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 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. config MMIOTRACE_HOOKS bool default n config MMIOTRACE tristate "Memory mapped IO tracing" depends on DEBUG_KERNEL && RELAY && DEBUG_FS select MMIOTRACE_HOOKS default n help This will build a kernel module called mmiotrace. Making this a built-in is heavily discouraged. Mmiotrace traces Memory Mapped I/O access and is meant for debugging and reverse engineering. The kernel module offers wrapped versions of the ioremap family of functions. The driver to be traced must be modified to call these wrappers. A user space program is required to collect the MMIO data. See http://nouveau.freedesktop.org/wiki/MmioTrace If you are not helping to develop drivers, say N. config MMIOTRACE_TEST tristate "Test module for mmiotrace" depends on MMIOTRACE && m default n help This is a dumb module for testing mmiotrace. It is very dangerous as it will write garbage to IO memory starting at a given address. However, it should be safe to use on e.g. unused portion of VRAM. Say N, unless you absolutely know what you are doing. # # 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'" depends on BROKEN 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. endmenu