1 # SPDX-License-Identifier: GPL-2.0-only
4 default "$(CC_VERSION_TEXT)"
6 This is used in unclear ways:
8 - Re-run Kconfig when the compiler is updated
9 The 'default' property references the environment variable,
10 CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd.
11 When the compiler is updated, Kconfig will be invoked.
13 - Ensure full rebuild when the compiler is updated
14 include/linux/compiler-version.h contains this option in the comment
15 line so fixdep adds include/config/CC_VERSION_TEXT into the
16 auto-generated dependency. When the compiler is updated, syncconfig
17 will touch it and then every file will be rebuilt.
20 def_bool $(success,test "$(cc-name)" = GCC)
24 default $(cc-version) if CC_IS_GCC
28 def_bool $(success,test "$(cc-name)" = Clang)
32 default $(cc-version) if CC_IS_CLANG
36 def_bool $(success,test "$(as-name)" = GNU)
39 def_bool $(success,test "$(as-name)" = LLVM)
43 # Use clang version if this is the integrated assembler
44 default CLANG_VERSION if AS_IS_LLVM
48 def_bool $(success,test "$(ld-name)" = BFD)
52 default $(ld-version) if LD_IS_BFD
56 def_bool $(success,test "$(ld-name)" = LLD)
60 default $(ld-version) if LD_IS_LLD
65 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT
66 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag))
68 config CC_CAN_LINK_STATIC
70 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag) -static) if 64BIT
71 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag) -static)
73 config CC_HAS_ASM_GOTO
74 def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
76 config CC_HAS_ASM_GOTO_OUTPUT
77 depends on CC_HAS_ASM_GOTO
78 def_bool $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
80 config TOOLS_SUPPORT_RELR
81 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
83 config CC_HAS_ASM_INLINE
84 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
86 config CC_HAS_NO_PROFILE_FN_ATTR
87 def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
95 config BUILDTIME_TABLE_SORT
98 config THREAD_INFO_IN_TASK
101 Select this to move thread_info off the stack into task_struct. To
102 make this work, an arch will need to remove all thread_info fields
103 except flags and fix any runtime bugs.
105 One subtle change that will be needed is to use try_get_task_stack()
106 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
115 depends on BROKEN || !SMP
118 config INIT_ENV_ARG_LIMIT
123 Maximum of each of the number of arguments and environment
124 variables passed to init from the kernel command line.
127 bool "Compile also drivers which will not load"
130 Some drivers can be compiled on a different platform than they are
131 intended to be run on. Despite they cannot be loaded there (or even
132 when they load they cannot be used due to missing HW support),
133 developers still, opposing to distributors, might want to build such
134 drivers to compile-test them.
136 If you are a developer and want to build everything available, say Y
137 here. If you are a user/distributor, say N here to exclude useless
138 drivers to be distributed.
140 config UAPI_HEADER_TEST
141 bool "Compile test UAPI headers"
142 depends on HEADERS_INSTALL && CC_CAN_LINK
144 Compile test headers exported to user-space to ensure they are
145 self-contained, i.e. compilable as standalone units.
147 If you are a developer or tester and want to ensure the exported
148 headers are self-contained, say Y here. Otherwise, choose N.
151 string "Local version - append to kernel release"
153 Append an extra string to the end of your kernel version.
154 This will show up when you type uname, for example.
155 The string you set here will be appended after the contents of
156 any files with a filename matching localversion* in your
157 object and source tree, in that order. Your total string can
158 be a maximum of 64 characters.
160 config LOCALVERSION_AUTO
161 bool "Automatically append version information to the version string"
163 depends on !COMPILE_TEST
165 This will try to automatically determine if the current tree is a
166 release tree by looking for git tags that belong to the current
167 top of tree revision.
169 A string of the format -gxxxxxxxx will be added to the localversion
170 if a git-based tree is found. The string generated by this will be
171 appended after any matching localversion* files, and after the value
172 set in CONFIG_LOCALVERSION.
174 (The actual string used here is the first eight characters produced
175 by running the command:
177 $ git rev-parse --verify HEAD
179 which is done within the script "scripts/setlocalversion".)
182 string "Build ID Salt"
185 The build ID is used to link binaries and their debug info. Setting
186 this option will use the value in the calculation of the build id.
187 This is mostly useful for distributions which want to ensure the
188 build is unique between builds. It's safe to leave the default.
190 config HAVE_KERNEL_GZIP
193 config HAVE_KERNEL_BZIP2
196 config HAVE_KERNEL_LZMA
199 config HAVE_KERNEL_XZ
202 config HAVE_KERNEL_LZO
205 config HAVE_KERNEL_LZ4
208 config HAVE_KERNEL_ZSTD
211 config HAVE_KERNEL_UNCOMPRESSED
215 prompt "Kernel compression mode"
217 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_ZSTD || HAVE_KERNEL_UNCOMPRESSED
219 The linux kernel is a kind of self-extracting executable.
220 Several compression algorithms are available, which differ
221 in efficiency, compression and decompression speed.
222 Compression speed is only relevant when building a kernel.
223 Decompression speed is relevant at each boot.
225 If you have any problems with bzip2 or lzma compressed
226 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
227 version of this functionality (bzip2 only), for 2.4, was
228 supplied by Christian Ludwig)
230 High compression options are mostly useful for users, who
231 are low on disk space (embedded systems), but for whom ram
234 If in doubt, select 'gzip'
238 depends on HAVE_KERNEL_GZIP
240 The old and tried gzip compression. It provides a good balance
241 between compression ratio and decompression speed.
245 depends on HAVE_KERNEL_BZIP2
247 Its compression ratio and speed is intermediate.
248 Decompression speed is slowest among the choices. The kernel
249 size is about 10% smaller with bzip2, in comparison to gzip.
250 Bzip2 uses a large amount of memory. For modern kernels you
251 will need at least 8MB RAM or more for booting.
255 depends on HAVE_KERNEL_LZMA
257 This compression algorithm's ratio is best. Decompression speed
258 is between gzip and bzip2. Compression is slowest.
259 The kernel size is about 33% smaller with LZMA in comparison to gzip.
263 depends on HAVE_KERNEL_XZ
265 XZ uses the LZMA2 algorithm and instruction set specific
266 BCJ filters which can improve compression ratio of executable
267 code. The size of the kernel is about 30% smaller with XZ in
268 comparison to gzip. On architectures for which there is a BCJ
269 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
270 will create a few percent smaller kernel than plain LZMA.
272 The speed is about the same as with LZMA: The decompression
273 speed of XZ is better than that of bzip2 but worse than gzip
274 and LZO. Compression is slow.
278 depends on HAVE_KERNEL_LZO
280 Its compression ratio is the poorest among the choices. The kernel
281 size is about 10% bigger than gzip; however its speed
282 (both compression and decompression) is the fastest.
286 depends on HAVE_KERNEL_LZ4
288 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
289 A preliminary version of LZ4 de/compression tool is available at
290 <https://code.google.com/p/lz4/>.
292 Its compression ratio is worse than LZO. The size of the kernel
293 is about 8% bigger than LZO. But the decompression speed is
298 depends on HAVE_KERNEL_ZSTD
300 ZSTD is a compression algorithm targeting intermediate compression
301 with fast decompression speed. It will compress better than GZIP and
302 decompress around the same speed as LZO, but slower than LZ4. You
303 will need at least 192 KB RAM or more for booting. The zstd command
304 line tool is required for compression.
306 config KERNEL_UNCOMPRESSED
308 depends on HAVE_KERNEL_UNCOMPRESSED
310 Produce uncompressed kernel image. This option is usually not what
311 you want. It is useful for debugging the kernel in slow simulation
312 environments, where decompressing and moving the kernel is awfully
313 slow. This option allows early boot code to skip the decompressor
314 and jump right at uncompressed kernel image.
319 string "Default init path"
322 This option determines the default init for the system if no init=
323 option is passed on the kernel command line. If the requested path is
324 not present, we will still then move on to attempting further
325 locations (e.g. /sbin/init, etc). If this is empty, we will just use
326 the fallback list when init= is not passed.
