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) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT
66 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m32-flag))
68 config CC_CAN_LINK_STATIC
70 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag) -static) if 64BIT
71 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(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)
91 default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
99 config BUILDTIME_TABLE_SORT
102 config THREAD_INFO_IN_TASK
105 Select this to move thread_info off the stack into task_struct. To
106 make this work, an arch will need to remove all thread_info fields
107 except flags and fix any runtime bugs.
109 One subtle change that will be needed is to use try_get_task_stack()
110 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
119 depends on BROKEN || !SMP
122 config INIT_ENV_ARG_LIMIT
127 Maximum of each of the number of arguments and environment
128 variables passed to init from the kernel command line.
131 bool "Compile also drivers which will not load"
134 Some drivers can be compiled on a different platform than they are
135 intended to be run on. Despite they cannot be loaded there (or even
136 when they load they cannot be used due to missing HW support),
137 developers still, opposing to distributors, might want to build such
138 drivers to compile-test them.
140 If you are a developer and want to build everything available, say Y
141 here. If you are a user/distributor, say N here to exclude useless
142 drivers to be distributed.
145 bool "Compile the kernel with warnings as errors"
148 A kernel build should not cause any compiler warnings, and this
149 enables the '-Werror' flag to enforce that rule by default.
151 However, if you have a new (or very old) compiler with odd and
152 unusual warnings, or you have some architecture with problems,
153 you may need to disable this config option in order to
154 successfully build the kernel.
158 config UAPI_HEADER_TEST
159 bool "Compile test UAPI headers"
160 depends on HEADERS_INSTALL && CC_CAN_LINK
162 Compile test headers exported to user-space to ensure they are
163 self-contained, i.e. compilable as standalone units.
165 If you are a developer or tester and want to ensure the exported
166 headers are self-contained, say Y here. Otherwise, choose N.
169 string "Local version - append to kernel release"
171 Append an extra string to the end of your kernel version.
172 This will show up when you type uname, for example.
173 The string you set here will be appended after the contents of
174 any files with a filename matching localversion* in your
175 object and source tree, in that order. Your total string can
176 be a maximum of 64 characters.
178 config LOCALVERSION_AUTO
179 bool "Automatically append version information to the version string"
181 depends on !COMPILE_TEST
183 This will try to automatically determine if the current tree is a
184 release tree by looking for git tags that belong to the current
185 top of tree revision.
187 A string of the format -gxxxxxxxx will be added to the localversion
188 if a git-based tree is found. The string generated by this will be
189 appended after any matching localversion* files, and after the value
190 set in CONFIG_LOCALVERSION.
192 (The actual string used here is the first eight characters produced
193 by running the command:
195 $ git rev-parse --verify HEAD
197 which is done within the script "scripts/setlocalversion".)
200 string "Build ID Salt"
203 The build ID is used to link binaries and their debug info. Setting
204 this option will use the value in the calculation of the build id.
205 This is mostly useful for distributions which want to ensure the
206 build is unique between builds. It's safe to leave the default.
208 config HAVE_KERNEL_GZIP
211 config HAVE_KERNEL_BZIP2
214 config HAVE_KERNEL_LZMA
217 config HAVE_KERNEL_XZ
220 config HAVE_KERNEL_LZO
223 config HAVE_KERNEL_LZ4
226 config HAVE_KERNEL_ZSTD
229 config HAVE_KERNEL_UNCOMPRESSED
233 prompt "Kernel compression mode"
235 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
237 The linux kernel is a kind of self-extracting executable.
238 Several compression algorithms are available, which differ
239 in efficiency, compression and decompression speed.
240 Compression speed is only relevant when building a kernel.
241 Decompression speed is relevant at each boot.
243 If you have any problems with bzip2 or lzma compressed
244 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
245 version of this functionality (bzip2 only), for 2.4, was
246 supplied by Christian Ludwig)
248 High compression options are mostly useful for users, who
249 are low on disk space (embedded systems), but for whom ram
252 If in doubt, select 'gzip'
256 depends on HAVE_KERNEL_GZIP
258 The old and tried gzip compression. It provides a good balance
259 between compression ratio and decompression speed.
263 depends on HAVE_KERNEL_BZIP2
265 Its compression ratio and speed is intermediate.
266 Decompression speed is slowest among the choices. The kernel
267 size is about 10% smaller with bzip2, in comparison to gzip.
268 Bzip2 uses a large amount of memory. For modern kernels you
269 will need at least 8MB RAM or more for booting.
273 depends on HAVE_KERNEL_LZMA
275 This compression algorithm's ratio is best. Decompression speed
276 is between gzip and bzip2. Compression is slowest.
277 The kernel size is about 33% smaller with LZMA in comparison to gzip.
281 depends on HAVE_KERNEL_XZ
283 XZ uses the LZMA2 algorithm and instruction set specific
284 BCJ filters which can improve compression ratio of executable
285 code. The size of the kernel is about 30% smaller with XZ in
286 comparison to gzip. On architectures for which there is a BCJ
287 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
288 will create a few percent smaller kernel than plain LZMA.
290 The speed is about the same as with LZMA: The decompression
291 speed of XZ is better than that of bzip2 but worse than gzip
292 and LZO. Compression is slow.
296 depends on HAVE_KERNEL_LZO
298 Its compression ratio is the poorest among the choices. The kernel
299 size is about 10% bigger than gzip; however its speed
300 (both compression and decompression) is the fastest.
304 depends on HAVE_KERNEL_LZ4
306 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
307 A preliminary version of LZ4 de/compression tool is available at
308 <https://code.google.com/p/lz4/>.
310 Its compression ratio is worse than LZO. The size of the kernel
311 is about 8% bigger than LZO. But the decompression speed is
316 depends on HAVE_KERNEL_ZSTD
318 ZSTD is a compression algorithm targeting intermediate compression
319 with fast decompression speed. It will compress better than GZIP and
320 decompress around the same speed as LZO, but slower than LZ4. You
321 will need at least 192 KB RAM or more for booting. The zstd command
322 line tool is required for compression.
324 config KERNEL_UNCOMPRESSED
326 depends on HAVE_KERNEL_UNCOMPRESSED
328 Produce uncompressed kernel image. This option is usually not what
329 you want. It is useful for debugging the kernel in slow simulation
330 environments, where decompressing and moving the kernel is awfully
331 slow. This option allows early boot code to skip the decompressor
332 and jump right at uncompressed kernel image.
337 string "Default init path"
340 This option determines the default init for the system if no init=
341 option is passed on the kernel command line. If the requested path is
342 not present, we will still then move on to attempting further
343 locations (e.g. /sbin/init, etc). If this is empty, we will just use
344 the fallback list when init= is not passed.
346 config DEFAULT_HOSTNAME
347 string "Default hostname"
350 This option determines the default system hostname before userspace
351 calls sethostname(2). The kernel traditionally uses "(none)" here,
352 but you may wish to use a different default here to make a minimal
353 system more usable with less configuration.
356 # For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can
357 # add proper SWAP support to them, in which case this can be remove.
363 bool "Support for paging of anonymous memory (swap)"
364 depends on MMU && BLOCK && !ARCH_NO_SWAP
367 This option allows you to choose whether you want to have support
368 for so called swap devices or swap files in your kernel that are
369 used to provide more virtual memory than the actual RAM present
370 in your computer. If unsure say Y.
375 Inter Process Communication is a suite of library functions and
376 system calls which let processes (running programs) synchronize and
377 exchange information. It is generally considered to be a good thing,
378 and some programs won't run unless you say Y here. In particular, if
379 you want to run the DOS emulator dosemu under Linux (read the
380 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
381 you'll need to say Y here.
383 You can find documentation about IPC with "info ipc" and also in
384 section 6.4 of the Linux Programmer's Guide, available from
385 <http://www.tldp.org/guides.html>.
387 config SYSVIPC_SYSCTL
394 bool "POSIX Message Queues"
397 POSIX variant of message queues is a part of IPC. In POSIX message
398 queues every message has a priority which decides about succession
399 of receiving it by a process. If you want to compile and run
400 programs written e.g. for Solaris with use of its POSIX message
401 queues (functions mq_*) say Y here.
