Protector buffer overflow detection"
419         depends on HAVE_CC_STACKPROTECTOR
420         default CC_STACKPROTECTOR_NONE
421         help
422           This option turns on the "stack-protector" GCC feature. This
423           feature puts, at the beginning of functions, a canary value on
424           the stack just before the return address, and validates
425           the value just before actually returning.  Stack based buffer
426           overflows (that need to overwrite this return address) now also
427           overwrite the canary, which gets detected and the attack is then
428           neutralized via a kernel panic.
429 
430 config CC_STACKPROTECTOR_NONE
431         bool "None"
432         help
433           Disable "stack-protector" GCC feature.
434 
435 config CC_STACKPROTECTOR_REGULAR
436         bool "Regular"
437         select CC_STACKPROTECTOR
438         help
439           Functions will have the stack-protector canary logic added if they
440           have an 8-byte or larger character array on the stack.
441 
442           This feature requires gcc version 4.2 or above, or a distribution
443           gcc with the feature backported ("-fstack-protector").
444 
445           On an x86 "defconfig" build, this feature adds canary checks to
446           about 3% of all kernel functions, which increases kernel code size
447           by about 0.3%.
448 
449 config CC_STACKPROTECTOR_STRONG
450         bool "Strong"
451         select CC_STACKPROTECTOR
452         help
453           Functions will have the stack-protector canary logic added in any
454           of the following conditions:
455 
456           - local variable's address used as part of the right hand side of an
457             assignment or function argument
458           - local variable is an array (or union containing an array),
459             regardless of array type or length
460           - uses register local variables
461 
462           This feature requires gcc version 4.9 or above, or a distribution
463           gcc with the feature backported ("-fstack-protector-strong").
464 
465           On an x86 "defconfig" build, this feature adds canary checks to
466           about 20% of all kernel functions, which increases the kernel code
467           size by about 2%.
468 
469 endchoice
470 
471 config THIN_ARCHIVES
472         bool
473         help
474           Select this if the architecture wants to use thin archives
475           instead of ld -r to create the built-in.o files.
476 
477 config LD_DEAD_CODE_DATA_ELIMINATION
478         bool
479         help
480           Select this if the architecture wants to do dead code and
481           data elimination with the linker by compiling with
482           -ffunction-sections -fdata-sections and linking with
483           --gc-sections.
484 
485           This requires that the arch annotates or otherwise protects
486           its external entry points from being discarded. Linker scripts
487           must also merge .text.*, .data.*, and .bss.* correctly into
488           output sections. Care must be taken not to pull in unrelated
489           sections (e.g., '.text.init'). Typically '.' in section names
490           is used to distinguish them from label names / C identifiers.
491 
492 config HAVE_ARCH_WITHIN_STACK_FRAMES
493         bool
494         help
495           An architecture should select this if it can walk the kernel stack
496           frames to determine if an object is part of either the arguments
497           or local variables (i.e. that it excludes saved return addresses,
498           and similar) by implementing an inline arch_within_stack_frames(),
499           which is used by CONFIG_HARDENED_USERCOPY.
500 
501 config HAVE_CONTEXT_TRACKING
502         bool
503         help
504           Provide kernel/user boundaries probes necessary for subsystems
505           that need it, such as userspace RCU extended quiescent state.
506           Syscalls need to be wrapped inside user_exit()-user_enter() through
507           the slow path using TIF_NOHZ flag. Exceptions handlers must be
508           wrapped as well. Irqs are already protected inside
509           rcu_irq_enter/rcu_irq_exit() but preemption or signal handling on
510           irq exit still need to be protected.
511 
512 config HAVE_VIRT_CPU_ACCOUNTING
513         bool
514 
515 config HAVE_VIRT_CPU_ACCOUNTING_GEN
516         bool
517         default y if 64BIT
518         help
519           With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
520           Before enabling this option, arch code must be audited
521           to ensure there are no races in concurrent read/write of
522           cputime_t. For example, reading/writing 64-bit cputime_t on
523           some 32-bit arches may require multiple accesses, so proper
524           locking is needed to protect against concurrent accesses.
