1menu "printk and dmesg options" 2 3config PRINTK_TIME 4 bool "Show timing information on printks" 5 depends on PRINTK 6 help 7 Selecting this option causes time stamps of the printk() 8 messages to be added to the output of the syslog() system 9 call and at the console. 10 11 The timestamp is always recorded internally, and exported 12 to /dev/kmsg. This flag just specifies if the timestamp should 13 be included, not that the timestamp is recorded. 14 15 The behavior is also controlled by the kernel command line 16 parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst 17 18config CONSOLE_LOGLEVEL_DEFAULT 19 int "Default console loglevel (1-15)" 20 range 1 15 21 default "7" 22 help 23 Default loglevel to determine what will be printed on the console. 24 25 Setting a default here is equivalent to passing in loglevel=<x> in 26 the kernel bootargs. loglevel=<x> continues to override whatever 27 value is specified here as well. 28 29 Note: This does not affect the log level of un-prefixed printk() 30 usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT 31 option. 32 33config MESSAGE_LOGLEVEL_DEFAULT 34 int "Default message log level (1-7)" 35 range 1 7 36 default "4" 37 help 38 Default log level for printk statements with no specified priority. 39 40 This was hard-coded to KERN_WARNING since at least 2.6.10 but folks 41 that are auditing their logs closely may want to set it to a lower 42 priority. 43 44 Note: This does not affect what message level gets printed on the console 45 by default. To change that, use loglevel=<x> in the kernel bootargs, 46 or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value. 47 48config BOOT_PRINTK_DELAY 49 bool "Delay each boot printk message by N milliseconds" 50 depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY 51 help 52 This build option allows you to read kernel boot messages 53 by inserting a short delay after each one. The delay is 54 specified in milliseconds on the kernel command line, 55 using "boot_delay=N". 56 57 It is likely that you would also need to use "lpj=M" to preset 58 the "loops per jiffie" value. 59 See a previous boot log for the "lpj" value to use for your 60 system, and then set "lpj=M" before setting "boot_delay=N". 61 NOTE: Using this option may adversely affect SMP systems. 62 I.e., processors other than the first one may not boot up. 63 BOOT_PRINTK_DELAY also may cause LOCKUP_DETECTOR to detect 64 what it believes to be lockup conditions. 65 66config DYNAMIC_DEBUG 67 bool "Enable dynamic printk() support" 68 default n 69 depends on PRINTK 70 depends on DEBUG_FS 71 help 72 73 Compiles debug level messages into the kernel, which would not 74 otherwise be available at runtime. These messages can then be 75 enabled/disabled based on various levels of scope - per source file, 76 function, module, format string, and line number. This mechanism 77 implicitly compiles in all pr_debug() and dev_dbg() calls, which 78 enlarges the kernel text size by about 2%. 79 80 If a source file is compiled with DEBUG flag set, any 81 pr_debug() calls in it are enabled by default, but can be 82 disabled at runtime as below. Note that DEBUG flag is 83 turned on by many CONFIG_*DEBUG* options. 84 85 Usage: 86 87 Dynamic debugging is controlled via the 'dynamic_debug/control' file, 88 which is contained in the 'debugfs' filesystem. Thus, the debugfs 89 filesystem must first be mounted before making use of this feature. 90 We refer the control file as: <debugfs>/dynamic_debug/control. This 91 file contains a list of the debug statements that can be enabled. The 92 format for each line of the file is: 93 94 filename:lineno [module]function flags format 95 96 filename : source file of the debug statement 97 lineno : line number of the debug statement 98 module : module that contains the debug statement 99 function : function that contains the debug statement 100 flags : '=p' means the line is turned 'on' for printing 101 format : the format used for the debug statement 102 103 From a live system: 104 105 nullarbor:~ # cat <debugfs>/dynamic_debug/control 106 # filename:lineno [module]function flags format 107 fs/aio.c:222 [aio]__put_ioctx =_ "__put_ioctx:\040freeing\040%p\012" 108 fs/aio.c:248 [aio]ioctx_alloc =_ "ENOMEM:\040nr_events\040too\040high\012" 109 fs/aio.c:1770 [aio]sys_io_cancel =_ "calling\040cancel\012" 110 111 Example usage: 112 113 // enable the message at line 1603 of file svcsock.c 114 nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' > 115 <debugfs>/dynamic_debug/control 116 117 // enable all the messages in file svcsock.c 118 nullarbor:~ # echo -n 'file svcsock.c +p' > 119 <debugfs>/dynamic_debug/control 120 121 // enable all the messages in the NFS server module 122 nullarbor:~ # echo -n 'module nfsd +p' > 123 <debugfs>/dynamic_debug/control 124 125 // enable all 12 messages in the function svc_process() 126 nullarbor:~ # echo -n 'func svc_process +p' > 127 <debugfs>/dynamic_debug/control 128 129 // disable all 12 messages in the function svc_process() 130 nullarbor:~ # echo -n 'func svc_process -p' > 131 <debugfs>/dynamic_debug/control 132 133 See Documentation/admin-guide/dynamic-debug-howto.rst for additional 134 information. 135 136endmenu # "printk and dmesg options" 137 138menu "Compile-time checks and compiler options" 139 140config DEBUG_INFO 141 bool "Compile the kernel with debug info" 142 depends on DEBUG_KERNEL && !COMPILE_TEST 143 help 144 If you say Y here the resulting kernel image will include 145 debugging info resulting in a larger kernel image. 146 This adds debug symbols to the kernel and modules (gcc -g), and 147 is needed if you intend to use kernel crashdump or binary object 148 tools like crash, kgdb, LKCD, gdb, etc on the kernel. 149 Say Y here only if you plan to debug the kernel. 150 151 If unsure, say N. 152 153config DEBUG_INFO_REDUCED 154 bool "Reduce debugging information" 155 depends on DEBUG_INFO 156 help 157 If you say Y here gcc is instructed to generate less debugging 158 information for structure types. This means that tools that 159 need full debugging information (like kgdb or systemtap) won't 160 be happy. But if you merely need debugging information to 161 resolve line numbers there is no loss. Advantage is that 162 build directory object sizes shrink dramatically over a full 163 DEBUG_INFO build and compile times are reduced too. 164 Only works with newer gcc versions. 165 166config DEBUG_INFO_SPLIT 167 bool "Produce split debuginfo in .dwo files" 168 depends on DEBUG_INFO && !FRV 169 help 170 Generate debug info into separate .dwo files. This significantly 171 reduces the build directory size for builds with DEBUG_INFO, 172 because it stores the information only once on disk in .dwo 173 files instead of multiple times in object files and executables. 174 In addition the debug information is also compressed. 175 176 Requires recent gcc (4.7+) and recent gdb/binutils. 177 Any tool that packages or reads debug information would need 178 to know about the .dwo files and include them. 179 Incompatible with older versions of ccache. 180 181config DEBUG_INFO_DWARF4 182 bool "Generate dwarf4 debuginfo" 183 depends on DEBUG_INFO 184 help 185 Generate dwarf4 debug info. This requires recent versions 186 of gcc and gdb. It makes the debug information larger. 187 But it significantly improves the success of resolving 188 variables in gdb on optimized code. 189 190config GDB_SCRIPTS 191 bool "Provide GDB scripts for kernel debugging" 192 depends on DEBUG_INFO 193 help 194 This creates the required links to GDB helper scripts in the 195 build directory. If you load vmlinux into gdb, the helper 196 scripts will be automatically imported by gdb as well, and 197 additional functions are available to analyze a Linux kernel 198 instance. See Documentation/dev-tools/gdb-kernel-debugging.rst 199 for further details. 200 201config ENABLE_WARN_DEPRECATED 202 bool "Enable __deprecated logic" 203 default y 204 help 205 Enable the __deprecated logic in the kernel build. 206 Disable this to suppress the "warning: 'foo' is deprecated 207 (declared at kernel/power/somefile.c:1234)" messages. 208 209config ENABLE_MUST_CHECK 210 bool "Enable __must_check logic" 211 default y 212 help 213 Enable the __must_check logic in the kernel build. Disable this to 214 suppress the "warning: ignoring return value of 'foo', declared with 215 attribute warn_unused_result" messages. 216 217config FRAME_WARN 218 int "Warn for stack frames larger than (needs gcc 4.4)" 219 range 0 8192 220 default 0 if KASAN 221 default 2048 if GCC_PLUGIN_LATENT_ENTROPY 222 default 1024 if !64BIT 223 default 2048 if 64BIT 224 help 225 Tell gcc to warn at build time for stack frames larger than this. 226 Setting this too low will cause a lot of warnings. 227 Setting it to 0 disables the warning. 228 Requires gcc 4.4 229 230config STRIP_ASM_SYMS 231 bool "Strip assembler-generated symbols during link" 232 default n 233 help 234 Strip internal assembler-generated symbols during a link (symbols 235 that look like '.Lxxx') so they don't pollute the output of 236 get_wchan() and suchlike. 