1 ==================
2 S390 Debug Feature
3 ==================
4
5 files:
6 - arch/s390/kernel/debug.c
7 - arch/s390/include/asm/debug.h
8
9 Description:
10 ------------
11 The goal of this feature is to provide a kerne
12 where log records can be stored efficiently in
13 (e.g. device drivers) can have one separate de
14 One purpose of this is to inspect the debug lo
15 in order to analyze the reason for the crash.
16
17 If the system still runs but only a subcompone
18 it is possible to look at the debug logs on a
19 debugfs filesystem.
20
21 The debug feature may also very useful for ker
22
23 Design:
24 -------
25 Kernel components (e.g. device drivers) can re
26 feature with the function call :c:func:`debug_
27 This function initializes a
28 debug log for the caller. For each debug log e
29 where exactly one is active at one time. Each
30 pages in memory. In the debug areas there are
31 which are written by event- and exception-call
32
33 An event-call writes the specified debug entry
34 area and updates the log pointer for the activ
35 of the active debug area is reached, a wrap ar
36 and the next debug entry will be written at th
37 debug area.
38
39 An exception-call writes the specified debug e
40 switches to the next debug area. This is done
41 that the records which describe the origin of
42 overwritten when a wrap around for the current
43
44 The debug areas themselves are also ordered in
45 When an exception is thrown in the last debug
46 entries are then written again in the very fir
47
48 There are four versions for the event- and exc
49 logging raw data, one for text, one for number
50 and one for sprintf-like formatted strings.
51
52 Each debug entry contains the following data:
53
54 - Timestamp
55 - Cpu-Number of calling task
56 - Level of debug entry (0...6)
57 - Return Address to caller
58 - Flag, if entry is an exception or not
59
60 The debug logs can be inspected in a live syst
61 the debugfs-filesystem. Under the toplevel dir
62 a directory for each registered component, whi
63 corresponding component. The debugfs normally
64 ``/sys/kernel/debug`` therefore the debug feat
65 ``/sys/kernel/debug/s390dbf``.
66
67 The content of the directories are files which
68 to the debug log. Each component can decide wh
69 used through registering them with the functio
70 Predefined views for hex/ascii and sprintf dat
71 It is also possible to define other views. The
72 a view can be inspected simply by reading the
73
74 All debug logs have an actual debug level (ran
75 The default level is 3. Event and Exception fu
76 parameter. Only debug entries with a level tha
77 than the actual level are written to the log.
78 writing events, high priority log entries shou
79 value whereas low priority entries should have
80 The actual debug level can be changed with the
81 through writing a number string "x" to the ``l
82 provided for every debug log. Debugging can be
83 by using "-" on the ``level`` debugfs file.
84
85 Example::
86
87 > echo "-" > /sys/kernel/debug/s390dbf
88
89 It is also possible to deactivate the debug fe
90 debug log. You can change the behavior using
91 ``/proc/sys/s390dbf``:
92
93 There are currently 2 possible triggers, which
94 globally. The first possibility is to use the
95 set to 1 the debug feature is running. If ``de
96 debug feature is turned off.
97
98 The second trigger which stops the debug featu
99 That prevents the debug feature from overwriti
100 happened before the oops. After an oops you ca
101 by piping 1 to ``/proc/sys/s390dbf/debug_activ
102 suggested to use an oopsed kernel in a product
103
104 If you want to disallow the deactivation of th
105 the ``debug_stoppable`` sysctl. If you set ``d
106 feature cannot be stopped. If the debug featur
107 will stay deactivated.