328 config DEFAULT_HOSTNAME
329 string "Default hostname"
332 This option determines the default system hostname before userspace
333 calls sethostname(2). The kernel traditionally uses "(none)" here,
334 but you may wish to use a different default here to make a minimal
335 system more usable with less configuration.
338 # For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can
339 # add proper SWAP support to them, in which case this can be remove.
345 bool "Support for paging of anonymous memory (swap)"
346 depends on MMU && BLOCK && !ARCH_NO_SWAP
349 This option allows you to choose whether you want to have support
350 for so called swap devices or swap files in your kernel that are
351 used to provide more virtual memory than the actual RAM present
352 in your computer. If unsure say Y.
357 Inter Process Communication is a suite of library functions and
358 system calls which let processes (running programs) synchronize and
359 exchange information. It is generally considered to be a good thing,
360 and some programs won't run unless you say Y here. In particular, if
361 you want to run the DOS emulator dosemu under Linux (read the
362 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
363 you'll need to say Y here.
365 You can find documentation about IPC with "info ipc" and also in
366 section 6.4 of the Linux Programmer's Guide, available from
367 <http://www.tldp.org/guides.html>.
369 config SYSVIPC_SYSCTL
376 bool "POSIX Message Queues"
379 POSIX variant of message queues is a part of IPC. In POSIX message
380 queues every message has a priority which decides about succession
381 of receiving it by a process. If you want to compile and run
382 programs written e.g. for Solaris with use of its POSIX message
383 queues (functions mq_*) say Y here.
385 POSIX message queues are visible as a filesystem called 'mqueue'
386 and can be mounted somewhere if you want to do filesystem
387 operations on message queues.
391 config POSIX_MQUEUE_SYSCTL
393 depends on POSIX_MQUEUE
398 bool "General notification queue"
402 This is a general notification queue for the kernel to pass events to
403 userspace by splicing them into pipes. It can be used in conjunction
404 with watches for key/keyring change notifications and device
407 See Documentation/watch_queue.rst
409 config CROSS_MEMORY_ATTACH
410 bool "Enable process_vm_readv/writev syscalls"
414 Enabling this option adds the system calls process_vm_readv and
415 process_vm_writev which allow a process with the correct privileges
416 to directly read from or write to another process' address space.
417 See the man page for more details.
420 bool "uselib syscall"
421 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
423 This option enables the uselib syscall, a system call used in the
424 dynamic linker from libc5 and earlier. glibc does not use this
425 system call. If you intend to run programs built on libc5 or
426 earlier, you may need to enable this syscall. Current systems
427 running glibc can safely disable this.
430 bool "Auditing support"
433 Enable auditing infrastructure that can be used with another
434 kernel subsystem, such as SELinux (which requires this for
435 logging of avc messages output). System call auditing is included
436 on architectures which support it.
438 config HAVE_ARCH_AUDITSYSCALL
443 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
446 source "kernel/irq/Kconfig"
447 source "kernel/time/Kconfig"
448 source "kernel/bpf/Kconfig"
449 source "kernel/Kconfig.preempt"
451 menu "CPU/Task time and stats accounting"
453 config VIRT_CPU_ACCOUNTING
457 prompt "Cputime accounting"
458 default TICK_CPU_ACCOUNTING if !PPC64
459 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
461 # Kind of a stub config for the pure tick based cputime accounting
462 config TICK_CPU_ACCOUNTING
463 bool "Simple tick based cputime accounting"
464 depends on !S390 && !NO_HZ_FULL
466 This is the basic tick based cputime accounting that maintains
467 statistics about user, system and idle time spent on per jiffies
472 config VIRT_CPU_ACCOUNTING_NATIVE
473 bool "Deterministic task and CPU time accounting"
474 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
475 select VIRT_CPU_ACCOUNTING
477 Select this option to enable more accurate task and CPU time
478 accounting. This is done by reading a CPU counter on each
479 kernel entry and exit and on transitions within the kernel
480 between system, softirq and hardirq state, so there is a
481 small performance impact. In the case of s390 or IBM POWER > 5,
482 this also enables accounting of stolen time on logically-partitioned
485 config VIRT_CPU_ACCOUNTING_GEN
486 bool "Full dynticks CPU time accounting"
487 depends on HAVE_CONTEXT_TRACKING
488 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
489 depends on GENERIC_CLOCKEVENTS
490 select VIRT_CPU_ACCOUNTING
491 select CONTEXT_TRACKING
493 Select this option to enable task and CPU time accounting on full
494 dynticks systems. This accounting is implemented by watching every
495 kernel-user boundaries using the context tracking subsystem.
496 The accounting is thus performed at the expense of some significant
499 For now this is only useful if you are working on the full
500 dynticks subsystem development.
506 config IRQ_TIME_ACCOUNTING
507 bool "Fine granularity task level IRQ time accounting"
508 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
510 Select this option to enable fine granularity task irq time
511 accounting. This is done by reading a timestamp on each
512 transitions between softirq and hardirq state, so there can be a
513 small performance impact.
515 If in doubt, say N here.
517 config HAVE_SCHED_AVG_IRQ
519 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
522 config SCHED_THERMAL_PRESSURE
524 default y if ARM && ARM_CPU_TOPOLOGY
527 depends on CPU_FREQ_THERMAL
529 Select this option to enable thermal pressure accounting in the
530 scheduler. Thermal pressure is the value conveyed to the scheduler
531 that reflects the reduction in CPU compute capacity resulted from
532 thermal throttling. Thermal throttling occurs when the performance of
533 a CPU is capped due to high operating temperatures.
535 If selected, the scheduler will be able to balance tasks accordingly,
536 i.e. put less load on throttled CPUs than on non/less throttled ones.
538 This requires the architecture to implement
539 arch_set_thermal_pressure() and arch_scale_thermal_pressure().
541 config BSD_PROCESS_ACCT
542 bool "BSD Process Accounting"
545 If you say Y here, a user level program will be able to instruct the
546 kernel (via a special system call) to write process accounting
547 information to a file: whenever a process exits, information about
548 that process will be appended to the file by the kernel. The
549 information includes things such as creation time, owning user,
550 command name, memory usage, controlling terminal etc. (the complete
551 list is in the struct acct in <file:include/linux/acct.h>). It is
552 up to the user level program to do useful things with this
553 information. This is generally a good idea, so say Y.
555 config BSD_PROCESS_ACCT_V3
556 bool "BSD Process Accounting version 3 file format"
557 depends on BSD_PROCESS_ACCT
560 If you say Y here, the process accounting information is written
561 in a new file format that also logs the process IDs of each
562 process and its parent. Note that this file format is incompatible
563 with previous v0/v1/v2 file formats, so you will need updated tools
564 for processing it. A preliminary version of these tools is available
565 at <http://www.gnu.org/software/acct/>.
568 bool "Export task/process statistics through netlink"
573 Export selected statistics for tasks/processes through the
574 generic netlink interface. Unlike BSD process accounting, the
575 statistics are available during the lifetime of tasks/processes as
576 responses to commands. Like BSD accounting, they are sent to user
581 config TASK_DELAY_ACCT
582 bool "Enable per-task delay accounting"
586 Collect information on time spent by a task waiting for system
587 resources like cpu, synchronous block I/O completion and swapping
588 in pages. Such statistics can help in setting a task's priorities
589 relative to other tasks for cpu, io, rss limits etc.
594 bool "Enable extended accounting over taskstats"
597 Collect extended task accounting data and send the data
598 to userland for processing over the taskstats interface.
602 config TASK_IO_ACCOUNTING
603 bool "Enable per-task storage I/O accounting"
604 depends on TASK_XACCT
606 Collect information on the number of bytes of storage I/O which this
612 bool "Pressure stall information tracking"
614 Collect metrics that indicate how overcommitted the CPU, memory,
615 and IO capacity are in the system.
617 If you say Y here, the kernel will create /proc/pressure/ with the
618 pressure statistics files cpu, memory, and io. These will indicate
619 the share of walltime in which some or all tasks in the system are
620 delayed due to contention of the respective resource.
