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 CC_HAS_ASM_GOTO_TIED_OUTPUT
81 depends on CC_HAS_ASM_GOTO_OUTPUT
82 # Detect buggy gcc and clang, fixed in gcc-11 clang-14.
83 def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)
85 config TOOLS_SUPPORT_RELR
86 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
88 config CC_HAS_ASM_INLINE
89 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
91 config CC_HAS_NO_PROFILE_FN_ATTR
92 def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror)
96 default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
104 config BUILDTIME_TABLE_SORT
107 config THREAD_INFO_IN_TASK
110 Select this to move thread_info off the stack into task_struct. To
111 make this work, an arch will need to remove all thread_info fields
112 except flags and fix any runtime bugs.
114 One subtle change that will be needed is to use try_get_task_stack()
115 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
124 depends on BROKEN || !SMP
127 config INIT_ENV_ARG_LIMIT
132 Maximum of each of the number of arguments and environment
133 variables passed to init from the kernel command line.
136 bool "Compile also drivers which will not load"
139 Some drivers can be compiled on a different platform than they are
140 intended to be run on. Despite they cannot be loaded there (or even
141 when they load they cannot be used due to missing HW support),
142 developers still, opposing to distributors, might want to build such
143 drivers to compile-test them.
145 If you are a developer and want to build everything available, say Y
146 here. If you are a user/distributor, say N here to exclude useless
147 drivers to be distributed.
150 bool "Compile the kernel with warnings as errors"
153 A kernel build should not cause any compiler warnings, and this
154 enables the '-Werror' flag to enforce that rule by default.
156 However, if you have a new (or very old) compiler with odd and
157 unusual warnings, or you have some architecture with problems,
158 you may need to disable this config option in order to
159 successfully build the kernel.
163 config UAPI_HEADER_TEST
164 bool "Compile test UAPI headers"
165 depends on HEADERS_INSTALL && CC_CAN_LINK
167 Compile test headers exported to user-space to ensure they are
168 self-contained, i.e. compilable as standalone units.
170 If you are a developer or tester and want to ensure the exported
171 headers are self-contained, say Y here. Otherwise, choose N.
174 string "Local version - append to kernel release"
176 Append an extra string to the end of your kernel version.
177 This will show up when you type uname, for example.
178 The string you set here will be appended after the contents of
179 any files with a filename matching localversion* in your
180 object and source tree, in that order. Your total string can
181 be a maximum of 64 characters.
183 config LOCALVERSION_AUTO
184 bool "Automatically append version information to the version string"
186 depends on !COMPILE_TEST
188 This will try to automatically determine if the current tree is a
189 release tree by looking for git tags that belong to the current
190 top of tree revision.
192 A string of the format -gxxxxxxxx will be added to the localversion
193 if a git-based tree is found. The string generated by this will be
194 appended after any matching localversion* files, and after the value
195 set in CONFIG_LOCALVERSION.
197 (The actual string used here is the first eight characters produced
198 by running the command:
200 $ git rev-parse --verify HEAD
202 which is done within the script "scripts/setlocalversion".)
205 string "Build ID Salt"
208 The build ID is used to link binaries and their debug info. Setting
209 this option will use the value in the calculation of the build id.
210 This is mostly useful for distributions which want to ensure the
211 build is unique between builds. It's safe to leave the default.
213 config HAVE_KERNEL_GZIP
216 config HAVE_KERNEL_BZIP2
219 config HAVE_KERNEL_LZMA
222 config HAVE_KERNEL_XZ
225 config HAVE_KERNEL_LZO
228 config HAVE_KERNEL_LZ4
231 config HAVE_KERNEL_ZSTD
234 config HAVE_KERNEL_UNCOMPRESSED
238 prompt "Kernel compression mode"
240 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
242 The linux kernel is a kind of self-extracting executable.
243 Several compression algorithms are available, which differ
244 in efficiency, compression and decompression speed.
245 Compression speed is only relevant when building a kernel.
246 Decompression speed is relevant at each boot.
248 If you have any problems with bzip2 or lzma compressed
249 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
250 version of this functionality (bzip2 only), for 2.4, was
251 supplied by Christian Ludwig)
253 High compression options are mostly useful for users, who
254 are low on disk space (embedded systems), but for whom ram
257 If in doubt, select 'gzip'
261 depends on HAVE_KERNEL_GZIP
263 The old and tried gzip compression. It provides a good balance
264 between compression ratio and decompression speed.
268 depends on HAVE_KERNEL_BZIP2
270 Its compression ratio and speed is intermediate.
271 Decompression speed is slowest among the choices. The kernel
272 size is about 10% smaller with bzip2, in comparison to gzip.
273 Bzip2 uses a large amount of memory. For modern kernels you
274 will need at least 8MB RAM or more for booting.
278 depends on HAVE_KERNEL_LZMA
280 This compression algorithm's ratio is best. Decompression speed
281 is between gzip and bzip2. Compression is slowest.
282 The kernel size is about 33% smaller with LZMA in comparison to gzip.
286 depends on HAVE_KERNEL_XZ
288 XZ uses the LZMA2 algorithm and instruction set specific
289 BCJ filters which can improve compression ratio of executable
290 code. The size of the kernel is about 30% smaller with XZ in
291 comparison to gzip. On architectures for which there is a BCJ
292 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
293 will create a few percent smaller kernel than plain LZMA.
295 The speed is about the same as with LZMA: The decompression
296 speed of XZ is better than that of bzip2 but worse than gzip
297 and LZO. Compression is slow.
301 depends on HAVE_KERNEL_LZO
303 Its compression ratio is the poorest among the choices. The kernel
304 size is about 10% bigger than gzip; however its speed
305 (both compression and decompression) is the fastest.
309 depends on HAVE_KERNEL_LZ4
311 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
312 A preliminary version of LZ4 de/compression tool is available at
313 <https://code.google.com/p/lz4/>.
315 Its compression ratio is worse than LZO. The size of the kernel
316 is about 8% bigger than LZO. But the decompression speed is
321 depends on HAVE_KERNEL_ZSTD
323 ZSTD is a compression algorithm targeting intermediate compression
324 with fast decompression speed. It will compress better than GZIP and
325 decompress around the same speed as LZO, but slower than LZ4. You
326 will need at least 192 KB RAM or more for booting. The zstd command
327 line tool is required for compression.
329 config KERNEL_UNCOMPRESSED
331 depends on HAVE_KERNEL_UNCOMPRESSED
333 Produce uncompressed kernel image. This option is usually not what
334 you want. It is useful for debugging the kernel in slow simulation
335 environments, where decompressing and moving the kernel is awfully
336 slow. This option allows early boot code to skip the decompressor
337 and jump right at uncompressed kernel image.
342 string "Default init path"
345 This option determines the default init for the system if no init=
346 option is passed on the kernel command line. If the requested path is
347 not present, we will still then move on to attempting further
348 locations (e.g. /sbin/init, etc). If this is empty, we will just use
349 the fallback list when init= is not passed.
351 config DEFAULT_HOSTNAME
352 string "Default hostname"
355 This option determines the default system hostname before userspace
356 calls sethostname(2). The kernel traditionally uses "(none)" here,
357 but you may wish to use a different default here to make a minimal
358 system more usable with less configuration.
363 Inter Process Communication is a suite of library functions and
364 system calls which let processes (running programs) synchronize and
365 exchange information. It is generally considered to be a good thing,
366 and some programs won't run unless you say Y here. In particular, if
367 you want to run the DOS emulator dosemu under Linux (read the
368 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
369 you'll need to say Y here.
