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 EMBEDDED
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_DBGP
bool "Early printk via EHCI debug port"
default n
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---
This option will cause messages to be printed if free stack space
drops below a certain limit.
config DEBUG_STACK_USAGE
bool "Stack utilization instrumentation"
depends on DEBUG_KERNEL
---help---
Enables the display of the minimum amount of free stack which each
task has ever had available in the sysrq-T and sysrq-P debug output.
This option will slow down process creation somewhat.
config DEBUG_PER_CPU_MAPS
bool "Debug access to per_cpu maps"
depends on DEBUG_KERNEL
depends on SMP
default n
---help---
Say Y to verify that the per_cpu map being accessed has
been setup. Adds a fair amount of code to kernel memory
and decreases performance.
Say N if unsure.
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_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 4KSTACKS
bool "Use 4Kb for kernel stacks instead of 8Kb"
depends on X86_32
---help---
If you say Y here the kernel will use a 4Kb stacksize for the
kernel stack attached to each process/thread. This facilitates
running more threads on a system and also reduces the pressure
on the VM subsystem for higher order allocations. This option
will also use IRQ stacks to compensate for the reduced stackspace.
config DOUBLEFAULT
default y
bool "Enable doublefault exception handler" if EMBEDDED
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 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_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 X86_DS_SELFTEST
bool "DS selftest"
default y
depends on DEBUG_KERNEL
depends on X86_DS
---help---
Perform Debug Store selftests at boot time.
If in doubt, say "N".
config HAVE_MMIOTRACE_SUPPORT
def_bool y
config X86_DECODER_SELFTEST
bool "x86 instruction decoder selftest"
depends on DEBUG_KERNEL
---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.
endmenu