403 POSIX message queues are visible as a filesystem called 'mqueue'
404 and can be mounted somewhere if you want to do filesystem
405 operations on message queues.
409 config POSIX_MQUEUE_SYSCTL
411 depends on POSIX_MQUEUE
416 bool "General notification queue"
420 This is a general notification queue for the kernel to pass events to
421 userspace by splicing them into pipes. It can be used in conjunction
422 with watches for key/keyring change notifications and device
425 See Documentation/watch_queue.rst
427 config CROSS_MEMORY_ATTACH
428 bool "Enable process_vm_readv/writev syscalls"
432 Enabling this option adds the system calls process_vm_readv and
433 process_vm_writev which allow a process with the correct privileges
434 to directly read from or write to another process' address space.
435 See the man page for more details.
438 bool "uselib syscall"
439 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
441 This option enables the uselib syscall, a system call used in the
442 dynamic linker from libc5 and earlier. glibc does not use this
443 system call. If you intend to run programs built on libc5 or
444 earlier, you may need to enable this syscall. Current systems
445 running glibc can safely disable this.
448 bool "Auditing support"
451 Enable auditing infrastructure that can be used with another
452 kernel subsystem, such as SELinux (which requires this for
453 logging of avc messages output). System call auditing is included
454 on architectures which support it.
456 config HAVE_ARCH_AUDITSYSCALL
461 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
464 source "kernel/irq/Kconfig"
465 source "kernel/time/Kconfig"
466 source "kernel/bpf/Kconfig"
467 source "kernel/Kconfig.preempt"
469 menu "CPU/Task time and stats accounting"
471 config VIRT_CPU_ACCOUNTING
475 prompt "Cputime accounting"
476 default TICK_CPU_ACCOUNTING if !PPC64
477 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
479 # Kind of a stub config for the pure tick based cputime accounting
480 config TICK_CPU_ACCOUNTING
481 bool "Simple tick based cputime accounting"
482 depends on !S390 && !NO_HZ_FULL
484 This is the basic tick based cputime accounting that maintains
485 statistics about user, system and idle time spent on per jiffies
490 config VIRT_CPU_ACCOUNTING_NATIVE
491 bool "Deterministic task and CPU time accounting"
492 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
493 select VIRT_CPU_ACCOUNTING
495 Select this option to enable more accurate task and CPU time
496 accounting. This is done by reading a CPU counter on each
497 kernel entry and exit and on transitions within the kernel
498 between system, softirq and hardirq state, so there is a
499 small performance impact. In the case of s390 or IBM POWER > 5,
500 this also enables accounting of stolen time on logically-partitioned
503 config VIRT_CPU_ACCOUNTING_GEN
504 bool "Full dynticks CPU time accounting"
505 depends on HAVE_CONTEXT_TRACKING
506 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
507 depends on GENERIC_CLOCKEVENTS
508 select VIRT_CPU_ACCOUNTING
509 select CONTEXT_TRACKING
511 Select this option to enable task and CPU time accounting on full
512 dynticks systems. This accounting is implemented by watching every
513 kernel-user boundaries using the context tracking subsystem.
514 The accounting is thus performed at the expense of some significant
517 For now this is only useful if you are working on the full
518 dynticks subsystem development.
524 config IRQ_TIME_ACCOUNTING
525 bool "Fine granularity task level IRQ time accounting"
526 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
528 Select this option to enable fine granularity task irq time
529 accounting. This is done by reading a timestamp on each
530 transitions between softirq and hardirq state, so there can be a
531 small performance impact.
533 If in doubt, say N here.
535 config HAVE_SCHED_AVG_IRQ
537 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
540 config SCHED_THERMAL_PRESSURE
542 default y if ARM && ARM_CPU_TOPOLOGY
545 depends on CPU_FREQ_THERMAL
547 Select this option to enable thermal pressure accounting in the
548 scheduler. Thermal pressure is the value conveyed to the scheduler
549 that reflects the reduction in CPU compute capacity resulted from
550 thermal throttling. Thermal throttling occurs when the performance of
551 a CPU is capped due to high operating temperatures.
553 If selected, the scheduler will be able to balance tasks accordingly,
554 i.e. put less load on throttled CPUs than on non/less throttled ones.
556 This requires the architecture to implement
557 arch_update_thermal_pressure() and arch_scale_thermal_pressure().
559 config BSD_PROCESS_ACCT
560 bool "BSD Process Accounting"
563 If you say Y here, a user level program will be able to instruct the
564 kernel (via a special system call) to write process accounting
565 information to a file: whenever a process exits, information about
566 that process will be appended to the file by the kernel. The
567 information includes things such as creation time, owning user,
568 command name, memory usage, controlling terminal etc. (the complete
569 list is in the struct acct in <file:include/linux/acct.h>). It is
570 up to the user level program to do useful things with this
571 information. This is generally a good idea, so say Y.
573 config BSD_PROCESS_ACCT_V3
574 bool "BSD Process Accounting version 3 file format"
575 depends on BSD_PROCESS_ACCT
578 If you say Y here, the process accounting information is written
579 in a new file format that also logs the process IDs of each
580 process and its parent. Note that this file format is incompatible
581 with previous v0/v1/v2 file formats, so you will need updated tools
582 for processing it. A preliminary version of these tools is available
583 at <http://www.gnu.org/software/acct/>.
586 bool "Export task/process statistics through netlink"
591 Export selected statistics for tasks/processes through the
592 generic netlink interface. Unlike BSD process accounting, the
593 statistics are available during the lifetime of tasks/processes as
594 responses to commands. Like BSD accounting, they are sent to user
599 config TASK_DELAY_ACCT
600 bool "Enable per-task delay accounting"
604 Collect information on time spent by a task waiting for system
605 resources like cpu, synchronous block I/O completion and swapping
606 in pages. Such statistics can help in setting a task's priorities
607 relative to other tasks for cpu, io, rss limits etc.
612 bool "Enable extended accounting over taskstats"
615 Collect extended task accounting data and send the data
616 to userland for processing over the taskstats interface.
620 config TASK_IO_ACCOUNTING
621 bool "Enable per-task storage I/O accounting"
622 depends on TASK_XACCT
624 Collect information on the number of bytes of storage I/O which this
630 bool "Pressure stall information tracking"
632 Collect metrics that indicate how overcommitted the CPU, memory,
633 and IO capacity are in the system.
635 If you say Y here, the kernel will create /proc/pressure/ with the
636 pressure statistics files cpu, memory, and io. These will indicate
637 the share of walltime in which some or all tasks in the system are
638 delayed due to contention of the respective resource.
640 In kernels with cgroup support, cgroups (cgroup2 only) will
641 have cpu.pressure, memory.pressure, and io.pressure files,
642 which aggregate pressure stalls for the grouped tasks only.
644 For more details see Documentation/accounting/psi.rst.
648 config PSI_DEFAULT_DISABLED
649 bool "Require boot parameter to enable pressure stall information tracking"
653 If set, pressure stall information tracking will be disabled
654 per default but can be enabled through passing psi=1 on the
655 kernel commandline during boot.
657 This feature adds some code to the task wakeup and sleep
658 paths of the scheduler. The overhead is too low to affect
659 common scheduling-intense workloads in practice (such as
660 webservers, memcache), but it does show up in artificial
661 scheduler stress tests, such as hackbench.
663 If you are paranoid and not sure what the kernel will be
668 endmenu # "CPU/Task time and stats accounting"
672 depends on SMP || COMPILE_TEST
675 Make sure that CPUs running critical tasks are not disturbed by
676 any source of "noise" such as unbound workqueues, timers, kthreads...
677 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
678 the "isolcpus=" boot parameter.
682 source "kernel/rcu/Kconfig"
689 tristate "Kernel .config support"
691 This option enables the complete Linux kernel ".config" file
692 contents to be saved in the kernel. It provides documentation
693 of which kernel options are used in a running kernel or in an
694 on-disk kernel. This information can be extracted from the kernel
695 image file with the script scripts/extract-ikconfig and used as
696 input to rebuild the current kernel or to build another kernel.
