xref: /openbmc/linux/lib/Kconfig.debug (revision 981ab3f1)
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	  For more information, see
378	  tools/objtool/Documentation/stack-validation.txt.
379
380config DEBUG_FORCE_WEAK_PER_CPU
381	bool "Force weak per-cpu definitions"
382	depends on DEBUG_KERNEL
383	help
384	  s390 and alpha require percpu variables in modules to be
385	  defined weak to work around addressing range issue which
386	  puts the following two restrictions on percpu variable
387	  definitions.
388
389	  1. percpu symbols must be unique whether static or not
390	  2. percpu variables can't be defined inside a function
391
392	  To ensure that generic code follows the above rules, this
393	  option forces all percpu variables to be defined as weak.
394
395endmenu # "Compiler options"
396
397config MAGIC_SYSRQ
398	bool "Magic SysRq key"
399	depends on !UML
400	help
401	  If you say Y here, you will have some control over the system even
402	  if the system crashes for example during kernel debugging (e.g., you
403	  will be able to flush the buffer cache to disk, reboot the system
404	  immediately or dump some status information). This is accomplished
405	  by pressing various keys while holding SysRq (Alt+PrintScreen). It
406	  also works on a serial console (on PC hardware at least), if you
407	  send a BREAK and then within 5 seconds a command keypress. The
408	  keys are documented in <file:Documentation/admin-guide/sysrq.rst>.
409	  Don't say Y unless you really know what this hack does.
410
411config MAGIC_SYSRQ_DEFAULT_ENABLE
412	hex "Enable magic SysRq key functions by default"
413	depends on MAGIC_SYSRQ
414	default 0x1
415	help
416	  Specifies which SysRq key functions are enabled by default.
417	  This may be set to 1 or 0 to enable or disable them all, or
418	  to a bitmask as described in Documentation/admin-guide/sysrq.rst.
419
420config MAGIC_SYSRQ_SERIAL
421	bool "Enable magic SysRq key over serial"
422	depends on MAGIC_SYSRQ
423	default y
424	help
425	  Many embedded boards have a disconnected TTL level serial which can
426	  generate some garbage that can lead to spurious false sysrq detects.
427	  This option allows you to decide whether you want to enable the
428	  magic SysRq key.
429
430config DEBUG_KERNEL
431	bool "Kernel debugging"
432	help
433	  Say Y here if you are developing drivers or trying to debug and
434	  identify kernel problems.
435
436menu "Memory Debugging"
437
438source mm/Kconfig.debug
439
440config DEBUG_OBJECTS
441	bool "Debug object operations"
442	depends on DEBUG_KERNEL
443	help
444	  If you say Y here, additional code will be inserted into the
445	  kernel to track the life time of various objects and validate
446	  the operations on those objects.
447
448config DEBUG_OBJECTS_SELFTEST
449	bool "Debug objects selftest"
450	depends on DEBUG_OBJECTS
451	help
452	  This enables the selftest of the object debug code.
453
454config DEBUG_OBJECTS_FREE
455	bool "Debug objects in freed memory"
456	depends on DEBUG_OBJECTS
457	help
458	  This enables checks whether a k/v free operation frees an area
459	  which contains an object which has not been deactivated
460	  properly. This can make kmalloc/kfree-intensive workloads
461	  much slower.
462
463config DEBUG_OBJECTS_TIMERS
464	bool "Debug timer objects"
465	depends on DEBUG_OBJECTS
466	help
467	  If you say Y here, additional code will be inserted into the
468	  timer routines to track the life time of timer objects and
469	  validate the timer operations.
470
471config DEBUG_OBJECTS_WORK
472	bool "Debug work objects"
473	depends on DEBUG_OBJECTS
474	help
475	  If you say Y here, additional code will be inserted into the
476	  work queue routines to track the life time of work objects and
477	  validate the work operations.
478
479config DEBUG_OBJECTS_RCU_HEAD
480	bool "Debug RCU callbacks objects"
481	depends on DEBUG_OBJECTS
482	help
483	  Enable this to turn on debugging of RCU list heads (call_rcu() usage).
484
485config DEBUG_OBJECTS_PERCPU_COUNTER
486	bool "Debug percpu counter objects"
487	depends on DEBUG_OBJECTS
488	help
489	  If you say Y here, additional code will be inserted into the
490	  percpu counter routines to track the life time of percpu counter
491	  objects and validate the percpu counter operations.
492
493config DEBUG_OBJECTS_ENABLE_DEFAULT
494	int "debug_objects bootup default value (0-1)"
495        range 0 1
496        default "1"
497        depends on DEBUG_OBJECTS
498        help
499          Debug objects boot parameter default value
500
501config DEBUG_SLAB
502	bool "Debug slab memory allocations"
503	depends on DEBUG_KERNEL && SLAB && !KMEMCHECK
504	help
505	  Say Y here to have the kernel do limited verification on memory
506	  allocation as well as poisoning memory on free to catch use of freed
507	  memory. This can make kmalloc/kfree-intensive workloads much slower.
508
509config DEBUG_SLAB_LEAK
510	bool "Memory leak debugging"
511	depends on DEBUG_SLAB
512
513config SLUB_DEBUG_ON
514	bool "SLUB debugging on by default"
515	depends on SLUB && SLUB_DEBUG && !KMEMCHECK
516	default n
517	help
518	  Boot with debugging on by default. SLUB boots by default with
519	  the runtime debug capabilities switched off. Enabling this is
520	  equivalent to specifying the "slub_debug" parameter on boot.
521	  There is no support for more fine grained debug control like
522	  possible with slub_debug=xxx. SLUB debugging may be switched
523	  off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying
524	  "slub_debug=-".
525
526config SLUB_STATS
527	default n
528	bool "Enable SLUB performance statistics"
529	depends on SLUB && SYSFS
530	help
531	  SLUB statistics are useful to debug SLUBs allocation behavior in
532	  order find ways to optimize the allocator. This should never be
533	  enabled for production use since keeping statistics slows down
534	  the allocator by a few percentage points. The slabinfo command
535	  supports the determination of the most active slabs to figure
536	  out which slabs are relevant to a particular load.
537	  Try running: slabinfo -DA
538
539config HAVE_DEBUG_KMEMLEAK
540	bool
541
542config DEBUG_KMEMLEAK
543	bool "Kernel memory leak detector"
544	depends on DEBUG_KERNEL && HAVE_DEBUG_KMEMLEAK
545	select DEBUG_FS
546	select STACKTRACE if STACKTRACE_SUPPORT
547	select KALLSYMS
548	select CRC32
549	help
550	  Say Y here if you want to enable the memory leak
551	  detector. The memory allocation/freeing is traced in a way
552	  similar to the Boehm's conservative garbage collector, the
553	  difference being that the orphan objects are not freed but
554	  only shown in /sys/kernel/debug/kmemleak. Enabling this
555	  feature will introduce an overhead to memory
556	  allocations. See Documentation/dev-tools/kmemleak.rst for more
557	  details.
558
559	  Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances
560	  of finding leaks due to the slab objects poisoning.
561
562	  In order to access the kmemleak file, debugfs needs to be
563	  mounted (usually at /sys/kernel/debug).
564
565config DEBUG_KMEMLEAK_EARLY_LOG_SIZE
566	int "Maximum kmemleak early log entries"
567	depends on DEBUG_KMEMLEAK
568	range 200 40000
569	default 400
570	help
571	  Kmemleak must track all the memory allocations to avoid
572	  reporting false positives. Since memory may be allocated or
573	  freed before kmemleak is initialised, an early log buffer is
574	  used to store these actions. If kmemleak reports "early log
575	  buffer exceeded", please increase this value.
