1# SPDX-License-Identifier: GPL-2.0-only 2config DEFCONFIG_LIST 3 string 4 depends on !UML 5 option defconfig_list 6 default "/lib/modules/$(shell,uname -r)/.config" 7 default "/etc/kernel-config" 8 default "/boot/config-$(shell,uname -r)" 9 default ARCH_DEFCONFIG 10 default "arch/$(ARCH)/defconfig" 11 12config CC_IS_GCC 13 def_bool $(success,$(CC) --version | head -n 1 | grep -q gcc) 14 15config GCC_VERSION 16 int 17 default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC 18 default 0 19 20config CC_IS_CLANG 21 def_bool $(success,$(CC) --version | head -n 1 | grep -q clang) 22 23config CLANG_VERSION 24 int 25 default $(shell,$(srctree)/scripts/clang-version.sh $(CC)) 26 27config CC_CAN_LINK 28 def_bool $(success,$(srctree)/scripts/cc-can-link.sh $(CC)) 29 30config CC_HAS_ASM_GOTO 31 def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) 32 33config TOOLS_SUPPORT_RELR 34 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh) 35 36config CC_HAS_ASM_INLINE 37 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null) 38 39config CC_HAS_WARN_MAYBE_UNINITIALIZED 40 def_bool $(cc-option,-Wmaybe-uninitialized) 41 help 42 GCC >= 4.7 supports this option. 43 44config CC_DISABLE_WARN_MAYBE_UNINITIALIZED 45 bool 46 depends on CC_HAS_WARN_MAYBE_UNINITIALIZED 47 default CC_IS_GCC && GCC_VERSION < 40900 # unreliable for GCC < 4.9 48 help 49 GCC's -Wmaybe-uninitialized is not reliable by definition. 50 Lots of false positive warnings are produced in some cases. 51 52 If this option is enabled, -Wno-maybe-uninitialzed is passed 53 to the compiler to suppress maybe-uninitialized warnings. 54 55config CONSTRUCTORS 56 bool 57 58config IRQ_WORK 59 bool 60 61config BUILDTIME_EXTABLE_SORT 62 bool 63 64config THREAD_INFO_IN_TASK 65 bool 66 help 67 Select this to move thread_info off the stack into task_struct. To 68 make this work, an arch will need to remove all thread_info fields 69 except flags and fix any runtime bugs. 70 71 One subtle change that will be needed is to use try_get_task_stack() 72 and put_task_stack() in save_thread_stack_tsk() and get_wchan(). 73 74menu "General setup" 75 76config BROKEN 77 bool 78 79config BROKEN_ON_SMP 80 bool 81 depends on BROKEN || !SMP 82 default y 83 84config INIT_ENV_ARG_LIMIT 85 int 86 default 32 if !UML 87 default 128 if UML 88 help 89 Maximum of each of the number of arguments and environment 90 variables passed to init from the kernel command line. 91 92config COMPILE_TEST 93 bool "Compile also drivers which will not load" 94 depends on !UML 95 default n 96 help 97 Some drivers can be compiled on a different platform than they are 98 intended to be run on. Despite they cannot be loaded there (or even 99 when they load they cannot be used due to missing HW support), 100 developers still, opposing to distributors, might want to build such 101 drivers to compile-test them. 102 103 If you are a developer and want to build everything available, say Y 104 here. If you are a user/distributor, say N here to exclude useless 105 drivers to be distributed. 106 107config HEADER_TEST 108 bool "Compile test headers that should be standalone compilable" 109 help 110 Compile test headers listed in header-test-y target to ensure they are 111 self-contained, i.e. compilable as standalone units. 112 113 If you are a developer or tester and want to ensure the requested 114 headers are self-contained, say Y here. Otherwise, choose N. 115 116config KERNEL_HEADER_TEST 117 bool "Compile test kernel headers" 118 depends on HEADER_TEST 119 help 120 Headers in include/ are used to build external moduls. 121 Compile test them to ensure they are self-contained, i.e. 122 compilable as standalone units. 123 124 If you are a developer or tester and want to ensure the headers 125 in include/ are self-contained, say Y here. Otherwise, choose N. 126 127config UAPI_HEADER_TEST 128 bool "Compile test UAPI headers" 129 depends on HEADER_TEST && HEADERS_INSTALL && CC_CAN_LINK 130 help 131 Compile test headers exported to user-space to ensure they are 132 self-contained, i.e. compilable as standalone units. 133 134 If you are a developer or tester and want to ensure the exported 135 headers are self-contained, say Y here. Otherwise, choose N. 136 137config LOCALVERSION 138 string "Local version - append to kernel release" 139 help 140 Append an extra string to the end of your kernel version. 141 This will show up when you type uname, for example. 142 The string you set here will be appended after the contents of 143 any files with a filename matching localversion* in your 144 object and source tree, in that order. Your total string can 145 be a maximum of 64 characters. 146 147config LOCALVERSION_AUTO 148 bool "Automatically append version information to the version string" 149 default y 150 depends on !COMPILE_TEST 151 help 152 This will try to automatically determine if the current tree is a 153 release tree by looking for git tags that belong to the current 154 top of tree revision. 155 156 A string of the format -gxxxxxxxx will be added to the localversion 157 if a git-based tree is found. The string generated by this will be 158 appended after any matching localversion* files, and after the value 159 set in CONFIG_LOCALVERSION. 160 161 (The actual string used here is the first eight characters produced 162 by running the command: 163 164 $ git rev-parse --verify HEAD 165 166 which is done within the script "scripts/setlocalversion".) 167 168config BUILD_SALT 169 string "Build ID Salt" 170 default "" 171 help 172 The build ID is used to link binaries and their debug info. Setting 173 this option will use the value in the calculation of the build id. 174 This is mostly useful for distributions which want to ensure the 175 build is unique between builds. It's safe to leave the default. 176 177config HAVE_KERNEL_GZIP 178 bool 179 180config HAVE_KERNEL_BZIP2 181 bool 182 183config HAVE_KERNEL_LZMA 184 bool 185 186config HAVE_KERNEL_XZ 187 bool 188 189config HAVE_KERNEL_LZO 190 bool 191 192config HAVE_KERNEL_LZ4 193 bool 194 195config HAVE_KERNEL_UNCOMPRESSED 196 bool 197 198choice 199 prompt "Kernel compression mode" 200 default KERNEL_GZIP 201 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_UNCOMPRESSED 202 help 203 The linux kernel is a kind of self-extracting executable. 204 Several compression algorithms are available, which differ 205 in efficiency, compression and decompression speed. 206 Compression speed is only relevant when building a kernel. 207 Decompression speed is relevant at each boot. 208 209 If you have any problems with bzip2 or lzma compressed 210 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older 211 version of this functionality (bzip2 only), for 2.4, was 212 supplied by Christian Ludwig) 213 214 High compression options are mostly useful for users, who 215 are low on disk space (embedded systems), but for whom ram 216 size matters less. 217 218 If in doubt, select 'gzip' 219 220config KERNEL_GZIP 221 bool "Gzip" 222 depends on HAVE_KERNEL_GZIP 223 help 224 The old and tried gzip compression. It provides a good balance 225 between compression ratio and decompression speed. 226 227config KERNEL_BZIP2 228 bool "Bzip2" 229 depends on HAVE_KERNEL_BZIP2 230 help 231 Its compression ratio and speed is intermediate. 232 Decompression speed is slowest among the choices. The kernel 233 size is about 10% smaller with bzip2, in comparison to gzip. 234 Bzip2 uses a large amount of memory. For modern kernels you 235 will need at least 8MB RAM or more for booting. 236 237config KERNEL_LZMA 238 bool "LZMA" 239 depends on HAVE_KERNEL_LZMA 240 help 241 This compression algorithm's ratio is best. Decompression speed 242 is between gzip and bzip2. Compression is slowest. 243 The kernel size is about 33% smaller with LZMA in comparison to gzip. 244 245config KERNEL_XZ 246 bool "XZ" 247 depends on HAVE_KERNEL_XZ 248 help 249 XZ uses the LZMA2 algorithm and instruction set specific 250 BCJ filters which can improve compression ratio of executable 251 code. The size of the kernel is about 30% smaller with XZ in 252 comparison to gzip. On architectures for which there is a BCJ 253 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ 254 will create a few percent smaller kernel than plain LZMA. 255 256 The speed is about the same as with LZMA: The decompression 257 speed of XZ is better than that of bzip2 but worse than gzip 258 and LZO. Compression is slow. 259 260config KERNEL_LZO 261 bool "LZO" 262 depends on HAVE_KERNEL_LZO 263 help 264 Its compression ratio is the poorest among the choices. The kernel 265 size is about 10% bigger than gzip; however its speed 266 (both compression and decompression) is the fastest. 267 268config KERNEL_LZ4 269 bool "LZ4" 270 depends on HAVE_KERNEL_LZ4 271 help 272 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding. 273 A preliminary version of LZ4 de/compression tool is available at 274 <https://code.google.com/p/lz4/>. 275 276 Its compression ratio is worse than LZO. The size of the kernel 277 is about 8% bigger than LZO. But the decompression speed is 278 faster than LZO. 279 280config KERNEL_UNCOMPRESSED 281 bool "None" 282 depends on HAVE_KERNEL_UNCOMPRESSED 283 help 284 Produce uncompressed kernel image. This option is usually not what 285 you want. It is useful for debugging the kernel in slow simulation 286 environments, where decompressing and moving the kernel is awfully 287 slow. This option allows early boot code to skip the decompressor 288 and jump right at uncompressed kernel image. 289 290endchoice 291 292config DEFAULT_HOSTNAME 293 string "Default hostname" 294 default "(none)" 295 help 296 This option determines the default system hostname before userspace 297 calls sethostname(2). The kernel traditionally uses "(none)" here, 298 but you may wish to use a different default here to make a minimal 299 system more usable with less configuration. 