237 238config READABLE_ASM 239 bool "Generate readable assembler code" 240 depends on DEBUG_KERNEL 241 help 242 Disable some compiler optimizations that tend to generate human unreadable 243 assembler output. This may make the kernel slightly slower, but it helps 244 to keep kernel developers who have to stare a lot at assembler listings 245 sane. 246 247config UNUSED_SYMBOLS 248 bool "Enable unused/obsolete exported symbols" 249 default y if X86 250 help 251 Unused but exported symbols make the kernel needlessly bigger. For 252 that reason most of these unused exports will soon be removed. This 253 option is provided temporarily to provide a transition period in case 254 some external kernel module needs one of these symbols anyway. If you 255 encounter such a case in your module, consider if you are actually 256 using the right API. (rationale: since nobody in the kernel is using 257 this in a module, there is a pretty good chance it's actually the 258 wrong interface to use). If you really need the symbol, please send a 259 mail to the linux kernel mailing list mentioning the symbol and why 260 you really need it, and what the merge plan to the mainline kernel for 261 your module is. 262 263config PAGE_OWNER 264 bool "Track page owner" 265 depends on DEBUG_KERNEL && STACKTRACE_SUPPORT 266 select DEBUG_FS 267 select STACKTRACE 268 select STACKDEPOT 269 select PAGE_EXTENSION 270 help 271 This keeps track of what call chain is the owner of a page, may 272 help to find bare alloc_page(s) leaks. Even if you include this 273 feature on your build, it is disabled in default. You should pass 274 "page_owner=on" to boot parameter in order to enable it. Eats 275 a fair amount of memory if enabled. See tools/vm/page_owner_sort.c 276 for user-space helper. 277 278 If unsure, say N. 279 280config DEBUG_FS 281 bool "Debug Filesystem" 282 select SRCU 283 help 284 debugfs is a virtual file system that kernel developers use to put 285 debugging files into. Enable this option to be able to read and 286 write to these files. 287 288 For detailed documentation on the debugfs API, see 289 Documentation/filesystems/. 290 291 If unsure, say N. 292 293config HEADERS_CHECK 294 bool "Run 'make headers_check' when building vmlinux" 295 depends on !UML 296 help 297 This option will extract the user-visible kernel headers whenever 298 building the kernel, and will run basic sanity checks on them to 299 ensure that exported files do not attempt to include files which 300 were not exported, etc. 301 302 If you're making modifications to header files which are 303 relevant for userspace, say 'Y', and check the headers 304 exported to $(INSTALL_HDR_PATH) (usually 'usr/include' in 305 your build tree), to make sure they're suitable. 306 307config DEBUG_SECTION_MISMATCH 308 bool "Enable full Section mismatch analysis" 309 help 310 The section mismatch analysis checks if there are illegal 311 references from one section to another section. 312 During linktime or runtime, some sections are dropped; 313 any use of code/data previously in these sections would 314 most likely result in an oops. 315 In the code, functions and variables are annotated with 316 __init,, etc. (see the full list in include/linux/init.h), 317 which results in the code/data being placed in specific sections. 318 The section mismatch analysis is always performed after a full 319 kernel build, and enabling this option causes the following 320 additional steps to occur: 321 - Add the option -fno-inline-functions-called-once to gcc commands. 322 When inlining a function annotated with __init in a non-init 323 function, we would lose the section information and thus 324 the analysis would not catch the illegal reference. 325 This option tells gcc to inline less (but it does result in 326 a larger kernel). 327 - Run the section mismatch analysis for each module/built-in.o file. 328 When we run the section mismatch analysis on vmlinux.o, we 329 lose valuable information about where the mismatch was 330 introduced. 331 Running the analysis for each module/built-in.o file 332 tells where the mismatch happens much closer to the 333 source. The drawback is that the same mismatch is 334 reported at least twice. 335 - Enable verbose reporting from modpost in order to help resolve 336 the section mismatches that are reported. 337 338config SECTION_MISMATCH_WARN_ONLY 339 bool "Make section mismatch errors non-fatal" 340 default y 341 help 342 If you say N here, the build process will fail if there are any 343 section mismatch, instead of just throwing warnings. 344 345 If unsure, say Y. 346 347# 348# Select this config option from the architecture Kconfig, if it 349# is preferred to always offer frame pointers as a config 350# option on the architecture (regardless of KERNEL_DEBUG): 351# 352config ARCH_WANT_FRAME_POINTERS 353 bool 354 help 355 356config FRAME_POINTER 357 bool "Compile the kernel with frame pointers" 358 depends on DEBUG_KERNEL && \ 359 (CRIS || M68K || FRV || UML || \ 360 SUPERH || BLACKFIN || MN10300 || METAG) || \ 361 ARCH_WANT_FRAME_POINTERS 362 default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS 363 help 364 If you say Y here the resulting kernel image will be slightly 365 larger and slower, but it gives very useful debugging information 366 in case of kernel bugs. (precise oopses/stacktraces/warnings) 367 368config STACK_VALIDATION 369 bool "Compile-time stack metadata validation" 370 depends on HAVE_STACK_VALIDATION 371 default n 372 help 373 Add compile-time checks to validate stack metadata, including frame 374 pointers (if CONFIG_FRAME_POINTER is enabled). This helps ensure 375 that runtime stack traces are more reliable. 376 377 This is also a prerequisite for generation of ORC unwind data, which 378 is needed for CONFIG_ORC_UNWINDER. 379 380 For more information, see 381 tools/objtool/Documentation/stack-validation.txt. 382 383config DEBUG_FORCE_WEAK_PER_CPU 384 bool "Force weak per-cpu definitions" 385 depends on DEBUG_KERNEL 386 help 387 s390 and alpha require percpu variables in modules to be 388 defined weak to work around addressing range issue which 389 puts the following two restrictions on percpu variable 390 definitions. 391 392 1. percpu symbols must be unique whether static or not 393 2. percpu variables can't be defined inside a function 394 395 To ensure that generic code follows the above rules, this 396 option forces all percpu variables to be defined as weak. 397 398endmenu # "Compiler options" 399 400config MAGIC_SYSRQ 401 bool "Magic SysRq key" 402 depends on !UML 403 help 404 If you say Y here, you will have some control over the system even 405 if the system crashes for example during kernel debugging (e.g., you 406 will be able to flush the buffer cache to disk, reboot the system 407 immediately or dump some status information). This is accomplished 408 by pressing various keys while holding SysRq (Alt+PrintScreen). It 409 also works on a serial console (on PC hardware at least), if you 410 send a BREAK and then within 5 seconds a command keypress. The 411 keys are documented in <file:Documentation/admin-guide/sysrq.rst>. 412 Don't say Y unless you really know what this hack does. 413 414config MAGIC_SYSRQ_DEFAULT_ENABLE 415 hex "Enable magic SysRq key functions by default" 416 depends on MAGIC_SYSRQ 417 default 0x1 418 help 419 Specifies which SysRq key functions are enabled by default. 420 This may be set to 1 or 0 to enable or disable them all, or 421 to a bitmask as described in Documentation/admin-guide/sysrq.rst. 422 423config MAGIC_SYSRQ_SERIAL 424 bool "Enable magic SysRq key over serial" 425 depends on MAGIC_SYSRQ 426 default y 427 help 428 Many embedded boards have a disconnected TTL level serial which can 429 generate some garbage that can lead to spurious false sysrq detects. 430 This option allows you to decide whether you want to enable the 431 magic SysRq key. 432 433config DEBUG_KERNEL 434 bool "Kernel debugging" 435 help 436 Say Y here if you are developing drivers or trying to debug and 437 identify kernel problems. 438 439menu "Memory Debugging" 440 441source mm/Kconfig.debug 442 443config DEBUG_OBJECTS 444 bool "Debug object operations" 445 depends on DEBUG_KERNEL 446 help 447 If you say Y here, additional code will be inserted into the 448 kernel to track the life time of various objects and validate 449 the operations on those objects. 450 451config DEBUG_OBJECTS_SELFTEST 452 bool "Debug objects selftest" 453 depends on DEBUG_OBJECTS 454 help 455 This enables the selftest of the object debug code. 456 457config DEBUG_OBJECTS_FREE 458 bool "Debug objects in freed memory" 459 depends on DEBUG_OBJECTS 460 help 461 This enables checks whether a k/v free operation frees an area 462 which contains an object which has not been deactivated 463 properly. This can make kmalloc/kfree-intensive workloads 464 much slower. 