576
577config DEBUG_KMEMLEAK_TEST
578	tristate "Simple test for the kernel memory leak detector"
579	depends on DEBUG_KMEMLEAK && m
580	help
581	  This option enables a module that explicitly leaks memory.
582
583	  If unsure, say N.
584
585config DEBUG_KMEMLEAK_DEFAULT_OFF
586	bool "Default kmemleak to off"
587	depends on DEBUG_KMEMLEAK
588	help
589	  Say Y here to disable kmemleak by default. It can then be enabled
590	  on the command line via kmemleak=on.
591
592config DEBUG_STACK_USAGE
593	bool "Stack utilization instrumentation"
594	depends on DEBUG_KERNEL && !IA64
595	help
596	  Enables the display of the minimum amount of free stack which each
597	  task has ever had available in the sysrq-T and sysrq-P debug output.
598
599	  This option will slow down process creation somewhat.
600
601config DEBUG_VM
602	bool "Debug VM"
603	depends on DEBUG_KERNEL
604	help
605	  Enable this to turn on extended checks in the virtual-memory system
606          that may impact performance.
607
608	  If unsure, say N.
609
610config DEBUG_VM_VMACACHE
611	bool "Debug VMA caching"
612	depends on DEBUG_VM
613	help
614	  Enable this to turn on VMA caching debug information. Doing so
615	  can cause significant overhead, so only enable it in non-production
616	  environments.
617
618	  If unsure, say N.
619
620config DEBUG_VM_RB
621	bool "Debug VM red-black trees"
622	depends on DEBUG_VM
623	help
624	  Enable VM red-black tree debugging information and extra validations.
625
626	  If unsure, say N.
627
628config DEBUG_VM_PGFLAGS
629	bool "Debug page-flags operations"
630	depends on DEBUG_VM
631	help
632	  Enables extra validation on page flags operations.
633
634	  If unsure, say N.
635
636config ARCH_HAS_DEBUG_VIRTUAL
637	bool
638
639config DEBUG_VIRTUAL
640	bool "Debug VM translations"
641	depends on DEBUG_KERNEL && ARCH_HAS_DEBUG_VIRTUAL
642	help
643	  Enable some costly sanity checks in virtual to page code. This can
644	  catch mistakes with virt_to_page() and friends.
645
646	  If unsure, say N.
647
648config DEBUG_NOMMU_REGIONS
649	bool "Debug the global anon/private NOMMU mapping region tree"
650	depends on DEBUG_KERNEL && !MMU
651	help
652	  This option causes the global tree of anonymous and private mapping
653	  regions to be regularly checked for invalid topology.
654
655config DEBUG_MEMORY_INIT
656	bool "Debug memory initialisation" if EXPERT
657	default !EXPERT
658	help
659	  Enable this for additional checks during memory initialisation.
660	  The sanity checks verify aspects of the VM such as the memory model
661	  and other information provided by the architecture. Verbose
662	  information will be printed at KERN_DEBUG loglevel depending
663	  on the mminit_loglevel= command-line option.
664
665	  If unsure, say Y
666
667config MEMORY_NOTIFIER_ERROR_INJECT
668	tristate "Memory hotplug notifier error injection module"
669	depends on MEMORY_HOTPLUG_SPARSE && NOTIFIER_ERROR_INJECTION
670	help
671	  This option provides the ability to inject artificial errors to
672	  memory hotplug notifier chain callbacks.  It is controlled through
673	  debugfs interface under /sys/kernel/debug/notifier-error-inject/memory
674
675	  If the notifier call chain should be failed with some events
676	  notified, write the error code to "actions/<notifier event>/error".
677
678	  Example: Inject memory hotplug offline error (-12 == -ENOMEM)
679
680	  # cd /sys/kernel/debug/notifier-error-inject/memory
681	  # echo -12 > actions/MEM_GOING_OFFLINE/error
682	  # echo offline > /sys/devices/system/memory/memoryXXX/state
683	  bash: echo: write error: Cannot allocate memory
684
685	  To compile this code as a module, choose M here: the module will
686	  be called memory-notifier-error-inject.
687
688	  If unsure, say N.
689
690config DEBUG_PER_CPU_MAPS
691	bool "Debug access to per_cpu maps"
692	depends on DEBUG_KERNEL
693	depends on SMP
694	help
695	  Say Y to verify that the per_cpu map being accessed has
696	  been set up. This adds a fair amount of code to kernel memory
697	  and decreases performance.
698
699	  Say N if unsure.
700
701config DEBUG_HIGHMEM
702	bool "Highmem debugging"
703	depends on DEBUG_KERNEL && HIGHMEM
704	help
705	  This option enables additional error checking for high memory
706	  systems.  Disable for production systems.
707
708config HAVE_DEBUG_STACKOVERFLOW
709	bool
710
711config DEBUG_STACKOVERFLOW
712	bool "Check for stack overflows"
713	depends on DEBUG_KERNEL && HAVE_DEBUG_STACKOVERFLOW
714	---help---
715	  Say Y here if you want to check for overflows of kernel, IRQ
716	  and exception stacks (if your architecture uses them). This
717	  option will show detailed messages if free stack space drops
718	  below a certain limit.
719
720	  These kinds of bugs usually occur when call-chains in the
721	  kernel get too deep, especially when interrupts are
722	  involved.
723
724	  Use this in cases where you see apparently random memory
725	  corruption, especially if it appears in 'struct thread_info'
726
727	  If in doubt, say "N".
728
729source "lib/Kconfig.kmemcheck"
730
731source "lib/Kconfig.kasan"
732
733endmenu # "Memory Debugging"
734
735config ARCH_HAS_KCOV
736	bool
737	help
738	  KCOV does not have any arch-specific code, but currently it is enabled
739	  only for x86_64. KCOV requires testing on other archs, and most likely
740	  disabling of instrumentation for some early boot code.
741
742config KCOV
743	bool "Code coverage for fuzzing"
744	depends on ARCH_HAS_KCOV
745	select DEBUG_FS
746	select GCC_PLUGINS if !COMPILE_TEST
747	select GCC_PLUGIN_SANCOV if !COMPILE_TEST
748	help
749	  KCOV exposes kernel code coverage information in a form suitable
750	  for coverage-guided fuzzing (randomized testing).
751
752	  If RANDOMIZE_BASE is enabled, PC values will not be stable across
753	  different machines and across reboots. If you need stable PC values,
754	  disable RANDOMIZE_BASE.
755
756	  For more details, see Documentation/dev-tools/kcov.rst.
757
758config KCOV_INSTRUMENT_ALL
759	bool "Instrument all code by default"
760	depends on KCOV
761	default y if KCOV
762	help
763	  If you are doing generic system call fuzzing (like e.g. syzkaller),
764	  then you will want to instrument the whole kernel and you should
765	  say y here. If you are doing more targeted fuzzing (like e.g.
766	  filesystem fuzzing with AFL) then you will want to enable coverage
767	  for more specific subsets of files, and should say n here.
768
769config DEBUG_SHIRQ
770	bool "Debug shared IRQ handlers"
771	depends on DEBUG_KERNEL
772	help
773	  Enable this to generate a spurious interrupt as soon as a shared
774	  interrupt handler is registered, and just before one is deregistered.
775	  Drivers ought to be able to handle interrupts coming in at those
776	  points; some don't and need to be caught.
777
778menu "Debug Lockups and Hangs"
779
780config LOCKUP_DETECTOR
781	bool
782
783config SOFTLOCKUP_DETECTOR
784	bool "Detect Soft Lockups"
785	depends on DEBUG_KERNEL && !S390
786	select LOCKUP_DETECTOR
787	help
788	  Say Y here to enable the kernel to act as a watchdog to detect
789	  soft lockups.