300 301# 302# For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can 303# add proper SWAP support to them, in which case this can be remove. 304# 305config ARCH_NO_SWAP 306 bool 307 308config SWAP 309 bool "Support for paging of anonymous memory (swap)" 310 depends on MMU && BLOCK && !ARCH_NO_SWAP 311 default y 312 help 313 This option allows you to choose whether you want to have support 314 for so called swap devices or swap files in your kernel that are 315 used to provide more virtual memory than the actual RAM present 316 in your computer. If unsure say Y. 317 318config SYSVIPC 319 bool "System V IPC" 320 ---help--- 321 Inter Process Communication is a suite of library functions and 322 system calls which let processes (running programs) synchronize and 323 exchange information. It is generally considered to be a good thing, 324 and some programs won't run unless you say Y here. In particular, if 325 you want to run the DOS emulator dosemu under Linux (read the 326 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>), 327 you'll need to say Y here. 328 329 You can find documentation about IPC with "info ipc" and also in 330 section 6.4 of the Linux Programmer's Guide, available from 331 <http://www.tldp.org/guides.html>. 332 333config SYSVIPC_SYSCTL 334 bool 335 depends on SYSVIPC 336 depends on SYSCTL 337 default y 338 339config POSIX_MQUEUE 340 bool "POSIX Message Queues" 341 depends on NET 342 ---help--- 343 POSIX variant of message queues is a part of IPC. In POSIX message 344 queues every message has a priority which decides about succession 345 of receiving it by a process. If you want to compile and run 346 programs written e.g. for Solaris with use of its POSIX message 347 queues (functions mq_*) say Y here. 348 349 POSIX message queues are visible as a filesystem called 'mqueue' 350 and can be mounted somewhere if you want to do filesystem 351 operations on message queues. 352 353 If unsure, say Y. 354 355config POSIX_MQUEUE_SYSCTL 356 bool 357 depends on POSIX_MQUEUE 358 depends on SYSCTL 359 default y 360 361config CROSS_MEMORY_ATTACH 362 bool "Enable process_vm_readv/writev syscalls" 363 depends on MMU 364 default y 365 help 366 Enabling this option adds the system calls process_vm_readv and 367 process_vm_writev which allow a process with the correct privileges 368 to directly read from or write to another process' address space. 369 See the man page for more details. 370 371config USELIB 372 bool "uselib syscall" 373 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION 374 help 375 This option enables the uselib syscall, a system call used in the 376 dynamic linker from libc5 and earlier. glibc does not use this 377 system call. If you intend to run programs built on libc5 or 378 earlier, you may need to enable this syscall. Current systems 379 running glibc can safely disable this. 380 381config AUDIT 382 bool "Auditing support" 383 depends on NET 384 help 385 Enable auditing infrastructure that can be used with another 386 kernel subsystem, such as SELinux (which requires this for 387 logging of avc messages output). System call auditing is included 388 on architectures which support it. 389 390config HAVE_ARCH_AUDITSYSCALL 391 bool 392 393config AUDITSYSCALL 394 def_bool y 395 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL 396 select FSNOTIFY 397 398source "kernel/irq/Kconfig" 399source "kernel/time/Kconfig" 400source "kernel/Kconfig.preempt" 401 402menu "CPU/Task time and stats accounting" 403 404config VIRT_CPU_ACCOUNTING 405 bool 406 407choice 408 prompt "Cputime accounting" 409 default TICK_CPU_ACCOUNTING if !PPC64 410 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64 411 412# Kind of a stub config for the pure tick based cputime accounting 413config TICK_CPU_ACCOUNTING 414 bool "Simple tick based cputime accounting" 415 depends on !S390 && !NO_HZ_FULL 416 help 417 This is the basic tick based cputime accounting that maintains 418 statistics about user, system and idle time spent on per jiffies 419 granularity. 420 421 If unsure, say Y. 422 423config VIRT_CPU_ACCOUNTING_NATIVE 424 bool "Deterministic task and CPU time accounting" 425 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL 426 select VIRT_CPU_ACCOUNTING 427 help 428 Select this option to enable more accurate task and CPU time 429 accounting. This is done by reading a CPU counter on each 430 kernel entry and exit and on transitions within the kernel 431 between system, softirq and hardirq state, so there is a 432 small performance impact. In the case of s390 or IBM POWER > 5, 433 this also enables accounting of stolen time on logically-partitioned 434 systems. 435 436config VIRT_CPU_ACCOUNTING_GEN 437 bool "Full dynticks CPU time accounting" 438 depends on HAVE_CONTEXT_TRACKING 439 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 440 depends on GENERIC_CLOCKEVENTS 441 select VIRT_CPU_ACCOUNTING 442 select CONTEXT_TRACKING 443 help 444 Select this option to enable task and CPU time accounting on full 445 dynticks systems. This accounting is implemented by watching every 446 kernel-user boundaries using the context tracking subsystem. 447 The accounting is thus performed at the expense of some significant 448 overhead. 449 450 For now this is only useful if you are working on the full 451 dynticks subsystem development. 452 453 If unsure, say N. 454 455endchoice 456 457config IRQ_TIME_ACCOUNTING 458 bool "Fine granularity task level IRQ time accounting" 459 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE 460 help 461 Select this option to enable fine granularity task irq time 462 accounting. This is done by reading a timestamp on each 463 transitions between softirq and hardirq state, so there can be a 464 small performance impact. 465 466 If in doubt, say N here. 467 468config HAVE_SCHED_AVG_IRQ 469 def_bool y 470 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING 471 depends on SMP 472 473config BSD_PROCESS_ACCT 474 bool "BSD Process Accounting" 475 depends on MULTIUSER 476 help 477 If you say Y here, a user level program will be able to instruct the 478 kernel (via a special system call) to write process accounting 479 information to a file: whenever a process exits, information about 480 that process will be appended to the file by the kernel. The 481 information includes things such as creation time, owning user, 482 command name, memory usage, controlling terminal etc. (the complete 483 list is in the struct acct in <file:include/linux/acct.h>). It is 484 up to the user level program to do useful things with this 485 information. This is generally a good idea, so say Y. 486 487config BSD_PROCESS_ACCT_V3 488 bool "BSD Process Accounting version 3 file format" 489 depends on BSD_PROCESS_ACCT 490 default n 491 help 492 If you say Y here, the process accounting information is written 493 in a new file format that also logs the process IDs of each 494 process and its parent. Note that this file format is incompatible 495 with previous v0/v1/v2 file formats, so you will need updated tools 496 for processing it. A preliminary version of these tools is available 497 at <http://www.gnu.org/software/acct/>. 498 499config TASKSTATS 500 bool "Export task/process statistics through netlink" 501 depends on NET 502 depends on MULTIUSER 503 default n 504 help 505 Export selected statistics for tasks/processes through the 506 generic netlink interface. Unlike BSD process accounting, the 507 statistics are available during the lifetime of tasks/processes as 508 responses to commands. Like BSD accounting, they are sent to user 509 space on task exit. 510 511 Say N if unsure. 512 513config TASK_DELAY_ACCT 514 bool "Enable per-task delay accounting" 515 depends on TASKSTATS 516 select SCHED_INFO 517 help 518 Collect information on time spent by a task waiting for system 519 resources like cpu, synchronous block I/O completion and swapping 520 in pages. Such statistics can help in setting a task's priorities 521 relative to other tasks for cpu, io, rss limits etc. 522 523 Say N if unsure. 524 525config TASK_XACCT 526 bool "Enable extended accounting over taskstats" 527 depends on TASKSTATS 528 help 529 Collect extended task accounting data and send the data 530 to userland for processing over the taskstats interface. 531 532 Say N if unsure. 533 534config TASK_IO_ACCOUNTING 535 bool "Enable per-task storage I/O accounting" 536 depends on TASK_XACCT 537 help 538 Collect information on the number of bytes of storage I/O which this 539 task has caused. 540 541 Say N if unsure. 542 543config PSI 544 bool "Pressure stall information tracking" 545 help 546 Collect metrics that indicate how overcommitted the CPU, memory, 547 and IO capacity are in the system. 548 549 If you say Y here, the kernel will create /proc/pressure/ with the 550 pressure statistics files cpu, memory, and io. These will indicate 551 the share of walltime in which some or all tasks in the system are 552 delayed due to contention of the respective resource. 553 554 In kernels with cgroup support, cgroups (cgroup2 only) will 555 have cpu.pressure, memory.pressure, and io.pressure files, 556 which aggregate pressure stalls for the grouped tasks only. 557 558 For more details see Documentation/accounting/psi.rst. 559 560 Say N if unsure. 561 562config PSI_DEFAULT_DISABLED 563 bool "Require boot parameter to enable pressure stall information tracking" 564 default n 565 depends on PSI 566 help 567 If set, pressure stall information tracking will be disabled 568 per default but can be enabled through passing psi=1 on the 569 kernel commandline during boot. 570 571 This feature adds some code to the task wakeup and sleep 572 paths of the scheduler. The overhead is too low to affect 573 common scheduling-intense workloads in practice (such as 574 webservers, memcache), but it does show up in artificial 575 scheduler stress tests, such as hackbench. 576 577 If you are paranoid and not sure what the kernel will be 578 used for, say Y. 579 580 Say N if unsure. 