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menu "Kernel hacking"
config TRACE_IRQFLAGS_SUPPORT
def_bool y
source "lib/Kconfig.debug"
config NONPROMISC_DEVMEM
bool "Disable promiscuous /dev/mem"
help
The /dev/mem file by default 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. With this config
option, you allow userspace access to all of memory, including
kernel and userspace memory. Accidental access to this is
obviously disasterous, but specific access can be used by people
debugging the kernel.
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 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_PAGEALLOC
bool "Debug page memory allocations"
depends on DEBUG_KERNEL
help
Unmap pages from the kernel linear mapping after free_pages().
This results in a large slowdown, but helps to find certain types
of memory corruptions.
config DEBUG_PER_CPU_MAPS
bool "Debug access to per_cpu maps"
depends on DEBUG_KERNEL
depends on X86_64_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 DIRECT_GBPAGES
bool "Enable gbpages-mapped kernel pagetables"
depends on DEBUG_KERNEL && EXPERIMENTAL && X86_64
help
Enable gigabyte pages support (if the CPU supports it). This can
improve the kernel's performance a tiny bit by reducing TLB
pressure.
This is experimental code.
If in doubt, say "N".
config DEBUG_RODATA_TEST
bool "Testcase for the DEBUG_RODATA feature"
depends on DEBUG_RODATA
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
default y
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 X86_FIND_SMP_CONFIG
def_bool y
depends on X86_LOCAL_APIC || X86_VOYAGER
depends on X86_32
config X86_MPPARSE
def_bool y
depends on (X86_32 && (X86_LOCAL_APIC && !X86_VISWS)) || X86_64
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_LEAK
bool "IOMMU leak tracing"
depends on DEBUG_KERNEL
depends on IOMMU_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.
#
# 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.
endmenu
config OPTIMIZE_INLINING
bool "Allow gcc to uninline functions marked 'inline'"
default y
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
disabling this option will generate a smaller kernel there. Hopefully
this algorithm is so good that allowing gcc4 to make the decision can
become the default in the future, until then this option is there to
test gcc for this.
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