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1Dynamic debug2+++++++++++++3 4 5Introduction6============7 8Dynamic debug allows you to dynamically enable/disable kernel9debug-print code to obtain additional kernel information.10 11If ``/proc/dynamic_debug/control`` exists, your kernel has dynamic12debug. 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 on20 any combination of 0 or 1 of:21 22 - source filename23 - function name24 - line number (including ranges of line numbers)25 - module name26 - format string27 - class name (as known/declared by each module)28 29NOTE: To actually get the debug-print output on the console, you may30need to adjust the kernel ``loglevel=``, or use ``ignore_loglevel``.31Read about these kernel parameters in32Documentation/admin-guide/kernel-parameters.rst.33 34Viewing Dynamic Debug Behaviour35===============================36 37You can view the currently configured behaviour in the *prdbg* catalog::38 39 :#> head -n7 /proc/dynamic_debug/control40 # filename:lineno [module]function flags format41 init/main.c:1179 [main]initcall_blacklist =_ "blacklisting initcall %s\01242 init/main.c:1218 [main]initcall_blacklisted =_ "initcall %s blacklisted\012"43 init/main.c:1424 [main]run_init_process =_ " with arguments:\012"44 init/main.c:1426 [main]run_init_process =_ " %s\012"45 init/main.c:1427 [main]run_init_process =_ " with environment:\012"46 init/main.c:1429 [main]run_init_process =_ " %s\012"47 48The 3rd space-delimited column shows the current flags, preceded by49a ``=`` for easy use with grep/cut. ``=p`` shows enabled callsites.50 51Controlling dynamic debug Behaviour52===================================53 54The behaviour of *prdbg* sites are controlled by writing55query/commands to the control file. Example::56 57 # grease the interface58 :#> alias ddcmd='echo $* > /proc/dynamic_debug/control'59 60 :#> ddcmd '-p; module main func run* +p'61 :#> grep =p /proc/dynamic_debug/control62 init/main.c:1424 [main]run_init_process =p " with arguments:\012"63 init/main.c:1426 [main]run_init_process =p " %s\012"64 init/main.c:1427 [main]run_init_process =p " with environment:\012"65 init/main.c:1429 [main]run_init_process =p " %s\012"66 67Error messages go to console/syslog::68 69 :#> ddcmd mode foo +p70 dyndbg: unknown keyword "mode"71 dyndbg: query parse failed72 bash: echo: write error: Invalid argument73 74If debugfs is also enabled and mounted, ``dynamic_debug/control`` is75also under the mount-dir, typically ``/sys/kernel/debug/``.76 77Command Language Reference78==========================79 80At the basic lexical level, a command is a sequence of words separated81by spaces or tabs. So these are all equivalent::82 83 :#> ddcmd file svcsock.c line 1603 +p84 :#> ddcmd "file svcsock.c line 1603 +p"85 :#> ddcmd ' file svcsock.c line 1603 +p '86 87Command submissions are bounded by a write() system call.88Multiple commands can be written together, separated by ``;`` or ``\n``::89 90 :#> ddcmd "func pnpacpi_get_resources +p; func pnp_assign_mem +p"91 :#> ddcmd <<"EOC"92 func pnpacpi_get_resources +p93 func pnp_assign_mem +p94 EOC95 :#> cat query-batch-file > /proc/dynamic_debug/control96 97You can also use wildcards in each query term. The match rule supports98``*`` (matches zero or more characters) and ``?`` (matches exactly one99character). For example, you can match all usb drivers::100 101 :#> ddcmd file "drivers/usb/*" +p # "" to suppress shell expansion102 103Syntactically, a command is pairs of keyword values, followed by a104flags change or setting::105 106 command ::= match-spec* flags-spec107 108The match-spec's select *prdbgs* from the catalog, upon which to apply109the flags-spec, all constraints are ANDed together. An absent keyword110is the same as keyword "*".111 112 113A match specification is a keyword, which selects the attribute of114the callsite to be compared, and a value to compare against. Possible115keywords are:::116 117 match-spec ::= 'func' string |118 'file' string |119 'module' string |120 'format' string |121 'class' string |122 'line' line-range123 124 line-range ::= lineno |125 '-'lineno |126 lineno'-' |127 lineno'-'lineno128 129 lineno ::= unsigned-int130 131.. note::132 133 ``line-range`` cannot contain space, e.g.134 "1-30" is valid range but "1 - 30" is not.135 136 137The meanings of each keyword are:138 139func140 The given string is compared against the function name141 of each callsite. Example::142 