linux/arch/x86/Kconfig.debug
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   1menu "Kernel hacking"
   2
   3config TRACE_IRQFLAGS_SUPPORT
   4        def_bool y
   5
   6source "lib/Kconfig.debug"
   7
   8config STRICT_DEVMEM
   9        bool "Filter access to /dev/mem"
  10        help
  11          If this option is disabled, you allow userspace (root) access to all
  12          of memory, including kernel and userspace memory. Accidental
  13          access to this is obviously disastrous, but specific access can
  14          be used by people debugging the kernel. Note that with PAT support
  15          enabled, even in this case there are restrictions on /dev/mem
  16          use due to the cache aliasing requirements.
  17
  18          If this option is switched on, the /dev/mem file only allows
  19          userspace access to PCI space and the BIOS code and data regions.
  20          This is sufficient for dosemu and X and all common users of
  21          /dev/mem.
  22
  23          If in doubt, say Y.
  24
  25config X86_VERBOSE_BOOTUP
  26        bool "Enable verbose x86 bootup info messages"
  27        default y
  28        help
  29          Enables the informational output from the decompression stage
  30          (e.g. bzImage) of the boot. If you disable this you will still
  31          see errors. Disable this if you want silent bootup.
  32
  33config EARLY_PRINTK
  34        bool "Early printk" if EMBEDDED
  35        default y
  36        help
  37          Write kernel log output directly into the VGA buffer or to a serial
  38          port.
  39
  40          This is useful for kernel debugging when your machine crashes very
  41          early before the console code is initialized. For normal operation
  42          it is not recommended because it looks ugly and doesn't cooperate
  43          with klogd/syslogd or the X server. You should normally N here,
  44          unless you want to debug such a crash.
  45
  46config EARLY_PRINTK_DBGP
  47        bool "Early printk via EHCI debug port"
  48        default n
  49        depends on EARLY_PRINTK && PCI
  50        help
  51          Write kernel log output directly into the EHCI debug port.
  52
  53          This is useful for kernel debugging when your machine crashes very
  54          early before the console code is initialized. For normal operation
  55          it is not recommended because it looks ugly and doesn't cooperate
  56          with klogd/syslogd or the X server. You should normally N here,
  57          unless you want to debug such a crash. You need usb debug device.
  58
  59config DEBUG_STACKOVERFLOW
  60        bool "Check for stack overflows"
  61        depends on DEBUG_KERNEL
  62        help
  63          This option will cause messages to be printed if free stack space
  64          drops below a certain limit.
  65
  66config DEBUG_STACK_USAGE
  67        bool "Stack utilization instrumentation"
  68        depends on DEBUG_KERNEL
  69        help
  70          Enables the display of the minimum amount of free stack which each
  71          task has ever had available in the sysrq-T and sysrq-P debug output.
  72
  73          This option will slow down process creation somewhat.
  74
  75config DEBUG_PAGEALLOC
  76        bool "Debug page memory allocations"
  77        depends on DEBUG_KERNEL
  78        help
  79          Unmap pages from the kernel linear mapping after free_pages().
  80          This results in a large slowdown, but helps to find certain types
  81          of memory corruptions.
  82
  83config DEBUG_PER_CPU_MAPS
  84        bool "Debug access to per_cpu maps"
  85        depends on DEBUG_KERNEL
  86        depends on X86_SMP
  87        default n
  88        help
  89          Say Y to verify that the per_cpu map being accessed has
  90          been setup.  Adds a fair amount of code to kernel memory
  91          and decreases performance.
  92
  93          Say N if unsure.
  94
  95config X86_PTDUMP
  96        bool "Export kernel pagetable layout to userspace via debugfs"
  97        depends on DEBUG_KERNEL
  98        select DEBUG_FS
  99        help
 100          Say Y here if you want to show the kernel pagetable layout in a
 101          debugfs file. This information is only useful for kernel developers
 102          who are working in architecture specific areas of the kernel.