790
791	  Softlockups are bugs that cause the kernel to loop in kernel
792	  mode for more than 20 seconds, without giving other tasks a
793	  chance to run.  The current stack trace is displayed upon
794	  detection and the system will stay locked up.
795
796config HARDLOCKUP_DETECTOR_PERF
797	bool
798	select SOFTLOCKUP_DETECTOR
799
800#
801# arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their own hard
802# lockup detector rather than the perf based detector.
803#
804config HARDLOCKUP_DETECTOR
805	bool "Detect Hard Lockups"
806	depends on DEBUG_KERNEL && !S390
807	depends on HAVE_HARDLOCKUP_DETECTOR_PERF || HAVE_HARDLOCKUP_DETECTOR_ARCH
808	select LOCKUP_DETECTOR
809	select HARDLOCKUP_DETECTOR_PERF if HAVE_HARDLOCKUP_DETECTOR_PERF
810	select HARDLOCKUP_DETECTOR_ARCH if HAVE_HARDLOCKUP_DETECTOR_ARCH
811	help
812	  Say Y here to enable the kernel to act as a watchdog to detect
813	  hard lockups.
814
815	  Hardlockups are bugs that cause the CPU to loop in kernel mode
816	  for more than 10 seconds, without letting other interrupts have a
817	  chance to run.  The current stack trace is displayed upon detection
818	  and the system will stay locked up.
819
820config BOOTPARAM_HARDLOCKUP_PANIC
821	bool "Panic (Reboot) On Hard Lockups"
822	depends on HARDLOCKUP_DETECTOR
823	help
824	  Say Y here to enable the kernel to panic on "hard lockups",
825	  which are bugs that cause the kernel to loop in kernel
826	  mode with interrupts disabled for more than 10 seconds (configurable
827	  using the watchdog_thresh sysctl).
828
829	  Say N if unsure.
830
831config BOOTPARAM_HARDLOCKUP_PANIC_VALUE
832	int
833	depends on HARDLOCKUP_DETECTOR
834	range 0 1
835	default 0 if !BOOTPARAM_HARDLOCKUP_PANIC
836	default 1 if BOOTPARAM_HARDLOCKUP_PANIC
837
838config BOOTPARAM_SOFTLOCKUP_PANIC
839	bool "Panic (Reboot) On Soft Lockups"
840	depends on SOFTLOCKUP_DETECTOR
841	help
842	  Say Y here to enable the kernel to panic on "soft lockups",
843	  which are bugs that cause the kernel to loop in kernel
844	  mode for more than 20 seconds (configurable using the watchdog_thresh
845	  sysctl), without giving other tasks a chance to run.
846
847	  The panic can be used in combination with panic_timeout,
848	  to cause the system to reboot automatically after a
849	  lockup has been detected. This feature is useful for
850	  high-availability systems that have uptime guarantees and
851	  where a lockup must be resolved ASAP.
852
853	  Say N if unsure.
854
855config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
856	int
857	depends on SOFTLOCKUP_DETECTOR
858	range 0 1
859	default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC
860	default 1 if BOOTPARAM_SOFTLOCKUP_PANIC
861
862config DETECT_HUNG_TASK
863	bool "Detect Hung Tasks"
864	depends on DEBUG_KERNEL
865	default SOFTLOCKUP_DETECTOR
866	help
867	  Say Y here to enable the kernel to detect "hung tasks",
868	  which are bugs that cause the task to be stuck in
869	  uninterruptible "D" state indefinitely.
870
871	  When a hung task is detected, the kernel will print the
872	  current stack trace (which you should report), but the
873	  task will stay in uninterruptible state. If lockdep is
874	  enabled then all held locks will also be reported. This
875	  feature has negligible overhead.
876
877config DEFAULT_HUNG_TASK_TIMEOUT
878	int "Default timeout for hung task detection (in seconds)"
879	depends on DETECT_HUNG_TASK
880	default 120
881	help
882	  This option controls the default timeout (in seconds) used
883	  to determine when a task has become non-responsive and should
884	  be considered hung.
885
886	  It can be adjusted at runtime via the kernel.hung_task_timeout_secs
887	  sysctl or by writing a value to
888	  /proc/sys/kernel/hung_task_timeout_secs.
889
890	  A timeout of 0 disables the check.  The default is two minutes.
891	  Keeping the default should be fine in most cases.
892
893config BOOTPARAM_HUNG_TASK_PANIC
894	bool "Panic (Reboot) On Hung Tasks"
895	depends on DETECT_HUNG_TASK
896	help
897	  Say Y here to enable the kernel to panic on "hung tasks",
898	  which are bugs that cause the kernel to leave a task stuck
899	  in uninterruptible "D" state.
900
901	  The panic can be used in combination with panic_timeout,
902	  to cause the system to reboot automatically after a
903	  hung task has been detected. This feature is useful for
904	  high-availability systems that have uptime guarantees and
905	  where a hung tasks must be resolved ASAP.
906
907	  Say N if unsure.
908
909config BOOTPARAM_HUNG_TASK_PANIC_VALUE
910	int
911	depends on DETECT_HUNG_TASK
912	range 0 1
913	default 0 if !BOOTPARAM_HUNG_TASK_PANIC
914	default 1 if BOOTPARAM_HUNG_TASK_PANIC
915
916config WQ_WATCHDOG
917	bool "Detect Workqueue Stalls"
918	depends on DEBUG_KERNEL
919	help
920	  Say Y here to enable stall detection on workqueues.  If a
921	  worker pool doesn't make forward progress on a pending work
922	  item for over a given amount of time, 30s by default, a
923	  warning message is printed along with dump of workqueue
924	  state.  This can be configured through kernel parameter
925	  "workqueue.watchdog_thresh" and its sysfs counterpart.
926
927endmenu # "Debug lockups and hangs"
928
929config PANIC_ON_OOPS
930	bool "Panic on Oops"
931	help
932	  Say Y here to enable the kernel to panic when it oopses. This
933	  has the same effect as setting oops=panic on the kernel command
934	  line.
935
936	  This feature is useful to ensure that the kernel does not do
937	  anything erroneous after an oops which could result in data
938	  corruption or other issues.
939
940	  Say N if unsure.
941
942config PANIC_ON_OOPS_VALUE
943	int
944	range 0 1
945	default 0 if !PANIC_ON_OOPS
946	default 1 if PANIC_ON_OOPS
947
948config PANIC_TIMEOUT
949	int "panic timeout"
950	default 0
951	help
952	  Set the timeout value (in seconds) until a reboot occurs when the
953	  the kernel panics. If n = 0, then we wait forever. A timeout
954	  value n > 0 will wait n seconds before rebooting, while a timeout
955	  value n < 0 will reboot immediately.
956
957config SCHED_DEBUG
958	bool "Collect scheduler debugging info"
959	depends on DEBUG_KERNEL && PROC_FS
960	default y
961	help
962	  If you say Y here, the /proc/sched_debug file will be provided
963	  that can help debug the scheduler. The runtime overhead of this
964	  option is minimal.
965
966config SCHED_INFO
967	bool
968	default n
969
970config SCHEDSTATS
971	bool "Collect scheduler statistics"
972	depends on DEBUG_KERNEL && PROC_FS
973	select SCHED_INFO
974	help
975	  If you say Y here, additional code will be inserted into the
976	  scheduler and related routines to collect statistics about
977	  scheduler behavior and provide them in /proc/schedstat.  These
978	  stats may be useful for both tuning and debugging the scheduler
979	  If you aren't debugging the scheduler or trying to tune a specific
980	  application, you can say N to avoid the very slight overhead
981	  this adds.