622 In kernels with cgroup support, cgroups (cgroup2 only) will
623 have cpu.pressure, memory.pressure, and io.pressure files,
624 which aggregate pressure stalls for the grouped tasks only.
626 For more details see Documentation/accounting/psi.rst.
630 config PSI_DEFAULT_DISABLED
631 bool "Require boot parameter to enable pressure stall information tracking"
635 If set, pressure stall information tracking will be disabled
636 per default but can be enabled through passing psi=1 on the
637 kernel commandline during boot.
639 This feature adds some code to the task wakeup and sleep
640 paths of the scheduler. The overhead is too low to affect
641 common scheduling-intense workloads in practice (such as
642 webservers, memcache), but it does show up in artificial
643 scheduler stress tests, such as hackbench.
645 If you are paranoid and not sure what the kernel will be
650 endmenu # "CPU/Task time and stats accounting"
654 depends on SMP || COMPILE_TEST
657 Make sure that CPUs running critical tasks are not disturbed by
658 any source of "noise" such as unbound workqueues, timers, kthreads...
659 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
660 the "isolcpus=" boot parameter.
664 source "kernel/rcu/Kconfig"
671 tristate "Kernel .config support"
673 This option enables the complete Linux kernel ".config" file
674 contents to be saved in the kernel. It provides documentation
675 of which kernel options are used in a running kernel or in an
676 on-disk kernel. This information can be extracted from the kernel
677 image file with the script scripts/extract-ikconfig and used as
678 input to rebuild the current kernel or to build another kernel.
679 It can also be extracted from a running kernel by reading
680 /proc/config.gz if enabled (below).
683 bool "Enable access to .config through /proc/config.gz"
684 depends on IKCONFIG && PROC_FS
686 This option enables access to the kernel configuration file
687 through /proc/config.gz.
690 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
693 This option enables access to the in-kernel headers that are generated during
694 the build process. These can be used to build eBPF tracing programs,
695 or similar programs. If you build the headers as a module, a module called
696 kheaders.ko is built which can be loaded on-demand to get access to headers.
699 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
700 range 12 25 if !H8300
705 Select the minimal kernel log buffer size as a power of 2.
706 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
707 parameter, see below. Any higher size also might be forced
708 by "log_buf_len" boot parameter.
718 config LOG_CPU_MAX_BUF_SHIFT
719 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
722 default 12 if !BASE_SMALL
723 default 0 if BASE_SMALL
726 This option allows to increase the default ring buffer size
727 according to the number of CPUs. The value defines the contribution
728 of each CPU as a power of 2. The used space is typically only few
729 lines however it might be much more when problems are reported,
732 The increased size means that a new buffer has to be allocated and
733 the original static one is unused. It makes sense only on systems
734 with more CPUs. Therefore this value is used only when the sum of
735 contributions is greater than the half of the default kernel ring
736 buffer as defined by LOG_BUF_SHIFT. The default values are set
737 so that more than 16 CPUs are needed to trigger the allocation.
739 Also this option is ignored when "log_buf_len" kernel parameter is
740 used as it forces an exact (power of two) size of the ring buffer.
742 The number of possible CPUs is used for this computation ignoring
743 hotplugging making the computation optimal for the worst case
744 scenario while allowing a simple algorithm to be used from bootup.
746 Examples shift values and their meaning:
747 17 => 128 KB for each CPU
748 16 => 64 KB for each CPU
749 15 => 32 KB for each CPU
750 14 => 16 KB for each CPU
751 13 => 8 KB for each CPU
752 12 => 4 KB for each CPU
754 config PRINTK_SAFE_LOG_BUF_SHIFT
755 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
760 Select the size of an alternate printk per-CPU buffer where messages
761 printed from usafe contexts are temporary stored. One example would
762 be NMI messages, another one - printk recursion. The messages are
763 copied to the main log buffer in a safe context to avoid a deadlock.
764 The value defines the size as a power of 2.
766 Those messages are rare and limited. The largest one is when
767 a backtrace is printed. It usually fits into 4KB. Select
768 8KB if you want to be on the safe side.
771 17 => 128 KB for each CPU
772 16 => 64 KB for each CPU
773 15 => 32 KB for each CPU
774 14 => 16 KB for each CPU
775 13 => 8 KB for each CPU
776 12 => 4 KB for each CPU
779 # Architectures with an unreliable sched_clock() should select this:
781 config HAVE_UNSTABLE_SCHED_CLOCK
784 config GENERIC_SCHED_CLOCK
787 menu "Scheduler features"
790 bool "Enable utilization clamping for RT/FAIR tasks"
791 depends on CPU_FREQ_GOV_SCHEDUTIL
793 This feature enables the scheduler to track the clamped utilization
794 of each CPU based on RUNNABLE tasks scheduled on that CPU.
796 With this option, the user can specify the min and max CPU
797 utilization allowed for RUNNABLE tasks. The max utilization defines
798 the maximum frequency a task should use while the min utilization
799 defines the minimum frequency it should use.
801 Both min and max utilization clamp values are hints to the scheduler,
802 aiming at improving its frequency selection policy, but they do not
803 enforce or grant any specific bandwidth for tasks.
807 config UCLAMP_BUCKETS_COUNT
808 int "Number of supported utilization clamp buckets"
811 depends on UCLAMP_TASK
813 Defines the number of clamp buckets to use. The range of each bucket
814 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
815 number of clamp buckets the finer their granularity and the higher
816 the precision of clamping aggregation and tracking at run-time.
818 For example, with the minimum configuration value we will have 5
819 clamp buckets tracking 20% utilization each. A 25% boosted tasks will
820 be refcounted in the [20..39]% bucket and will set the bucket clamp
821 effective value to 25%.
822 If a second 30% boosted task should be co-scheduled on the same CPU,
823 that task will be refcounted in the same bucket of the first task and
824 it will boost the bucket clamp effective value to 30%.
825 The clamp effective value of a bucket is reset to its nominal value
826 (20% in the example above) when there are no more tasks refcounted in
829 An additional boost/capping margin can be added to some tasks. In the
830 example above the 25% task will be boosted to 30% until it exits the
831 CPU. If that should be considered not acceptable on certain systems,
832 it's always possible to reduce the margin by increasing the number of
833 clamp buckets to trade off used memory for run-time tracking
836 If in doubt, use the default value.
841 # For architectures that want to enable the support for NUMA-affine scheduler
844 config ARCH_SUPPORTS_NUMA_BALANCING
848 # For architectures that prefer to flush all TLBs after a number of pages
849 # are unmapped instead of sending one IPI per page to flush. The architecture
850 # must provide guarantees on what happens if a clean TLB cache entry is
851 # written after the unmap. Details are in mm/rmap.c near the check for
852 # should_defer_flush. The architecture should also consider if the full flush
853 # and the refill costs are offset by the savings of sending fewer IPIs.
854 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
858 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
861 # For architectures that know their GCC __int128 support is sound
863 config ARCH_SUPPORTS_INT128
866 # For architectures that (ab)use NUMA to represent different memory regions
867 # all cpu-local but of different latencies, such as SuperH.
869 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
872 config NUMA_BALANCING
873 bool "Memory placement aware NUMA scheduler"
874 depends on ARCH_SUPPORTS_NUMA_BALANCING
875 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
876 depends on SMP && NUMA && MIGRATION
878 This option adds support for automatic NUMA aware memory/task placement.
879 The mechanism is quite primitive and is based on migrating memory when
880 it has references to the node the task is running on.
882 This system will be inactive on UMA systems.
884 config NUMA_BALANCING_DEFAULT_ENABLED
885 bool "Automatically enable NUMA aware memory/task placement"
887 depends on NUMA_BALANCING
889 If set, automatic NUMA balancing will be enabled if running on a NUMA
893 bool "Control Group support"
896 This option adds support for grouping sets of processes together, for
897 use with process control subsystems such as Cpusets, CFS, memory
898 controls or device isolation.