697 It can also be extracted from a running kernel by reading
698 /proc/config.gz if enabled (below).
701 bool "Enable access to .config through /proc/config.gz"
702 depends on IKCONFIG && PROC_FS
704 This option enables access to the kernel configuration file
705 through /proc/config.gz.
708 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
711 This option enables access to the in-kernel headers that are generated during
712 the build process. These can be used to build eBPF tracing programs,
713 or similar programs. If you build the headers as a module, a module called
714 kheaders.ko is built which can be loaded on-demand to get access to headers.
717 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
718 range 12 25 if !H8300
723 Select the minimal kernel log buffer size as a power of 2.
724 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
725 parameter, see below. Any higher size also might be forced
726 by "log_buf_len" boot parameter.
736 config LOG_CPU_MAX_BUF_SHIFT
737 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
740 default 12 if !BASE_SMALL
741 default 0 if BASE_SMALL
744 This option allows to increase the default ring buffer size
745 according to the number of CPUs. The value defines the contribution
746 of each CPU as a power of 2. The used space is typically only few
747 lines however it might be much more when problems are reported,
750 The increased size means that a new buffer has to be allocated and
751 the original static one is unused. It makes sense only on systems
752 with more CPUs. Therefore this value is used only when the sum of
753 contributions is greater than the half of the default kernel ring
754 buffer as defined by LOG_BUF_SHIFT. The default values are set
755 so that more than 16 CPUs are needed to trigger the allocation.
757 Also this option is ignored when "log_buf_len" kernel parameter is
758 used as it forces an exact (power of two) size of the ring buffer.
760 The number of possible CPUs is used for this computation ignoring
761 hotplugging making the computation optimal for the worst case
762 scenario while allowing a simple algorithm to be used from bootup.
764 Examples shift values and their meaning:
765 17 => 128 KB for each CPU
766 16 => 64 KB for each CPU
767 15 => 32 KB for each CPU
768 14 => 16 KB for each CPU
769 13 => 8 KB for each CPU
770 12 => 4 KB for each CPU
772 config PRINTK_SAFE_LOG_BUF_SHIFT
773 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
778 Select the size of an alternate printk per-CPU buffer where messages
779 printed from usafe contexts are temporary stored. One example would
780 be NMI messages, another one - printk recursion. The messages are
781 copied to the main log buffer in a safe context to avoid a deadlock.
782 The value defines the size as a power of 2.
784 Those messages are rare and limited. The largest one is when
785 a backtrace is printed. It usually fits into 4KB. Select
786 8KB if you want to be on the safe side.
789 17 => 128 KB for each CPU
790 16 => 64 KB for each CPU
791 15 => 32 KB for each CPU
792 14 => 16 KB for each CPU
793 13 => 8 KB for each CPU
794 12 => 4 KB for each CPU
797 bool "Printk indexing debugfs interface"
798 depends on PRINTK && DEBUG_FS
800 Add support for indexing of all printk formats known at compile time
801 at <debugfs>/printk/index/<module>.
803 This can be used as part of maintaining daemons which monitor
804 /dev/kmsg, as it permits auditing the printk formats present in a
805 kernel, allowing detection of cases where monitored printks are
806 changed or no longer present.
808 There is no additional runtime cost to printk with this enabled.
811 # Architectures with an unreliable sched_clock() should select this:
813 config HAVE_UNSTABLE_SCHED_CLOCK
816 config GENERIC_SCHED_CLOCK
819 menu "Scheduler features"
822 bool "Enable utilization clamping for RT/FAIR tasks"
823 depends on CPU_FREQ_GOV_SCHEDUTIL
825 This feature enables the scheduler to track the clamped utilization
826 of each CPU based on RUNNABLE tasks scheduled on that CPU.
828 With this option, the user can specify the min and max CPU
829 utilization allowed for RUNNABLE tasks. The max utilization defines
830 the maximum frequency a task should use while the min utilization
831 defines the minimum frequency it should use.
833 Both min and max utilization clamp values are hints to the scheduler,
834 aiming at improving its frequency selection policy, but they do not
835 enforce or grant any specific bandwidth for tasks.
839 config UCLAMP_BUCKETS_COUNT
840 int "Number of supported utilization clamp buckets"
843 depends on UCLAMP_TASK
845 Defines the number of clamp buckets to use. The range of each bucket
846 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
847 number of clamp buckets the finer their granularity and the higher
848 the precision of clamping aggregation and tracking at run-time.
850 For example, with the minimum configuration value we will have 5
851 clamp buckets tracking 20% utilization each. A 25% boosted tasks will
852 be refcounted in the [20..39]% bucket and will set the bucket clamp
853 effective value to 25%.
854 If a second 30% boosted task should be co-scheduled on the same CPU,
855 that task will be refcounted in the same bucket of the first task and
856 it will boost the bucket clamp effective value to 30%.
857 The clamp effective value of a bucket is reset to its nominal value
858 (20% in the example above) when there are no more tasks refcounted in
861 An additional boost/capping margin can be added to some tasks. In the
862 example above the 25% task will be boosted to 30% until it exits the
863 CPU. If that should be considered not acceptable on certain systems,
864 it's always possible to reduce the margin by increasing the number of
865 clamp buckets to trade off used memory for run-time tracking
868 If in doubt, use the default value.
873 # For architectures that want to enable the support for NUMA-affine scheduler
876 config ARCH_SUPPORTS_NUMA_BALANCING
880 # For architectures that prefer to flush all TLBs after a number of pages
881 # are unmapped instead of sending one IPI per page to flush. The architecture
882 # must provide guarantees on what happens if a clean TLB cache entry is
883 # written after the unmap. Details are in mm/rmap.c near the check for
884 # should_defer_flush. The architecture should also consider if the full flush
885 # and the refill costs are offset by the savings of sending fewer IPIs.
886 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
890 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
892 config CC_IMPLICIT_FALLTHROUGH
894 default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5)
895 default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough)
898 # For architectures that know their GCC __int128 support is sound
900 config ARCH_SUPPORTS_INT128
903 # For architectures that (ab)use NUMA to represent different memory regions
904 # all cpu-local but of different latencies, such as SuperH.
906 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
909 config NUMA_BALANCING
910 bool "Memory placement aware NUMA scheduler"
911 depends on ARCH_SUPPORTS_NUMA_BALANCING
912 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
913 depends on SMP && NUMA && MIGRATION && !PREEMPT_RT
915 This option adds support for automatic NUMA aware memory/task placement.
916 The mechanism is quite primitive and is based on migrating memory when
917 it has references to the node the task is running on.
919 This system will be inactive on UMA systems.
921 config NUMA_BALANCING_DEFAULT_ENABLED
922 bool "Automatically enable NUMA aware memory/task placement"
924 depends on NUMA_BALANCING
926 If set, automatic NUMA balancing will be enabled if running on a NUMA
930 bool "Control Group support"
933 This option adds support for grouping sets of processes together, for
934 use with process control subsystems such as Cpusets, CFS, memory
935 controls or device isolation.
937 - Documentation/scheduler/sched-design-CFS.rst (CFS)
938 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
939 and resource control)
949 bool "Memory controller"
953 Provides control over the memory footprint of tasks in a cgroup.
957 depends on MEMCG && SWAP
962 depends on MEMCG && !SLOB
970 Generic block IO controller cgroup interface. This is the common
971 cgroup interface which should be used by various IO controlling
974 Currently, CFQ IO scheduler uses it to recognize task groups and
975 control disk bandwidth allocation (proportional time slice allocation)
976 to such task groups. It is also used by bio throttling logic in
977 block layer to implement upper limit in IO rates on a device.
