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-rw-r--r--Documentation/DocBook/kgdb.tmpl692
-rw-r--r--Documentation/kernel-parameters.txt6
-rw-r--r--include/linux/kgdb.h12
3 files changed, 532 insertions, 178 deletions
diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl
index 5cff41a5fa7c..55f12ac37acd 100644
--- a/Documentation/DocBook/kgdb.tmpl
+++ b/Documentation/DocBook/kgdb.tmpl
@@ -4,7 +4,7 @@
4 4
5<book id="kgdbOnLinux"> 5<book id="kgdbOnLinux">
6 <bookinfo> 6 <bookinfo>
7 <title>Using kgdb and the kgdb Internals</title> 7 <title>Using kgdb, kdb and the kernel debugger internals</title>
8 8
9 <authorgroup> 9 <authorgroup>
10 <author> 10 <author>
@@ -17,33 +17,8 @@
17 </affiliation> 17 </affiliation>
18 </author> 18 </author>
19 </authorgroup> 19 </authorgroup>
20
21 <authorgroup>
22 <author>
23 <firstname>Tom</firstname>
24 <surname>Rini</surname>
25 <affiliation>
26 <address>
27 <email>trini@kernel.crashing.org</email>
28 </address>
29 </affiliation>
30 </author>
31 </authorgroup>
32
33 <authorgroup>
34 <author>
35 <firstname>Amit S.</firstname>
36 <surname>Kale</surname>
37 <affiliation>
38 <address>
39 <email>amitkale@linsyssoft.com</email>
40 </address>
41 </affiliation>
42 </author>
43 </authorgroup>
44
45 <copyright> 20 <copyright>
46 <year>2008</year> 21 <year>2008,2010</year>
47 <holder>Wind River Systems, Inc.</holder> 22 <holder>Wind River Systems, Inc.</holder>
48 </copyright> 23 </copyright>
49 <copyright> 24 <copyright>
@@ -69,41 +44,76 @@
69 <chapter id="Introduction"> 44 <chapter id="Introduction">
70 <title>Introduction</title> 45 <title>Introduction</title>
71 <para> 46 <para>
72 kgdb is a source level debugger for linux kernel. It is used along 47 The kernel has two different debugger front ends (kdb and kgdb)
73 with gdb to debug a linux kernel. The expectation is that gdb can 48 which interface to the debug core. It is possible to use either
74 be used to "break in" to the kernel to inspect memory, variables 49 of the debugger front ends and dynamically transition between them
75 and look through call stack information similar to what an 50 if you configure the kernel properly at compile and runtime.
76 application developer would use gdb for. It is possible to place 51 </para>
77 breakpoints in kernel code and perform some limited execution 52 <para>
78 stepping. 53 Kdb is simplistic shell-style interface which you can use on a
54 system console with a keyboard or serial console. You can use it
55 to inspect memory, registers, process lists, dmesg, and even set
56 breakpoints to stop in a certain location. Kdb is not a source
57 level debugger, although you can set breakpoints and execute some
58 basic kernel run control. Kdb is mainly aimed at doing some
59 analysis to aid in development or diagnosing kernel problems. You
60 can access some symbols by name in kernel built-ins or in kernel
61 modules if the code was built
62 with <symbol>CONFIG_KALLSYMS</symbol>.
63 </para>
64 <para>
65 Kgdb is intended to be used as a source level debugger for the
66 Linux kernel. It is used along with gdb to debug a Linux kernel.
67 The expectation is that gdb can be used to "break in" to the
68 kernel to inspect memory, variables and look through call stack
69 information similar to the way an application developer would use
70 gdb to debug an application. It is possible to place breakpoints
71 in kernel code and perform some limited execution stepping.
79 </para> 72 </para>
80 <para> 73 <para>
81 Two machines are required for using kgdb. One of these machines is a 74 Two machines are required for using kgdb. One of these machines is
82 development machine and the other is a test machine. The kernel 75 a development machine and the other is the target machine. The
83 to be debugged runs on the test machine. The development machine 76 kernel to be debugged runs on the target machine. The development
84 runs an instance of gdb against the vmlinux file which contains 77 machine runs an instance of gdb against the vmlinux file which
85 the symbols (not boot image such as bzImage, zImage, uImage...). 78 contains the symbols (not boot image such as bzImage, zImage,
86 In gdb the developer specifies the connection parameters and 79 uImage...). In gdb the developer specifies the connection
87 connects to kgdb. The type of connection a developer makes with 80 parameters and connects to kgdb. The type of connection a
88 gdb depends on the availability of kgdb I/O modules compiled as 81 developer makes with gdb depends on the availability of kgdb I/O
89 builtin's or kernel modules in the test machine's kernel. 82 modules compiled as built-ins or loadable kernel modules in the test
83 machine's kernel.
