1Dynamic debug 2+++++++++++++ 3 4 5Introduction 6============ 7 8Dynamic debug allows you to dynamically enable/disable kernel 9debug-print code to obtain additional kernel information. 10 11If ``/proc/dynamic_debug/control`` exists, your kernel has dynamic 12debug. You'll need root access (sudo su) to use this. 13 14Dynamic debug provides: 15 16 * a Catalog of all *prdbgs* in your kernel. 17 ``cat /proc/dynamic_debug/control`` to see them. 18 19 * a Simple query/command language to alter *prdbgs* by selecting on 20 any combination of 0 or 1 of: 21 22 - source filename 23 - function name 24 - line number (including ranges of line numbers) 25 - module name 26 - format string 27 - class name (as known/declared by each module) 28 29Viewing Dynamic Debug Behaviour 30=============================== 31 32You can view the currently configured behaviour in the *prdbg* catalog:: 33 34 :#> head -n7 /proc/dynamic_debug/control 35 # filename:lineno [module]function flags format 36 init/main.c:1179 [main]initcall_blacklist =_ "blacklisting initcall %s\012 37 init/main.c:1218 [main]initcall_blacklisted =_ "initcall %s blacklisted\012" 38 init/main.c:1424 [main]run_init_process =_ " with arguments:\012" 39 init/main.c:1426 [main]run_init_process =_ " %s\012" 40 init/main.c:1427 [main]run_init_process =_ " with environment:\012" 41 init/main.c:1429 [main]run_init_process =_ " %s\012" 42 43The 3rd space-delimited column shows the current flags, preceded by 44a ``=`` for easy use with grep/cut. ``=p`` shows enabled callsites. 45 46Controlling dynamic debug Behaviour 47=================================== 48 49The behaviour of *prdbg* sites are controlled by writing 50query/commands to the control file. Example:: 51 52 # grease the interface 53 :#> alias ddcmd='echo $* > /proc/dynamic_debug/control' 54 55 :#> ddcmd '-p; module main func run* +p' 56 :#> grep =p /proc/dynamic_debug/control 57 init/main.c:1424 [main]run_init_process =p " with arguments:\012" 58 init/main.c:1426 [main]run_init_process =p " %s\012" 59 init/main.c:1427 [main]run_init_process =p " with environment:\012" 60 init/main.c:1429 [main]run_init_process =p " %s\012" 61 62Error messages go to console/syslog:: 63 64 :#> ddcmd mode foo +p 65 dyndbg: unknown keyword "mode" 66 dyndbg: query parse failed 67 bash: echo: write error: Invalid argument 68 69If debugfs is also enabled and mounted, ``dynamic_debug/control`` is 70also under the mount-dir, typically ``/sys/kernel/debug/``. 71 72Command Language Reference 73========================== 74 75At the basic lexical level, a command is a sequence of words separated 76by spaces or tabs. So these are all equivalent:: 77 78 :#> ddcmd file svcsock.c line 1603 +p 79 :#> ddcmd "file svcsock.c line 1603 +p" 80 :#> ddcmd ' file svcsock.c line 1603 +p ' 81 82Command submissions are bounded by a write() system call. 83Multiple commands can be written together, separated by ``;`` or ``\n``:: 84 85 :#> ddcmd "func pnpacpi_get_resources +p; func pnp_assign_mem +p" 86 :#> ddcmd <<"EOC" 87 func pnpacpi_get_resources +p 88 func pnp_assign_mem +p 89 EOC 90 :#> cat query-batch-file > /proc/dynamic_debug/control 91 92You can also use wildcards in each query term. The match rule supports 93``*`` (matches zero or more characters) and ``?`` (matches exactly one 94character). For example, you can match all usb drivers:: 95 96 :#> ddcmd file "drivers/usb/*" +p # "" to suppress shell expansion 97 98Syntactically, a command is pairs of keyword values, followed by a 99flags change or setting:: 100 101 command ::= match-spec* flags-spec 102 103The match-spec's select *prdbgs* from the catalog, upon which to apply 104the flags-spec, all constraints are ANDed together. An absent keyword 105is the same as keyword "*". 106 107 108A match specification is a keyword, which selects the attribute of 109the callsite to be compared, and a value to compare against. Possible 110keywords are::: 111 112 match-spec ::= 'func' string | 113 'file' string | 114 'module' string | 115 'format' string | 116 'class' string | 117 'line' line-range 118 119 line-range ::= lineno | 120 '-'lineno | 121 lineno'-' | 122 lineno'-'lineno 123 124 lineno ::= unsigned-int 125 126.. note:: 127 128 ``line-range`` cannot contain space, e.g. 129 "1-30" is valid range but "1 - 30" is not. 130 131 132The meanings of each keyword are: 133 134func 135 The given string is compared against the function name 136 of each callsite. Example:: 137 138 func svc_tcp_accept 139 func *recv* # in rfcomm, bluetooth, ping, tcp 140 141file 142 The given string is compared against either the src-root relative 143 pathname, or the basename of the source file of each callsite. 