371 You can find documentation about IPC with "info ipc" and also in
372 section 6.4 of the Linux Programmer's Guide, available from
373 <http://www.tldp.org/guides.html>.
375 config SYSVIPC_SYSCTL
382 bool "POSIX Message Queues"
385 POSIX variant of message queues is a part of IPC. In POSIX message
386 queues every message has a priority which decides about succession
387 of receiving it by a process. If you want to compile and run
388 programs written e.g. for Solaris with use of its POSIX message
389 queues (functions mq_*) say Y here.
391 POSIX message queues are visible as a filesystem called 'mqueue'
392 and can be mounted somewhere if you want to do filesystem
393 operations on message queues.
397 config POSIX_MQUEUE_SYSCTL
399 depends on POSIX_MQUEUE
404 bool "General notification queue"
408 This is a general notification queue for the kernel to pass events to
409 userspace by splicing them into pipes. It can be used in conjunction
410 with watches for key/keyring change notifications and device
413 See Documentation/watch_queue.rst
415 config CROSS_MEMORY_ATTACH
416 bool "Enable process_vm_readv/writev syscalls"
420 Enabling this option adds the system calls process_vm_readv and
421 process_vm_writev which allow a process with the correct privileges
422 to directly read from or write to another process' address space.
423 See the man page for more details.
426 bool "uselib syscall"
427 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
429 This option enables the uselib syscall, a system call used in the
430 dynamic linker from libc5 and earlier. glibc does not use this
431 system call. If you intend to run programs built on libc5 or
432 earlier, you may need to enable this syscall. Current systems
433 running glibc can safely disable this.
436 bool "Auditing support"
439 Enable auditing infrastructure that can be used with another
440 kernel subsystem, such as SELinux (which requires this for
441 logging of avc messages output). System call auditing is included
442 on architectures which support it.
444 config HAVE_ARCH_AUDITSYSCALL
449 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
452 source "kernel/irq/Kconfig"
453 source "kernel/time/Kconfig"
454 source "kernel/bpf/Kconfig"
455 source "kernel/Kconfig.preempt"
457 menu "CPU/Task time and stats accounting"
459 config VIRT_CPU_ACCOUNTING
463 prompt "Cputime accounting"
464 default TICK_CPU_ACCOUNTING if !PPC64
465 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
467 # Kind of a stub config for the pure tick based cputime accounting
468 config TICK_CPU_ACCOUNTING
469 bool "Simple tick based cputime accounting"
470 depends on !S390 && !NO_HZ_FULL
472 This is the basic tick based cputime accounting that maintains
473 statistics about user, system and idle time spent on per jiffies
478 config VIRT_CPU_ACCOUNTING_NATIVE
479 bool "Deterministic task and CPU time accounting"
480 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
481 select VIRT_CPU_ACCOUNTING
483 Select this option to enable more accurate task and CPU time
484 accounting. This is done by reading a CPU counter on each
485 kernel entry and exit and on transitions within the kernel
486 between system, softirq and hardirq state, so there is a
487 small performance impact. In the case of s390 or IBM POWER > 5,
488 this also enables accounting of stolen time on logically-partitioned
491 config VIRT_CPU_ACCOUNTING_GEN
492 bool "Full dynticks CPU time accounting"
493 depends on HAVE_CONTEXT_TRACKING
494 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
495 depends on GENERIC_CLOCKEVENTS
496 select VIRT_CPU_ACCOUNTING
497 select CONTEXT_TRACKING
499 Select this option to enable task and CPU time accounting on full
500 dynticks systems. This accounting is implemented by watching every
501 kernel-user boundaries using the context tracking subsystem.
502 The accounting is thus performed at the expense of some significant
505 For now this is only useful if you are working on the full
506 dynticks subsystem development.
512 config IRQ_TIME_ACCOUNTING
513 bool "Fine granularity task level IRQ time accounting"
514 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
516 Select this option to enable fine granularity task irq time
517 accounting. This is done by reading a timestamp on each
518 transitions between softirq and hardirq state, so there can be a
519 small performance impact.
521 If in doubt, say N here.
523 config HAVE_SCHED_AVG_IRQ
525 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
528 config SCHED_THERMAL_PRESSURE
530 default y if ARM && ARM_CPU_TOPOLOGY
533 depends on CPU_FREQ_THERMAL
535 Select this option to enable thermal pressure accounting in the
536 scheduler. Thermal pressure is the value conveyed to the scheduler
537 that reflects the reduction in CPU compute capacity resulted from
538 thermal throttling. Thermal throttling occurs when the performance of
539 a CPU is capped due to high operating temperatures.
541 If selected, the scheduler will be able to balance tasks accordingly,
542 i.e. put less load on throttled CPUs than on non/less throttled ones.
544 This requires the architecture to implement
545 arch_update_thermal_pressure() and arch_scale_thermal_pressure().
547 config BSD_PROCESS_ACCT
548 bool "BSD Process Accounting"
551 If you say Y here, a user level program will be able to instruct the
552 kernel (via a special system call) to write process accounting
553 information to a file: whenever a process exits, information about
554 that process will be appended to the file by the kernel. The
555 information includes things such as creation time, owning user,
556 command name, memory usage, controlling terminal etc. (the complete
557 list is in the struct acct in <file:include/linux/acct.h>). It is
558 up to the user level program to do useful things with this
559 information. This is generally a good idea, so say Y.
561 config BSD_PROCESS_ACCT_V3
562 bool "BSD Process Accounting version 3 file format"
563 depends on BSD_PROCESS_ACCT
566 If you say Y here, the process accounting information is written
567 in a new file format that also logs the process IDs of each
568 process and its parent. Note that this file format is incompatible
569 with previous v0/v1/v2 file formats, so you will need updated tools
570 for processing it. A preliminary version of these tools is available
571 at <http://www.gnu.org/software/acct/>.
574 bool "Export task/process statistics through netlink"
579 Export selected statistics for tasks/processes through the
580 generic netlink interface. Unlike BSD process accounting, the
581 statistics are available during the lifetime of tasks/processes as
582 responses to commands. Like BSD accounting, they are sent to user
587 config TASK_DELAY_ACCT
588 bool "Enable per-task delay accounting"
592 Collect information on time spent by a task waiting for system
593 resources like cpu, synchronous block I/O completion and swapping
594 in pages. Such statistics can help in setting a task's priorities
595 relative to other tasks for cpu, io, rss limits etc.
600 bool "Enable extended accounting over taskstats"
603 Collect extended task accounting data and send the data
604 to userland for processing over the taskstats interface.
608 config TASK_IO_ACCOUNTING
609 bool "Enable per-task storage I/O accounting"
610 depends on TASK_XACCT
612 Collect information on the number of bytes of storage I/O which this
618 bool "Pressure stall information tracking"
620 Collect metrics that indicate how overcommitted the CPU, memory,
621 and IO capacity are in the system.
623 If you say Y here, the kernel will create /proc/pressure/ with the
624 pressure statistics files cpu, memory, and io. These will indicate
625 the share of walltime in which some or all tasks in the system are
626 delayed due to contention of the respective resource.
628 In kernels with cgroup support, cgroups (cgroup2 only) will
629 have cpu.pressure, memory.pressure, and io.pressure files,
630 which aggregate pressure stalls for the grouped tasks only.
632 For more details see Documentation/accounting/psi.rst.
636 config PSI_DEFAULT_DISABLED
637 bool "Require boot parameter to enable pressure stall information tracking"
641 If set, pressure stall information tracking will be disabled
642 per default but can be enabled through passing psi=1 on the
643 kernel commandline during boot.