143 func svc_tcp_accept144 func *recv* # in rfcomm, bluetooth, ping, tcp145 146file147 The given string is compared against either the src-root relative148 pathname, or the basename of the source file of each callsite.149 Examples::150 151 file svcsock.c152 file kernel/freezer.c # ie column 1 of control file153 file drivers/usb/* # all callsites under it154 file inode.c:start_* # parse :tail as a func (above)155 file inode.c:1-100 # parse :tail as a line-range (above)156 157module158 The given string is compared against the module name159 of each callsite. The module name is the string as160 seen in ``lsmod``, i.e. without the directory or the ``.ko``161 suffix and with ``-`` changed to ``_``. Examples::162 163 module sunrpc164 module nfsd165 module drm* # both drm, drm_kms_helper166 167format168 The given string is searched for in the dynamic debug format169 string. Note that the string does not need to match the170 entire format, only some part. Whitespace and other171 special characters can be escaped using C octal character172 escape ``\ooo`` notation, e.g. the space character is ``\040``.173 Alternatively, the string can be enclosed in double quote174 characters (``"``) or single quote characters (``'``).175 Examples::176 177 format svcrdma: // many of the NFS/RDMA server pr_debugs178 format readahead // some pr_debugs in the readahead cache179 format nfsd:\040SETATTR // one way to match a format with whitespace180 format "nfsd: SETATTR" // a neater way to match a format with whitespace181 format 'nfsd: SETATTR' // yet another way to match a format with whitespace182 183class184 The given class_name is validated against each module, which may185 have declared a list of known class_names. If the class_name is186 found for a module, callsite & class matching and adjustment187 proceeds. Examples::188 189 class DRM_UT_KMS # a DRM.debug category190 class JUNK # silent non-match191 // class TLD_* # NOTICE: no wildcard in class names192 193line194 The given line number or range of line numbers is compared195 against the line number of each ``pr_debug()`` callsite. A single196 line number matches the callsite line number exactly. A197 range of line numbers matches any callsite between the first198 and last line number inclusive. An empty first number means199 the first line in the file, an empty last line number means the200 last line number in the file. Examples::201 202 line 1603 // exactly line 1603203 line 1600-1605 // the six lines from line 1600 to line 1605204 line -1605 // the 1605 lines from line 1 to line 1605205 line 1600- // all lines from line 1600 to the end of the file206 207The flags specification comprises a change operation followed208by one or more flag characters. The change operation is one209of the characters::210 211 - remove the given flags212 + add the given flags213 = set the flags to the given flags214 215The flags are::216 217 p enables the pr_debug() callsite.218 _ enables no flags.219 220 Decorator flags add to the message-prefix, in order:221 t Include thread ID, or <intr>222 m Include module name223 f Include the function name224 s Include the source file name225 l Include line number226 227For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only228the ``p`` flag has meaning, other flags are ignored.229 230Note the regexp ``^[-+=][fslmpt_]+$`` matches a flags specification.231To clear all flags at once, use ``=_`` or ``-fslmpt``.232 233 234Debug messages during Boot Process235==================================236 237To activate debug messages for core code and built-in modules during238the boot process, even before userspace and debugfs exists, use239``dyndbg="QUERY"`` or ``module.dyndbg="QUERY"``. QUERY follows240the syntax described above, but must not exceed 1023 characters. Your241bootloader may impose lower limits.242 243These ``dyndbg`` params are processed just after the ddebug tables are244processed, as part of the early_initcall. Thus you can enable debug245messages in all code run after this early_initcall via this boot246parameter.247 248On an x86 system for example ACPI enablement is a subsys_initcall and::249 250 dyndbg="file ec.c +p"251 252will show early Embedded Controller transactions during ACPI setup if253your machine (typically a laptop) has an Embedded Controller.254PCI (or other devices) initialization also is a hot candidate for using255this boot parameter for debugging purposes.256 257If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at258boot time, without effect, but will be reprocessed when module is259loaded later. Bare ``dyndbg=`` is only processed at boot.260 261 262Debug Messages at Module Initialization Time263============================================264 265When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for266``foo.params``, strips ``foo.