1# SPDX-License-Identifier: GPL-2.0-only 2config DEFCONFIG_LIST 3 string 4 depends on !UML 5 option defconfig_list 6 default "/lib/modules/$(shell,uname -r)/.config" 7 default "/etc/kernel-config" 8 default "/boot/config-$(shell,uname -r)" 9 default "arch/$(SRCARCH)/configs/$(KBUILD_DEFCONFIG)" 10 11config CC_VERSION_TEXT 12 string 13 default "$(CC_VERSION_TEXT)" 14 help 15 This is used in unclear ways: 16 17 - Re-run Kconfig when the compiler is updated 18 The 'default' property references the environment variable, 19 CC_VERSION_TEXT so it is recorded in include/config/auto.conf.cmd. 20 When the compiler is updated, Kconfig will be invoked. 21 22 - Ensure full rebuild when the compier is updated 23 include/linux/kconfig.h contains this option in the comment line so 24 fixdep adds include/config/cc/version/text.h into the auto-generated 25 dependency. When the compiler is updated, syncconfig will touch it 26 and then every file will be rebuilt. 27 28config CC_IS_GCC 29 def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q gcc) 30 31config GCC_VERSION 32 int 33 default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC 34 default 0 35 36config LD_VERSION 37 int 38 default $(shell,$(LD) --version | $(srctree)/scripts/ld-version.sh) 39 40config CC_IS_CLANG 41 def_bool $(success,echo "$(CC_VERSION_TEXT)" | grep -q clang) 42 43config LD_IS_LLD 44 def_bool $(success,$(LD) -v | head -n 1 | grep -q LLD) 45 46config CLANG_VERSION 47 int 48 default $(shell,$(srctree)/scripts/clang-version.sh $(CC)) 49 50config LLD_VERSION 51 int 52 default $(shell,$(srctree)/scripts/lld-version.sh $(LD)) 53 54config CC_CAN_LINK 55 bool 56 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag)) if 64BIT 57 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag)) 58 59config CC_CAN_LINK_STATIC 60 bool 61 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m64-flag) -static) if 64BIT 62 default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(m32-flag) -static) 63 64config CC_HAS_ASM_GOTO 65 def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) 66 67config CC_HAS_ASM_GOTO_OUTPUT 68 depends on CC_HAS_ASM_GOTO 69 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) 70 71config TOOLS_SUPPORT_RELR 72 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh) 73 74config CC_HAS_ASM_INLINE 75 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null) 76 77config CONSTRUCTORS 78 bool 79 depends on !UML 80 81config IRQ_WORK 82 bool 83 84config BUILDTIME_TABLE_SORT 85 bool 86 87config THREAD_INFO_IN_TASK 88 bool 89 help 90 Select this to move thread_info off the stack into task_struct. To 91 make this work, an arch will need to remove all thread_info fields 92 except flags and fix any runtime bugs. 93 94 One subtle change that will be needed is to use try_get_task_stack() 95 and put_task_stack() in save_thread_stack_tsk() and get_wchan(). 96 97menu "General setup" 98 99config BROKEN 100 bool 101 102config BROKEN_ON_SMP 103 bool 104 depends on BROKEN || !SMP 105 default y 106 107config INIT_ENV_ARG_LIMIT 108 int 109 default 32 if !UML 110 default 128 if UML 111 help 112 Maximum of each of the number of arguments and environment 113 variables passed to init from the kernel command line. 114 115config COMPILE_TEST 116 bool "Compile also drivers which will not load" 117 depends on HAS_IOMEM 118 help 119 Some drivers can be compiled on a different platform than they are 120 intended to be run on. Despite they cannot be loaded there (or even 121 when they load they cannot be used due to missing HW support), 122 developers still, opposing to distributors, might want to build such 123 drivers to compile-test them. 124 125 If you are a developer and want to build everything available, say Y 126 here. If you are a user/distributor, say N here to exclude useless 127 drivers to be distributed. 128 129config UAPI_HEADER_TEST 130 bool "Compile test UAPI headers" 131 depends on HEADERS_INSTALL && CC_CAN_LINK 132 help 133 Compile test headers exported to user-space to ensure they are 134 self-contained, i.e. compilable as standalone units. 135 136 If you are a developer or tester and want to ensure the exported 137 headers are self-contained, say Y here. Otherwise, choose N. 138 139config LOCALVERSION 140 string "Local version - append to kernel release" 141 help 142 Append an extra string to the end of your kernel version. 143 This will show up when you type uname, for example. 144 The string you set here will be appended after the contents of 145 any files with a filename matching localversion* in your 146 object and source tree, in that order. Your total string can 147 be a maximum of 64 characters. 148 149config LOCALVERSION_AUTO 150 bool "Automatically append version information to the version string" 151 default y 152 depends on !COMPILE_TEST 153 help 154 This will try to automatically determine if the current tree is a 155 release tree by looking for git tags that belong to the current 156 top of tree revision. 157 158 A string of the format -gxxxxxxxx will be added to the localversion 159 if a git-based tree is found. The string generated by this will be 160 appended after any matching localversion* files, and after the value 161 set in CONFIG_LOCALVERSION. 162 163 (The actual string used here is the first eight characters produced 164 by running the command: 165 166 $ git rev-parse --verify HEAD 167 168 which is done within the script "scripts/setlocalversion".) 169 170config BUILD_SALT 171 string "Build ID Salt" 172 default "" 173 help 174 The build ID is used to link binaries and their debug info. Setting 175 this option will use the value in the calculation of the build id. 176 This is mostly useful for distributions which want to ensure the 177 build is unique between builds. It's safe to leave the default. 178 179config HAVE_KERNEL_GZIP 180 bool 181 182config HAVE_KERNEL_BZIP2 183 bool 184 185config HAVE_KERNEL_LZMA 186 bool 187 188config HAVE_KERNEL_XZ 189 bool 190 191config HAVE_KERNEL_LZO 192 bool 193 194config HAVE_KERNEL_LZ4 195 bool 196 197config HAVE_KERNEL_ZSTD 198 bool 199 200config HAVE_KERNEL_UNCOMPRESSED 201 bool 202 203choice 204 prompt "Kernel compression mode" 205 default KERNEL_GZIP 206 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 207 help 208 The linux kernel is a kind of self-extracting executable. 209 Several compression algorithms are available, which differ 210 in efficiency, compression and decompression speed. 211 Compression speed is only relevant when building a kernel. 212 Decompression speed is relevant at each boot. 213 214 If you have any problems with bzip2 or lzma compressed 215 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older 216 version of this functionality (bzip2 only), for 2.4, was 217 supplied by Christian Ludwig) 218 219 High compression options are mostly useful for users, who 220 are low on disk space (embedded systems), but for whom ram 221 size matters less. 222 223 If in doubt, select 'gzip' 224 225config KERNEL_GZIP 226 bool "Gzip" 227 depends on HAVE_KERNEL_GZIP 228 help 229 The old and tried gzip compression. It provides a good balance 230 between compression ratio and decompression speed. 231 232config KERNEL_BZIP2 233 bool "Bzip2" 234 depends on HAVE_KERNEL_BZIP2 235 help 236 Its compression ratio and speed is intermediate. 237 Decompression speed is slowest among the choices. The kernel 238 size is about 10% smaller with bzip2, in comparison to gzip. 239 Bzip2 uses a large amount of memory. For modern kernels you 240 will need at least 8MB RAM or more for booting. 241 242config KERNEL_LZMA 243 bool "LZMA" 244 depends on HAVE_KERNEL_LZMA 245 help 246 This compression algorithm's ratio is best. Decompression speed 247 is between gzip and bzip2. Compression is slowest. 248 The kernel size is about 33% smaller with LZMA in comparison to gzip. 249 250config KERNEL_XZ 251 bool "XZ" 252 depends on HAVE_KERNEL_XZ 253 help 254 XZ uses the LZMA2 algorithm and instruction set specific 255 BCJ filters which can improve compression ratio of executable 256 code. The size of the kernel is about 30% smaller with XZ in 257 comparison to gzip. On architectures for which there is a BCJ 258 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ 259 will create a few percent smaller kernel than plain LZMA. 260 261 The speed is about the same as with LZMA: The decompression 262 speed of XZ is better than that of bzip2 but worse than gzip 263 and LZO. Compression is slow. 264 265config KERNEL_LZO 266 bool "LZO" 267 depends on HAVE_KERNEL_LZO 268 help 269 Its compression ratio is the poorest among the choices. The kernel 270 size is about 10% bigger than gzip; however its speed 271 (both compression and decompression) is the fastest. 272 273config KERNEL_LZ4 274 bool "LZ4" 275 depends on HAVE_KERNEL_LZ4 276 help 277 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding. 278 A preliminary version of LZ4 de/compression tool is available at 279 <https://code.google.com/p/lz4/>. 280 281 Its compression ratio is worse than LZO. The size of the kernel 282 is about 8% bigger than LZO. But the decompression speed is 283 faster than LZO. 284 285config KERNEL_ZSTD 286 bool "ZSTD" 287 depends on HAVE_KERNEL_ZSTD 288 help 289 ZSTD is a compression algorithm targeting intermediate compression 290 with fast decompression speed. It will compress better than GZIP and 291 decompress around the same speed as LZO, but slower than LZ4. You 292 will need at least 192 KB RAM or more for booting. The zstd command 293 line tool is required for compression. 294 295config KERNEL_UNCOMPRESSED 296 bool "None" 297 depends on HAVE_KERNEL_UNCOMPRESSED 298 help 299 Produce uncompressed kernel image. This option is usually not what 300 you want. It is useful for debugging the kernel in slow simulation 301 environments, where decompressing and moving the kernel is awfully 302 slow. This option allows early boot code to skip the decompressor 303 and jump right at uncompressed kernel image. 304 305endchoice 306 307config DEFAULT_INIT 308 string "Default init path" 309 default "" 310 help 311 This option determines the default init for the system if no init= 312 option is passed on the kernel command line. If the requested path is 313 not present, we will still then move on to attempting further 314 locations (e.g. /sbin/init, etc). If this is empty, we will just use 315 the fallback list when init= is not passed. 316 317config DEFAULT_HOSTNAME 318 string "Default hostname" 319 default "(none)" 320 help 321 This option determines the default system hostname before userspace 322 calls sethostname(2). The kernel traditionally uses "(none)" here, 323 but you may wish to use a different default here to make a minimal 324 system more usable with less configuration. 