645 This feature adds some code to the task wakeup and sleep
646 paths of the scheduler. The overhead is too low to affect
647 common scheduling-intense workloads in practice (such as
648 webservers, memcache), but it does show up in artificial
649 scheduler stress tests, such as hackbench.
651 If you are paranoid and not sure what the kernel will be
656 endmenu # "CPU/Task time and stats accounting"
660 depends on SMP || COMPILE_TEST
663 Make sure that CPUs running critical tasks are not disturbed by
664 any source of "noise" such as unbound workqueues, timers, kthreads...
665 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
666 the "isolcpus=" boot parameter.
670 source "kernel/rcu/Kconfig"
677 tristate "Kernel .config support"
679 This option enables the complete Linux kernel ".config" file
680 contents to be saved in the kernel. It provides documentation
681 of which kernel options are used in a running kernel or in an
682 on-disk kernel. This information can be extracted from the kernel
683 image file with the script scripts/extract-ikconfig and used as
684 input to rebuild the current kernel or to build another kernel.
685 It can also be extracted from a running kernel by reading
686 /proc/config.gz if enabled (below).
689 bool "Enable access to .config through /proc/config.gz"
690 depends on IKCONFIG && PROC_FS
692 This option enables access to the kernel configuration file
693 through /proc/config.gz.
696 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
699 This option enables access to the in-kernel headers that are generated during
700 the build process. These can be used to build eBPF tracing programs,
701 or similar programs. If you build the headers as a module, a module called
702 kheaders.ko is built which can be loaded on-demand to get access to headers.
705 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
710 Select the minimal kernel log buffer size as a power of 2.
711 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
712 parameter, see below. Any higher size also might be forced
713 by "log_buf_len" boot parameter.
723 config LOG_CPU_MAX_BUF_SHIFT
724 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
727 default 12 if !BASE_SMALL
728 default 0 if BASE_SMALL
731 This option allows to increase the default ring buffer size
732 according to the number of CPUs. The value defines the contribution
733 of each CPU as a power of 2. The used space is typically only few
734 lines however it might be much more when problems are reported,
737 The increased size means that a new buffer has to be allocated and
738 the original static one is unused. It makes sense only on systems
739 with more CPUs. Therefore this value is used only when the sum of
740 contributions is greater than the half of the default kernel ring
741 buffer as defined by LOG_BUF_SHIFT. The default values are set
742 so that more than 16 CPUs are needed to trigger the allocation.
744 Also this option is ignored when "log_buf_len" kernel parameter is
745 used as it forces an exact (power of two) size of the ring buffer.
747 The number of possible CPUs is used for this computation ignoring
748 hotplugging making the computation optimal for the worst case
749 scenario while allowing a simple algorithm to be used from bootup.
751 Examples shift values and their meaning:
752 17 => 128 KB for each CPU
753 16 => 64 KB for each CPU
754 15 => 32 KB for each CPU
755 14 => 16 KB for each CPU
756 13 => 8 KB for each CPU
757 12 => 4 KB for each CPU
759 config PRINTK_SAFE_LOG_BUF_SHIFT
760 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
765 Select the size of an alternate printk per-CPU buffer where messages
766 printed from usafe contexts are temporary stored. One example would
767 be NMI messages, another one - printk recursion. The messages are
768 copied to the main log buffer in a safe context to avoid a deadlock.
769 The value defines the size as a power of 2.
771 Those messages are rare and limited. The largest one is when
772 a backtrace is printed. It usually fits into 4KB. Select
773 8KB if you want to be on the safe side.
776 17 => 128 KB for each CPU
777 16 => 64 KB for each CPU
778 15 => 32 KB for each CPU
779 14 => 16 KB for each CPU
780 13 => 8 KB for each CPU
781 12 => 4 KB for each CPU
784 bool "Printk indexing debugfs interface"
785 depends on PRINTK && DEBUG_FS
787 Add support for indexing of all printk formats known at compile time
788 at <debugfs>/printk/index/<module>.
790 This can be used as part of maintaining daemons which monitor
791 /dev/kmsg, as it permits auditing the printk formats present in a
792 kernel, allowing detection of cases where monitored printks are
793 changed or no longer present.
795 There is no additional runtime cost to printk with this enabled.
798 # Architectures with an unreliable sched_clock() should select this:
800 config HAVE_UNSTABLE_SCHED_CLOCK
803 config GENERIC_SCHED_CLOCK
806 menu "Scheduler features"
809 bool "Enable utilization clamping for RT/FAIR tasks"
810 depends on CPU_FREQ_GOV_SCHEDUTIL
812 This feature enables the scheduler to track the clamped utilization
813 of each CPU based on RUNNABLE tasks scheduled on that CPU.
815 With this option, the user can specify the min and max CPU
816 utilization allowed for RUNNABLE tasks. The max utilization defines
817 the maximum frequency a task should use while the min utilization
818 defines the minimum frequency it should use.
820 Both min and max utilization clamp values are hints to the scheduler,
821 aiming at improving its frequency selection policy, but they do not
822 enforce or grant any specific bandwidth for tasks.
826 config UCLAMP_BUCKETS_COUNT
827 int "Number of supported utilization clamp buckets"
830 depends on UCLAMP_TASK
832 Defines the number of clamp buckets to use. The range of each bucket
833 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
834 number of clamp buckets the finer their granularity and the higher
835 the precision of clamping aggregation and tracking at run-time.
837 For example, with the minimum configuration value we will have 5
838 clamp buckets tracking 20% utilization each. A 25% boosted tasks will
839 be refcounted in the [20..39]% bucket and will set the bucket clamp
840 effective value to 25%.
841 If a second 30% boosted task should be co-scheduled on the same CPU,
842 that task will be refcounted in the same bucket of the first task and
843 it will boost the bucket clamp effective value to 30%.
844 The clamp effective value of a bucket is reset to its nominal value
845 (20% in the example above) when there are no more tasks refcounted in
848 An additional boost/capping margin can be added to some tasks. In the
849 example above the 25% task will be boosted to 30% until it exits the
850 CPU. If that should be considered not acceptable on certain systems,
851 it's always possible to reduce the margin by increasing the number of
852 clamp buckets to trade off used memory for run-time tracking
855 If in doubt, use the default value.
860 # For architectures that want to enable the support for NUMA-affine scheduler
863 config ARCH_SUPPORTS_NUMA_BALANCING
867 # For architectures that prefer to flush all TLBs after a number of pages
868 # are unmapped instead of sending one IPI per page to flush. The architecture
869 # must provide guarantees on what happens if a clean TLB cache entry is
870 # written after the unmap. Details are in mm/rmap.c near the check for
871 # should_defer_flush. The architecture should also consider if the full flush
872 # and the refill costs are offset by the savings of sending fewer IPIs.
873 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
877 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
879 config CC_IMPLICIT_FALLTHROUGH
881 default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5)
882 default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough)
885 # For architectures that know their GCC __int128 support is sound
887 config ARCH_SUPPORTS_INT128
890 # For architectures that (ab)use NUMA to represent different memory regions
891 # all cpu-local but of different latencies, such as SuperH.
893 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
896 config NUMA_BALANCING
897 bool "Memory placement aware NUMA scheduler"
898 depends on ARCH_SUPPORTS_NUMA_BALANCING
899 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
900 depends on SMP && NUMA && MIGRATION && !PREEMPT_RT
902 This option adds support for automatic NUMA aware memory/task placement.
903 The mechanism is quite primitive and is based on migrating memory when
904 it has references to the node the task is running on.
