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