325 326# 327# For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can 328# add proper SWAP support to them, in which case this can be remove. 329# 330config ARCH_NO_SWAP 331 bool 332 333config SWAP 334 bool "Support for paging of anonymous memory (swap)" 335 depends on MMU && BLOCK && !ARCH_NO_SWAP 336 default y 337 help 338 This option allows you to choose whether you want to have support 339 for so called swap devices or swap files in your kernel that are 340 used to provide more virtual memory than the actual RAM present 341 in your computer. If unsure say Y. 342 343config SYSVIPC 344 bool "System V IPC" 345 help 346 Inter Process Communication is a suite of library functions and 347 system calls which let processes (running programs) synchronize and 348 exchange information. It is generally considered to be a good thing, 349 and some programs won't run unless you say Y here. In particular, if 350 you want to run the DOS emulator dosemu under Linux (read the 351 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>), 352 you'll need to say Y here. 353 354 You can find documentation about IPC with "info ipc" and also in 355 section 6.4 of the Linux Programmer's Guide, available from 356 <http://www.tldp.org/guides.html>. 357 358config SYSVIPC_SYSCTL 359 bool 360 depends on SYSVIPC 361 depends on SYSCTL 362 default y 363 364config POSIX_MQUEUE 365 bool "POSIX Message Queues" 366 depends on NET 367 help 368 POSIX variant of message queues is a part of IPC. In POSIX message 369 queues every message has a priority which decides about succession 370 of receiving it by a process. If you want to compile and run 371 programs written e.g. for Solaris with use of its POSIX message 372 queues (functions mq_*) say Y here. 373 374 POSIX message queues are visible as a filesystem called 'mqueue' 375 and can be mounted somewhere if you want to do filesystem 376 operations on message queues. 377 378 If unsure, say Y. 379 380config POSIX_MQUEUE_SYSCTL 381 bool 382 depends on POSIX_MQUEUE 383 depends on SYSCTL 384 default y 385 386config WATCH_QUEUE 387 bool "General notification queue" 388 default n 389 help 390 391 This is a general notification queue for the kernel to pass events to 392 userspace by splicing them into pipes. It can be used in conjunction 393 with watches for key/keyring change notifications and device 394 notifications. 395 396 See Documentation/watch_queue.rst 397 398config CROSS_MEMORY_ATTACH 399 bool "Enable process_vm_readv/writev syscalls" 400 depends on MMU 401 default y 402 help 403 Enabling this option adds the system calls process_vm_readv and 404 process_vm_writev which allow a process with the correct privileges 405 to directly read from or write to another process' address space. 406 See the man page for more details. 407 408config USELIB 409 bool "uselib syscall" 410 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION 411 help 412 This option enables the uselib syscall, a system call used in the 413 dynamic linker from libc5 and earlier. glibc does not use this 414 system call. If you intend to run programs built on libc5 or 415 earlier, you may need to enable this syscall. Current systems 416 running glibc can safely disable this. 417 418config AUDIT 419 bool "Auditing support" 420 depends on NET 421 help 422 Enable auditing infrastructure that can be used with another 423 kernel subsystem, such as SELinux (which requires this for 424 logging of avc messages output). System call auditing is included 425 on architectures which support it. 426 427config HAVE_ARCH_AUDITSYSCALL 428 bool 429 430config AUDITSYSCALL 431 def_bool y 432 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL 433 select FSNOTIFY 434 435source "kernel/irq/Kconfig" 436source "kernel/time/Kconfig" 437source "kernel/Kconfig.preempt" 438 439menu "CPU/Task time and stats accounting" 440 441config VIRT_CPU_ACCOUNTING 442 bool 443 444choice 445 prompt "Cputime accounting" 446 default TICK_CPU_ACCOUNTING if !PPC64 447 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64 448 449# Kind of a stub config for the pure tick based cputime accounting 450config TICK_CPU_ACCOUNTING 451 bool "Simple tick based cputime accounting" 452 depends on !S390 && !NO_HZ_FULL 453 help 454 This is the basic tick based cputime accounting that maintains 455 statistics about user, system and idle time spent on per jiffies 456 granularity. 457 458 If unsure, say Y. 459 460config VIRT_CPU_ACCOUNTING_NATIVE 461 bool "Deterministic task and CPU time accounting" 462 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL 463 select VIRT_CPU_ACCOUNTING 464 help 465 Select this option to enable more accurate task and CPU time 466 accounting. This is done by reading a CPU counter on each 467 kernel entry and exit and on transitions within the kernel 468 between system, softirq and hardirq state, so there is a 469 small performance impact. In the case of s390 or IBM POWER > 5, 470 this also enables accounting of stolen time on logically-partitioned 471 systems. 472 473config VIRT_CPU_ACCOUNTING_GEN 474 bool "Full dynticks CPU time accounting" 475 depends on HAVE_CONTEXT_TRACKING 476 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 477 depends on GENERIC_CLOCKEVENTS 478 select VIRT_CPU_ACCOUNTING 479 select CONTEXT_TRACKING 480 help 481 Select this option to enable task and CPU time accounting on full 482 dynticks systems. This accounting is implemented by watching every 483 kernel-user boundaries using the context tracking subsystem. 484 The accounting is thus performed at the expense of some significant 485 overhead. 486 487 For now this is only useful if you are working on the full 488 dynticks subsystem development. 489 490 If unsure, say N. 491 492endchoice 493 494config IRQ_TIME_ACCOUNTING 495 bool "Fine granularity task level IRQ time accounting" 496 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE 497 help 498 Select this option to enable fine granularity task irq time 499 accounting. This is done by reading a timestamp on each 500 transitions between softirq and hardirq state, so there can be a 501 small performance impact. 502 503 If in doubt, say N here. 504 505config HAVE_SCHED_AVG_IRQ 506 def_bool y 507 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING 508 depends on SMP 509 510config SCHED_THERMAL_PRESSURE 511 bool 512 default y if ARM && ARM_CPU_TOPOLOGY 513 default y if ARM64 514 depends on SMP 515 depends on CPU_FREQ_THERMAL 516 help 517 Select this option to enable thermal pressure accounting in the 518 scheduler. Thermal pressure is the value conveyed to the scheduler 519 that reflects the reduction in CPU compute capacity resulted from 520 thermal throttling. Thermal throttling occurs when the performance of 521 a CPU is capped due to high operating temperatures. 522 523 If selected, the scheduler will be able to balance tasks accordingly, 524 i.e. put less load on throttled CPUs than on non/less throttled ones. 525 526 This requires the architecture to implement 527 arch_set_thermal_pressure() and arch_get_thermal_pressure(). 528 529config SCHED_WALT 530 bool "Support window based load tracking" 531 depends on SMP 532 help 533 This feature will allow the scheduler to maintain a tunable window 534 based set of metrics for tasks and runqueues. These metrics can be 535 used to guide task placement as well as task frequency requirements 536 for cpufreq governors. 537 538config BSD_PROCESS_ACCT 539 bool "BSD Process Accounting" 540 depends on MULTIUSER 541 help 542 If you say Y here, a user level program will be able to instruct the 543 kernel (via a special system call) to write process accounting 544 information to a file: whenever a process exits, information about 545 that process will be appended to the file by the kernel. The 546 information includes things such as creation time, owning user, 547 command name, memory usage, controlling terminal etc. (the complete 548 list is in the struct acct in <file:include/linux/acct.h>). It is 549 up to the user level program to do useful things with this 550 information. This is generally a good idea, so say Y. 551 552config BSD_PROCESS_ACCT_V3 553 bool "BSD Process Accounting version 3 file format" 554 depends on BSD_PROCESS_ACCT 555 default n 556 help 557 If you say Y here, the process accounting information is written 558 in a new file format that also logs the process IDs of each 559 process and its parent. Note that this file format is incompatible 560 with previous v0/v1/v2 file formats, so you will need updated tools 561 for processing it. A preliminary version of these tools is available 562 at <http://www.gnu.org/software/acct/>. 563 564config TASKSTATS 565 bool "Export task/process statistics through netlink" 566 depends on NET 567 depends on MULTIUSER 568 default n 569 help 570 Export selected statistics for tasks/processes through the 571 generic netlink interface. Unlike BSD process accounting, the 572 statistics are available during the lifetime of tasks/processes as 573 responses to commands. Like BSD accounting, they are sent to user 574 space on task exit. 575 576 Say N if unsure. 577 578config TASK_DELAY_ACCT 579 bool "Enable per-task delay accounting" 580 depends on TASKSTATS 581 select SCHED_INFO 582 help 583 Collect information on time spent by a task waiting for system 584 resources like cpu, synchronous block I/O completion and swapping 585 in pages. Such statistics can help in setting a task's priorities 586 relative to other tasks for cpu, io, rss limits etc. 587 588 Say N if unsure. 589 590config TASK_XACCT 591 bool "Enable extended accounting over taskstats" 592 depends on TASKSTATS 593 help 594 Collect extended task accounting data and send the data 595 to userland for processing over the taskstats interface. 596 597 Say N if unsure. 598 599config TASK_IO_ACCOUNTING 600 bool "Enable per-task storage I/O accounting" 601 depends on TASK_XACCT 602 help 603 Collect information on the number of bytes of storage I/O which this 604 task has caused. 605 606 Say N if unsure. 607 608config PSI 609 bool "Pressure stall information tracking" 610 help 611 Collect metrics that indicate how overcommitted the CPU, memory, 612 and IO capacity are in the system. 613 614 If you say Y here, the kernel will create /proc/pressure/ with the 615 pressure statistics files cpu, memory, and io. These will indicate 616 the share of walltime in which some or all tasks in the system are 617 delayed due to contention of the respective resource. 618 619 In kernels with cgroup support, cgroups (cgroup2 only) will 620 have cpu.pressure, memory.pressure, and io.pressure files, 621 which aggregate pressure stalls for the grouped tasks only. 622 623 For more details see Documentation/accounting/psi.rst. 624 625 Say N if unsure. 