982
983config SCHED_STACK_END_CHECK
984	bool "Detect stack corruption on calls to schedule()"
985	depends on DEBUG_KERNEL
986	default n
987	help
988	  This option checks for a stack overrun on calls to schedule().
989	  If the stack end location is found to be over written always panic as
990	  the content of the corrupted region can no longer be trusted.
991	  This is to ensure no erroneous behaviour occurs which could result in
992	  data corruption or a sporadic crash at a later stage once the region
993	  is examined. The runtime overhead introduced is minimal.
994
995config DEBUG_TIMEKEEPING
996	bool "Enable extra timekeeping sanity checking"
997	help
998	  This option will enable additional timekeeping sanity checks
999	  which may be helpful when diagnosing issues where timekeeping
1000	  problems are suspected.
1001
1002	  This may include checks in the timekeeping hotpaths, so this
1003	  option may have a (very small) performance impact to some
1004	  workloads.
1005
1006	  If unsure, say N.
1007
1008config DEBUG_PREEMPT
1009	bool "Debug preemptible kernel"
1010	depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT
1011	default y
1012	help
1013	  If you say Y here then the kernel will use a debug variant of the
1014	  commonly used smp_processor_id() function and will print warnings
1015	  if kernel code uses it in a preemption-unsafe way. Also, the kernel
1016	  will detect preemption count underflows.
1017
1018menu "Lock Debugging (spinlocks, mutexes, etc...)"
1019
1020config DEBUG_RT_MUTEXES
1021	bool "RT Mutex debugging, deadlock detection"
1022	depends on DEBUG_KERNEL && RT_MUTEXES
1023	help
1024	 This allows rt mutex semantics violations and rt mutex related
1025	 deadlocks (lockups) to be detected and reported automatically.
1026
1027config DEBUG_SPINLOCK
1028	bool "Spinlock and rw-lock debugging: basic checks"
1029	depends on DEBUG_KERNEL
1030	select UNINLINE_SPIN_UNLOCK
1031	help
1032	  Say Y here and build SMP to catch missing spinlock initialization
1033	  and certain other kinds of spinlock errors commonly made.  This is
1034	  best used in conjunction with the NMI watchdog so that spinlock
1035	  deadlocks are also debuggable.
1036
1037config DEBUG_MUTEXES
1038	bool "Mutex debugging: basic checks"
1039	depends on DEBUG_KERNEL
1040	help
1041	 This feature allows mutex semantics violations to be detected and
1042	 reported.
1043
1044config DEBUG_WW_MUTEX_SLOWPATH
1045	bool "Wait/wound mutex debugging: Slowpath testing"
1046	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
1047	select DEBUG_LOCK_ALLOC
1048	select DEBUG_SPINLOCK
1049	select DEBUG_MUTEXES
1050	help
1051	 This feature enables slowpath testing for w/w mutex users by
1052	 injecting additional -EDEADLK wound/backoff cases. Together with
1053	 the full mutex checks enabled with (CONFIG_PROVE_LOCKING) this
1054	 will test all possible w/w mutex interface abuse with the
1055	 exception of simply not acquiring all the required locks.
1056	 Note that this feature can introduce significant overhead, so
1057	 it really should not be enabled in a production or distro kernel,
1058	 even a debug kernel.  If you are a driver writer, enable it.  If
1059	 you are a distro, do not.
1060
1061config DEBUG_LOCK_ALLOC
1062	bool "Lock debugging: detect incorrect freeing of live locks"
1063	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
1064	select DEBUG_SPINLOCK
1065	select DEBUG_MUTEXES
1066	select DEBUG_RT_MUTEXES if RT_MUTEXES
1067	select LOCKDEP
1068	help
1069	 This feature will check whether any held lock (spinlock, rwlock,
1070	 mutex or rwsem) is incorrectly freed by the kernel, via any of the
1071	 memory-freeing routines (kfree(), kmem_cache_free(), free_pages(),
1072	 vfree(), etc.), whether a live lock is incorrectly reinitialized via
1073	 spin_lock_init()/mutex_init()/etc., or whether there is any lock
1074	 held during task exit.
1075
1076config PROVE_LOCKING
1077	bool "Lock debugging: prove locking correctness"
1078	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
1079	select LOCKDEP
1080	select DEBUG_SPINLOCK
1081	select DEBUG_MUTEXES
1082	select DEBUG_RT_MUTEXES if RT_MUTEXES
1083	select DEBUG_LOCK_ALLOC
1084	select TRACE_IRQFLAGS
1085	default n
1086	help
1087	 This feature enables the kernel to prove that all locking
1088	 that occurs in the kernel runtime is mathematically
1089	 correct: that under no circumstance could an arbitrary (and
1090	 not yet triggered) combination of observed locking
1091	 sequences (on an arbitrary number of CPUs, running an
1092	 arbitrary number of tasks and interrupt contexts) cause a
1093	 deadlock.
1094
1095	 In short, this feature enables the kernel to report locking
1096	 related deadlocks before they actually occur.
1097
1098	 The proof does not depend on how hard and complex a
1099	 deadlock scenario would be to trigger: how many
1100	 participant CPUs, tasks and irq-contexts would be needed
1101	 for it to trigger. The proof also does not depend on
1102	 timing: if a race and a resulting deadlock is possible
1103	 theoretically (no matter how unlikely the race scenario
1104	 is), it will be proven so and will immediately be
1105	 reported by the kernel (once the event is observed that
1106	 makes the deadlock theoretically possible).
1107
1108	 If a deadlock is impossible (i.e. the locking rules, as
1109	 observed by the kernel, are mathematically correct), the
1110	 kernel reports nothing.
1111
1112	 NOTE: this feature can also be enabled for rwlocks, mutexes
1113	 and rwsems - in which case all dependencies between these
1114	 different locking variants are observed and mapped too, and
1115	 the proof of observed correctness is also maintained for an
1116	 arbitrary combination of these separate locking variants.
1117
1118	 For more details, see Documentation/locking/lockdep-design.txt.
1119
1120config LOCKDEP
1121	bool
1122	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
1123	select STACKTRACE
1124	select FRAME_POINTER if !MIPS && !PPC && !ARM_UNWIND && !S390 && !MICROBLAZE && !ARC && !SCORE
1125	select KALLSYMS
1126	select KALLSYMS_ALL
1127
1128config LOCKDEP_SMALL
1129	bool
1130
1131config LOCK_STAT
1132	bool "Lock usage statistics"
1133	depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
1134	select LOCKDEP
1135	select DEBUG_SPINLOCK
1136	select DEBUG_MUTEXES
1137	select DEBUG_RT_MUTEXES if RT_MUTEXES
1138	select DEBUG_LOCK_ALLOC
1139	default n
1140	help
1141	 This feature enables tracking lock contention points
1142
1143	 For more details, see Documentation/locking/lockstat.txt
1144
1145	 This also enables lock events required by "perf lock",
1146	 subcommand of perf.
1147	 If you want to use "perf lock", you also need to turn on
1148	 CONFIG_EVENT_TRACING.
1149
1150	 CONFIG_LOCK_STAT defines "contended" and "acquired" lock events.
1151	 (CONFIG_LOCKDEP defines "acquire" and "release" events.)
1152
1153config DEBUG_LOCKDEP
1154	bool "Lock dependency engine debugging"
1155	depends on DEBUG_KERNEL && LOCKDEP
1156	help
1157	  If you say Y here, the lock dependency engine will do
1158	  additional runtime checks to debug itself, at the price
1159	  of more runtime overhead.
