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