906 This system will be inactive on UMA systems.
908 config NUMA_BALANCING_DEFAULT_ENABLED
909 bool "Automatically enable NUMA aware memory/task placement"
911 depends on NUMA_BALANCING
913 If set, automatic NUMA balancing will be enabled if running on a NUMA
917 bool "Control Group support"
920 This option adds support for grouping sets of processes together, for
921 use with process control subsystems such as Cpusets, CFS, memory
922 controls or device isolation.
924 - Documentation/scheduler/sched-design-CFS.rst (CFS)
925 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
926 and resource control)
936 bool "Memory controller"
940 Provides control over the memory footprint of tasks in a cgroup.
944 depends on MEMCG && SWAP
949 depends on MEMCG && !SLOB
957 Generic block IO controller cgroup interface. This is the common
958 cgroup interface which should be used by various IO controlling
961 Currently, CFQ IO scheduler uses it to recognize task groups and
962 control disk bandwidth allocation (proportional time slice allocation)
963 to such task groups. It is also used by bio throttling logic in
964 block layer to implement upper limit in IO rates on a device.
966 This option only enables generic Block IO controller infrastructure.
967 One needs to also enable actual IO controlling logic/policy. For
968 enabling proportional weight division of disk bandwidth in CFQ, set
969 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
970 CONFIG_BLK_DEV_THROTTLING=y.
972 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
974 config CGROUP_WRITEBACK
976 depends on MEMCG && BLK_CGROUP
979 menuconfig CGROUP_SCHED
980 bool "CPU controller"
983 This feature lets CPU scheduler recognize task groups and control CPU
984 bandwidth allocation to such task groups. It uses cgroups to group
988 config FAIR_GROUP_SCHED
989 bool "Group scheduling for SCHED_OTHER"
990 depends on CGROUP_SCHED
994 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
995 depends on FAIR_GROUP_SCHED
998 This option allows users to define CPU bandwidth rates (limits) for
999 tasks running within the fair group scheduler. Groups with no limit
1000 set are considered to be unconstrained and will run with no
1002 See Documentation/scheduler/sched-bwc.rst for more information.
1004 config RT_GROUP_SCHED
1005 bool "Group scheduling for SCHED_RR/FIFO"
1006 depends on CGROUP_SCHED
1009 This feature lets you explicitly allocate real CPU bandwidth
1010 to task groups. If enabled, it will also make it impossible to
1011 schedule realtime tasks for non-root users until you allocate
1012 realtime bandwidth for them.
1013 See Documentation/scheduler/sched-rt-group.rst for more information.
1017 config UCLAMP_TASK_GROUP
1018 bool "Utilization clamping per group of tasks"
1019 depends on CGROUP_SCHED
1020 depends on UCLAMP_TASK
1023 This feature enables the scheduler to track the clamped utilization
1024 of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
1026 When this option is enabled, the user can specify a min and max
1027 CPU bandwidth which is allowed for each single task in a group.
1028 The max bandwidth allows to clamp the maximum frequency a task
1029 can use, while the min bandwidth allows to define a minimum
1030 frequency a task will always use.
1032 When task group based utilization clamping is enabled, an eventually
1033 specified task-specific clamp value is constrained by the cgroup
1034 specified clamp value. Both minimum and maximum task clamping cannot
1035 be bigger than the corresponding clamping defined at task group level.
1040 bool "PIDs controller"
1042 Provides enforcement of process number limits in the scope of a
1043 cgroup. Any attempt to fork more processes than is allowed in the
1044 cgroup will fail. PIDs are fundamentally a global resource because it
1045 is fairly trivial to reach PID exhaustion before you reach even a
1046 conservative kmemcg limit. As a result, it is possible to grind a
1047 system to halt without being limited by other cgroup policies. The
1048 PIDs controller is designed to stop this from happening.
1050 It should be noted that organisational operations (such as attaching
1051 to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
1052 since the PIDs limit only affects a process's ability to fork, not to
1056 bool "RDMA controller"
1058 Provides enforcement of RDMA resources defined by IB stack.
1059 It is fairly easy for consumers to exhaust RDMA resources, which
1060 can result into resource unavailability to other consumers.
1061 RDMA controller is designed to stop this from happening.
1062 Attaching processes with active RDMA resources to the cgroup
1063 hierarchy is allowed even if can cross the hierarchy's limit.
1065 config CGROUP_FREEZER
1066 bool "Freezer controller"
1068 Provides a way to freeze and unfreeze all tasks in a
1071 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
1072 controller includes important in-kernel memory consumers per default.
1074 If you're using cgroup2, say N.
1076 config CGROUP_HUGETLB
1077 bool "HugeTLB controller"
1078 depends on HUGETLB_PAGE
1082 Provides a cgroup controller for HugeTLB pages.
1083 When you enable this, you can put a per cgroup limit on HugeTLB usage.
1084 The limit is enforced during page fault. Since HugeTLB doesn't
1085 support page reclaim, enforcing the limit at page fault time implies
1086 that, the application will get SIGBUS signal if it tries to access
1087 HugeTLB pages beyond its limit. This requires the application to know
1088 beforehand how much HugeTLB pages it would require for its use. The
1089 control group is tracked in the third page lru pointer. This means
1090 that we cannot use the controller with huge page less than 3 pages.
1093 bool "Cpuset controller"
1096 This option will let you create and manage CPUSETs which
1097 allow dynamically partitioning a system into sets of CPUs and
1098 Memory Nodes and assigning tasks to run only within those sets.
1099 This is primarily useful on large SMP or NUMA systems.
1103 config PROC_PID_CPUSET
1104 bool "Include legacy /proc/<pid>/cpuset file"
1108 config CGROUP_DEVICE
1109 bool "Device controller"
1111 Provides a cgroup controller implementing whitelists for
1112 devices which a process in the cgroup can mknod or open.
1114 config CGROUP_CPUACCT
1115 bool "Simple CPU accounting controller"
1117 Provides a simple controller for monitoring the
1118 total CPU consumed by the tasks in a cgroup.
1121 bool "Perf controller"
1122 depends on PERF_EVENTS
1124 This option extends the perf per-cpu mode to restrict monitoring
1125 to threads which belong to the cgroup specified and run on the
1126 designated cpu. Or this can be used to have cgroup ID in samples
1127 so that it can monitor performance events among cgroups.
1132 bool "Support for eBPF programs attached to cgroups"
1133 depends on BPF_SYSCALL
1134 select SOCK_CGROUP_DATA
1136 Allow attaching eBPF programs to a cgroup using the bpf(2)
1137 syscall command BPF_PROG_ATTACH.
1139 In which context these programs are accessed depends on the type
1140 of attachment. For instance, programs that are attached using
1141 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1145 bool "Misc resource controller"
1148 Provides a controller for miscellaneous resources on a host.
1150 Miscellaneous scalar resources are the resources on the host system
1151 which cannot be abstracted like the other cgroups. This controller
1152 tracks and limits the miscellaneous resources used by a process
1153 attached to a cgroup hierarchy.
1155 For more information, please check misc cgroup section in
1156 /Documentation/admin-guide/cgroup-v2.rst.
1159 bool "Debug controller"
1161 depends on DEBUG_KERNEL
1163 This option enables a simple controller that exports
1164 debugging information about the cgroups framework. This
1165 controller is for control cgroup debugging only. Its
1166 interfaces are not stable.
