377 lines
13 KiB
ReStructuredText
377 lines
13 KiB
ReStructuredText
Dynamic debug
|
|
+++++++++++++
|
|
|
|
|
|
Introduction
|
|
============
|
|
|
|
Dynamic debug allows you to dynamically enable/disable kernel
|
|
debug-print code to obtain additional kernel information.
|
|
|
|
If ``/proc/dynamic_debug/control`` exists, your kernel has dynamic
|
|
debug. You'll need root access (sudo su) to use this.
|
|
|
|
Dynamic debug provides:
|
|
|
|
* a Catalog of all *prdbgs* in your kernel.
|
|
``cat /proc/dynamic_debug/control`` to see them.
|
|
|
|
* a Simple query/command language to alter *prdbgs* by selecting on
|
|
any combination of 0 or 1 of:
|
|
|
|
- source filename
|
|
- function name
|
|
- line number (including ranges of line numbers)
|
|
- module name
|
|
- format string
|
|
- class name (as known/declared by each module)
|
|
|
|
Viewing Dynamic Debug Behaviour
|
|
===============================
|
|
|
|
You can view the currently configured behaviour in the *prdbg* catalog::
|
|
|
|
:#> head -n7 /proc/dynamic_debug/control
|
|
# filename:lineno [module]function flags format
|
|
init/main.c:1179 [main]initcall_blacklist =_ "blacklisting initcall %s\012
|
|
init/main.c:1218 [main]initcall_blacklisted =_ "initcall %s blacklisted\012"
|
|
init/main.c:1424 [main]run_init_process =_ " with arguments:\012"
|
|
init/main.c:1426 [main]run_init_process =_ " %s\012"
|
|
init/main.c:1427 [main]run_init_process =_ " with environment:\012"
|
|
init/main.c:1429 [main]run_init_process =_ " %s\012"
|
|
|
|
The 3rd space-delimited column shows the current flags, preceded by
|
|
a ``=`` for easy use with grep/cut. ``=p`` shows enabled callsites.
|
|
|
|
Controlling dynamic debug Behaviour
|
|
===================================
|
|
|
|
The behaviour of *prdbg* sites are controlled by writing
|
|
query/commands to the control file. Example::
|
|
|
|
# grease the interface
|
|
:#> alias ddcmd='echo $* > /proc/dynamic_debug/control'
|
|
|
|
:#> ddcmd '-p; module main func run* +p'
|
|
:#> grep =p /proc/dynamic_debug/control
|
|
init/main.c:1424 [main]run_init_process =p " with arguments:\012"
|
|
init/main.c:1426 [main]run_init_process =p " %s\012"
|
|
init/main.c:1427 [main]run_init_process =p " with environment:\012"
|
|
init/main.c:1429 [main]run_init_process =p " %s\012"
|
|
|
|
Error messages go to console/syslog::
|
|
|
|
:#> ddcmd mode foo +p
|
|
dyndbg: unknown keyword "mode"
|
|
dyndbg: query parse failed
|
|
bash: echo: write error: Invalid argument
|
|
|
|
If debugfs is also enabled and mounted, ``dynamic_debug/control`` is
|
|
also under the mount-dir, typically ``/sys/kernel/debug/``.
|
|
|
|
Command Language Reference
|
|
==========================
|
|
|
|
At the basic lexical level, a command is a sequence of words separated
|
|
by spaces or tabs. So these are all equivalent::
|
|
|
|
:#> ddcmd file svcsock.c line 1603 +p
|
|
:#> ddcmd "file svcsock.c line 1603 +p"
|
|
:#> ddcmd ' file svcsock.c line 1603 +p '
|
|
|
|
Command submissions are bounded by a write() system call.