465 466config DEBUG_OBJECTS_TIMERS 467 bool "Debug timer objects" 468 depends on DEBUG_OBJECTS 469 help 470 If you say Y here, additional code will be inserted into the 471 timer routines to track the life time of timer objects and 472 validate the timer operations. 473 474config DEBUG_OBJECTS_WORK 475 bool "Debug work objects" 476 depends on DEBUG_OBJECTS 477 help 478 If you say Y here, additional code will be inserted into the 479 work queue routines to track the life time of work objects and 480 validate the work operations. 481 482config DEBUG_OBJECTS_RCU_HEAD 483 bool "Debug RCU callbacks objects" 484 depends on DEBUG_OBJECTS 485 help 486 Enable this to turn on debugging of RCU list heads (call_rcu() usage). 487 488config DEBUG_OBJECTS_PERCPU_COUNTER 489 bool "Debug percpu counter objects" 490 depends on DEBUG_OBJECTS 491 help 492 If you say Y here, additional code will be inserted into the 493 percpu counter routines to track the life time of percpu counter 494 objects and validate the percpu counter operations. 495 496config DEBUG_OBJECTS_ENABLE_DEFAULT 497 int "debug_objects bootup default value (0-1)" 498 range 0 1 499 default "1" 500 depends on DEBUG_OBJECTS 501 help 502 Debug objects boot parameter default value 503 504config DEBUG_SLAB 505 bool "Debug slab memory allocations" 506 depends on DEBUG_KERNEL && SLAB && !KMEMCHECK 507 help 508 Say Y here to have the kernel do limited verification on memory 509 allocation as well as poisoning memory on free to catch use of freed 510 memory. This can make kmalloc/kfree-intensive workloads much slower. 511 512config DEBUG_SLAB_LEAK 513 bool "Memory leak debugging" 514 depends on DEBUG_SLAB 515 516config SLUB_DEBUG_ON 517 bool "SLUB debugging on by default" 518 depends on SLUB && SLUB_DEBUG && !KMEMCHECK 519 default n 520 help 521 Boot with debugging on by default. SLUB boots by default with 522 the runtime debug capabilities switched off. Enabling this is 523 equivalent to specifying the "slub_debug" parameter on boot. 524 There is no support for more fine grained debug control like 525 possible with slub_debug=xxx. SLUB debugging may be switched 526 off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying 527 "slub_debug=-". 528 529config SLUB_STATS 530 default n 531 bool "Enable SLUB performance statistics" 532 depends on SLUB && SYSFS 533 help 534 SLUB statistics are useful to debug SLUBs allocation behavior in 535 order find ways to optimize the allocator. This should never be 536 enabled for production use since keeping statistics slows down 537 the allocator by a few percentage points. The slabinfo command 538 supports the determination of the most active slabs to figure 539 out which slabs are relevant to a particular load. 540 Try running: slabinfo -DA 541 542config HAVE_DEBUG_KMEMLEAK 543 bool 544 545config DEBUG_KMEMLEAK 546 bool "Kernel memory leak detector" 547 depends on DEBUG_KERNEL && HAVE_DEBUG_KMEMLEAK 548 select DEBUG_FS 549 select STACKTRACE if STACKTRACE_SUPPORT 550 select KALLSYMS 551 select CRC32 552 help 553 Say Y here if you want to enable the memory leak 554 detector. The memory allocation/freeing is traced in a way 555 similar to the Boehm's conservative garbage collector, the 556 difference being that the orphan objects are not freed but 557 only shown in /sys/kernel/debug/kmemleak. Enabling this 558 feature will introduce an overhead to memory 559 allocations. See Documentation/dev-tools/kmemleak.rst for more 560 details. 561 562 Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances 563 of finding leaks due to the slab objects poisoning. 564 565 In order to access the kmemleak file, debugfs needs to be 566 mounted (usually at /sys/kernel/debug). 567 568config DEBUG_KMEMLEAK_EARLY_LOG_SIZE 569 int "Maximum kmemleak early log entries" 570 depends on DEBUG_KMEMLEAK 571 range 200 40000 572 default 400 573 help 574 Kmemleak must track all the memory allocations to avoid 575 reporting false positives. Since memory may be allocated or 576 freed before kmemleak is initialised, an early log buffer is 577 used to store these actions. If kmemleak reports "early log 578 buffer exceeded", please increase this value. 579 580config DEBUG_KMEMLEAK_TEST 581 tristate "Simple test for the kernel memory leak detector" 582 depends on DEBUG_KMEMLEAK && m 583 help 584 This option enables a module that explicitly leaks memory. 585 586 If unsure, say N. 587 588config DEBUG_KMEMLEAK_DEFAULT_OFF 589 bool "Default kmemleak to off" 590 depends on DEBUG_KMEMLEAK 591 help 592 Say Y here to disable kmemleak by default. It can then be enabled 593 on the command line via kmemleak=on. 594 595config DEBUG_STACK_USAGE 596 bool "Stack utilization instrumentation" 597 depends on DEBUG_KERNEL && !IA64 598 help 599 Enables the display of the minimum amount of free stack which each 600 task has ever had available in the sysrq-T and sysrq-P debug output. 601 602 This option will slow down process creation somewhat. 603 604config DEBUG_VM 605 bool "Debug VM" 606 depends on DEBUG_KERNEL 607 help 608 Enable this to turn on extended checks in the virtual-memory system 609 that may impact performance. 610 611 If unsure, say N. 612 613config DEBUG_VM_VMACACHE 614 bool "Debug VMA caching" 615 depends on DEBUG_VM 616 help 617 Enable this to turn on VMA caching debug information. Doing so 618 can cause significant overhead, so only enable it in non-production 619 environments. 620 621 If unsure, say N. 622 623config DEBUG_VM_RB 624 bool "Debug VM red-black trees" 625 depends on DEBUG_VM 626 help 627 Enable VM red-black tree debugging information and extra validations. 628 629 If unsure, say N. 630 631config DEBUG_VM_PGFLAGS 632 bool "Debug page-flags operations" 633 depends on DEBUG_VM 634 help 635 Enables extra validation on page flags operations. 636 637 If unsure, say N. 638 639config ARCH_HAS_DEBUG_VIRTUAL 640 bool 641 642config DEBUG_VIRTUAL 643 bool "Debug VM translations" 644 depends on DEBUG_KERNEL && ARCH_HAS_DEBUG_VIRTUAL 645 help 646 Enable some costly sanity checks in virtual to page code. This can 647 catch mistakes with virt_to_page() and friends. 648 649 If unsure, say N. 650 651config DEBUG_NOMMU_REGIONS 652 bool "Debug the global anon/private NOMMU mapping region tree" 653 depends on DEBUG_KERNEL && !MMU 654 help 655 This option causes the global tree of anonymous and private mapping 656 regions to be regularly checked for invalid topology. 657 658config DEBUG_MEMORY_INIT 659 bool "Debug memory initialisation" if EXPERT 660 default !EXPERT 661 help 662 Enable this for additional checks during memory initialisation. 663 The sanity checks verify aspects of the VM such as the memory model 664 and other information provided by the architecture. Verbose 665 information will be printed at KERN_DEBUG loglevel depending 666 on the mminit_loglevel= command-line option. 667 668 If unsure, say Y 669 670config MEMORY_NOTIFIER_ERROR_INJECT 671 tristate "Memory hotplug notifier error injection module" 672 depends on MEMORY_HOTPLUG_SPARSE && NOTIFIER_ERROR_INJECTION 673 help 674 This option provides the ability to inject artificial errors to 675 memory hotplug notifier chain callbacks. It is controlled through 676 debugfs interface under /sys/kernel/debug/notifier-error-inject/memory 677 678 If the notifier call chain should be failed with some events 679 notified, write the error code to "actions/<notifier event>/error". 680 681 Example: Inject memory hotplug offline error (-12 == -ENOMEM) 682 683 # cd /sys/kernel/debug/notifier-error-inject/memory 684 # echo -12 > actions/MEM_GOING_OFFLINE/error 685 # echo offline > /sys/devices/system/memory/memoryXXX/state 686 bash: echo: write error: Cannot allocate memory 687 688 To compile this code as a module, choose M here: the module will 689 be called memory-notifier-error-inject. 690 691 If unsure, say N. 692 693config DEBUG_PER_CPU_MAPS 694 bool "Debug access to per_cpu maps" 695 depends on DEBUG_KERNEL 696 depends on SMP 697 help 698 Say Y to verify that the per_cpu map being accessed has 699 been set up. This adds a fair amount of code to kernel memory 700 and decreases performance. 701 702 Say N if unsure. 703 704config DEBUG_HIGHMEM 705 bool "Highmem debugging" 706 depends on DEBUG_KERNEL && HIGHMEM 707 help 708 This option enables additional error checking for high memory 709 systems. Disable for production systems. 710 711config HAVE_DEBUG_STACKOVERFLOW 712 bool 713 714config DEBUG_STACKOVERFLOW 715 bool "Check for stack overflows" 716 depends on DEBUG_KERNEL && HAVE_DEBUG_STACKOVERFLOW 717 ---help--- 718 Say Y here if you want to check for overflows of kernel, IRQ 719 and exception stacks (if your architecture uses them). This 720 option will show detailed messages if free stack space drops 721 below a certain limit. 722 723 These kinds of bugs usually occur when call-chains in the 724 kernel get too deep, especially when interrupts are 725 involved. 726 727 Use this in cases where you see apparently random memory 728 corruption, especially if it appears in 'struct thread_info' 729 730 If in doubt, say "N". 