# SPDX-License-Identifier: GPL-2.0-onlymenu "Kernel hacking" menu "printk and dmesg options" config PRINTK_TIME	bool "Show timing information on printks"	depends on PRINTK	help	  Selecting this option causes time stamps of the printk()	  messages to be added to the output of the syslog() system	  call and at the console. 	  The timestamp is always recorded internally, and exported	  to /dev/kmsg. This flag just specifies if the timestamp should	  be included, not that the timestamp is recorded. 	  The behavior is also controlled by the kernel command line	  parameter printk.time=1. See Documentation/admin-guide/kernel-parameters.rst config PRINTK_CALLER	bool "Show caller information on printks"	depends on PRINTK	help	  Selecting this option causes printk() to add a caller "thread id" (if	  in task context) or a caller "processor id" (if not in task context)	  to every message. 	  This option is intended for environments where multiple threads	  concurrently call printk() for many times, for it is difficult to	  interpret without knowing where these lines (or sometimes individual	  line which was divided into multiple lines due to race) came from. 	  Since toggling after boot makes the code racy, currently there is	  no option to enable/disable at the kernel command line parameter or	  sysfs interface. config STACKTRACE_BUILD_ID	bool "Show build ID information in stacktraces"	depends on PRINTK	help	  Selecting this option adds build ID information for symbols in	  stacktraces printed with the printk format '%p[SR]b'. 	  This option is intended for distros where debuginfo is not easily	  accessible but can be downloaded given the build ID of the vmlinux or	  kernel module where the function is located. config CONSOLE_LOGLEVEL_DEFAULT	int "Default console loglevel (1-15)"	range 1 15	default "7"	help	  Default loglevel to determine what will be printed on the console. 	  Setting a default here is equivalent to passing in loglevel=<x> in	  the kernel bootargs. loglevel=<x> continues to override whatever	  value is specified here as well. 	  Note: This does not affect the log level of un-prefixed printk()	  usage in the kernel. That is controlled by the MESSAGE_LOGLEVEL_DEFAULT	  option. config CONSOLE_LOGLEVEL_QUIET	int "quiet console loglevel (1-15)"	range 1 15	default "4"	help	  loglevel to use when "quiet" is passed on the kernel commandline. 	  When "quiet" is passed on the kernel commandline this loglevel	  will be used as the loglevel. IOW passing "quiet" will be the	  equivalent of passing "loglevel=<CONSOLE_LOGLEVEL_QUIET>" config MESSAGE_LOGLEVEL_DEFAULT	int "Default message log level (1-7)"	range 1 7	default "4"	help	  Default log level for printk statements with no specified priority. 	  This was hard-coded to KERN_WARNING since at least 2.6.10 but folks	  that are auditing their logs closely may want to set it to a lower	  priority. 	  Note: This does not affect what message level gets printed on the console	  by default. To change that, use loglevel=<x> in the kernel bootargs,	  or pick a different CONSOLE_LOGLEVEL_DEFAULT configuration value. config BOOT_PRINTK_DELAY	bool "Delay each boot printk message by N milliseconds"	depends on DEBUG_KERNEL && PRINTK && GENERIC_CALIBRATE_DELAY	help	  This build option allows you to read kernel boot messages	  by inserting a short delay after each one.  The delay is	  specified in milliseconds on the kernel command line,	  using "boot_delay=N". 	  It is likely that you would also need to use "lpj=M" to preset	  the "loops per jiffie" value.	  See a previous boot log for the "lpj" value to use for your	  system, and then set "lpj=M" before setting "boot_delay=N".	  NOTE:  Using this option may adversely affect SMP systems.	  I.e., processors other than the first one may not boot up.	  BOOT_PRINTK_DELAY also may cause LOCKUP_DETECTOR to detect	  what it believes to be lockup conditions. config DYNAMIC_DEBUG	bool "Enable dynamic printk() support"	default n	depends on PRINTK	depends on (DEBUG_FS || PROC_FS)	select DYNAMIC_DEBUG_CORE	help 	  Compiles debug level messages into the kernel, which would not	  otherwise be available at runtime. These messages can then be	  enabled/disabled based on various levels of scope - per source file,	  function, module, format string, and line number. This mechanism	  implicitly compiles in all pr_debug() and dev_dbg() calls, which	  enlarges the kernel text size by about 2%. 	  If a source file is compiled with DEBUG flag set, any	  pr_debug() calls in it are enabled by default, but can be	  disabled at runtime as below.  Note that DEBUG flag is	  turned on by many CONFIG_*DEBUG* options. 	  