581 582endmenu # "CPU/Task time and stats accounting" 583 584config CPU_ISOLATION 585 bool "CPU isolation" 586 depends on SMP || COMPILE_TEST 587 default y 588 help 589 Make sure that CPUs running critical tasks are not disturbed by 590 any source of "noise" such as unbound workqueues, timers, kthreads... 591 Unbound jobs get offloaded to housekeeping CPUs. This is driven by 592 the "isolcpus=" boot parameter. 593 594 Say Y if unsure. 595 596source "kernel/rcu/Kconfig" 597 598config BUILD_BIN2C 599 bool 600 default n 601 602config IKCONFIG 603 tristate "Kernel .config support" 604 ---help--- 605 This option enables the complete Linux kernel ".config" file 606 contents to be saved in the kernel. It provides documentation 607 of which kernel options are used in a running kernel or in an 608 on-disk kernel. This information can be extracted from the kernel 609 image file with the script scripts/extract-ikconfig and used as 610 input to rebuild the current kernel or to build another kernel. 611 It can also be extracted from a running kernel by reading 612 /proc/config.gz if enabled (below). 613 614config IKCONFIG_PROC 615 bool "Enable access to .config through /proc/config.gz" 616 depends on IKCONFIG && PROC_FS 617 ---help--- 618 This option enables access to the kernel configuration file 619 through /proc/config.gz. 620 621config IKHEADERS 622 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz" 623 depends on SYSFS 624 help 625 This option enables access to the in-kernel headers that are generated during 626 the build process. These can be used to build eBPF tracing programs, 627 or similar programs. If you build the headers as a module, a module called 628 kheaders.ko is built which can be loaded on-demand to get access to headers. 629 630config LOG_BUF_SHIFT 631 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" 632 range 12 25 633 default 17 634 depends on PRINTK 635 help 636 Select the minimal kernel log buffer size as a power of 2. 637 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config 638 parameter, see below. Any higher size also might be forced 639 by "log_buf_len" boot parameter. 640 641 Examples: 642 17 => 128 KB 643 16 => 64 KB 644 15 => 32 KB 645 14 => 16 KB 646 13 => 8 KB 647 12 => 4 KB 648 649config LOG_CPU_MAX_BUF_SHIFT 650 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)" 651 depends on SMP 652 range 0 21 653 default 12 if !BASE_SMALL 654 default 0 if BASE_SMALL 655 depends on PRINTK 656 help 657 This option allows to increase the default ring buffer size 658 according to the number of CPUs. The value defines the contribution 659 of each CPU as a power of 2. The used space is typically only few 660 lines however it might be much more when problems are reported, 661 e.g. backtraces. 662 663 The increased size means that a new buffer has to be allocated and 664 the original static one is unused. It makes sense only on systems 665 with more CPUs. Therefore this value is used only when the sum of 666 contributions is greater than the half of the default kernel ring 667 buffer as defined by LOG_BUF_SHIFT. The default values are set 668 so that more than 64 CPUs are needed to trigger the allocation. 669 670 Also this option is ignored when "log_buf_len" kernel parameter is 671 used as it forces an exact (power of two) size of the ring buffer. 672 673 The number of possible CPUs is used for this computation ignoring 674 hotplugging making the computation optimal for the worst case 675 scenario while allowing a simple algorithm to be used from bootup. 676 677 Examples shift values and their meaning: 678 17 => 128 KB for each CPU 679 16 => 64 KB for each CPU 680 15 => 32 KB for each CPU 681 14 => 16 KB for each CPU 682 13 => 8 KB for each CPU 683 12 => 4 KB for each CPU 684 685config PRINTK_SAFE_LOG_BUF_SHIFT 686 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)" 687 range 10 21 688 default 13 689 depends on PRINTK 690 help 691 Select the size of an alternate printk per-CPU buffer where messages 692 printed from usafe contexts are temporary stored. One example would 693 be NMI messages, another one - printk recursion. The messages are 694 copied to the main log buffer in a safe context to avoid a deadlock. 695 The value defines the size as a power of 2. 696 697 Those messages are rare and limited. The largest one is when 698 a backtrace is printed. It usually fits into 4KB. Select 699 8KB if you want to be on the safe side. 700 701 Examples: 702 17 => 128 KB for each CPU 703 16 => 64 KB for each CPU 704 15 => 32 KB for each CPU 705 14 => 16 KB for each CPU 706 13 => 8 KB for each CPU 707 12 => 4 KB for each CPU 708 709# 710# Architectures with an unreliable sched_clock() should select this: 711# 712config HAVE_UNSTABLE_SCHED_CLOCK 713 bool 714 715config GENERIC_SCHED_CLOCK 716 bool 717 718menu "Scheduler features" 719 720config UCLAMP_TASK 721 bool "Enable utilization clamping for RT/FAIR tasks" 722 depends on CPU_FREQ_GOV_SCHEDUTIL 723 help 724 This feature enables the scheduler to track the clamped utilization 725 of each CPU based on RUNNABLE tasks scheduled on that CPU. 726 727 With this option, the user can specify the min and max CPU 728 utilization allowed for RUNNABLE tasks. The max utilization defines 729 the maximum frequency a task should use while the min utilization 730 defines the minimum frequency it should use. 731 732 Both min and max utilization clamp values are hints to the scheduler, 733 aiming at improving its frequency selection policy, but they do not 734 enforce or grant any specific bandwidth for tasks. 735 736 If in doubt, say N. 737 738config UCLAMP_BUCKETS_COUNT 739 int "Number of supported utilization clamp buckets" 740 range 5 20 741 default 5 742 depends on UCLAMP_TASK 743 help 744 Defines the number of clamp buckets to use. The range of each bucket 745 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the 746 number of clamp buckets the finer their granularity and the higher 747 the precision of clamping aggregation and tracking at run-time. 748 749 For example, with the minimum configuration value we will have 5 750 clamp buckets tracking 20% utilization each. A 25% boosted tasks will 751 be refcounted in the [20..39]% bucket and will set the bucket clamp 752 effective value to 25%. 753 If a second 30% boosted task should be co-scheduled on the same CPU, 754 that task will be refcounted in the same bucket of the first task and 755 it will boost the bucket clamp effective value to 30%. 756 The clamp effective value of a bucket is reset to its nominal value 757 (20% in the example above) when there are no more tasks refcounted in 758 that bucket. 759 760 An additional boost/capping margin can be added to some tasks. In the 761 example above the 25% task will be boosted to 30% until it exits the 762 CPU. If that should be considered not acceptable on certain systems, 763 it's always possible to reduce the margin by increasing the number of 764 clamp buckets to trade off used memory for run-time tracking 765 precision. 766 767 If in doubt, use the default value. 768 769endmenu 770 771# 772# For architectures that want to enable the support for NUMA-affine scheduler 773# balancing logic: 774# 775config ARCH_SUPPORTS_NUMA_BALANCING 776 bool 777 778# 779# For architectures that prefer to flush all TLBs after a number of pages 780# are unmapped instead of sending one IPI per page to flush. The architecture 781# must provide guarantees on what happens if a clean TLB cache entry is 782# written after the unmap. Details are in mm/rmap.c near the check for 783# should_defer_flush. The architecture should also consider if the full flush 784# and the refill costs are offset by the savings of sending fewer IPIs. 785config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH 786 bool 787 788config CC_HAS_INT128 789 def_bool y 790 depends on !$(cc-option,-D__SIZEOF_INT128__=0) 791 792# 793# For architectures that know their GCC __int128 support is sound 794# 795config ARCH_SUPPORTS_INT128 796 bool 797 798# For architectures that (ab)use NUMA to represent different memory regions 799# all cpu-local but of different latencies, such as SuperH. 800# 801config ARCH_WANT_NUMA_VARIABLE_LOCALITY 802 bool 803 804config NUMA_BALANCING 805 bool "Memory placement aware NUMA scheduler" 806 depends on ARCH_SUPPORTS_NUMA_BALANCING 807 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY 808 depends on SMP && NUMA && MIGRATION 809 help 810 This option adds support for automatic NUMA aware memory/task placement. 811 The mechanism is quite primitive and is based on migrating memory when 812 it has references to the node the task is running on. 813 814 This system will be inactive on UMA systems. 815 816config NUMA_BALANCING_DEFAULT_ENABLED 817 bool "Automatically enable NUMA aware memory/task placement" 818 default y 819 depends on NUMA_BALANCING 820 help 821 If set, automatic NUMA balancing will be enabled if running on a NUMA 822 machine. 823 824menuconfig CGROUPS 825 bool "Control Group support" 826 select KERNFS 827 help 828 This option adds support for grouping sets of processes together, for 829 use with process control subsystems such as Cpusets, CFS, memory 830 controls or device isolation. 831 See 832 - Documentation/scheduler/sched-design-CFS.rst (CFS) 833 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation 834 and resource control) 835 836 Say N if unsure. 837 838if CGROUPS 839 840config PAGE_COUNTER 841 bool 842 843config MEMCG 844 bool "Memory controller" 845 select PAGE_COUNTER 846 select EVENTFD 847 help 848 Provides control over the memory footprint of tasks in a cgroup. 849 850config MEMCG_SWAP 851 bool "Swap controller" 852 depends on MEMCG && SWAP 853 help 854 Provides control over the swap space consumed by tasks in a cgroup. 