979 This option only enables generic Block IO controller infrastructure.
980 One needs to also enable actual IO controlling logic/policy. For
981 enabling proportional weight division of disk bandwidth in CFQ, set
982 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
983 CONFIG_BLK_DEV_THROTTLING=y.
985 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
987 config CGROUP_WRITEBACK
989 depends on MEMCG && BLK_CGROUP
992 menuconfig CGROUP_SCHED
993 bool "CPU controller"
996 This feature lets CPU scheduler recognize task groups and control CPU
997 bandwidth allocation to such task groups. It uses cgroups to group
1001 config FAIR_GROUP_SCHED
1002 bool "Group scheduling for SCHED_OTHER"
1003 depends on CGROUP_SCHED
1004 default CGROUP_SCHED
1006 config CFS_BANDWIDTH
1007 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
1008 depends on FAIR_GROUP_SCHED
1011 This option allows users to define CPU bandwidth rates (limits) for
1012 tasks running within the fair group scheduler. Groups with no limit
1013 set are considered to be unconstrained and will run with no
1015 See Documentation/scheduler/sched-bwc.rst for more information.
1017 config RT_GROUP_SCHED
1018 bool "Group scheduling for SCHED_RR/FIFO"
1019 depends on CGROUP_SCHED
1022 This feature lets you explicitly allocate real CPU bandwidth
1023 to task groups. If enabled, it will also make it impossible to
1024 schedule realtime tasks for non-root users until you allocate
1025 realtime bandwidth for them.
1026 See Documentation/scheduler/sched-rt-group.rst for more information.
1030 config UCLAMP_TASK_GROUP
1031 bool "Utilization clamping per group of tasks"
1032 depends on CGROUP_SCHED
1033 depends on UCLAMP_TASK
1036 This feature enables the scheduler to track the clamped utilization
1037 of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
1039 When this option is enabled, the user can specify a min and max
1040 CPU bandwidth which is allowed for each single task in a group.
1041 The max bandwidth allows to clamp the maximum frequency a task
1042 can use, while the min bandwidth allows to define a minimum
1043 frequency a task will always use.
1045 When task group based utilization clamping is enabled, an eventually
1046 specified task-specific clamp value is constrained by the cgroup
1047 specified clamp value. Both minimum and maximum task clamping cannot
1048 be bigger than the corresponding clamping defined at task group level.
1053 bool "PIDs controller"
1055 Provides enforcement of process number limits in the scope of a
1056 cgroup. Any attempt to fork more processes than is allowed in the
1057 cgroup will fail. PIDs are fundamentally a global resource because it
1058 is fairly trivial to reach PID exhaustion before you reach even a
1059 conservative kmemcg limit. As a result, it is possible to grind a
1060 system to halt without being limited by other cgroup policies. The
1061 PIDs controller is designed to stop this from happening.
1063 It should be noted that organisational operations (such as attaching
1064 to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
1065 since the PIDs limit only affects a process's ability to fork, not to
1069 bool "RDMA controller"
1071 Provides enforcement of RDMA resources defined by IB stack.
1072 It is fairly easy for consumers to exhaust RDMA resources, which
1073 can result into resource unavailability to other consumers.
1074 RDMA controller is designed to stop this from happening.
1075 Attaching processes with active RDMA resources to the cgroup
1076 hierarchy is allowed even if can cross the hierarchy's limit.
1078 config CGROUP_FREEZER
1079 bool "Freezer controller"
1081 Provides a way to freeze and unfreeze all tasks in a
1084 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1085 controller includes important in-kernel memory consumers per default.
1087 If you're using cgroup2, say N.
1089 config CGROUP_HUGETLB
1090 bool "HugeTLB controller"
1091 depends on HUGETLB_PAGE
1095 Provides a cgroup controller for HugeTLB pages.
1096 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1097 The limit is enforced during page fault. Since HugeTLB doesn't
1098 support page reclaim, enforcing the limit at page fault time implies
1099 that, the application will get SIGBUS signal if it tries to access
1100 HugeTLB pages beyond its limit. This requires the application to know
1101 beforehand how much HugeTLB pages it would require for its use. The
1102 control group is tracked in the third page lru pointer. This means
1103 that we cannot use the controller with huge page less than 3 pages.
1106 bool "Cpuset controller"
1109 This option will let you create and manage CPUSETs which
1110 allow dynamically partitioning a system into sets of CPUs and
1111 Memory Nodes and assigning tasks to run only within those sets.
1112 This is primarily useful on large SMP or NUMA systems.
1116 config PROC_PID_CPUSET
1117 bool "Include legacy /proc/<pid>/cpuset file"
1121 config CGROUP_DEVICE
1122 bool "Device controller"
1124 Provides a cgroup controller implementing whitelists for
1125 devices which a process in the cgroup can mknod or open.
1127 config CGROUP_CPUACCT
1128 bool "Simple CPU accounting controller"
1130 Provides a simple controller for monitoring the
1131 total CPU consumed by the tasks in a cgroup.
1134 bool "Perf controller"
1135 depends on PERF_EVENTS
1137 This option extends the perf per-cpu mode to restrict monitoring
1138 to threads which belong to the cgroup specified and run on the
1139 designated cpu. Or this can be used to have cgroup ID in samples
1140 so that it can monitor performance events among cgroups.
1145 bool "Support for eBPF programs attached to cgroups"
1146 depends on BPF_SYSCALL
1147 select SOCK_CGROUP_DATA
1149 Allow attaching eBPF programs to a cgroup using the bpf(2)
1150 syscall command BPF_PROG_ATTACH.
1152 In which context these programs are accessed depends on the type
1153 of attachment. For instance, programs that are attached using
1154 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1158 bool "Misc resource controller"
1161 Provides a controller for miscellaneous resources on a host.
1163 Miscellaneous scalar resources are the resources on the host system
1164 which cannot be abstracted like the other cgroups. This controller
1165 tracks and limits the miscellaneous resources used by a process
1166 attached to a cgroup hierarchy.
1168 For more information, please check misc cgroup section in
1169 /Documentation/admin-guide/cgroup-v2.rst.
1172 bool "Debug controller"
1174 depends on DEBUG_KERNEL
1176 This option enables a simple controller that exports
1177 debugging information about the cgroups framework. This
1178 controller is for control cgroup debugging only. Its
1179 interfaces are not stable.
1183 config SOCK_CGROUP_DATA
1189 menuconfig NAMESPACES
1190 bool "Namespaces support" if EXPERT
1191 depends on MULTIUSER
1194 Provides the way to make tasks work with different objects using
1195 the same id. For example same IPC id may refer to different objects
1196 or same user id or pid may refer to different tasks when used in
1197 different namespaces.
1202 bool "UTS namespace"
1205 In this namespace tasks see different info provided with the
1209 bool "TIME namespace"
1210 depends on GENERIC_VDSO_TIME_NS
1213 In this namespace boottime and monotonic clocks can be set.
1214 The time will keep going with the same pace.
1217 bool "IPC namespace"
1218 depends on (SYSVIPC || POSIX_MQUEUE)
1221 In this namespace tasks work with IPC ids which correspond to
1222 different IPC objects in different namespaces.
1225 bool "User namespace"
1228 This allows containers, i.e. vservers, to use user namespaces
1229 to provide different user info for different servers.
1231 When user namespaces are enabled in the kernel it is
1232 recommended that the MEMCG option also be enabled and that
1233 user-space use the memory control groups to limit the amount
1234 of memory a memory unprivileged users can use.
1239 bool "PID Namespaces"
1242 Support process id namespaces. This allows having multiple
1243 processes with the same pid as long as they are in different
1244 pid namespaces. This is a building block of containers.
1247 bool "Network namespace"
1251 Allow user space to create what appear to be multiple instances
1252 of the network stack.
