xref: /freebsd/sys/ddb/db_capture.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
1 /*-
2  * Copyright (c) 2007 Robert N. M. Watson
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24  * SUCH DAMAGE.
25  */
26 
27 /*
28  * DDB capture support: capture kernel debugger output into a fixed-size
29  * buffer for later dumping to disk or extraction from user space.
30  */
31 
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
34 
35 #include <sys/param.h>
36 #include <sys/conf.h>
37 #include <sys/kernel.h>
38 #include <sys/kerneldump.h>
39 #include <sys/malloc.h>
40 #include <sys/msgbuf.h>
41 #include <sys/priv.h>
42 #include <sys/sx.h>
43 #include <sys/sysctl.h>
44 #include <sys/systm.h>
45 
46 #include <ddb/ddb.h>
47 #include <ddb/db_lex.h>
48 
49 /*
50  * While it would be desirable to use a small block-sized buffer and dump
51  * incrementally to disk in fixed-size blocks, it's not possible to enter
52  * kernel dumper routines without restarting the kernel, which is undesirable
53  * in the midst of debugging.  Instead, we maintain a large static global
54  * buffer that we fill from DDB's output routines.
55  */
56 static MALLOC_DEFINE(M_DB_CAPTURE, "db_capture", "DDB capture buffer");
57 
58 #define	DB_CAPTURE_DEFAULTBUFSIZE	48*1024
59 #define	DB_CAPTURE_MAXBUFSIZE	512*1024
60 #define	DB_CAPTURE_FILENAME	"ddb.txt"	/* Captured DDB output. */
61 
62 static char *db_capture_buf;
63 static u_int db_capture_bufsize = DB_CAPTURE_DEFAULTBUFSIZE;
64 static u_int db_capture_maxbufsize = DB_CAPTURE_MAXBUFSIZE; /* Read-only. */
65 static u_int db_capture_bufoff;		/* Next location to write in buffer. */
66 static u_int db_capture_bufpadding;	/* Amount of zero padding. */
67 static int db_capture_inpager;		/* Suspend capture in pager. */
68 static int db_capture_inprogress;	/* DDB capture currently in progress. */
69 
70 struct sx db_capture_sx;		/* Lock against user thread races. */
71 SX_SYSINIT(db_capture_sx, &db_capture_sx, "db_capture_sx");
72 
73 static SYSCTL_NODE(_debug_ddb, OID_AUTO, capture, CTLFLAG_RW, 0,
74     "DDB capture options");
75 
76 SYSCTL_UINT(_debug_ddb_capture, OID_AUTO, bytes, CTLFLAG_RD,
77     &db_capture_bufoff, 0, "Bytes of data in DDB capture buffer");
78 
79 SYSCTL_UINT(_debug_ddb_capture, OID_AUTO, maxbufsize, CTLFLAG_RD,
80     &db_capture_maxbufsize, 0,
81     "Maximum value for debug.ddb.capture.bufsize");
82 
83 /*
84  * Various compile-time assertions: defaults must be even multiples of
85  * textdump block size.  We also perform run-time checking of
86  * user-configurable values.
87  */
88 CTASSERT(DB_CAPTURE_DEFAULTBUFSIZE % TEXTDUMP_BLOCKSIZE == 0);
89 CTASSERT(DB_CAPTURE_MAXBUFSIZE % TEXTDUMP_BLOCKSIZE == 0);
90 
91 /*
92  * Boot-time allocation of the DDB capture buffer, if any.
93  */
94 static void
95 db_capture_sysinit(__unused void *dummy)
96 {
97 
98 	TUNABLE_INT_FETCH("debug.ddb.capture.bufsize", &db_capture_bufsize);
99 	db_capture_bufsize = roundup(db_capture_bufsize, TEXTDUMP_BLOCKSIZE);
100 	if (db_capture_bufsize > DB_CAPTURE_MAXBUFSIZE)
101 		db_capture_bufsize = DB_CAPTURE_MAXBUFSIZE;
102 	if (db_capture_bufsize != 0)
103 		db_capture_buf = malloc(db_capture_bufsize, M_DB_CAPTURE,
104 		    M_WAITOK);
105 }
106 SYSINIT(db_capture, SI_SUB_DDB_SERVICES, SI_ORDER_ANY, db_capture_sysinit,
107     NULL);
108 
109 /*
110  * Run-time adjustment of the capture buffer.