Usage: 	  Dynamic debugging is controlled via the 'dynamic_debug/control' file,	  which is contained in the 'debugfs' filesystem or procfs.	  Thus, the debugfs or procfs filesystem must first be mounted before	  making use of this feature.	  We refer the control file as: <debugfs>/dynamic_debug/control. This	  file contains a list of the debug statements that can be enabled. The	  format for each line of the file is: 		filename:lineno [module]function flags format 	  filename : source file of the debug statement	  lineno : line number of the debug statement	  module : module that contains the debug statement	  function : function that contains the debug statement	  flags : '=p' means the line is turned 'on' for printing	  format : the format used for the debug statement 	  From a live system: 		nullarbor:~ # cat <debugfs>/dynamic_debug/control		# filename:lineno [module]function flags format		fs/aio.c:222 [aio]__put_ioctx =_ "__put_ioctx:\040freeing\040%p\012"		fs/aio.c:248 [aio]ioctx_alloc =_ "ENOMEM:\040nr_events\040too\040high\012"		fs/aio.c:1770 [aio]sys_io_cancel =_ "calling\040cancel\012" 	  Example usage: 		// enable the message at line 1603 of file svcsock.c		nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >						<debugfs>/dynamic_debug/control 		// enable all the messages in file svcsock.c		nullarbor:~ # echo -n 'file svcsock.c +p' >						<debugfs>/dynamic_debug/control 		// enable all the messages in the NFS server module		nullarbor:~ # echo -n 'module nfsd +p' >						<debugfs>/dynamic_debug/control 		// enable all 12 messages in the function svc_process()		nullarbor:~ # echo -n 'func svc_process +p' >						<debugfs>/dynamic_debug/control 		// disable all 12 messages in the function svc_process()		nullarbor:~ # echo -n 'func svc_process -p' >						<debugfs>/dynamic_debug/control 	  See Documentation/admin-guide/dynamic-debug-howto.rst for additional	  information. config DYNAMIC_DEBUG_CORE	bool "Enable core function of dynamic debug support"	depends on PRINTK	depends on (DEBUG_FS || PROC_FS)	help	  Enable core functional support of dynamic debug. It is useful	  when you want to tie dynamic debug to your kernel modules with	  DYNAMIC_DEBUG_MODULE defined for each of them, especially for	  the case of embedded system where the kernel image size is	  sensitive for people. config SYMBOLIC_ERRNAME	bool "Support symbolic error names in printf"	default y if PRINTK	help	  If you say Y here, the kernel's printf implementation will	  be able to print symbolic error names such as ENOSPC instead	  of the number 28. It makes the kernel image slightly larger	  (about 3KB), but can make the kernel logs easier to read. config DEBUG_BUGVERBOSE	bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EXPERT	depends on BUG && (GENERIC_BUG || HAVE_DEBUG_BUGVERBOSE)	default y	help	  Say Y here to make BUG() panics output the file name and line number	  of the BUG call as well as the EIP and oops trace.  This aids	  debugging but costs about 70-100K of memory. endmenu # "printk and dmesg options" menu "Compile-time checks and compiler options" config DEBUG_INFO	bool "Compile the kernel with debug info"	depends on DEBUG_KERNEL && !COMPILE_TEST	help	  If you say Y here the resulting kernel image will include	  debugging info resulting in a larger kernel image.	  This adds debug symbols to the kernel and modules (gcc -g), and	  is needed if you intend to use kernel crashdump or binary object	  tools like crash, kgdb, LKCD, gdb, etc on the kernel.	  Say Y here only if you plan to debug the kernel. 	  If unsure, say N. if DEBUG_INFO config DEBUG_INFO_REDUCED	bool "Reduce debugging information"	help	  If you say Y here gcc is instructed to generate less debugging	  information for structure types. This means that tools that	  need full debugging information (like kgdb or systemtap) won't	  be happy. But if you merely need debugging information to	  resolve line numbers there is no loss. Advantage is that	  build directory object sizes shrink dramatically over a full	  DEBUG_INFO build and compile times are reduced too.	  Only works with newer gcc versions. config DEBUG_INFO_COMPRESSED	bool "Compressed debugging information"	depends on $(cc-option,-gz=zlib)	depends on $(ld-option,--compress-debug-sections=zlib)	help	  Compress the debug information using zlib.  Requires GCC 5.0+ or Clang	  5.0+, binutils 2.26+, and zlib. 	  