 103          It is probably not a good idea to enable this feature in a production
 104          kernel.
 105          If in doubt, say "N"
 106
 107config DEBUG_RODATA
 108        bool "Write protect kernel read-only data structures"
 109        default y
 110        depends on DEBUG_KERNEL
 111        help
 112          Mark the kernel read-only data as write-protected in the pagetables,
 113          in order to catch accidental (and incorrect) writes to such const
 114          data. This is recommended so that we can catch kernel bugs sooner.
 115          If in doubt, say "Y".
 116
 117config DIRECT_GBPAGES
 118        bool "Enable gbpages-mapped kernel pagetables"
 119        depends on DEBUG_KERNEL && EXPERIMENTAL && X86_64
 120        help
 121          Enable gigabyte pages support (if the CPU supports it). This can
 122          improve the kernel's performance a tiny bit by reducing TLB
 123          pressure.
 124
 125          This is experimental code.
 126
 127          If in doubt, say "N".
 128
 129config DEBUG_RODATA_TEST
 130        bool "Testcase for the DEBUG_RODATA feature"
 131        depends on DEBUG_RODATA
 132        help
 133          This option enables a testcase for the DEBUG_RODATA
 134          feature as well as for the change_page_attr() infrastructure.
 135          If in doubt, say "N"
 136
 137config DEBUG_NX_TEST
 138        tristate "Testcase for the NX non-executable stack feature"
 139        depends on DEBUG_KERNEL && m
 140        help
 141          This option enables a testcase for the CPU NX capability
 142          and the software setup of this feature.
 143          If in doubt, say "N"
 144
 145config 4KSTACKS
 146        bool "Use 4Kb for kernel stacks instead of 8Kb"
 147        depends on X86_32
 148        help
 149          If you say Y here the kernel will use a 4Kb stacksize for the
 150          kernel stack attached to each process/thread. This facilitates
 151          running more threads on a system and also reduces the pressure
 152          on the VM subsystem for higher order allocations. This option
 153          will also use IRQ stacks to compensate for the reduced stackspace.
 154
 155config DOUBLEFAULT
 156        default y
 157        bool "Enable doublefault exception handler" if EMBEDDED
 158        depends on X86_32
 159        help
 160          This option allows trapping of rare doublefault exceptions that
 161          would otherwise cause a system to silently reboot. Disabling this
 162          option saves about 4k and might cause you much additional grey
 163          hair.
 164
 165config IOMMU_DEBUG
 166        bool "Enable IOMMU debugging"
 167        depends on GART_IOMMU && DEBUG_KERNEL
 168        depends on X86_64
 169        help
 170          Force the IOMMU to on even when you have less than 4GB of
 171          memory and add debugging code. On overflow always panic. And
 172          allow to enable IOMMU leak tracing. Can be disabled at boot
 173          time with iommu=noforce. This will also enable scatter gather
 174          list merging.  Currently not recommended for production
 175          code. When you use it make sure you have a big enough
 176          IOMMU/AGP aperture.  Most of the options enabled by this can
 177          be set more finegrained using the iommu= command line
 178          options. See Documentation/x86_64/boot-options.txt for more
 179          details.
 180
 181config IOMMU_LEAK
 182        bool "IOMMU leak tracing"
 183        depends on DEBUG_KERNEL
 184        depends on IOMMU_DEBUG
 185        help
 186          Add a simple leak tracer to the IOMMU code. This is useful when you
 187          are debugging a buggy device driver that leaks IOMMU mappings.
 188
 189config MMIOTRACE_HOOKS
 190        bool
 191
 192config MMIOTRACE
 193        bool "Memory mapped IO tracing"
 194        depends on DEBUG_KERNEL && PCI
 195        select TRACING
 196        select MMIOTRACE_HOOKS
 197        help
 198          Mmiotrace traces Memory Mapped I/O access and is meant for
 199          debugging and reverse engineering. It is called from the ioremap
 200          implementation and works via page faults. Tracing is disabled by
 201          default and can be enabled at run-time.