855 856config MEMCG_SWAP_ENABLED 857 bool "Swap controller enabled by default" 858 depends on MEMCG_SWAP 859 default y 860 help 861 Memory Resource Controller Swap Extension comes with its price in 862 a bigger memory consumption. General purpose distribution kernels 863 which want to enable the feature but keep it disabled by default 864 and let the user enable it by swapaccount=1 boot command line 865 parameter should have this option unselected. 866 For those who want to have the feature enabled by default should 867 select this option (if, for some reason, they need to disable it 868 then swapaccount=0 does the trick). 869 870config MEMCG_KMEM 871 bool 872 depends on MEMCG && !SLOB 873 default y 874 875config BLK_CGROUP 876 bool "IO controller" 877 depends on BLOCK 878 default n 879 ---help--- 880 Generic block IO controller cgroup interface. This is the common 881 cgroup interface which should be used by various IO controlling 882 policies. 883 884 Currently, CFQ IO scheduler uses it to recognize task groups and 885 control disk bandwidth allocation (proportional time slice allocation) 886 to such task groups. It is also used by bio throttling logic in 887 block layer to implement upper limit in IO rates on a device. 888 889 This option only enables generic Block IO controller infrastructure. 890 One needs to also enable actual IO controlling logic/policy. For 891 enabling proportional weight division of disk bandwidth in CFQ, set 892 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set 893 CONFIG_BLK_DEV_THROTTLING=y. 894 895 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information. 896 897config CGROUP_WRITEBACK 898 bool 899 depends on MEMCG && BLK_CGROUP 900 default y 901 902menuconfig CGROUP_SCHED 903 bool "CPU controller" 904 default n 905 help 906 This feature lets CPU scheduler recognize task groups and control CPU 907 bandwidth allocation to such task groups. It uses cgroups to group 908 tasks. 909 910if CGROUP_SCHED 911config FAIR_GROUP_SCHED 912 bool "Group scheduling for SCHED_OTHER" 913 depends on CGROUP_SCHED 914 default CGROUP_SCHED 915 916config CFS_BANDWIDTH 917 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED" 918 depends on FAIR_GROUP_SCHED 919 default n 920 help 921 This option allows users to define CPU bandwidth rates (limits) for 922 tasks running within the fair group scheduler. Groups with no limit 923 set are considered to be unconstrained and will run with no 924 restriction. 925 See Documentation/scheduler/sched-bwc.rst for more information. 926 927config RT_GROUP_SCHED 928 bool "Group scheduling for SCHED_RR/FIFO" 929 depends on CGROUP_SCHED 930 default n 931 help 932 This feature lets you explicitly allocate real CPU bandwidth 933 to task groups. If enabled, it will also make it impossible to 934 schedule realtime tasks for non-root users until you allocate 935 realtime bandwidth for them. 936 See Documentation/scheduler/sched-rt-group.rst for more information. 937 938endif #CGROUP_SCHED 939 940config UCLAMP_TASK_GROUP 941 bool "Utilization clamping per group of tasks" 942 depends on CGROUP_SCHED 943 depends on UCLAMP_TASK 944 default n 945 help 946 This feature enables the scheduler to track the clamped utilization 947 of each CPU based on RUNNABLE tasks currently scheduled on that CPU. 948 949 When this option is enabled, the user can specify a min and max 950 CPU bandwidth which is allowed for each single task in a group. 951 The max bandwidth allows to clamp the maximum frequency a task 952 can use, while the min bandwidth allows to define a minimum 953 frequency a task will always use. 954 955 When task group based utilization clamping is enabled, an eventually 956 specified task-specific clamp value is constrained by the cgroup 957 specified clamp value. Both minimum and maximum task clamping cannot 958 be bigger than the corresponding clamping defined at task group level. 959 960 If in doubt, say N. 961 962config CGROUP_PIDS 963 bool "PIDs controller" 964 help 965 Provides enforcement of process number limits in the scope of a 966 cgroup. Any attempt to fork more processes than is allowed in the 967 cgroup will fail. PIDs are fundamentally a global resource because it 968 is fairly trivial to reach PID exhaustion before you reach even a 969 conservative kmemcg limit. As a result, it is possible to grind a 970 system to halt without being limited by other cgroup policies. The 971 PIDs controller is designed to stop this from happening. 972 973 It should be noted that organisational operations (such as attaching 974 to a cgroup hierarchy) will *not* be blocked by the PIDs controller, 975 since the PIDs limit only affects a process's ability to fork, not to 976 attach to a cgroup. 977 978config CGROUP_RDMA 979 bool "RDMA controller" 980 help 981 Provides enforcement of RDMA resources defined by IB stack. 982 It is fairly easy for consumers to exhaust RDMA resources, which 983 can result into resource unavailability to other consumers. 984 RDMA controller is designed to stop this from happening. 985 Attaching processes with active RDMA resources to the cgroup 986 hierarchy is allowed even if can cross the hierarchy's limit. 987 988config CGROUP_FREEZER 989 bool "Freezer controller" 990 help 991 Provides a way to freeze and unfreeze all tasks in a 992 cgroup. 993 994 This option affects the ORIGINAL cgroup interface. The cgroup2 memory 995 controller includes important in-kernel memory consumers per default. 996 997 If you're using cgroup2, say N. 998 999config CGROUP_HUGETLB 1000 bool "HugeTLB controller" 1001 depends on HUGETLB_PAGE 1002 select PAGE_COUNTER 1003 default n 1004 help 1005 Provides a cgroup controller for HugeTLB pages. 1006 When you enable this, you can put a per cgroup limit on HugeTLB usage. 1007 The limit is enforced during page fault. Since HugeTLB doesn't 1008 support page reclaim, enforcing the limit at page fault time implies 1009 that, the application will get SIGBUS signal if it tries to access 1010 HugeTLB pages beyond its limit. This requires the application to know 1011 beforehand how much HugeTLB pages it would require for its use. The 1012 control group is tracked in the third page lru pointer. This means 1013 that we cannot use the controller with huge page less than 3 pages. 1014 1015config CPUSETS 1016 bool "Cpuset controller" 1017 depends on SMP 1018 help 1019 This option will let you create and manage CPUSETs which 1020 allow dynamically partitioning a system into sets of CPUs and 1021 Memory Nodes and assigning tasks to run only within those sets. 1022 This is primarily useful on large SMP or NUMA systems. 1023 1024 Say N if unsure. 1025 1026config PROC_PID_CPUSET 1027 bool "Include legacy /proc/<pid>/cpuset file" 1028 depends on CPUSETS 1029 default y 1030 1031config CGROUP_DEVICE 1032 bool "Device controller" 1033 help 1034 Provides a cgroup controller implementing whitelists for 1035 devices which a process in the cgroup can mknod or open. 1036 1037config CGROUP_CPUACCT 1038 bool "Simple CPU accounting controller" 1039 help 1040 Provides a simple controller for monitoring the 1041 total CPU consumed by the tasks in a cgroup. 1042 1043config CGROUP_PERF 1044 bool "Perf controller" 1045 depends on PERF_EVENTS 1046 help 1047 This option extends the perf per-cpu mode to restrict monitoring 1048 to threads which belong to the cgroup specified and run on the 1049 designated cpu. 1050 1051 Say N if unsure. 1052 1053config CGROUP_BPF 1054 bool "Support for eBPF programs attached to cgroups" 1055 depends on BPF_SYSCALL 1056 select SOCK_CGROUP_DATA 1057 help 1058 Allow attaching eBPF programs to a cgroup using the bpf(2) 1059 syscall command BPF_PROG_ATTACH. 1060 1061 In which context these programs are accessed depends on the type 1062 of attachment. For instance, programs that are attached using 1063 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of 1064 inet sockets. 1065 1066config CGROUP_DEBUG 1067 bool "Debug controller" 1068 default n 1069 depends on DEBUG_KERNEL 1070 help 1071 This option enables a simple controller that exports 1072 debugging information about the cgroups framework. This 1073 controller is for control cgroup debugging only. Its 1074 interfaces are not stable. 1075 1076 Say N. 1077 1078config SOCK_CGROUP_DATA 1079 bool 1080 default n 1081 1082endif # CGROUPS 1083 1084menuconfig NAMESPACES 1085 bool "Namespaces support" if EXPERT 1086 depends on MULTIUSER 1087 default !EXPERT 1088 help 1089 Provides the way to make tasks work with different objects using 1090 the same id. For example same IPC id may refer to different objects 1091 or same user id or pid may refer to different tasks when used in 1092 different namespaces. 1093 1094if NAMESPACES 1095 1096config UTS_NS 1097 bool "UTS namespace" 1098 default y 1099 help 1100 In this namespace tasks see different info provided with the 1101 uname() system call 1102 1103config IPC_NS 1104 bool "IPC namespace" 1105 depends on (SYSVIPC || POSIX_MQUEUE) 1106 default y 1107 help 1108 In this namespace tasks work with IPC ids which correspond to 1109 different IPC objects in different namespaces. 1110 1111config USER_NS 1112 bool "User namespace" 1113 default n 1114 help 1115 This allows containers, i.e. vservers, to use user namespaces 1116 to provide different user info for different servers. 1117 1118 When user namespaces are enabled in the kernel it is 1119 recommended that the MEMCG option also be enabled and that 1120 user-space use the memory control groups to limit the amount 1121 of memory a memory unprivileged users can use. 1122 1123 If unsure, say N. 1124 1125config PID_NS 1126 bool "PID Namespaces" 1127 default y 1128 help 1129 Support process id namespaces. This allows having multiple 1130 processes with the same pid as long as they are in different 1131 pid namespaces. This is a building block of containers. 1132 1133config NET_NS 1134 bool "Network namespace" 1135 depends on NET 1136 default y 1137 help 1138 Allow user space to create what appear to be multiple instances 1139 of the network stack. 