144 Examples:: 145 146 file svcsock.c 147 file kernel/freezer.c # ie column 1 of control file 148 file drivers/usb/* # all callsites under it 149 file inode.c:start_* # parse :tail as a func (above) 150 file inode.c:1-100 # parse :tail as a line-range (above) 151 152module 153 The given string is compared against the module name 154 of each callsite. The module name is the string as 155 seen in ``lsmod``, i.e. without the directory or the ``.ko`` 156 suffix and with ``-`` changed to ``_``. Examples:: 157 158 module sunrpc 159 module nfsd 160 module drm* # both drm, drm_kms_helper 161 162format 163 The given string is searched for in the dynamic debug format 164 string. Note that the string does not need to match the 165 entire format, only some part. Whitespace and other 166 special characters can be escaped using C octal character 167 escape ``\ooo`` notation, e.g. the space character is ``\040``. 168 Alternatively, the string can be enclosed in double quote 169 characters (``"``) or single quote characters (``'``). 170 Examples:: 171 172 format svcrdma: // many of the NFS/RDMA server pr_debugs 173 format readahead // some pr_debugs in the readahead cache 174 format nfsd:\040SETATTR // one way to match a format with whitespace 175 format "nfsd: SETATTR" // a neater way to match a format with whitespace 176 format 'nfsd: SETATTR' // yet another way to match a format with whitespace 177 178class 179 The given class_name is validated against each module, which may 180 have declared a list of known class_names. If the class_name is 181 found for a module, callsite & class matching and adjustment 182 proceeds. Examples:: 183 184 class DRM_UT_KMS # a DRM.debug category 185 class JUNK # silent non-match 186 // class TLD_* # NOTICE: no wildcard in class names 187 188line 189 The given line number or range of line numbers is compared 190 against the line number of each ``pr_debug()`` callsite. A single 191 line number matches the callsite line number exactly. A 192 range of line numbers matches any callsite between the first 193 and last line number inclusive. An empty first number means 194 the first line in the file, an empty last line number means the 195 last line number in the file. Examples:: 196 197 line 1603 // exactly line 1603 198 line 1600-1605 // the six lines from line 1600 to line 1605 199 line -1605 // the 1605 lines from line 1 to line 1605 200 line 1600- // all lines from line 1600 to the end of the file 201 202The flags specification comprises a change operation followed 203by one or more flag characters. The change operation is one 204of the characters:: 205 206 - remove the given flags 207 + add the given flags 208 = set the flags to the given flags 209 210The flags are:: 211 212 p enables the pr_debug() callsite. 213 _ enables no flags. 214 215 Decorator flags add to the message-prefix, in order: 216 t Include thread ID, or <intr> 217 m Include module name 218 f Include the function name 219 s Include the source file name 220 l Include line number 221 222For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only 223the ``p`` flag has meaning, other flags are ignored. 224 225Note the regexp ``^[-+=][fslmpt_]+$`` matches a flags specification. 226To clear all flags at once, use ``=_`` or ``-fslmpt``. 227 228 229Debug messages during Boot Process 230================================== 231 232To activate debug messages for core code and built-in modules during 233the boot process, even before userspace and debugfs exists, use 234``dyndbg="QUERY"`` or ``module.dyndbg="QUERY"``. QUERY follows 235the syntax described above, but must not exceed 1023 characters. Your 236bootloader may impose lower limits. 237 238These ``dyndbg`` params are processed just after the ddebug tables are 239processed, as part of the early_initcall. Thus you can enable debug 240messages in all code run after this early_initcall via this boot 241parameter. 242 243On an x86 system for example ACPI enablement is a subsys_initcall and:: 244 245 dyndbg="file ec.c +p" 246 247will show early Embedded Controller transactions during ACPI setup if 248your machine (typically a laptop) has an Embedded Controller. 249PCI (or other devices) initialization also is a hot candidate for using 250this boot parameter for debugging purposes. 