731 732source "lib/Kconfig.kmemcheck" 733 734source "lib/Kconfig.kasan" 735 736endmenu # "Memory Debugging" 737 738config ARCH_HAS_KCOV 739 bool 740 help 741 KCOV does not have any arch-specific code, but currently it is enabled 742 only for x86_64. KCOV requires testing on other archs, and most likely 743 disabling of instrumentation for some early boot code. 744 745config KCOV 746 bool "Code coverage for fuzzing" 747 depends on ARCH_HAS_KCOV 748 select DEBUG_FS 749 select GCC_PLUGINS if !COMPILE_TEST 750 select GCC_PLUGIN_SANCOV if !COMPILE_TEST 751 help 752 KCOV exposes kernel code coverage information in a form suitable 753 for coverage-guided fuzzing (randomized testing). 754 755 If RANDOMIZE_BASE is enabled, PC values will not be stable across 756 different machines and across reboots. If you need stable PC values, 757 disable RANDOMIZE_BASE. 758 759 For more details, see Documentation/dev-tools/kcov.rst. 760 761config KCOV_INSTRUMENT_ALL 762 bool "Instrument all code by default" 763 depends on KCOV 764 default y if KCOV 765 help 766 If you are doing generic system call fuzzing (like e.g. syzkaller), 767 then you will want to instrument the whole kernel and you should 768 say y here. If you are doing more targeted fuzzing (like e.g. 769 filesystem fuzzing with AFL) then you will want to enable coverage 770 for more specific subsets of files, and should say n here. 771 772config DEBUG_SHIRQ 773 bool "Debug shared IRQ handlers" 774 depends on DEBUG_KERNEL 775 help 776 Enable this to generate a spurious interrupt as soon as a shared 777 interrupt handler is registered, and just before one is deregistered. 778 Drivers ought to be able to handle interrupts coming in at those 779 points; some don't and need to be caught. 780 781menu "Debug Lockups and Hangs" 782 783config LOCKUP_DETECTOR 784 bool 785 786config SOFTLOCKUP_DETECTOR 787 bool "Detect Soft Lockups" 788 depends on DEBUG_KERNEL && !S390 789 select LOCKUP_DETECTOR 790 help 791 Say Y here to enable the kernel to act as a watchdog to detect 792 soft lockups. 793 794 Softlockups are bugs that cause the kernel to loop in kernel 795 mode for more than 20 seconds, without giving other tasks a 796 chance to run. The current stack trace is displayed upon 797 detection and the system will stay locked up. 798 799config HARDLOCKUP_DETECTOR_PERF 800 bool 801 select SOFTLOCKUP_DETECTOR 802 803# 804# Enables a timestamp based low pass filter to compensate for perf based 805# hard lockup detection which runs too fast due to turbo modes. 806# 807config HARDLOCKUP_CHECK_TIMESTAMP 808 bool 809 810# 811# arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard 812# lockup detector rather than the perf based detector. 813# 814config HARDLOCKUP_DETECTOR 815 bool "Detect Hard Lockups" 816 depends on DEBUG_KERNEL && !S390 817 depends on HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_ARCH 818 select LOCKUP_DETECTOR 819 select HARDLOCKUP_DETECTOR_PERF if HAVE_HARDLOCKUP_DETECTOR_PERF 820 select HARDLOCKUP_DETECTOR_ARCH if HAVE_HARDLOCKUP_DETECTOR_ARCH 821 help 822 Say Y here to enable the kernel to act as a watchdog to detect 823 hard lockups. 824 825 Hardlockups are bugs that cause the CPU to loop in kernel mode 826 for more than 10 seconds, without letting other interrupts have a 827 chance to run. The current stack trace is displayed upon detection 828 and the system will stay locked up. 829 830config BOOTPARAM_HARDLOCKUP_PANIC 831 bool "Panic (Reboot) On Hard Lockups" 832 depends on HARDLOCKUP_DETECTOR 833 help 834 Say Y here to enable the kernel to panic on "hard lockups", 835 which are bugs that cause the kernel to loop in kernel 836 mode with interrupts disabled for more than 10 seconds (configurable 837 using the watchdog_thresh sysctl). 838 839 Say N if unsure. 840 841config BOOTPARAM_HARDLOCKUP_PANIC_VALUE 842 int 843 depends on HARDLOCKUP_DETECTOR 844 range 0 1 845 default 0 if !BOOTPARAM_HARDLOCKUP_PANIC 846 default 1 if BOOTPARAM_HARDLOCKUP_PANIC 847 848config BOOTPARAM_SOFTLOCKUP_PANIC 849 bool "Panic (Reboot) On Soft Lockups" 850 depends on SOFTLOCKUP_DETECTOR 851 help 852 Say Y here to enable the kernel to panic on "soft lockups", 853 which are bugs that cause the kernel to loop in kernel 854 mode for more than 20 seconds (configurable using the watchdog_thresh 855 sysctl), without giving other tasks a chance to run. 856 857 The panic can be used in combination with panic_timeout, 858 to cause the system to reboot automatically after a 859 lockup has been detected. This feature is useful for 860 high-availability systems that have uptime guarantees and 861 where a lockup must be resolved ASAP. 862 863 Say N if unsure. 864 865config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE 866 int 867 depends on SOFTLOCKUP_DETECTOR 868 range 0 1 869 default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC 870 default 1 if BOOTPARAM_SOFTLOCKUP_PANIC 871 872config DETECT_HUNG_TASK 873 bool "Detect Hung Tasks" 874 depends on DEBUG_KERNEL 875 default SOFTLOCKUP_DETECTOR 876 help 877 Say Y here to enable the kernel to detect "hung tasks", 878 which are bugs that cause the task to be stuck in 879 uninterruptible "D" state indefinitely. 880 881 When a hung task is detected, the kernel will print the 882 current stack trace (which you should report), but the 883 task will stay in uninterruptible state. If lockdep is 884 enabled then all held locks will also be reported. This 885 feature has negligible overhead. 886 887config DEFAULT_HUNG_TASK_TIMEOUT 888 int "Default timeout for hung task detection (in seconds)" 889 depends on DETECT_HUNG_TASK 890 default 120 891 help 892 This option controls the default timeout (in seconds) used 893 to determine when a task has become non-responsive and should 894 be considered hung. 895 896 It can be adjusted at runtime via the kernel.hung_task_timeout_secs 897 sysctl or by writing a value to 898 /proc/sys/kernel/hung_task_timeout_secs. 899 900 A timeout of 0 disables the check. The default is two minutes. 901 Keeping the default should be fine in most cases. 902 903config BOOTPARAM_HUNG_TASK_PANIC 904 bool "Panic (Reboot) On Hung Tasks" 905 depends on DETECT_HUNG_TASK 906 help 907 Say Y here to enable the kernel to panic on "hung tasks", 908 which are bugs that cause the kernel to leave a task stuck 909 in uninterruptible "D" state. 910 911 The panic can be used in combination with panic_timeout, 912 to cause the system to reboot automatically after a 913 hung task has been detected. This feature is useful for 914 high-availability systems that have uptime guarantees and 915 where a hung tasks must be resolved ASAP. 916 917 Say N if unsure. 918 919config BOOTPARAM_HUNG_TASK_PANIC_VALUE 920 int 921 depends on DETECT_HUNG_TASK 922 range 0 1 923 default 0 if !BOOTPARAM_HUNG_TASK_PANIC 924 default 1 if BOOTPARAM_HUNG_TASK_PANIC 925 926config WQ_WATCHDOG 927 bool "Detect Workqueue Stalls" 928 depends on DEBUG_KERNEL 929 help 930 Say Y here to enable stall detection on workqueues. If a 931 worker pool doesn't make forward progress on a pending work 932 item for over a given amount of time, 30s by default, a 933 warning message is printed along with dump of workqueue 934 state. This can be configured through kernel parameter 935 "workqueue.watchdog_thresh" and its sysfs counterpart. 936 937endmenu # "Debug lockups and hangs" 938 939config PANIC_ON_OOPS 940 bool "Panic on Oops" 941 help 942 Say Y here to enable the kernel to panic when it oopses. This 943 has the same effect as setting oops=panic on the kernel command 944 line. 945 946 This feature is useful to ensure that the kernel does not do 947 anything erroneous after an oops which could result in data 948 corruption or other issues. 949 950 Say N if unsure. 951 952config PANIC_ON_OOPS_VALUE 953 int 954 range 0 1 955 default 0 if !PANIC_ON_OOPS 956 default 1 if PANIC_ON_OOPS 957 958config PANIC_TIMEOUT 959 int "panic timeout" 960 default 0 961 help 962 Set the timeout value (in seconds) until a reboot occurs when the 963 the kernel panics. If n = 0, then we wait forever. A timeout 964 value n > 0 will wait n seconds before rebooting, while a timeout 965 value n < 0 will reboot immediately. 966 967config SCHED_DEBUG 968 bool "Collect scheduler debugging info" 969 depends on DEBUG_KERNEL && PROC_FS 970 default y 971 help 972 If you say Y here, the /proc/sched_debug file will be provided 973 that can help debug the scheduler. The runtime overhead of this 974 option is minimal. 975 976config SCHED_INFO 977 bool 978 default n 979 980config SCHEDSTATS 981 bool "Collect scheduler statistics" 982 depends on DEBUG_KERNEL && PROC_FS 983 select SCHED_INFO 984 help 985 If you say Y here, additional code will be inserted into the 986 scheduler and related routines to collect statistics about 987 scheduler behavior and provide them in /proc/schedstat. These 988 stats may be useful for both tuning and debugging the scheduler 989 If you aren't debugging the scheduler or trying to tune a specific 990 application, you can say N to avoid the very slight overhead 991 this adds. 992 993config SCHED_STACK_END_CHECK 994 bool "Detect stack corruption on calls to schedule()" 995 depends on DEBUG_KERNEL 996 default n 997 help 998 This option checks for a stack overrun on calls to schedule(). 