900 - Documentation/scheduler/sched-design-CFS.rst (CFS)
901 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
902 and resource control)
912 bool "Memory controller"
916 Provides control over the memory footprint of tasks in a cgroup.
920 depends on MEMCG && SWAP
925 depends on MEMCG && !SLOB
933 Generic block IO controller cgroup interface. This is the common
934 cgroup interface which should be used by various IO controlling
937 Currently, CFQ IO scheduler uses it to recognize task groups and
938 control disk bandwidth allocation (proportional time slice allocation)
939 to such task groups. It is also used by bio throttling logic in
940 block layer to implement upper limit in IO rates on a device.
942 This option only enables generic Block IO controller infrastructure.
943 One needs to also enable actual IO controlling logic/policy. For
944 enabling proportional weight division of disk bandwidth in CFQ, set
945 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
946 CONFIG_BLK_DEV_THROTTLING=y.
948 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
950 config CGROUP_WRITEBACK
952 depends on MEMCG && BLK_CGROUP
955 menuconfig CGROUP_SCHED
956 bool "CPU controller"
959 This feature lets CPU scheduler recognize task groups and control CPU
960 bandwidth allocation to such task groups. It uses cgroups to group
964 config FAIR_GROUP_SCHED
965 bool "Group scheduling for SCHED_OTHER"
966 depends on CGROUP_SCHED
970 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
971 depends on FAIR_GROUP_SCHED
974 This option allows users to define CPU bandwidth rates (limits) for
975 tasks running within the fair group scheduler. Groups with no limit
976 set are considered to be unconstrained and will run with no
978 See Documentation/scheduler/sched-bwc.rst for more information.
980 config RT_GROUP_SCHED
981 bool "Group scheduling for SCHED_RR/FIFO"
982 depends on CGROUP_SCHED
985 This feature lets you explicitly allocate real CPU bandwidth
986 to task groups. If enabled, it will also make it impossible to
987 schedule realtime tasks for non-root users until you allocate
988 realtime bandwidth for them.
989 See Documentation/scheduler/sched-rt-group.rst for more information.
993 config UCLAMP_TASK_GROUP
994 bool "Utilization clamping per group of tasks"
995 depends on CGROUP_SCHED
996 depends on UCLAMP_TASK
999 This feature enables the scheduler to track the clamped utilization
1000 of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
1002 When this option is enabled, the user can specify a min and max
1003 CPU bandwidth which is allowed for each single task in a group.
1004 The max bandwidth allows to clamp the maximum frequency a task
1005 can use, while the min bandwidth allows to define a minimum
1006 frequency a task will always use.
1008 When task group based utilization clamping is enabled, an eventually
1009 specified task-specific clamp value is constrained by the cgroup
1010 specified clamp value. Both minimum and maximum task clamping cannot
1011 be bigger than the corresponding clamping defined at task group level.
1016 bool "PIDs controller"
1018 Provides enforcement of process number limits in the scope of a
1019 cgroup. Any attempt to fork more processes than is allowed in the
1020 cgroup will fail. PIDs are fundamentally a global resource because it
1021 is fairly trivial to reach PID exhaustion before you reach even a
1022 conservative kmemcg limit. As a result, it is possible to grind a
1023 system to halt without being limited by other cgroup policies. The
1024 PIDs controller is designed to stop this from happening.
1026 It should be noted that organisational operations (such as attaching
1027 to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
1028 since the PIDs limit only affects a process's ability to fork, not to
1032 bool "RDMA controller"
1034 Provides enforcement of RDMA resources defined by IB stack.
1035 It is fairly easy for consumers to exhaust RDMA resources, which
1036 can result into resource unavailability to other consumers.
1037 RDMA controller is designed to stop this from happening.
1038 Attaching processes with active RDMA resources to the cgroup
1039 hierarchy is allowed even if can cross the hierarchy's limit.
1041 config CGROUP_FREEZER
1042 bool "Freezer controller"
1044 Provides a way to freeze and unfreeze all tasks in a
1047 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1048 controller includes important in-kernel memory consumers per default.
1050 If you're using cgroup2, say N.
1052 config CGROUP_HUGETLB
1053 bool "HugeTLB controller"
1054 depends on HUGETLB_PAGE
1058 Provides a cgroup controller for HugeTLB pages.
1059 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1060 The limit is enforced during page fault. Since HugeTLB doesn't
1061 support page reclaim, enforcing the limit at page fault time implies
1062 that, the application will get SIGBUS signal if it tries to access
1063 HugeTLB pages beyond its limit. This requires the application to know
1064 beforehand how much HugeTLB pages it would require for its use. The
1065 control group is tracked in the third page lru pointer. This means
1066 that we cannot use the controller with huge page less than 3 pages.
1069 bool "Cpuset controller"
1072 This option will let you create and manage CPUSETs which
1073 allow dynamically partitioning a system into sets of CPUs and
1074 Memory Nodes and assigning tasks to run only within those sets.
1075 This is primarily useful on large SMP or NUMA systems.
1079 config PROC_PID_CPUSET
1080 bool "Include legacy /proc/<pid>/cpuset file"
1084 config CGROUP_DEVICE
1085 bool "Device controller"
1087 Provides a cgroup controller implementing whitelists for
1088 devices which a process in the cgroup can mknod or open.
1090 config CGROUP_CPUACCT
1091 bool "Simple CPU accounting controller"
1093 Provides a simple controller for monitoring the
1094 total CPU consumed by the tasks in a cgroup.
1097 bool "Perf controller"
1098 depends on PERF_EVENTS
1100 This option extends the perf per-cpu mode to restrict monitoring
1101 to threads which belong to the cgroup specified and run on the
1102 designated cpu. Or this can be used to have cgroup ID in samples
1103 so that it can monitor performance events among cgroups.
1108 bool "Support for eBPF programs attached to cgroups"
1109 depends on BPF_SYSCALL
1110 select SOCK_CGROUP_DATA
1112 Allow attaching eBPF programs to a cgroup using the bpf(2)
1113 syscall command BPF_PROG_ATTACH.
1115 In which context these programs are accessed depends on the type
1116 of attachment. For instance, programs that are attached using
1117 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1121 bool "Misc resource controller"
1124 Provides a controller for miscellaneous resources on a host.
1126 Miscellaneous scalar resources are the resources on the host system
1127 which cannot be abstracted like the other cgroups. This controller
1128 tracks and limits the miscellaneous resources used by a process
1129 attached to a cgroup hierarchy.
1131 For more information, please check misc cgroup section in
1132 /Documentation/admin-guide/cgroup-v2.rst.
1135 bool "Debug controller"
1137 depends on DEBUG_KERNEL
1139 This option enables a simple controller that exports
1140 debugging information about the cgroups framework. This
1141 controller is for control cgroup debugging only. Its
1142 interfaces are not stable.
1146 config SOCK_CGROUP_DATA
1152 menuconfig NAMESPACES
1153 bool "Namespaces support" if EXPERT
1154 depends on MULTIUSER
1157 Provides the way to make tasks work with different objects using
1158 the same id. For example same IPC id may refer to different objects
1159 or same user id or pid may refer to different tasks when used in
1160 different namespaces.
1165 bool "UTS namespace"
1168 In this namespace tasks see different info provided with the
1172 bool "TIME namespace"
1173 depends on GENERIC_VDSO_TIME_NS
1176 In this namespace boottime and monotonic clocks can be set.
1177 The time will keep going with the same pace.
1180 bool "IPC namespace"
1181 depends on (SYSVIPC || POSIX_MQUEUE)
1184 In this namespace tasks work with IPC ids which correspond to
1185 different IPC objects in different namespaces.
1188 bool "User namespace"
1191 This allows containers, i.e. vservers, to use user namespaces
1192 to provide different user info for different servers.
1194 When user namespaces are enabled in the kernel it is
1195 recommended that the MEMCG option also be enabled and that
1196 user-space use the memory control groups to limit the amount
1197 of memory a memory unprivileged users can use.
1202 bool "PID Namespaces"
1205 Support process id namespaces. This allows having multiple
1206 processes with the same pid as long as they are in different
1207 pid namespaces. This is a building block of containers.