626 627config PSI_DEFAULT_DISABLED 628 bool "Require boot parameter to enable pressure stall information tracking" 629 default n 630 depends on PSI 631 help 632 If set, pressure stall information tracking will be disabled 633 per default but can be enabled through passing psi=1 on the 634 kernel commandline during boot. 635 636 This feature adds some code to the task wakeup and sleep 637 paths of the scheduler. The overhead is too low to affect 638 common scheduling-intense workloads in practice (such as 639 webservers, memcache), but it does show up in artificial 640 scheduler stress tests, such as hackbench. 641 642 If you are paranoid and not sure what the kernel will be 643 used for, say Y. 644 645 Say N if unsure. 646 647endmenu # "CPU/Task time and stats accounting" 648 649config CPU_ISOLATION 650 bool "CPU isolation" 651 depends on SMP || COMPILE_TEST 652 default y 653 help 654 Make sure that CPUs running critical tasks are not disturbed by 655 any source of "noise" such as unbound workqueues, timers, kthreads... 656 Unbound jobs get offloaded to housekeeping CPUs. This is driven by 657 the "isolcpus=" boot parameter. 658 659 Say Y if unsure. 660 661config SCHED_RUNNING_AVG 662 bool "per-rq and per-cluster running average statistics" 663 default n 664 665config CPU_ISOLATION_OPT 666 bool "CPU isolation optimization" 667 depends on SMP 668 default n 669 help 670 This option enables cpu isolation optimization, which allows 671 to isolate cpu dynamically. The isolated cpu will be unavailable 672 to scheduler and load balancer, and all its non-pinned timers, 673 IRQs and tasks will be migrated to other cpus, only pinned 674 kthread and IRQS are still allowed to run, this achieves 675 similar effect as hotplug but at lower latency cost. 676 677config SCHED_CORE_CTRL 678 bool "Core control" 679 depends on CPU_ISOLATION_OPT 680 select SCHED_RUNNING_AVG 681 default n 682 help 683 This option enables the core control functionality in 684 the scheduler. Core control automatically isolate and 685 unisolate cores based on cpu load and utilization. 686 687source "kernel/rcu/Kconfig" 688 689config BUILD_BIN2C 690 bool 691 default n 692 693config IKCONFIG 694 tristate "Kernel .config support" 695 help 696 This option enables the complete Linux kernel ".config" file 697 contents to be saved in the kernel. It provides documentation 698 of which kernel options are used in a running kernel or in an 699 on-disk kernel. This information can be extracted from the kernel 700 image file with the script scripts/extract-ikconfig and used as 701 input to rebuild the current kernel or to build another kernel. 702 It can also be extracted from a running kernel by reading 703 /proc/config.gz if enabled (below). 704 705config IKCONFIG_PROC 706 bool "Enable access to .config through /proc/config.gz" 707 depends on IKCONFIG && PROC_FS 708 help 709 This option enables access to the kernel configuration file 710 through /proc/config.gz. 711 712config IKHEADERS 713 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz" 714 depends on SYSFS 715 help 716 This option enables access to the in-kernel headers that are generated during 717 the build process. These can be used to build eBPF tracing programs, 718 or similar programs. If you build the headers as a module, a module called 719 kheaders.ko is built which can be loaded on-demand to get access to headers. 720 721config LOG_BUF_SHIFT 722 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" 723 range 12 25 if !H8300 724 range 12 19 if H8300 725 default 17 726 depends on PRINTK 727 help 728 Select the minimal kernel log buffer size as a power of 2. 729 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config 730 parameter, see below. Any higher size also might be forced 731 by "log_buf_len" boot parameter. 732 733 Examples: 734 17 => 128 KB 735 16 => 64 KB 736 15 => 32 KB 737 14 => 16 KB 738 13 => 8 KB 739 12 => 4 KB 740 741config LOG_CPU_MAX_BUF_SHIFT 742 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)" 743 depends on SMP 744 range 0 21 745 default 12 if !BASE_SMALL 746 default 0 if BASE_SMALL 747 depends on PRINTK 748 help 749 This option allows to increase the default ring buffer size 750 according to the number of CPUs. The value defines the contribution 751 of each CPU as a power of 2. The used space is typically only few 752 lines however it might be much more when problems are reported, 753 e.g. backtraces. 754 755 The increased size means that a new buffer has to be allocated and 756 the original static one is unused. It makes sense only on systems 757 with more CPUs. Therefore this value is used only when the sum of 758 contributions is greater than the half of the default kernel ring 759 buffer as defined by LOG_BUF_SHIFT. The default values are set 760 so that more than 16 CPUs are needed to trigger the allocation. 761 762 Also this option is ignored when "log_buf_len" kernel parameter is 763 used as it forces an exact (power of two) size of the ring buffer. 764 765 The number of possible CPUs is used for this computation ignoring 766 hotplugging making the computation optimal for the worst case 767 scenario while allowing a simple algorithm to be used from bootup. 768 769 Examples shift values and their meaning: 770 17 => 128 KB for each CPU 771 16 => 64 KB for each CPU 772 15 => 32 KB for each CPU 773 14 => 16 KB for each CPU 774 13 => 8 KB for each CPU 775 12 => 4 KB for each CPU 776 777config PRINTK_SAFE_LOG_BUF_SHIFT 778 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)" 779 range 10 21 780 default 13 781 depends on PRINTK 782 help 783 Select the size of an alternate printk per-CPU buffer where messages 784 printed from usafe contexts are temporary stored. One example would 785 be NMI messages, another one - printk recursion. The messages are 786 copied to the main log buffer in a safe context to avoid a deadlock. 787 The value defines the size as a power of 2. 788 789 Those messages are rare and limited. The largest one is when 790 a backtrace is printed. It usually fits into 4KB. Select 791 8KB if you want to be on the safe side. 792 793 Examples: 794 17 => 128 KB for each CPU 795 16 => 64 KB for each CPU 796 15 => 32 KB for each CPU 797 14 => 16 KB for each CPU 798 13 => 8 KB for each CPU 799 12 => 4 KB for each CPU 800 801# 802# Architectures with an unreliable sched_clock() should select this: 803# 804config HAVE_UNSTABLE_SCHED_CLOCK 805 bool 806 807config GENERIC_SCHED_CLOCK 808 bool 809 810menu "Scheduler features" 811 812config UCLAMP_TASK 813 bool "Enable utilization clamping for RT/FAIR tasks" 814 depends on CPU_FREQ_GOV_SCHEDUTIL 815 help 816 This feature enables the scheduler to track the clamped utilization 817 of each CPU based on RUNNABLE tasks scheduled on that CPU. 818 819 With this option, the user can specify the min and max CPU 820 utilization allowed for RUNNABLE tasks. The max utilization defines 821 the maximum frequency a task should use while the min utilization 822 defines the minimum frequency it should use. 823 824 Both min and max utilization clamp values are hints to the scheduler, 825 aiming at improving its frequency selection policy, but they do not 826 enforce or grant any specific bandwidth for tasks. 827 828 If in doubt, say N. 829 830config UCLAMP_BUCKETS_COUNT 831 int "Number of supported utilization clamp buckets" 832 range 5 20 833 default 5 834 depends on UCLAMP_TASK 835 help 836 Defines the number of clamp buckets to use. The range of each bucket 837 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the 838 number of clamp buckets the finer their granularity and the higher 839 the precision of clamping aggregation and tracking at run-time. 840 841 For example, with the minimum configuration value we will have 5 842 clamp buckets tracking 20% utilization each. A 25% boosted tasks will 843 be refcounted in the [20..39]% bucket and will set the bucket clamp 844 effective value to 25%. 845 If a second 30% boosted task should be co-scheduled on the same CPU, 846 that task will be refcounted in the same bucket of the first task and 847 it will boost the bucket clamp effective value to 30%. 848 The clamp effective value of a bucket is reset to its nominal value 849 (20% in the example above) when there are no more tasks refcounted in 850 that bucket. 851 852 An additional boost/capping margin can be added to some tasks. In the 853 example above the 25% task will be boosted to 30% until it exits the 854 CPU. If that should be considered not acceptable on certain systems, 855 it's always possible to reduce the margin by increasing the number of 856 clamp buckets to trade off used memory for run-time tracking 857 precision. 858 859 If in doubt, use the default value. 860 861config SCHED_LATENCY_NICE 862 bool "Enable latency feature for FAIR tasks" 863 default n 864 help 865 This feature use latency nice priority to decide if a cfs task can 866 preempt the current running task. 867 868source "kernel/sched/rtg/Kconfig" 869 870config SCHED_EAS 871 bool "EAS scheduler optimization" 872 default n 873 help 874 Check and migrate the CFS process to a more suitable CPU in the tick. 875 876config SCHED_RT_CAS 877 bool "rt-cas optimization" 878 depends on SCHED_EAS 879 default n 880 help 881 RT task detects capacity during CPU selection 882 883config SCHED_RT_ACTIVE_LB 884 bool "RT Capacity Aware Misfit Task" 885 depends on SCHED_EAS 886 default n 887 help 888 Check and migrate the RT process to a more suitable CPU in the tick. 889 890endmenu 891 892# 893# For architectures that want to enable the support for NUMA-affine scheduler 894# balancing logic: 895# 896config ARCH_SUPPORTS_NUMA_BALANCING 897 bool 898 899# 900# For architectures that prefer to flush all TLBs after a number of pages 901# are unmapped instead of sending one IPI per page to flush. The architecture 902# must provide guarantees on what happens if a clean TLB cache entry is 903# written after the unmap. Details are in mm/rmap.c near the check for 904# should_defer_flush. The architecture should also consider if the full flush 905# and the refill costs are offset by the savings of sending fewer IPIs. 906config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH 907 bool 908 909config CC_HAS_INT128 910 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT 911 912# 913# For architectures that know their GCC __int128 support is sound 914# 915config ARCH_SUPPORTS_INT128 916 bool 917 918# For architectures that (ab)use NUMA to represent different memory regions 919# all cpu-local but of different latencies, such as SuperH. 920# 921config ARCH_WANT_NUMA_VARIABLE_LOCALITY 922 bool 923 924config NUMA_BALANCING 925 bool "Memory placement aware NUMA scheduler" 926 depends on ARCH_SUPPORTS_NUMA_BALANCING 927 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY 928 depends on SMP && NUMA && MIGRATION 929 help 930 This option adds support for automatic NUMA aware memory/task placement. 