1# SPDX-License-Identifier: GPL-2.0-only 2config CC_VERSION_TEXT 3 string 4 default "$(CC_VERSION_TEXT)" 5 help 6 This is used in unclear ways: 7 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. 12 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. 18 19config CC_IS_GCC 20 def_bool $(success,test "$(cc-name)" = GCC) 21 22config GCC_VERSION 23 int 24 default $(cc-version) if CC_IS_GCC 25 default 0 26 27config CC_IS_CLANG 28 def_bool $(success,test "$(cc-name)" = Clang) 29 30config CLANG_VERSION 31 int 32 default $(cc-version) if CC_IS_CLANG 33 default 0 34 35config AS_IS_GNU 36 def_bool $(success,test "$(as-name)" = GNU) 37 38config AS_IS_LLVM 39 def_bool $(success,test "$(as-name)" = LLVM) 40 41config AS_VERSION 42 int 43 # Use clang version if this is the integrated assembler 44 default CLANG_VERSION if AS_IS_LLVM 45 default $(as-version) 46 47config LD_IS_BFD 48 def_bool $(success,test "$(ld-name)" = BFD) 49 50config LD_VERSION 51 int 52 default $(ld-version) if LD_IS_BFD 53 default 0 54 55config LD_IS_LLD 56 def_bool $(success,test "$(ld-name)" = LLD) 57 58config LLD_VERSION 59 int 60 default $(ld-version) if LD_IS_LLD 61 default 0 62 63config CC_CAN_LINK 64 bool 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)) 67 68config CC_CAN_LINK_STATIC 69 bool 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) 72 73config CC_HAS_ASM_GOTO 74 def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) 75 76config 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) 79 80config TOOLS_SUPPORT_RELR 81 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh) 82 83config CC_HAS_ASM_INLINE 84 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null) 85 86config CC_HAS_NO_PROFILE_FN_ATTR 87 def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror) 88 89config PAHOLE_VERSION 90 int 91 default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE)) 92 93config CONSTRUCTORS 94 bool 95 96config IRQ_WORK 97 bool 98 99config BUILDTIME_TABLE_SORT 100 bool 101 102config THREAD_INFO_IN_TASK 103 bool 104 help 105 Select this to move thread_info off the stack into task_struct. To 106 make this work, an arch will need to remove all thread_info fields 107 except flags and fix any runtime bugs. 108 109 One subtle change that will be needed is to use try_get_task_stack() 110 and put_task_stack() in save_thread_stack_tsk() and get_wchan(). 111 112menu "General setup" 113 114config BROKEN 115 bool 116 117config BROKEN_ON_SMP 118 bool 119 depends on BROKEN || !SMP 120 default y 121 122config INIT_ENV_ARG_LIMIT 123 int 124 default 32 if !UML 125 default 128 if UML 126 help 127 Maximum of each of the number of arguments and environment 128 variables passed to init from the kernel command line. 129 130config COMPILE_TEST 131 bool "Compile also drivers which will not load" 132 depends on HAS_IOMEM 133 help 134 Some drivers can be compiled on a different platform than they are 135 intended to be run on. Despite they cannot be loaded there (or even 136 when they load they cannot be used due to missing HW support), 137 developers still, opposing to distributors, might want to build such 138 drivers to compile-test them. 139 140 If you are a developer and want to build everything available, say Y 141 here. If you are a user/distributor, say N here to exclude useless 142 drivers to be distributed. 143 144config WERROR 145 bool "Compile the kernel with warnings as errors" 146 default COMPILE_TEST 147 help 148 A kernel build should not cause any compiler warnings, and this 149 enables the '-Werror' flag to enforce that rule by default. 150 151 However, if you have a new (or very old) compiler with odd and 152 unusual warnings, or you have some architecture with problems, 153 you may need to disable this config option in order to 154 successfully build the kernel. 155 156 If in doubt, say Y. 157 158config UAPI_HEADER_TEST 159 bool "Compile test UAPI headers" 160 depends on HEADERS_INSTALL && CC_CAN_LINK 161 help 162 Compile test headers exported to user-space to ensure they are 163 self-contained, i.e. compilable as standalone units. 164 165 If you are a developer or tester and want to ensure the exported 166 headers are self-contained, say Y here. Otherwise, choose N. 167 168config LOCALVERSION 169 string "Local version - append to kernel release" 170 help 171 Append an extra string to the end of your kernel version. 172 This will show up when you type uname, for example. 173 The string you set here will be appended after the contents of 174 any files with a filename matching localversion* in your 175 object and source tree, in that order. Your total string can 176 be a maximum of 64 characters. 177 178config LOCALVERSION_AUTO 179 bool "Automatically append version information to the version string" 180 default y 181 depends on !COMPILE_TEST 182 help 183 This will try to automatically determine if the current tree is a 184 release tree by looking for git tags that belong to the current 185 top of tree revision. 186 187 A string of the format -gxxxxxxxx will be added to the localversion 188 if a git-based tree is found. The string generated by this will be 189 appended after any matching localversion* files, and after the value 190 set in CONFIG_LOCALVERSION. 191 192 (The actual string used here is the first eight characters produced 193 by running the command: 194 195 $ git rev-parse --verify HEAD 196 197 which is done within the script "scripts/setlocalversion".) 198 199config BUILD_SALT 200 string "Build ID Salt" 201 default "" 202 help 203 The build ID is used to link binaries and their debug info. Setting 204 this option will use the value in the calculation of the build id. 205 This is mostly useful for distributions which want to ensure the 206 build is unique between builds. It's safe to leave the default. 207 208config HAVE_KERNEL_GZIP 209 bool 210 211config HAVE_KERNEL_BZIP2 212 bool 213 214config HAVE_KERNEL_LZMA 215 bool 216 217config HAVE_KERNEL_XZ 218 bool 219 220config HAVE_KERNEL_LZO 221 bool 222 223config HAVE_KERNEL_LZ4 224 bool 225 226config HAVE_KERNEL_ZSTD 227 bool 228 229config HAVE_KERNEL_UNCOMPRESSED 230 bool 231 232choice 233 prompt "Kernel compression mode" 234 default KERNEL_GZIP 235 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_ZSTD || HAVE_KERNEL_UNCOMPRESSED 236 help 237 The linux kernel is a kind of self-extracting executable. 238 Several compression algorithms are available, which differ 239 in efficiency, compression and decompression speed. 240 Compression speed is only relevant when building a kernel. 241 Decompression speed is relevant at each boot. 242 243 If you have any problems with bzip2 or lzma compressed 244 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older 245 version of this functionality (bzip2 only), for 2.4, was 246 supplied by Christian Ludwig) 247 248 High compression options are mostly useful for users, who 249 are low on disk space (embedded systems), but for whom ram 250 size matters less. 251 252 If in doubt, select 'gzip' 253 254config KERNEL_GZIP 255 bool "Gzip" 256 depends on HAVE_KERNEL_GZIP 257 help 258 The old and tried gzip compression. It provides a good balance 259 between compression ratio and decompression speed. 260 261config KERNEL_BZIP2 262 bool "Bzip2" 263 depends on HAVE_KERNEL_BZIP2 264 help 265 Its compression ratio and speed is intermediate. 266 Decompression speed is slowest among the choices. The kernel 267 size is about 10% smaller with bzip2, in comparison to gzip. 268 Bzip2 uses a large amount of memory. For modern kernels you 269 will need at least 8MB RAM or more for booting. 270 271config KERNEL_LZMA 272 bool "LZMA" 273 depends on HAVE_KERNEL_LZMA 274 help 275 This compression algorithm's ratio is best. Decompression speed 276 is between gzip and bzip2. Compression is slowest. 277 The kernel size is about 33% smaller with LZMA in comparison to gzip. 278 279config KERNEL_XZ 280 bool "XZ" 281 depends on HAVE_KERNEL_XZ 282 help 283 XZ uses the LZMA2 algorithm and instruction set specific 284 BCJ filters which can improve compression ratio of executable 285 code. The size of the kernel is about 30% smaller with XZ in 286 comparison to gzip. On architectures for which there is a BCJ 287 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ 288 will create a few percent smaller kernel than plain LZMA. 289 290 The speed is about the same as with LZMA: The decompression 291 speed of XZ is better than that of bzip2 but worse than gzip 292 and LZO. Compression is slow. 293 294config KERNEL_LZO 295 bool "LZO" 296 depends on HAVE_KERNEL_LZO 297 help 298 Its compression ratio is the poorest among the choices. The kernel 299 size is about 10% bigger than gzip; however its speed 300 (both compression and decompression) is the fastest. 301 302config KERNEL_LZ4 303 bool "LZ4" 304 depends on HAVE_KERNEL_LZ4 305 help 306 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding. 307 A preliminary version of LZ4 de/compression tool is available at 308 <https://code.google.com/p/lz4/>. 309 310 Its compression ratio is worse than LZO. The size of the kernel 311 is about 8% bigger than LZO. But the decompression speed is 312 faster than LZO. 313 314config KERNEL_ZSTD 315 bool "ZSTD" 316 depends on HAVE_KERNEL_ZSTD 317 help 318 ZSTD is a compression algorithm targeting intermediate compression 319 with fast decompression speed. It will compress better than GZIP and 320 decompress around the same speed as LZO, but slower than LZ4. You 321 will need at least 192 KB RAM or more for booting. The zstd command 322 line tool is required for compression. 323 324config KERNEL_UNCOMPRESSED 325 bool "None" 326 depends on HAVE_KERNEL_UNCOMPRESSED 327 help 328 Produce uncompressed kernel image. This option is usually not what 329 you want. It is useful for debugging the kernel in slow simulation 330 environments, where decompressing and moving the kernel is awfully 331 slow. This option allows early boot code to skip the decompressor 332 and jump right at uncompressed kernel image. 333 334endchoice 335 336config DEFAULT_INIT 337 string "Default init path" 338 default "" 339 help 340 This option determines the default init for the system if no init= 341 option is passed on the kernel command line. If the requested path is 342 not present, we will still then move on to attempting further 343 locations (e.g. /sbin/init, etc). If this is empty, we will just use 344 the fallback list when init= is not passed. 