linux_kernel/arch/x86/Kconfig.debug

# SPDX-License-Identifier: GPL-2.0
menu "Kernel hacking"

config TRACE_IRQFLAGS_SUPPORT
	def_bool y

source "lib/Kconfig.debug"

config EARLY_PRINTK_USB
	bool

config X86_VERBOSE_BOOTUP
	bool "Enable verbose x86 bootup info messages"
	default y
	---help---
	  Enables the informational output from the decompression stage
	  (e.g. bzImage) of the boot. If you disable this you will still
	  see errors. Disable this if you want silent bootup.

config EARLY_PRINTK
	bool "Early printk" if EXPERT
	default y
	---help---
	  Write kernel log output directly into the VGA buffer or to a serial
	  port.

	  This is useful for kernel debugging when your machine crashes very
	  early before the console code is initialized. For normal operation
	  it is not recommended because it looks ugly and doesn't cooperate
	  with klogd/syslogd or the X server. You should normally say N here,
	  unless you want to debug such a crash.

config EARLY_PRINTK_DBGP
	bool "Early printk via EHCI debug port"
	depends on EARLY_PRINTK && PCI
	select EARLY_PRINTK_USB
	---help---
	  Write kernel log output directly into the EHCI debug port.

	  This is useful for kernel debugging when your machine crashes very
	  early before the console code is initialized. For normal operation
	  it is not recommended because it looks ugly and doesn't cooperate
	  with klogd/syslogd or the X server. You should normally say N here,
	  unless you want to debug such a crash. You need usb debug device.

config EARLY_PRINTK_EFI
	bool "Early printk via the EFI framebuffer"
	depends on EFI && EARLY_PRINTK
	select FONT_SUPPORT
	---help---
	  Write kernel log output directly into the EFI framebuffer.

	  This is useful for kernel debugging when your machine crashes very
	  early before the console code is initialized.

config EARLY_PRINTK_USB_XDBC
	bool "Early printk via the xHCI debug port"
	depends on EARLY_PRINTK && PCI
	select EARLY_PRINTK_USB
	---help---
	  Write kernel log output directly into the xHCI debug port.

	  One use for this feature is kernel debugging, for example when your
	  machine crashes very early before the regular console code is
	  initialized. Other uses include simpler, lockless logging instead of
	  a full-blown printk console driver + klogd.

	  For normal production environments this is normally not recommended,
	  because it doesn't feed events into klogd/syslogd and doesn't try to
	  print anything on the screen.

	  You should normally say N here, unless you want to debug early
	  crashes or need a very simple printk logging facility.

config MCSAFE_TEST
	def_bool n

config X86_PTDUMP_CORE
	def_bool n

config X86_PTDUMP
	tristate "Export kernel pagetable layout to userspace via debugfs"
	depends on DEBUG_KERNEL
	select DEBUG_FS
	select X86_PTDUMP_CORE
	---help---
	  Say Y here if you want to show the kernel pagetable layout in a
	  debugfs file. This information is only useful for kernel developers
	  who are working in architecture specific areas of the kernel.
	  It is probably not a good idea to enable this feature in a production
	  kernel.
	  If in doubt, say "N"

config EFI_PGT_DUMP
	bool "Dump the EFI pagetable"
	depends on EFI
	select X86_PTDUMP_CORE
	---help---
	  Enable this if you want to dump the EFI page table before
	  enabling virtual mode. This can be used to debug miscellaneous
	  issues with the mapping of the EFI runtime regions into that
	  table.

config DEBUG_WX
	bool "Warn on W+X mappings at boot"
	select X86_PTDUMP_CORE
	---help---
	  Generate a warning if any W+X mappings are found at boot.

	  This is useful for discovering cases where the kernel is leaving
	  W+X mappings after applying NX, as such mappings are a security risk.

	  Look for a message in dmesg output like this:

	    x86/mm: Checked W+X mappings: passed, no W+X pages found.

	  or like this, if the check failed:

	    x86/mm: Checked W+X mappings: FAILED, <N> W+X pages found.

	  Note that even if the check fails, your kernel is possibly
	  still fine, as W+X mappings are not a security hole in
	  themselves, what they do is that they make the exploitation
	  of other unfixed kernel bugs easier.

	  There is no runtime or memory usage effect of this option
	  once the kernel has booted up - it's a one time check.