1256 config CHECKPOINT_RESTORE
1257 bool "Checkpoint/restore support"
1258 select PROC_CHILDREN
1262 Enables additional kernel features in a sake of checkpoint/restore.
1263 In particular it adds auxiliary prctl codes to setup process text,
1264 data and heap segment sizes, and a few additional /proc filesystem
1267 If unsure, say N here.
1269 config SCHED_AUTOGROUP
1270 bool "Automatic process group scheduling"
1273 select FAIR_GROUP_SCHED
1275 This option optimizes the scheduler for common desktop workloads by
1276 automatically creating and populating task groups. This separation
1277 of workloads isolates aggressive CPU burners (like build jobs) from
1278 desktop applications. Task group autogeneration is currently based
1281 config SYSFS_DEPRECATED
1282 bool "Enable deprecated sysfs features to support old userspace tools"
1286 This option adds code that switches the layout of the "block" class
1287 devices, to not show up in /sys/class/block/, but only in
1290 This switch is only active when the sysfs.deprecated=1 boot option is
1291 passed or the SYSFS_DEPRECATED_V2 option is set.
1293 This option allows new kernels to run on old distributions and tools,
1294 which might get confused by /sys/class/block/. Since 2007/2008 all
1295 major distributions and tools handle this just fine.
1297 Recent distributions and userspace tools after 2009/2010 depend on
1298 the existence of /sys/class/block/, and will not work with this
1301 Only if you are using a new kernel on an old distribution, you might
1304 config SYSFS_DEPRECATED_V2
1305 bool "Enable deprecated sysfs features by default"
1308 depends on SYSFS_DEPRECATED
1310 Enable deprecated sysfs by default.
1312 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1315 Only if you are using a new kernel on an old distribution, you might
1316 need to say Y here. Even then, odds are you would not need it
1317 enabled, you can always pass the boot option if absolutely necessary.
1320 bool "Kernel->user space relay support (formerly relayfs)"
1323 This option enables support for relay interface support in
1324 certain file systems (such as debugfs).
1325 It is designed to provide an efficient mechanism for tools and
1326 facilities to relay large amounts of data from kernel space to
1331 config BLK_DEV_INITRD
1332 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1334 The initial RAM filesystem is a ramfs which is loaded by the
1335 boot loader (loadlin or lilo) and that is mounted as root
1336 before the normal boot procedure. It is typically used to
1337 load modules needed to mount the "real" root file system,
1338 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1340 If RAM disk support (BLK_DEV_RAM) is also included, this
1341 also enables initial RAM disk (initrd) support and adds
1342 15 Kbytes (more on some other architectures) to the kernel size.
1348 source "usr/Kconfig"
1353 bool "Boot config support"
1354 select BLK_DEV_INITRD
1356 Extra boot config allows system admin to pass a config file as
1357 complemental extension of kernel cmdline when booting.
1358 The boot config file must be attached at the end of initramfs
1359 with checksum, size and magic word.
1360 See <file:Documentation/admin-guide/bootconfig.rst> for details.
1365 prompt "Compiler optimization level"
1366 default CC_OPTIMIZE_FOR_PERFORMANCE
1368 config CC_OPTIMIZE_FOR_PERFORMANCE
1369 bool "Optimize for performance (-O2)"
1371 This is the default optimization level for the kernel, building
1372 with the "-O2" compiler flag for best performance and most
1373 helpful compile-time warnings.
1375 config CC_OPTIMIZE_FOR_PERFORMANCE_O3
1376 bool "Optimize more for performance (-O3)"
1379 Choosing this option will pass "-O3" to your compiler to optimize
1380 the kernel yet more for performance.
1382 config CC_OPTIMIZE_FOR_SIZE
1383 bool "Optimize for size (-Os)"
1385 Choosing this option will pass "-Os" to your compiler resulting
1386 in a smaller kernel.
1390 config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1393 This requires that the arch annotates or otherwise protects
1394 its external entry points from being discarded. Linker scripts
1395 must also merge .text.*, .data.*, and .bss.* correctly into
1396 output sections. Care must be taken not to pull in unrelated
1397 sections (e.g., '.text.init'). Typically '.' in section names
1398 is used to distinguish them from label names / C identifiers.
1400 config LD_DEAD_CODE_DATA_ELIMINATION
1401 bool "Dead code and data elimination (EXPERIMENTAL)"
1402 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1404 depends on $(cc-option,-ffunction-sections -fdata-sections)
1405 depends on $(ld-option,--gc-sections)
1407 Enable this if you want to do dead code and data elimination with
1408 the linker by compiling with -ffunction-sections -fdata-sections,
1409 and linking with --gc-sections.
1411 This can reduce on disk and in-memory size of the kernel
1412 code and static data, particularly for small configs and
1413 on small systems. This has the possibility of introducing
1414 silently broken kernel if the required annotations are not
1415 present. This option is not well tested yet, so use at your
1418 config LD_ORPHAN_WARN
1420 depends on ARCH_WANT_LD_ORPHAN_WARN
1421 depends on $(ld-option,--orphan-handling=warn)
1429 config SYSCTL_EXCEPTION_TRACE
1432 Enable support for /proc/sys/debug/exception-trace.
1434 config SYSCTL_ARCH_UNALIGN_NO_WARN
1437 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1438 Allows arch to define/use @no_unaligned_warning to possibly warn
1439 about unaligned access emulation going on under the hood.
1441 config SYSCTL_ARCH_UNALIGN_ALLOW
1444 Enable support for /proc/sys/kernel/unaligned-trap
1445 Allows arches to define/use @unaligned_enabled to runtime toggle
1446 the unaligned access emulation.
1447 see arch/parisc/kernel/unaligned.c for reference
1449 config HAVE_PCSPKR_PLATFORM
1452 # interpreter that classic socket filters depend on
1457 bool "Configure standard kernel features (expert users)"
1458 # Unhide debug options, to make the on-by-default options visible
1461 This option allows certain base kernel options and settings
1462 to be disabled or tweaked. This is for specialized
1463 environments which can tolerate a "non-standard" kernel.
1464 Only use this if you really know what you are doing.
1467 bool "Enable 16-bit UID system calls" if EXPERT
1468 depends on HAVE_UID16 && MULTIUSER
1471 This enables the legacy 16-bit UID syscall wrappers.
1474 bool "Multiple users, groups and capabilities support" if EXPERT
1477 This option enables support for non-root users, groups and
1480 If you say N here, all processes will run with UID 0, GID 0, and all
1481 possible capabilities. Saying N here also compiles out support for
1482 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1485 If unsure, say Y here.
1487 config SGETMASK_SYSCALL
1488 bool "sgetmask/ssetmask syscalls support" if EXPERT
1489 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
1491 sys_sgetmask and sys_ssetmask are obsolete system calls
1492 no longer supported in libc but still enabled by default in some
1495 If unsure, leave the default option here.
1497 config SYSFS_SYSCALL
1498 bool "Sysfs syscall support" if EXPERT
1501 sys_sysfs is an obsolete system call no longer supported in libc.
1502 Note that disabling this option is more secure but might break
1503 compatibility with some systems.
1505 If unsure say Y here.
1508 bool "open by fhandle syscalls" if EXPERT
1512 If you say Y here, a user level program will be able to map
1513 file names to handle and then later use the handle for
1514 different file system operations. This is useful in implementing
1515 userspace file servers, which now track files using handles instead
1516 of names. The handle would remain the same even if file names
1517 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1521 bool "Posix Clocks & timers" if EXPERT
1524 This includes native support for POSIX timers to the kernel.
1525 Some embedded systems have no use for them and therefore they
1526 can be configured out to reduce the size of the kernel image.
1528 When this option is disabled, the following syscalls won't be
1529 available: timer_create, timer_gettime: timer_getoverrun,
1530 timer_settime, timer_delete, clock_adjtime, getitimer,
1531 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1532 clock_getres and clock_nanosleep syscalls will be limited to
1533 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1539 bool "Enable support for printk" if EXPERT
1542 This option enables normal printk support. Removing it
1543 eliminates most of the message strings from the kernel image
1544 and makes the kernel more or less silent. As this makes it
1545 very difficult to diagnose system problems, saying N here is
1546 strongly discouraged.
1549 bool "BUG() support" if EXPERT
1552 Disabling this option eliminates support for BUG and WARN, reducing
1553 the size of your kernel image and potentially quietly ignoring
1554 numerous fatal conditions. You should only consider disabling this
1555 option for embedded systems with no facilities for reporting errors.