345 346config DEFAULT_HOSTNAME 347 string "Default hostname" 348 default "(none)" 349 help 350 This option determines the default system hostname before userspace 351 calls sethostname(2). The kernel traditionally uses "(none)" here, 352 but you may wish to use a different default here to make a minimal 353 system more usable with less configuration. 354 355# 356# For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can 357# add proper SWAP support to them, in which case this can be remove. 358# 359config ARCH_NO_SWAP 360 bool 361 362config SWAP 363 bool "Support for paging of anonymous memory (swap)" 364 depends on MMU && BLOCK && !ARCH_NO_SWAP 365 default y 366 help 367 This option allows you to choose whether you want to have support 368 for so called swap devices or swap files in your kernel that are 369 used to provide more virtual memory than the actual RAM present 370 in your computer. If unsure say Y. 371 372config SYSVIPC 373 bool "System V IPC" 374 help 375 Inter Process Communication is a suite of library functions and 376 system calls which let processes (running programs) synchronize and 377 exchange information. It is generally considered to be a good thing, 378 and some programs won't run unless you say Y here. In particular, if 379 you want to run the DOS emulator dosemu under Linux (read the 380 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>), 381 you'll need to say Y here. 382 383 You can find documentation about IPC with "info ipc" and also in 384 section 6.4 of the Linux Programmer's Guide, available from 385 <http://www.tldp.org/guides.html>. 386 387config SYSVIPC_SYSCTL 388 bool 389 depends on SYSVIPC 390 depends on SYSCTL 391 default y 392 393config SYSVIPC_COMPAT 394 def_bool y 395 depends on COMPAT && SYSVIPC 396 397config POSIX_MQUEUE 398 bool "POSIX Message Queues" 399 depends on NET 400 help 401 POSIX variant of message queues is a part of IPC. In POSIX message 402 queues every message has a priority which decides about succession 403 of receiving it by a process. If you want to compile and run 404 programs written e.g. for Solaris with use of its POSIX message 405 queues (functions mq_*) say Y here. 406 407 POSIX message queues are visible as a filesystem called 'mqueue' 408 and can be mounted somewhere if you want to do filesystem 409 operations on message queues. 410 411 If unsure, say Y. 412 413config POSIX_MQUEUE_SYSCTL 414 bool 415 depends on POSIX_MQUEUE 416 depends on SYSCTL 417 default y 418 419config WATCH_QUEUE 420 bool "General notification queue" 421 default n 422 help 423 424 This is a general notification queue for the kernel to pass events to 425 userspace by splicing them into pipes. It can be used in conjunction 426 with watches for key/keyring change notifications and device 427 notifications. 428 429 See Documentation/watch_queue.rst 430 431config CROSS_MEMORY_ATTACH 432 bool "Enable process_vm_readv/writev syscalls" 433 depends on MMU 434 default y 435 help 436 Enabling this option adds the system calls process_vm_readv and 437 process_vm_writev which allow a process with the correct privileges 438 to directly read from or write to another process' address space. 439 See the man page for more details. 440 441config USELIB 442 bool "uselib syscall" 443 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION 444 help 445 This option enables the uselib syscall, a system call used in the 446 dynamic linker from libc5 and earlier. glibc does not use this 447 system call. If you intend to run programs built on libc5 or 448 earlier, you may need to enable this syscall. Current systems 449 running glibc can safely disable this. 450 451config AUDIT 452 bool "Auditing support" 453 depends on NET 454 help 455 Enable auditing infrastructure that can be used with another 456 kernel subsystem, such as SELinux (which requires this for 457 logging of avc messages output). System call auditing is included 458 on architectures which support it. 459 460config HAVE_ARCH_AUDITSYSCALL 461 bool 462 463config AUDITSYSCALL 464 def_bool y 465 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL 466 select FSNOTIFY 467 468source "kernel/irq/Kconfig" 469source "kernel/time/Kconfig" 470source "kernel/bpf/Kconfig" 471source "kernel/Kconfig.preempt" 472 473menu "CPU/Task time and stats accounting" 474 475config VIRT_CPU_ACCOUNTING 476 bool 477 478choice 479 prompt "Cputime accounting" 480 default TICK_CPU_ACCOUNTING if !PPC64 481 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64 482 483# Kind of a stub config for the pure tick based cputime accounting 484config TICK_CPU_ACCOUNTING 485 bool "Simple tick based cputime accounting" 486 depends on !S390 && !NO_HZ_FULL 487 help 488 This is the basic tick based cputime accounting that maintains 489 statistics about user, system and idle time spent on per jiffies 490 granularity. 491 492 If unsure, say Y. 493 494config VIRT_CPU_ACCOUNTING_NATIVE 495 bool "Deterministic task and CPU time accounting" 496 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL 497 select VIRT_CPU_ACCOUNTING 498 help 499 Select this option to enable more accurate task and CPU time 500 accounting. This is done by reading a CPU counter on each 501 kernel entry and exit and on transitions within the kernel 502 between system, softirq and hardirq state, so there is a 503 small performance impact. In the case of s390 or IBM POWER > 5, 504 this also enables accounting of stolen time on logically-partitioned 505 systems. 506 507config VIRT_CPU_ACCOUNTING_GEN 508 bool "Full dynticks CPU time accounting" 509 depends on HAVE_CONTEXT_TRACKING 510 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 511 depends on GENERIC_CLOCKEVENTS 512 select VIRT_CPU_ACCOUNTING 513 select CONTEXT_TRACKING 514 help 515 Select this option to enable task and CPU time accounting on full 516 dynticks systems. This accounting is implemented by watching every 517 kernel-user boundaries using the context tracking subsystem. 518 The accounting is thus performed at the expense of some significant 519 overhead. 520 521 For now this is only useful if you are working on the full 522 dynticks subsystem development. 523 524 If unsure, say N. 525 526endchoice 527 528config IRQ_TIME_ACCOUNTING 529 bool "Fine granularity task level IRQ time accounting" 530 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE 531 help 532 Select this option to enable fine granularity task irq time 533 accounting. This is done by reading a timestamp on each 534 transitions between softirq and hardirq state, so there can be a 535 small performance impact. 536 537 If in doubt, say N here. 538 539config HAVE_SCHED_AVG_IRQ 540 def_bool y 541 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING 542 depends on SMP 543 544config SCHED_THERMAL_PRESSURE 545 bool 546 default y if ARM && ARM_CPU_TOPOLOGY 547 default y if ARM64 548 depends on SMP 549 depends on CPU_FREQ_THERMAL 550 help 551 Select this option to enable thermal pressure accounting in the 552 scheduler. Thermal pressure is the value conveyed to the scheduler 553 that reflects the reduction in CPU compute capacity resulted from 554 thermal throttling. Thermal throttling occurs when the performance of 555 a CPU is capped due to high operating temperatures. 556 557 If selected, the scheduler will be able to balance tasks accordingly, 558 i.e. put less load on throttled CPUs than on non/less throttled ones. 559 560 This requires the architecture to implement 561 arch_update_thermal_pressure() and arch_scale_thermal_pressure(). 562 563config BSD_PROCESS_ACCT 564 bool "BSD Process Accounting" 565 depends on MULTIUSER 566 help 567 If you say Y here, a user level program will be able to instruct the 568 kernel (via a special system call) to write process accounting 569 information to a file: whenever a process exits, information about 570 that process will be appended to the file by the kernel. The 571 information includes things such as creation time, owning user, 572 command name, memory usage, controlling terminal etc. (the complete 573 list is in the struct acct in <file:include/linux/acct.h>). It is 574 up to the user level program to do useful things with this 575 information. This is generally a good idea, so say Y. 576 577config BSD_PROCESS_ACCT_V3 578 bool "BSD Process Accounting version 3 file format" 579 depends on BSD_PROCESS_ACCT 580 default n 581 help 582 If you say Y here, the process accounting information is written 583 in a new file format that also logs the process IDs of each 584 process and its parent. Note that this file format is incompatible 585 with previous v0/v1/v2 file formats, so you will need updated tools 586 for processing it. A preliminary version of these tools is available 587 at <http://www.gnu.org/software/acct/>. 588 589config TASKSTATS 590 bool "Export task/process statistics through netlink" 591 depends on NET 592 depends on MULTIUSER 593 default n 594 help 595 Export selected statistics for tasks/processes through the 596 generic netlink interface. Unlike BSD process accounting, the 597 statistics are available during the lifetime of tasks/processes as 598 responses to commands. Like BSD accounting, they are sent to user 599 space on task exit. 600 601 Say N if unsure. 602 603config TASK_DELAY_ACCT 604 bool "Enable per-task delay accounting" 605 depends on TASKSTATS 606 select SCHED_INFO 607 help 608 Collect information on time spent by a task waiting for system 609 resources like cpu, synchronous block I/O completion and swapping 610 in pages. Such statistics can help in setting a task's priorities 611 relative to other tasks for cpu, io, rss limits etc. 612 613 Say N if unsure. 614 615config TASK_XACCT 616 bool "Enable extended accounting over taskstats" 617 depends on TASKSTATS 618 help 619 Collect extended task accounting data and send the data 620 to userland for processing over the taskstats interface. 621 622 Say N if unsure. 623 624config TASK_IO_ACCOUNTING 625 bool "Enable per-task storage I/O accounting" 626 depends on TASK_XACCT 627 help 628 Collect information on the number of bytes of storage I/O which this 629 task has caused. 630 631 Say N if unsure. 632 633config PSI 634 bool "Pressure stall information tracking" 635 help 636 Collect metrics that indicate how overcommitted the CPU, memory, 637 and IO capacity are in the system. 638 639 If you say Y here, the kernel will create /proc/pressure/ with the 640 pressure statistics files cpu, memory, and io. These will indicate 641 the share of walltime in which some or all tasks in the system are 642 delayed due to contention of the respective resource. 