Users of dpkg-deb via scripts/package/builddeb may find an increase in	  size of their debug .deb packages with this config set, due to the	  debug info being compressed with zlib, then the object files being	  recompressed with a different compression scheme. But this is still	  preferable to setting $KDEB_COMPRESS to "none" which would be even	  larger. config DEBUG_INFO_SPLIT	bool "Produce split debuginfo in .dwo files"	depends on $(cc-option,-gsplit-dwarf)	help	  Generate debug info into separate .dwo files. This significantly	  reduces the build directory size for builds with DEBUG_INFO,	  because it stores the information only once on disk in .dwo	  files instead of multiple times in object files and executables.	  In addition the debug information is also compressed. 	  Requires recent gcc (4.7+) and recent gdb/binutils.	  Any tool that packages or reads debug information would need	  to know about the .dwo files and include them.	  Incompatible with older versions of ccache. choice	prompt "DWARF version"	help	  Which version of DWARF debug info to emit. config DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT	bool "Rely on the toolchain's implicit default DWARF version"	help	  The implicit default version of DWARF debug info produced by a	  toolchain changes over time. 	  This can break consumers of the debug info that haven't upgraded to	  support newer revisions, and prevent testing newer versions, but	  those should be less common scenarios. 	  If unsure, say Y. config DEBUG_INFO_DWARF4	bool "Generate DWARF Version 4 debuginfo"	help	  Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+. 	  If you have consumers of DWARF debug info that are not ready for	  newer revisions of DWARF, you may wish to choose this or have your	  config select this. config DEBUG_INFO_DWARF5	bool "Generate DWARF Version 5 debuginfo"	depends on GCC_VERSION >= 50000 || (CC_IS_CLANG && (AS_IS_LLVM || (AS_IS_GNU && AS_VERSION >= 23502)))	depends on !DEBUG_INFO_BTF	help	  Generate DWARF v5 debug info. Requires binutils 2.35.2, gcc 5.0+ (gcc	  5.0+ accepts the -gdwarf-5 flag but only had partial support for some	  draft features until 7.0), and gdb 8.0+. 	  Changes to the structure of debug info in Version 5 allow for around	  15-18% savings in resulting image and debug info section sizes as	  compared to DWARF Version 4. DWARF Version 5 standardizes previous	  extensions such as accelerators for symbol indexing and the format	  for fission (.dwo/.dwp) files. Users may not want to select this	  config if they rely on tooling that has not yet been updated to	  support DWARF Version 5. endchoice # "DWARF version" config DEBUG_INFO_BTF	bool "Generate BTF typeinfo"	depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED	depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST	help	  Generate deduplicated BTF type information from DWARF debug info.	  Turning this on expects presence of pahole tool, which will convert	  DWARF type info into equivalent deduplicated BTF type info. config PAHOLE_HAS_SPLIT_BTF	def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119") config DEBUG_INFO_BTF_MODULES	def_bool y	depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF	help	  Generate compact split BTF type information for kernel modules. config GDB_SCRIPTS	bool "Provide GDB scripts for kernel debugging"	help	  This creates the required links to GDB helper scripts in the	  build directory. If you load vmlinux into gdb, the helper	  scripts will be automatically imported by gdb as well, and	  additional functions are available to analyze a Linux kernel	  instance. See Documentation/dev-tools/gdb-kernel-debugging.rst	  for further details. endif # DEBUG_INFO config FRAME_WARN	int "Warn for stack frames larger than"	range 0 8192	default 2048 if GCC_PLUGIN_LATENT_ENTROPY	default 1280 if (!64BIT && PARISC)	default 1024 if (!64BIT && !PARISC)	default 2048 if 64BIT	help	  Tell gcc to warn at build time for stack frames larger than this.	  Setting this too low will cause a lot of warnings.	  Setting it to 0 disables the warning. config STRIP_ASM_SYMS	bool "Strip assembler-generated symbols during link"	default n	help	  Strip internal assembler-generated symbols during a link (symbols	  that look like '.Lxxx') so they don't pollute the output of	  get_wchan() and suchlike. config READABLE_ASM	bool "Generate readable assembler code"	depends on DEBUG_KERNEL	help	  Disable some compiler optimizations that tend to generate human unreadable	  assembler output. This may make the kernel slightly slower, but it helps	  to keep kernel developers who have to stare a lot at assembler listings	  sane. config HEADERS_INSTALL	bool "Install uapi headers to usr/include"	depends on !UML	help	  This option will install uapi headers (headers exported to user-space)	  into the usr/include directory for use during the kernel build.	  