 202
 203          See Documentation/tracers/mmiotrace.txt.
 204          If you are not helping to develop drivers, say N.
 205
 206config MMIOTRACE_TEST
 207        tristate "Test module for mmiotrace"
 208        depends on MMIOTRACE && m
 209        help
 210          This is a dumb module for testing mmiotrace. It is very dangerous
 211          as it will write garbage to IO memory starting at a given address.
 212          However, it should be safe to use on e.g. unused portion of VRAM.
 213
 214          Say N, unless you absolutely know what you are doing.
 215
 216#
 217# IO delay types:
 218#
 219
 220config IO_DELAY_TYPE_0X80
 221        int
 222        default "0"
 223
 224config IO_DELAY_TYPE_0XED
 225        int
 226        default "1"
 227
 228config IO_DELAY_TYPE_UDELAY
 229        int
 230        default "2"
 231
 232config IO_DELAY_TYPE_NONE
 233        int
 234        default "3"
 235
 236choice
 237        prompt "IO delay type"
 238        default IO_DELAY_0X80
 239
 240config IO_DELAY_0X80
 241        bool "port 0x80 based port-IO delay [recommended]"
 242        help
 243          This is the traditional Linux IO delay used for in/out_p.
 244          It is the most tested hence safest selection here.
 245
 246config IO_DELAY_0XED
 247        bool "port 0xed based port-IO delay"
 248        help
 249          Use port 0xed as the IO delay. This frees up port 0x80 which is
 250          often used as a hardware-debug port.
 251
 252config IO_DELAY_UDELAY
 253        bool "udelay based port-IO delay"
 254        help
 255          Use udelay(2) as the IO delay method. This provides the delay
 256          while not having any side-effect on the IO port space.
 257
 258config IO_DELAY_NONE
 259        bool "no port-IO delay"
 260        help
 261          No port-IO delay. Will break on old boxes that require port-IO
 262          delay for certain operations. Should work on most new machines.
 263
 264endchoice
 265
 266if IO_DELAY_0X80
 267config DEFAULT_IO_DELAY_TYPE
 268        int
 269        default IO_DELAY_TYPE_0X80
 270endif
 271
 272if IO_DELAY_0XED
 273config DEFAULT_IO_DELAY_TYPE
 274        int
 275        default IO_DELAY_TYPE_0XED
 276endif
 277
 278if IO_DELAY_UDELAY
 279config DEFAULT_IO_DELAY_TYPE
 280        int
 281        default IO_DELAY_TYPE_UDELAY
 282endif
 283
 284if IO_DELAY_NONE
 285config DEFAULT_IO_DELAY_TYPE
 286        int
 287        default IO_DELAY_TYPE_NONE
 288endif
 289
 290config DEBUG_BOOT_PARAMS
 291        bool "Debug boot parameters"
 292        depends on DEBUG_KERNEL
 293        depends on DEBUG_FS
 294        help
 295          This option will cause struct boot_params to be exported via debugfs.
 296
 297config CPA_DEBUG
 298        bool "CPA self-test code"
 299        depends on DEBUG_KERNEL
 300        help
 301          Do change_page_attr() self-tests every 30 seconds.
 302
 303config OPTIMIZE_INLINING
 304        bool "Allow gcc to uninline functions marked 'inline'"
 305        help
 306          This option determines if the kernel forces gcc to inline the functions
 307          developers have marked 'inline'. Doing so takes away freedom from gcc to
 308          do what it thinks is best, which is desirable for the gcc 3.x series of
 309          compilers. The gcc 4.x series have a rewritten inlining algorithm and
 310          disabling this option will generate a smaller kernel there. Hopefully
 311          this algorithm is so good that allowing gcc4 to make the decision can
 312          become the default in the future, until then this option is there to
 313          test gcc for this.
 314
 315          If unsure, say N.
 316
 317endmenu
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