643 644 In kernels with cgroup support, cgroups (cgroup2 only) will 645 have cpu.pressure, memory.pressure, and io.pressure files, 646 which aggregate pressure stalls for the grouped tasks only. 647 648 For more details see Documentation/accounting/psi.rst. 649 650 Say N if unsure. 651 652config PSI_DEFAULT_DISABLED 653 bool "Require boot parameter to enable pressure stall information tracking" 654 default n 655 depends on PSI 656 help 657 If set, pressure stall information tracking will be disabled 658 per default but can be enabled through passing psi=1 on the 659 kernel commandline during boot. 660 661 This feature adds some code to the task wakeup and sleep 662 paths of the scheduler. The overhead is too low to affect 663 common scheduling-intense workloads in practice (such as 664 webservers, memcache), but it does show up in artificial 665 scheduler stress tests, such as hackbench. 666 667 If you are paranoid and not sure what the kernel will be 668 used for, say Y. 669 670 Say N if unsure. 671 672endmenu # "CPU/Task time and stats accounting" 673 674config CPU_ISOLATION 675 bool "CPU isolation" 676 depends on SMP || COMPILE_TEST 677 default y 678 help 679 Make sure that CPUs running critical tasks are not disturbed by 680 any source of "noise" such as unbound workqueues, timers, kthreads... 681 Unbound jobs get offloaded to housekeeping CPUs. This is driven by 682 the "isolcpus=" boot parameter. 683 684 Say Y if unsure. 685 686source "kernel/rcu/Kconfig" 687 688config BUILD_BIN2C 689 bool 690 default n 691 692config IKCONFIG 693 tristate "Kernel .config support" 694 help 695 This option enables the complete Linux kernel ".config" file 696 contents to be saved in the kernel. It provides documentation 697 of which kernel options are used in a running kernel or in an 698 on-disk kernel. This information can be extracted from the kernel 699 image file with the script scripts/extract-ikconfig and used as 700 input to rebuild the current kernel or to build another kernel. 701 It can also be extracted from a running kernel by reading 702 /proc/config.gz if enabled (below). 703 704config IKCONFIG_PROC 705 bool "Enable access to .config through /proc/config.gz" 706 depends on IKCONFIG && PROC_FS 707 help 708 This option enables access to the kernel configuration file 709 through /proc/config.gz. 710 711config IKHEADERS 712 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz" 713 depends on SYSFS 714 help 715 This option enables access to the in-kernel headers that are generated during 716 the build process. These can be used to build eBPF tracing programs, 717 or similar programs. If you build the headers as a module, a module called 718 kheaders.ko is built which can be loaded on-demand to get access to headers. 719 720config LOG_BUF_SHIFT 721 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" 722 range 12 25 if !H8300 723 range 12 19 if H8300 724 default 17 725 depends on PRINTK 726 help 727 Select the minimal kernel log buffer size as a power of 2. 728 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config 729 parameter, see below. Any higher size also might be forced 730 by "log_buf_len" boot parameter. 731 732 Examples: 733 17 => 128 KB 734 16 => 64 KB 735 15 => 32 KB 736 14 => 16 KB 737 13 => 8 KB 738 12 => 4 KB 739 740config LOG_CPU_MAX_BUF_SHIFT 741 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)" 742 depends on SMP 743 range 0 21 744 default 12 if !BASE_SMALL 745 default 0 if BASE_SMALL 746 depends on PRINTK 747 help 748 This option allows to increase the default ring buffer size 749 according to the number of CPUs. The value defines the contribution 750 of each CPU as a power of 2. The used space is typically only few 751 lines however it might be much more when problems are reported, 752 e.g. backtraces. 753 754 The increased size means that a new buffer has to be allocated and 755 the original static one is unused. It makes sense only on systems 756 with more CPUs. Therefore this value is used only when the sum of 757 contributions is greater than the half of the default kernel ring 758 buffer as defined by LOG_BUF_SHIFT. The default values are set 759 so that more than 16 CPUs are needed to trigger the allocation. 760 761 Also this option is ignored when "log_buf_len" kernel parameter is 762 used as it forces an exact (power of two) size of the ring buffer. 763 764 The number of possible CPUs is used for this computation ignoring 765 hotplugging making the computation optimal for the worst case 766 scenario while allowing a simple algorithm to be used from bootup. 767 768 Examples shift values and their meaning: 769 17 => 128 KB for each CPU 770 16 => 64 KB for each CPU 771 15 => 32 KB for each CPU 772 14 => 16 KB for each CPU 773 13 => 8 KB for each CPU 774 12 => 4 KB for each CPU 775 776config PRINTK_SAFE_LOG_BUF_SHIFT 777 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)" 778 range 10 21 779 default 13 780 depends on PRINTK 781 help 782 Select the size of an alternate printk per-CPU buffer where messages 783 printed from usafe contexts are temporary stored. One example would 784 be NMI messages, another one - printk recursion. The messages are 785 copied to the main log buffer in a safe context to avoid a deadlock. 786 The value defines the size as a power of 2. 787 788 Those messages are rare and limited. The largest one is when 789 a backtrace is printed. It usually fits into 4KB. Select 790 8KB if you want to be on the safe side. 791 792 Examples: 793 17 => 128 KB for each CPU 794 16 => 64 KB for each CPU 795 15 => 32 KB for each CPU 796 14 => 16 KB for each CPU 797 13 => 8 KB for each CPU 798 12 => 4 KB for each CPU 799 800config PRINTK_INDEX 801 bool "Printk indexing debugfs interface" 802 depends on PRINTK && DEBUG_FS 803 help 804 Add support for indexing of all printk formats known at compile time 805 at <debugfs>/printk/index/<module>. 806 807 This can be used as part of maintaining daemons which monitor 808 /dev/kmsg, as it permits auditing the printk formats present in a 809 kernel, allowing detection of cases where monitored printks are 810 changed or no longer present. 811 812 There is no additional runtime cost to printk with this enabled. 813 814# 815# Architectures with an unreliable sched_clock() should select this: 816# 817config HAVE_UNSTABLE_SCHED_CLOCK 818 bool 819 820config GENERIC_SCHED_CLOCK 821 bool 822 823menu "Scheduler features" 824 825config UCLAMP_TASK 826 bool "Enable utilization clamping for RT/FAIR tasks" 827 depends on CPU_FREQ_GOV_SCHEDUTIL 828 help 829 This feature enables the scheduler to track the clamped utilization 830 of each CPU based on RUNNABLE tasks scheduled on that CPU. 831 832 With this option, the user can specify the min and max CPU 833 utilization allowed for RUNNABLE tasks. The max utilization defines 834 the maximum frequency a task should use while the min utilization 835 defines the minimum frequency it should use. 836 837 Both min and max utilization clamp values are hints to the scheduler, 838 aiming at improving its frequency selection policy, but they do not 839 enforce or grant any specific bandwidth for tasks. 840 841 If in doubt, say N. 842 843config UCLAMP_BUCKETS_COUNT 844 int "Number of supported utilization clamp buckets" 845 range 5 20 846 default 5 847 depends on UCLAMP_TASK 848 help 849 Defines the number of clamp buckets to use. The range of each bucket 850 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the 851 number of clamp buckets the finer their granularity and the higher 852 the precision of clamping aggregation and tracking at run-time. 853 854 For example, with the minimum configuration value we will have 5 855 clamp buckets tracking 20% utilization each. A 25% boosted tasks will 856 be refcounted in the [20..39]% bucket and will set the bucket clamp 857 effective value to 25%. 858 If a second 30% boosted task should be co-scheduled on the same CPU, 859 that task will be refcounted in the same bucket of the first task and 860 it will boost the bucket clamp effective value to 30%. 861 The clamp effective value of a bucket is reset to its nominal value 862 (20% in the example above) when there are no more tasks refcounted in 863 that bucket. 864 865 An additional boost/capping margin can be added to some tasks. In the 866 example above the 25% task will be boosted to 30% until it exits the 867 CPU. If that should be considered not acceptable on certain systems, 868 it's always possible to reduce the margin by increasing the number of 869 clamp buckets to trade off used memory for run-time tracking 870 precision. 871 872 If in doubt, use the default value. 873 874endmenu 875 876# 877# For architectures that want to enable the support for NUMA-affine scheduler 878# balancing logic: 879# 880config ARCH_SUPPORTS_NUMA_BALANCING 881 bool 882 883# 884# For architectures that prefer to flush all TLBs after a number of pages 885# are unmapped instead of sending one IPI per page to flush. The architecture 886# must provide guarantees on what happens if a clean TLB cache entry is 887# written after the unmap. Details are in mm/rmap.c near the check for 888# should_defer_flush. The architecture should also consider if the full flush 889# and the refill costs are offset by the savings of sending fewer IPIs. 890config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH 891 bool 892 893config CC_HAS_INT128 894 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT 895 896config CC_IMPLICIT_FALLTHROUGH 897 string 898 default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5) 899 default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough) 900 901# 902# For architectures that know their GCC __int128 support is sound 903# 904config ARCH_SUPPORTS_INT128 905 bool 906 907# For architectures that (ab)use NUMA to represent different memory regions 908# all cpu-local but of different latencies, such as SuperH. 909# 910config ARCH_WANT_NUMA_VARIABLE_LOCALITY 911 bool 912 913config NUMA_BALANCING 914 bool "Memory placement aware NUMA scheduler" 915 depends on ARCH_SUPPORTS_NUMA_BALANCING 916 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY 917 depends on SMP && NUMA && MIGRATION && !PREEMPT_RT 918 help 919 This option adds support for automatic NUMA aware memory/task placement. 