1140 1141endif # NAMESPACES 1142 1143config CHECKPOINT_RESTORE 1144 bool "Checkpoint/restore support" 1145 select PROC_CHILDREN 1146 default n 1147 help 1148 Enables additional kernel features in a sake of checkpoint/restore. 1149 In particular it adds auxiliary prctl codes to setup process text, 1150 data and heap segment sizes, and a few additional /proc filesystem 1151 entries. 1152 1153 If unsure, say N here. 1154 1155config SCHED_AUTOGROUP 1156 bool "Automatic process group scheduling" 1157 select CGROUPS 1158 select CGROUP_SCHED 1159 select FAIR_GROUP_SCHED 1160 help 1161 This option optimizes the scheduler for common desktop workloads by 1162 automatically creating and populating task groups. This separation 1163 of workloads isolates aggressive CPU burners (like build jobs) from 1164 desktop applications. Task group autogeneration is currently based 1165 upon task session. 1166 1167config SYSFS_DEPRECATED 1168 bool "Enable deprecated sysfs features to support old userspace tools" 1169 depends on SYSFS 1170 default n 1171 help 1172 This option adds code that switches the layout of the "block" class 1173 devices, to not show up in /sys/class/block/, but only in 1174 /sys/block/. 1175 1176 This switch is only active when the sysfs.deprecated=1 boot option is 1177 passed or the SYSFS_DEPRECATED_V2 option is set. 1178 1179 This option allows new kernels to run on old distributions and tools, 1180 which might get confused by /sys/class/block/. Since 2007/2008 all 1181 major distributions and tools handle this just fine. 1182 1183 Recent distributions and userspace tools after 2009/2010 depend on 1184 the existence of /sys/class/block/, and will not work with this 1185 option enabled. 1186 1187 Only if you are using a new kernel on an old distribution, you might 1188 need to say Y here. 1189 1190config SYSFS_DEPRECATED_V2 1191 bool "Enable deprecated sysfs features by default" 1192 default n 1193 depends on SYSFS 1194 depends on SYSFS_DEPRECATED 1195 help 1196 Enable deprecated sysfs by default. 1197 1198 See the CONFIG_SYSFS_DEPRECATED option for more details about this 1199 option. 1200 1201 Only if you are using a new kernel on an old distribution, you might 1202 need to say Y here. Even then, odds are you would not need it 1203 enabled, you can always pass the boot option if absolutely necessary. 1204 1205config RELAY 1206 bool "Kernel->user space relay support (formerly relayfs)" 1207 select IRQ_WORK 1208 help 1209 This option enables support for relay interface support in 1210 certain file systems (such as debugfs). 1211 It is designed to provide an efficient mechanism for tools and 1212 facilities to relay large amounts of data from kernel space to 1213 user space. 1214 1215 If unsure, say N. 1216 1217config BLK_DEV_INITRD 1218 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support" 1219 help 1220 The initial RAM filesystem is a ramfs which is loaded by the 1221 boot loader (loadlin or lilo) and that is mounted as root 1222 before the normal boot procedure. It is typically used to 1223 load modules needed to mount the "real" root file system, 1224 etc. See <file:Documentation/admin-guide/initrd.rst> for details. 1225 1226 If RAM disk support (BLK_DEV_RAM) is also included, this 1227 also enables initial RAM disk (initrd) support and adds 1228 15 Kbytes (more on some other architectures) to the kernel size. 1229 1230 If unsure say Y. 1231 1232if BLK_DEV_INITRD 1233 1234source "usr/Kconfig" 1235 1236endif 1237 1238choice 1239 prompt "Compiler optimization level" 1240 default CC_OPTIMIZE_FOR_PERFORMANCE 1241 1242config CC_OPTIMIZE_FOR_PERFORMANCE 1243 bool "Optimize for performance (-O2)" 1244 help 1245 This is the default optimization level for the kernel, building 1246 with the "-O2" compiler flag for best performance and most 1247 helpful compile-time warnings. 1248 1249config CC_OPTIMIZE_FOR_PERFORMANCE_O3 1250 bool "Optimize more for performance (-O3)" 1251 depends on ARC 1252 imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives 1253 help 1254 Choosing this option will pass "-O3" to your compiler to optimize 1255 the kernel yet more for performance. 1256 1257config CC_OPTIMIZE_FOR_SIZE 1258 bool "Optimize for size (-Os)" 1259 imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives 1260 help 1261 Choosing this option will pass "-Os" to your compiler resulting 1262 in a smaller kernel. 1263 1264endchoice 1265 1266config HAVE_LD_DEAD_CODE_DATA_ELIMINATION 1267 bool 1268 help 1269 This requires that the arch annotates or otherwise protects 1270 its external entry points from being discarded. Linker scripts 1271 must also merge .text.*, .data.*, and .bss.* correctly into 1272 output sections. Care must be taken not to pull in unrelated 1273 sections (e.g., '.text.init'). Typically '.' in section names 1274 is used to distinguish them from label names / C identifiers. 1275 1276config LD_DEAD_CODE_DATA_ELIMINATION 1277 bool "Dead code and data elimination (EXPERIMENTAL)" 1278 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION 1279 depends on EXPERT 1280 depends on !(FUNCTION_TRACER && CC_IS_GCC && GCC_VERSION < 40800) 1281 depends on $(cc-option,-ffunction-sections -fdata-sections) 1282 depends on $(ld-option,--gc-sections) 1283 help 1284 Enable this if you want to do dead code and data elimination with 1285 the linker by compiling with -ffunction-sections -fdata-sections, 1286 and linking with --gc-sections. 1287 1288 This can reduce on disk and in-memory size of the kernel 1289 code and static data, particularly for small configs and 1290 on small systems. This has the possibility of introducing 1291 silently broken kernel if the required annotations are not 1292 present. This option is not well tested yet, so use at your 1293 own risk. 1294 1295config SYSCTL 1296 bool 1297 1298config HAVE_UID16 1299 bool 1300 1301config SYSCTL_EXCEPTION_TRACE 1302 bool 1303 help 1304 Enable support for /proc/sys/debug/exception-trace. 1305 1306config SYSCTL_ARCH_UNALIGN_NO_WARN 1307 bool 1308 help 1309 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap 1310 Allows arch to define/use @no_unaligned_warning to possibly warn 1311 about unaligned access emulation going on under the hood. 1312 1313config SYSCTL_ARCH_UNALIGN_ALLOW 1314 bool 1315 help 1316 Enable support for /proc/sys/kernel/unaligned-trap 1317 Allows arches to define/use @unaligned_enabled to runtime toggle 1318 the unaligned access emulation. 1319 see arch/parisc/kernel/unaligned.c for reference 1320 1321config HAVE_PCSPKR_PLATFORM 1322 bool 1323 1324# interpreter that classic socket filters depend on 1325config BPF 1326 bool 1327 1328menuconfig EXPERT 1329 bool "Configure standard kernel features (expert users)" 1330 # Unhide debug options, to make the on-by-default options visible 1331 select DEBUG_KERNEL 1332 help 1333 This option allows certain base kernel options and settings 1334 to be disabled or tweaked. This is for specialized 1335 environments which can tolerate a "non-standard" kernel. 1336 Only use this if you really know what you are doing. 1337 1338config UID16 1339 bool "Enable 16-bit UID system calls" if EXPERT 1340 depends on HAVE_UID16 && MULTIUSER 1341 default y 1342 help 1343 This enables the legacy 16-bit UID syscall wrappers. 1344 1345config MULTIUSER 1346 bool "Multiple users, groups and capabilities support" if EXPERT 1347 default y 1348 help 1349 This option enables support for non-root users, groups and 1350 capabilities. 1351 1352 If you say N here, all processes will run with UID 0, GID 0, and all 1353 possible capabilities. Saying N here also compiles out support for 1354 system calls related to UIDs, GIDs, and capabilities, such as setuid, 1355 setgid, and capset. 1356 1357 If unsure, say Y here. 1358 1359config SGETMASK_SYSCALL 1360 bool "sgetmask/ssetmask syscalls support" if EXPERT 1361 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH 1362 ---help--- 1363 sys_sgetmask and sys_ssetmask are obsolete system calls 1364 no longer supported in libc but still enabled by default in some 1365 architectures. 1366 1367 If unsure, leave the default option here. 1368 1369config SYSFS_SYSCALL 1370 bool "Sysfs syscall support" if EXPERT 1371 default y 1372 ---help--- 1373 sys_sysfs is an obsolete system call no longer supported in libc. 1374 Note that disabling this option is more secure but might break 1375 compatibility with some systems. 1376 1377 If unsure say Y here. 1378 1379config FHANDLE 1380 bool "open by fhandle syscalls" if EXPERT 1381 select EXPORTFS 1382 default y 1383 help 1384 If you say Y here, a user level program will be able to map 1385 file names to handle and then later use the handle for 1386 different file system operations. This is useful in implementing 1387 userspace file servers, which now track files using handles instead 1388 of names. The handle would remain the same even if file names 1389 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) 1390 syscalls. 1391 1392config POSIX_TIMERS 1393 bool "Posix Clocks & timers" if EXPERT 1394 default y 1395 help 1396 This includes native support for POSIX timers to the kernel. 1397 Some embedded systems have no use for them and therefore they 1398 can be configured out to reduce the size of the kernel image. 1399 1400 When this option is disabled, the following syscalls won't be 1401 available: timer_create, timer_gettime: timer_getoverrun, 1402 timer_settime, timer_delete, clock_adjtime, getitimer, 1403 setitimer, alarm. Furthermore, the clock_settime, clock_gettime, 1404 clock_getres and clock_nanosleep syscalls will be limited to 1405 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only. 1406 1407 If unsure say y. 1408 1409config PRINTK 1410 default y 1411 bool "Enable support for printk" if EXPERT 1412 select IRQ_WORK 1413 help 1414 This option enables normal printk support. Removing it 1415 eliminates most of the message strings from the kernel image 1416 and makes the kernel more or less silent. As this makes it 1417 very difficult to diagnose system problems, saying N here is 1418 strongly discouraged. 