1561 bool "Enable ELF core dumps" if EXPERT
1563 Enable support for generating core dumps. Disabling saves about 4k.
1566 config PCSPKR_PLATFORM
1567 bool "Enable PC-Speaker support" if EXPERT
1568 depends on HAVE_PCSPKR_PLATFORM
1572 This option allows to disable the internal PC-Speaker
1573 support, saving some memory.
1577 bool "Enable full-sized data structures for core" if EXPERT
1579 Disabling this option reduces the size of miscellaneous core
1580 kernel data structures. This saves memory on small machines,
1581 but may reduce performance.
1584 bool "Enable futex support" if EXPERT
1585 depends on !(SPARC32 && SMP)
1589 Disabling this option will cause the kernel to be built without
1590 support for "fast userspace mutexes". The resulting kernel may not
1591 run glibc-based applications correctly.
1595 depends on FUTEX && RT_MUTEXES
1599 bool "Enable eventpoll support" if EXPERT
1602 Disabling this option will cause the kernel to be built without
1603 support for epoll family of system calls.
1606 bool "Enable signalfd() system call" if EXPERT
1609 Enable the signalfd() system call that allows to receive signals
1610 on a file descriptor.
1615 bool "Enable timerfd() system call" if EXPERT
1618 Enable the timerfd() system call that allows to receive timer
1619 events on a file descriptor.
1624 bool "Enable eventfd() system call" if EXPERT
1627 Enable the eventfd() system call that allows to receive both
1628 kernel notification (ie. KAIO) or userspace notifications.
1633 bool "Use full shmem filesystem" if EXPERT
1637 The shmem is an internal filesystem used to manage shared memory.
1638 It is backed by swap and manages resource limits. It is also exported
1639 to userspace as tmpfs if TMPFS is enabled. Disabling this
1640 option replaces shmem and tmpfs with the much simpler ramfs code,
1641 which may be appropriate on small systems without swap.
1644 bool "Enable AIO support" if EXPERT
1647 This option enables POSIX asynchronous I/O which may by used
1648 by some high performance threaded applications. Disabling
1649 this option saves about 7k.
1652 bool "Enable IO uring support" if EXPERT
1656 This option enables support for the io_uring interface, enabling
1657 applications to submit and complete IO through submission and
1658 completion rings that are shared between the kernel and application.
1660 config ADVISE_SYSCALLS
1661 bool "Enable madvise/fadvise syscalls" if EXPERT
1664 This option enables the madvise and fadvise syscalls, used by
1665 applications to advise the kernel about their future memory or file
1666 usage, improving performance. If building an embedded system where no
1667 applications use these syscalls, you can disable this option to save
1670 config HAVE_ARCH_USERFAULTFD_WP
1673 Arch has userfaultfd write protection support
1675 config HAVE_ARCH_USERFAULTFD_MINOR
1678 Arch has userfaultfd minor fault support
1681 bool "Enable membarrier() system call" if EXPERT
1684 Enable the membarrier() system call that allows issuing memory
1685 barriers across all running threads, which can be used to distribute
1686 the cost of user-space memory barriers asymmetrically by transforming
1687 pairs of memory barriers into pairs consisting of membarrier() and a
1693 bool "Load all symbols for debugging/ksymoops" if EXPERT
1696 Say Y here to let the kernel print out symbolic crash information and
1697 symbolic stack backtraces. This increases the size of the kernel
1698 somewhat, as all symbols have to be loaded into the kernel image.
1701 bool "Include all symbols in kallsyms"
1702 depends on DEBUG_KERNEL && KALLSYMS
1704 Normally kallsyms only contains the symbols of functions for nicer
1705 OOPS messages and backtraces (i.e., symbols from the text and inittext
1706 sections). This is sufficient for most cases. And only in very rare
1707 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1708 names of variables from the data sections, etc).
1710 This option makes sure that all symbols are loaded into the kernel
1711 image (i.e., symbols from all sections) in cost of increased kernel
1712 size (depending on the kernel configuration, it may be 300KiB or
1713 something like this).
1715 Say N unless you really need all symbols.
1717 config KALLSYMS_ABSOLUTE_PERCPU
1720 default X86_64 && SMP
1722 config KALLSYMS_BASE_RELATIVE
1727 Instead of emitting them as absolute values in the native word size,
1728 emit the symbol references in the kallsyms table as 32-bit entries,
1729 each containing a relative value in the range [base, base + U32_MAX]
1730 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1731 an absolute value in the range [0, S32_MAX] or a relative value in the
1732 range [base, base + S32_MAX], where base is the lowest relative symbol
1733 address encountered in the image.
1735 On 64-bit builds, this reduces the size of the address table by 50%,
1736 but more importantly, it results in entries whose values are build
1737 time constants, and no relocation pass is required at runtime to fix
1738 up the entries based on the runtime load address of the kernel.
1740 # end of the "standard kernel features (expert users)" menu
1742 # syscall, maps, verifier
1745 bool "Enable userfaultfd() system call"
1748 Enable the userfaultfd() system call that allows to intercept and
1749 handle page faults in userland.
1751 config ARCH_HAS_MEMBARRIER_CALLBACKS
1754 config ARCH_HAS_MEMBARRIER_SYNC_CORE
1758 bool "Enable kcmp() system call" if EXPERT
1760 Enable the kernel resource comparison system call. It provides
1761 user-space with the ability to compare two processes to see if they
1762 share a common resource, such as a file descriptor or even virtual
1768 bool "Enable rseq() system call" if EXPERT
1770 depends on HAVE_RSEQ
1773 Enable the restartable sequences system call. It provides a
1774 user-space cache for the current CPU number value, which
1775 speeds up getting the current CPU number from user-space,
1776 as well as an ABI to speed up user-space operations on
1783 bool "Enabled debugging of rseq() system call" if EXPERT
1784 depends on RSEQ && DEBUG_KERNEL
1786 Enable extra debugging checks for the rseq system call.
1791 bool "Embedded system"
1794 This option should be enabled if compiling the kernel for
1795 an embedded system so certain expert options are available
1798 config HAVE_PERF_EVENTS
1801 See tools/perf/design.txt for details.
1803 config GUEST_PERF_EVENTS
1805 depends on HAVE_PERF_EVENTS
1807 config PERF_USE_VMALLOC
1810 See tools/perf/design.txt for details
1813 bool "PC/104 support" if EXPERT
1815 Expose PC/104 form factor device drivers and options available for
1816 selection and configuration. Enable this option if your target
1817 machine has a PC/104 bus.
1819 menu "Kernel Performance Events And Counters"
1822 bool "Kernel performance events and counters"
1823 default y if PROFILING
1824 depends on HAVE_PERF_EVENTS
1828 Enable kernel support for various performance events provided
1829 by software and hardware.
1831 Software events are supported either built-in or via the
1832 use of generic tracepoints.
1834 Most modern CPUs support performance events via performance
1835 counter registers. These registers count the number of certain
1836 types of hw events: such as instructions executed, cachemisses
1837 suffered, or branches mis-predicted - without slowing down the
1838 kernel or applications. These registers can also trigger interrupts
1839 when a threshold number of events have passed - and can thus be
1840 used to profile the code that runs on that CPU.
1842 The Linux Performance Event subsystem provides an abstraction of
1843 these software and hardware event capabilities, available via a
1844 system call and used by the "perf" utility in tools/perf/. It
1845 provides per task and per CPU counters, and it provides event
1846 capabilities on top of those.
1850 config DEBUG_PERF_USE_VMALLOC
1852 bool "Debug: use vmalloc to back perf mmap() buffers"
1853 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1854 select PERF_USE_VMALLOC
1856 Use vmalloc memory to back perf mmap() buffers.
1858 Mostly useful for debugging the vmalloc code on platforms
1859 that don't require it.
1865 config VM_EVENT_COUNTERS
1867 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1869 VM event counters are needed for event counts to be shown.
1870 This option allows the disabling of the VM event counters
1871 on EXPERT systems. /proc/vmstat will only show page counts
1872 if VM event counters are disabled.
