arch/x86/Kconfig.debug

menu "Kernel hacking"

config TRACE_IRQFLAGS_SUPPORT
	def_bool y

source "lib/Kconfig.debug"

config STRICT_DEVMEM
	bool "Filter access to /dev/mem"
	---help---
	  If this option is disabled, you allow userspace (root) access to all
	  of memory, including kernel and userspace memory. Accidental
	  access to this is obviously disastrous, but specific access can
	  be used by people debugging the kernel. Note that with PAT support
	  enabled, even in this case there are restrictions on /dev/mem
	  use due to the cache aliasing requirements.

	  If this option is switched on, the /dev/mem file only allows
	  userspace access to PCI space and the BIOS code and data regions.
	  This is sufficient for dosemu and X and all common users of
	  /dev/mem.

	  If in doubt, say Y.

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 N here,
	  unless you want to debug such a crash.

config EARLY_PRINTK_INTEL_MID
	bool "Early printk for Intel MID platform support"
	depends on EARLY_PRINTK && X86_INTEL_MID

config EARLY_PRINTK_DBGP
	bool "Early printk via EHCI debug port"
	depends on EARLY_PRINTK && PCI
	---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 N here,
	  unless you want to debug such a crash. You need usb debug device.

config DEBUG_STACKOVERFLOW
	bool "Check for stack overflows"
	depends on DEBUG_KERNEL
	---help---
	  Say Y here if you want to check the overflows of kernel, IRQ
	  and exception stacks. This option will cause messages of the
	  stacks in detail when free stack space drops below a certain
	  limit.
	  If in doubt, say "N".

config X86_PTDUMP
	bool "Export kernel pagetable layout to userspace via debugfs"
	depends on DEBUG_KERNEL
	select DEBUG_FS
	---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 DEBUG_RODATA
	bool "Write protect kernel read-only data structures"
	default y
	depends on DEBUG_KERNEL
	---help---
	  Mark the kernel read-only data as write-protected in the pagetables,
	  in order to catch accidental (and incorrect) writes to such const
	  data. This is recommended so that we can catch kernel bugs sooner.
	  If in doubt, say "Y".

config DEBUG_RODATA_TEST
	bool "Testcase for the DEBUG_RODATA feature"
	depends on DEBUG_RODATA
	default y
	---help---
	  This option enables a testcase for the DEBUG_RODATA
	  feature as well as for the change_page_attr() infrastructure.
	  If in doubt, say "N"

config DEBUG_SET_MODULE_RONX
	bool "Set loadable kernel module data as NX and text as RO"
	depends on MODULES
	---help---
	  This option helps catch unintended modifications to loadable
	  kernel module's text and read-only data. It also prevents execution
	  of module data. Such protection may interfere with run-time code
	  patching and dynamic kernel tracing - and they might also protect
	  against certain classes of kernel exploits.
	  If in doubt, say "N".

config DEBUG_NX_TEST
	tristate "Testcase for the NX non-executable stack feature"
	depends on DEBUG_KERNEL && m
	---help---
	  This option enables a testcase for the CPU NX capability
	  and the software setup of this feature.
	  If in doubt, say "N"

config DOUBLEFAULT
	default y
	bool "Enable doublefault exception handler" if EXPERT
	depends on X86_32
	---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_STRESS
	bool "Enable IOMMU stress-test mode"
	---help---
	  This option disables various optimizations in IOMMU related
	  code to do real stress testing of the IOMMU code. This option
	  will cause a performance drop and should only be enabled for
	  testing.

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
	---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_STRICT_USER_COPY_CHECKS
	bool "Strict copy size checks"
	depends on DEBUG_KERNEL && !TRACE_BRANCH_PROFILING
	---help---
	  Enabling this option turns a certain set of sanity checks for user
	  copy operations into compile time failures.

	  The copy_from_user() etc checks are there to help test if there
	  are sufficient security checks on the length argument of
	  the copy operation, by having gcc prove that the argument is
	  within bounds.

	  If unsure, or if you run an older (pre 4.4) gcc, 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.

endmenu