920 The mechanism is quite primitive and is based on migrating memory when 921 it has references to the node the task is running on. 922 923 This system will be inactive on UMA systems. 924 925config NUMA_BALANCING_DEFAULT_ENABLED 926 bool "Automatically enable NUMA aware memory/task placement" 927 default y 928 depends on NUMA_BALANCING 929 help 930 If set, automatic NUMA balancing will be enabled if running on a NUMA 931 machine. 932 933menuconfig CGROUPS 934 bool "Control Group support" 935 select KERNFS 936 help 937 This option adds support for grouping sets of processes together, for 938 use with process control subsystems such as Cpusets, CFS, memory 939 controls or device isolation. 940 See 941 - Documentation/scheduler/sched-design-CFS.rst (CFS) 942 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation 943 and resource control) 944 945 Say N if unsure. 946 947if CGROUPS 948 949config PAGE_COUNTER 950 bool 951 952config MEMCG 953 bool "Memory controller" 954 select PAGE_COUNTER 955 select EVENTFD 956 help 957 Provides control over the memory footprint of tasks in a cgroup. 958 959config MEMCG_SWAP 960 bool 961 depends on MEMCG && SWAP 962 default y 963 964config MEMCG_KMEM 965 bool 966 depends on MEMCG && !SLOB 967 default y 968 969config BLK_CGROUP 970 bool "IO controller" 971 depends on BLOCK 972 default n 973 help 974 Generic block IO controller cgroup interface. This is the common 975 cgroup interface which should be used by various IO controlling 976 policies. 977 978 Currently, CFQ IO scheduler uses it to recognize task groups and 979 control disk bandwidth allocation (proportional time slice allocation) 980 to such task groups. It is also used by bio throttling logic in 981 block layer to implement upper limit in IO rates on a device. 982 983 This option only enables generic Block IO controller infrastructure. 984 One needs to also enable actual IO controlling logic/policy. For 985 enabling proportional weight division of disk bandwidth in CFQ, set 986 CONFIG_BFQ_GROUP_IOSCHED=y; for enabling throttling policy, set 987 CONFIG_BLK_DEV_THROTTLING=y. 988 989 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information. 990 991config CGROUP_WRITEBACK 992 bool 993 depends on MEMCG && BLK_CGROUP 994 default y 995 996menuconfig CGROUP_SCHED 997 bool "CPU controller" 998 default n 999 help 1000 This feature lets CPU scheduler recognize task groups and control CPU 1001 bandwidth allocation to such task groups. It uses cgroups to group 1002 tasks. 1003 1004if CGROUP_SCHED 1005config FAIR_GROUP_SCHED 1006 bool "Group scheduling for SCHED_OTHER" 1007 depends on CGROUP_SCHED 1008 default CGROUP_SCHED 1009 1010config CFS_BANDWIDTH 1011 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED" 1012 depends on FAIR_GROUP_SCHED 1013 default n 1014 help 1015 This option allows users to define CPU bandwidth rates (limits) for 1016 tasks running within the fair group scheduler. Groups with no limit 1017 set are considered to be unconstrained and will run with no 1018 restriction. 1019 See Documentation/scheduler/sched-bwc.rst for more information. 1020 1021config RT_GROUP_SCHED 1022 bool "Group scheduling for SCHED_RR/FIFO" 1023 depends on CGROUP_SCHED 1024 default n 1025 help 1026 This feature lets you explicitly allocate real CPU bandwidth 1027 to task groups. If enabled, it will also make it impossible to 1028 schedule realtime tasks for non-root users until you allocate 1029 realtime bandwidth for them. 1030 See Documentation/scheduler/sched-rt-group.rst for more information. 1031 1032endif #CGROUP_SCHED 1033 1034config UCLAMP_TASK_GROUP 1035 bool "Utilization clamping per group of tasks" 1036 depends on CGROUP_SCHED 1037 depends on UCLAMP_TASK 1038 default n 1039 help 1040 This feature enables the scheduler to track the clamped utilization 1041 of each CPU based on RUNNABLE tasks currently scheduled on that CPU. 1042 1043 When this option is enabled, the user can specify a min and max 1044 CPU bandwidth which is allowed for each single task in a group. 1045 The max bandwidth allows to clamp the maximum frequency a task 1046 can use, while the min bandwidth allows to define a minimum 1047 frequency a task will always use. 1048 1049 When task group based utilization clamping is enabled, an eventually 1050 specified task-specific clamp value is constrained by the cgroup 1051 specified clamp value. Both minimum and maximum task clamping cannot 1052 be bigger than the corresponding clamping defined at task group level. 1053 1054 If in doubt, say N. 1055 1056config CGROUP_PIDS 1057 bool "PIDs controller" 1058 help 1059 Provides enforcement of process number limits in the scope of a 1060 cgroup. Any attempt to fork more processes than is allowed in the 1061 cgroup will fail. PIDs are fundamentally a global resource because it 1062 is fairly trivial to reach PID exhaustion before you reach even a 1063 conservative kmemcg limit. As a result, it is possible to grind a 1064 system to halt without being limited by other cgroup policies. The 1065 PIDs controller is designed to stop this from happening. 1066 1067 It should be noted that organisational operations (such as attaching 1068 to a cgroup hierarchy) will *not* be blocked by the PIDs controller, 1069 since the PIDs limit only affects a process's ability to fork, not to 1070 attach to a cgroup. 1071 1072config CGROUP_RDMA 1073 bool "RDMA controller" 1074 help 1075 Provides enforcement of RDMA resources defined by IB stack. 1076 It is fairly easy for consumers to exhaust RDMA resources, which 1077 can result into resource unavailability to other consumers. 1078 RDMA controller is designed to stop this from happening. 1079 Attaching processes with active RDMA resources to the cgroup 1080 hierarchy is allowed even if can cross the hierarchy's limit. 1081 1082config CGROUP_FREEZER 1083 bool "Freezer controller" 1084 help 1085 Provides a way to freeze and unfreeze all tasks in a 1086 cgroup. 1087 1088 This option affects the ORIGINAL cgroup interface. The cgroup2 memory 1089 controller includes important in-kernel memory consumers per default. 1090 1091 If you're using cgroup2, say N. 1092 1093config CGROUP_HUGETLB 1094 bool "HugeTLB controller" 1095 depends on HUGETLB_PAGE 1096 select PAGE_COUNTER 1097 default n 1098 help 1099 Provides a cgroup controller for HugeTLB pages. 1100 When you enable this, you can put a per cgroup limit on HugeTLB usage. 1101 The limit is enforced during page fault. Since HugeTLB doesn't 1102 support page reclaim, enforcing the limit at page fault time implies 1103 that, the application will get SIGBUS signal if it tries to access 1104 HugeTLB pages beyond its limit. This requires the application to know 1105 beforehand how much HugeTLB pages it would require for its use. The 1106 control group is tracked in the third page lru pointer. This means 1107 that we cannot use the controller with huge page less than 3 pages. 1108 1109config CPUSETS 1110 bool "Cpuset controller" 1111 depends on SMP 1112 help 1113 This option will let you create and manage CPUSETs which 1114 allow dynamically partitioning a system into sets of CPUs and 1115 Memory Nodes and assigning tasks to run only within those sets. 1116 This is primarily useful on large SMP or NUMA systems. 1117 1118 Say N if unsure. 1119 1120config PROC_PID_CPUSET 1121 bool "Include legacy /proc/<pid>/cpuset file" 1122 depends on CPUSETS 1123 default y 1124 1125config CGROUP_DEVICE 1126 bool "Device controller" 1127 help 1128 Provides a cgroup controller implementing whitelists for 1129 devices which a process in the cgroup can mknod or open. 1130 1131config CGROUP_CPUACCT 1132 bool "Simple CPU accounting controller" 1133 help 1134 Provides a simple controller for monitoring the 1135 total CPU consumed by the tasks in a cgroup. 1136 1137config CGROUP_PERF 1138 bool "Perf controller" 1139 depends on PERF_EVENTS 1140 help 1141 This option extends the perf per-cpu mode to restrict monitoring 1142 to threads which belong to the cgroup specified and run on the 1143 designated cpu. Or this can be used to have cgroup ID in samples 1144 so that it can monitor performance events among cgroups. 1145 1146 Say N if unsure. 1147 1148config CGROUP_BPF 1149 bool "Support for eBPF programs attached to cgroups" 1150 depends on BPF_SYSCALL 1151 select SOCK_CGROUP_DATA 1152 help 1153 Allow attaching eBPF programs to a cgroup using the bpf(2) 1154 syscall command BPF_PROG_ATTACH. 1155 1156 In which context these programs are accessed depends on the type 1157 of attachment. For instance, programs that are attached using 1158 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of 1159 inet sockets. 1160 1161config CGROUP_MISC 1162 bool "Misc resource controller" 1163 default n 1164 help 1165 Provides a controller for miscellaneous resources on a host. 1166 1167 Miscellaneous scalar resources are the resources on the host system 1168 which cannot be abstracted like the other cgroups. This controller 1169 tracks and limits the miscellaneous resources used by a process 1170 attached to a cgroup hierarchy. 1171 1172 For more information, please check misc cgroup section in 1173 /Documentation/admin-guide/cgroup-v2.rst. 1174 1175config CGROUP_DEBUG 1176 bool "Debug controller" 1177 default n 1178 depends on DEBUG_KERNEL 1179 help 1180 This option enables a simple controller that exports 1181 debugging information about the cgroups framework. This 1182 controller is for control cgroup debugging only. Its 1183 interfaces are not stable. 1184 1185 Say N. 1186 1187config SOCK_CGROUP_DATA 1188 bool 1189 default n 1190 1191endif # CGROUPS 1192 1193menuconfig NAMESPACES 1194 bool "Namespaces support" if EXPERT 1195 depends on MULTIUSER 1196 default !EXPERT 1197 help 1198 Provides the way to make tasks work with different objects using 1199 the same id. For example same IPC id may refer to different objects 1200 or same user id or pid may refer to different tasks when used in 1201 different namespaces. 1202 1203if NAMESPACES 1204 1205config UTS_NS 1206 bool "UTS namespace" 1207 default y 1208 help 1209 In this namespace tasks see different info provided with the 1210 uname() system call 1211 1212config TIME_NS 1213 bool "TIME namespace" 1214 depends on GENERIC_VDSO_TIME_NS 1215 default y 1216 help 1217 In this namespace boottime and monotonic clocks can be set. 1218 The time will keep going with the same pace. 1219 1220config IPC_NS 1221 bool "IPC namespace" 1222 depends on (SYSVIPC || POSIX_MQUEUE) 1223 default y 1224 help 1225 In this namespace tasks work with IPC ids which correspond to 1226 different IPC objects in different namespaces. 