999 If the stack end location is found to be over written always panic as 1000 the content of the corrupted region can no longer be trusted. 1001 This is to ensure no erroneous behaviour occurs which could result in 1002 data corruption or a sporadic crash at a later stage once the region 1003 is examined. The runtime overhead introduced is minimal. 1004 1005config DEBUG_TIMEKEEPING 1006 bool "Enable extra timekeeping sanity checking" 1007 help 1008 This option will enable additional timekeeping sanity checks 1009 which may be helpful when diagnosing issues where timekeeping 1010 problems are suspected. 1011 1012 This may include checks in the timekeeping hotpaths, so this 1013 option may have a (very small) performance impact to some 1014 workloads. 1015 1016 If unsure, say N. 1017 1018config DEBUG_PREEMPT 1019 bool "Debug preemptible kernel" 1020 depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT 1021 default y 1022 help 1023 If you say Y here then the kernel will use a debug variant of the 1024 commonly used smp_processor_id() function and will print warnings 1025 if kernel code uses it in a preemption-unsafe way. Also, the kernel 1026 will detect preemption count underflows. 1027 1028menu "Lock Debugging (spinlocks, mutexes, etc...)" 1029 1030config DEBUG_RT_MUTEXES 1031 bool "RT Mutex debugging, deadlock detection" 1032 depends on DEBUG_KERNEL && RT_MUTEXES 1033 help 1034 This allows rt mutex semantics violations and rt mutex related 1035 deadlocks (lockups) to be detected and reported automatically. 1036 1037config DEBUG_SPINLOCK 1038 bool "Spinlock and rw-lock debugging: basic checks" 1039 depends on DEBUG_KERNEL 1040 select UNINLINE_SPIN_UNLOCK 1041 help 1042 Say Y here and build SMP to catch missing spinlock initialization 1043 and certain other kinds of spinlock errors commonly made. This is 1044 best used in conjunction with the NMI watchdog so that spinlock 1045 deadlocks are also debuggable. 1046 1047config DEBUG_MUTEXES 1048 bool "Mutex debugging: basic checks" 1049 depends on DEBUG_KERNEL 1050 help 1051 This feature allows mutex semantics violations to be detected and 1052 reported. 1053 1054config DEBUG_WW_MUTEX_SLOWPATH 1055 bool "Wait/wound mutex debugging: Slowpath testing" 1056 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1057 select DEBUG_LOCK_ALLOC 1058 select DEBUG_SPINLOCK 1059 select DEBUG_MUTEXES 1060 help 1061 This feature enables slowpath testing for w/w mutex users by 1062 injecting additional -EDEADLK wound/backoff cases. Together with 1063 the full mutex checks enabled with (CONFIG_PROVE_LOCKING) this 1064 will test all possible w/w mutex interface abuse with the 1065 exception of simply not acquiring all the required locks. 1066 Note that this feature can introduce significant overhead, so 1067 it really should not be enabled in a production or distro kernel, 1068 even a debug kernel. If you are a driver writer, enable it. If 1069 you are a distro, do not. 1070 1071config DEBUG_LOCK_ALLOC 1072 bool "Lock debugging: detect incorrect freeing of live locks" 1073 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1074 select DEBUG_SPINLOCK 1075 select DEBUG_MUTEXES 1076 select DEBUG_RT_MUTEXES if RT_MUTEXES 1077 select LOCKDEP 1078 help 1079 This feature will check whether any held lock (spinlock, rwlock, 1080 mutex or rwsem) is incorrectly freed by the kernel, via any of the 1081 memory-freeing routines (kfree(), kmem_cache_free(), free_pages(), 1082 vfree(), etc.), whether a live lock is incorrectly reinitialized via 1083 spin_lock_init()/mutex_init()/etc., or whether there is any lock 1084 held during task exit. 1085 1086config PROVE_LOCKING 1087 bool "Lock debugging: prove locking correctness" 1088 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1089 select LOCKDEP 1090 select DEBUG_SPINLOCK 1091 select DEBUG_MUTEXES 1092 select DEBUG_RT_MUTEXES if RT_MUTEXES 1093 select DEBUG_LOCK_ALLOC 1094 select LOCKDEP_CROSSRELEASE 1095 select LOCKDEP_COMPLETIONS 1096 select TRACE_IRQFLAGS 1097 default n 1098 help 1099 This feature enables the kernel to prove that all locking 1100 that occurs in the kernel runtime is mathematically 1101 correct: that under no circumstance could an arbitrary (and 1102 not yet triggered) combination of observed locking 1103 sequences (on an arbitrary number of CPUs, running an 1104 arbitrary number of tasks and interrupt contexts) cause a 1105 deadlock. 1106 1107 In short, this feature enables the kernel to report locking 1108 related deadlocks before they actually occur. 1109 1110 The proof does not depend on how hard and complex a 1111 deadlock scenario would be to trigger: how many 1112 participant CPUs, tasks and irq-contexts would be needed 1113 for it to trigger. The proof also does not depend on 1114 timing: if a race and a resulting deadlock is possible 1115 theoretically (no matter how unlikely the race scenario 1116 is), it will be proven so and will immediately be 1117 reported by the kernel (once the event is observed that 1118 makes the deadlock theoretically possible). 1119 1120 If a deadlock is impossible (i.e. the locking rules, as 1121 observed by the kernel, are mathematically correct), the 1122 kernel reports nothing. 1123 1124 NOTE: this feature can also be enabled for rwlocks, mutexes 1125 and rwsems - in which case all dependencies between these 1126 different locking variants are observed and mapped too, and 1127 the proof of observed correctness is also maintained for an 1128 arbitrary combination of these separate locking variants. 1129 1130 For more details, see Documentation/locking/lockdep-design.txt. 1131 1132config LOCKDEP 1133 bool 1134 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1135 select STACKTRACE 1136 select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !SCORE && !X86 1137 select KALLSYMS 1138 select KALLSYMS_ALL 1139 1140config LOCKDEP_SMALL 1141 bool 1142 1143config LOCK_STAT 1144 bool "Lock usage statistics" 1145 depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT 1146 select LOCKDEP 1147 select DEBUG_SPINLOCK 1148 select DEBUG_MUTEXES 1149 select DEBUG_RT_MUTEXES if RT_MUTEXES 1150 select DEBUG_LOCK_ALLOC 1151 default n 1152 help 1153 This feature enables tracking lock contention points 1154 1155 For more details, see Documentation/locking/lockstat.txt 1156 1157 This also enables lock events required by "perf lock", 1158 subcommand of perf. 1159 If you want to use "perf lock", you also need to turn on 1160 CONFIG_EVENT_TRACING. 1161 1162 CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. 1163 (CONFIG_LOCKDEP defines "acquire" and "release" events.) 1164 1165config LOCKDEP_CROSSRELEASE 1166 bool 1167 help 1168 This makes lockdep work for crosslock which is a lock allowed to 1169 be released in a different context from the acquisition context. 1170 Normally a lock must be released in the context acquiring the lock. 1171 However, relexing this constraint helps synchronization primitives 1172 such as page locks or completions can use the lock correctness 1173 detector, lockdep. 1174 1175config LOCKDEP_COMPLETIONS 1176 bool 1177 help 1178 A deadlock caused by wait_for_completion() and complete() can be 1179 detected by lockdep using crossrelease feature. 1180 1181config DEBUG_LOCKDEP 1182 bool "Lock dependency engine debugging" 1183 depends on DEBUG_KERNEL && LOCKDEP 1184 help 1185 If you say Y here, the lock dependency engine will do 1186 additional runtime checks to debug itself, at the price 1187 of more runtime overhead. 1188 1189config DEBUG_ATOMIC_SLEEP 1190 bool "Sleep inside atomic section checking" 1191 select PREEMPT_COUNT 1192 depends on DEBUG_KERNEL 1193 help 1194 If you say Y here, various routines which may sleep will become very 1195 noisy if they are called inside atomic sections: when a spinlock is 1196 held, inside an rcu read side critical section, inside preempt disabled 1197 sections, inside an interrupt, etc... 1198 1199config DEBUG_LOCKING_API_SELFTESTS 1200 bool "Locking API boot-time self-tests" 1201 depends on DEBUG_KERNEL 1202 help 1203 Say Y here if you want the kernel to run a short self-test during 1204 bootup. The self-test checks whether common types of locking bugs 1205 are detected by debugging mechanisms or not. (if you disable 1206 lock debugging then those bugs wont be detected of course.) 1207 The following locking APIs are covered: spinlocks, rwlocks, 1208 mutexes and rwsems. 1209 1210config LOCK_TORTURE_TEST 1211 tristate "torture tests for locking" 1212 depends on DEBUG_KERNEL 1213 select TORTURE_TEST 1214 default n 1215 help 1216 This option provides a kernel module that runs torture tests 1217 on kernel locking primitives. The kernel module may be built 1218 after the fact on the running kernel to be tested, if desired. 1219 1220 Say Y here if you want kernel locking-primitive torture tests 1221 to be built into the kernel. 