1210 bool "Network namespace"
1214 Allow user space to create what appear to be multiple instances
1215 of the network stack.
1219 config CHECKPOINT_RESTORE
1220 bool "Checkpoint/restore support"
1221 select PROC_CHILDREN
1225 Enables additional kernel features in a sake of checkpoint/restore.
1226 In particular it adds auxiliary prctl codes to setup process text,
1227 data and heap segment sizes, and a few additional /proc filesystem
1230 If unsure, say N here.
1232 config SCHED_AUTOGROUP
1233 bool "Automatic process group scheduling"
1236 select FAIR_GROUP_SCHED
1238 This option optimizes the scheduler for common desktop workloads by
1239 automatically creating and populating task groups. This separation
1240 of workloads isolates aggressive CPU burners (like build jobs) from
1241 desktop applications. Task group autogeneration is currently based
1244 config SYSFS_DEPRECATED
1245 bool "Enable deprecated sysfs features to support old userspace tools"
1249 This option adds code that switches the layout of the "block" class
1250 devices, to not show up in /sys/class/block/, but only in
1253 This switch is only active when the sysfs.deprecated=1 boot option is
1254 passed or the SYSFS_DEPRECATED_V2 option is set.
1256 This option allows new kernels to run on old distributions and tools,
1257 which might get confused by /sys/class/block/. Since 2007/2008 all
1258 major distributions and tools handle this just fine.
1260 Recent distributions and userspace tools after 2009/2010 depend on
1261 the existence of /sys/class/block/, and will not work with this
1264 Only if you are using a new kernel on an old distribution, you might
1267 config SYSFS_DEPRECATED_V2
1268 bool "Enable deprecated sysfs features by default"
1271 depends on SYSFS_DEPRECATED
1273 Enable deprecated sysfs by default.
1275 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1278 Only if you are using a new kernel on an old distribution, you might
1279 need to say Y here. Even then, odds are you would not need it
1280 enabled, you can always pass the boot option if absolutely necessary.
1283 bool "Kernel->user space relay support (formerly relayfs)"
1286 This option enables support for relay interface support in
1287 certain file systems (such as debugfs).
1288 It is designed to provide an efficient mechanism for tools and
1289 facilities to relay large amounts of data from kernel space to
1294 config BLK_DEV_INITRD
1295 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1297 The initial RAM filesystem is a ramfs which is loaded by the
1298 boot loader (loadlin or lilo) and that is mounted as root
1299 before the normal boot procedure. It is typically used to
1300 load modules needed to mount the "real" root file system,
1301 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1303 If RAM disk support (BLK_DEV_RAM) is also included, this
1304 also enables initial RAM disk (initrd) support and adds
1305 15 Kbytes (more on some other architectures) to the kernel size.
1311 source "usr/Kconfig"
1316 bool "Boot config support"
1317 select BLK_DEV_INITRD
1319 Extra boot config allows system admin to pass a config file as
1320 complemental extension of kernel cmdline when booting.
1321 The boot config file must be attached at the end of initramfs
1322 with checksum, size and magic word.
1323 See <file:Documentation/admin-guide/bootconfig.rst> for details.
1328 prompt "Compiler optimization level"
1329 default CC_OPTIMIZE_FOR_PERFORMANCE
1331 config CC_OPTIMIZE_FOR_PERFORMANCE
1332 bool "Optimize for performance (-O2)"
1334 This is the default optimization level for the kernel, building
1335 with the "-O2" compiler flag for best performance and most
1336 helpful compile-time warnings.
1338 config CC_OPTIMIZE_FOR_PERFORMANCE_O3
1339 bool "Optimize more for performance (-O3)"
1342 Choosing this option will pass "-O3" to your compiler to optimize
1343 the kernel yet more for performance.
1345 config CC_OPTIMIZE_FOR_SIZE
1346 bool "Optimize for size (-Os)"
1348 Choosing this option will pass "-Os" to your compiler resulting
1349 in a smaller kernel.
1353 config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1356 This requires that the arch annotates or otherwise protects
1357 its external entry points from being discarded. Linker scripts
1358 must also merge .text.*, .data.*, and .bss.* correctly into
1359 output sections. Care must be taken not to pull in unrelated
1360 sections (e.g., '.text.init'). Typically '.' in section names
1361 is used to distinguish them from label names / C identifiers.
1363 config LD_DEAD_CODE_DATA_ELIMINATION
1364 bool "Dead code and data elimination (EXPERIMENTAL)"
1365 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1367 depends on $(cc-option,-ffunction-sections -fdata-sections)
1368 depends on $(ld-option,--gc-sections)
1370 Enable this if you want to do dead code and data elimination with
1371 the linker by compiling with -ffunction-sections -fdata-sections,
1372 and linking with --gc-sections.
1374 This can reduce on disk and in-memory size of the kernel
1375 code and static data, particularly for small configs and
1376 on small systems. This has the possibility of introducing
1377 silently broken kernel if the required annotations are not
1378 present. This option is not well tested yet, so use at your
1381 config LD_ORPHAN_WARN
1383 depends on ARCH_WANT_LD_ORPHAN_WARN
1384 depends on !LD_IS_LLD || LLD_VERSION >= 110000
1385 depends on $(ld-option,--orphan-handling=warn)
1393 config SYSCTL_EXCEPTION_TRACE
1396 Enable support for /proc/sys/debug/exception-trace.
1398 config SYSCTL_ARCH_UNALIGN_NO_WARN
1401 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1402 Allows arch to define/use @no_unaligned_warning to possibly warn
1403 about unaligned access emulation going on under the hood.
1405 config SYSCTL_ARCH_UNALIGN_ALLOW
1408 Enable support for /proc/sys/kernel/unaligned-trap
1409 Allows arches to define/use @unaligned_enabled to runtime toggle
1410 the unaligned access emulation.
1411 see arch/parisc/kernel/unaligned.c for reference
1413 config HAVE_PCSPKR_PLATFORM
1416 # interpreter that classic socket filters depend on
1421 bool "Configure standard kernel features (expert users)"
1422 # Unhide debug options, to make the on-by-default options visible
1425 This option allows certain base kernel options and settings
1426 to be disabled or tweaked. This is for specialized
1427 environments which can tolerate a "non-standard" kernel.
1428 Only use this if you really know what you are doing.
1431 bool "Enable 16-bit UID system calls" if EXPERT
1432 depends on HAVE_UID16 && MULTIUSER
1435 This enables the legacy 16-bit UID syscall wrappers.
1438 bool "Multiple users, groups and capabilities support" if EXPERT
1441 This option enables support for non-root users, groups and
1444 If you say N here, all processes will run with UID 0, GID 0, and all
1445 possible capabilities. Saying N here also compiles out support for
1446 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1449 If unsure, say Y here.
1451 config SGETMASK_SYSCALL
1452 bool "sgetmask/ssetmask syscalls support" if EXPERT
1453 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
1455 sys_sgetmask and sys_ssetmask are obsolete system calls
1456 no longer supported in libc but still enabled by default in some
1459 If unsure, leave the default option here.
1461 config SYSFS_SYSCALL
1462 bool "Sysfs syscall support" if EXPERT
1465 sys_sysfs is an obsolete system call no longer supported in libc.
1466 Note that disabling this option is more secure but might break
1467 compatibility with some systems.
1469 If unsure say Y here.
1472 bool "open by fhandle syscalls" if EXPERT
1476 If you say Y here, a user level program will be able to map
1477 file names to handle and then later use the handle for
1478 different file system operations. This is useful in implementing
1479 userspace file servers, which now track files using handles instead
1480 of names. The handle would remain the same even if file names
1481 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1485 bool "Posix Clocks & timers" if EXPERT
1488 This includes native support for POSIX timers to the kernel.
1489 Some embedded systems have no use for them and therefore they
1490 can be configured out to reduce the size of the kernel image.