1419 1420config PRINTK_NMI 1421 def_bool y 1422 depends on PRINTK 1423 depends on HAVE_NMI 1424 1425config BUG 1426 bool "BUG() support" if EXPERT 1427 default y 1428 help 1429 Disabling this option eliminates support for BUG and WARN, reducing 1430 the size of your kernel image and potentially quietly ignoring 1431 numerous fatal conditions. You should only consider disabling this 1432 option for embedded systems with no facilities for reporting errors. 1433 Just say Y. 1434 1435config ELF_CORE 1436 depends on COREDUMP 1437 default y 1438 bool "Enable ELF core dumps" if EXPERT 1439 help 1440 Enable support for generating core dumps. Disabling saves about 4k. 1441 1442 1443config PCSPKR_PLATFORM 1444 bool "Enable PC-Speaker support" if EXPERT 1445 depends on HAVE_PCSPKR_PLATFORM 1446 select I8253_LOCK 1447 default y 1448 help 1449 This option allows to disable the internal PC-Speaker 1450 support, saving some memory. 1451 1452config BASE_FULL 1453 default y 1454 bool "Enable full-sized data structures for core" if EXPERT 1455 help 1456 Disabling this option reduces the size of miscellaneous core 1457 kernel data structures. This saves memory on small machines, 1458 but may reduce performance. 1459 1460config FUTEX 1461 bool "Enable futex support" if EXPERT 1462 default y 1463 imply RT_MUTEXES 1464 help 1465 Disabling this option will cause the kernel to be built without 1466 support for "fast userspace mutexes". The resulting kernel may not 1467 run glibc-based applications correctly. 1468 1469config FUTEX_PI 1470 bool 1471 depends on FUTEX && RT_MUTEXES 1472 default y 1473 1474config HAVE_FUTEX_CMPXCHG 1475 bool 1476 depends on FUTEX 1477 help 1478 Architectures should select this if futex_atomic_cmpxchg_inatomic() 1479 is implemented and always working. This removes a couple of runtime 1480 checks. 1481 1482config EPOLL 1483 bool "Enable eventpoll support" if EXPERT 1484 default y 1485 help 1486 Disabling this option will cause the kernel to be built without 1487 support for epoll family of system calls. 1488 1489config SIGNALFD 1490 bool "Enable signalfd() system call" if EXPERT 1491 default y 1492 help 1493 Enable the signalfd() system call that allows to receive signals 1494 on a file descriptor. 1495 1496 If unsure, say Y. 1497 1498config TIMERFD 1499 bool "Enable timerfd() system call" if EXPERT 1500 default y 1501 help 1502 Enable the timerfd() system call that allows to receive timer 1503 events on a file descriptor. 1504 1505 If unsure, say Y. 1506 1507config EVENTFD 1508 bool "Enable eventfd() system call" if EXPERT 1509 default y 1510 help 1511 Enable the eventfd() system call that allows to receive both 1512 kernel notification (ie. KAIO) or userspace notifications. 1513 1514 If unsure, say Y. 1515 1516config SHMEM 1517 bool "Use full shmem filesystem" if EXPERT 1518 default y 1519 depends on MMU 1520 help 1521 The shmem is an internal filesystem used to manage shared memory. 1522 It is backed by swap and manages resource limits. It is also exported 1523 to userspace as tmpfs if TMPFS is enabled. Disabling this 1524 option replaces shmem and tmpfs with the much simpler ramfs code, 1525 which may be appropriate on small systems without swap. 1526 1527config AIO 1528 bool "Enable AIO support" if EXPERT 1529 default y 1530 help 1531 This option enables POSIX asynchronous I/O which may by used 1532 by some high performance threaded applications. Disabling 1533 this option saves about 7k. 1534 1535config IO_URING 1536 bool "Enable IO uring support" if EXPERT 1537 select ANON_INODES 1538 select IO_WQ 1539 default y 1540 help 1541 This option enables support for the io_uring interface, enabling 1542 applications to submit and complete IO through submission and 1543 completion rings that are shared between the kernel and application. 1544 1545config ADVISE_SYSCALLS 1546 bool "Enable madvise/fadvise syscalls" if EXPERT 1547 default y 1548 help 1549 This option enables the madvise and fadvise syscalls, used by 1550 applications to advise the kernel about their future memory or file 1551 usage, improving performance. If building an embedded system where no 1552 applications use these syscalls, you can disable this option to save 1553 space. 1554 1555config MEMBARRIER 1556 bool "Enable membarrier() system call" if EXPERT 1557 default y 1558 help 1559 Enable the membarrier() system call that allows issuing memory 1560 barriers across all running threads, which can be used to distribute 1561 the cost of user-space memory barriers asymmetrically by transforming 1562 pairs of memory barriers into pairs consisting of membarrier() and a 1563 compiler barrier. 1564 1565 If unsure, say Y. 1566 1567config KALLSYMS 1568 bool "Load all symbols for debugging/ksymoops" if EXPERT 1569 default y 1570 help 1571 Say Y here to let the kernel print out symbolic crash information and 1572 symbolic stack backtraces. This increases the size of the kernel 1573 somewhat, as all symbols have to be loaded into the kernel image. 1574 1575config KALLSYMS_ALL 1576 bool "Include all symbols in kallsyms" 1577 depends on DEBUG_KERNEL && KALLSYMS 1578 help 1579 Normally kallsyms only contains the symbols of functions for nicer 1580 OOPS messages and backtraces (i.e., symbols from the text and inittext 1581 sections). This is sufficient for most cases. And only in very rare 1582 cases (e.g., when a debugger is used) all symbols are required (e.g., 1583 names of variables from the data sections, etc). 1584 1585 This option makes sure that all symbols are loaded into the kernel 1586 image (i.e., symbols from all sections) in cost of increased kernel 1587 size (depending on the kernel configuration, it may be 300KiB or 1588 something like this). 1589 1590 Say N unless you really need all symbols. 1591 1592config KALLSYMS_ABSOLUTE_PERCPU 1593 bool 1594 depends on KALLSYMS 1595 default X86_64 && SMP 1596 1597config KALLSYMS_BASE_RELATIVE 1598 bool 1599 depends on KALLSYMS 1600 default !IA64 1601 help 1602 Instead of emitting them as absolute values in the native word size, 1603 emit the symbol references in the kallsyms table as 32-bit entries, 1604 each containing a relative value in the range [base, base + U32_MAX] 1605 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either 1606 an absolute value in the range [0, S32_MAX] or a relative value in the 1607 range [base, base + S32_MAX], where base is the lowest relative symbol 1608 address encountered in the image. 1609 1610 On 64-bit builds, this reduces the size of the address table by 50%, 1611 but more importantly, it results in entries whose values are build 1612 time constants, and no relocation pass is required at runtime to fix 1613 up the entries based on the runtime load address of the kernel. 1614 1615# end of the "standard kernel features (expert users)" menu 1616 1617# syscall, maps, verifier 1618config BPF_SYSCALL 1619 bool "Enable bpf() system call" 1620 select BPF 1621 select IRQ_WORK 1622 default n 1623 help 1624 Enable the bpf() system call that allows to manipulate eBPF 1625 programs and maps via file descriptors. 1626 1627config BPF_JIT_ALWAYS_ON 1628 bool "Permanently enable BPF JIT and remove BPF interpreter" 1629 depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT 1630 help 1631 Enables BPF JIT and removes BPF interpreter to avoid 1632 speculative execution of BPF instructions by the interpreter 1633 1634config USERFAULTFD 1635 bool "Enable userfaultfd() system call" 1636 depends on MMU 1637 help 1638 Enable the userfaultfd() system call that allows to intercept and 1639 handle page faults in userland. 1640 1641config ARCH_HAS_MEMBARRIER_CALLBACKS 1642 bool 1643 1644config ARCH_HAS_MEMBARRIER_SYNC_CORE 1645 bool 1646 1647config RSEQ 1648 bool "Enable rseq() system call" if EXPERT 1649 default y 1650 depends on HAVE_RSEQ 1651 select MEMBARRIER 1652 help 1653 Enable the restartable sequences system call. It provides a 1654 user-space cache for the current CPU number value, which 1655 speeds up getting the current CPU number from user-space, 1656 as well as an ABI to speed up user-space operations on 1657 per-CPU data. 1658 1659 If unsure, say Y. 1660 1661config DEBUG_RSEQ 1662 default n 1663 bool "Enabled debugging of rseq() system call" if EXPERT 1664 depends on RSEQ && DEBUG_KERNEL 1665 help 1666 Enable extra debugging checks for the rseq system call. 1667 1668 If unsure, say N. 1669 1670config EMBEDDED 1671 bool "Embedded system" 1672 option allnoconfig_y 1673 select EXPERT 1674 help 1675 This option should be enabled if compiling the kernel for 1676 an embedded system so certain expert options are available 1677 for configuration. 1678 1679config HAVE_PERF_EVENTS 1680 bool 1681 help 1682 See tools/perf/design.txt for details. 1683 1684config PERF_USE_VMALLOC 1685 bool 1686 help 1687 See tools/perf/design.txt for details 1688 1689config PC104 1690 bool "PC/104 support" if EXPERT 1691 help 1692 Expose PC/104 form factor device drivers and options available for 1693 selection and configuration. Enable this option if your target 1694 machine has a PC/104 bus. 1695 1696menu "Kernel Performance Events And Counters" 1697 1698config PERF_EVENTS 1699 bool "Kernel performance events and counters" 1700 default y if PROFILING 1701 depends on HAVE_PERF_EVENTS 1702 select IRQ_WORK 1703 select SRCU 1704 help 1705 Enable kernel support for various performance events provided 1706 by software and hardware. 1707 1708 Software events are supported either built-in or via the 1709 use of generic tracepoints. 