1222 Say M if you want these torture tests to build as a module. 1223 Say N if you are unsure. 1224 1225config WW_MUTEX_SELFTEST 1226 tristate "Wait/wound mutex selftests" 1227 help 1228 This option provides a kernel module that runs tests on the 1229 on the struct ww_mutex locking API. 1230 1231 It is recommended to enable DEBUG_WW_MUTEX_SLOWPATH in conjunction 1232 with this test harness. 1233 1234 Say M if you want these self tests to build as a module. 1235 Say N if you are unsure. 1236 1237endmenu # lock debugging 1238 1239config TRACE_IRQFLAGS 1240 bool 1241 help 1242 Enables hooks to interrupt enabling and disabling for 1243 either tracing or lock debugging. 1244 1245config STACKTRACE 1246 bool "Stack backtrace support" 1247 depends on STACKTRACE_SUPPORT 1248 help 1249 This option causes the kernel to create a /proc/pid/stack for 1250 every process, showing its current stack trace. 1251 It is also used by various kernel debugging features that require 1252 stack trace generation. 1253 1254config WARN_ALL_UNSEEDED_RANDOM 1255 bool "Warn for all uses of unseeded randomness" 1256 default n 1257 help 1258 Some parts of the kernel contain bugs relating to their use of 1259 cryptographically secure random numbers before it's actually possible 1260 to generate those numbers securely. This setting ensures that these 1261 flaws don't go unnoticed, by enabling a message, should this ever 1262 occur. This will allow people with obscure setups to know when things 1263 are going wrong, so that they might contact developers about fixing 1264 it. 1265 1266 Unfortunately, on some models of some architectures getting 1267 a fully seeded CRNG is extremely difficult, and so this can 1268 result in dmesg getting spammed for a surprisingly long 1269 time. This is really bad from a security perspective, and 1270 so architecture maintainers really need to do what they can 1271 to get the CRNG seeded sooner after the system is booted. 1272 However, since users can not do anything actionble to 1273 address this, by default the kernel will issue only a single 1274 warning for the first use of unseeded randomness. 1275 1276 Say Y here if you want to receive warnings for all uses of 1277 unseeded randomness. This will be of use primarily for 1278 those developers interersted in improving the security of 1279 Linux kernels running on their architecture (or 1280 subarchitecture). 1281 1282config DEBUG_KOBJECT 1283 bool "kobject debugging" 1284 depends on DEBUG_KERNEL 1285 help 1286 If you say Y here, some extra kobject debugging messages will be sent 1287 to the syslog. 1288 1289config DEBUG_KOBJECT_RELEASE 1290 bool "kobject release debugging" 1291 depends on DEBUG_OBJECTS_TIMERS 1292 help 1293 kobjects are reference counted objects. This means that their 1294 last reference count put is not predictable, and the kobject can 1295 live on past the point at which a driver decides to drop it's 1296 initial reference to the kobject gained on allocation. An 1297 example of this would be a struct device which has just been 1298 unregistered. 1299 1300 However, some buggy drivers assume that after such an operation, 1301 the memory backing the kobject can be immediately freed. This 1302 goes completely against the principles of a refcounted object. 1303 1304 If you say Y here, the kernel will delay the release of kobjects 1305 on the last reference count to improve the visibility of this 1306 kind of kobject release bug. 1307 1308config HAVE_DEBUG_BUGVERBOSE 1309 bool 1310 1311config DEBUG_BUGVERBOSE 1312 bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EXPERT 1313 depends on BUG && (GENERIC_BUG || HAVE_DEBUG_BUGVERBOSE) 1314 default y 1315 help 1316 Say Y here to make BUG() panics output the file name and line number 1317 of the BUG call as well as the EIP and oops trace. This aids 1318 debugging but costs about 70-100K of memory. 1319 1320config DEBUG_LIST 1321 bool "Debug linked list manipulation" 1322 depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION 1323 help 1324 Enable this to turn on extended checks in the linked-list 1325 walking routines. 1326 1327 If unsure, say N. 1328 1329config DEBUG_PI_LIST 1330 bool "Debug priority linked list manipulation" 1331 depends on DEBUG_KERNEL 1332 help 1333 Enable this to turn on extended checks in the priority-ordered 1334 linked-list (plist) walking routines. This checks the entire 1335 list multiple times during each manipulation. 1336 1337 If unsure, say N. 1338 1339config DEBUG_SG 1340 bool "Debug SG table operations" 1341 depends on DEBUG_KERNEL 1342 help 1343 Enable this to turn on checks on scatter-gather tables. This can 1344 help find problems with drivers that do not properly initialize 1345 their sg tables. 1346 1347 If unsure, say N. 1348 1349config DEBUG_NOTIFIERS 1350 bool "Debug notifier call chains" 1351 depends on DEBUG_KERNEL 1352 help 1353 Enable this to turn on sanity checking for notifier call chains. 1354 This is most useful for kernel developers to make sure that 1355 modules properly unregister themselves from notifier chains. 1356 This is a relatively cheap check but if you care about maximum 1357 performance, say N. 1358 1359config DEBUG_CREDENTIALS 1360 bool "Debug credential management" 1361 depends on DEBUG_KERNEL 1362 help 1363 Enable this to turn on some debug checking for credential 1364 management. The additional code keeps track of the number of 1365 pointers from task_structs to any given cred struct, and checks to 1366 see that this number never exceeds the usage count of the cred 1367 struct. 1368 1369 Furthermore, if SELinux is enabled, this also checks that the 1370 security pointer in the cred struct is never seen to be invalid. 1371 1372 If unsure, say N. 1373 1374source "kernel/rcu/Kconfig.debug" 1375 1376config DEBUG_WQ_FORCE_RR_CPU 1377 bool "Force round-robin CPU selection for unbound work items" 1378 depends on DEBUG_KERNEL 1379 default n 1380 help 1381 Workqueue used to implicitly guarantee that work items queued 1382 without explicit CPU specified are put on the local CPU. This 1383 guarantee is no longer true and while local CPU is still 1384 preferred work items may be put on foreign CPUs. Kernel 1385 parameter "workqueue.debug_force_rr_cpu" is added to force 1386 round-robin CPU selection to flush out usages which depend on the 1387 now broken guarantee. This config option enables the debug 1388 feature by default. When enabled, memory and cache locality will 1389 be impacted. 1390 1391config DEBUG_BLOCK_EXT_DEVT 1392 bool "Force extended block device numbers and spread them" 1393 depends on DEBUG_KERNEL 1394 depends on BLOCK 1395 default n 1396 help 1397 BIG FAT WARNING: ENABLING THIS OPTION MIGHT BREAK BOOTING ON 1398 SOME DISTRIBUTIONS. DO NOT ENABLE THIS UNLESS YOU KNOW WHAT 1399 YOU ARE DOING. Distros, please enable this and fix whatever 1400 is broken. 1401 1402 Conventionally, block device numbers are allocated from 1403 predetermined contiguous area. However, extended block area 1404 may introduce non-contiguous block device numbers. This 1405 option forces most block device numbers to be allocated from 1406 the extended space and spreads them to discover kernel or 1407 userland code paths which assume predetermined contiguous 1408 device number allocation. 1409 1410 Note that turning on this debug option shuffles all the 1411 device numbers for all IDE and SCSI devices including libata 1412 ones, so root partition specified using device number 1413 directly (via rdev or root=MAJ:MIN) won't work anymore. 1414 Textual device names (root=/dev/sdXn) will continue to work. 1415 1416 Say N if you are unsure. 1417 1418config CPU_HOTPLUG_STATE_CONTROL 1419 bool "Enable CPU hotplug state control" 1420 depends on DEBUG_KERNEL 1421 depends on HOTPLUG_CPU 1422 default n 1423 help 1424 Allows to write steps between "offline" and "online" to the CPUs 1425 sysfs target file so states can be stepped granular. This is a debug 1426 option for now as the hotplug machinery cannot be stopped and 1427 restarted at arbitrary points yet. 1428 1429 Say N if your are unsure. 1430 1431config NOTIFIER_ERROR_INJECTION 1432 tristate "Notifier error injection" 1433 depends on DEBUG_KERNEL 1434 select DEBUG_FS 1435 help 1436 This option provides the ability to inject artificial errors to 1437 specified notifier chain callbacks. It is useful to test the error 1438 handling of notifier call chain failures. 1439 1440 Say N if unsure. 1441 1442config PM_NOTIFIER_ERROR_INJECT 1443 tristate "PM notifier error injection module" 1444 depends on PM && NOTIFIER_ERROR_INJECTION 1445 default m if PM_DEBUG 1446 help 1447 This option provides the ability to inject artificial errors to 1448 PM notifier chain callbacks. It is controlled through debugfs 1449 interface /sys/kernel/debug/notifier-error-inject/pm 1450 1451 If the notifier call chain should be failed with some events 1452 notified, write the error code to "actions/<notifier event>/error". 