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