90 </para> 84 </para>
91 </chapter> 85 </chapter>
92 <chapter id="CompilingAKernel"> 86 <chapter id="CompilingAKernel">
93 <title>Compiling a kernel</title> 87 <title>Compiling a kernel</title>
88 <para>
89 <itemizedlist>
90 <listitem><para>In order to enable compilation of kdb, you must first enable kgdb.</para></listitem>
91 <listitem><para>The kgdb test compile options are described in the kgdb test suite chapter.</para></listitem>
92 </itemizedlist>
93 </para>
94 <sect1 id="CompileKGDB">
95 <title>Kernel config options for kgdb</title>
94 <para> 96 <para>
95 To enable <symbol>CONFIG_KGDB</symbol> you should first turn on 97 To enable <symbol>CONFIG_KGDB</symbol> you should first turn on
96 "Prompt for development and/or incomplete code/drivers" 98 "Prompt for development and/or incomplete code/drivers"
97 (CONFIG_EXPERIMENTAL) in "General setup", then under the 99 (CONFIG_EXPERIMENTAL) in "General setup", then under the
98 "Kernel debugging" select "KGDB: kernel debugging with remote gdb". 100 "Kernel debugging" select "KGDB: kernel debugger".
101 </para>
102 <para>
103 While it is not a hard requirement that you have symbols in your
104 vmlinux file, gdb tends not to be very useful without the symbolic
105 data, so you will want to turn
106 on <symbol>CONFIG_DEBUG_INFO</symbol> which is called "Compile the
107 kernel with debug info" in the config menu.
99 </para> 108 </para>
100 <para> 109 <para>
101 It is advised, but not required that you turn on the 110 It is advised, but not required that you turn on the
102 CONFIG_FRAME_POINTER kernel option. This option inserts code to 111 <symbol>CONFIG_FRAME_POINTER</symbol> kernel option which is called "Compile the
103 into the compiled executable which saves the frame information in 112 kernel with frame pointers" in the config menu. This option
104 registers or on the stack at different points which will allow a 113 inserts code to into the compiled executable which saves the frame
105 debugger such as gdb to more accurately construct stack back traces 114 information in registers or on the stack at different points which
106 while debugging the kernel. 115 allows a debugger such as gdb to more accurately construct
116 stack back traces while debugging the kernel.
107 </para> 117 </para>
108 <para> 118 <para>
109 If the architecture that you are using supports the kernel option 119 If the architecture that you are using supports the kernel option
@@ -116,38 +126,160 @@
116 this option. 126 this option.
117 </para> 127 </para>
118 <para> 128 <para>
119 Next you should choose one of more I/O drivers to interconnect debugging 129 Next you should choose one of more I/O drivers to interconnect
120 host and debugged target. Early boot debugging requires a KGDB 130 debugging host and debugged target. Early boot debugging requires
121 I/O driver that supports early debugging and the driver must be 131 a KGDB I/O driver that supports early debugging and the driver
122 built into the kernel directly. Kgdb I/O driver configuration 132 must be built into the kernel directly. Kgdb I/O driver
123 takes place via kernel or module parameters, see following 133 configuration takes place via kernel or module parameters which
124 chapter. 134 you can learn more about in the in the section that describes the
135 parameter "kgdboc".