``, and passes them to the kernel along with267params given in modprobe args or ``/etc/modprobe.d/*.conf`` files,268in the following order:269 2701. parameters given via ``/etc/modprobe.d/*.conf``::271 272 options foo dyndbg=+pt273 options foo dyndbg # defaults to +p274 2752. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed::276 277 foo.dyndbg=" func bar +p; func buz +mp"278 2793. args to modprobe::280 281 modprobe foo dyndbg==pmf # override previous settings282 283These ``dyndbg`` queries are applied in order, with last having final say.284This allows boot args to override or modify those from ``/etc/modprobe.d``285(sensible, since 1 is system wide, 2 is kernel or boot specific), and286modprobe args to override both.287 288In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``.289``foo`` is extracted from the param-name, and applied to each query in290``QUERY``, and only 1 match-spec of each type is allowed.291 292The ``dyndbg`` option is a "fake" module parameter, which means:293 294- modules do not need to define it explicitly295- every module gets it tacitly, whether they use pr_debug or not296- it doesn't appear in ``/sys/module/$module/parameters/``297 To see it, grep the control file, or inspect ``/proc/cmdline.``298 299For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or300enabled by ``-DDEBUG`` flag during compilation) can be disabled later via301the debugfs interface if the debug messages are no longer needed::302 303 echo "module module_name -p" > /proc/dynamic_debug/control304 305Examples306========307 308::309 310 // enable the message at line 1603 of file svcsock.c311 :#> ddcmd 'file svcsock.c line 1603 +p'312 313 // enable all the messages in file svcsock.c314 :#> ddcmd 'file svcsock.c +p'315 316 // enable all the messages in the NFS server module317 :#> ddcmd 'module nfsd +p'318 319 // enable all 12 messages in the function svc_process()320 :#> ddcmd 'func svc_process +p'321 322 // disable all 12 messages in the function svc_process()323 :#> ddcmd 'func svc_process -p'324 325 // enable messages for NFS calls READ, READLINK, READDIR and READDIR+.326 :#> ddcmd 'format "nfsd: READ" +p'327 328 // enable messages in files of which the paths include string "usb"329 :#> ddcmd 'file *usb* +p'330 331 // enable all messages332 :#> ddcmd '+p'333 334 // add module, function to all enabled messages335 :#> ddcmd '+mf'336 337 // boot-args example, with newlines and comments for readability338 Kernel command line: ...339 // see what's going on in dyndbg=value processing340 dynamic_debug.verbose=3341 // enable pr_debugs in the btrfs module (can be builtin or loadable)342 btrfs.dyndbg="+p"343 // enable pr_debugs in all files under init/344 // and the function parse_one, #cmt is stripped345 dyndbg="file init/* +p #cmt ; func parse_one +p"346 // enable pr_debugs in 2 functions in a module loaded later347 pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"348 349Kernel Configuration350====================351 352Dynamic Debug is enabled via kernel config items::353 354 CONFIG_DYNAMIC_DEBUG=y # build catalog, enables CORE355 CONFIG_DYNAMIC_DEBUG_CORE=y # enable mechanics only, skip catalog356 357If you do not want to enable dynamic debug globally (i.e. in some embedded358system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic359debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any360modules which you'd like to dynamically debug later.361 362 363Kernel *prdbg* API364==================365 366The following functions are cataloged and controllable when dynamic367debug is enabled::368 369 pr_debug()370 dev_dbg()371 print_hex_dump_debug()372 print_hex_dump_bytes()373 374Otherwise, they are off by default; ``ccflags += -DDEBUG`` or375``#define DEBUG`` in a source file will enable them appropriately.376 377If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is378just a shortcut for ``print_hex_dump(KERN_DEBUG)``.379 380For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is381its ``prefix_str`` argument, if it is constant string; or ``hexdump``382in case ``prefix_str`` is built dynamically.383