1492 When this option is disabled, the following syscalls won't be
1493 available: timer_create, timer_gettime: timer_getoverrun,
1494 timer_settime, timer_delete, clock_adjtime, getitimer,
1495 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1496 clock_getres and clock_nanosleep syscalls will be limited to
1497 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1503 bool "Enable support for printk" if EXPERT
1506 This option enables normal printk support. Removing it
1507 eliminates most of the message strings from the kernel image
1508 and makes the kernel more or less silent. As this makes it
1509 very difficult to diagnose system problems, saying N here is
1510 strongly discouraged.
1518 bool "BUG() support" if EXPERT
1521 Disabling this option eliminates support for BUG and WARN, reducing
1522 the size of your kernel image and potentially quietly ignoring
1523 numerous fatal conditions. You should only consider disabling this
1524 option for embedded systems with no facilities for reporting errors.
1530 bool "Enable ELF core dumps" if EXPERT
1532 Enable support for generating core dumps. Disabling saves about 4k.
1535 config PCSPKR_PLATFORM
1536 bool "Enable PC-Speaker support" if EXPERT
1537 depends on HAVE_PCSPKR_PLATFORM
1541 This option allows to disable the internal PC-Speaker
1542 support, saving some memory.
1546 bool "Enable full-sized data structures for core" if EXPERT
1548 Disabling this option reduces the size of miscellaneous core
1549 kernel data structures. This saves memory on small machines,
1550 but may reduce performance.
1553 bool "Enable futex support" if EXPERT
1557 Disabling this option will cause the kernel to be built without
1558 support for "fast userspace mutexes". The resulting kernel may not
1559 run glibc-based applications correctly.
1563 depends on FUTEX && RT_MUTEXES
1566 config HAVE_FUTEX_CMPXCHG
1570 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1571 is implemented and always working. This removes a couple of runtime
1575 bool "Enable eventpoll support" if EXPERT
1578 Disabling this option will cause the kernel to be built without
1579 support for epoll family of system calls.
1582 bool "Enable signalfd() system call" if EXPERT
1585 Enable the signalfd() system call that allows to receive signals
1586 on a file descriptor.
1591 bool "Enable timerfd() system call" if EXPERT
1594 Enable the timerfd() system call that allows to receive timer
1595 events on a file descriptor.
1600 bool "Enable eventfd() system call" if EXPERT
1603 Enable the eventfd() system call that allows to receive both
1604 kernel notification (ie. KAIO) or userspace notifications.
1609 bool "Use full shmem filesystem" if EXPERT
1613 The shmem is an internal filesystem used to manage shared memory.
1614 It is backed by swap and manages resource limits. It is also exported
1615 to userspace as tmpfs if TMPFS is enabled. Disabling this
1616 option replaces shmem and tmpfs with the much simpler ramfs code,
1617 which may be appropriate on small systems without swap.
1620 bool "Enable AIO support" if EXPERT
1623 This option enables POSIX asynchronous I/O which may by used
1624 by some high performance threaded applications. Disabling
1625 this option saves about 7k.
1628 bool "Enable IO uring support" if EXPERT
1632 This option enables support for the io_uring interface, enabling
1633 applications to submit and complete IO through submission and
1634 completion rings that are shared between the kernel and application.
1636 config ADVISE_SYSCALLS
1637 bool "Enable madvise/fadvise syscalls" if EXPERT
1640 This option enables the madvise and fadvise syscalls, used by
1641 applications to advise the kernel about their future memory or file
1642 usage, improving performance. If building an embedded system where no
1643 applications use these syscalls, you can disable this option to save
1646 config HAVE_ARCH_USERFAULTFD_WP
1649 Arch has userfaultfd write protection support
1651 config HAVE_ARCH_USERFAULTFD_MINOR
1654 Arch has userfaultfd minor fault support
1657 bool "Enable membarrier() system call" if EXPERT
1660 Enable the membarrier() system call that allows issuing memory
1661 barriers across all running threads, which can be used to distribute
1662 the cost of user-space memory barriers asymmetrically by transforming
1663 pairs of memory barriers into pairs consisting of membarrier() and a
1669 bool "Load all symbols for debugging/ksymoops" if EXPERT
1672 Say Y here to let the kernel print out symbolic crash information and
1673 symbolic stack backtraces. This increases the size of the kernel
1674 somewhat, as all symbols have to be loaded into the kernel image.
1677 bool "Include all symbols in kallsyms"
1678 depends on DEBUG_KERNEL && KALLSYMS
1680 Normally kallsyms only contains the symbols of functions for nicer
1681 OOPS messages and backtraces (i.e., symbols from the text and inittext
1682 sections). This is sufficient for most cases. And only in very rare
1683 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1684 names of variables from the data sections, etc).
1686 This option makes sure that all symbols are loaded into the kernel
1687 image (i.e., symbols from all sections) in cost of increased kernel
1688 size (depending on the kernel configuration, it may be 300KiB or
1689 something like this).
1691 Say N unless you really need all symbols.
1693 config KALLSYMS_ABSOLUTE_PERCPU
1696 default X86_64 && SMP
1698 config KALLSYMS_BASE_RELATIVE
1703 Instead of emitting them as absolute values in the native word size,
1704 emit the symbol references in the kallsyms table as 32-bit entries,
1705 each containing a relative value in the range [base, base + U32_MAX]
1706 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1707 an absolute value in the range [0, S32_MAX] or a relative value in the
1708 range [base, base + S32_MAX], where base is the lowest relative symbol
1709 address encountered in the image.
1711 On 64-bit builds, this reduces the size of the address table by 50%,
1712 but more importantly, it results in entries whose values are build
1713 time constants, and no relocation pass is required at runtime to fix
1714 up the entries based on the runtime load address of the kernel.
1716 # end of the "standard kernel features (expert users)" menu
1718 # syscall, maps, verifier
1721 bool "Enable userfaultfd() system call"
1724 Enable the userfaultfd() system call that allows to intercept and
1725 handle page faults in userland.
1727 config ARCH_HAS_MEMBARRIER_CALLBACKS
1730 config ARCH_HAS_MEMBARRIER_SYNC_CORE
1734 bool "Enable kcmp() system call" if EXPERT
1736 Enable the kernel resource comparison system call. It provides
1737 user-space with the ability to compare two processes to see if they
1738 share a common resource, such as a file descriptor or even virtual
1744 bool "Enable rseq() system call" if EXPERT
1746 depends on HAVE_RSEQ
1749 Enable the restartable sequences system call. It provides a
1750 user-space cache for the current CPU number value, which
1751 speeds up getting the current CPU number from user-space,
1752 as well as an ABI to speed up user-space operations on
1759 bool "Enabled debugging of rseq() system call" if EXPERT
1760 depends on RSEQ && DEBUG_KERNEL
1762 Enable extra debugging checks for the rseq system call.
1767 bool "Embedded system"
1770 This option should be enabled if compiling the kernel for
1771 an embedded system so certain expert options are available
1774 config HAVE_PERF_EVENTS
1777 See tools/perf/design.txt for details.
1779 config PERF_USE_VMALLOC
1782 See tools/perf/design.txt for details
1785 bool "PC/104 support" if EXPERT
1787 Expose PC/104 form factor device drivers and options available for
1788 selection and configuration. Enable this option if your target
1789 machine has a PC/104 bus.
1791 menu "Kernel Performance Events And Counters"
1794 bool "Kernel performance events and counters"
1795 default y if PROFILING
1796 depends on HAVE_PERF_EVENTS
1800 Enable kernel support for various performance events provided
1801 by software and hardware.
1803 Software events are supported either built-in or via the
1804 use of generic tracepoints.
1806 Most modern CPUs support performance events via performance
1807 counter registers. These registers count the number of certain
1808 types of hw events: such as instructions executed, cachemisses
1809 suffered, or branches mis-predicted - without slowing down the
1810 kernel or applications. These registers can also trigger interrupts
1811 when a threshold number of events have passed - and can thus be
1812 used to profile the code that runs on that CPU.
1814 The Linux Performance Event subsystem provides an abstraction of
1815 these software and hardware event capabilities, available via a
1816 system call and used by the "perf" utility in tools/perf/. It
1817 provides per task and per CPU counters, and it provides event
1818 capabilities on top of those.