931 The mechanism is quite primitive and is based on migrating memory when 932 it has references to the node the task is running on. 933 934 This system will be inactive on UMA systems. 935 936config NUMA_BALANCING_DEFAULT_ENABLED 937 bool "Automatically enable NUMA aware memory/task placement" 938 default y 939 depends on NUMA_BALANCING 940 help 941 If set, automatic NUMA balancing will be enabled if running on a NUMA 942 machine. 943 944menuconfig CGROUPS 945 bool "Control Group support" 946 select KERNFS 947 help 948 This option adds support for grouping sets of processes together, for 949 use with process control subsystems such as Cpusets, CFS, memory 950 controls or device isolation. 951 See 952 - Documentation/scheduler/sched-design-CFS.rst (CFS) 953 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation 954 and resource control) 955 956 Say N if unsure. 957 958if CGROUPS 959 960config PAGE_COUNTER 961 bool 962 963config MEMCG 964 bool "Memory controller" 965 select PAGE_COUNTER 966 select EVENTFD 967 help 968 Provides control over the memory footprint of tasks in a cgroup. 969 970config MEMCG_SWAP 971 bool 972 depends on MEMCG && SWAP 973 default y 974 975config MEMCG_KMEM 976 bool 977 depends on MEMCG && !SLOB 978 default y 979 980config BLK_CGROUP 981 bool "IO controller" 982 depends on BLOCK 983 default n 984 help 985 Generic block IO controller cgroup interface. This is the common 986 cgroup interface which should be used by various IO controlling 987 policies. 988 989 Currently, CFQ IO scheduler uses it to recognize task groups and 990 control disk bandwidth allocation (proportional time slice allocation) 991 to such task groups. It is also used by bio throttling logic in 992 block layer to implement upper limit in IO rates on a device. 993 994 This option only enables generic Block IO controller infrastructure. 995 One needs to also enable actual IO controlling logic/policy. For 996 enabling proportional weight division of disk bandwidth in CFQ, set 997 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set 998 CONFIG_BLK_DEV_THROTTLING=y. 999 1000 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information. 1001 1002config CGROUP_WRITEBACK 1003 bool 1004 depends on MEMCG && BLK_CGROUP 1005 default y 1006 1007menuconfig CGROUP_SCHED 1008 bool "CPU controller" 1009 default n 1010 help 1011 This feature lets CPU scheduler recognize task groups and control CPU 1012 bandwidth allocation to such task groups. It uses cgroups to group 1013 tasks. 1014 1015if CGROUP_SCHED 1016config FAIR_GROUP_SCHED 1017 bool "Group scheduling for SCHED_OTHER" 1018 depends on CGROUP_SCHED 1019 default CGROUP_SCHED 1020 1021config CFS_BANDWIDTH 1022 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED" 1023 depends on FAIR_GROUP_SCHED 1024 default n 1025 help 1026 This option allows users to define CPU bandwidth rates (limits) for 1027 tasks running within the fair group scheduler. Groups with no limit 1028 set are considered to be unconstrained and will run with no 1029 restriction. 1030 See Documentation/scheduler/sched-bwc.rst for more information. 1031 1032config RT_GROUP_SCHED 1033 bool "Group scheduling for SCHED_RR/FIFO" 1034 depends on CGROUP_SCHED 1035 default n 1036 help 1037 This feature lets you explicitly allocate real CPU bandwidth 1038 to task groups. If enabled, it will also make it impossible to 1039 schedule realtime tasks for non-root users until you allocate 1040 realtime bandwidth for them. 1041 See Documentation/scheduler/sched-rt-group.rst for more information. 1042 1043endif #CGROUP_SCHED 1044 1045config UCLAMP_TASK_GROUP 1046 bool "Utilization clamping per group of tasks" 1047 depends on CGROUP_SCHED 1048 depends on UCLAMP_TASK 1049 default n 1050 help 1051 This feature enables the scheduler to track the clamped utilization 1052 of each CPU based on RUNNABLE tasks currently scheduled on that CPU. 1053 1054 When this option is enabled, the user can specify a min and max 1055 CPU bandwidth which is allowed for each single task in a group. 1056 The max bandwidth allows to clamp the maximum frequency a task 1057 can use, while the min bandwidth allows to define a minimum 1058 frequency a task will always use. 1059 1060 When task group based utilization clamping is enabled, an eventually 1061 specified task-specific clamp value is constrained by the cgroup 1062 specified clamp value. Both minimum and maximum task clamping cannot 1063 be bigger than the corresponding clamping defined at task group level. 1064 1065 If in doubt, say N. 1066 1067config CGROUP_PIDS 1068 bool "PIDs controller" 1069 help 1070 Provides enforcement of process number limits in the scope of a 1071 cgroup. Any attempt to fork more processes than is allowed in the 1072 cgroup will fail. PIDs are fundamentally a global resource because it 1073 is fairly trivial to reach PID exhaustion before you reach even a 1074 conservative kmemcg limit. As a result, it is possible to grind a 1075 system to halt without being limited by other cgroup policies. The 1076 PIDs controller is designed to stop this from happening. 1077 1078 It should be noted that organisational operations (such as attaching 1079 to a cgroup hierarchy) will *not* be blocked by the PIDs controller, 1080 since the PIDs limit only affects a process's ability to fork, not to 1081 attach to a cgroup. 1082 1083config CGROUP_RDMA 1084 bool "RDMA controller" 1085 help 1086 Provides enforcement of RDMA resources defined by IB stack. 1087 It is fairly easy for consumers to exhaust RDMA resources, which 1088 can result into resource unavailability to other consumers. 1089 RDMA controller is designed to stop this from happening. 1090 Attaching processes with active RDMA resources to the cgroup 1091 hierarchy is allowed even if can cross the hierarchy's limit. 1092 1093config CGROUP_FREEZER 1094 bool "Freezer controller" 1095 help 1096 Provides a way to freeze and unfreeze all tasks in a 1097 cgroup. 1098 1099 This option affects the ORIGINAL cgroup interface. The cgroup2 memory 1100 controller includes important in-kernel memory consumers per default. 1101 1102 If you're using cgroup2, say N. 1103 1104config CGROUP_HUGETLB 1105 bool "HugeTLB controller" 1106 depends on HUGETLB_PAGE 1107 select PAGE_COUNTER 1108 default n 1109 help 1110 Provides a cgroup controller for HugeTLB pages. 1111 When you enable this, you can put a per cgroup limit on HugeTLB usage. 1112 The limit is enforced during page fault. Since HugeTLB doesn't 1113 support page reclaim, enforcing the limit at page fault time implies 1114 that, the application will get SIGBUS signal if it tries to access 1115 HugeTLB pages beyond its limit. This requires the application to know 1116 beforehand how much HugeTLB pages it would require for its use. The 1117 control group is tracked in the third page lru pointer. This means 1118 that we cannot use the controller with huge page less than 3 pages. 1119 1120config CPUSETS 1121 bool "Cpuset controller" 1122 depends on SMP 1123 help 1124 This option will let you create and manage CPUSETs which 1125 allow dynamically partitioning a system into sets of CPUs and 1126 Memory Nodes and assigning tasks to run only within those sets. 1127 This is primarily useful on large SMP or NUMA systems. 1128 1129 Say N if unsure. 1130 1131config PROC_PID_CPUSET 1132 bool "Include legacy /proc/<pid>/cpuset file" 1133 depends on CPUSETS 1134 default y 1135 1136config CGROUP_DEVICE 1137 bool "Device controller" 1138 help 1139 Provides a cgroup controller implementing whitelists for 1140 devices which a process in the cgroup can mknod or open. 1141 1142config CGROUP_CPUACCT 1143 bool "Simple CPU accounting controller" 1144 help 1145 Provides a simple controller for monitoring the 1146 total CPU consumed by the tasks in a cgroup. 1147 1148config CGROUP_PERF 1149 bool "Perf controller" 1150 depends on PERF_EVENTS 1151 help 1152 This option extends the perf per-cpu mode to restrict monitoring 1153 to threads which belong to the cgroup specified and run on the 1154 designated cpu. Or this can be used to have cgroup ID in samples 1155 so that it can monitor performance events among cgroups. 1156 1157 Say N if unsure. 1158 1159config CGROUP_BPF 1160 bool "Support for eBPF programs attached to cgroups" 1161 depends on BPF_SYSCALL 1162 select SOCK_CGROUP_DATA 1163 help 1164 Allow attaching eBPF programs to a cgroup using the bpf(2) 1165 syscall command BPF_PROG_ATTACH. 1166 1167 In which context these programs are accessed depends on the type 1168 of attachment. For instance, programs that are attached using 1169 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of 1170 inet sockets. 1171 1172config CGROUP_DEBUG 1173 bool "Debug controller" 1174 default n 1175 depends on DEBUG_KERNEL 1176 help 1177 This option enables a simple controller that exports 1178 debugging information about the cgroups framework. This 1179 controller is for control cgroup debugging only. Its 1180 interfaces are not stable. 1181 1182 Say N. 1183 1184config SOCK_CGROUP_DATA 1185 bool 1186 default n 1187 1188endif # CGROUPS 1189 1190menuconfig NAMESPACES 1191 bool "Namespaces support" if EXPERT 1192 depends on MULTIUSER 1193 default !EXPERT 1194 help 1195 Provides the way to make tasks work with different objects using 1196 the same id. For example same IPC id may refer to different objects 1197 or same user id or pid may refer to different tasks when used in 1198 different namespaces. 1199 1200if NAMESPACES 1201 1202config UTS_NS 1203 bool "UTS namespace" 1204 default y 1205 help 1206 In this namespace tasks see different info provided with the 1207 uname() system call 1208 1209config TIME_NS 1210 bool "TIME namespace" 1211 depends on GENERIC_VDSO_TIME_NS 1212 default y 1213 help 1214 In this namespace boottime and monotonic clocks can be set. 1215 The time will keep going with the same pace. 1216 1217config IPC_NS 1218 bool "IPC namespace" 1219 depends on (SYSVIPC || POSIX_MQUEUE) 1220 default y 1221 help 1222 In this namespace tasks work with IPC ids which correspond to 1223 different IPC objects in different namespaces. 1224 1225config USER_NS 1226 bool "User namespace" 1227 default n 1228 help 1229 This allows containers, i.e. vservers, to use user namespaces 1230 to provide different user info for different servers. 1231 1232 When user namespaces are enabled in the kernel it is 1233 recommended that the MEMCG option also be enabled and that 1234 user-space use the memory control groups to limit the amount 1235 of memory a memory unprivileged users can use. 1236 1237 If unsure, say N. 1238 1239config PID_NS 1240 bool "PID Namespaces" 1241 default y 1242 help 1243 Support process id namespaces. This allows having multiple 1244 processes with the same pid as long as they are in different 1245 pid namespaces. This is a building block of containers. 