1876 bool "Enable SLUB debugging support" if EXPERT
1877 depends on SLUB && SYSFS
1879 SLUB has extensive debug support features. Disabling these can
1880 result in significant savings in code size. This also disables
1881 SLUB sysfs support. /sys/slab will not exist and there will be
1882 no support for cache validation etc.
1885 bool "Disable heap randomization"
1888 Randomizing heap placement makes heap exploits harder, but it
1889 also breaks ancient binaries (including anything libc5 based).
1890 This option changes the bootup default to heap randomization
1891 disabled, and can be overridden at runtime by setting
1892 /proc/sys/kernel/randomize_va_space to 2.
1894 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1897 prompt "Choose SLAB allocator"
1900 This option allows to select a slab allocator.
1904 depends on !PREEMPT_RT
1905 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1907 The regular slab allocator that is established and known to work
1908 well in all environments. It organizes cache hot objects in
1909 per cpu and per node queues.
1912 bool "SLUB (Unqueued Allocator)"
1913 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1915 SLUB is a slab allocator that minimizes cache line usage
1916 instead of managing queues of cached objects (SLAB approach).
1917 Per cpu caching is realized using slabs of objects instead
1918 of queues of objects. SLUB can use memory efficiently
1919 and has enhanced diagnostics. SLUB is the default choice for
1924 bool "SLOB (Simple Allocator)"
1925 depends on !PREEMPT_RT
1927 SLOB replaces the stock allocator with a drastically simpler
1928 allocator. SLOB is generally more space efficient but
1929 does not perform as well on large systems.
1933 config SLAB_MERGE_DEFAULT
1934 bool "Allow slab caches to be merged"
1936 depends on SLAB || SLUB
1938 For reduced kernel memory fragmentation, slab caches can be
1939 merged when they share the same size and other characteristics.
1940 This carries a risk of kernel heap overflows being able to
1941 overwrite objects from merged caches (and more easily control
1942 cache layout), which makes such heap attacks easier to exploit
1943 by attackers. By keeping caches unmerged, these kinds of exploits
1944 can usually only damage objects in the same cache. To disable
1945 merging at runtime, "slab_nomerge" can be passed on the kernel
1948 config SLAB_FREELIST_RANDOM
1949 bool "Randomize slab freelist"
1950 depends on SLAB || SLUB
1952 Randomizes the freelist order used on creating new pages. This
1953 security feature reduces the predictability of the kernel slab
1954 allocator against heap overflows.
1956 config SLAB_FREELIST_HARDENED
1957 bool "Harden slab freelist metadata"
1958 depends on SLAB || SLUB
1960 Many kernel heap attacks try to target slab cache metadata and
1961 other infrastructure. This options makes minor performance
1962 sacrifices to harden the kernel slab allocator against common
1963 freelist exploit methods. Some slab implementations have more
1964 sanity-checking than others. This option is most effective with
1967 config SHUFFLE_PAGE_ALLOCATOR
1968 bool "Page allocator randomization"
1969 default SLAB_FREELIST_RANDOM && ACPI_NUMA
1971 Randomization of the page allocator improves the average
1972 utilization of a direct-mapped memory-side-cache. See section
1973 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
1974 6.2a specification for an example of how a platform advertises
1975 the presence of a memory-side-cache. There are also incidental
1976 security benefits as it reduces the predictability of page
1977 allocations to compliment SLAB_FREELIST_RANDOM, but the
1978 default granularity of shuffling on the "MAX_ORDER - 1" i.e,
1979 10th order of pages is selected based on cache utilization
1982 While the randomization improves cache utilization it may
1983 negatively impact workloads on platforms without a cache. For
1984 this reason, by default, the randomization is enabled only
1985 after runtime detection of a direct-mapped memory-side-cache.
1986 Otherwise, the randomization may be force enabled with the
1987 'page_alloc.shuffle' kernel command line parameter.
1991 config SLUB_CPU_PARTIAL
1993 depends on SLUB && SMP
1994 bool "SLUB per cpu partial cache"
1996 Per cpu partial caches accelerate objects allocation and freeing
1997 that is local to a processor at the price of more indeterminism
1998 in the latency of the free. On overflow these caches will be cleared
1999 which requires the taking of locks that may cause latency spikes.
2000 Typically one would choose no for a realtime system.
2002 config MMAP_ALLOW_UNINITIALIZED
2003 bool "Allow mmapped anonymous memory to be uninitialized"
2004 depends on EXPERT && !MMU
2007 Normally, and according to the Linux spec, anonymous memory obtained
2008 from mmap() has its contents cleared before it is passed to
2009 userspace. Enabling this config option allows you to request that
2010 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
2011 providing a huge performance boost. If this option is not enabled,
2012 then the flag will be ignored.
2014 This is taken advantage of by uClibc's malloc(), and also by
2015 ELF-FDPIC binfmt's brk and stack allocator.
2017 Because of the obvious security issues, this option should only be
2018 enabled on embedded devices where you control what is run in
2019 userspace. Since that isn't generally a problem on no-MMU systems,
2020 it is normally safe to say Y here.
2022 See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
2024 config SYSTEM_DATA_VERIFICATION
2026 select SYSTEM_TRUSTED_KEYRING
2030 select ASYMMETRIC_KEY_TYPE
2031 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
2034 select X509_CERTIFICATE_PARSER
2035 select PKCS7_MESSAGE_PARSER
2037 Provide PKCS#7 message verification using the contents of the system
2038 trusted keyring to provide public keys. This then can be used for
2039 module verification, kexec image verification and firmware blob
2043 bool "Profiling support"
2045 Say Y here to enable the extended profiling support mechanisms used
2049 # Place an empty function call at each tracepoint site. Can be
2050 # dynamically changed for a probe function.
2055 endmenu # General setup
2057 source "arch/Kconfig"
2061 default y if PREEMPT_RT
2065 default 0 if BASE_FULL
2066 default 1 if !BASE_FULL
2068 config MODULE_SIG_FORMAT
2070 select SYSTEM_DATA_VERIFICATION
2073 bool "Enable loadable module support"
2076 Kernel modules are small pieces of compiled code which can
2077 be inserted in the running kernel, rather than being
2078 permanently built into the kernel. You use the "modprobe"
2079 tool to add (and sometimes remove) them. If you say Y here,
2080 many parts of the kernel can be built as modules (by
2081 answering M instead of Y where indicated): this is most
2082 useful for infrequently used options which are not required
2083 for booting. For more information, see the man pages for
2084 modprobe, lsmod, modinfo, insmod and rmmod.
2086 If you say Y here, you will need to run "make
2087 modules_install" to put the modules under /lib/modules/
2088 where modprobe can find them (you may need to be root to do
2095 config MODULE_FORCE_LOAD
2096 bool "Forced module loading"
2099 Allow loading of modules without version information (ie. modprobe
2100 --force). Forced module loading sets the 'F' (forced) taint flag and
2101 is usually a really bad idea.
2103 config MODULE_UNLOAD
2104 bool "Module unloading"
2106 Without this option you will not be able to unload any
2107 modules (note that some modules may not be unloadable
2108 anyway), which makes your kernel smaller, faster
2109 and simpler. If unsure, say Y.
2111 config MODULE_FORCE_UNLOAD
2112 bool "Forced module unloading"
2113 depends on MODULE_UNLOAD
2115 This option allows you to force a module to unload, even if the
2116 kernel believes it is unsafe: the kernel will remove the module
2117 without waiting for anyone to stop using it (using the -f option to
2118 rmmod). This is mainly for kernel developers and desperate users.
2122 bool "Module versioning support"
2124 Usually, you have to use modules compiled with your kernel.
2125 Saying Y here makes it sometimes possible to use modules
2126 compiled for different kernels, by adding enough information
2127 to the modules to (hopefully) spot any changes which would
2128 make them incompatible with the kernel you are running. If
2131 config ASM_MODVERSIONS
2133 default HAVE_ASM_MODVERSIONS && MODVERSIONS
2135 This enables module versioning for exported symbols also from
2136 assembly. This can be enabled only when the target architecture
2139 config MODULE_REL_CRCS
2141 depends on MODVERSIONS
2143 config MODULE_SRCVERSION_ALL
2144 bool "Source checksum for all modules"
2146 Modules which contain a MODULE_VERSION get an extra "srcversion"
2147 field inserted into their modinfo section, which contains a
2148 sum of the source files which made it. This helps maintainers
2149 see exactly which source was used to build a module (since
2150 others sometimes change the module source without updating
2151 the version). With this option, such a "srcversion" field
2152 will be created for all modules. If unsure, say N.