525 
526 
527 config HAVE_IRQ_TIME_ACCOUNTING
528         bool
529         help
530           Archs need to ensure they use a high enough resolution clock to
531           support irq time accounting and then call enable_sched_clock_irqtime().
532 
533 config HAVE_ARCH_TRANSPARENT_HUGEPAGE
534         bool
535 
536 config HAVE_ARCH_HUGE_VMAP
537         bool
538 
539 config HAVE_ARCH_SOFT_DIRTY
540         bool
541 
542 config HAVE_MOD_ARCH_SPECIFIC
543         bool
544         help
545           The arch uses struct mod_arch_specific to store data.  Many arches
546           just need a simple module loader without arch specific data - those
547           should not enable this.
548 
549 config MODULES_USE_ELF_RELA
550         bool
551         help
552           Modules only use ELF RELA relocations.  Modules with ELF REL
553           relocations will give an error.
554 
555 config MODULES_USE_ELF_REL
556         bool
557         help
558           Modules only use ELF REL relocations.  Modules with ELF RELA
559           relocations will give an error.
560 
561 config HAVE_UNDERSCORE_SYMBOL_PREFIX
562         bool
563         help
564           Some architectures generate an _ in front of C symbols; things like
565           module loading and assembly files need to know about this.
566 
567 config HAVE_IRQ_EXIT_ON_IRQ_STACK
568         bool
569         help
570           Architecture doesn't only execute the irq handler on the irq stack
571           but also irq_exit(). This way we can process softirqs on this irq
572           stack instead of switching to a new one when we call __do_softirq()
573           in the end of an hardirq.
574           This spares a stack switch and improves cache usage on softirq
575           processing.
576 
577 config PGTABLE_LEVELS
578         int
579         default 2
580 
581 config ARCH_HAS_ELF_RANDOMIZE
582         bool
583         help
584           An architecture supports choosing randomized locations for
585           stack, mmap, brk, and ET_DYN. Defined functions:
586           - arch_mmap_rnd()
587           - arch_randomize_brk()
588 
589 config HAVE_ARCH_MMAP_RND_BITS
590         bool
591         help
592           An arch should select this symbol if it supports setting a variable
593           number of bits for use in establishing the base address for mmap
594           allocations, has MMU enabled and provides values for both:
595           - ARCH_MMAP_RND_BITS_MIN
596           - ARCH_MMAP_RND_BITS_MAX
597 
598 config HAVE_EXIT_THREAD
599         bool
600         help
601           An architecture implements exit_thread.
602 
603 config ARCH_MMAP_RND_BITS_MIN
604         int
605 
606 config ARCH_MMAP_RND_BITS_MAX
607         int
608 
609 config ARCH_MMAP_RND_BITS_DEFAULT
610         int
611 
612 config ARCH_MMAP_RND_BITS
613         int "Number of bits to use for ASLR of mmap base address" if EXPERT
614         range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
615         default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
616         default ARCH_MMAP_RND_BITS_MIN
617         depends on HAVE_ARCH_MMAP_RND_BITS
618         help
619           This value can be used to select the number of bits to use to
620           determine the random offset to the base address of vma regions
621           resulting from mmap allocations. This value will be bounded
622           by the architecture's minimum and maximum supported values.
623 
624           This value can be changed after boot using the
625           /proc/sys/vm/mmap_rnd_bits tunable
626 
627 config HAVE_ARCH_MMAP_RND_COMPAT_BITS
628         bool
629         help
630           An arch should select this symbol if it supports running applications
631           in compatibility mode, supports setting a variable number of bits for
632           use in establishing the base address for mmap allocations, has MMU
633           enabled and provides values for both:
634           - ARCH_MMAP_RND_COMPAT_BITS_MIN
635           - ARCH_MMAP_RND_COMPAT_BITS_MAX
636 
637 config ARCH_MMAP_RND_COMPAT_BITS_MIN
638         int
639 
640 config ARCH_MMAP_RND_COMPAT_BITS_MAX
641         int
642 
643 config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
644         int
645 
646 config ARCH_MMAP_RND_COMPAT_BITS
647         int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
648         range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
649         default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
650         default ARCH_MMAP_RND_COMPAT_BITS_MIN
651         depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
652         help
653           This value can be used to select the number of bits to use to
654           determine the random offset to the base address of vma regions
655           resulting from mmap allocations for compatible applications This
656           value will be bounded by the architecture's minimum and maximum
657           supported values.