1246 1247config NET_NS 1248 bool "Network namespace" 1249 depends on NET 1250 default y 1251 help 1252 Allow user space to create what appear to be multiple instances 1253 of the network stack. 1254 1255endif # NAMESPACES 1256 1257config CHECKPOINT_RESTORE 1258 bool "Checkpoint/restore support" 1259 select PROC_CHILDREN 1260 select KCMP 1261 default n 1262 help 1263 Enables additional kernel features in a sake of checkpoint/restore. 1264 In particular it adds auxiliary prctl codes to setup process text, 1265 data and heap segment sizes, and a few additional /proc filesystem 1266 entries. 1267 1268 If unsure, say N here. 1269 1270config SCHED_AUTOGROUP 1271 bool "Automatic process group scheduling" 1272 select CGROUPS 1273 select CGROUP_SCHED 1274 select FAIR_GROUP_SCHED 1275 help 1276 This option optimizes the scheduler for common desktop workloads by 1277 automatically creating and populating task groups. This separation 1278 of workloads isolates aggressive CPU burners (like build jobs) from 1279 desktop applications. Task group autogeneration is currently based 1280 upon task session. 1281 1282config SYSFS_DEPRECATED 1283 bool "Enable deprecated sysfs features to support old userspace tools" 1284 depends on SYSFS 1285 default n 1286 help 1287 This option adds code that switches the layout of the "block" class 1288 devices, to not show up in /sys/class/block/, but only in 1289 /sys/block/. 1290 1291 This switch is only active when the sysfs.deprecated=1 boot option is 1292 passed or the SYSFS_DEPRECATED_V2 option is set. 1293 1294 This option allows new kernels to run on old distributions and tools, 1295 which might get confused by /sys/class/block/. Since 2007/2008 all 1296 major distributions and tools handle this just fine. 1297 1298 Recent distributions and userspace tools after 2009/2010 depend on 1299 the existence of /sys/class/block/, and will not work with this 1300 option enabled. 1301 1302 Only if you are using a new kernel on an old distribution, you might 1303 need to say Y here. 1304 1305config SYSFS_DEPRECATED_V2 1306 bool "Enable deprecated sysfs features by default" 1307 default n 1308 depends on SYSFS 1309 depends on SYSFS_DEPRECATED 1310 help 1311 Enable deprecated sysfs by default. 1312 1313 See the CONFIG_SYSFS_DEPRECATED option for more details about this 1314 option. 1315 1316 Only if you are using a new kernel on an old distribution, you might 1317 need to say Y here. Even then, odds are you would not need it 1318 enabled, you can always pass the boot option if absolutely necessary. 1319 1320config RELAY 1321 bool "Kernel->user space relay support (formerly relayfs)" 1322 select IRQ_WORK 1323 help 1324 This option enables support for relay interface support in 1325 certain file systems (such as debugfs). 1326 It is designed to provide an efficient mechanism for tools and 1327 facilities to relay large amounts of data from kernel space to 1328 user space. 1329 1330 If unsure, say N. 1331 1332config BLK_DEV_INITRD 1333 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support" 1334 help 1335 The initial RAM filesystem is a ramfs which is loaded by the 1336 boot loader (loadlin or lilo) and that is mounted as root 1337 before the normal boot procedure. It is typically used to 1338 load modules needed to mount the "real" root file system, 1339 etc. See <file:Documentation/admin-guide/initrd.rst> for details. 1340 1341 If RAM disk support (BLK_DEV_RAM) is also included, this 1342 also enables initial RAM disk (initrd) support and adds 1343 15 Kbytes (more on some other architectures) to the kernel size. 1344 1345 If unsure say Y. 1346 1347if BLK_DEV_INITRD 1348 1349source "usr/Kconfig" 1350 1351endif 1352 1353config BOOT_CONFIG 1354 bool "Boot config support" 1355 select BLK_DEV_INITRD 1356 help 1357 Extra boot config allows system admin to pass a config file as 1358 complemental extension of kernel cmdline when booting. 1359 The boot config file must be attached at the end of initramfs 1360 with checksum, size and magic word. 1361 See <file:Documentation/admin-guide/bootconfig.rst> for details. 1362 1363 If unsure, say Y. 1364 1365choice 1366 prompt "Compiler optimization level" 1367 default CC_OPTIMIZE_FOR_PERFORMANCE 1368 1369config CC_OPTIMIZE_FOR_PERFORMANCE 1370 bool "Optimize for performance (-O2)" 1371 help 1372 This is the default optimization level for the kernel, building 1373 with the "-O2" compiler flag for best performance and most 1374 helpful compile-time warnings. 1375 1376config CC_OPTIMIZE_FOR_PERFORMANCE_O3 1377 bool "Optimize more for performance (-O3)" 1378 depends on ARC 1379 help 1380 Choosing this option will pass "-O3" to your compiler to optimize 1381 the kernel yet more for performance. 1382 1383config CC_OPTIMIZE_FOR_SIZE 1384 bool "Optimize for size (-Os)" 1385 help 1386 Choosing this option will pass "-Os" to your compiler resulting 1387 in a smaller kernel. 1388 1389endchoice 1390 1391config HAVE_LD_DEAD_CODE_DATA_ELIMINATION 1392 bool 1393 help 1394 This requires that the arch annotates or otherwise protects 1395 its external entry points from being discarded. Linker scripts 1396 must also merge .text.*, .data.*, and .bss.* correctly into 1397 output sections. Care must be taken not to pull in unrelated 1398 sections (e.g., '.text.init'). Typically '.' in section names 1399 is used to distinguish them from label names / C identifiers. 1400 1401config LD_DEAD_CODE_DATA_ELIMINATION 1402 bool "Dead code and data elimination (EXPERIMENTAL)" 1403 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION 1404 depends on EXPERT 1405 depends on $(cc-option,-ffunction-sections -fdata-sections) 1406 depends on $(ld-option,--gc-sections) 1407 help 1408 Enable this if you want to do dead code and data elimination with 1409 the linker by compiling with -ffunction-sections -fdata-sections, 1410 and linking with --gc-sections. 1411 1412 This can reduce on disk and in-memory size of the kernel 1413 code and static data, particularly for small configs and 1414 on small systems. This has the possibility of introducing 1415 silently broken kernel if the required annotations are not 1416 present. This option is not well tested yet, so use at your 1417 own risk. 1418 1419config LD_ORPHAN_WARN 1420 def_bool y 1421 depends on ARCH_WANT_LD_ORPHAN_WARN 1422 depends on !LD_IS_LLD || LLD_VERSION >= 110000 1423 depends on $(ld-option,--orphan-handling=warn) 1424 1425config SYSCTL 1426 bool 1427 1428config HAVE_UID16 1429 bool 1430 1431config SYSCTL_EXCEPTION_TRACE 1432 bool 1433 help 1434 Enable support for /proc/sys/debug/exception-trace. 1435 1436config SYSCTL_ARCH_UNALIGN_NO_WARN 1437 bool 1438 help 1439 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap 1440 Allows arch to define/use @no_unaligned_warning to possibly warn 1441 about unaligned access emulation going on under the hood. 1442 1443config SYSCTL_ARCH_UNALIGN_ALLOW 1444 bool 1445 help 1446 Enable support for /proc/sys/kernel/unaligned-trap 1447 Allows arches to define/use @unaligned_enabled to runtime toggle 1448 the unaligned access emulation. 1449 see arch/parisc/kernel/unaligned.c for reference 1450 1451config HAVE_PCSPKR_PLATFORM 1452 bool 1453 1454# interpreter that classic socket filters depend on 1455config BPF 1456 bool 1457 1458menuconfig EXPERT 1459 bool "Configure standard kernel features (expert users)" 1460 # Unhide debug options, to make the on-by-default options visible 1461 select DEBUG_KERNEL 1462 help 1463 This option allows certain base kernel options and settings 1464 to be disabled or tweaked. This is for specialized 1465 environments which can tolerate a "non-standard" kernel. 1466 Only use this if you really know what you are doing. 1467 1468config UID16 1469 bool "Enable 16-bit UID system calls" if EXPERT 1470 depends on HAVE_UID16 && MULTIUSER 1471 default y 1472 help 1473 This enables the legacy 16-bit UID syscall wrappers. 1474 1475config MULTIUSER 1476 bool "Multiple users, groups and capabilities support" if EXPERT 1477 default y 1478 help 1479 This option enables support for non-root users, groups and 1480 capabilities. 1481 1482 If you say N here, all processes will run with UID 0, GID 0, and all 1483 possible capabilities. Saying N here also compiles out support for 1484 system calls related to UIDs, GIDs, and capabilities, such as setuid, 1485 setgid, and capset. 1486 1487 If unsure, say Y here. 1488 1489config SGETMASK_SYSCALL 1490 bool "sgetmask/ssetmask syscalls support" if EXPERT 1491 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH 1492 help 1493 sys_sgetmask and sys_ssetmask are obsolete system calls 1494 no longer supported in libc but still enabled by default in some 1495 architectures. 1496 1497 If unsure, leave the default option here. 1498 1499config SYSFS_SYSCALL 1500 bool "Sysfs syscall support" if EXPERT 1501 default y 1502 help 1503 sys_sysfs is an obsolete system call no longer supported in libc. 1504 Note that disabling this option is more secure but might break 1505 compatibility with some systems. 1506 1507 If unsure say Y here. 1508 1509config FHANDLE 1510 bool "open by fhandle syscalls" if EXPERT 1511 select EXPORTFS 1512 default y 1513 help 1514 If you say Y here, a user level program will be able to map 1515 file names to handle and then later use the handle for 1516 different file system operations. This is useful in implementing 1517 userspace file servers, which now track files using handles instead 1518 of names. The handle would remain the same even if file names 1519 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) 1520 syscalls. 1521 1522config POSIX_TIMERS 1523 bool "Posix Clocks & timers" if EXPERT 1524 default y 1525 help 1526 This includes native support for POSIX timers to the kernel. 1527 Some embedded systems have no use for them and therefore they 1528 can be configured out to reduce the size of the kernel image. 1529 1530 When this option is disabled, the following syscalls won't be 1531 available: timer_create, timer_gettime: timer_getoverrun, 1532 timer_settime, timer_delete, clock_adjtime, getitimer, 1533 setitimer, alarm. Furthermore, the clock_settime, clock_gettime, 1534 clock_getres and clock_nanosleep syscalls will be limited to 1535 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only. 1536 1537 If unsure say y. 1538 1539config PRINTK 1540 default y 1541 bool "Enable support for printk" if EXPERT 1542 select IRQ_WORK 1543 help 1544 This option enables normal printk support. Removing it 1545 eliminates most of the message strings from the kernel image 1546 and makes the kernel more or less silent. As this makes it 1547 very difficult to diagnose system problems, saying N here is 1548 strongly discouraged. 