1160
1161config DEBUG_ATOMIC_SLEEP
1162	bool "Sleep inside atomic section checking"
1163	select PREEMPT_COUNT
1164	depends on DEBUG_KERNEL
1165	help
1166	  If you say Y here, various routines which may sleep will become very
1167	  noisy if they are called inside atomic sections: when a spinlock is
1168	  held, inside an rcu read side critical section, inside preempt disabled
1169	  sections, inside an interrupt, etc...
1170
1171config DEBUG_LOCKING_API_SELFTESTS
1172	bool "Locking API boot-time self-tests"
1173	depends on DEBUG_KERNEL
1174	help
1175	  Say Y here if you want the kernel to run a short self-test during
1176	  bootup. The self-test checks whether common types of locking bugs
1177	  are detected by debugging mechanisms or not. (if you disable
1178	  lock debugging then those bugs wont be detected of course.)
1179	  The following locking APIs are covered: spinlocks, rwlocks,
1180	  mutexes and rwsems.
1181
1182config LOCK_TORTURE_TEST
1183	tristate "torture tests for locking"
1184	depends on DEBUG_KERNEL
1185	select TORTURE_TEST
1186	default n
1187	help
1188	  This option provides a kernel module that runs torture tests
1189	  on kernel locking primitives.  The kernel module may be built
1190	  after the fact on the running kernel to be tested, if desired.
1191
1192	  Say Y here if you want kernel locking-primitive torture tests
1193	  to be built into the kernel.
1194	  Say M if you want these torture tests to build as a module.
1195	  Say N if you are unsure.
1196
1197config WW_MUTEX_SELFTEST
1198	tristate "Wait/wound mutex selftests"
1199	help
1200	  This option provides a kernel module that runs tests on the
1201	  on the struct ww_mutex locking API.
1202
1203	  It is recommended to enable DEBUG_WW_MUTEX_SLOWPATH in conjunction
1204	  with this test harness.
1205
1206	  Say M if you want these self tests to build as a module.
1207	  Say N if you are unsure.
1208
1209endmenu # lock debugging
1210
1211config TRACE_IRQFLAGS
1212	bool
1213	help
1214	  Enables hooks to interrupt enabling and disabling for
1215	  either tracing or lock debugging.
1216
1217config STACKTRACE
1218	bool "Stack backtrace support"
1219	depends on STACKTRACE_SUPPORT
1220	help
1221	  This option causes the kernel to create a /proc/pid/stack for
1222	  every process, showing its current stack trace.
1223	  It is also used by various kernel debugging features that require
1224	  stack trace generation.
1225
1226config WARN_ALL_UNSEEDED_RANDOM
1227	bool "Warn for all uses of unseeded randomness"
1228	default n
1229	help
1230	  Some parts of the kernel contain bugs relating to their use of
1231	  cryptographically secure random numbers before it's actually possible
1232	  to generate those numbers securely. This setting ensures that these
1233	  flaws don't go unnoticed, by enabling a message, should this ever
1234	  occur. This will allow people with obscure setups to know when things
1235	  are going wrong, so that they might contact developers about fixing
1236	  it.
1237
1238	  Unfortunately, on some models of some architectures getting
1239	  a fully seeded CRNG is extremely difficult, and so this can
1240	  result in dmesg getting spammed for a surprisingly long
1241	  time.  This is really bad from a security perspective, and
1242	  so architecture maintainers really need to do what they can
1243	  to get the CRNG seeded sooner after the system is booted.
1244	  However, since users can not do anything actionble to
1245	  address this, by default the kernel will issue only a single
1246	  warning for the first use of unseeded randomness.
1247
1248	  Say Y here if you want to receive warnings for all uses of
1249	  unseeded randomness.  This will be of use primarily for
1250	  those developers interersted in improving the security of
1251	  Linux kernels running on their architecture (or
1252	  subarchitecture).
1253
1254config DEBUG_KOBJECT
1255	bool "kobject debugging"
1256	depends on DEBUG_KERNEL
1257	help
1258	  If you say Y here, some extra kobject debugging messages will be sent
1259	  to the syslog.
1260
1261config DEBUG_KOBJECT_RELEASE
1262	bool "kobject release debugging"
1263	depends on DEBUG_OBJECTS_TIMERS
1264	help
1265	  kobjects are reference counted objects.  This means that their
1266	  last reference count put is not predictable, and the kobject can
1267	  live on past the point at which a driver decides to drop it's
1268	  initial reference to the kobject gained on allocation.  An
1269	  example of this would be a struct device which has just been
1270	  unregistered.
1271
1272	  However, some buggy drivers assume that after such an operation,
1273	  the memory backing the kobject can be immediately freed.  This
1274	  goes completely against the principles of a refcounted object.
1275
1276	  If you say Y here, the kernel will delay the release of kobjects
1277	  on the last reference count to improve the visibility of this
1278	  kind of kobject release bug.
1279
1280config HAVE_DEBUG_BUGVERBOSE
1281	bool
1282
1283config DEBUG_BUGVERBOSE
1284	bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EXPERT
1285	depends on BUG && (GENERIC_BUG || HAVE_DEBUG_BUGVERBOSE)
1286	default y
1287	help
1288	  Say Y here to make BUG() panics output the file name and line number
1289	  of the BUG call as well as the EIP and oops trace.  This aids
1290	  debugging but costs about 70-100K of memory.
1291
1292config DEBUG_LIST
1293	bool "Debug linked list manipulation"
1294	depends on DEBUG_KERNEL || BUG_ON_DATA_CORRUPTION
1295	help
1296	  Enable this to turn on extended checks in the linked-list
1297	  walking routines.
1298
1299	  If unsure, say N.
1300
1301config DEBUG_PI_LIST
1302	bool "Debug priority linked list manipulation"
1303	depends on DEBUG_KERNEL
1304	help
1305	  Enable this to turn on extended checks in the priority-ordered
1306	  linked-list (plist) walking routines.  This checks the entire
1307	  list multiple times during each manipulation.
1308
1309	  If unsure, say N.
1310
1311config DEBUG_SG
1312	bool "Debug SG table operations"
1313	depends on DEBUG_KERNEL
1314	help
1315	  Enable this to turn on checks on scatter-gather tables. This can
1316	  help find problems with drivers that do not properly initialize
1317	  their sg tables.
1318
1319	  If unsure, say N.
1320
1321config DEBUG_NOTIFIERS
1322	bool "Debug notifier call chains"
1323	depends on DEBUG_KERNEL
1324	help
1325	  Enable this to turn on sanity checking for notifier call chains.
1326	  This is most useful for kernel developers to make sure that
1327	  modules properly unregister themselves from notifier chains.
1328	  This is a relatively cheap check but if you care about maximum
1329	  performance, say N.
1330
1331config DEBUG_CREDENTIALS
1332	bool "Debug credential management"
1333	depends on DEBUG_KERNEL
1334	help
1335	  Enable this to turn on some debug checking for credential
1336	  management.  The additional code keeps track of the number of
1337	  pointers from task_structs to any given cred struct, and checks to
1338	  see that this number never exceeds the usage count of the cred
1339	  struct.
1340
1341	  Furthermore, if SELinux is enabled, this also checks that the
1342	  security pointer in the cred struct is never seen to be invalid.