	  If in doubt, say "Y".

config DOUBLEFAULT
	default y
	bool "Enable doublefault exception handler" if EXPERT
	---help---
	  This option allows trapping of rare doublefault exceptions that
	  would otherwise cause a system to silently reboot. Disabling this
	  option saves about 4k and might cause you much additional grey
	  hair.

config DEBUG_TLBFLUSH
	bool "Set upper limit of TLB entries to flush one-by-one"
	depends on DEBUG_KERNEL
	---help---

	X86-only for now.

	This option allows the user to tune the amount of TLB entries the
	kernel flushes one-by-one instead of doing a full TLB flush. In
	certain situations, the former is cheaper. This is controlled by the
	tlb_flushall_shift knob under /sys/kernel/debug/x86. If you set it
	to -1, the code flushes the whole TLB unconditionally. Otherwise,
	for positive values of it, the kernel will use single TLB entry
	invalidating instructions according to the following formula:

	flush_entries <= active_tlb_entries / 2^tlb_flushall_shift

	If in doubt, say "N".

config IOMMU_DEBUG
	bool "Enable IOMMU debugging"
	depends on GART_IOMMU && DEBUG_KERNEL
	depends on X86_64
	---help---
	  Force the IOMMU to on even when you have less than 4GB of
	  memory and add debugging code. On overflow always panic. And
	  allow to enable IOMMU leak tracing. Can be disabled at boot
	  time with iommu=noforce. This will also enable scatter gather
	  list merging.  Currently not recommended for production
	  code. When you use it make sure you have a big enough
	  IOMMU/AGP aperture.  Most of the options enabled by this can
	  be set more finegrained using the iommu= command line
	  options. See Documentation/x86/x86_64/boot-options.txt for more
	  details.

config IOMMU_LEAK
	bool "IOMMU leak tracing"
	depends on IOMMU_DEBUG && DMA_API_DEBUG
	---help---
	  Add a simple leak tracer to the IOMMU code. This is useful when you
	  are debugging a buggy device driver that leaks IOMMU mappings.

config HAVE_MMIOTRACE_SUPPORT
	def_bool y

config X86_DECODER_SELFTEST
	bool "x86 instruction decoder selftest"
	depends on DEBUG_KERNEL && KPROBES
	depends on !COMPILE_TEST
	---help---
	 Perform x86 instruction decoder selftests at build time.
	 This option is useful for checking the sanity of x86 instruction
	 decoder code.
	 If unsure, say "N".

#
# IO delay types:
#

config IO_DELAY_TYPE_0X80
	int
	default "0"

config IO_DELAY_TYPE_0XED
	int
	default "1"

config IO_DELAY_TYPE_UDELAY
	int
	default "2"

config IO_DELAY_TYPE_NONE
	int
	default "3"

choice
	prompt "IO delay type"
	default IO_DELAY_0X80

config IO_DELAY_0X80
	bool "port 0x80 based port-IO delay [recommended]"
	---help---
	  This is the traditional Linux IO delay used for in/out_p.
	  It is the most tested hence safest selection here.

config IO_DELAY_0XED
	bool "port 0xed based port-IO delay"
	---help---
	  Use port 0xed as the IO delay. This frees up port 0x80 which is
	  often used as a hardware-debug port.

config IO_DELAY_UDELAY
	bool "udelay based port-IO delay"
	---help---
	  Use udelay(2) as the IO delay method. This provides the delay
	  while not having any side-effect on the IO port space.

config IO_DELAY_NONE
	bool "no port-IO delay"
	---help---
	  No port-IO delay. Will break on old boxes that require port-IO
	  delay for certain operations. Should work on most new machines.

endchoice

if IO_DELAY_0X80
config DEFAULT_IO_DELAY_TYPE
	int
	default IO_DELAY_TYPE_0X80
endif

if IO_DELAY_0XED
config DEFAULT_IO_DELAY_TYPE
	int
	default IO_DELAY_TYPE_0XED
endif

if IO_DELAY_UDELAY
config DEFAULT_IO_DELAY_TYPE
	int
	default IO_DELAY_TYPE_UDELAY
endif

if IO_DELAY_NONE
config DEFAULT_IO_DELAY_TYPE
	int
	default IO_DELAY_TYPE_NONE
endif

config DEBUG_BOOT_PARAMS
	bool "Debug boot parameters"
	depends on DEBUG_KERNEL
	depends on DEBUG_FS
	---help---
	  This option will cause struct boot_params to be exported via debugfs.

config CPA_DEBUG
	bool "CPA self-test code"
	depends on DEBUG_KERNEL
	---help---
	  Do change_page_attr() self-tests every 30 seconds.

config OPTIMIZE_INLINING
	bool "Allow gcc to uninline functions marked 'inline'"
	---help---
	  This option determines if the kernel forces gcc to inline the functions
	  developers have marked 'inline'. Doing so takes away freedom from gcc to
	  do what it thinks is best, which is desirable for the gcc 3.x series of
	  compilers. The gcc 4.x series have a rewritten inlining algorithm and
	  enabling this option will generate a smaller kernel there. Hopefully
	  this algorithm is so good that allowing gcc 4.x and above to make the
	  decision will become the default in the future. Until then this option
	  is there to test gcc for this.