1549 1550config PRINTK_NMI 1551 def_bool y 1552 depends on PRINTK 1553 depends on HAVE_NMI 1554 1555config BUG 1556 bool "BUG() support" if EXPERT 1557 default y 1558 help 1559 Disabling this option eliminates support for BUG and WARN, reducing 1560 the size of your kernel image and potentially quietly ignoring 1561 numerous fatal conditions. You should only consider disabling this 1562 option for embedded systems with no facilities for reporting errors. 1563 Just say Y. 1564 1565config ELF_CORE 1566 depends on COREDUMP 1567 default y 1568 bool "Enable ELF core dumps" if EXPERT 1569 help 1570 Enable support for generating core dumps. Disabling saves about 4k. 1571 1572 1573config PCSPKR_PLATFORM 1574 bool "Enable PC-Speaker support" if EXPERT 1575 depends on HAVE_PCSPKR_PLATFORM 1576 select I8253_LOCK 1577 default y 1578 help 1579 This option allows to disable the internal PC-Speaker 1580 support, saving some memory. 1581 1582config BASE_FULL 1583 default y 1584 bool "Enable full-sized data structures for core" if EXPERT 1585 help 1586 Disabling this option reduces the size of miscellaneous core 1587 kernel data structures. This saves memory on small machines, 1588 but may reduce performance. 1589 1590config FUTEX 1591 bool "Enable futex support" if EXPERT 1592 default y 1593 imply RT_MUTEXES 1594 help 1595 Disabling this option will cause the kernel to be built without 1596 support for "fast userspace mutexes". The resulting kernel may not 1597 run glibc-based applications correctly. 1598 1599config FUTEX_PI 1600 bool 1601 depends on FUTEX && RT_MUTEXES 1602 default y 1603 1604config HAVE_FUTEX_CMPXCHG 1605 bool 1606 depends on FUTEX 1607 help 1608 Architectures should select this if futex_atomic_cmpxchg_inatomic() 1609 is implemented and always working. This removes a couple of runtime 1610 checks. 1611 1612config EPOLL 1613 bool "Enable eventpoll support" if EXPERT 1614 default y 1615 help 1616 Disabling this option will cause the kernel to be built without 1617 support for epoll family of system calls. 1618 1619config SIGNALFD 1620 bool "Enable signalfd() system call" if EXPERT 1621 default y 1622 help 1623 Enable the signalfd() system call that allows to receive signals 1624 on a file descriptor. 1625 1626 If unsure, say Y. 1627 1628config TIMERFD 1629 bool "Enable timerfd() system call" if EXPERT 1630 default y 1631 help 1632 Enable the timerfd() system call that allows to receive timer 1633 events on a file descriptor. 1634 1635 If unsure, say Y. 1636 1637config EVENTFD 1638 bool "Enable eventfd() system call" if EXPERT 1639 default y 1640 help 1641 Enable the eventfd() system call that allows to receive both 1642 kernel notification (ie. KAIO) or userspace notifications. 1643 1644 If unsure, say Y. 1645 1646config SHMEM 1647 bool "Use full shmem filesystem" if EXPERT 1648 default y 1649 depends on MMU 1650 help 1651 The shmem is an internal filesystem used to manage shared memory. 1652 It is backed by swap and manages resource limits. It is also exported 1653 to userspace as tmpfs if TMPFS is enabled. Disabling this 1654 option replaces shmem and tmpfs with the much simpler ramfs code, 1655 which may be appropriate on small systems without swap. 1656 1657config AIO 1658 bool "Enable AIO support" if EXPERT 1659 default y 1660 help 1661 This option enables POSIX asynchronous I/O which may by used 1662 by some high performance threaded applications. Disabling 1663 this option saves about 7k. 1664 1665config IO_URING 1666 bool "Enable IO uring support" if EXPERT 1667 select IO_WQ 1668 default y 1669 help 1670 This option enables support for the io_uring interface, enabling 1671 applications to submit and complete IO through submission and 1672 completion rings that are shared between the kernel and application. 1673 1674config ADVISE_SYSCALLS 1675 bool "Enable madvise/fadvise syscalls" if EXPERT 1676 default y 1677 help 1678 This option enables the madvise and fadvise syscalls, used by 1679 applications to advise the kernel about their future memory or file 1680 usage, improving performance. If building an embedded system where no 1681 applications use these syscalls, you can disable this option to save 1682 space. 1683 1684config HAVE_ARCH_USERFAULTFD_WP 1685 bool 1686 help 1687 Arch has userfaultfd write protection support 1688 1689config MEMBARRIER 1690 bool "Enable membarrier() system call" if EXPERT 1691 default y 1692 help 1693 Enable the membarrier() system call that allows issuing memory 1694 barriers across all running threads, which can be used to distribute 1695 the cost of user-space memory barriers asymmetrically by transforming 1696 pairs of memory barriers into pairs consisting of membarrier() and a 1697 compiler barrier. 1698 1699 If unsure, say Y. 1700 1701config KALLSYMS 1702 bool "Load all symbols for debugging/ksymoops" if EXPERT 1703 default y 1704 help 1705 Say Y here to let the kernel print out symbolic crash information and 1706 symbolic stack backtraces. This increases the size of the kernel 1707 somewhat, as all symbols have to be loaded into the kernel image. 1708 1709config KALLSYMS_ALL 1710 bool "Include all symbols in kallsyms" 1711 depends on DEBUG_KERNEL && KALLSYMS 1712 help 1713 Normally kallsyms only contains the symbols of functions for nicer 1714 OOPS messages and backtraces (i.e., symbols from the text and inittext 1715 sections). This is sufficient for most cases. And only in very rare 1716 cases (e.g., when a debugger is used) all symbols are required (e.g., 1717 names of variables from the data sections, etc). 1718 1719 This option makes sure that all symbols are loaded into the kernel 1720 image (i.e., symbols from all sections) in cost of increased kernel 1721 size (depending on the kernel configuration, it may be 300KiB or 1722 something like this). 1723 1724 Say N unless you really need all symbols. 1725 1726config KALLSYMS_ABSOLUTE_PERCPU 1727 bool 1728 depends on KALLSYMS 1729 default X86_64 && SMP 1730 1731config KALLSYMS_BASE_RELATIVE 1732 bool 1733 depends on KALLSYMS 1734 default !IA64 1735 help 1736 Instead of emitting them as absolute values in the native word size, 1737 emit the symbol references in the kallsyms table as 32-bit entries, 1738 each containing a relative value in the range [base, base + U32_MAX] 1739 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either 1740 an absolute value in the range [0, S32_MAX] or a relative value in the 1741 range [base, base + S32_MAX], where base is the lowest relative symbol 1742 address encountered in the image. 1743 1744 On 64-bit builds, this reduces the size of the address table by 50%, 1745 but more importantly, it results in entries whose values are build 1746 time constants, and no relocation pass is required at runtime to fix 1747 up the entries based on the runtime load address of the kernel. 1748 1749# end of the "standard kernel features (expert users)" menu 1750 1751# syscall, maps, verifier 1752 1753config BPF_LSM 1754 bool "LSM Instrumentation with BPF" 1755 depends on BPF_EVENTS 1756 depends on BPF_SYSCALL 1757 depends on SECURITY 1758 depends on BPF_JIT 1759 help 1760 Enables instrumentation of the security hooks with eBPF programs for 1761 implementing dynamic MAC and Audit Policies. 1762 1763 If you are unsure how to answer this question, answer N. 1764 1765config BPF_SYSCALL 1766 bool "Enable bpf() system call" 1767 select BPF 1768 select IRQ_WORK 1769 select TASKS_TRACE_RCU 1770 default n 1771 help 1772 Enable the bpf() system call that allows to manipulate eBPF 1773 programs and maps via file descriptors. 1774 1775config ARCH_WANT_DEFAULT_BPF_JIT 1776 bool 1777 1778config BPF_JIT_ALWAYS_ON 1779 bool "Permanently enable BPF JIT and remove BPF interpreter" 1780 depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT 1781 help 1782 Enables BPF JIT and removes BPF interpreter to avoid 1783 speculative execution of BPF instructions by the interpreter 1784 1785config BPF_JIT_DEFAULT_ON 1786 def_bool ARCH_WANT_DEFAULT_BPF_JIT || BPF_JIT_ALWAYS_ON 1787 depends on HAVE_EBPF_JIT && BPF_JIT 1788 1789config BPF_UNPRIV_DEFAULT_OFF 1790 bool "Disable unprivileged BPF by default" 1791 depends on BPF_SYSCALL 1792 help 1793 Disables unprivileged BPF by default by setting the corresponding 1794 /proc/sys/kernel/unprivileged_bpf_disabled knob to 2. An admin can 1795 still reenable it by setting it to 0 later on, or permanently 1796 disable it by setting it to 1 (from which no other transition to 1797 0 is possible anymore). 1798 1799source "kernel/bpf/preload/Kconfig" 1800 1801config USERFAULTFD 1802 bool "Enable userfaultfd() system call" 1803 depends on MMU 1804 help 1805 Enable the userfaultfd() system call that allows to intercept and 1806 handle page faults in userland. 1807 1808config ARCH_HAS_MEMBARRIER_CALLBACKS 1809 bool 1810 1811config ARCH_HAS_MEMBARRIER_SYNC_CORE 1812 bool 1813 1814config KCMP 1815 bool "Enable kcmp() system call" if EXPERT 1816 help 1817 Enable the kernel resource comparison system call. It provides 1818 user-space with the ability to compare two processes to see if they 1819 share a common resource, such as a file descriptor or even virtual 1820 memory space. 1821 1822 If unsure, say N. 1823 1824config RSEQ 1825 bool "Enable rseq() system call" if EXPERT 1826 default y 1827 depends on HAVE_RSEQ 1828 select MEMBARRIER 1829 help 1830 Enable the restartable sequences system call. It provides a 1831 user-space cache for the current CPU number value, which 1832 speeds up getting the current CPU number from user-space, 1833 as well as an ABI to speed up user-space operations on 1834 per-CPU data. 1835 1836 If unsure, say Y. 1837 1838config DEBUG_RSEQ 1839 default n 1840 bool "Enabled debugging of rseq() system call" if EXPERT 1841 depends on RSEQ && DEBUG_KERNEL 1842 help 1843 Enable extra debugging checks for the rseq system call. 1844 1845 If unsure, say N. 1846 1847config EMBEDDED 1848 bool "Embedded system" 1849 option allnoconfig_y 1850 select EXPERT 1851 help 1852 This option should be enabled if compiling the kernel for 1853 an embedded system so certain expert options are available 1854 for configuration. 1855 1856config HAVE_PERF_EVENTS 1857 bool 1858 help 1859 See tools/perf/design.txt for details. 