1822 config DEBUG_PERF_USE_VMALLOC
1824 bool "Debug: use vmalloc to back perf mmap() buffers"
1825 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1826 select PERF_USE_VMALLOC
1828 Use vmalloc memory to back perf mmap() buffers.
1830 Mostly useful for debugging the vmalloc code on platforms
1831 that don't require it.
1837 config VM_EVENT_COUNTERS
1839 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1841 VM event counters are needed for event counts to be shown.
1842 This option allows the disabling of the VM event counters
1843 on EXPERT systems. /proc/vmstat will only show page counts
1844 if VM event counters are disabled.
1848 bool "Enable SLUB debugging support" if EXPERT
1849 depends on SLUB && SYSFS
1851 SLUB has extensive debug support features. Disabling these can
1852 result in significant savings in code size. This also disables
1853 SLUB sysfs support. /sys/slab will not exist and there will be
1854 no support for cache validation etc.
1857 bool "Disable heap randomization"
1860 Randomizing heap placement makes heap exploits harder, but it
1861 also breaks ancient binaries (including anything libc5 based).
1862 This option changes the bootup default to heap randomization
1863 disabled, and can be overridden at runtime by setting
1864 /proc/sys/kernel/randomize_va_space to 2.
1866 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1869 prompt "Choose SLAB allocator"
1872 This option allows to select a slab allocator.
1876 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1878 The regular slab allocator that is established and known to work
1879 well in all environments. It organizes cache hot objects in
1880 per cpu and per node queues.
1883 bool "SLUB (Unqueued Allocator)"
1884 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1886 SLUB is a slab allocator that minimizes cache line usage
1887 instead of managing queues of cached objects (SLAB approach).
1888 Per cpu caching is realized using slabs of objects instead
1889 of queues of objects. SLUB can use memory efficiently
1890 and has enhanced diagnostics. SLUB is the default choice for
1895 bool "SLOB (Simple Allocator)"
1897 SLOB replaces the stock allocator with a drastically simpler
1898 allocator. SLOB is generally more space efficient but
1899 does not perform as well on large systems.
1903 config SLAB_MERGE_DEFAULT
1904 bool "Allow slab caches to be merged"
1907 For reduced kernel memory fragmentation, slab caches can be
1908 merged when they share the same size and other characteristics.
1909 This carries a risk of kernel heap overflows being able to
1910 overwrite objects from merged caches (and more easily control
1911 cache layout), which makes such heap attacks easier to exploit
1912 by attackers. By keeping caches unmerged, these kinds of exploits
1913 can usually only damage objects in the same cache. To disable
1914 merging at runtime, "slab_nomerge" can be passed on the kernel
1917 config SLAB_FREELIST_RANDOM
1918 bool "Randomize slab freelist"
1919 depends on SLAB || SLUB
1921 Randomizes the freelist order used on creating new pages. This
1922 security feature reduces the predictability of the kernel slab
1923 allocator against heap overflows.
1925 config SLAB_FREELIST_HARDENED
1926 bool "Harden slab freelist metadata"
1927 depends on SLAB || SLUB
1929 Many kernel heap attacks try to target slab cache metadata and
1930 other infrastructure. This options makes minor performance
1931 sacrifices to harden the kernel slab allocator against common
1932 freelist exploit methods. Some slab implementations have more
1933 sanity-checking than others. This option is most effective with
1936 config SHUFFLE_PAGE_ALLOCATOR
1937 bool "Page allocator randomization"
1938 default SLAB_FREELIST_RANDOM && ACPI_NUMA
1940 Randomization of the page allocator improves the average
1941 utilization of a direct-mapped memory-side-cache. See section
1942 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
1943 6.2a specification for an example of how a platform advertises
1944 the presence of a memory-side-cache. There are also incidental
1945 security benefits as it reduces the predictability of page
1946 allocations to compliment SLAB_FREELIST_RANDOM, but the
1947 default granularity of shuffling on the "MAX_ORDER - 1" i.e,
1948 10th order of pages is selected based on cache utilization
1951 While the randomization improves cache utilization it may
1952 negatively impact workloads on platforms without a cache. For
1953 this reason, by default, the randomization is enabled only
1954 after runtime detection of a direct-mapped memory-side-cache.
1955 Otherwise, the randomization may be force enabled with the
1956 'page_alloc.shuffle' kernel command line parameter.
1960 config SLUB_CPU_PARTIAL
1962 depends on SLUB && SMP
1963 bool "SLUB per cpu partial cache"
1965 Per cpu partial caches accelerate objects allocation and freeing
1966 that is local to a processor at the price of more indeterminism
1967 in the latency of the free. On overflow these caches will be cleared
1968 which requires the taking of locks that may cause latency spikes.
1969 Typically one would choose no for a realtime system.
1971 config MMAP_ALLOW_UNINITIALIZED
1972 bool "Allow mmapped anonymous memory to be uninitialized"
1973 depends on EXPERT && !MMU
1976 Normally, and according to the Linux spec, anonymous memory obtained
1977 from mmap() has its contents cleared before it is passed to
1978 userspace. Enabling this config option allows you to request that
1979 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1980 providing a huge performance boost. If this option is not enabled,
1981 then the flag will be ignored.
1983 This is taken advantage of by uClibc's malloc(), and also by
1984 ELF-FDPIC binfmt's brk and stack allocator.
1986 Because of the obvious security issues, this option should only be
1987 enabled on embedded devices where you control what is run in
1988 userspace. Since that isn't generally a problem on no-MMU systems,
1989 it is normally safe to say Y here.
1991 See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
1993 config SYSTEM_DATA_VERIFICATION
1995 select SYSTEM_TRUSTED_KEYRING
1999 select ASYMMETRIC_KEY_TYPE
2000 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
2003 select X509_CERTIFICATE_PARSER
2004 select PKCS7_MESSAGE_PARSER
2006 Provide PKCS#7 message verification using the contents of the system
2007 trusted keyring to provide public keys. This then can be used for
2008 module verification, kexec image verification and firmware blob
2012 bool "Profiling support"
2014 Say Y here to enable the extended profiling support mechanisms used
2018 # Place an empty function call at each tracepoint site. Can be
2019 # dynamically changed for a probe function.
2024 endmenu # General setup
2026 source "arch/Kconfig"
2033 default 0 if BASE_FULL
2034 default 1 if !BASE_FULL
2036 config MODULE_SIG_FORMAT
2038 select SYSTEM_DATA_VERIFICATION
2041 bool "Enable loadable module support"
2044 Kernel modules are small pieces of compiled code which can
2045 be inserted in the running kernel, rather than being
2046 permanently built into the kernel. You use the "modprobe"
2047 tool to add (and sometimes remove) them. If you say Y here,
2048 many parts of the kernel can be built as modules (by
2049 answering M instead of Y where indicated): this is most
2050 useful for infrequently used options which are not required
2051 for booting. For more information, see the man pages for
2052 modprobe, lsmod, modinfo, insmod and rmmod.
2054 If you say Y here, you will need to run "make
2055 modules_install" to put the modules under /lib/modules/
2056 where modprobe can find them (you may need to be root to do
2063 config MODULE_FORCE_LOAD
2064 bool "Forced module loading"
2067 Allow loading of modules without version information (ie. modprobe
2068 --force). Forced module loading sets the 'F' (forced) taint flag and
2069 is usually a really bad idea.
2071 config MODULE_UNLOAD
2072 bool "Module unloading"
2074 Without this option you will not be able to unload any
2075 modules (note that some modules may not be unloadable
2076 anyway), which makes your kernel smaller, faster
2077 and simpler. If unsure, say Y.
2079 config MODULE_FORCE_UNLOAD
2080 bool "Forced module unloading"
2081 depends on MODULE_UNLOAD
2083 This option allows you to force a module to unload, even if the
2084 kernel believes it is unsafe: the kernel will remove the module
2085 without waiting for anyone to stop using it (using the -f option to
2086 rmmod). This is mainly for kernel developers and desperate users.