1170 config SOCK_CGROUP_DATA
1176 menuconfig NAMESPACES
1177 bool "Namespaces support" if EXPERT
1178 depends on MULTIUSER
1181 Provides the way to make tasks work with different objects using
1182 the same id. For example same IPC id may refer to different objects
1183 or same user id or pid may refer to different tasks when used in
1184 different namespaces.
1189 bool "UTS namespace"
1192 In this namespace tasks see different info provided with the
1196 bool "TIME namespace"
1197 depends on GENERIC_VDSO_TIME_NS
1200 In this namespace boottime and monotonic clocks can be set.
1201 The time will keep going with the same pace.
1204 bool "IPC namespace"
1205 depends on (SYSVIPC || POSIX_MQUEUE)
1208 In this namespace tasks work with IPC ids which correspond to
1209 different IPC objects in different namespaces.
1212 bool "User namespace"
1215 This allows containers, i.e. vservers, to use user namespaces
1216 to provide different user info for different servers.
1218 When user namespaces are enabled in the kernel it is
1219 recommended that the MEMCG option also be enabled and that
1220 user-space use the memory control groups to limit the amount
1221 of memory a memory unprivileged users can use.
1226 bool "PID Namespaces"
1229 Support process id namespaces. This allows having multiple
1230 processes with the same pid as long as they are in different
1231 pid namespaces. This is a building block of containers.
1234 bool "Network namespace"
1238 Allow user space to create what appear to be multiple instances
1239 of the network stack.
1243 config CHECKPOINT_RESTORE
1244 bool "Checkpoint/restore support"
1245 select PROC_CHILDREN
1249 Enables additional kernel features in a sake of checkpoint/restore.
1250 In particular it adds auxiliary prctl codes to setup process text,
1251 data and heap segment sizes, and a few additional /proc filesystem
1254 If unsure, say N here.
1256 config SCHED_AUTOGROUP
1257 bool "Automatic process group scheduling"
1260 select FAIR_GROUP_SCHED
1262 This option optimizes the scheduler for common desktop workloads by
1263 automatically creating and populating task groups. This separation
1264 of workloads isolates aggressive CPU burners (like build jobs) from
1265 desktop applications. Task group autogeneration is currently based
1268 config SYSFS_DEPRECATED
1269 bool "Enable deprecated sysfs features to support old userspace tools"
1273 This option adds code that switches the layout of the "block" class
1274 devices, to not show up in /sys/class/block/, but only in
1277 This switch is only active when the sysfs.deprecated=1 boot option is
1278 passed or the SYSFS_DEPRECATED_V2 option is set.
1280 This option allows new kernels to run on old distributions and tools,
1281 which might get confused by /sys/class/block/. Since 2007/2008 all
1282 major distributions and tools handle this just fine.
1284 Recent distributions and userspace tools after 2009/2010 depend on
1285 the existence of /sys/class/block/, and will not work with this
1288 Only if you are using a new kernel on an old distribution, you might
1291 config SYSFS_DEPRECATED_V2
1292 bool "Enable deprecated sysfs features by default"
1295 depends on SYSFS_DEPRECATED
1297 Enable deprecated sysfs by default.
1299 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1302 Only if you are using a new kernel on an old distribution, you might
1303 need to say Y here. Even then, odds are you would not need it
1304 enabled, you can always pass the boot option if absolutely necessary.
1307 bool "Kernel->user space relay support (formerly relayfs)"
1310 This option enables support for relay interface support in
1311 certain file systems (such as debugfs).
1312 It is designed to provide an efficient mechanism for tools and
1313 facilities to relay large amounts of data from kernel space to
1318 config BLK_DEV_INITRD
1319 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1321 The initial RAM filesystem is a ramfs which is loaded by the
1322 boot loader (loadlin or lilo) and that is mounted as root
1323 before the normal boot procedure. It is typically used to
1324 load modules needed to mount the "real" root file system,
1325 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1327 If RAM disk support (BLK_DEV_RAM) is also included, this
1328 also enables initial RAM disk (initrd) support and adds
1329 15 Kbytes (more on some other architectures) to the kernel size.
1335 source "usr/Kconfig"
1340 bool "Boot config support"
1341 select BLK_DEV_INITRD
1343 Extra boot config allows system admin to pass a config file as
1344 complemental extension of kernel cmdline when booting.
1345 The boot config file must be attached at the end of initramfs
1346 with checksum, size and magic word.
1347 See <file:Documentation/admin-guide/bootconfig.rst> for details.
1352 prompt "Compiler optimization level"
1353 default CC_OPTIMIZE_FOR_PERFORMANCE
1355 config CC_OPTIMIZE_FOR_PERFORMANCE
1356 bool "Optimize for performance (-O2)"
1358 This is the default optimization level for the kernel, building
1359 with the "-O2" compiler flag for best performance and most
1360 helpful compile-time warnings.
1362 config CC_OPTIMIZE_FOR_PERFORMANCE_O3
1363 bool "Optimize more for performance (-O3)"
1366 Choosing this option will pass "-O3" to your compiler to optimize
1367 the kernel yet more for performance.
1369 config CC_OPTIMIZE_FOR_SIZE
1370 bool "Optimize for size (-Os)"
1372 Choosing this option will pass "-Os" to your compiler resulting
1373 in a smaller kernel.
1377 config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1380 This requires that the arch annotates or otherwise protects
1381 its external entry points from being discarded. Linker scripts
1382 must also merge .text.*, .data.*, and .bss.* correctly into
1383 output sections. Care must be taken not to pull in unrelated
1384 sections (e.g., '.text.init'). Typically '.' in section names
1385 is used to distinguish them from label names / C identifiers.
1387 config LD_DEAD_CODE_DATA_ELIMINATION
1388 bool "Dead code and data elimination (EXPERIMENTAL)"
1389 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1391 depends on $(cc-option,-ffunction-sections -fdata-sections)
1392 depends on $(ld-option,--gc-sections)
1394 Enable this if you want to do dead code and data elimination with
1395 the linker by compiling with -ffunction-sections -fdata-sections,
1396 and linking with --gc-sections.
1398 This can reduce on disk and in-memory size of the kernel
1399 code and static data, particularly for small configs and
1400 on small systems. This has the possibility of introducing
1401 silently broken kernel if the required annotations are not
1402 present. This option is not well tested yet, so use at your
1405 config LD_ORPHAN_WARN
1407 depends on ARCH_WANT_LD_ORPHAN_WARN
1408 depends on $(ld-option,--orphan-handling=warn)
1416 config SYSCTL_EXCEPTION_TRACE
1419 Enable support for /proc/sys/debug/exception-trace.
1421 config SYSCTL_ARCH_UNALIGN_NO_WARN
1424 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1425 Allows arch to define/use @no_unaligned_warning to possibly warn
1426 about unaligned access emulation going on under the hood.
1428 config SYSCTL_ARCH_UNALIGN_ALLOW
1431 Enable support for /proc/sys/kernel/unaligned-trap
1432 Allows arches to define/use @unaligned_enabled to runtime toggle
1433 the unaligned access emulation.
1434 see arch/parisc/kernel/unaligned.c for reference
1436 config HAVE_PCSPKR_PLATFORM
1439 # interpreter that classic socket filters depend on
1444 bool "Configure standard kernel features (expert users)"
1445 # Unhide debug options, to make the on-by-default options visible
1448 This option allows certain base kernel options and settings
1449 to be disabled or tweaked. This is for specialized
1450 environments which can tolerate a "non-standard" kernel.