658 
659           This value can be changed after boot using the
660           /proc/sys/vm/mmap_rnd_compat_bits tunable
661 
662 config HAVE_COPY_THREAD_TLS
663         bool
664         help
665           Architecture provides copy_thread_tls to accept tls argument via
666           normal C parameter passing, rather than extracting the syscall
667           argument from pt_regs.
668 
669 config HAVE_STACK_VALIDATION
670         bool
671         help
672           Architecture supports the 'objtool check' host tool command, which
673           performs compile-time stack metadata validation.
674 
675 config HAVE_ARCH_HASH
676         bool
677         default n
678         help
679           If this is set, the architecture provides an <asm/hash.h>
680           file which provides platform-specific implementations of some
681           functions in <linux/hash.h> or fs/namei.c.
682 
683 config ISA_BUS_API
684         def_bool ISA
685 
686 #
687 # ABI hall of shame
688 #
689 config CLONE_BACKWARDS
690         bool
691         help
692           Architecture has tls passed as the 4th argument of clone(2),
693           not the 5th one.
694 
695 config CLONE_BACKWARDS2
696         bool
697         help
698           Architecture has the first two arguments of clone(2) swapped.
699 
700 config CLONE_BACKWARDS3
701         bool
702         help
703           Architecture has tls passed as the 3rd argument of clone(2),
704           not the 5th one.
705 
706 config ODD_RT_SIGACTION
707         bool
708         help
709           Architecture has unusual rt_sigaction(2) arguments
710 
711 config OLD_SIGSUSPEND
712         bool
713         help
714           Architecture has old sigsuspend(2) syscall, of one-argument variety
715 
716 config OLD_SIGSUSPEND3
717         bool
718         help
719           Even weirder antique ABI - three-argument sigsuspend(2)
720 
721 config OLD_SIGACTION
722         bool
723         help
724           Architecture has old sigaction(2) syscall.  Nope, not the same
725           as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
726           but fairly different variant of sigaction(2), thanks to OSF/1
727           compatibility...
728 
729 config COMPAT_OLD_SIGACTION
730         bool
731 
732 config ARCH_NO_COHERENT_DMA_MMAP
733         bool
734 
735 config CPU_NO_EFFICIENT_FFS
736         def_bool n
737 
738 config HAVE_ARCH_VMAP_STACK
739         def_bool n
740         help
741           An arch should select this symbol if it can support kernel stacks
742           in vmalloc space.  This means:
743 
744           - vmalloc space must be large enough to hold many kernel stacks.
745             This may rule out many 32-bit architectures.
746 
747           - Stacks in vmalloc space need to work reliably.  For example, if
748             vmap page tables are created on demand, either this mechanism
749             needs to work while the stack points to a virtual address with
750             unpopulated page tables or arch code (switch_to() and switch_mm(),
751             most likely) needs to ensure that the stack's page table entries
752             are populated before running on a possibly unpopulated stack.
753 
754           - If the stack overflows into a guard page, something reasonable
755             should happen.  The definition of "reasonable" is flexible, but
756             instantly rebooting without logging anything would be unfriendly.
757 
758 config VMAP_STACK
759         default y
760         bool "Use a virtually-mapped stack"
761         depends on HAVE_ARCH_VMAP_STACK && !KASAN
762         ---help---
763           Enable this if you want the use virtually-mapped kernel stacks
764           with guard pages.  This causes kernel stack overflows to be
765           caught immediately rather than causing difficult-to-diagnose
766           corruption.
767 
768           This is presently incompatible with KASAN because KASAN expects
769           the stack to map directly to the KASAN shadow map using a formula
770           that is incorrect if the stack is in vmalloc space.
771 
772 source "kernel/gcov/Kconfig"

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