108
109 Kernel Interfaces:
110 ------------------
111
112 .. kernel-doc:: arch/s390/kernel/debug.c
113 .. kernel-doc:: arch/s390/include/asm/debug.h
114
115 Predefined views:
116 -----------------
117
118 .. code-block:: c
119
120 extern struct debug_view debug_hex_ascii_vie
121
122 extern struct debug_view debug_sprintf_view;
123
124 Examples
125 --------
126
127 .. code-block:: c
128
129 /*
130 * hex_ascii-view Example
131 */
132
133 #include <linux/init.h>
134 #include <asm/debug.h>
135
136 static debug_info_t *debug_info;
137
138 static int init(void)
139 {
140 /* register 4 debug areas with one page
141
142 debug_info = debug_register("test", 1, 4
143 debug_register_view(debug_info, &debug_h
144
145 debug_text_event(debug_info, 4 , "one ")
146 debug_int_exception(debug_info, 4, 4711)
147 debug_event(debug_info, 3, &debug_info,
148
149 return 0;
150 }
151
152 static void cleanup(void)
153 {
154 debug_unregister(debug_info);
155 }
156
157 module_init(init);
158 module_exit(cleanup);
159
160 .. code-block:: c
161
162 /*
163 * sprintf-view Example
164 */
165
166 #include <linux/init.h>
167 #include <asm/debug.h>
168
169 static debug_info_t *debug_info;
170
171 static int init(void)
172 {
173 /* register 4 debug areas with one page
174 /* format string pointer + 2 varargs (=
175
176 debug_info = debug_register("test", 1, 4
177 debug_register_view(debug_info, &debug_s
178
179 debug_sprintf_event(debug_info, 2 , "fir
180 debug_sprintf_exception(debug_info, 1, "
181
182 return 0;
183 }
184
185 static void cleanup(void)
186 {
187 debug_unregister(debug_info);
188 }
189
190 module_init(init);
191 module_exit(cleanup);
192
193 Debugfs Interface
194 -----------------
195 Views to the debug logs can be investigated th
196 debugfs-files:
197
198 Example::
199
200 > ls /sys/kernel/debug/s390dbf/dasd
201 flush hex_ascii level pages
202 > cat /sys/kernel/debug/s390dbf/dasd/hex_asc
203 00 00974733272:680099 2 - 02 0006ad7e 07 ea
204 00 00974733272:682210 2 - 02 0006ade6 46 52
205 00 00974733272:682213 2 - 02 0006adf6 07 ea
206 00 00974733272:682281 1 * 02 0006ab08 41 4c
207 01 00974733272:682284 2 - 02 0006ab16 45 43
208 01 00974733272:682287 2 - 02 0006ab28 00 00
209 01 00974733272:682289 2 - 02 0006ab3e 00 00
210 01 00974733272:682297 2 - 02 0006ad7e 07 ea
211 01 00974733272:684384 2 - 00 0006ade6 46 52
212 01 00974733272:684388 2 - 00 0006adf6 07 ea
213
214 See section about predefined views for explana
215
216 Changing the debug level
217 ------------------------
218
219 Example::
220
221
222 > cat /sys/kernel/debug/s390dbf/dasd/level
223 3
224 > echo "5" > /sys/kernel/debug/s390dbf/dasd/
225 > cat /sys/kernel/debug/s390dbf/dasd/level
226 5
227
228 Flushing debug areas
229 --------------------
230 Debug areas can be flushed with piping the num
231 area (0...n) to the debugfs file "flush". When
232 are flushed.
233
234 Examples:
235
236 1. Flush debug area 0::
237
238 > echo "0" > /sys/kernel/debug/s390dbf/da
239
240 2. Flush all debug areas::
241
242 > echo "-" > /sys/kernel/debug/s390dbf/da
243
244 Changing the size of debug areas
245 ------------------------------------
246 It is possible the change the size of debug ar
247 the number of pages to the debugfs file "pages
248 also flush the debug areas.
249
250 Example:
251
252 Define 4 pages for the debug areas of debug fe
253
254 > echo "4" > /sys/kernel/debug/s390dbf/dasd/
255
256 Stopping the debug feature
257 --------------------------
258 Example:
259
260 1. Check if stopping is allowed::
261
262 > cat /proc/sys/s390dbf/debug_stoppable
263
264 2. Stop debug feature::
265
266 > echo 0 > /proc/sys/s390dbf/debug_active
267
268 crash Interface
269 ----------------
270 The ``crash`` tool since v5.1.0 has a built-in
271 ``s390dbf`` to display all the debug logs or e
272 With this tool it is possible
273 to investigate the debug logs on a live system
274 a system crash.
275
276 Investigating raw memory
277 ------------------------
278 One last possibility to investigate the debug
279 system and after a system crash is to look at
280 under VM or at the Service Element.
281 It is possible to find the anchor of the debug
282 the ``debug_area_first`` symbol in the System
283 to follow the correct pointers of the data-str
284 in debug.h and find the debug-areas in memory.
285 Normally modules which use the debug feature w
286 a global variable with the pointer to the debu
287 this pointer it will also be possible to find
288 memory.
289
290 For this method it is recommended to use '16 *
291 for the length of the data field in :c:func:`d
292 order to see the debug entries well formatted.
293
294
295 Predefined Views
296 ----------------
297
298 There are two predefined views: hex_ascii and
299 The hex_ascii view shows the data field in hex
300 (e.g. ``45 43 4b 44 | ECKD``).
301
302 The sprintf view formats the debug entries in
303 function would do. The sprintf event/exception
304 debug entry a pointer to the format string (si
305 and for each vararg a long value. So e.g. for
306 string plus two varargs one would need to allo
307 byte data area in the debug_register() functio
308
309 IMPORTANT:
310 Using "%s" in sprintf event functions is dan
311 use "%s" in the sprintf event functions, if
312 is available as long as the debug feature ex
313 that due to performance considerations only
314 in the debug feature. If you log a string t
315 get an OOPS when inspecting the debug featur
316 will access the already freed memory.