1227 1228config USER_NS 1229 bool "User namespace" 1230 default n 1231 help 1232 This allows containers, i.e. vservers, to use user namespaces 1233 to provide different user info for different servers. 1234 1235 When user namespaces are enabled in the kernel it is 1236 recommended that the MEMCG option also be enabled and that 1237 user-space use the memory control groups to limit the amount 1238 of memory a memory unprivileged users can use. 1239 1240 If unsure, say N. 1241 1242config PID_NS 1243 bool "PID Namespaces" 1244 default y 1245 help 1246 Support process id namespaces. This allows having multiple 1247 processes with the same pid as long as they are in different 1248 pid namespaces. This is a building block of containers. 1249 1250config NET_NS 1251 bool "Network namespace" 1252 depends on NET 1253 default y 1254 help 1255 Allow user space to create what appear to be multiple instances 1256 of the network stack. 1257 1258endif # NAMESPACES 1259 1260config CHECKPOINT_RESTORE 1261 bool "Checkpoint/restore support" 1262 select PROC_CHILDREN 1263 select KCMP 1264 default n 1265 help 1266 Enables additional kernel features in a sake of checkpoint/restore. 1267 In particular it adds auxiliary prctl codes to setup process text, 1268 data and heap segment sizes, and a few additional /proc filesystem 1269 entries. 1270 1271 If unsure, say N here. 1272 1273config SCHED_AUTOGROUP 1274 bool "Automatic process group scheduling" 1275 select CGROUPS 1276 select CGROUP_SCHED 1277 select FAIR_GROUP_SCHED 1278 help 1279 This option optimizes the scheduler for common desktop workloads by 1280 automatically creating and populating task groups. This separation 1281 of workloads isolates aggressive CPU burners (like build jobs) from 1282 desktop applications. Task group autogeneration is currently based 1283 upon task session. 1284 1285config SYSFS_DEPRECATED 1286 bool "Enable deprecated sysfs features to support old userspace tools" 1287 depends on SYSFS 1288 default n 1289 help 1290 This option adds code that switches the layout of the "block" class 1291 devices, to not show up in /sys/class/block/, but only in 1292 /sys/block/. 1293 1294 This switch is only active when the sysfs.deprecated=1 boot option is 1295 passed or the SYSFS_DEPRECATED_V2 option is set. 1296 1297 This option allows new kernels to run on old distributions and tools, 1298 which might get confused by /sys/class/block/. Since 2007/2008 all 1299 major distributions and tools handle this just fine. 1300 1301 Recent distributions and userspace tools after 2009/2010 depend on 1302 the existence of /sys/class/block/, and will not work with this 1303 option enabled. 1304 1305 Only if you are using a new kernel on an old distribution, you might 1306 need to say Y here. 1307 1308config SYSFS_DEPRECATED_V2 1309 bool "Enable deprecated sysfs features by default" 1310 default n 1311 depends on SYSFS 1312 depends on SYSFS_DEPRECATED 1313 help 1314 Enable deprecated sysfs by default. 1315 1316 See the CONFIG_SYSFS_DEPRECATED option for more details about this 1317 option. 1318 1319 Only if you are using a new kernel on an old distribution, you might 1320 need to say Y here. Even then, odds are you would not need it 1321 enabled, you can always pass the boot option if absolutely necessary. 1322 1323config RELAY 1324 bool "Kernel->user space relay support (formerly relayfs)" 1325 select IRQ_WORK 1326 help 1327 This option enables support for relay interface support in 1328 certain file systems (such as debugfs). 1329 It is designed to provide an efficient mechanism for tools and 1330 facilities to relay large amounts of data from kernel space to 1331 user space. 1332 1333 If unsure, say N. 1334 1335config BLK_DEV_INITRD 1336 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support" 1337 help 1338 The initial RAM filesystem is a ramfs which is loaded by the 1339 boot loader (loadlin or lilo) and that is mounted as root 1340 before the normal boot procedure. It is typically used to 1341 load modules needed to mount the "real" root file system, 1342 etc. See <file:Documentation/admin-guide/initrd.rst> for details. 1343 1344 If RAM disk support (BLK_DEV_RAM) is also included, this 1345 also enables initial RAM disk (initrd) support and adds 1346 15 Kbytes (more on some other architectures) to the kernel size. 1347 1348 If unsure say Y. 1349 1350if BLK_DEV_INITRD 1351 1352source "usr/Kconfig" 1353 1354endif 1355 1356config BOOT_CONFIG 1357 bool "Boot config support" 1358 select BLK_DEV_INITRD 1359 help 1360 Extra boot config allows system admin to pass a config file as 1361 complemental extension of kernel cmdline when booting. 1362 The boot config file must be attached at the end of initramfs 1363 with checksum, size and magic word. 1364 See <file:Documentation/admin-guide/bootconfig.rst> for details. 1365 1366 If unsure, say Y. 1367 1368choice 1369 prompt "Compiler optimization level" 1370 default CC_OPTIMIZE_FOR_PERFORMANCE 1371 1372config CC_OPTIMIZE_FOR_PERFORMANCE 1373 bool "Optimize for performance (-O2)" 1374 help 1375 This is the default optimization level for the kernel, building 1376 with the "-O2" compiler flag for best performance and most 1377 helpful compile-time warnings. 1378 1379config CC_OPTIMIZE_FOR_PERFORMANCE_O3 1380 bool "Optimize more for performance (-O3)" 1381 depends on ARC 1382 help 1383 Choosing this option will pass "-O3" to your compiler to optimize 1384 the kernel yet more for performance. 1385 1386config CC_OPTIMIZE_FOR_SIZE 1387 bool "Optimize for size (-Os)" 1388 help 1389 Choosing this option will pass "-Os" to your compiler resulting 1390 in a smaller kernel. 1391 1392endchoice 1393 1394config HAVE_LD_DEAD_CODE_DATA_ELIMINATION 1395 bool 1396 help 1397 This requires that the arch annotates or otherwise protects 1398 its external entry points from being discarded. Linker scripts 1399 must also merge .text.*, .data.*, and .bss.* correctly into 1400 output sections. Care must be taken not to pull in unrelated 1401 sections (e.g., '.text.init'). Typically '.' in section names 1402 is used to distinguish them from label names / C identifiers. 1403 1404config LD_DEAD_CODE_DATA_ELIMINATION 1405 bool "Dead code and data elimination (EXPERIMENTAL)" 1406 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION 1407 depends on EXPERT 1408 depends on $(cc-option,-ffunction-sections -fdata-sections) 1409 depends on $(ld-option,--gc-sections) 1410 help 1411 Enable this if you want to do dead code and data elimination with 1412 the linker by compiling with -ffunction-sections -fdata-sections, 1413 and linking with --gc-sections. 1414 1415 This can reduce on disk and in-memory size of the kernel 1416 code and static data, particularly for small configs and 1417 on small systems. This has the possibility of introducing 1418 silently broken kernel if the required annotations are not 1419 present. This option is not well tested yet, so use at your 1420 own risk. 1421 1422config LD_ORPHAN_WARN 1423 def_bool y 1424 depends on ARCH_WANT_LD_ORPHAN_WARN 1425 depends on $(ld-option,--orphan-handling=warn) 1426 1427config SYSCTL 1428 bool 1429 1430config HAVE_UID16 1431 bool 1432 1433config SYSCTL_EXCEPTION_TRACE 1434 bool 1435 help 1436 Enable support for /proc/sys/debug/exception-trace. 1437 1438config SYSCTL_ARCH_UNALIGN_NO_WARN 1439 bool 1440 help 1441 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap 1442 Allows arch to define/use @no_unaligned_warning to possibly warn 1443 about unaligned access emulation going on under the hood. 1444 1445config SYSCTL_ARCH_UNALIGN_ALLOW 1446 bool 1447 help 1448 Enable support for /proc/sys/kernel/unaligned-trap 1449 Allows arches to define/use @unaligned_enabled to runtime toggle 1450 the unaligned access emulation. 1451 see arch/parisc/kernel/unaligned.c for reference 1452 1453config HAVE_PCSPKR_PLATFORM 1454 bool 1455 1456# interpreter that classic socket filters depend on 1457config BPF 1458 bool 1459 1460menuconfig EXPERT 1461 bool "Configure standard kernel features (expert users)" 1462 # Unhide debug options, to make the on-by-default options visible 1463 select DEBUG_KERNEL 1464 help 1465 This option allows certain base kernel options and settings 1466 to be disabled or tweaked. This is for specialized 1467 environments which can tolerate a "non-standard" kernel. 1468 Only use this if you really know what you are doing. 1469 1470config UID16 1471 bool "Enable 16-bit UID system calls" if EXPERT 1472 depends on HAVE_UID16 && MULTIUSER 1473 default y 1474 help 1475 This enables the legacy 16-bit UID syscall wrappers. 1476 1477config MULTIUSER 1478 bool "Multiple users, groups and capabilities support" if EXPERT 1479 default y 1480 help 1481 This option enables support for non-root users, groups and 1482 capabilities. 1483 1484 If you say N here, all processes will run with UID 0, GID 0, and all 1485 possible capabilities. Saying N here also compiles out support for 1486 system calls related to UIDs, GIDs, and capabilities, such as setuid, 1487 setgid, and capset. 1488 1489 If unsure, say Y here. 1490 1491config SGETMASK_SYSCALL 1492 bool "sgetmask/ssetmask syscalls support" if EXPERT 1493 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH 1494 help 1495 sys_sgetmask and sys_ssetmask are obsolete system calls 1496 no longer supported in libc but still enabled by default in some 1497 architectures. 1498 1499 If unsure, leave the default option here. 1500 1501config SYSFS_SYSCALL 1502 bool "Sysfs syscall support" if EXPERT 1503 default y 1504 help 1505 sys_sysfs is an obsolete system call no longer supported in libc. 1506 Note that disabling this option is more secure but might break 1507 compatibility with some systems. 1508 1509 If unsure say Y here. 1510 1511config FHANDLE 1512 bool "open by fhandle syscalls" if EXPERT 1513 select EXPORTFS 1514 default y 1515 help 1516 If you say Y here, a user level program will be able to map 1517 file names to handle and then later use the handle for 1518 different file system operations. This is useful in implementing 1519 userspace file servers, which now track files using handles instead 1520 of names. The handle would remain the same even if file names 1521 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) 1522 syscalls. 1523 1524config POSIX_TIMERS 1525 bool "Posix Clocks & timers" if EXPERT 1526 default y 1527 help 1528 This includes native support for POSIX timers to the kernel. 