|
|
Multiple commands can be written together, separated by ``;`` or ``\n``::
|
|
|
|
:#> ddcmd "func pnpacpi_get_resources +p; func pnp_assign_mem +p"
|
|
:#> ddcmd <<"EOC"
|
|
func pnpacpi_get_resources +p
|
|
func pnp_assign_mem +p
|
|
EOC
|
|
:#> cat query-batch-file > /proc/dynamic_debug/control
|
|
|
|
You can also use wildcards in each query term. The match rule supports
|
|
``*`` (matches zero or more characters) and ``?`` (matches exactly one
|
|
character). For example, you can match all usb drivers::
|
|
|
|
:#> ddcmd file "drivers/usb/*" +p # "" to suppress shell expansion
|
|
|
|
Syntactically, a command is pairs of keyword values, followed by a
|
|
flags change or setting::
|
|
|
|
command ::= match-spec* flags-spec
|
|
|
|
The match-spec's select *prdbgs* from the catalog, upon which to apply
|
|
the flags-spec, all constraints are ANDed together. An absent keyword
|
|
is the same as keyword "*".
|
|
|
|
|
|
A match specification is a keyword, which selects the attribute of
|
|
the callsite to be compared, and a value to compare against. Possible
|
|
keywords are:::
|
|
|
|
match-spec ::= 'func' string |
|
|
'file' string |
|
|
'module' string |
|
|
'format' string |
|
|
'class' string |
|
|
'line' line-range
|
|
|
|
line-range ::= lineno |
|
|
'-'lineno |
|
|
lineno'-' |
|
|
lineno'-'lineno
|
|
|
|
lineno ::= unsigned-int
|
|
|
|
.. note::
|
|
|
|
``line-range`` cannot contain space, e.g.
|
|
"1-30" is valid range but "1 - 30" is not.
|
|
|
|
|
|
The meanings of each keyword are:
|
|
|
|
func
|
|
The given string is compared against the function name
|
|
of each callsite. Example::
|
|
|
|
func svc_tcp_accept
|
|
func *recv* # in rfcomm, bluetooth, ping, tcp
|
|
|
|
file
|
|
The given string is compared against either the src-root relative
|
|
pathname, or the basename of the source file of each callsite.
|
|
Examples::
|
|
|
|
file svcsock.c
|
|
file kernel/freezer.c # ie column 1 of control file
|
|
file drivers/usb/* # all callsites under it
|
|
file inode.c:start_* # parse :tail as a func (above)
|
|
file inode.c:1-100 # parse :tail as a line-range (above)
|
|
|
|
module
|
|
The given string is compared against the module name
|
|
of each callsite. The module name is the string as
|
|
seen in ``lsmod``, i.e. without the directory or the ``.ko``
|
|
suffix and with ``-`` changed to ``_``. Examples::
|
|
|
|
module sunrpc
|
|
module nfsd
|
|
module drm* # both drm, drm_kms_helper
|
|
|
|
format
|
|
The given string is searched for in the dynamic debug format
|
|
string. Note that the string does not need to match the
|
|
entire format, only some part. Whitespace and other
|
|
special characters can be escaped using C octal character
|
|
escape ``\ooo`` notation, e.g. the space character is ``\040``.
|
|
Alternatively, the string can be enclosed in double quote
|
|
characters (``"``) or single quote characters (``'``).
|
|
Examples::
|
|
|
|
format svcrdma: // many of the NFS/RDMA server pr_debugs
|
|
format readahead // some pr_debugs in the readahead cache
|
|
format nfsd:\040SETATTR // one way to match a format with whitespace
|
|
format "nfsd: SETATTR" // a neater way to match a format with whitespace
|
|
format 'nfsd: SETATTR' // yet another way to match a format with whitespace
|
|
|
|
class
|
|
The given class_name is validated against each module, which may
|
|
have declared a list of known class_names. If the class_name is
|
|
found for a module, callsite & class matching and adjustment
|
|
proceeds. Examples::
|
|
|
|
class DRM_UT_KMS # a DRM.debug category
|
|
class JUNK # silent non-match
|
|
// class TLD_* # NOTICE: no wildcard in class names
|
|
|
|
line
|
|
The given line number or range of line numbers is compared
|
|
against the line number of each ``pr_debug()`` callsite. A single
|
|
line number matches the callsite line number exactly. A
|
|
range of line numbers matches any callsite between the first
|
|
and last line number inclusive. An empty first number means
|
|
the first line in the file, an empty last line number means the
|
|
last line number in the file. Examples::
|
|
|
|
line 1603 // exactly line 1603
|
|
line 1600-1605 // the six lines from line 1600 to line 1605
|
|
line -1605 // the 1605 lines from line 1 to line 1605
|
|
line 1600- // all lines from line 1600 to the end of the file
|
|
|
|
The flags specification comprises a change operation followed
|
|
by one or more flag characters. The change operation is one
|
|
of the characters::
|
|
|
|
- remove the given flags
|
|
+ add the given flags
|
|
= set the flags to the given flags
|
|
|
|
The flags are::
|
|
|
|
p enables the pr_debug() callsite.