111  */
112 static int
113 sysctl_debug_ddb_capture_bufsize(SYSCTL_HANDLER_ARGS)
114 {
115 	u_int len, size;
116 	char *buf;
117 	int error;
118 
119 	size = db_capture_bufsize;
120 	error = sysctl_handle_int(oidp, &size, 0, req);
121 	if (error || req->newptr == NULL)
122 		return (error);
123 	size = roundup(size, TEXTDUMP_BLOCKSIZE);
124 	if (size > DB_CAPTURE_MAXBUFSIZE)
125 		return (EINVAL);
126 	sx_xlock(&db_capture_sx);
127 	if (size != 0) {
128 		/*
129 		 * Potentially the buffer is quite large, so if we can't
130 		 * allocate it, fail rather than waiting.
131 		 */
132 		buf = malloc(size, M_DB_CAPTURE, M_NOWAIT);
133 		if (buf == NULL) {
134 			sx_xunlock(&db_capture_sx);
135 			return (ENOMEM);
136 		}
137 		len = min(db_capture_bufoff, size);
138 	} else {
139 		buf = NULL;
140 		len = 0;
141 	}
142 	if (db_capture_buf != NULL && buf != NULL)
143 		bcopy(db_capture_buf, buf, len);
144 	if (db_capture_buf != NULL)
145 		free(db_capture_buf, M_DB_CAPTURE);
146 	db_capture_bufoff = len;
147 	db_capture_buf = buf;
148 	db_capture_bufsize = size;
149 	sx_xunlock(&db_capture_sx);
150 
151 	KASSERT(db_capture_bufoff <= db_capture_bufsize,
152 	    ("sysctl_debug_ddb_capture_bufsize: bufoff > bufsize"));
153 	KASSERT(db_capture_bufsize <= DB_CAPTURE_MAXBUFSIZE,
154 	    ("sysctl_debug_ddb_capture_maxbufsize: bufsize > maxbufsize"));
155 
156 	return (0);
157 }
158 SYSCTL_PROC(_debug_ddb_capture, OID_AUTO, bufsize, CTLTYPE_UINT|CTLFLAG_RW,
159     0, 0, sysctl_debug_ddb_capture_bufsize, "IU",
160     "Size of DDB capture buffer");
161 
162 /*
163  * Sysctl to read out the capture buffer from userspace.  We require
164  * privilege as sensitive process/memory information may be accessed.
165  */
166 static int
167 sysctl_debug_ddb_capture_data(SYSCTL_HANDLER_ARGS)
168 {
169 	int error;
170 	char ch;
171 
172 	error = priv_check(req->td, PRIV_DDB_CAPTURE);
173 	if (error)
174 		return (error);
175 
176 	sx_slock(&db_capture_sx);
177 	error = SYSCTL_OUT(req, db_capture_buf, db_capture_bufoff);
178 	sx_sunlock(&db_capture_sx);
179 	if (error)
180 		return (error);
181 	ch = '\0';
182 	return (SYSCTL_OUT(req, &ch, sizeof(ch)));
183 }
184 SYSCTL_PROC(_debug_ddb_capture, OID_AUTO, data, CTLTYPE_STRING | CTLFLAG_RD,
185     NULL, 0, sysctl_debug_ddb_capture_data, "A", "DDB capture data");
186 
187 /*
188  * Routines for capturing DDB output into a fixed-size buffer.  These are
189  * invoked from DDB's input and output routines.  If we hit the limit on the
190  * buffer, we simply drop further data.
191  */
192 void
193 db_capture_write(char *buffer, u_int buflen)
194 {
195 	u_int len;
196 
197 	if (db_capture_inprogress == 0 || db_capture_inpager)
198 		return;
199 	len = min(buflen, db_capture_bufsize - db_capture_bufoff);
200 	bcopy(buffer, db_capture_buf + db_capture_bufoff, len);
201 	db_capture_bufoff += len;
202 
203 	KASSERT(db_capture_bufoff <= db_capture_bufsize,
204 	    ("db_capture_write: bufoff > bufsize"));
205 }
206 
207 void
208 db_capture_writech(char ch)
209 {
210 
211 	return (db_capture_write(&ch, sizeof(ch)));
212 }
213 
214 void
215 db_capture_enterpager(void)
216 {
217 
218 	db_capture_inpager = 1;
219 }
220 
221 void
222 db_capture_exitpager(void)
223 {
224 
225 	db_capture_inpager = 0;
226 }
227 
228 /*
229  * Zero out any bytes left in the last block of the DDB capture buffer.  This
230  * is run shortly before writing the blocks to disk, rather than when output
231  * capture is stopped, in order to avoid injecting nul's into the middle of
232  * output.