1529 Some embedded systems have no use for them and therefore they 1530 can be configured out to reduce the size of the kernel image. 1531 1532 When this option is disabled, the following syscalls won't be 1533 available: timer_create, timer_gettime: timer_getoverrun, 1534 timer_settime, timer_delete, clock_adjtime, getitimer, 1535 setitimer, alarm. Furthermore, the clock_settime, clock_gettime, 1536 clock_getres and clock_nanosleep syscalls will be limited to 1537 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only. 1538 1539 If unsure say y. 1540 1541config PRINTK 1542 default y 1543 bool "Enable support for printk" if EXPERT 1544 select IRQ_WORK 1545 help 1546 This option enables normal printk support. Removing it 1547 eliminates most of the message strings from the kernel image 1548 and makes the kernel more or less silent. As this makes it 1549 very difficult to diagnose system problems, saying N here is 1550 strongly discouraged. 1551 1552config BUG 1553 bool "BUG() support" if EXPERT 1554 default y 1555 help 1556 Disabling this option eliminates support for BUG and WARN, reducing 1557 the size of your kernel image and potentially quietly ignoring 1558 numerous fatal conditions. You should only consider disabling this 1559 option for embedded systems with no facilities for reporting errors. 1560 Just say Y. 1561 1562config ELF_CORE 1563 depends on COREDUMP 1564 default y 1565 bool "Enable ELF core dumps" if EXPERT 1566 help 1567 Enable support for generating core dumps. Disabling saves about 4k. 1568 1569 1570config PCSPKR_PLATFORM 1571 bool "Enable PC-Speaker support" if EXPERT 1572 depends on HAVE_PCSPKR_PLATFORM 1573 select I8253_LOCK 1574 default y 1575 help 1576 This option allows to disable the internal PC-Speaker 1577 support, saving some memory. 1578 1579config BASE_FULL 1580 default y 1581 bool "Enable full-sized data structures for core" if EXPERT 1582 help 1583 Disabling this option reduces the size of miscellaneous core 1584 kernel data structures. This saves memory on small machines, 1585 but may reduce performance. 1586 1587config FUTEX 1588 bool "Enable futex support" if EXPERT 1589 depends on !(SPARC32 && SMP) 1590 default y 1591 imply RT_MUTEXES 1592 help 1593 Disabling this option will cause the kernel to be built without 1594 support for "fast userspace mutexes". The resulting kernel may not 1595 run glibc-based applications correctly. 1596 1597config FUTEX_PI 1598 bool 1599 depends on FUTEX && RT_MUTEXES 1600 default y 1601 1602config EPOLL 1603 bool "Enable eventpoll support" if EXPERT 1604 default y 1605 help 1606 Disabling this option will cause the kernel to be built without 1607 support for epoll family of system calls. 1608 1609config SIGNALFD 1610 bool "Enable signalfd() system call" if EXPERT 1611 default y 1612 help 1613 Enable the signalfd() system call that allows to receive signals 1614 on a file descriptor. 1615 1616 If unsure, say Y. 1617 1618config TIMERFD 1619 bool "Enable timerfd() system call" if EXPERT 1620 default y 1621 help 1622 Enable the timerfd() system call that allows to receive timer 1623 events on a file descriptor. 1624 1625 If unsure, say Y. 1626 1627config EVENTFD 1628 bool "Enable eventfd() system call" if EXPERT 1629 default y 1630 help 1631 Enable the eventfd() system call that allows to receive both 1632 kernel notification (ie. KAIO) or userspace notifications. 1633 1634 If unsure, say Y. 1635 1636config SHMEM 1637 bool "Use full shmem filesystem" if EXPERT 1638 default y 1639 depends on MMU 1640 help 1641 The shmem is an internal filesystem used to manage shared memory. 1642 It is backed by swap and manages resource limits. It is also exported 1643 to userspace as tmpfs if TMPFS is enabled. Disabling this 1644 option replaces shmem and tmpfs with the much simpler ramfs code, 1645 which may be appropriate on small systems without swap. 1646 1647config AIO 1648 bool "Enable AIO support" if EXPERT 1649 default y 1650 help 1651 This option enables POSIX asynchronous I/O which may by used 1652 by some high performance threaded applications. Disabling 1653 this option saves about 7k. 1654 1655config IO_URING 1656 bool "Enable IO uring support" if EXPERT 1657 select IO_WQ 1658 default y 1659 help 1660 This option enables support for the io_uring interface, enabling 1661 applications to submit and complete IO through submission and 1662 completion rings that are shared between the kernel and application. 1663 1664config ADVISE_SYSCALLS 1665 bool "Enable madvise/fadvise syscalls" if EXPERT 1666 default y 1667 help 1668 This option enables the madvise and fadvise syscalls, used by 1669 applications to advise the kernel about their future memory or file 1670 usage, improving performance. If building an embedded system where no 1671 applications use these syscalls, you can disable this option to save 1672 space. 1673 1674config HAVE_ARCH_USERFAULTFD_WP 1675 bool 1676 help 1677 Arch has userfaultfd write protection support 1678 1679config HAVE_ARCH_USERFAULTFD_MINOR 1680 bool 1681 help 1682 Arch has userfaultfd minor fault support 1683 1684config MEMBARRIER 1685 bool "Enable membarrier() system call" if EXPERT 1686 default y 1687 help 1688 Enable the membarrier() system call that allows issuing memory 1689 barriers across all running threads, which can be used to distribute 1690 the cost of user-space memory barriers asymmetrically by transforming 1691 pairs of memory barriers into pairs consisting of membarrier() and a 1692 compiler barrier. 1693 1694 If unsure, say Y. 1695 1696config KALLSYMS 1697 bool "Load all symbols for debugging/ksymoops" if EXPERT 1698 default y 1699 help 1700 Say Y here to let the kernel print out symbolic crash information and 1701 symbolic stack backtraces. This increases the size of the kernel 1702 somewhat, as all symbols have to be loaded into the kernel image. 1703 1704config KALLSYMS_ALL 1705 bool "Include all symbols in kallsyms" 1706 depends on DEBUG_KERNEL && KALLSYMS 1707 help 1708 Normally kallsyms only contains the symbols of functions for nicer 1709 OOPS messages and backtraces (i.e., symbols from the text and inittext 1710 sections). This is sufficient for most cases. And only in very rare 1711 cases (e.g., when a debugger is used) all symbols are required (e.g., 1712 names of variables from the data sections, etc). 1713 1714 This option makes sure that all symbols are loaded into the kernel 1715 image (i.e., symbols from all sections) in cost of increased kernel 1716 size (depending on the kernel configuration, it may be 300KiB or 1717 something like this). 1718 1719 Say N unless you really need all symbols. 1720 1721config KALLSYMS_ABSOLUTE_PERCPU 1722 bool 1723 depends on KALLSYMS 1724 default X86_64 && SMP 1725 1726config KALLSYMS_BASE_RELATIVE 1727 bool 1728 depends on KALLSYMS 1729 default !IA64 1730 help 1731 Instead of emitting them as absolute values in the native word size, 1732 emit the symbol references in the kallsyms table as 32-bit entries, 1733 each containing a relative value in the range [base, base + U32_MAX] 1734 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either 1735 an absolute value in the range [0, S32_MAX] or a relative value in the 1736 range [base, base + S32_MAX], where base is the lowest relative symbol 1737 address encountered in the image. 1738 1739 On 64-bit builds, this reduces the size of the address table by 50%, 1740 but more importantly, it results in entries whose values are build 1741 time constants, and no relocation pass is required at runtime to fix 1742 up the entries based on the runtime load address of the kernel. 1743 1744# end of the "standard kernel features (expert users)" menu 1745 1746# syscall, maps, verifier 1747 1748config USERFAULTFD 1749 bool "Enable userfaultfd() system call" 1750 depends on MMU 1751 help 1752 Enable the userfaultfd() system call that allows to intercept and 1753 handle page faults in userland. 1754 1755config ARCH_HAS_MEMBARRIER_CALLBACKS 1756 bool 1757 1758config ARCH_HAS_MEMBARRIER_SYNC_CORE 1759 bool 1760 1761config KCMP 1762 bool "Enable kcmp() system call" if EXPERT 1763 help 1764 Enable the kernel resource comparison system call. It provides 1765 user-space with the ability to compare two processes to see if they 1766 share a common resource, such as a file descriptor or even virtual 1767 memory space. 1768 1769 If unsure, say N. 1770 1771config RSEQ 1772 bool "Enable rseq() system call" if EXPERT 1773 default y 1774 depends on HAVE_RSEQ 1775 select MEMBARRIER 1776 help 1777 Enable the restartable sequences system call. It provides a 1778 user-space cache for the current CPU number value, which 1779 speeds up getting the current CPU number from user-space, 1780 as well as an ABI to speed up user-space operations on 1781 per-CPU data. 1782 1783 If unsure, say Y. 1784 1785config DEBUG_RSEQ 1786 default n 1787 bool "Enabled debugging of rseq() system call" if EXPERT 1788 depends on RSEQ && DEBUG_KERNEL 1789 help 1790 Enable extra debugging checks for the rseq system call. 1791 1792 If unsure, say N. 1793 1794config EMBEDDED 1795 bool "Embedded system" 1796 select EXPERT 1797 help 1798 This option should be enabled if compiling the kernel for 1799 an embedded system so certain expert options are available 1800 for configuration. 1801 1802config HAVE_PERF_EVENTS 1803 bool 1804 help 1805 See tools/perf/design.txt for details. 1806 1807config GUEST_PERF_EVENTS 1808 bool 1809 depends on HAVE_PERF_EVENTS 1810 1811config PERF_USE_VMALLOC 1812 bool 1813 help 1814 See tools/perf/design.txt for details 1815 1816config PC104 1817 bool "PC/104 support" if EXPERT 1818 help 1819 Expose PC/104 form factor device drivers and options available for 1820 selection and configuration. Enable this option if your target 1821 machine has a PC/104 bus. 1822 1823menu "Kernel Performance Events And Counters" 1824 1825config PERF_EVENTS 1826 bool "Kernel performance events and counters" 1827 default y if PROFILING 1828 depends on HAVE_PERF_EVENTS 1829 select IRQ_WORK 1830 select SRCU 1831 help 1832 Enable kernel support for various performance events provided 1833 by software and hardware. 1834 1835 Software events are supported either built-in or via the 1836 use of generic tracepoints. 