|
|
_ enables no flags.
|
|
|
|
Decorator flags add to the message-prefix, in order:
|
|
t Include thread ID, or <intr>
|
|
m Include module name
|
|
f Include the function name
|
|
l Include line number
|
|
|
|
For ``print_hex_dump_debug()`` and ``print_hex_dump_bytes()``, only
|
|
the ``p`` flag has meaning, other flags are ignored.
|
|
|
|
Note the regexp ``^[-+=][flmpt_]+$`` matches a flags specification.
|
|
To clear all flags at once, use ``=_`` or ``-flmpt``.
|
|
|
|
|
|
Debug messages during Boot Process
|
|
==================================
|
|
|
|
To activate debug messages for core code and built-in modules during
|
|
the boot process, even before userspace and debugfs exists, use
|
|
``dyndbg="QUERY"`` or ``module.dyndbg="QUERY"``. QUERY follows
|
|
the syntax described above, but must not exceed 1023 characters. Your
|
|
bootloader may impose lower limits.
|
|
|
|
These ``dyndbg`` params are processed just after the ddebug tables are
|
|
processed, as part of the early_initcall. Thus you can enable debug
|
|
messages in all code run after this early_initcall via this boot
|
|
parameter.
|
|
|
|
On an x86 system for example ACPI enablement is a subsys_initcall and::
|
|
|
|
dyndbg="file ec.c +p"
|
|
|
|
will show early Embedded Controller transactions during ACPI setup if
|
|
your machine (typically a laptop) has an Embedded Controller.
|
|
PCI (or other devices) initialization also is a hot candidate for using
|
|
this boot parameter for debugging purposes.
|
|
|
|
If ``foo`` module is not built-in, ``foo.dyndbg`` will still be processed at
|
|
boot time, without effect, but will be reprocessed when module is
|
|
loaded later. Bare ``dyndbg=`` is only processed at boot.
|
|
|
|
|
|
Debug Messages at Module Initialization Time
|
|
============================================
|
|
|
|
When ``modprobe foo`` is called, modprobe scans ``/proc/cmdline`` for
|
|
``foo.params``, strips ``foo.``, and passes them to the kernel along with
|
|
params given in modprobe args or ``/etc/modprob.d/*.conf`` files,
|
|
in the following order:
|
|
|
|
1. parameters given via ``/etc/modprobe.d/*.conf``::
|
|
|
|
options foo dyndbg=+pt
|
|
options foo dyndbg # defaults to +p
|
|
|
|
2. ``foo.dyndbg`` as given in boot args, ``foo.`` is stripped and passed::
|
|
|
|
foo.dyndbg=" func bar +p; func buz +mp"
|
|
|
|
3. args to modprobe::
|
|
|
|
modprobe foo dyndbg==pmf # override previous settings
|
|
|
|
These ``dyndbg`` queries are applied in order, with last having final say.
|
|
This allows boot args to override or modify those from ``/etc/modprobe.d``
|
|
(sensible, since 1 is system wide, 2 is kernel or boot specific), and
|
|
modprobe args to override both.
|
|
|
|
In the ``foo.dyndbg="QUERY"`` form, the query must exclude ``module foo``.
|
|
``foo`` is extracted from the param-name, and applied to each query in
|
|
``QUERY``, and only 1 match-spec of each type is allowed.