317
318 NOTE:
319 If using the sprintf view do NOT use other e
320 than the sprintf-event and -exception functi
321
322 The format of the hex_ascii and sprintf view i
323
324 - Number of area
325 - Timestamp (formatted as seconds and microsec
326 Universal Time (UTC), January 1, 1970)
327 - level of debug entry
328 - Exception flag (* = Exception)
329 - Cpu-Number of calling task
330 - Return Address to caller
331 - data field
332
333 A typical line of the hex_ascii view will look
334 is only for explanation and will not be displa
335
336 area time level exception cpu cal
337 --------------------------------------------
338 00 00964419409:440690 1 - 00 880
339
340
341 Defining views
342 --------------
343
344 Views are specified with the 'debug_view' stru
345 callback functions which are used for reading
346
347 .. code-block:: c
348
349 struct debug_view {
350 char name[DEBUG_MAX_PROCF_LEN];
351 debug_prolog_proc_t* prolog_proc;
352 debug_header_proc_t* header_proc;
353 debug_format_proc_t* format_proc;
354 debug_input_proc_t* input_proc;
355 void* private_data;
356 };
357
358 where:
359
360 .. code-block:: c
361
362 typedef int (debug_header_proc_t) (debug_inf
363 struct de
364 int area,
365 debug_ent
366 char* out
367
368 typedef int (debug_format_proc_t) (debug_inf
369 struct de
370 const cha
371 typedef int (debug_prolog_proc_t) (debug_inf
372 struct de
373 char* out
374 typedef int (debug_input_proc_t) (debug_info
375 struct deb
376 struct fil
377 size_t in_
378
379
380 The "private_data" member can be used as point
381 It is not used by the debug feature itself.
382
383 The output when reading a debugfs file is stru
384
385 "prolog_proc output"
386
387 "header_proc output 1" "format_proc output
388 "header_proc output 2" "format_proc output
389 "header_proc output 3" "format_proc output
390 ...
391
392 When a view is read from the debugfs, the Debu
393 'prolog_proc' once for writing the prolog.
394 Then 'header_proc' and 'format_proc' are calle
395 existing debug entry.
396
397 The input_proc can be used to implement functi
398 the view (e.g. like with ``echo "0" > /sys/ker
399
400 For header_proc there can be used the default
401 :c:func:`debug_dflt_header_fn()` which is defi
402 and which produces the same header output as t
403 E.g::
404
405 00 00964419409:440761 2 - 00 88023ec
406
407 In order to see how to use the callback functi
408 of the default views!
409
410 Example:
411
412 .. code-block:: c
413
414 #include <asm/debug.h>
415
416 #define UNKNOWNSTR "data: %08x"
417
418 const char* messages[] =
419 {"This error...........\n",
420 "That error...........\n",
421 "Problem..............\n",
422 "Something went wrong.\n",
423 "Everything ok........\n",
424 NULL
425 };
426
427 static int debug_test_format_fn(
428 debug_info_t *id, struct debug_view *view
429 char *out_buf, const char *in_buf
430 )
431 {
432 int i, rc = 0;
433
434 if (id->buf_size >= 4) {
435 int msg_nr = *((int*)in_buf);
436 if (msg_nr < sizeof(messages) / sizeof(
437 rc += sprintf(out_buf, "%s", message
438 else
439 rc += sprintf(out_buf, UNKNOWNSTR, m
440 }
441 return rc;
442 }
443
444 struct debug_view debug_test_view = {
445 "myview", /* name of view
446 NULL, /* no prolog */
447 &debug_dflt_header_fn, /* default heade
448 &debug_test_format_fn, /* our own forma
449 NULL, /* no input func
450 NULL /* no private da
451 };
452
453 test:
454 =====
455
456 .. code-block:: c
457
458 debug_info_t *debug_info;
459 int i;
460 ...
461 debug_info = debug_register("test", 0, 4, 4)
462 debug_register_view(debug_info, &debug_test_
463 for (i = 0; i < 10; i ++)
464 debug_int_event(debug_info, 1, i);
465
466 ::
467
468 > cat /sys/kernel/debug/s390dbf/test/myview
469 00 00964419734:611402 1 - 00 88042ca This
470 00 00964419734:611405 1 - 00 88042ca That
471 00 00964419734:611408 1 - 00 88042ca Probl
472 00 00964419734:611411 1 - 00 88042ca Somet
473 00 00964419734:611414 1 - 00 88042ca Every
474 00 00964419734:611417 1 - 00 88042ca data:
475 00 00964419734:611419 1 - 00 88042ca data:
476 00 00964419734:611422 1 - 00 88042ca data:
477 00 00964419734:611425 1 - 00 88042ca data:
478 00 00964419734:611428 1 - 00 88042ca data:
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