This is unneeded for building the kernel itself, but needed for some	  user-space program samples. It is also needed by some features such	  as uapi header sanity checks. config DEBUG_SECTION_MISMATCH	bool "Enable full Section mismatch analysis"	help	  The section mismatch analysis checks if there are illegal	  references from one section to another section.	  During linktime or runtime, some sections are dropped;	  any use of code/data previously in these sections would	  most likely result in an oops.	  In the code, functions and variables are annotated with	  __init,, etc. (see the full list in include/linux/init.h),	  which results in the code/data being placed in specific sections.	  The section mismatch analysis is always performed after a full	  kernel build, and enabling this option causes the following	  additional step to occur:	  - Add the option -fno-inline-functions-called-once to gcc commands.	    When inlining a function annotated with __init in a non-init	    function, we would lose the section information and thus	    the analysis would not catch the illegal reference.	    This option tells gcc to inline less (but it does result in	    a larger kernel). config SECTION_MISMATCH_WARN_ONLY	bool "Make section mismatch errors non-fatal"	default y	help	  If you say N here, the build process will fail if there are any	  section mismatch, instead of just throwing warnings. 	  If unsure, say Y. config DEBUG_FORCE_FUNCTION_ALIGN_64B	bool "Force all function address 64B aligned" if EXPERT	help	  There are cases that a commit from one domain changes the function	  address alignment of other domains, and cause magic performance	  bump (regression or improvement). Enable this option will help to	  verify if the bump is caused by function alignment changes, while	  it will slightly increase the kernel size and affect icache usage. 	  It is mainly for debug and performance tuning use. ## Select this config option from the architecture Kconfig, if it# is preferred to always offer frame pointers as a config# option on the architecture (regardless of KERNEL_DEBUG):#config ARCH_WANT_FRAME_POINTERS	bool config FRAME_POINTER	bool "Compile the kernel with frame pointers"	depends on DEBUG_KERNEL && (M68K || UML || SUPERH) || ARCH_WANT_FRAME_POINTERS	default y if (DEBUG_INFO && UML) || ARCH_WANT_FRAME_POINTERS	help	  If you say Y here the resulting kernel image will be slightly	  larger and slower, but it gives very useful debugging information	  in case of kernel bugs. (precise oopses/stacktraces/warnings) config STACK_VALIDATION	bool "Compile-time stack metadata validation"	depends on HAVE_STACK_VALIDATION	default n	help	  Add compile-time checks to validate stack metadata, including frame	  pointers (if CONFIG_FRAME_POINTER is enabled).  This helps ensure	  that runtime stack traces are more reliable. 	  This is also a prerequisite for generation of ORC unwind data, which	  is needed for CONFIG_UNWINDER_ORC. 	  For more information, see	  tools/objtool/Documentation/stack-validation.txt. config VMLINUX_VALIDATION	bool	depends on STACK_VALIDATION && DEBUG_ENTRY && !PARAVIRT	default y config VMLINUX_MAP	bool "Generate vmlinux.map file when linking"	depends on EXPERT	help	  Selecting this option will pass "-Map=vmlinux.map" to ld	  when linking vmlinux. That file can be useful for verifying	  and debugging magic section games, and for seeing which	  pieces of code get eliminated with	  CONFIG_LD_DEAD_CODE_DATA_ELIMINATION. config DEBUG_FORCE_WEAK_PER_CPU	bool "Force weak per-cpu definitions"	depends on DEBUG_KERNEL	help	  s390 and alpha require percpu variables in modules to be	  defined weak to work around addressing range issue which	  puts the following two restrictions on percpu variable	  definitions. 	  1. percpu symbols must be unique whether static or not	  2. percpu variables can't be defined inside a function 	  To ensure that generic code follows the above rules, this	  option forces all percpu variables to be defined as weak. endmenu # "Compiler options" menu "Generic Kernel Debugging Instruments" config MAGIC_SYSRQ	bool "Magic SysRq key"	depends on !UML	help	  If you say Y here, you will have some control over the system even	  if the system crashes for example during kernel debugging (e.g., you	  will be able to flush the buffer cache to disk, reboot the system	  immediately or dump some status information). This is accomplished	  by pressing various keys while holding SysRq (Alt+PrintScreen). It	  also works on a serial console (on PC hardware at least), if you

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