1860 1861config PERF_USE_VMALLOC 1862 bool 1863 help 1864 See tools/perf/design.txt for details 1865 1866config PC104 1867 bool "PC/104 support" if EXPERT 1868 help 1869 Expose PC/104 form factor device drivers and options available for 1870 selection and configuration. Enable this option if your target 1871 machine has a PC/104 bus. 1872 1873menu "Kernel Performance Events And Counters" 1874 1875config PERF_EVENTS 1876 bool "Kernel performance events and counters" 1877 default y if PROFILING 1878 depends on HAVE_PERF_EVENTS 1879 select IRQ_WORK 1880 select SRCU 1881 help 1882 Enable kernel support for various performance events provided 1883 by software and hardware. 1884 1885 Software events are supported either built-in or via the 1886 use of generic tracepoints. 1887 1888 Most modern CPUs support performance events via performance 1889 counter registers. These registers count the number of certain 1890 types of hw events: such as instructions executed, cachemisses 1891 suffered, or branches mis-predicted - without slowing down the 1892 kernel or applications. These registers can also trigger interrupts 1893 when a threshold number of events have passed - and can thus be 1894 used to profile the code that runs on that CPU. 1895 1896 The Linux Performance Event subsystem provides an abstraction of 1897 these software and hardware event capabilities, available via a 1898 system call and used by the "perf" utility in tools/perf/. It 1899 provides per task and per CPU counters, and it provides event 1900 capabilities on top of those. 1901 1902 Say Y if unsure. 1903 1904config DEBUG_PERF_USE_VMALLOC 1905 default n 1906 bool "Debug: use vmalloc to back perf mmap() buffers" 1907 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC 1908 select PERF_USE_VMALLOC 1909 help 1910 Use vmalloc memory to back perf mmap() buffers. 1911 1912 Mostly useful for debugging the vmalloc code on platforms 1913 that don't require it. 1914 1915 Say N if unsure. 1916 1917endmenu 1918 1919config VM_EVENT_COUNTERS 1920 default y 1921 bool "Enable VM event counters for /proc/vmstat" if EXPERT 1922 help 1923 VM event counters are needed for event counts to be shown. 1924 This option allows the disabling of the VM event counters 1925 on EXPERT systems. /proc/vmstat will only show page counts 1926 if VM event counters are disabled. 1927 1928config SLUB_DEBUG 1929 default y 1930 bool "Enable SLUB debugging support" if EXPERT 1931 depends on SLUB && SYSFS 1932 help 1933 SLUB has extensive debug support features. Disabling these can 1934 result in significant savings in code size. This also disables 1935 SLUB sysfs support. /sys/slab will not exist and there will be 1936 no support for cache validation etc. 1937 1938config SLUB_MEMCG_SYSFS_ON 1939 default n 1940 bool "Enable memcg SLUB sysfs support by default" if EXPERT 1941 depends on SLUB && SYSFS && MEMCG 1942 help 1943 SLUB creates a directory under /sys/kernel/slab for each 1944 allocation cache to host info and debug files. If memory 1945 cgroup is enabled, each cache can have per memory cgroup 1946 caches. SLUB can create the same sysfs directories for these 1947 caches under /sys/kernel/slab/CACHE/cgroup but it can lead 1948 to a very high number of debug files being created. This is 1949 controlled by slub_memcg_sysfs boot parameter and this 1950 config option determines the parameter's default value. 1951 1952config COMPAT_BRK 1953 bool "Disable heap randomization" 1954 default y 1955 help 1956 Randomizing heap placement makes heap exploits harder, but it 1957 also breaks ancient binaries (including anything libc5 based). 1958 This option changes the bootup default to heap randomization 1959 disabled, and can be overridden at runtime by setting 1960 /proc/sys/kernel/randomize_va_space to 2. 1961 1962 On non-ancient distros (post-2000 ones) N is usually a safe choice. 1963 1964choice 1965 prompt "Choose SLAB allocator" 1966 default SLUB 1967 help 1968 This option allows to select a slab allocator. 1969 1970config SLAB 1971 bool "SLAB" 1972 select HAVE_HARDENED_USERCOPY_ALLOCATOR 1973 help 1974 The regular slab allocator that is established and known to work 1975 well in all environments. It organizes cache hot objects in 1976 per cpu and per node queues. 1977 1978config SLUB 1979 bool "SLUB (Unqueued Allocator)" 1980 select HAVE_HARDENED_USERCOPY_ALLOCATOR 1981 help 1982 SLUB is a slab allocator that minimizes cache line usage 1983 instead of managing queues of cached objects (SLAB approach). 1984 Per cpu caching is realized using slabs of objects instead 1985 of queues of objects. SLUB can use memory efficiently 1986 and has enhanced diagnostics. SLUB is the default choice for 1987 a slab allocator. 1988 1989config SLOB 1990 depends on EXPERT 1991 bool "SLOB (Simple Allocator)" 1992 help 1993 SLOB replaces the stock allocator with a drastically simpler 1994 allocator. SLOB is generally more space efficient but 1995 does not perform as well on large systems. 1996 1997endchoice 1998 1999config SLAB_MERGE_DEFAULT 2000 bool "Allow slab caches to be merged" 2001 default y 2002 help 2003 For reduced kernel memory fragmentation, slab caches can be 2004 merged when they share the same size and other characteristics. 2005 This carries a risk of kernel heap overflows being able to 2006 overwrite objects from merged caches (and more easily control 2007 cache layout), which makes such heap attacks easier to exploit 2008 by attackers. By keeping caches unmerged, these kinds of exploits 2009 can usually only damage objects in the same cache. To disable 2010 merging at runtime, "slab_nomerge" can be passed on the kernel 2011 command line. 2012 2013config SLAB_FREELIST_RANDOM 2014 bool "Randomize slab freelist" 2015 depends on SLAB || SLUB 2016 help 2017 Randomizes the freelist order used on creating new pages. This 2018 security feature reduces the predictability of the kernel slab 2019 allocator against heap overflows. 2020 2021config SLAB_FREELIST_HARDENED 2022 bool "Harden slab freelist metadata" 2023 depends on SLAB || SLUB 2024 help 2025 Many kernel heap attacks try to target slab cache metadata and 2026 other infrastructure. This options makes minor performance 2027 sacrifices to harden the kernel slab allocator against common 2028 freelist exploit methods. Some slab implementations have more 2029 sanity-checking than others. This option is most effective with 2030 CONFIG_SLUB. 2031 2032config SHUFFLE_PAGE_ALLOCATOR 2033 bool "Page allocator randomization" 2034 default SLAB_FREELIST_RANDOM && ACPI_NUMA 2035 help 2036 Randomization of the page allocator improves the average 2037 utilization of a direct-mapped memory-side-cache. See section 2038 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI 2039 6.2a specification for an example of how a platform advertises 2040 the presence of a memory-side-cache. There are also incidental 2041 security benefits as it reduces the predictability of page 2042 allocations to compliment SLAB_FREELIST_RANDOM, but the 2043 default granularity of shuffling on the "MAX_ORDER - 1" i.e, 2044 10th order of pages is selected based on cache utilization 2045 benefits on x86. 2046 2047 While the randomization improves cache utilization it may 2048 negatively impact workloads on platforms without a cache. For 2049 this reason, by default, the randomization is enabled only 2050 after runtime detection of a direct-mapped memory-side-cache. 2051 Otherwise, the randomization may be force enabled with the 2052 'page_alloc.shuffle' kernel command line parameter. 2053 2054 Say Y if unsure. 2055 2056config SLUB_CPU_PARTIAL 2057 default y 2058 depends on SLUB && SMP 2059 bool "SLUB per cpu partial cache" 2060 help 2061 Per cpu partial caches accelerate objects allocation and freeing 2062 that is local to a processor at the price of more indeterminism 2063 in the latency of the free. On overflow these caches will be cleared 2064 which requires the taking of locks that may cause latency spikes. 2065 Typically one would choose no for a realtime system. 2066 2067config MMAP_ALLOW_UNINITIALIZED 2068 bool "Allow mmapped anonymous memory to be uninitialized" 2069 depends on EXPERT && !MMU 2070 default n 2071 help 2072 Normally, and according to the Linux spec, anonymous memory obtained 2073 from mmap() has its contents cleared before it is passed to 2074 userspace. Enabling this config option allows you to request that 2075 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus 2076 providing a huge performance boost. If this option is not enabled, 2077 then the flag will be ignored. 2078 2079 This is taken advantage of by uClibc's malloc(), and also by 2080 ELF-FDPIC binfmt's brk and stack allocator. 2081 2082 Because of the obvious security issues, this option should only be 2083 enabled on embedded devices where you control what is run in 2084 userspace. Since that isn't generally a problem on no-MMU systems, 2085 it is normally safe to say Y here. 2086 2087 See Documentation/admin-guide/mm/nommu-mmap.rst for more information. 2088 2089config SYSTEM_DATA_VERIFICATION 2090 def_bool n 2091 select SYSTEM_TRUSTED_KEYRING 2092 select KEYS 2093 select CRYPTO 2094 select CRYPTO_RSA 2095 select ASYMMETRIC_KEY_TYPE 2096 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE 2097 select ASN1 2098 select OID_REGISTRY 2099 select X509_CERTIFICATE_PARSER 2100 select PKCS7_MESSAGE_PARSER 2101 help 2102 Provide PKCS#7 message verification using the contents of the system 2103 trusted keyring to provide public keys. This then can be used for 2104 module verification, kexec image verification and firmware blob 2105 verification. 2106 2107config PROFILING 2108 bool "Profiling support" 2109 help 2110 Say Y here to enable the extended profiling support mechanisms used 2111 by profilers such as OProfile. 2112 2113# 2114# Place an empty function call at each tracepoint site. Can be 2115# dynamically changed for a probe function. 2116# 2117config TRACEPOINTS 2118 bool 2119 2120endmenu # General setup 2121 2122source "arch/Kconfig" 2123 2124config RT_MUTEXES 2125 bool 2126 2127config BASE_SMALL 2128 int 2129 default 0 if BASE_FULL 2130 default 1 if !BASE_FULL 2131 2132config MODULE_SIG_FORMAT 2133 def_bool n 2134 select SYSTEM_DATA_VERIFICATION 2135 2136menuconfig MODULES 2137 bool "Enable loadable module support" 2138 option modules 2139 help 2140 Kernel modules are small pieces of compiled code which can 2141 be inserted in the running kernel, rather than being 2142 permanently built into the kernel. You use the "modprobe" 2143 tool to add (and sometimes remove) them. If you say Y here, 2144 many parts of the kernel can be built as modules (by 2145 answering M instead of Y where indicated): this is most 2146 useful for infrequently used options which are not required 2147 for booting. For more information, see the man pages for 2148 modprobe, lsmod, modinfo, insmod and rmmod. 2149 2150 If you say Y here, you will need to run "make 2151 modules_install" to put the modules under /lib/modules/ 2152 where modprobe can find them (you may need to be root to do 2153 this). 