1343
1344	  If unsure, say N.
1345
1346source "kernel/rcu/Kconfig.debug"
1347
1348config DEBUG_WQ_FORCE_RR_CPU
1349	bool "Force round-robin CPU selection for unbound work items"
1350	depends on DEBUG_KERNEL
1351	default n
1352	help
1353	  Workqueue used to implicitly guarantee that work items queued
1354	  without explicit CPU specified are put on the local CPU.  This
1355	  guarantee is no longer true and while local CPU is still
1356	  preferred work items may be put on foreign CPUs.  Kernel
1357	  parameter "workqueue.debug_force_rr_cpu" is added to force
1358	  round-robin CPU selection to flush out usages which depend on the
1359	  now broken guarantee.  This config option enables the debug
1360	  feature by default.  When enabled, memory and cache locality will
1361	  be impacted.
1362
1363config DEBUG_BLOCK_EXT_DEVT
1364        bool "Force extended block device numbers and spread them"
1365	depends on DEBUG_KERNEL
1366	depends on BLOCK
1367	default n
1368	help
1369	  BIG FAT WARNING: ENABLING THIS OPTION MIGHT BREAK BOOTING ON
1370	  SOME DISTRIBUTIONS.  DO NOT ENABLE THIS UNLESS YOU KNOW WHAT
1371	  YOU ARE DOING.  Distros, please enable this and fix whatever
1372	  is broken.
1373
1374	  Conventionally, block device numbers are allocated from
1375	  predetermined contiguous area.  However, extended block area
1376	  may introduce non-contiguous block device numbers.  This
1377	  option forces most block device numbers to be allocated from
1378	  the extended space and spreads them to discover kernel or
1379	  userland code paths which assume predetermined contiguous
1380	  device number allocation.
1381
1382	  Note that turning on this debug option shuffles all the
1383	  device numbers for all IDE and SCSI devices including libata
1384	  ones, so root partition specified using device number
1385	  directly (via rdev or root=MAJ:MIN) won't work anymore.
1386	  Textual device names (root=/dev/sdXn) will continue to work.
1387
1388	  Say N if you are unsure.
1389
1390config CPU_HOTPLUG_STATE_CONTROL
1391	bool "Enable CPU hotplug state control"
1392	depends on DEBUG_KERNEL
1393	depends on HOTPLUG_CPU
1394	default n
1395	help
1396	  Allows to write steps between "offline" and "online" to the CPUs
1397	  sysfs target file so states can be stepped granular. This is a debug
1398	  option for now as the hotplug machinery cannot be stopped and
1399	  restarted at arbitrary points yet.
1400
1401	  Say N if your are unsure.
1402
1403config NOTIFIER_ERROR_INJECTION
1404	tristate "Notifier error injection"
1405	depends on DEBUG_KERNEL
1406	select DEBUG_FS
1407	help
1408	  This option provides the ability to inject artificial errors to
1409	  specified notifier chain callbacks. It is useful to test the error
1410	  handling of notifier call chain failures.
1411
1412	  Say N if unsure.
1413
1414config PM_NOTIFIER_ERROR_INJECT
1415	tristate "PM notifier error injection module"
1416	depends on PM && NOTIFIER_ERROR_INJECTION
1417	default m if PM_DEBUG
1418	help
1419	  This option provides the ability to inject artificial errors to
1420	  PM notifier chain callbacks.  It is controlled through debugfs
1421	  interface /sys/kernel/debug/notifier-error-inject/pm
1422
1423	  If the notifier call chain should be failed with some events
1424	  notified, write the error code to "actions/<notifier event>/error".
1425
1426	  Example: Inject PM suspend error (-12 = -ENOMEM)
1427
1428	  # cd /sys/kernel/debug/notifier-error-inject/pm/
1429	  # echo -12 > actions/PM_SUSPEND_PREPARE/error
1430	  # echo mem > /sys/power/state
1431	  bash: echo: write error: Cannot allocate memory
1432
1433	  To compile this code as a module, choose M here: the module will
1434	  be called pm-notifier-error-inject.
1435
1436	  If unsure, say N.
1437
1438config OF_RECONFIG_NOTIFIER_ERROR_INJECT
1439	tristate "OF reconfig notifier error injection module"
1440	depends on OF_DYNAMIC && NOTIFIER_ERROR_INJECTION
1441	help
1442	  This option provides the ability to inject artificial errors to
1443	  OF reconfig notifier chain callbacks.  It is controlled
1444	  through debugfs interface under
1445	  /sys/kernel/debug/notifier-error-inject/OF-reconfig/
1446
1447	  If the notifier call chain should be failed with some events
1448	  notified, write the error code to "actions/<notifier event>/error".
1449
1450	  To compile this code as a module, choose M here: the module will
1451	  be called of-reconfig-notifier-error-inject.
1452
1453	  If unsure, say N.
1454
1455config NETDEV_NOTIFIER_ERROR_INJECT
1456	tristate "Netdev notifier error injection module"
1457	depends on NET && NOTIFIER_ERROR_INJECTION
1458	help
1459	  This option provides the ability to inject artificial errors to
1460	  netdevice notifier chain callbacks.  It is controlled through debugfs
1461	  interface /sys/kernel/debug/notifier-error-inject/netdev
1462
1463	  If the notifier call chain should be failed with some events
1464	  notified, write the error code to "actions/<notifier event>/error".
1465
1466	  Example: Inject netdevice mtu change error (-22 = -EINVAL)
1467
1468	  # cd /sys/kernel/debug/notifier-error-inject/netdev
1469	  # echo -22 > actions/NETDEV_CHANGEMTU/error
1470	  # ip link set eth0 mtu 1024
1471	  RTNETLINK answers: Invalid argument
1472
1473	  To compile this code as a module, choose M here: the module will
1474	  be called netdev-notifier-error-inject.
1475
1476	  If unsure, say N.
1477
1478config FAULT_INJECTION
1479	bool "Fault-injection framework"
1480	depends on DEBUG_KERNEL
1481	help
1482	  Provide fault-injection framework.
1483	  For more details, see Documentation/fault-injection/.
1484
1485config FAILSLAB
1486	bool "Fault-injection capability for kmalloc"
1487	depends on FAULT_INJECTION
1488	depends on SLAB || SLUB
1489	help
1490	  Provide fault-injection capability for kmalloc.
1491
1492config FAIL_PAGE_ALLOC
1493	bool "Fault-injection capabilitiy for alloc_pages()"
1494	depends on FAULT_INJECTION
1495	help
1496	  Provide fault-injection capability for alloc_pages().
1497
1498config FAIL_MAKE_REQUEST
1499	bool "Fault-injection capability for disk IO"
1500	depends on FAULT_INJECTION && BLOCK
1501	help
1502	  Provide fault-injection capability for disk IO.
1503
1504config FAIL_IO_TIMEOUT
1505	bool "Fault-injection capability for faking disk interrupts"
1506	depends on FAULT_INJECTION && BLOCK
1507	help
1508	  Provide fault-injection capability on end IO handling. This
1509	  will make the block layer "forget" an interrupt as configured,
1510	  thus exercising the error handling.
1511
1512	  Only works with drivers that use the generic timeout handling,
1513	  for others it wont do anything.
1514
1515config FAIL_MMC_REQUEST
1516	bool "Fault-injection capability for MMC IO"
1517	depends on FAULT_INJECTION_DEBUG_FS && MMC
1518	help
1519	  Provide fault-injection capability for MMC IO.
1520	  This will make the mmc core return data errors. This is
1521	  useful to test the error handling in the mmc block device
1522	  and to test how the mmc host driver handles retries from
1523	  the block device.