1451 Only use this if you really know what you are doing.
1454 bool "Enable 16-bit UID system calls" if EXPERT
1455 depends on HAVE_UID16 && MULTIUSER
1458 This enables the legacy 16-bit UID syscall wrappers.
1461 bool "Multiple users, groups and capabilities support" if EXPERT
1464 This option enables support for non-root users, groups and
1467 If you say N here, all processes will run with UID 0, GID 0, and all
1468 possible capabilities. Saying N here also compiles out support for
1469 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1472 If unsure, say Y here.
1474 config SGETMASK_SYSCALL
1475 bool "sgetmask/ssetmask syscalls support" if EXPERT
1476 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
1478 sys_sgetmask and sys_ssetmask are obsolete system calls
1479 no longer supported in libc but still enabled by default in some
1482 If unsure, leave the default option here.
1484 config SYSFS_SYSCALL
1485 bool "Sysfs syscall support" if EXPERT
1488 sys_sysfs is an obsolete system call no longer supported in libc.
1489 Note that disabling this option is more secure but might break
1490 compatibility with some systems.
1492 If unsure say Y here.
1495 bool "open by fhandle syscalls" if EXPERT
1499 If you say Y here, a user level program will be able to map
1500 file names to handle and then later use the handle for
1501 different file system operations. This is useful in implementing
1502 userspace file servers, which now track files using handles instead
1503 of names. The handle would remain the same even if file names
1504 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1508 bool "Posix Clocks & timers" if EXPERT
1511 This includes native support for POSIX timers to the kernel.
1512 Some embedded systems have no use for them and therefore they
1513 can be configured out to reduce the size of the kernel image.
1515 When this option is disabled, the following syscalls won't be
1516 available: timer_create, timer_gettime: timer_getoverrun,
1517 timer_settime, timer_delete, clock_adjtime, getitimer,
1518 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1519 clock_getres and clock_nanosleep syscalls will be limited to
1520 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1526 bool "Enable support for printk" if EXPERT
1529 This option enables normal printk support. Removing it
1530 eliminates most of the message strings from the kernel image
1531 and makes the kernel more or less silent. As this makes it
1532 very difficult to diagnose system problems, saying N here is
1533 strongly discouraged.
1536 bool "BUG() support" if EXPERT
1539 Disabling this option eliminates support for BUG and WARN, reducing
1540 the size of your kernel image and potentially quietly ignoring
1541 numerous fatal conditions. You should only consider disabling this
1542 option for embedded systems with no facilities for reporting errors.
1548 bool "Enable ELF core dumps" if EXPERT
1550 Enable support for generating core dumps. Disabling saves about 4k.
1553 config PCSPKR_PLATFORM
1554 bool "Enable PC-Speaker support" if EXPERT
1555 depends on HAVE_PCSPKR_PLATFORM
1559 This option allows to disable the internal PC-Speaker
1560 support, saving some memory.
1564 bool "Enable full-sized data structures for core" if EXPERT
1566 Disabling this option reduces the size of miscellaneous core
1567 kernel data structures. This saves memory on small machines,
1568 but may reduce performance.
1571 bool "Enable futex support" if EXPERT
1572 depends on !(SPARC32 && SMP)
1576 Disabling this option will cause the kernel to be built without
1577 support for "fast userspace mutexes". The resulting kernel may not
1578 run glibc-based applications correctly.
1582 depends on FUTEX && RT_MUTEXES
1586 bool "Enable eventpoll support" if EXPERT
1589 Disabling this option will cause the kernel to be built without
1590 support for epoll family of system calls.
1593 bool "Enable signalfd() system call" if EXPERT
1596 Enable the signalfd() system call that allows to receive signals
1597 on a file descriptor.
1602 bool "Enable timerfd() system call" if EXPERT
1605 Enable the timerfd() system call that allows to receive timer
1606 events on a file descriptor.
1611 bool "Enable eventfd() system call" if EXPERT
1614 Enable the eventfd() system call that allows to receive both
1615 kernel notification (ie. KAIO) or userspace notifications.
1620 bool "Use full shmem filesystem" if EXPERT
1624 The shmem is an internal filesystem used to manage shared memory.
1625 It is backed by swap and manages resource limits. It is also exported
1626 to userspace as tmpfs if TMPFS is enabled. Disabling this
1627 option replaces shmem and tmpfs with the much simpler ramfs code,
1628 which may be appropriate on small systems without swap.
1631 bool "Enable AIO support" if EXPERT
1634 This option enables POSIX asynchronous I/O which may by used
1635 by some high performance threaded applications. Disabling
1636 this option saves about 7k.
1639 bool "Enable IO uring support" if EXPERT
1643 This option enables support for the io_uring interface, enabling
1644 applications to submit and complete IO through submission and
1645 completion rings that are shared between the kernel and application.
1647 config ADVISE_SYSCALLS
1648 bool "Enable madvise/fadvise syscalls" if EXPERT
1651 This option enables the madvise and fadvise syscalls, used by
1652 applications to advise the kernel about their future memory or file
1653 usage, improving performance. If building an embedded system where no
1654 applications use these syscalls, you can disable this option to save
1658 bool "Enable membarrier() system call" if EXPERT
1661 Enable the membarrier() system call that allows issuing memory
1662 barriers across all running threads, which can be used to distribute
1663 the cost of user-space memory barriers asymmetrically by transforming
1664 pairs of memory barriers into pairs consisting of membarrier() and a
1670 bool "Load all symbols for debugging/ksymoops" if EXPERT
1673 Say Y here to let the kernel print out symbolic crash information and
1674 symbolic stack backtraces. This increases the size of the kernel
1675 somewhat, as all symbols have to be loaded into the kernel image.
1678 bool "Include all symbols in kallsyms"
1679 depends on DEBUG_KERNEL && KALLSYMS
1681 Normally kallsyms only contains the symbols of functions for nicer
1682 OOPS messages and backtraces (i.e., symbols from the text and inittext
1683 sections). This is sufficient for most cases. And only in very rare
1684 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1685 names of variables from the data sections, etc).
1687 This option makes sure that all symbols are loaded into the kernel
1688 image (i.e., symbols from all sections) in cost of increased kernel
1689 size (depending on the kernel configuration, it may be 300KiB or
1690 something like this).
1692 Say N unless you really need all symbols.
1694 config KALLSYMS_ABSOLUTE_PERCPU
1697 default X86_64 && SMP
1699 config KALLSYMS_BASE_RELATIVE
1704 Instead of emitting them as absolute values in the native word size,
1705 emit the symbol references in the kallsyms table as 32-bit entries,
1706 each containing a relative value in the range [base, base + U32_MAX]
1707 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1708 an absolute value in the range [0, S32_MAX] or a relative value in the
1709 range [base, base + S32_MAX], where base is the lowest relative symbol
1710 address encountered in the image.
1712 On 64-bit builds, this reduces the size of the address table by 50%,
1713 but more importantly, it results in entries whose values are build
1714 time constants, and no relocation pass is required at runtime to fix
1715 up the entries based on the runtime load address of the kernel.