1837 1838 Most modern CPUs support performance events via performance 1839 counter registers. These registers count the number of certain 1840 types of hw events: such as instructions executed, cachemisses 1841 suffered, or branches mis-predicted - without slowing down the 1842 kernel or applications. These registers can also trigger interrupts 1843 when a threshold number of events have passed - and can thus be 1844 used to profile the code that runs on that CPU. 1845 1846 The Linux Performance Event subsystem provides an abstraction of 1847 these software and hardware event capabilities, available via a 1848 system call and used by the "perf" utility in tools/perf/. It 1849 provides per task and per CPU counters, and it provides event 1850 capabilities on top of those. 1851 1852 Say Y if unsure. 1853 1854config DEBUG_PERF_USE_VMALLOC 1855 default n 1856 bool "Debug: use vmalloc to back perf mmap() buffers" 1857 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC 1858 select PERF_USE_VMALLOC 1859 help 1860 Use vmalloc memory to back perf mmap() buffers. 1861 1862 Mostly useful for debugging the vmalloc code on platforms 1863 that don't require it. 1864 1865 Say N if unsure. 1866 1867endmenu 1868 1869config VM_EVENT_COUNTERS 1870 default y 1871 bool "Enable VM event counters for /proc/vmstat" if EXPERT 1872 help 1873 VM event counters are needed for event counts to be shown. 1874 This option allows the disabling of the VM event counters 1875 on EXPERT systems. /proc/vmstat will only show page counts 1876 if VM event counters are disabled. 1877 1878config SLUB_DEBUG 1879 default y 1880 bool "Enable SLUB debugging support" if EXPERT 1881 depends on SLUB && SYSFS 1882 help 1883 SLUB has extensive debug support features. Disabling these can 1884 result in significant savings in code size. This also disables 1885 SLUB sysfs support. /sys/slab will not exist and there will be 1886 no support for cache validation etc. 1887 1888config COMPAT_BRK 1889 bool "Disable heap randomization" 1890 default y 1891 help 1892 Randomizing heap placement makes heap exploits harder, but it 1893 also breaks ancient binaries (including anything libc5 based). 1894 This option changes the bootup default to heap randomization 1895 disabled, and can be overridden at runtime by setting 1896 /proc/sys/kernel/randomize_va_space to 2. 1897 1898 On non-ancient distros (post-2000 ones) N is usually a safe choice. 1899 1900choice 1901 prompt "Choose SLAB allocator" 1902 default SLUB 1903 help 1904 This option allows to select a slab allocator. 1905 1906config SLAB 1907 bool "SLAB" 1908 depends on !PREEMPT_RT 1909 select HAVE_HARDENED_USERCOPY_ALLOCATOR 1910 help 1911 The regular slab allocator that is established and known to work 1912 well in all environments. It organizes cache hot objects in 1913 per cpu and per node queues. 1914 1915config SLUB 1916 bool "SLUB (Unqueued Allocator)" 1917 select HAVE_HARDENED_USERCOPY_ALLOCATOR 1918 help 1919 SLUB is a slab allocator that minimizes cache line usage 1920 instead of managing queues of cached objects (SLAB approach). 1921 Per cpu caching is realized using slabs of objects instead 1922 of queues of objects. SLUB can use memory efficiently 1923 and has enhanced diagnostics. SLUB is the default choice for 1924 a slab allocator. 1925 1926config SLOB 1927 depends on EXPERT 1928 bool "SLOB (Simple Allocator)" 1929 depends on !PREEMPT_RT 1930 help 1931 SLOB replaces the stock allocator with a drastically simpler 1932 allocator. SLOB is generally more space efficient but 1933 does not perform as well on large systems. 1934 1935endchoice 1936 1937config SLAB_MERGE_DEFAULT 1938 bool "Allow slab caches to be merged" 1939 default y 1940 depends on SLAB || SLUB 1941 help 1942 For reduced kernel memory fragmentation, slab caches can be 1943 merged when they share the same size and other characteristics. 1944 This carries a risk of kernel heap overflows being able to 1945 overwrite objects from merged caches (and more easily control 1946 cache layout), which makes such heap attacks easier to exploit 1947 by attackers. By keeping caches unmerged, these kinds of exploits 1948 can usually only damage objects in the same cache. To disable 1949 merging at runtime, "slab_nomerge" can be passed on the kernel 1950 command line. 1951 1952config SLAB_FREELIST_RANDOM 1953 bool "Randomize slab freelist" 1954 depends on SLAB || SLUB 1955 help 1956 Randomizes the freelist order used on creating new pages. This 1957 security feature reduces the predictability of the kernel slab 1958 allocator against heap overflows. 1959 1960config SLAB_FREELIST_HARDENED 1961 bool "Harden slab freelist metadata" 1962 depends on SLAB || SLUB 1963 help 1964 Many kernel heap attacks try to target slab cache metadata and 1965 other infrastructure. This options makes minor performance 1966 sacrifices to harden the kernel slab allocator against common 1967 freelist exploit methods. Some slab implementations have more 1968 sanity-checking than others. This option is most effective with 1969 CONFIG_SLUB. 1970 1971config SHUFFLE_PAGE_ALLOCATOR 1972 bool "Page allocator randomization" 1973 default SLAB_FREELIST_RANDOM && ACPI_NUMA 1974 help 1975 Randomization of the page allocator improves the average 1976 utilization of a direct-mapped memory-side-cache. See section 1977 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI 1978 6.2a specification for an example of how a platform advertises 1979 the presence of a memory-side-cache. There are also incidental 1980 security benefits as it reduces the predictability of page 1981 allocations to compliment SLAB_FREELIST_RANDOM, but the 1982 default granularity of shuffling on the "MAX_ORDER - 1" i.e, 1983 10th order of pages is selected based on cache utilization 1984 benefits on x86. 1985 1986 While the randomization improves cache utilization it may 1987 negatively impact workloads on platforms without a cache. For 1988 this reason, by default, the randomization is enabled only 1989 after runtime detection of a direct-mapped memory-side-cache. 1990 Otherwise, the randomization may be force enabled with the 1991 'page_alloc.shuffle' kernel command line parameter. 1992 1993 Say Y if unsure. 1994 1995config SLUB_CPU_PARTIAL 1996 default y 1997 depends on SLUB && SMP 1998 bool "SLUB per cpu partial cache" 1999 help 2000 Per cpu partial caches accelerate objects allocation and freeing 2001 that is local to a processor at the price of more indeterminism 2002 in the latency of the free. On overflow these caches will be cleared 2003 which requires the taking of locks that may cause latency spikes. 2004 Typically one would choose no for a realtime system. 2005 2006config MMAP_ALLOW_UNINITIALIZED 2007 bool "Allow mmapped anonymous memory to be uninitialized" 2008 depends on EXPERT && !MMU 2009 default n 2010 help 2011 Normally, and according to the Linux spec, anonymous memory obtained 2012 from mmap() has its contents cleared before it is passed to 2013 userspace. Enabling this config option allows you to request that 2014 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus 2015 providing a huge performance boost. If this option is not enabled, 2016 then the flag will be ignored. 2017 2018 This is taken advantage of by uClibc's malloc(), and also by 2019 ELF-FDPIC binfmt's brk and stack allocator. 2020 2021 Because of the obvious security issues, this option should only be 2022 enabled on embedded devices where you control what is run in 2023 userspace. Since that isn't generally a problem on no-MMU systems, 2024 it is normally safe to say Y here. 2025 2026 See Documentation/admin-guide/mm/nommu-mmap.rst for more information. 2027 2028config SYSTEM_DATA_VERIFICATION 2029 def_bool n 2030 select SYSTEM_TRUSTED_KEYRING 2031 select KEYS 2032 select CRYPTO 2033 select CRYPTO_RSA 2034 select ASYMMETRIC_KEY_TYPE 2035 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE 2036 select ASN1 2037 select OID_REGISTRY 2038 select X509_CERTIFICATE_PARSER 2039 select PKCS7_MESSAGE_PARSER 2040 help 2041 Provide PKCS#7 message verification using the contents of the system 2042 trusted keyring to provide public keys. This then can be used for 2043 module verification, kexec image verification and firmware blob 2044 verification. 2045 2046config PROFILING 2047 bool "Profiling support" 2048 help 2049 Say Y here to enable the extended profiling support mechanisms used 2050 by profilers. 2051 2052# 2053# Place an empty function call at each tracepoint site. Can be 2054# dynamically changed for a probe function. 2055# 2056config TRACEPOINTS 2057 bool 2058 2059endmenu # General setup 2060 2061source "arch/Kconfig" 2062 2063config RT_MUTEXES 2064 bool 2065 default y if PREEMPT_RT 2066 2067config BASE_SMALL 2068 int 2069 default 0 if BASE_FULL 2070 default 1 if !BASE_FULL 2071 2072config MODULE_SIG_FORMAT 2073 def_bool n 2074 select SYSTEM_DATA_VERIFICATION 2075 2076menuconfig MODULES 2077 bool "Enable loadable module support" 2078 modules 2079 help 2080 Kernel modules are small pieces of compiled code which can 2081 be inserted in the running kernel, rather than being 2082 permanently built into the kernel. You use the "modprobe" 2083 tool to add (and sometimes remove) them. If you say Y here, 2084 many parts of the kernel can be built as modules (by 2085 answering M instead of Y where indicated): this is most 2086 useful for infrequently used options which are not required 2087 for booting. For more information, see the man pages for 2088 modprobe, lsmod, modinfo, insmod and rmmod. 2089 2090 If you say Y here, you will need to run "make 2091 modules_install" to put the modules under /lib/modules/ 2092 where modprobe can find them (you may need to be root to do 2093 this). 2094 2095 If unsure, say Y. 2096 2097if MODULES 2098 2099config MODULE_FORCE_LOAD 2100 bool "Forced module loading" 2101 default n 2102 help 2103 Allow loading of modules without version information (ie. modprobe 2104 --force). Forced module loading sets the 'F' (forced) taint flag and 2105 is usually a really bad idea. 2106 2107config MODULE_UNLOAD 2108 bool "Module unloading" 2109 help 2110 Without this option you will not be able to unload any 2111 modules (note that some modules may not be unloadable 2112 anyway), which makes your kernel smaller, faster 2113 and simpler. If unsure, say Y. 2114 2115config MODULE_FORCE_UNLOAD 2116 bool "Forced module unloading" 2117 depends on MODULE_UNLOAD 2118 help 2119 This option allows you to force a module to unload, even if the 2120 kernel believes it is unsafe: the kernel will remove the module 2121 without waiting for anyone to stop using it (using the -f option to 2122 rmmod). This is mainly for kernel developers and desperate users. 