2155 bool "Module signature verification"
2156 select MODULE_SIG_FORMAT
2158 Check modules for valid signatures upon load: the signature
2159 is simply appended to the module. For more information see
2160 <file:Documentation/admin-guide/module-signing.rst>.
2162 Note that this option adds the OpenSSL development packages as a
2163 kernel build dependency so that the signing tool can use its crypto
2166 You should enable this option if you wish to use either
2167 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
2168 another LSM - otherwise unsigned modules will be loadable regardless
2169 of the lockdown policy.
2171 !!!WARNING!!! If you enable this option, you MUST make sure that the
2172 module DOES NOT get stripped after being signed. This includes the
2173 debuginfo strip done by some packagers (such as rpmbuild) and
2174 inclusion into an initramfs that wants the module size reduced.
2176 config MODULE_SIG_FORCE
2177 bool "Require modules to be validly signed"
2178 depends on MODULE_SIG
2180 Reject unsigned modules or signed modules for which we don't have a
2181 key. Without this, such modules will simply taint the kernel.
2183 config MODULE_SIG_ALL
2184 bool "Automatically sign all modules"
2186 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2188 Sign all modules during make modules_install. Without this option,
2189 modules must be signed manually, using the scripts/sign-file tool.
2191 comment "Do not forget to sign required modules with scripts/sign-file"
2192 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2195 prompt "Which hash algorithm should modules be signed with?"
2196 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2198 This determines which sort of hashing algorithm will be used during
2199 signature generation. This algorithm _must_ be built into the kernel
2200 directly so that signature verification can take place. It is not
2201 possible to load a signed module containing the algorithm to check
2202 the signature on that module.
2204 config MODULE_SIG_SHA1
2205 bool "Sign modules with SHA-1"
2208 config MODULE_SIG_SHA224
2209 bool "Sign modules with SHA-224"
2210 select CRYPTO_SHA256
2212 config MODULE_SIG_SHA256
2213 bool "Sign modules with SHA-256"
2214 select CRYPTO_SHA256
2216 config MODULE_SIG_SHA384
2217 bool "Sign modules with SHA-384"
2218 select CRYPTO_SHA512
2220 config MODULE_SIG_SHA512
2221 bool "Sign modules with SHA-512"
2222 select CRYPTO_SHA512
2226 config MODULE_SIG_HASH
2228 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2229 default "sha1" if MODULE_SIG_SHA1
2230 default "sha224" if MODULE_SIG_SHA224
2231 default "sha256" if MODULE_SIG_SHA256
2232 default "sha384" if MODULE_SIG_SHA384
2233 default "sha512" if MODULE_SIG_SHA512
2236 prompt "Module compression mode"
2238 This option allows you to choose the algorithm which will be used to
2239 compress modules when 'make modules_install' is run. (or, you can
2240 choose to not compress modules at all.)
2242 External modules will also be compressed in the same way during the
2245 For modules inside an initrd or initramfs, it's more efficient to
2246 compress the whole initrd or initramfs instead.
2248 This is fully compatible with signed modules.
2250 Please note that the tool used to load modules needs to support the
2251 corresponding algorithm. module-init-tools MAY support gzip, and kmod
2252 MAY support gzip, xz and zstd.
2254 Your build system needs to provide the appropriate compression tool
2255 to compress the modules.
2257 If in doubt, select 'None'.
2259 config MODULE_COMPRESS_NONE
2262 Do not compress modules. The installed modules are suffixed
2265 config MODULE_COMPRESS_GZIP
2268 Compress modules with GZIP. The installed modules are suffixed
2271 config MODULE_COMPRESS_XZ
2274 Compress modules with XZ. The installed modules are suffixed
2277 config MODULE_COMPRESS_ZSTD
2280 Compress modules with ZSTD. The installed modules are suffixed
2285 config MODULE_DECOMPRESS
2286 bool "Support in-kernel module decompression"
2287 depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ
2288 select ZLIB_INFLATE if MODULE_COMPRESS_GZIP
2289 select XZ_DEC if MODULE_COMPRESS_XZ
2292 Support for decompressing kernel modules by the kernel itself
2293 instead of relying on userspace to perform this task. Useful when
2294 load pinning security policy is enabled.
2298 config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
2299 bool "Allow loading of modules with missing namespace imports"
2301 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
2302 a namespace. A module that makes use of a symbol exported with such a
2303 namespace is required to import the namespace via MODULE_IMPORT_NS().
2304 There is no technical reason to enforce correct namespace imports,
2305 but it creates consistency between symbols defining namespaces and
2306 users importing namespaces they make use of. This option relaxes this
2307 requirement and lifts the enforcement when loading a module.
2311 config MODPROBE_PATH
2312 string "Path to modprobe binary"
2313 default "/sbin/modprobe"
2315 When kernel code requests a module, it does so by calling
2316 the "modprobe" userspace utility. This option allows you to
2317 set the path where that binary is found. This can be changed
2318 at runtime via the sysctl file
2319 /proc/sys/kernel/modprobe. Setting this to the empty string
2320 removes the kernel's ability to request modules (but
2321 userspace can still load modules explicitly).
2323 config TRIM_UNUSED_KSYMS
2324 bool "Trim unused exported kernel symbols" if EXPERT
2325 depends on !COMPILE_TEST
2327 The kernel and some modules make many symbols available for
2328 other modules to use via EXPORT_SYMBOL() and variants. Depending
2329 on the set of modules being selected in your kernel configuration,
2330 many of those exported symbols might never be used.
2332 This option allows for unused exported symbols to be dropped from
2333 the build. In turn, this provides the compiler more opportunities
2334 (especially when using LTO) for optimizing the code and reducing
2335 binary size. This might have some security advantages as well.
2337 If unsure, or if you need to build out-of-tree modules, say N.
2339 config UNUSED_KSYMS_WHITELIST
2340 string "Whitelist of symbols to keep in ksymtab"
2341 depends on TRIM_UNUSED_KSYMS
2343 By default, all unused exported symbols will be un-exported from the
2344 build when TRIM_UNUSED_KSYMS is selected.
2346 UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
2347 exported at all times, even in absence of in-tree users. The value to
2348 set here is the path to a text file containing the list of symbols,
2349 one per line. The path can be absolute, or relative to the kernel
2354 config MODULES_TREE_LOOKUP
2356 depends on PERF_EVENTS || TRACING || CFI_CLANG
2358 config INIT_ALL_POSSIBLE
2361 Back when each arch used to define their own cpu_online_mask and
2362 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2363 with all 1s, and others with all 0s. When they were centralised,
2364 it was better to provide this option than to break all the archs
2365 and have several arch maintainers pursuing me down dark alleys.
2367 source "block/Kconfig"
2369 config PREEMPT_NOTIFIERS
2379 Build a simple ASN.1 grammar compiler that produces a bytecode output
2380 that can be interpreted by the ASN.1 stream decoder and used to
2381 inform it as to what tags are to be expected in a stream and what
2382 functions to call on what tags.
2384 source "kernel/Kconfig.locks"
2386 config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
2389 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
2392 # It may be useful for an architecture to override the definitions of the
2393 # SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
2394 # and the COMPAT_ variants in <linux/compat.h>, in particular to use a
2395 # different calling convention for syscalls. They can also override the
2396 # macros for not-implemented syscalls in kernel/sys_ni.c and
2397 # kernel/time/posix-stubs.c. All these overrides need to be available in
2398 # <asm/syscall_wrapper.h>.
2399 config ARCH_HAS_SYSCALL_WRAPPER
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