233  */
234 static void
235 db_capture_zeropad(void)
236 {
237 	u_int len;
238 
239 	len = min(TEXTDUMP_BLOCKSIZE, (db_capture_bufsize -
240 	    db_capture_bufoff) % TEXTDUMP_BLOCKSIZE);
241 	bzero(db_capture_buf + db_capture_bufoff, len);
242 	db_capture_bufpadding = len;
243 }
244 
245 /*
246  * Reset capture state, which flushes buffers.
247  */
248 static void
249 db_capture_reset(void)
250 {
251 
252 	db_capture_inprogress = 0;
253 	db_capture_bufoff = 0;
254 	db_capture_bufpadding = 0;
255 }
256 
257 /*
258  * Start capture.  Only one session is allowed at any time, but we may
259  * continue a previous session, so the buffer isn't reset.
260  */
261 static void
262 db_capture_start(void)
263 {
264 
265 	if (db_capture_inprogress) {
266 		db_printf("Capture already started\n");
267 		return;
268 	}
269 	db_capture_inprogress = 1;
270 }
271 
272 /*
273  * Terminate DDB output capture--real work is deferred to db_capture_dump,
274  * which executes outside of the DDB context.  We don't zero pad here because
275  * capture may be started again before the dump takes place.
276  */
277 static void
278 db_capture_stop(void)
279 {
280 
281 	if (db_capture_inprogress == 0) {
282 		db_printf("Capture not started\n");
283 		return;
284 	}
285 	db_capture_inprogress = 0;
286 }
287 
288 /*
289  * Dump DDB(4) captured output (and resets capture buffers).
290  */
291 void
292 db_capture_dump(struct dumperinfo *di)
293 {
294 	u_int offset;
295 
296 	if (db_capture_bufoff == 0)
297 		return;
298 
299 	db_capture_zeropad();
300 	textdump_mkustar(textdump_block_buffer, DB_CAPTURE_FILENAME,
301 	    db_capture_bufoff);
302 	(void)textdump_writenextblock(di, textdump_block_buffer);
303 	for (offset = 0; offset < db_capture_bufoff + db_capture_bufpadding;
304 	    offset += TEXTDUMP_BLOCKSIZE)
305 		(void)textdump_writenextblock(di, db_capture_buf + offset);
306 	db_capture_bufoff = 0;
307 	db_capture_bufpadding = 0;
308 }
309 
310 /*-
311  * DDB(4) command to manage capture:
312  *
313  * capture on          - start DDB output capture
314  * capture off         - stop DDB output capture
315  * capture reset       - reset DDB capture buffer (also stops capture)
316  * capture status      - print DDB output capture status
317  */
318 static void
319 db_capture_usage(void)
320 {
321 
322 	db_error("capture [on|off|reset|status]\n");
323 }
324 
325 void
326 db_capture_cmd(db_expr_t addr, boolean_t have_addr, db_expr_t count,
327     char *modif)
328 {
329 	int t;
330 
331 	t = db_read_token();
332 	if (t != tIDENT) {
333 		db_capture_usage();
334 		return;
335 	}
336 	if (db_read_token() != tEOL)
337 		db_error("?\n");
338 	if (strcmp(db_tok_string, "on") == 0)
339 		db_capture_start();
340 	else if (strcmp(db_tok_string, "off") == 0)
341 		db_capture_stop();
342 	else if (strcmp(db_tok_string, "reset") == 0)
343 		db_capture_reset();
344 	else if (strcmp(db_tok_string, "status") == 0) {
345 		db_printf("%u/%u bytes used\n", db_capture_bufoff,
346 		    db_capture_bufsize);
347 		if (db_capture_inprogress)
348 			db_printf("capture is on\n");
349 		else
350 			db_printf("capture is off\n");
351 	} else
352 		db_capture_usage();
353 }
354