2123 If unsure, say N. 2124 2125config MODVERSIONS 2126 bool "Module versioning support" 2127 help 2128 Usually, you have to use modules compiled with your kernel. 2129 Saying Y here makes it sometimes possible to use modules 2130 compiled for different kernels, by adding enough information 2131 to the modules to (hopefully) spot any changes which would 2132 make them incompatible with the kernel you are running. If 2133 unsure, say N. 2134 2135config ASM_MODVERSIONS 2136 bool 2137 default HAVE_ASM_MODVERSIONS && MODVERSIONS 2138 help 2139 This enables module versioning for exported symbols also from 2140 assembly. This can be enabled only when the target architecture 2141 supports it. 2142 2143config MODULE_REL_CRCS 2144 bool 2145 depends on MODVERSIONS 2146 2147config MODULE_SRCVERSION_ALL 2148 bool "Source checksum for all modules" 2149 help 2150 Modules which contain a MODULE_VERSION get an extra "srcversion" 2151 field inserted into their modinfo section, which contains a 2152 sum of the source files which made it. This helps maintainers 2153 see exactly which source was used to build a module (since 2154 others sometimes change the module source without updating 2155 the version). With this option, such a "srcversion" field 2156 will be created for all modules. If unsure, say N. 2157 2158config MODULE_SIG 2159 bool "Module signature verification" 2160 select MODULE_SIG_FORMAT 2161 help 2162 Check modules for valid signatures upon load: the signature 2163 is simply appended to the module. For more information see 2164 <file:Documentation/admin-guide/module-signing.rst>. 2165 2166 Note that this option adds the OpenSSL development packages as a 2167 kernel build dependency so that the signing tool can use its crypto 2168 library. 2169 2170 You should enable this option if you wish to use either 2171 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via 2172 another LSM - otherwise unsigned modules will be loadable regardless 2173 of the lockdown policy. 2174 2175 !!!WARNING!!! If you enable this option, you MUST make sure that the 2176 module DOES NOT get stripped after being signed. This includes the 2177 debuginfo strip done by some packagers (such as rpmbuild) and 2178 inclusion into an initramfs that wants the module size reduced. 2179 2180config MODULE_SIG_FORCE 2181 bool "Require modules to be validly signed" 2182 depends on MODULE_SIG 2183 help 2184 Reject unsigned modules or signed modules for which we don't have a 2185 key. Without this, such modules will simply taint the kernel. 2186 2187config MODULE_SIG_ALL 2188 bool "Automatically sign all modules" 2189 default y 2190 depends on MODULE_SIG || IMA_APPRAISE_MODSIG 2191 help 2192 Sign all modules during make modules_install. Without this option, 2193 modules must be signed manually, using the scripts/sign-file tool. 2194 2195comment "Do not forget to sign required modules with scripts/sign-file" 2196 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL 2197 2198choice 2199 prompt "Which hash algorithm should modules be signed with?" 2200 depends on MODULE_SIG || IMA_APPRAISE_MODSIG 2201 help 2202 This determines which sort of hashing algorithm will be used during 2203 signature generation. This algorithm _must_ be built into the kernel 2204 directly so that signature verification can take place. It is not 2205 possible to load a signed module containing the algorithm to check 2206 the signature on that module. 2207 2208config MODULE_SIG_SHA1 2209 bool "Sign modules with SHA-1" 2210 select CRYPTO_SHA1 2211 2212config MODULE_SIG_SHA224 2213 bool "Sign modules with SHA-224" 2214 select CRYPTO_SHA256 2215 2216config MODULE_SIG_SHA256 2217 bool "Sign modules with SHA-256" 2218 select CRYPTO_SHA256 2219 2220config MODULE_SIG_SHA384 2221 bool "Sign modules with SHA-384" 2222 select CRYPTO_SHA512 2223 2224config MODULE_SIG_SHA512 2225 bool "Sign modules with SHA-512" 2226 select CRYPTO_SHA512 2227 2228endchoice 2229 2230config MODULE_SIG_HASH 2231 string 2232 depends on MODULE_SIG || IMA_APPRAISE_MODSIG 2233 default "sha1" if MODULE_SIG_SHA1 2234 default "sha224" if MODULE_SIG_SHA224 2235 default "sha256" if MODULE_SIG_SHA256 2236 default "sha384" if MODULE_SIG_SHA384 2237 default "sha512" if MODULE_SIG_SHA512 2238 2239choice 2240 prompt "Module compression mode" 2241 help 2242 This option allows you to choose the algorithm which will be used to 2243 compress modules when 'make modules_install' is run. (or, you can 2244 choose to not compress modules at all.) 2245 2246 External modules will also be compressed in the same way during the 2247 installation. 2248 2249 For modules inside an initrd or initramfs, it's more efficient to 2250 compress the whole initrd or initramfs instead. 2251 2252 This is fully compatible with signed modules. 2253 2254 Please note that the tool used to load modules needs to support the 2255 corresponding algorithm. module-init-tools MAY support gzip, and kmod 2256 MAY support gzip, xz and zstd. 2257 2258 Your build system needs to provide the appropriate compression tool 2259 to compress the modules. 2260 2261 If in doubt, select 'None'. 2262 2263config MODULE_COMPRESS_NONE 2264 bool "None" 2265 help 2266 Do not compress modules. The installed modules are suffixed 2267 with .ko. 2268 2269config MODULE_COMPRESS_GZIP 2270 bool "GZIP" 2271 help 2272 Compress modules with GZIP. The installed modules are suffixed 2273 with .ko.gz. 2274 2275config MODULE_COMPRESS_XZ 2276 bool "XZ" 2277 help 2278 Compress modules with XZ. The installed modules are suffixed 2279 with .ko.xz. 2280 2281config MODULE_COMPRESS_ZSTD 2282 bool "ZSTD" 2283 help 2284 Compress modules with ZSTD. The installed modules are suffixed 2285 with .ko.zst. 2286 2287endchoice 2288 2289config MODULE_DECOMPRESS 2290 bool "Support in-kernel module decompression" 2291 depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ 2292 select ZLIB_INFLATE if MODULE_COMPRESS_GZIP 2293 select XZ_DEC if MODULE_COMPRESS_XZ 2294 help 2295 2296 Support for decompressing kernel modules by the kernel itself 2297 instead of relying on userspace to perform this task. Useful when 2298 load pinning security policy is enabled. 2299 2300 If unsure, say N. 2301 2302config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS 2303 bool "Allow loading of modules with missing namespace imports" 2304 help 2305 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in 2306 a namespace. A module that makes use of a symbol exported with such a 2307 namespace is required to import the namespace via MODULE_IMPORT_NS(). 2308 There is no technical reason to enforce correct namespace imports, 2309 but it creates consistency between symbols defining namespaces and 2310 users importing namespaces they make use of. This option relaxes this 2311 requirement and lifts the enforcement when loading a module. 2312 2313 If unsure, say N. 2314 2315config MODPROBE_PATH 2316 string "Path to modprobe binary" 2317 default "/sbin/modprobe" 2318 help 2319 When kernel code requests a module, it does so by calling 2320 the "modprobe" userspace utility. This option allows you to 2321 set the path where that binary is found. This can be changed 2322 at runtime via the sysctl file 2323 /proc/sys/kernel/modprobe. Setting this to the empty string 2324 removes the kernel's ability to request modules (but 2325 userspace can still load modules explicitly). 2326 2327config TRIM_UNUSED_KSYMS 2328 bool "Trim unused exported kernel symbols" if EXPERT 2329 depends on !COMPILE_TEST 2330 help 2331 The kernel and some modules make many symbols available for 2332 other modules to use via EXPORT_SYMBOL() and variants. Depending 2333 on the set of modules being selected in your kernel configuration, 2334 many of those exported symbols might never be used. 2335 2336 This option allows for unused exported symbols to be dropped from 2337 the build. In turn, this provides the compiler more opportunities 2338 (especially when using LTO) for optimizing the code and reducing 2339 binary size. This might have some security advantages as well. 2340 2341 If unsure, or if you need to build out-of-tree modules, say N. 2342 2343config UNUSED_KSYMS_WHITELIST 2344 string "Whitelist of symbols to keep in ksymtab" 2345 depends on TRIM_UNUSED_KSYMS 2346 help 2347 By default, all unused exported symbols will be un-exported from the 2348 build when TRIM_UNUSED_KSYMS is selected. 2349 2350 UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept 2351 exported at all times, even in absence of in-tree users. The value to 2352 set here is the path to a text file containing the list of symbols, 2353 one per line. The path can be absolute, or relative to the kernel 2354 source tree. 2355 2356endif # MODULES 2357 2358config MODULES_TREE_LOOKUP 2359 def_bool y 2360 depends on PERF_EVENTS || TRACING || CFI_CLANG 2361 2362config INIT_ALL_POSSIBLE 2363 bool 2364 help 2365 Back when each arch used to define their own cpu_online_mask and 2366 cpu_possible_mask, some of them chose to initialize cpu_possible_mask 2367 with all 1s, and others with all 0s. When they were centralised, 2368 it was better to provide this option than to break all the archs 2369 and have several arch maintainers pursuing me down dark alleys. 2370 2371source "block/Kconfig" 2372 2373config PREEMPT_NOTIFIERS 2374 bool 2375 2376config PADATA 2377 depends on SMP 2378 bool 2379 2380config ASN1 2381 tristate 2382 help 2383 Build a simple ASN.1 grammar compiler that produces a bytecode output 2384 that can be interpreted by the ASN.1 stream decoder and used to 2385 inform it as to what tags are to be expected in a stream and what 2386 functions to call on what tags. 2387 2388source "kernel/Kconfig.locks" 2389 2390config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE 2391 bool 2392 2393config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE 2394 bool 2395 2396# It may be useful for an architecture to override the definitions of the 2397# SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h> 2398# and the COMPAT_ variants in <linux/compat.h>, in particular to use a 2399# different calling convention for syscalls. They can also override the 2400# macros for not-implemented syscalls in kernel/sys_ni.c and 2401# kernel/time/posix-stubs.c. All these overrides need to be available in 2402# <asm/syscall_wrapper.h>. 2403config ARCH_HAS_SYSCALL_WRAPPER 2404 def_bool n 2405