1524
1525config FAIL_FUTEX
1526	bool "Fault-injection capability for futexes"
1527	select DEBUG_FS
1528	depends on FAULT_INJECTION && FUTEX
1529	help
1530	  Provide fault-injection capability for futexes.
1531
1532config FAULT_INJECTION_DEBUG_FS
1533	bool "Debugfs entries for fault-injection capabilities"
1534	depends on FAULT_INJECTION && SYSFS && DEBUG_FS
1535	help
1536	  Enable configuration of fault-injection capabilities via debugfs.
1537
1538config FAULT_INJECTION_STACKTRACE_FILTER
1539	bool "stacktrace filter for fault-injection capabilities"
1540	depends on FAULT_INJECTION_DEBUG_FS && STACKTRACE_SUPPORT
1541	depends on !X86_64
1542	select STACKTRACE
1543	select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC && !SCORE
1544	help
1545	  Provide stacktrace filter for fault-injection capabilities
1546
1547config LATENCYTOP
1548	bool "Latency measuring infrastructure"
1549	depends on DEBUG_KERNEL
1550	depends on STACKTRACE_SUPPORT
1551	depends on PROC_FS
1552	select FRAME_POINTER if !MIPS && !PPC && !S390 && !MICROBLAZE && !ARM_UNWIND && !ARC
1553	select KALLSYMS
1554	select KALLSYMS_ALL
1555	select STACKTRACE
1556	select SCHEDSTATS
1557	select SCHED_DEBUG
1558	help
1559	  Enable this option if you want to use the LatencyTOP tool
1560	  to find out which userspace is blocking on what kernel operations.
1561
1562source kernel/trace/Kconfig
1563
1564menu "Runtime Testing"
1565
1566config LKDTM
1567	tristate "Linux Kernel Dump Test Tool Module"
1568	depends on DEBUG_FS
1569	depends on BLOCK
1570	default n
1571	help
1572	This module enables testing of the different dumping mechanisms by
1573	inducing system failures at predefined crash points.
1574	If you don't need it: say N
1575	Choose M here to compile this code as a module. The module will be
1576	called lkdtm.
1577
1578	Documentation on how to use the module can be found in
1579	Documentation/fault-injection/provoke-crashes.txt
1580
1581config TEST_LIST_SORT
1582	tristate "Linked list sorting test"
1583	depends on DEBUG_KERNEL || m
1584	help
1585	  Enable this to turn on 'list_sort()' function test. This test is
1586	  executed only once during system boot (so affects only boot time),
1587	  or at module load time.
1588
1589	  If unsure, say N.
1590
1591config TEST_SORT
1592	tristate "Array-based sort test"
1593	depends on DEBUG_KERNEL || m
1594	help
1595	  This option enables the self-test function of 'sort()' at boot,
1596	  or at module load time.
1597
1598	  If unsure, say N.
1599
1600config KPROBES_SANITY_TEST
1601	bool "Kprobes sanity tests"
1602	depends on DEBUG_KERNEL
1603	depends on KPROBES
1604	default n
1605	help
1606	  This option provides for testing basic kprobes functionality on
1607	  boot. A sample kprobe, jprobe and kretprobe are inserted and
1608	  verified for functionality.
1609
1610	  Say N if you are unsure.
1611
1612config BACKTRACE_SELF_TEST
1613	tristate "Self test for the backtrace code"
1614	depends on DEBUG_KERNEL
1615	default n
1616	help
1617	  This option provides a kernel module that can be used to test
1618	  the kernel stack backtrace code. This option is not useful
1619	  for distributions or general kernels, but only for kernel
1620	  developers working on architecture code.
1621
1622	  Note that if you want to also test saved backtraces, you will
1623	  have to enable STACKTRACE as well.
1624
1625	  Say N if you are unsure.
1626
1627config RBTREE_TEST
1628	tristate "Red-Black tree test"
1629	depends on DEBUG_KERNEL
1630	help
1631	  A benchmark measuring the performance of the rbtree library.
1632	  Also includes rbtree invariant checks.
1633
1634config INTERVAL_TREE_TEST
1635	tristate "Interval tree test"
1636	depends on DEBUG_KERNEL
1637	select INTERVAL_TREE
1638	help
1639	  A benchmark measuring the performance of the interval tree library
1640
1641config PERCPU_TEST
1642	tristate "Per cpu operations test"
1643	depends on m && DEBUG_KERNEL
1644	help
1645	  Enable this option to build test module which validates per-cpu
1646	  operations.
1647
1648	  If unsure, say N.
1649
1650config ATOMIC64_SELFTEST
1651	tristate "Perform an atomic64_t self-test"
1652	help
1653	  Enable this option to test the atomic64_t functions at boot or
1654	  at module load time.
1655
1656	  If unsure, say N.
1657
1658config ASYNC_RAID6_TEST
1659	tristate "Self test for hardware accelerated raid6 recovery"
1660	depends on ASYNC_RAID6_RECOV
1661	select ASYNC_MEMCPY
1662	---help---
1663	  This is a one-shot self test that permutes through the
1664	  recovery of all the possible two disk failure scenarios for a
1665	  N-disk array.  Recovery is performed with the asynchronous
1666	  raid6 recovery routines, and will optionally use an offload
1667	  engine if one is available.
1668
1669	  If unsure, say N.
1670
1671config TEST_HEXDUMP
1672	tristate "Test functions located in the hexdump module at runtime"
1673
1674config TEST_STRING_HELPERS
1675	tristate "Test functions located in the string_helpers module at runtime"
1676
1677config TEST_KSTRTOX
1678	tristate "Test kstrto*() family of functions at runtime"
1679
1680config TEST_PRINTF
1681	tristate "Test printf() family of functions at runtime"
1682
1683config TEST_BITMAP
1684	tristate "Test bitmap_*() family of functions at runtime"
1685	default n
1686	help
1687	  Enable this option to test the bitmap functions at boot.
1688
1689	  If unsure, say N.
1690
1691config TEST_UUID
1692	tristate "Test functions located in the uuid module at runtime"
1693
1694config TEST_RHASHTABLE
1695	tristate "Perform selftest on resizable hash table"
1696	default n
1697	help
1698	  Enable this option to test the rhashtable functions at boot.
1699
1700	  If unsure, say N.
1701
1702config TEST_HASH
1703	tristate "Perform selftest on hash functions"
1704	default n
1705	help
1706	  Enable this option to test the kernel's integer (<linux/hash.h>),
1707	  string (<linux/stringhash.h>), and siphash (<linux/siphash.h>)
1708	  hash functions on boot (or module load).
1709
1710	  This is intended to help people writing architecture-specific
1711	  optimized versions.  If unsure, say N.
1712
1713config TEST_PARMAN
1714	tristate "Perform selftest on priority array manager"
1715	default n
1716	depends on PARMAN
1717	help
1718	  Enable this option to test priority array manager on boot
1719	  (or module load).
1720
1721	  If unsure, say N.
1722
1723endmenu # runtime tests
1724
1725config PROVIDE_OHCI1394_DMA_INIT
1726	bool "Remote debugging over FireWire early on boot"
1727	depends on PCI && X86
1728	help
1729	  If you want to debug problems which hang or crash the kernel early
1730	  on boot and the crashing machine has a FireWire port, you can use
1731	  this feature to remotely access the memory of the crashed machine
1732	  over FireWire. This employs remote DMA as part of the OHCI1394
1733	  specification which is now the standard for FireWire controllers.
1734
1735	  With remote DMA, you can monitor the printk buffer remotely using
1736	  firescope and access all memory below 4GB using fireproxy from gdb.
1737	  Even controlling a kernel debugger is possible using remote DMA.
1738
1739	  Usage:
1740
1741	  If ohci1394_dma=early is used as boot parameter, it will initialize
1742	  all OHCI1394 controllers which are found in the PCI config space.