1453 1454 Example: Inject PM suspend error (-12 = -ENOMEM) 1455 1456 # cd /sys/kernel/debug/notifier-error-inject/pm/ 1457 # echo -12 > actions/PM_SUSPEND_PREPARE/error 1458 # echo mem > /sys/power/state 1459 bash: echo: write error: Cannot allocate memory 1460 1461 To compile this code as a module, choose M here: the module will 1462 be called pm-notifier-error-inject. 1463 1464 If unsure, say N. 1465 1466config OF_RECONFIG_NOTIFIER_ERROR_INJECT 1467 tristate "OF reconfig notifier error injection module" 1468 depends on OF_DYNAMIC && NOTIFIER_ERROR_INJECTION 1469 help 1470 This option provides the ability to inject artificial errors to 1471 OF reconfig notifier chain callbacks. It is controlled 1472 through debugfs interface under 1473 /sys/kernel/debug/notifier-error-inject/OF-reconfig/ 1474 1475 If the notifier call chain should be failed with some events 1476 notified, write the error code to "actions/<notifier event>/error". 1477 1478 To compile this code as a module, choose M here: the module will 1479 be called of-reconfig-notifier-error-inject. 1480 1481 If unsure, say N. 1482 1483config NETDEV_NOTIFIER_ERROR_INJECT 1484 tristate "Netdev notifier error injection module" 1485 depends on NET && NOTIFIER_ERROR_INJECTION 1486 help 1487 This option provides the ability to inject artificial errors to 1488 netdevice notifier chain callbacks. It is controlled through debugfs 1489 interface /sys/kernel/debug/notifier-error-inject/netdev 1490 1491 If the notifier call chain should be failed with some events 1492 notified, write the error code to "actions/<notifier event>/error". 1493 1494 Example: Inject netdevice mtu change error (-22 = -EINVAL) 1495 1496 # cd /sys/kernel/debug/notifier-error-inject/netdev 1497 # echo -22 > actions/NETDEV_CHANGEMTU/error 1498 # ip link set eth0 mtu 1024 1499 RTNETLINK answers: Invalid argument 1500 1501 To compile this code as a module, choose M here: the module will 1502 be called netdev-notifier-error-inject. 1503 1504 If unsure, say N. 1505 1506config FAULT_INJECTION 1507 bool "Fault-injection framework" 1508 depends on DEBUG_KERNEL 1509 help 1510 Provide fault-injection framework. 1511 For more details, see Documentation/fault-injection/. 1512 1513config FAILSLAB 1514 bool "Fault-injection capability for kmalloc" 1515 depends on FAULT_INJECTION 1516 depends on SLAB || SLUB 1517 help 1518 Provide fault-injection capability for kmalloc. 1519 1520config FAIL_PAGE_ALLOC 1521 bool "Fault-injection capabilitiy for alloc_pages()" 1522 depends on FAULT_INJECTION 1523 help 1524 Provide fault-injection capability for alloc_pages(). 1525 1526config FAIL_MAKE_REQUEST 1527 bool "Fault-injection capability for disk IO" 1528 depends on FAULT_INJECTION && BLOCK 1529 help 1530 Provide fault-injection capability for disk IO. 1531 1532config FAIL_IO_TIMEOUT 1533 bool "Fault-injection capability for faking disk interrupts" 1534 depends on FAULT_INJECTION && BLOCK 1535 help 1536 Provide fault-injection capability on end IO handling. This 1537 will make the block layer "forget" an interrupt as configured, 1538 thus exercising the error handling. 1539 1540 Only works with drivers that use the generic timeout handling, 1541 for others it wont do anything. 1542 1543config FAIL_MMC_REQUEST 1544 bool "Fault-injection capability for MMC IO" 1545 depends on FAULT_INJECTION_DEBUG_FS && MMC 1546 help 1547 Provide fault-injection capability for MMC IO. 1548 This will make the mmc core return data errors. This is 1549 useful to test the error handling in the mmc block device 1550 and to test how the mmc host driver handles retries from 1551 the block device. 1552 1553config FAIL_FUTEX 1554 bool "Fault-injection capability for futexes" 1555 select DEBUG_FS 1556 depends on FAULT_INJECTION && FUTEX 1557 help 1558 Provide fault-injection capability for futexes. 1559 1560config FAULT_INJECTION_DEBUG_FS 1561 bool "Debugfs entries for fault-injection capabilities" 1562 depends on FAULT_INJECTION && SYSFS && DEBUG_FS 1563 help 1564 Enable configuration of fault-injection capabilities via debugfs. 1565 1566config FAULT_INJECTION_STACKTRACE_FILTER 1567 bool "stacktrace filter for fault-injection capabilities" 1568 depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT 1569 depends on !X86_64 1570 select STACKTRACE 1571 select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !SCORE && !X86 1572 help 1573 Provide stacktrace filter for fault-injection capabilities 1574 1575config LATENCYTOP 1576 bool "Latency measuring infrastructure" 1577 depends on DEBUG_KERNEL 1578 depends on STACKTRACE_SUPPORT 1579 depends on PROC_FS 1580 select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !X86 1581 select KALLSYMS 1582 select KALLSYMS_ALL 1583 select STACKTRACE 1584 select SCHEDSTATS 1585 select SCHED_DEBUG 1586 help 1587 Enable this option if you want to use the LatencyTOP tool 1588 to find out which userspace is blocking on what kernel operations. 1589 1590source kernel/trace/Kconfig 1591 1592menu "Runtime Testing" 1593 1594config LKDTM 1595 tristate "Linux Kernel Dump Test Tool Module" 1596 depends on DEBUG_FS 1597 depends on BLOCK 1598 default n 1599 help 1600 This module enables testing of the different dumping mechanisms by 1601 inducing system failures at predefined crash points. 1602 If you don't need it: say N 1603 Choose M here to compile this code as a module. The module will be 1604 called lkdtm. 1605 1606 Documentation on how to use the module can be found in 1607 Documentation/fault-injection/provoke-crashes.txt 1608 1609config TEST_LIST_SORT 1610 tristate "Linked list sorting test" 1611 depends on DEBUG_KERNEL || m 1612 help 1613 Enable this to turn on 'list_sort()' function test. This test is 1614 executed only once during system boot (so affects only boot time), 1615 or at module load time. 1616 1617 If unsure, say N. 1618 1619config TEST_SORT 1620 tristate "Array-based sort test" 1621 depends on DEBUG_KERNEL || m 1622 help 1623 This option enables the self-test function of 'sort()' at boot, 1624 or at module load time. 1625 1626 If unsure, say N. 1627 1628config KPROBES_SANITY_TEST 1629 bool "Kprobes sanity tests" 1630 depends on DEBUG_KERNEL 1631 depends on KPROBES 1632 default n 1633 help 1634 This option provides for testing basic kprobes functionality on 1635 boot. A sample kprobe, jprobe and kretprobe are inserted and 1636 verified for functionality. 1637 1638 Say N if you are unsure. 1639 1640config BACKTRACE_SELF_TEST 1641 tristate "Self test for the backtrace code" 1642 depends on DEBUG_KERNEL 1643 default n 1644 help 1645 This option provides a kernel module that can be used to test 1646 the kernel stack backtrace code. This option is not useful 1647 for distributions or general kernels, but only for kernel 1648 developers working on architecture code. 1649 1650 Note that if you want to also test saved backtraces, you will 1651 have to enable STACKTRACE as well. 1652 1653 Say N if you are unsure. 1654 1655config RBTREE_TEST 1656 tristate "Red-Black tree test" 1657 depends on DEBUG_KERNEL 1658 help 1659 A benchmark measuring the performance of the rbtree library. 1660 Also includes rbtree invariant checks. 1661 1662config INTERVAL_TREE_TEST 1663 tristate "Interval tree test" 1664 depends on DEBUG_KERNEL 1665 select INTERVAL_TREE 1666 help 1667 A benchmark measuring the performance of the interval tree library 1668 1669config PERCPU_TEST 1670 tristate "Per cpu operations test" 1671 depends on m && DEBUG_KERNEL 1672 help 1673 Enable this option to build test module which validates per-cpu 1674 operations. 1675 1676 If unsure, say N. 1677 1678config ATOMIC64_SELFTEST 1679 tristate "Perform an atomic64_t self-test" 1680 help 1681 Enable this option to test the atomic64_t functions at boot or 1682 at module load time. 1683 1684 If unsure, say N. 1685 1686config ASYNC_RAID6_TEST 1687 tristate "Self test for hardware accelerated raid6 recovery" 1688 depends on ASYNC_RAID6_RECOV 1689 select ASYNC_MEMCPY 1690 ---help--- 1691 This is a one-shot self test that permutes through the 1692 recovery of all the possible two disk failure scenarios for a 1693 N-disk array. Recovery is performed with the asynchronous 1694 raid6 recovery routines, and will optionally use an offload 1695 engine if one is available. 1696 1697 If unsure, say N. 1698 1699config TEST_HEXDUMP 1700 tristate "Test functions located in the hexdump module at runtime" 1701 1702config TEST_STRING_HELPERS 1703 tristate "Test functions located in the string_helpers module at runtime" 1704 1705config TEST_KSTRTOX 1706 tristate "Test kstrto*() family of functions at runtime" 1707 1708config TEST_PRINTF 1709 tristate "Test printf() family of functions at runtime" 1710 1711config TEST_BITMAP 1712 tristate "Test bitmap_*() family of functions at runtime" 1713 default n 1714 help 1715 Enable this option to test the bitmap functions at boot. 1716 1717 If unsure, say N. 1718 1719config TEST_UUID 1720 tristate "Test functions located in the uuid module at runtime" 1721 1722config TEST_RHASHTABLE 1723 tristate "Perform selftest on resizable hash table" 1724 default n 1725 help 1726 Enable this option to test the rhashtable functions at boot. 1727 1728 If unsure, say N. 1729 1730config TEST_HASH 1731 tristate "Perform selftest on hash functions" 1732 default n 1733 help 1734 Enable this option to test the kernel's integer (<linux/hash.h>), 1735 string (<linux/stringhash.h>), and siphash (<linux/siphash.h>) 1736 hash functions on boot (or module load). 