2154 2155 If unsure, say Y. 2156 2157if MODULES 2158 2159config MODULE_FORCE_LOAD 2160 bool "Forced module loading" 2161 default n 2162 help 2163 Allow loading of modules without version information (ie. modprobe 2164 --force). Forced module loading sets the 'F' (forced) taint flag and 2165 is usually a really bad idea. 2166 2167config MODULE_UNLOAD 2168 bool "Module unloading" 2169 help 2170 Without this option you will not be able to unload any 2171 modules (note that some modules may not be unloadable 2172 anyway), which makes your kernel smaller, faster 2173 and simpler. If unsure, say Y. 2174 2175config MODULE_FORCE_UNLOAD 2176 bool "Forced module unloading" 2177 depends on MODULE_UNLOAD 2178 help 2179 This option allows you to force a module to unload, even if the 2180 kernel believes it is unsafe: the kernel will remove the module 2181 without waiting for anyone to stop using it (using the -f option to 2182 rmmod). This is mainly for kernel developers and desperate users. 2183 If unsure, say N. 2184 2185config MODVERSIONS 2186 bool "Module versioning support" 2187 help 2188 Usually, you have to use modules compiled with your kernel. 2189 Saying Y here makes it sometimes possible to use modules 2190 compiled for different kernels, by adding enough information 2191 to the modules to (hopefully) spot any changes which would 2192 make them incompatible with the kernel you are running. If 2193 unsure, say N. 2194 2195config ASM_MODVERSIONS 2196 bool 2197 default HAVE_ASM_MODVERSIONS && MODVERSIONS 2198 help 2199 This enables module versioning for exported symbols also from 2200 assembly. This can be enabled only when the target architecture 2201 supports it. 2202 2203config MODULE_REL_CRCS 2204 bool 2205 depends on MODVERSIONS 2206 2207config MODULE_SRCVERSION_ALL 2208 bool "Source checksum for all modules" 2209 help 2210 Modules which contain a MODULE_VERSION get an extra "srcversion" 2211 field inserted into their modinfo section, which contains a 2212 sum of the source files which made it. This helps maintainers 2213 see exactly which source was used to build a module (since 2214 others sometimes change the module source without updating 2215 the version). With this option, such a "srcversion" field 2216 will be created for all modules. If unsure, say N. 2217 2218config MODULE_SIG 2219 bool "Module signature verification" 2220 select MODULE_SIG_FORMAT 2221 help 2222 Check modules for valid signatures upon load: the signature 2223 is simply appended to the module. For more information see 2224 <file:Documentation/admin-guide/module-signing.rst>. 2225 2226 Note that this option adds the OpenSSL development packages as a 2227 kernel build dependency so that the signing tool can use its crypto 2228 library. 2229 2230 You should enable this option if you wish to use either 2231 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via 2232 another LSM - otherwise unsigned modules will be loadable regardless 2233 of the lockdown policy. 2234 2235 !!!WARNING!!! If you enable this option, you MUST make sure that the 2236 module DOES NOT get stripped after being signed. This includes the 2237 debuginfo strip done by some packagers (such as rpmbuild) and 2238 inclusion into an initramfs that wants the module size reduced. 2239 2240config MODULE_SIG_FORCE 2241 bool "Require modules to be validly signed" 2242 depends on MODULE_SIG 2243 help 2244 Reject unsigned modules or signed modules for which we don't have a 2245 key. Without this, such modules will simply taint the kernel. 2246 2247config MODULE_SIG_ALL 2248 bool "Automatically sign all modules" 2249 default y 2250 depends on MODULE_SIG 2251 help 2252 Sign all modules during make modules_install. Without this option, 2253 modules must be signed manually, using the scripts/sign-file tool. 2254 2255comment "Do not forget to sign required modules with scripts/sign-file" 2256 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL 2257 2258choice 2259 prompt "Which hash algorithm should modules be signed with?" 2260 depends on MODULE_SIG 2261 help 2262 This determines which sort of hashing algorithm will be used during 2263 signature generation. This algorithm _must_ be built into the kernel 2264 directly so that signature verification can take place. It is not 2265 possible to load a signed module containing the algorithm to check 2266 the signature on that module. 2267 2268config MODULE_SIG_SHA1 2269 bool "Sign modules with SHA-1" 2270 select CRYPTO_SHA1 2271 2272config MODULE_SIG_SHA224 2273 bool "Sign modules with SHA-224" 2274 select CRYPTO_SHA256 2275 2276config MODULE_SIG_SHA256 2277 bool "Sign modules with SHA-256" 2278 select CRYPTO_SHA256 2279 2280config MODULE_SIG_SHA384 2281 bool "Sign modules with SHA-384" 2282 select CRYPTO_SHA512 2283 2284config MODULE_SIG_SHA512 2285 bool "Sign modules with SHA-512" 2286 select CRYPTO_SHA512 2287 2288endchoice 2289 2290config MODULE_SIG_HASH 2291 string 2292 depends on MODULE_SIG 2293 default "sha1" if MODULE_SIG_SHA1 2294 default "sha224" if MODULE_SIG_SHA224 2295 default "sha256" if MODULE_SIG_SHA256 2296 default "sha384" if MODULE_SIG_SHA384 2297 default "sha512" if MODULE_SIG_SHA512 2298 2299config MODULE_COMPRESS 2300 bool "Compress modules on installation" 2301 help 2302 2303 Compresses kernel modules when 'make modules_install' is run; gzip or 2304 xz depending on "Compression algorithm" below. 2305 2306 module-init-tools MAY support gzip, and kmod MAY support gzip and xz. 2307 2308 Out-of-tree kernel modules installed using Kbuild will also be 2309 compressed upon installation. 2310 2311 Note: for modules inside an initrd or initramfs, it's more efficient 2312 to compress the whole initrd or initramfs instead. 2313 2314 Note: This is fully compatible with signed modules. 2315 2316 If in doubt, say N. 2317 2318choice 2319 prompt "Compression algorithm" 2320 depends on MODULE_COMPRESS 2321 default MODULE_COMPRESS_GZIP 2322 help 2323 This determines which sort of compression will be used during 2324 'make modules_install'. 2325 2326 GZIP (default) and XZ are supported. 2327 2328config MODULE_COMPRESS_GZIP 2329 bool "GZIP" 2330 2331config MODULE_COMPRESS_XZ 2332 bool "XZ" 2333 2334endchoice 2335 2336config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS 2337 bool "Allow loading of modules with missing namespace imports" 2338 help 2339 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in 2340 a namespace. A module that makes use of a symbol exported with such a 2341 namespace is required to import the namespace via MODULE_IMPORT_NS(). 2342 There is no technical reason to enforce correct namespace imports, 2343 but it creates consistency between symbols defining namespaces and 2344 users importing namespaces they make use of. This option relaxes this 2345 requirement and lifts the enforcement when loading a module. 2346 2347 If unsure, say N. 2348 2349config UNUSED_SYMBOLS 2350 bool "Enable unused/obsolete exported symbols" 2351 default y if X86 2352 help 2353 Unused but exported symbols make the kernel needlessly bigger. For 2354 that reason most of these unused exports will soon be removed. This 2355 option is provided temporarily to provide a transition period in case 2356 some external kernel module needs one of these symbols anyway. If you 2357 encounter such a case in your module, consider if you are actually 2358 using the right API. (rationale: since nobody in the kernel is using 2359 this in a module, there is a pretty good chance it's actually the 2360 wrong interface to use). If you really need the symbol, please send a 2361 mail to the linux kernel mailing list mentioning the symbol and why 2362 you really need it, and what the merge plan to the mainline kernel for 2363 your module is. 2364 2365config TRIM_UNUSED_KSYMS 2366 bool "Trim unused exported kernel symbols" 2367 depends on !UNUSED_SYMBOLS 2368 help 2369 The kernel and some modules make many symbols available for 2370 other modules to use via EXPORT_SYMBOL() and variants. Depending 2371 on the set of modules being selected in your kernel configuration, 2372 many of those exported symbols might never be used. 2373 2374 This option allows for unused exported symbols to be dropped from 2375 the build. In turn, this provides the compiler more opportunities 2376 (especially when using LTO) for optimizing the code and reducing 2377 binary size. This might have some security advantages as well. 2378 2379 If unsure, or if you need to build out-of-tree modules, say N. 2380 2381config UNUSED_KSYMS_WHITELIST 2382 string "Whitelist of symbols to keep in ksymtab" 2383 depends on TRIM_UNUSED_KSYMS 2384 help 2385 By default, all unused exported symbols will be un-exported from the 2386 build when TRIM_UNUSED_KSYMS is selected. 2387 2388 UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept 2389 exported at all times, even in absence of in-tree users. The value to 2390 set here is the path to a text file containing the list of symbols, 2391 one per line. The path can be absolute, or relative to the kernel 2392 source tree. 2393 2394endif # MODULES 2395 2396config MODULES_TREE_LOOKUP 2397 def_bool y 2398 depends on PERF_EVENTS || TRACING || CFI_CLANG 2399 2400config INIT_ALL_POSSIBLE 2401 bool 2402 help 2403 Back when each arch used to define their own cpu_online_mask and 2404 cpu_possible_mask, some of them chose to initialize cpu_possible_mask 2405 with all 1s, and others with all 0s. When they were centralised, 2406 it was better to provide this option than to break all the archs 2407 and have several arch maintainers pursuing me down dark alleys. 2408 2409source "block/Kconfig" 2410 2411config PREEMPT_NOTIFIERS 2412 bool 2413 2414config PADATA 2415 depends on SMP 2416 bool 2417 2418config ASN1 2419 tristate 2420 help 2421 Build a simple ASN.1 grammar compiler that produces a bytecode output 2422 that can be interpreted by the ASN.1 stream decoder and used to 2423 inform it as to what tags are to be expected in a stream and what 2424 functions to call on what tags. 2425 2426source "kernel/Kconfig.locks" 2427 2428config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE 2429 bool 2430 2431config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE 2432 bool 2433 2434# It may be useful for an architecture to override the definitions of the 2435# SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h> 2436# and the COMPAT_ variants in <linux/compat.h>, in particular to use a 2437# different calling convention for syscalls. They can also override the 2438# macros for not-implemented syscalls in kernel/sys_ni.c and 2439# kernel/time/posix-stubs.c. All these overrides need to be available in 2440# <asm/syscall_wrapper.h>. 2441config ARCH_HAS_SYSCALL_WRAPPER 2442 def_bool n 2443