1743
1744	  As all changes to the FireWire bus such as enabling and disabling
1745	  devices cause a bus reset and thereby disable remote DMA for all
1746	  devices, be sure to have the cable plugged and FireWire enabled on
1747	  the debugging host before booting the debug target for debugging.
1748
1749	  This code (~1k) is freed after boot. By then, the firewire stack
1750	  in charge of the OHCI-1394 controllers should be used instead.
1751
1752	  See Documentation/debugging-via-ohci1394.txt for more information.
1753
1754config DMA_API_DEBUG
1755	bool "Enable debugging of DMA-API usage"
1756	depends on HAVE_DMA_API_DEBUG
1757	help
1758	  Enable this option to debug the use of the DMA API by device drivers.
1759	  With this option you will be able to detect common bugs in device
1760	  drivers like double-freeing of DMA mappings or freeing mappings that
1761	  were never allocated.
1762
1763	  This also attempts to catch cases where a page owned by DMA is
1764	  accessed by the cpu in a way that could cause data corruption.  For
1765	  example, this enables cow_user_page() to check that the source page is
1766	  not undergoing DMA.
1767
1768	  This option causes a performance degradation.  Use only if you want to
1769	  debug device drivers and dma interactions.
1770
1771	  If unsure, say N.
1772
1773config TEST_LKM
1774	tristate "Test module loading with 'hello world' module"
1775	default n
1776	depends on m
1777	help
1778	  This builds the "test_module" module that emits "Hello, world"
1779	  on printk when loaded. It is designed to be used for basic
1780	  evaluation of the module loading subsystem (for example when
1781	  validating module verification). It lacks any extra dependencies,
1782	  and will not normally be loaded by the system unless explicitly
1783	  requested by name.
1784
1785	  If unsure, say N.
1786
1787config TEST_USER_COPY
1788	tristate "Test user/kernel boundary protections"
1789	default n
1790	depends on m
1791	help
1792	  This builds the "test_user_copy" module that runs sanity checks
1793	  on the copy_to/from_user infrastructure, making sure basic
1794	  user/kernel boundary testing is working. If it fails to load,
1795	  a regression has been detected in the user/kernel memory boundary
1796	  protections.
1797
1798	  If unsure, say N.
1799
1800config TEST_BPF
1801	tristate "Test BPF filter functionality"
1802	default n
1803	depends on m && NET
1804	help
1805	  This builds the "test_bpf" module that runs various test vectors
1806	  against the BPF interpreter or BPF JIT compiler depending on the
1807	  current setting. This is in particular useful for BPF JIT compiler
1808	  development, but also to run regression tests against changes in
1809	  the interpreter code. It also enables test stubs for eBPF maps and
1810	  verifier used by user space verifier testsuite.
1811
1812	  If unsure, say N.
1813
1814config TEST_FIRMWARE
1815	tristate "Test firmware loading via userspace interface"
1816	default n
1817	depends on FW_LOADER
1818	help
1819	  This builds the "test_firmware" module that creates a userspace
1820	  interface for testing firmware loading. This can be used to
1821	  control the triggering of firmware loading without needing an
1822	  actual firmware-using device. The contents can be rechecked by
1823	  userspace.
1824
1825	  If unsure, say N.
1826
1827config TEST_SYSCTL
1828	tristate "sysctl test driver"
1829	default n
1830	depends on PROC_SYSCTL
1831	help
1832	  This builds the "test_sysctl" module. This driver enables to test the
1833	  proc sysctl interfaces available to drivers safely without affecting
1834	  production knobs which might alter system functionality.
1835
1836	  If unsure, say N.
1837
1838config TEST_UDELAY
1839	tristate "udelay test driver"
1840	default n
1841	help
1842	  This builds the "udelay_test" module that helps to make sure
1843	  that udelay() is working properly.
1844
1845	  If unsure, say N.
1846
1847config MEMTEST
1848	bool "Memtest"
1849	depends on HAVE_MEMBLOCK
1850	---help---
1851	  This option adds a kernel parameter 'memtest', which allows memtest
1852	  to be set.
1853	        memtest=0, mean disabled; -- default
1854	        memtest=1, mean do 1 test pattern;
1855	        ...
1856	        memtest=17, mean do 17 test patterns.
1857	  If you are unsure how to answer this question, answer N.
1858
1859config TEST_STATIC_KEYS
1860	tristate "Test static keys"
1861	default n
1862	depends on m
1863	help
1864	  Test the static key interfaces.
1865
1866	  If unsure, say N.
1867
1868config BUG_ON_DATA_CORRUPTION
1869	bool "Trigger a BUG when data corruption is detected"
1870	select DEBUG_LIST
1871	help
1872	  Select this option if the kernel should BUG when it encounters
1873	  data corruption in kernel memory structures when they get checked
1874	  for validity.
1875
1876	  If unsure, say N.
1877
1878config TEST_KMOD
1879	tristate "kmod stress tester"
1880	default n
1881	depends on m
1882	depends on BLOCK && (64BIT || LBDAF)	  # for XFS, BTRFS
1883	depends on NETDEVICES && NET_CORE && INET # for TUN
1884	select TEST_LKM
1885	select XFS_FS
1886	select TUN
1887	select BTRFS_FS
1888	help
1889	  Test the kernel's module loading mechanism: kmod. kmod implements
1890	  support to load modules using the Linux kernel's usermode helper.
1891	  This test provides a series of tests against kmod.
1892
1893	  Although technically you can either build test_kmod as a module or
1894	  into the kernel we disallow building it into the kernel since
1895	  it stress tests request_module() and this will very likely cause
1896	  some issues by taking over precious threads available from other
1897	  module load requests, ultimately this could be fatal.
1898
1899	  To run tests run:
1900
1901	  tools/testing/selftests/kmod/kmod.sh --help
1902
1903	  If unsure, say N.
1904
1905source "samples/Kconfig"
1906
1907source "lib/Kconfig.kgdb"
1908
1909source "lib/Kconfig.ubsan"
1910
1911config ARCH_HAS_DEVMEM_IS_ALLOWED
1912	bool
1913
1914config STRICT_DEVMEM
1915	bool "Filter access to /dev/mem"
1916	depends on MMU && DEVMEM
1917	depends on ARCH_HAS_DEVMEM_IS_ALLOWED
1918	default y if TILE || PPC
1919	---help---
1920	  If this option is disabled, you allow userspace (root) access to all
1921	  of memory, including kernel and userspace memory. Accidental
1922	  access to this is obviously disastrous, but specific access can
1923	  be used by people debugging the kernel. Note that with PAT support
1924	  enabled, even in this case there are restrictions on /dev/mem
1925	  use due to the cache aliasing requirements.
1926
1927	  If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem
1928	  file only allows userspace access to PCI space and the BIOS code and
1929	  data regions.  This is sufficient for dosemu and X and all common
1930	  users of /dev/mem.
1931
1932	  If in doubt, say Y.
1933
1934config IO_STRICT_DEVMEM
1935	bool "Filter I/O access to /dev/mem"
1936	depends on STRICT_DEVMEM
1937	---help---
1938	  If this option is disabled, you allow userspace (root) access to all
1939	  io-memory regardless of whether a driver is actively using that
1940	  range.  Accidental access to this is obviously disastrous, but
1941	  specific access can be used by people debugging kernel drivers.
1942
1943	  If this option is switched on, the /dev/mem file only allows
1944	  userspace access to *idle* io-memory ranges (see /proc/iomem) This
1945	  may break traditional users of /dev/mem (dosemu, legacy X, etc...)
1946	  if the driver using a given range cannot be disabled.
1947
1948	  If in doubt, say Y.
1949