1737 1738 This is intended to help people writing architecture-specific 1739 optimized versions. If unsure, say N. 1740 1741config TEST_PARMAN 1742 tristate "Perform selftest on priority array manager" 1743 default n 1744 depends on PARMAN 1745 help 1746 Enable this option to test priority array manager on boot 1747 (or module load). 1748 1749 If unsure, say N. 1750 1751endmenu # runtime tests 1752 1753config PROVIDE_OHCI1394_DMA_INIT 1754 bool "Remote debugging over FireWire early on boot" 1755 depends on PCI && X86 1756 help 1757 If you want to debug problems which hang or crash the kernel early 1758 on boot and the crashing machine has a FireWire port, you can use 1759 this feature to remotely access the memory of the crashed machine 1760 over FireWire. This employs remote DMA as part of the OHCI1394 1761 specification which is now the standard for FireWire controllers. 1762 1763 With remote DMA, you can monitor the printk buffer remotely using 1764 firescope and access all memory below 4GB using fireproxy from gdb. 1765 Even controlling a kernel debugger is possible using remote DMA. 1766 1767 Usage: 1768 1769 If ohci1394_dma=early is used as boot parameter, it will initialize 1770 all OHCI1394 controllers which are found in the PCI config space. 1771 1772 As all changes to the FireWire bus such as enabling and disabling 1773 devices cause a bus reset and thereby disable remote DMA for all 1774 devices, be sure to have the cable plugged and FireWire enabled on 1775 the debugging host before booting the debug target for debugging. 1776 1777 This code (~1k) is freed after boot. By then, the firewire stack 1778 in charge of the OHCI-1394 controllers should be used instead. 1779 1780 See Documentation/debugging-via-ohci1394.txt for more information. 1781 1782config DMA_API_DEBUG 1783 bool "Enable debugging of DMA-API usage" 1784 depends on HAVE_DMA_API_DEBUG 1785 help 1786 Enable this option to debug the use of the DMA API by device drivers. 1787 With this option you will be able to detect common bugs in device 1788 drivers like double-freeing of DMA mappings or freeing mappings that 1789 were never allocated. 1790 1791 This also attempts to catch cases where a page owned by DMA is 1792 accessed by the cpu in a way that could cause data corruption. For 1793 example, this enables cow_user_page() to check that the source page is 1794 not undergoing DMA. 1795 1796 This option causes a performance degradation. Use only if you want to 1797 debug device drivers and dma interactions. 1798 1799 If unsure, say N. 1800 1801config TEST_LKM 1802 tristate "Test module loading with 'hello world' module" 1803 default n 1804 depends on m 1805 help 1806 This builds the "test_module" module that emits "Hello, world" 1807 on printk when loaded. It is designed to be used for basic 1808 evaluation of the module loading subsystem (for example when 1809 validating module verification). It lacks any extra dependencies, 1810 and will not normally be loaded by the system unless explicitly 1811 requested by name. 1812 1813 If unsure, say N. 1814 1815config TEST_USER_COPY 1816 tristate "Test user/kernel boundary protections" 1817 default n 1818 depends on m 1819 help 1820 This builds the "test_user_copy" module that runs sanity checks 1821 on the copy_to/from_user infrastructure, making sure basic 1822 user/kernel boundary testing is working. If it fails to load, 1823 a regression has been detected in the user/kernel memory boundary 1824 protections. 1825 1826 If unsure, say N. 1827 1828config TEST_BPF 1829 tristate "Test BPF filter functionality" 1830 default n 1831 depends on m && NET 1832 help 1833 This builds the "test_bpf" module that runs various test vectors 1834 against the BPF interpreter or BPF JIT compiler depending on the 1835 current setting. This is in particular useful for BPF JIT compiler 1836 development, but also to run regression tests against changes in 1837 the interpreter code. It also enables test stubs for eBPF maps and 1838 verifier used by user space verifier testsuite. 1839 1840 If unsure, say N. 1841 1842config TEST_FIRMWARE 1843 tristate "Test firmware loading via userspace interface" 1844 default n 1845 depends on FW_LOADER 1846 help 1847 This builds the "test_firmware" module that creates a userspace 1848 interface for testing firmware loading. This can be used to 1849 control the triggering of firmware loading without needing an 1850 actual firmware-using device. The contents can be rechecked by 1851 userspace. 1852 1853 If unsure, say N. 1854 1855config TEST_SYSCTL 1856 tristate "sysctl test driver" 1857 default n 1858 depends on PROC_SYSCTL 1859 help 1860 This builds the "test_sysctl" module. This driver enables to test the 1861 proc sysctl interfaces available to drivers safely without affecting 1862 production knobs which might alter system functionality. 1863 1864 If unsure, say N. 1865 1866config TEST_UDELAY 1867 tristate "udelay test driver" 1868 default n 1869 help 1870 This builds the "udelay_test" module that helps to make sure 1871 that udelay() is working properly. 1872 1873 If unsure, say N. 1874 1875config MEMTEST 1876 bool "Memtest" 1877 depends on HAVE_MEMBLOCK 1878 ---help--- 1879 This option adds a kernel parameter 'memtest', which allows memtest 1880 to be set. 1881 memtest=0, mean disabled; -- default 1882 memtest=1, mean do 1 test pattern; 1883 ... 1884 memtest=17, mean do 17 test patterns. 1885 If you are unsure how to answer this question, answer N. 1886 1887config TEST_STATIC_KEYS 1888 tristate "Test static keys" 1889 default n 1890 depends on m 1891 help 1892 Test the static key interfaces. 1893 1894 If unsure, say N. 1895 1896config BUG_ON_DATA_CORRUPTION 1897 bool "Trigger a BUG when data corruption is detected" 1898 select DEBUG_LIST 1899 help 1900 Select this option if the kernel should BUG when it encounters 1901 data corruption in kernel memory structures when they get checked 1902 for validity. 1903 1904 If unsure, say N. 1905 1906config TEST_KMOD 1907 tristate "kmod stress tester" 1908 default n 1909 depends on m 1910 depends on BLOCK && (64BIT || LBDAF) # for XFS, BTRFS 1911 depends on NETDEVICES && NET_CORE && INET # for TUN 1912 select TEST_LKM 1913 select XFS_FS 1914 select TUN 1915 select BTRFS_FS 1916 help 1917 Test the kernel's module loading mechanism: kmod. kmod implements 1918 support to load modules using the Linux kernel's usermode helper. 1919 This test provides a series of tests against kmod. 1920 1921 Although technically you can either build test_kmod as a module or 1922 into the kernel we disallow building it into the kernel since 1923 it stress tests request_module() and this will very likely cause 1924 some issues by taking over precious threads available from other 1925 module load requests, ultimately this could be fatal. 1926 1927 To run tests run: 1928 1929 tools/testing/selftests/kmod/kmod.sh --help 1930 1931 If unsure, say N. 1932 1933source "samples/Kconfig" 1934 1935source "lib/Kconfig.kgdb" 1936 1937source "lib/Kconfig.ubsan" 1938 1939config ARCH_HAS_DEVMEM_IS_ALLOWED 1940 bool 1941 1942config STRICT_DEVMEM 1943 bool "Filter access to /dev/mem" 1944 depends on MMU && DEVMEM 1945 depends on ARCH_HAS_DEVMEM_IS_ALLOWED 1946 default y if TILE || PPC 1947 ---help--- 1948 If this option is disabled, you allow userspace (root) access to all 1949 of memory, including kernel and userspace memory. Accidental 1950 access to this is obviously disastrous, but specific access can 1951 be used by people debugging the kernel. Note that with PAT support 1952 enabled, even in this case there are restrictions on /dev/mem 1953 use due to the cache aliasing requirements. 1954 1955 If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem 1956 file only allows userspace access to PCI space and the BIOS code and 1957 data regions. This is sufficient for dosemu and X and all common 1958 users of /dev/mem. 1959 1960 If in doubt, say Y. 1961 1962config IO_STRICT_DEVMEM 1963 bool "Filter I/O access to /dev/mem" 1964 depends on STRICT_DEVMEM 1965 ---help--- 1966 If this option is disabled, you allow userspace (root) access to all 1967 io-memory regardless of whether a driver is actively using that 1968 range. Accidental access to this is obviously disastrous, but 1969 specific access can be used by people debugging kernel drivers. 1970 1971 If this option is switched on, the /dev/mem file only allows 1972 userspace access to *idle* io-memory ranges (see /proc/iomem) This 1973 may break traditional users of /dev/mem (dosemu, legacy X, etc...) 1974 if the driver using a given range cannot be disabled. 1975 1976 If in doubt, say Y. 1977