1710 1711 Most modern CPUs support performance events via performance 1712 counter registers. These registers count the number of certain 1713 types of hw events: such as instructions executed, cachemisses 1714 suffered, or branches mis-predicted - without slowing down the 1715 kernel or applications. These registers can also trigger interrupts 1716 when a threshold number of events have passed - and can thus be 1717 used to profile the code that runs on that CPU. 1718 1719 The Linux Performance Event subsystem provides an abstraction of 1720 these software and hardware event capabilities, available via a 1721 system call and used by the "perf" utility in tools/perf/. It 1722 provides per task and per CPU counters, and it provides event 1723 capabilities on top of those. 1724 1725 Say Y if unsure. 1726 1727config DEBUG_PERF_USE_VMALLOC 1728 default n 1729 bool "Debug: use vmalloc to back perf mmap() buffers" 1730 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC 1731 select PERF_USE_VMALLOC 1732 help 1733 Use vmalloc memory to back perf mmap() buffers. 1734 1735 Mostly useful for debugging the vmalloc code on platforms 1736 that don't require it. 1737 1738 Say N if unsure. 1739 1740endmenu 1741 1742config VM_EVENT_COUNTERS 1743 default y 1744 bool "Enable VM event counters for /proc/vmstat" if EXPERT 1745 help 1746 VM event counters are needed for event counts to be shown. 1747 This option allows the disabling of the VM event counters 1748 on EXPERT systems. /proc/vmstat will only show page counts 1749 if VM event counters are disabled. 1750 1751config SLUB_DEBUG 1752 default y 1753 bool "Enable SLUB debugging support" if EXPERT 1754 depends on SLUB && SYSFS 1755 help 1756 SLUB has extensive debug support features. Disabling these can 1757 result in significant savings in code size. This also disables 1758 SLUB sysfs support. /sys/slab will not exist and there will be 1759 no support for cache validation etc. 1760 1761config SLUB_MEMCG_SYSFS_ON 1762 default n 1763 bool "Enable memcg SLUB sysfs support by default" if EXPERT 1764 depends on SLUB && SYSFS && MEMCG 1765 help 1766 SLUB creates a directory under /sys/kernel/slab for each 1767 allocation cache to host info and debug files. If memory 1768 cgroup is enabled, each cache can have per memory cgroup 1769 caches. SLUB can create the same sysfs directories for these 1770 caches under /sys/kernel/slab/CACHE/cgroup but it can lead 1771 to a very high number of debug files being created. This is 1772 controlled by slub_memcg_sysfs boot parameter and this 1773 config option determines the parameter's default value. 1774 1775config COMPAT_BRK 1776 bool "Disable heap randomization" 1777 default y 1778 help 1779 Randomizing heap placement makes heap exploits harder, but it 1780 also breaks ancient binaries (including anything libc5 based). 1781 This option changes the bootup default to heap randomization 1782 disabled, and can be overridden at runtime by setting 1783 /proc/sys/kernel/randomize_va_space to 2. 1784 1785 On non-ancient distros (post-2000 ones) N is usually a safe choice. 1786 1787choice 1788 prompt "Choose SLAB allocator" 1789 default SLUB 1790 help 1791 This option allows to select a slab allocator. 1792 1793config SLAB 1794 bool "SLAB" 1795 select HAVE_HARDENED_USERCOPY_ALLOCATOR 1796 help 1797 The regular slab allocator that is established and known to work 1798 well in all environments. It organizes cache hot objects in 1799 per cpu and per node queues. 1800 1801config SLUB 1802 bool "SLUB (Unqueued Allocator)" 1803 select HAVE_HARDENED_USERCOPY_ALLOCATOR 1804 help 1805 SLUB is a slab allocator that minimizes cache line usage 1806 instead of managing queues of cached objects (SLAB approach). 1807 Per cpu caching is realized using slabs of objects instead 1808 of queues of objects. SLUB can use memory efficiently 1809 and has enhanced diagnostics. SLUB is the default choice for 1810 a slab allocator. 1811 1812config SLOB 1813 depends on EXPERT 1814 bool "SLOB (Simple Allocator)" 1815 help 1816 SLOB replaces the stock allocator with a drastically simpler 1817 allocator. SLOB is generally more space efficient but 1818 does not perform as well on large systems. 1819 1820endchoice 1821 1822config SLAB_MERGE_DEFAULT 1823 bool "Allow slab caches to be merged" 1824 default y 1825 help 1826 For reduced kernel memory fragmentation, slab caches can be 1827 merged when they share the same size and other characteristics. 1828 This carries a risk of kernel heap overflows being able to 1829 overwrite objects from merged caches (and more easily control 1830 cache layout), which makes such heap attacks easier to exploit 1831 by attackers. By keeping caches unmerged, these kinds of exploits 1832 can usually only damage objects in the same cache. To disable 1833 merging at runtime, "slab_nomerge" can be passed on the kernel 1834 command line. 1835 1836config SLAB_FREELIST_RANDOM 1837 default n 1838 depends on SLAB || SLUB 1839 bool "SLAB freelist randomization" 1840 help 1841 Randomizes the freelist order used on creating new pages. This 1842 security feature reduces the predictability of the kernel slab 1843 allocator against heap overflows. 1844 1845config SLAB_FREELIST_HARDENED 1846 bool "Harden slab freelist metadata" 1847 depends on SLUB 1848 help 1849 Many kernel heap attacks try to target slab cache metadata and 1850 other infrastructure. This options makes minor performance 1851 sacrifices to harden the kernel slab allocator against common 1852 freelist exploit methods. 1853 1854config SHUFFLE_PAGE_ALLOCATOR 1855 bool "Page allocator randomization" 1856 default SLAB_FREELIST_RANDOM && ACPI_NUMA 1857 help 1858 Randomization of the page allocator improves the average 1859 utilization of a direct-mapped memory-side-cache. See section 1860 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI 1861 6.2a specification for an example of how a platform advertises 1862 the presence of a memory-side-cache. There are also incidental 1863 security benefits as it reduces the predictability of page 1864 allocations to compliment SLAB_FREELIST_RANDOM, but the 1865 default granularity of shuffling on the "MAX_ORDER - 1" i.e, 1866 10th order of pages is selected based on cache utilization 1867 benefits on x86. 1868 1869 While the randomization improves cache utilization it may 1870 negatively impact workloads on platforms without a cache. For 1871 this reason, by default, the randomization is enabled only 1872 after runtime detection of a direct-mapped memory-side-cache. 1873 Otherwise, the randomization may be force enabled with the 1874 'page_alloc.shuffle' kernel command line parameter. 1875 1876 Say Y if unsure. 1877 1878config SLUB_CPU_PARTIAL 1879 default y 1880 depends on SLUB && SMP 1881 bool "SLUB per cpu partial cache" 1882 help 1883 Per cpu partial caches accelerate objects allocation and freeing 1884 that is local to a processor at the price of more indeterminism 1885 in the latency of the free. On overflow these caches will be cleared 1886 which requires the taking of locks that may cause latency spikes. 1887 Typically one would choose no for a realtime system. 1888 1889config MMAP_ALLOW_UNINITIALIZED 1890 bool "Allow mmapped anonymous memory to be uninitialized" 1891 depends on EXPERT && !MMU 1892 default n 1893 help 1894 Normally, and according to the Linux spec, anonymous memory obtained 1895 from mmap() has its contents cleared before it is passed to 1896 userspace. Enabling this config option allows you to request that 1897 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus 1898 providing a huge performance boost. If this option is not enabled, 1899 then the flag will be ignored. 1900 1901 This is taken advantage of by uClibc's malloc(), and also by 1902 ELF-FDPIC binfmt's brk and stack allocator. 1903 1904 Because of the obvious security issues, this option should only be 1905 enabled on embedded devices where you control what is run in 1906 userspace. Since that isn't generally a problem on no-MMU systems, 1907 it is normally safe to say Y here. 1908 1909 See Documentation/nommu-mmap.txt for more information. 1910 1911config SYSTEM_DATA_VERIFICATION 1912 def_bool n 1913 select SYSTEM_TRUSTED_KEYRING 1914 select KEYS 1915 select CRYPTO 1916 select CRYPTO_RSA 1917 select ASYMMETRIC_KEY_TYPE 1918 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE 1919 select ASN1 1920 select OID_REGISTRY 1921 select X509_CERTIFICATE_PARSER 1922 select PKCS7_MESSAGE_PARSER 1923 help 1924 Provide PKCS#7 message verification using the contents of the system 1925 trusted keyring to provide public keys. This then can be used for 1926 module verification, kexec image verification and firmware blob 1927 verification. 1928 1929config PROFILING 1930 bool "Profiling support" 1931 help 1932 Say Y here to enable the extended profiling support mechanisms used 1933 by profilers such as OProfile. 1934 1935# 1936# Place an empty function call at each tracepoint site. Can be 1937# dynamically changed for a probe function. 1938# 1939config TRACEPOINTS 1940 bool 1941 1942endmenu # General setup 1943 1944source "arch/Kconfig" 1945 1946config RT_MUTEXES 1947 bool 1948 1949config BASE_SMALL 1950 int 1951 default 0 if BASE_FULL 1952 default 1 if !BASE_FULL 1953 1954config MODULE_SIG_FORMAT 1955 def_bool n 1956 select SYSTEM_DATA_VERIFICATION 1957 1958menuconfig MODULES 1959 bool "Enable loadable module support" 1960 option modules 1961 help 1962 Kernel modules are small pieces of compiled code which can 1963 be inserted in the running kernel, rather than being 1964 permanently built into the kernel. You use the "modprobe" 1965 tool to add (and sometimes remove) them. If you say Y here, 1966 many parts of the kernel can be built as modules (by 1967 answering M instead of Y where indicated): this is most 1968 useful for infrequently used options which are not required 1969 for booting. For more information, see the man pages for 1970 modprobe, lsmod, modinfo, insmod and rmmod. 1971 1972 If you say Y here, you will need to run "make 1973 modules_install" to put the modules under /lib/modules/ 1974 where modprobe can find them (you may need to be root to do 1975 this). 