2090 bool "Module versioning support"
2092 Usually, you have to use modules compiled with your kernel.
2093 Saying Y here makes it sometimes possible to use modules
2094 compiled for different kernels, by adding enough information
2095 to the modules to (hopefully) spot any changes which would
2096 make them incompatible with the kernel you are running. If
2099 config ASM_MODVERSIONS
2101 default HAVE_ASM_MODVERSIONS && MODVERSIONS
2103 This enables module versioning for exported symbols also from
2104 assembly. This can be enabled only when the target architecture
2107 config MODULE_REL_CRCS
2109 depends on MODVERSIONS
2111 config MODULE_SRCVERSION_ALL
2112 bool "Source checksum for all modules"
2114 Modules which contain a MODULE_VERSION get an extra "srcversion"
2115 field inserted into their modinfo section, which contains a
2116 sum of the source files which made it. This helps maintainers
2117 see exactly which source was used to build a module (since
2118 others sometimes change the module source without updating
2119 the version). With this option, such a "srcversion" field
2120 will be created for all modules. If unsure, say N.
2123 bool "Module signature verification"
2124 select MODULE_SIG_FORMAT
2126 Check modules for valid signatures upon load: the signature
2127 is simply appended to the module. For more information see
2128 <file:Documentation/admin-guide/module-signing.rst>.
2130 Note that this option adds the OpenSSL development packages as a
2131 kernel build dependency so that the signing tool can use its crypto
2134 You should enable this option if you wish to use either
2135 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
2136 another LSM - otherwise unsigned modules will be loadable regardless
2137 of the lockdown policy.
2139 !!!WARNING!!! If you enable this option, you MUST make sure that the
2140 module DOES NOT get stripped after being signed. This includes the
2141 debuginfo strip done by some packagers (such as rpmbuild) and
2142 inclusion into an initramfs that wants the module size reduced.
2144 config MODULE_SIG_FORCE
2145 bool "Require modules to be validly signed"
2146 depends on MODULE_SIG
2148 Reject unsigned modules or signed modules for which we don't have a
2149 key. Without this, such modules will simply taint the kernel.
2151 config MODULE_SIG_ALL
2152 bool "Automatically sign all modules"
2154 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2156 Sign all modules during make modules_install. Without this option,
2157 modules must be signed manually, using the scripts/sign-file tool.
2159 comment "Do not forget to sign required modules with scripts/sign-file"
2160 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2163 prompt "Which hash algorithm should modules be signed with?"
2164 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2166 This determines which sort of hashing algorithm will be used during
2167 signature generation. This algorithm _must_ be built into the kernel
2168 directly so that signature verification can take place. It is not
2169 possible to load a signed module containing the algorithm to check
2170 the signature on that module.
2172 config MODULE_SIG_SHA1
2173 bool "Sign modules with SHA-1"
2176 config MODULE_SIG_SHA224
2177 bool "Sign modules with SHA-224"
2178 select CRYPTO_SHA256
2180 config MODULE_SIG_SHA256
2181 bool "Sign modules with SHA-256"
2182 select CRYPTO_SHA256
2184 config MODULE_SIG_SHA384
2185 bool "Sign modules with SHA-384"
2186 select CRYPTO_SHA512
2188 config MODULE_SIG_SHA512
2189 bool "Sign modules with SHA-512"
2190 select CRYPTO_SHA512
2194 config MODULE_SIG_HASH
2196 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2197 default "sha1" if MODULE_SIG_SHA1
2198 default "sha224" if MODULE_SIG_SHA224
2199 default "sha256" if MODULE_SIG_SHA256
2200 default "sha384" if MODULE_SIG_SHA384
2201 default "sha512" if MODULE_SIG_SHA512
2204 prompt "Module compression mode"
2206 This option allows you to choose the algorithm which will be used to
2207 compress modules when 'make modules_install' is run. (or, you can
2208 choose to not compress modules at all.)
2210 External modules will also be compressed in the same way during the
2213 For modules inside an initrd or initramfs, it's more efficient to
2214 compress the whole initrd or initramfs instead.
2216 This is fully compatible with signed modules.
2218 Please note that the tool used to load modules needs to support the
2219 corresponding algorithm. module-init-tools MAY support gzip, and kmod
2220 MAY support gzip, xz and zstd.
2222 Your build system needs to provide the appropriate compression tool
2223 to compress the modules.
2225 If in doubt, select 'None'.
2227 config MODULE_COMPRESS_NONE
2230 Do not compress modules. The installed modules are suffixed
2233 config MODULE_COMPRESS_GZIP
2236 Compress modules with GZIP. The installed modules are suffixed
2239 config MODULE_COMPRESS_XZ
2242 Compress modules with XZ. The installed modules are suffixed
2245 config MODULE_COMPRESS_ZSTD
2248 Compress modules with ZSTD. The installed modules are suffixed
2253 config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
2254 bool "Allow loading of modules with missing namespace imports"
2256 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
2257 a namespace. A module that makes use of a symbol exported with such a
2258 namespace is required to import the namespace via MODULE_IMPORT_NS().
2259 There is no technical reason to enforce correct namespace imports,
2260 but it creates consistency between symbols defining namespaces and
2261 users importing namespaces they make use of. This option relaxes this
2262 requirement and lifts the enforcement when loading a module.
2266 config MODPROBE_PATH
2267 string "Path to modprobe binary"
2268 default "/sbin/modprobe"
2270 When kernel code requests a module, it does so by calling
2271 the "modprobe" userspace utility. This option allows you to
2272 set the path where that binary is found. This can be changed
2273 at runtime via the sysctl file
2274 /proc/sys/kernel/modprobe. Setting this to the empty string
2275 removes the kernel's ability to request modules (but
2276 userspace can still load modules explicitly).
2278 config TRIM_UNUSED_KSYMS
2279 bool "Trim unused exported kernel symbols" if EXPERT
2280 depends on !COMPILE_TEST
2282 The kernel and some modules make many symbols available for
2283 other modules to use via EXPORT_SYMBOL() and variants. Depending
2284 on the set of modules being selected in your kernel configuration,
2285 many of those exported symbols might never be used.
2287 This option allows for unused exported symbols to be dropped from
2288 the build. In turn, this provides the compiler more opportunities
2289 (especially when using LTO) for optimizing the code and reducing
2290 binary size. This might have some security advantages as well.
2292 If unsure, or if you need to build out-of-tree modules, say N.
2294 config UNUSED_KSYMS_WHITELIST
2295 string "Whitelist of symbols to keep in ksymtab"
2296 depends on TRIM_UNUSED_KSYMS
2298 By default, all unused exported symbols will be un-exported from the
2299 build when TRIM_UNUSED_KSYMS is selected.
2301 UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
2302 exported at all times, even in absence of in-tree users. The value to
2303 set here is the path to a text file containing the list of symbols,
2304 one per line. The path can be absolute, or relative to the kernel
2309 config MODULES_TREE_LOOKUP
2311 depends on PERF_EVENTS || TRACING || CFI_CLANG
2313 config INIT_ALL_POSSIBLE
2316 Back when each arch used to define their own cpu_online_mask and
2317 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2318 with all 1s, and others with all 0s. When they were centralised,
2319 it was better to provide this option than to break all the archs
2320 and have several arch maintainers pursuing me down dark alleys.
2322 source "block/Kconfig"
2324 config PREEMPT_NOTIFIERS
2334 Build a simple ASN.1 grammar compiler that produces a bytecode output
2335 that can be interpreted by the ASN.1 stream decoder and used to
2336 inform it as to what tags are to be expected in a stream and what
2337 functions to call on what tags.
2339 source "kernel/Kconfig.locks"
2341 config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
2344 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
2347 # It may be useful for an architecture to override the definitions of the
2348 # SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
2349 # and the COMPAT_ variants in <linux/compat.h>, in particular to use a
2350 # different calling convention for syscalls. They can also override the
2351 # macros for not-implemented syscalls in kernel/sys_ni.c and
2352 # kernel/time/posix-stubs.c. All these overrides need to be available in
2353 # <asm/syscall_wrapper.h>.
2354 config ARCH_HAS_SYSCALL_WRAPPER
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