251 252If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at 253boot time, without effect, but will be reprocessed when module is 254loaded later. Bare ``dyndbg=`` is only processed at boot. 255 256 257Debug Messages at Module Initialization Time 258============================================ 259 260When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for 261``foo.params``, strips ``foo.``, and passes them to the kernel along with 262params given in modprobe args or ``/etc/modprobe.d/*.conf`` files, 263in the following order: 264 2651. parameters given via ``/etc/modprobe.d/*.conf``:: 266 267 options foo dyndbg=+pt 268 options foo dyndbg # defaults to +p 269 2702. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed:: 271 272 foo.dyndbg=" func bar +p; func buz +mp" 273 2743. args to modprobe:: 275 276 modprobe foo dyndbg==pmf # override previous settings 277 278These ``dyndbg`` queries are applied in order, with last having final say. 279This allows boot args to override or modify those from ``/etc/modprobe.d`` 280(sensible, since 1 is system wide, 2 is kernel or boot specific), and 281modprobe args to override both. 282 283In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``. 284``foo`` is extracted from the param-name, and applied to each query in 285``QUERY``, and only 1 match-spec of each type is allowed. 286 287The ``dyndbg`` option is a "fake" module parameter, which means: 288 289- modules do not need to define it explicitly 290- every module gets it tacitly, whether they use pr_debug or not 291- it doesn't appear in ``/sys/module/$module/parameters/`` 292 To see it, grep the control file, or inspect ``/proc/cmdline.`` 293 294For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or 295enabled by ``-DDEBUG`` flag during compilation) can be disabled later via 296the debugfs interface if the debug messages are no longer needed:: 297 298 echo "module module_name -p" > /proc/dynamic_debug/control 299 300Examples 301======== 302 303:: 304 305 // enable the message at line 1603 of file svcsock.c 306 :#> ddcmd 'file svcsock.c line 1603 +p' 307 308 // enable all the messages in file svcsock.c 309 :#> ddcmd 'file svcsock.c +p' 310 311 // enable all the messages in the NFS server module 312 :#> ddcmd 'module nfsd +p' 313 314 // enable all 12 messages in the function svc_process() 315 :#> ddcmd 'func svc_process +p' 316 317 // disable all 12 messages in the function svc_process() 318 :#> ddcmd 'func svc_process -p' 319 320 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+. 321 :#> ddcmd 'format "nfsd: READ" +p' 322 323 // enable messages in files of which the paths include string "usb" 324 :#> ddcmd 'file *usb* +p' 325 326 // enable all messages 327 :#> ddcmd '+p' 328 329 // add module, function to all enabled messages 330 :#> ddcmd '+mf' 331 332 // boot-args example, with newlines and comments for readability 333 Kernel command line: ... 334 // see what's going on in dyndbg=value processing 335 dynamic_debug.verbose=3 336 // enable pr_debugs in the btrfs module (can be builtin or loadable) 337 btrfs.dyndbg="+p" 338 // enable pr_debugs in all files under init/ 339 // and the function parse_one, #cmt is stripped 340 dyndbg="file init/* +p #cmt ; func parse_one +p" 341 // enable pr_debugs in 2 functions in a module loaded later 342 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p" 343 344Kernel Configuration 345==================== 346 347Dynamic Debug is enabled via kernel config items:: 348 349 CONFIG_DYNAMIC_DEBUG=y # build catalog, enables CORE 350 CONFIG_DYNAMIC_DEBUG_CORE=y # enable mechanics only, skip catalog 351 352If you do not want to enable dynamic debug globally (i.e. in some embedded 353system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic 354debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any 355modules which you'd like to dynamically debug later. 356 357 358Kernel *prdbg* API 359================== 360 361The following functions are cataloged and controllable when dynamic 362debug is enabled:: 363 364 pr_debug() 365 dev_dbg() 366 print_hex_dump_debug() 367 print_hex_dump_bytes() 368 369Otherwise, they are off by default; ``ccflags += -DDEBUG`` or 370``#define DEBUG`` in a source file will enable them appropriately. 371 372If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is 373just a shortcut for ``print_hex_dump(KERN_DEBUG)``. 374 375For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is 376its ``prefix_str`` argument, if it is constant string; or ``hexdump`` 377in case ``prefix_str`` is built dynamically. 378