1976 1977 If unsure, say Y. 1978 1979if MODULES 1980 1981config MODULE_FORCE_LOAD 1982 bool "Forced module loading" 1983 default n 1984 help 1985 Allow loading of modules without version information (ie. modprobe 1986 --force). Forced module loading sets the 'F' (forced) taint flag and 1987 is usually a really bad idea. 1988 1989config MODULE_UNLOAD 1990 bool "Module unloading" 1991 help 1992 Without this option you will not be able to unload any 1993 modules (note that some modules may not be unloadable 1994 anyway), which makes your kernel smaller, faster 1995 and simpler. If unsure, say Y. 1996 1997config MODULE_FORCE_UNLOAD 1998 bool "Forced module unloading" 1999 depends on MODULE_UNLOAD 2000 help 2001 This option allows you to force a module to unload, even if the 2002 kernel believes it is unsafe: the kernel will remove the module 2003 without waiting for anyone to stop using it (using the -f option to 2004 rmmod). This is mainly for kernel developers and desperate users. 2005 If unsure, say N. 2006 2007config MODVERSIONS 2008 bool "Module versioning support" 2009 help 2010 Usually, you have to use modules compiled with your kernel. 2011 Saying Y here makes it sometimes possible to use modules 2012 compiled for different kernels, by adding enough information 2013 to the modules to (hopefully) spot any changes which would 2014 make them incompatible with the kernel you are running. If 2015 unsure, say N. 2016 2017config ASM_MODVERSIONS 2018 bool 2019 default HAVE_ASM_MODVERSIONS && MODVERSIONS 2020 help 2021 This enables module versioning for exported symbols also from 2022 assembly. This can be enabled only when the target architecture 2023 supports it. 2024 2025config MODULE_REL_CRCS 2026 bool 2027 depends on MODVERSIONS 2028 2029config MODULE_SRCVERSION_ALL 2030 bool "Source checksum for all modules" 2031 help 2032 Modules which contain a MODULE_VERSION get an extra "srcversion" 2033 field inserted into their modinfo section, which contains a 2034 sum of the source files which made it. This helps maintainers 2035 see exactly which source was used to build a module (since 2036 others sometimes change the module source without updating 2037 the version). With this option, such a "srcversion" field 2038 will be created for all modules. If unsure, say N. 2039 2040config MODULE_SIG 2041 bool "Module signature verification" 2042 select MODULE_SIG_FORMAT 2043 help 2044 Check modules for valid signatures upon load: the signature 2045 is simply appended to the module. For more information see 2046 <file:Documentation/admin-guide/module-signing.rst>. 2047 2048 Note that this option adds the OpenSSL development packages as a 2049 kernel build dependency so that the signing tool can use its crypto 2050 library. 2051 2052 You should enable this option if you wish to use either 2053 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via 2054 another LSM - otherwise unsigned modules will be loadable regardless 2055 of the lockdown policy. 2056 2057 !!!WARNING!!! If you enable this option, you MUST make sure that the 2058 module DOES NOT get stripped after being signed. This includes the 2059 debuginfo strip done by some packagers (such as rpmbuild) and 2060 inclusion into an initramfs that wants the module size reduced. 2061 2062config MODULE_SIG_FORCE 2063 bool "Require modules to be validly signed" 2064 depends on MODULE_SIG 2065 help 2066 Reject unsigned modules or signed modules for which we don't have a 2067 key. Without this, such modules will simply taint the kernel. 2068 2069config MODULE_SIG_ALL 2070 bool "Automatically sign all modules" 2071 default y 2072 depends on MODULE_SIG 2073 help 2074 Sign all modules during make modules_install. Without this option, 2075 modules must be signed manually, using the scripts/sign-file tool. 2076 2077comment "Do not forget to sign required modules with scripts/sign-file" 2078 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL 2079 2080choice 2081 prompt "Which hash algorithm should modules be signed with?" 2082 depends on MODULE_SIG 2083 help 2084 This determines which sort of hashing algorithm will be used during 2085 signature generation. This algorithm _must_ be built into the kernel 2086 directly so that signature verification can take place. It is not 2087 possible to load a signed module containing the algorithm to check 2088 the signature on that module. 2089 2090config MODULE_SIG_SHA1 2091 bool "Sign modules with SHA-1" 2092 select CRYPTO_SHA1 2093 2094config MODULE_SIG_SHA224 2095 bool "Sign modules with SHA-224" 2096 select CRYPTO_SHA256 2097 2098config MODULE_SIG_SHA256 2099 bool "Sign modules with SHA-256" 2100 select CRYPTO_SHA256 2101 2102config MODULE_SIG_SHA384 2103 bool "Sign modules with SHA-384" 2104 select CRYPTO_SHA512 2105 2106config MODULE_SIG_SHA512 2107 bool "Sign modules with SHA-512" 2108 select CRYPTO_SHA512 2109 2110endchoice 2111 2112config MODULE_SIG_HASH 2113 string 2114 depends on MODULE_SIG 2115 default "sha1" if MODULE_SIG_SHA1 2116 default "sha224" if MODULE_SIG_SHA224 2117 default "sha256" if MODULE_SIG_SHA256 2118 default "sha384" if MODULE_SIG_SHA384 2119 default "sha512" if MODULE_SIG_SHA512 2120 2121config MODULE_COMPRESS 2122 bool "Compress modules on installation" 2123 help 2124 2125 Compresses kernel modules when 'make modules_install' is run; gzip or 2126 xz depending on "Compression algorithm" below. 2127 2128 module-init-tools MAY support gzip, and kmod MAY support gzip and xz. 2129 2130 Out-of-tree kernel modules installed using Kbuild will also be 2131 compressed upon installation. 2132 2133 Note: for modules inside an initrd or initramfs, it's more efficient 2134 to compress the whole initrd or initramfs instead. 2135 2136 Note: This is fully compatible with signed modules. 2137 2138 If in doubt, say N. 2139 2140choice 2141 prompt "Compression algorithm" 2142 depends on MODULE_COMPRESS 2143 default MODULE_COMPRESS_GZIP 2144 help 2145 This determines which sort of compression will be used during 2146 'make modules_install'. 2147 2148 GZIP (default) and XZ are supported. 2149 2150config MODULE_COMPRESS_GZIP 2151 bool "GZIP" 2152 2153config MODULE_COMPRESS_XZ 2154 bool "XZ" 2155 2156endchoice 2157 2158config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS 2159 bool "Allow loading of modules with missing namespace imports" 2160 help 2161 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in 2162 a namespace. A module that makes use of a symbol exported with such a 2163 namespace is required to import the namespace via MODULE_IMPORT_NS(). 2164 There is no technical reason to enforce correct namespace imports, 2165 but it creates consistency between symbols defining namespaces and 2166 users importing namespaces they make use of. This option relaxes this 2167 requirement and lifts the enforcement when loading a module. 2168 2169 If unsure, say N. 2170 2171config UNUSED_SYMBOLS 2172 bool "Enable unused/obsolete exported symbols" 2173 default y if X86 2174 help 2175 Unused but exported symbols make the kernel needlessly bigger. For 2176 that reason most of these unused exports will soon be removed. This 2177 option is provided temporarily to provide a transition period in case 2178 some external kernel module needs one of these symbols anyway. If you 2179 encounter such a case in your module, consider if you are actually 2180 using the right API. (rationale: since nobody in the kernel is using 2181 this in a module, there is a pretty good chance it's actually the 2182 wrong interface to use). If you really need the symbol, please send a 2183 mail to the linux kernel mailing list mentioning the symbol and why 2184 you really need it, and what the merge plan to the mainline kernel for 2185 your module is. 2186 2187config TRIM_UNUSED_KSYMS 2188 bool "Trim unused exported kernel symbols" 2189 depends on !UNUSED_SYMBOLS 2190 help 2191 The kernel and some modules make many symbols available for 2192 other modules to use via EXPORT_SYMBOL() and variants. Depending 2193 on the set of modules being selected in your kernel configuration, 2194 many of those exported symbols might never be used. 2195 2196 This option allows for unused exported symbols to be dropped from 2197 the build. In turn, this provides the compiler more opportunities 2198 (especially when using LTO) for optimizing the code and reducing 2199 binary size. This might have some security advantages as well. 2200 2201 If unsure, or if you need to build out-of-tree modules, say N. 2202 2203endif # MODULES 2204 2205config MODULES_TREE_LOOKUP 2206 def_bool y 2207 depends on PERF_EVENTS || TRACING 2208 2209config INIT_ALL_POSSIBLE 2210 bool 2211 help 2212 Back when each arch used to define their own cpu_online_mask and 2213 cpu_possible_mask, some of them chose to initialize cpu_possible_mask 2214 with all 1s, and others with all 0s. When they were centralised, 2215 it was better to provide this option than to break all the archs 2216 and have several arch maintainers pursuing me down dark alleys. 2217 2218source "block/Kconfig" 2219 2220config PREEMPT_NOTIFIERS 2221 bool 2222 2223config PADATA 2224 depends on SMP 2225 bool 2226 2227config ASN1 2228 tristate 2229 help 2230 Build a simple ASN.1 grammar compiler that produces a bytecode output 2231 that can be interpreted by the ASN.1 stream decoder and used to 2232 inform it as to what tags are to be expected in a stream and what 2233 functions to call on what tags. 2234 2235source "kernel/Kconfig.locks" 2236 2237config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE 2238 bool 2239 2240# It may be useful for an architecture to override the definitions of the 2241# SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h> 2242# and the COMPAT_ variants in <linux/compat.h>, in particular to use a 2243# different calling convention for syscalls. They can also override the 2244# macros for not-implemented syscalls in kernel/sys_ni.c and 2245# kernel/time/posix-stubs.c. All these overrides need to be available in 2246# <asm/syscall_wrapper.h>. 2247config ARCH_HAS_SYSCALL_WRAPPER 2248 def_bool n 2249