1717 # end of the "standard kernel features (expert users)" menu
1719 # syscall, maps, verifier
1721 config ARCH_HAS_MEMBARRIER_CALLBACKS
1724 config ARCH_HAS_MEMBARRIER_SYNC_CORE
1728 bool "Enable kcmp() system call" if EXPERT
1730 Enable the kernel resource comparison system call. It provides
1731 user-space with the ability to compare two processes to see if they
1732 share a common resource, such as a file descriptor or even virtual
1738 bool "Enable rseq() system call" if EXPERT
1740 depends on HAVE_RSEQ
1743 Enable the restartable sequences system call. It provides a
1744 user-space cache for the current CPU number value, which
1745 speeds up getting the current CPU number from user-space,
1746 as well as an ABI to speed up user-space operations on
1753 bool "Enabled debugging of rseq() system call" if EXPERT
1754 depends on RSEQ && DEBUG_KERNEL
1756 Enable extra debugging checks for the rseq system call.
1761 bool "Embedded system"
1764 This option should be enabled if compiling the kernel for
1765 an embedded system so certain expert options are available
1768 config HAVE_PERF_EVENTS
1771 See tools/perf/design.txt for details.
1773 config GUEST_PERF_EVENTS
1775 depends on HAVE_PERF_EVENTS
1777 config PERF_USE_VMALLOC
1780 See tools/perf/design.txt for details
1783 bool "PC/104 support" if EXPERT
1785 Expose PC/104 form factor device drivers and options available for
1786 selection and configuration. Enable this option if your target
1787 machine has a PC/104 bus.
1789 menu "Kernel Performance Events And Counters"
1792 bool "Kernel performance events and counters"
1793 default y if PROFILING
1794 depends on HAVE_PERF_EVENTS
1798 Enable kernel support for various performance events provided
1799 by software and hardware.
1801 Software events are supported either built-in or via the
1802 use of generic tracepoints.
1804 Most modern CPUs support performance events via performance
1805 counter registers. These registers count the number of certain
1806 types of hw events: such as instructions executed, cachemisses
1807 suffered, or branches mis-predicted - without slowing down the
1808 kernel or applications. These registers can also trigger interrupts
1809 when a threshold number of events have passed - and can thus be
1810 used to profile the code that runs on that CPU.
1812 The Linux Performance Event subsystem provides an abstraction of
1813 these software and hardware event capabilities, available via a
1814 system call and used by the "perf" utility in tools/perf/. It
1815 provides per task and per CPU counters, and it provides event
1816 capabilities on top of those.
1820 config DEBUG_PERF_USE_VMALLOC
1822 bool "Debug: use vmalloc to back perf mmap() buffers"
1823 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1824 select PERF_USE_VMALLOC
1826 Use vmalloc memory to back perf mmap() buffers.
1828 Mostly useful for debugging the vmalloc code on platforms
1829 that don't require it.
1835 config VM_EVENT_COUNTERS
1837 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1839 VM event counters are needed for event counts to be shown.
1840 This option allows the disabling of the VM event counters
1841 on EXPERT systems. /proc/vmstat will only show page counts
1842 if VM event counters are disabled.
1846 bool "Enable SLUB debugging support" if EXPERT
1847 depends on SLUB && SYSFS
1848 select STACKDEPOT if STACKTRACE_SUPPORT
1850 SLUB has extensive debug support features. Disabling these can
1851 result in significant savings in code size. This also disables
1852 SLUB sysfs support. /sys/slab will not exist and there will be
1853 no support for cache validation etc.
1856 bool "Disable heap randomization"
1859 Randomizing heap placement makes heap exploits harder, but it
1860 also breaks ancient binaries (including anything libc5 based).
1861 This option changes the bootup default to heap randomization
1862 disabled, and can be overridden at runtime by setting
1863 /proc/sys/kernel/randomize_va_space to 2.
1865 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1867 config MMAP_ALLOW_UNINITIALIZED
1868 bool "Allow mmapped anonymous memory to be uninitialized"
1869 depends on EXPERT && !MMU
1872 Normally, and according to the Linux spec, anonymous memory obtained
1873 from mmap() has its contents cleared before it is passed to
1874 userspace. Enabling this config option allows you to request that
1875 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1876 providing a huge performance boost. If this option is not enabled,
1877 then the flag will be ignored.
1879 This is taken advantage of by uClibc's malloc(), and also by
1880 ELF-FDPIC binfmt's brk and stack allocator.
1882 Because of the obvious security issues, this option should only be
1883 enabled on embedded devices where you control what is run in
1884 userspace. Since that isn't generally a problem on no-MMU systems,
1885 it is normally safe to say Y here.
1887 See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
1889 config SYSTEM_DATA_VERIFICATION
1891 select SYSTEM_TRUSTED_KEYRING
1895 select ASYMMETRIC_KEY_TYPE
1896 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1899 select X509_CERTIFICATE_PARSER
1900 select PKCS7_MESSAGE_PARSER
1902 Provide PKCS#7 message verification using the contents of the system
1903 trusted keyring to provide public keys. This then can be used for
1904 module verification, kexec image verification and firmware blob
1908 bool "Profiling support"
1910 Say Y here to enable the extended profiling support mechanisms used
1914 # Place an empty function call at each tracepoint site. Can be
1915 # dynamically changed for a probe function.
1920 endmenu # General setup
1922 source "arch/Kconfig"
1926 default y if PREEMPT_RT
1930 default 0 if BASE_FULL
1931 default 1 if !BASE_FULL
1933 config MODULE_SIG_FORMAT
1935 select SYSTEM_DATA_VERIFICATION
1938 bool "Enable loadable module support"
1941 Kernel modules are small pieces of compiled code which can
1942 be inserted in the running kernel, rather than being
1943 permanently built into the kernel. You use the "modprobe"
1944 tool to add (and sometimes remove) them. If you say Y here,
1945 many parts of the kernel can be built as modules (by
1946 answering M instead of Y where indicated): this is most
1947 useful for infrequently used options which are not required
1948 for booting. For more information, see the man pages for
1949 modprobe, lsmod, modinfo, insmod and rmmod.
1951 If you say Y here, you will need to run "make
1952 modules_install" to put the modules under /lib/modules/
1953 where modprobe can find them (you may need to be root to do
1960 config MODULE_FORCE_LOAD
1961 bool "Forced module loading"
1964 Allow loading of modules without version information (ie. modprobe
1965 --force). Forced module loading sets the 'F' (forced) taint flag and
1966 is usually a really bad idea.
1968 config MODULE_UNLOAD
1969 bool "Module unloading"
1971 Without this option you will not be able to unload any
1972 modules (note that some modules may not be unloadable
1973 anyway), which makes your kernel smaller, faster
1974 and simpler. If unsure, say Y.
1976 config MODULE_FORCE_UNLOAD
1977 bool "Forced module unloading"
1978 depends on MODULE_UNLOAD
1980 This option allows you to force a module to unload, even if the
1981 kernel believes it is unsafe: the kernel will remove the module
1982 without waiting for anyone to stop using it (using the -f option to
1983 rmmod). This is mainly for kernel developers and desperate users.
1987 bool "Module versioning support"
1989 Usually, you have to use modules compiled with your kernel.
1990 Saying Y here makes it sometimes possible to use modules
1991 compiled for different kernels, by adding enough information
1992 to the modules to (hopefully) spot any changes which would
1993 make them incompatible with the kernel you are running. If
1996 config ASM_MODVERSIONS
1998 default HAVE_ASM_MODVERSIONS && MODVERSIONS
2000 This enables module versioning for exported symbols also from
2001 assembly. This can be enabled only when the target architecture
2004 config MODULE_SRCVERSION_ALL
2005 bool "Source checksum for all modules"
2007 Modules which contain a MODULE_VERSION get an extra "srcversion"
2008 field inserted into their modinfo section, which contains a
2009 sum of the source files which made it. This helps maintainers
2010 see exactly which source was used to build a module (since
2011 others sometimes change the module source without updating
2012 the version). With this option, such a "srcversion" field
2013 will be created for all modules. If unsure, say N.
