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Linux/arch/Kconfig

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

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