|
|
|
|
The ``dyndbg`` option is a "fake" module parameter, which means:
|
|
|
|
- modules do not need to define it explicitly
|
|
- every module gets it tacitly, whether they use pr_debug or not
|
|
- it doesn't appear in ``/sys/module/$module/parameters/``
|
|
To see it, grep the control file, or inspect ``/proc/cmdline.``
|
|
|
|
For ``CONFIG_DYNAMIC_DEBUG`` kernels, any settings given at boot-time (or
|
|
enabled by ``-DDEBUG`` flag during compilation) can be disabled later via
|
|
the debugfs interface if the debug messages are no longer needed::
|
|
|
|
echo "module module_name -p" > /proc/dynamic_debug/control
|
|
|
|
Examples
|
|
========
|
|
|
|
::
|
|
|
|
// enable the message at line 1603 of file svcsock.c
|
|
:#> ddcmd 'file svcsock.c line 1603 +p'
|
|
|
|
// enable all the messages in file svcsock.c
|
|
:#> ddcmd 'file svcsock.c +p'
|
|
|
|
// enable all the messages in the NFS server module
|
|
:#> ddcmd 'module nfsd +p'
|
|
|
|
// enable all 12 messages in the function svc_process()
|
|
:#> ddcmd 'func svc_process +p'
|
|
|
|
// disable all 12 messages in the function svc_process()
|
|
:#> ddcmd 'func svc_process -p'
|
|
|
|
// enable messages for NFS calls READ, READLINK, READDIR and READDIR+.
|
|
:#> ddcmd 'format "nfsd: READ" +p'
|
|
|
|
// enable messages in files of which the paths include string "usb"
|
|
:#> ddcmd 'file *usb* +p' > /proc/dynamic_debug/control
|
|
|
|
// enable all messages
|
|
:#> ddcmd '+p' > /proc/dynamic_debug/control
|
|
|
|
// add module, function to all enabled messages
|
|
:#> ddcmd '+mf' > /proc/dynamic_debug/control
|
|
|
|
// boot-args example, with newlines and comments for readability
|
|
Kernel command line: ...
|
|
// see whats going on in dyndbg=value processing
|
|
dynamic_debug.verbose=3
|
|
// enable pr_debugs in the btrfs module (can be builtin or loadable)
|
|
btrfs.dyndbg="+p"
|
|
// enable pr_debugs in all files under init/
|
|
// and the function parse_one, #cmt is stripped
|
|
dyndbg="file init/* +p #cmt ; func parse_one +p"
|
|
// enable pr_debugs in 2 functions in a module loaded later
|
|
pc87360.dyndbg="func pc87360_init_device +p; func pc87360_find +p"
|
|
|
|
Kernel Configuration
|
|
====================
|
|
|
|
Dynamic Debug is enabled via kernel config items::
|
|
|
|
CONFIG_DYNAMIC_DEBUG=y # build catalog, enables CORE
|
|
CONFIG_DYNAMIC_DEBUG_CORE=y # enable mechanics only, skip catalog
|
|
|
|
If you do not want to enable dynamic debug globally (i.e. in some embedded
|
|
system), you may set ``CONFIG_DYNAMIC_DEBUG_CORE`` as basic support of dynamic
|
|
debug and add ``ccflags := -DDYNAMIC_DEBUG_MODULE`` into the Makefile of any
|
|
modules which you'd like to dynamically debug later.
|
|
|
|
|
|
Kernel *prdbg* API
|
|
==================
|
|
|
|
The following functions are cataloged and controllable when dynamic
|
|
debug is enabled::
|
|
|
|
pr_debug()
|
|
dev_dbg()
|
|
print_hex_dump_debug()
|
|
print_hex_dump_bytes()
|
|
|
|
Otherwise, they are off by default; ``ccflags += -DDEBUG`` or
|
|
``#define DEBUG`` in a source file will enable them appropriately.
|
|
|
|
If ``CONFIG_DYNAMIC_DEBUG`` is not set, ``print_hex_dump_debug()`` is
|
|
just a shortcut for ``print_hex_dump(KERN_DEBUG)``.
|
|
|
|
For ``print_hex_dump_debug()``/``print_hex_dump_bytes()``, format string is
|
|
its ``prefix_str`` argument, if it is constant string; or ``hexdump``
|
|
in case ``prefix_str`` is built dynamically.
|