2016 bool "Module signature verification"
2017 select MODULE_SIG_FORMAT
2019 Check modules for valid signatures upon load: the signature
2020 is simply appended to the module. For more information see
2021 <file:Documentation/admin-guide/module-signing.rst>.
2023 Note that this option adds the OpenSSL development packages as a
2024 kernel build dependency so that the signing tool can use its crypto
2027 You should enable this option if you wish to use either
2028 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
2029 another LSM - otherwise unsigned modules will be loadable regardless
2030 of the lockdown policy.
2032 !!!WARNING!!! If you enable this option, you MUST make sure that the
2033 module DOES NOT get stripped after being signed. This includes the
2034 debuginfo strip done by some packagers (such as rpmbuild) and
2035 inclusion into an initramfs that wants the module size reduced.
2037 config MODULE_SIG_FORCE
2038 bool "Require modules to be validly signed"
2039 depends on MODULE_SIG
2041 Reject unsigned modules or signed modules for which we don't have a
2042 key. Without this, such modules will simply taint the kernel.
2044 config MODULE_SIG_ALL
2045 bool "Automatically sign all modules"
2047 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2049 Sign all modules during make modules_install. Without this option,
2050 modules must be signed manually, using the scripts/sign-file tool.
2052 comment "Do not forget to sign required modules with scripts/sign-file"
2053 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2056 prompt "Which hash algorithm should modules be signed with?"
2057 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2059 This determines which sort of hashing algorithm will be used during
2060 signature generation. This algorithm _must_ be built into the kernel
2061 directly so that signature verification can take place. It is not
2062 possible to load a signed module containing the algorithm to check
2063 the signature on that module.
2065 config MODULE_SIG_SHA1
2066 bool "Sign modules with SHA-1"
2069 config MODULE_SIG_SHA224
2070 bool "Sign modules with SHA-224"
2071 select CRYPTO_SHA256
2073 config MODULE_SIG_SHA256
2074 bool "Sign modules with SHA-256"
2075 select CRYPTO_SHA256
2077 config MODULE_SIG_SHA384
2078 bool "Sign modules with SHA-384"
2079 select CRYPTO_SHA512
2081 config MODULE_SIG_SHA512
2082 bool "Sign modules with SHA-512"
2083 select CRYPTO_SHA512
2087 config MODULE_SIG_HASH
2089 depends on MODULE_SIG || IMA_APPRAISE_MODSIG
2090 default "sha1" if MODULE_SIG_SHA1
2091 default "sha224" if MODULE_SIG_SHA224
2092 default "sha256" if MODULE_SIG_SHA256
2093 default "sha384" if MODULE_SIG_SHA384
2094 default "sha512" if MODULE_SIG_SHA512
2097 prompt "Module compression mode"
2099 This option allows you to choose the algorithm which will be used to
2100 compress modules when 'make modules_install' is run. (or, you can
2101 choose to not compress modules at all.)
2103 External modules will also be compressed in the same way during the
2106 For modules inside an initrd or initramfs, it's more efficient to
2107 compress the whole initrd or initramfs instead.
2109 This is fully compatible with signed modules.
2111 Please note that the tool used to load modules needs to support the
2112 corresponding algorithm. module-init-tools MAY support gzip, and kmod
2113 MAY support gzip, xz and zstd.
2115 Your build system needs to provide the appropriate compression tool
2116 to compress the modules.
2118 If in doubt, select 'None'.
2120 config MODULE_COMPRESS_NONE
2123 Do not compress modules. The installed modules are suffixed
2126 config MODULE_COMPRESS_GZIP
2129 Compress modules with GZIP. The installed modules are suffixed
2132 config MODULE_COMPRESS_XZ
2135 Compress modules with XZ. The installed modules are suffixed
2138 config MODULE_COMPRESS_ZSTD
2141 Compress modules with ZSTD. The installed modules are suffixed
2146 config MODULE_DECOMPRESS
2147 bool "Support in-kernel module decompression"
2148 depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ
2149 select ZLIB_INFLATE if MODULE_COMPRESS_GZIP
2150 select XZ_DEC if MODULE_COMPRESS_XZ
2153 Support for decompressing kernel modules by the kernel itself
2154 instead of relying on userspace to perform this task. Useful when
2155 load pinning security policy is enabled.
2159 config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
2160 bool "Allow loading of modules with missing namespace imports"
2162 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
2163 a namespace. A module that makes use of a symbol exported with such a
2164 namespace is required to import the namespace via MODULE_IMPORT_NS().
2165 There is no technical reason to enforce correct namespace imports,
2166 but it creates consistency between symbols defining namespaces and
2167 users importing namespaces they make use of. This option relaxes this
2168 requirement and lifts the enforcement when loading a module.
2172 config MODPROBE_PATH
2173 string "Path to modprobe binary"
2174 default "/sbin/modprobe"
2176 When kernel code requests a module, it does so by calling
2177 the "modprobe" userspace utility. This option allows you to
2178 set the path where that binary is found. This can be changed
2179 at runtime via the sysctl file
2180 /proc/sys/kernel/modprobe. Setting this to the empty string
2181 removes the kernel's ability to request modules (but
2182 userspace can still load modules explicitly).
2184 config TRIM_UNUSED_KSYMS
2185 bool "Trim unused exported kernel symbols" if EXPERT
2186 depends on !COMPILE_TEST
2188 The kernel and some modules make many symbols available for
2189 other modules to use via EXPORT_SYMBOL() and variants. Depending
2190 on the set of modules being selected in your kernel configuration,
2191 many of those exported symbols might never be used.
2193 This option allows for unused exported symbols to be dropped from
2194 the build. In turn, this provides the compiler more opportunities
2195 (especially when using LTO) for optimizing the code and reducing
2196 binary size. This might have some security advantages as well.
2198 If unsure, or if you need to build out-of-tree modules, say N.
2200 config UNUSED_KSYMS_WHITELIST
2201 string "Whitelist of symbols to keep in ksymtab"
2202 depends on TRIM_UNUSED_KSYMS
2204 By default, all unused exported symbols will be un-exported from the
2205 build when TRIM_UNUSED_KSYMS is selected.
2207 UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept
2208 exported at all times, even in absence of in-tree users. The value to
2209 set here is the path to a text file containing the list of symbols,
2210 one per line. The path can be absolute, or relative to the kernel
2215 config MODULES_TREE_LOOKUP
2217 depends on PERF_EVENTS || TRACING || CFI_CLANG
2219 config INIT_ALL_POSSIBLE
2222 Back when each arch used to define their own cpu_online_mask and
2223 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2224 with all 1s, and others with all 0s. When they were centralised,
2225 it was better to provide this option than to break all the archs
2226 and have several arch maintainers pursuing me down dark alleys.
2228 source "block/Kconfig"
2230 config PREEMPT_NOTIFIERS
2240 Build a simple ASN.1 grammar compiler that produces a bytecode output
2241 that can be interpreted by the ASN.1 stream decoder and used to
2242 inform it as to what tags are to be expected in a stream and what
2243 functions to call on what tags.
2245 source "kernel/Kconfig.locks"
2247 config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
2250 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
2253 # It may be useful for an architecture to override the definitions of the
2254 # SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
2255 # and the COMPAT_ variants in <linux/compat.h>, in particular to use a
2256 # different calling convention for syscalls. They can also override the
2257 # macros for not-implemented syscalls in kernel/sys_ni.c and
2258 # kernel/time/posix-stubs.c. All these overrides need to be available in
2259 # <asm/syscall_wrapper.h>.
2260 config ARCH_HAS_SYSCALL_WRAPPER
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