	  If unsure, say N.

config DEBUG_ENTRY
	bool "Debug low-level entry code"
	depends on DEBUG_KERNEL
	---help---
	  This option enables sanity checks in x86's low-level entry code.
	  Some of these sanity checks may slow down kernel entries and
	  exits or otherwise impact performance.

	  If unsure, say N.

config DEBUG_NMI_SELFTEST
	bool "NMI Selftest"
	depends on DEBUG_KERNEL && X86_LOCAL_APIC
	---help---
	  Enabling this option turns on a quick NMI selftest to verify
	  that the NMI behaves correctly.

	  This might help diagnose strange hangs that rely on NMI to
	  function properly.

	  If unsure, say N.

config DEBUG_IMR_SELFTEST
	bool "Isolated Memory Region self test"
	default n
	depends on INTEL_IMR
	---help---
	  This option enables automated sanity testing of the IMR code.
	  Some simple tests are run to verify IMR bounds checking, alignment
	  and overlapping. This option is really only useful if you are
	  debugging an IMR memory map or are modifying the IMR code and want to
	  test your changes.

	  If unsure say N here.

config X86_DEBUG_FPU
	bool "Debug the x86 FPU code"
	depends on DEBUG_KERNEL
	default y
	---help---
	  If this option is enabled then there will be extra sanity
	  checks and (boot time) debug printouts added to the kernel.
	  This debugging adds some small amount of runtime overhead
	  to the kernel.

	  If unsure, say N.

config PUNIT_ATOM_DEBUG
	tristate "ATOM Punit debug driver"
	depends on PCI
	select DEBUG_FS
	select IOSF_MBI
	---help---
	  This is a debug driver, which gets the power states
	  of all Punit North Complex devices. The power states of
	  each device is exposed as part of the debugfs interface.
	  The current power state can be read from
	  /sys/kernel/debug/punit_atom/dev_power_state

choice
	prompt "Choose kernel unwinder"
	default UNWINDER_ORC if X86_64
	default UNWINDER_FRAME_POINTER if X86_32
	---help---
	  This determines which method will be used for unwinding kernel stack
	  traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack,
	  livepatch, lockdep, and more.

config UNWINDER_ORC
	bool "ORC unwinder"
	depends on X86_64
	select STACK_VALIDATION
	---help---
	  This option enables the ORC (Oops Rewind Capability) unwinder for
	  unwinding kernel stack traces.  It uses a custom data format which is
	  a simplified version of the DWARF Call Frame Information standard.

	  This unwinder is more accurate across interrupt entry frames than the
	  frame pointer unwinder.  It also enables a 5-10% performance
	  improvement across the entire kernel compared to frame pointers.

	  Enabling this option will increase the kernel's runtime memory usage
	  by roughly 2-4MB, depending on your kernel config.

config UNWINDER_FRAME_POINTER
	bool "Frame pointer unwinder"
	select FRAME_POINTER
	---help---
	  This option enables the frame pointer unwinder for unwinding kernel
	  stack traces.

	  The unwinder itself is fast and it uses less RAM than the ORC
	  unwinder, but the kernel text size will grow by ~3% and the kernel's
	  overall performance will degrade by roughly 5-10%.

	  This option is recommended if you want to use the livepatch
	  consistency model, as this is currently the only way to get a
	  reliable stack trace (CONFIG_HAVE_RELIABLE_STACKTRACE).

config UNWINDER_GUESS
	bool "Guess unwinder"
	depends on EXPERT
	depends on !STACKDEPOT
	---help---
	  This option enables the "guess" unwinder for unwinding kernel stack
	  traces.  It scans the stack and reports every kernel text address it
	  finds.  Some of the addresses it reports may be incorrect.

	  While this option often produces false positives, it can still be
	  useful in many cases.  Unlike the other unwinders, it has no runtime
	  overhead.

endchoice

config FRAME_POINTER
	depends on !UNWINDER_ORC && !UNWINDER_GUESS
	bool

endmenu