125 </para> 136 </para>
126 <para> 137 <para>Here is an example set of .config symbols to enable or
127 The kgdb test compile options are described in the kgdb test suite chapter. 138 disable for kgdb:
139 <itemizedlist>
140 <listitem><para># CONFIG_DEBUG_RODATA is not set</para></listitem>
141 <listitem><para>CONFIG_FRAME_POINTER=y</para></listitem>
142 <listitem><para>CONFIG_KGDB=y</para></listitem>
143 <listitem><para>CONFIG_KGDB_SERIAL_CONSOLE=y</para></listitem>
144 </itemizedlist>
128 </para> 145 </para>
129 146 </sect1>
147 <sect1 id="CompileKDB">
148 <title>Kernel config options for kdb</title>
149 <para>Kdb is quite a bit more complex than the simple gdbstub
150 sitting on top of the kernel's debug core. Kdb must implement a
151 shell, and also adds some helper functions in other parts of the
152 kernel, responsible for printing out interesting data such as what
153 you would see if you ran "lsmod", or "ps". In order to build kdb
154 into the kernel you follow the same steps as you would for kgdb.
155 </para>
156 <para>The main config option for kdb
157 is <symbol>CONFIG_KGDB_KDB</symbol> which is called "KGDB_KDB:
158 include kdb frontend for kgdb" in the config menu. In theory you
159 would have already also selected an I/O driver such as the
160 CONFIG_KGDB_SERIAL_CONSOLE interface if you plan on using kdb on a
161 serial port, when you were configuring kgdb.
162 </para>
163 <para>If you want to use a PS/2-style keyboard with kdb, you would
164 select CONFIG_KDB_KEYBOARD which is called "KGDB_KDB: keyboard as
165 input device" in the config menu. The CONFIG_KDB_KEYBOARD option
166 is not used for anything in the gdb interface to kgdb. The
167 CONFIG_KDB_KEYBOARD option only works with kdb.
168 </para>
169 <para>Here is an example set of .config symbols to enable/disable kdb:
170 <itemizedlist>
171 <listitem><para># CONFIG_DEBUG_RODATA is not set</para></listitem>
172 <listitem><para>CONFIG_FRAME_POINTER=y</para></listitem>
173 <listitem><para>CONFIG_KGDB=y</para></listitem>
174 <listitem><para>CONFIG_KGDB_SERIAL_CONSOLE=y</para></listitem>
175 <listitem><para>CONFIG_KGDB_KDB=y</para></listitem>
176 <listitem><para>CONFIG_KDB_KEYBOARD=y</para></listitem>
177 </itemizedlist>
178 </para>
179 </sect1>
130 </chapter> 180 </chapter>
131 <chapter id="EnableKGDB"> 181 <chapter id="kgdbKernelArgs">
132 <title>Enable kgdb for debugging</title> 182 <title>Kernel Debugger Boot Arguments</title>
133 <para> 183 <para>This section describes the various runtime kernel
134 In order to use kgdb you must activate it by passing configuration 184 parameters that affect the configuration of the kernel debugger.
135 information to one of the kgdb I/O drivers. If you do not pass any 185 The following chapter covers using kdb and kgdb as well as
136 configuration information kgdb will not do anything at all. Kgdb 186 provides some examples of the configuration parameters.</para>
137 will only actively hook up to the kernel trap hooks if a kgdb I/O 187 <sect1 id="kgdboc">
138 driver is loaded and configured. If you unconfigure a kgdb I/O 188 <title>Kernel parameter: kgdboc</title>
139 driver, kgdb will unregister all the kernel hook points. 189 <para>The kgdboc driver was originally an abbreviation meant to
190 stand for "kgdb over console". Today it is the primary mechanism
191 to configure how to communicate from gdb to kgdb as well as the
192 devices you want to use to interact with the kdb shell.
193 </para>
194 <para>For kgdb/gdb, kgdboc is designed to work with a single serial
195 port. It is intended to cover the circumstance where you want to
196 use a serial console as your primary console as well as using it to
197 perform kernel debugging. It is also possible to use kgdb on a
198 serial port which is not designated as a system console. Kgdboc
199 may be configured as a kernel built-in or a kernel loadable module.
200 You can only make use of <constant>kgdbwait</constant> and early
201 debugging if you build kgdboc into the kernel as a built-in.
140 </para> 202 </para>
203 <sect2 id="kgdbocArgs">
204 <title>kgdboc arguments</title>
205 <para>Usage: <constant>kgdboc=[kbd][[,]serial_device][,baud]</constant></para>
206 <sect3 id="kgdbocArgs1">
207 <title>Using loadable module or built-in</title>
141 <para> 208 <para>
142 All drivers can be reconfigured at run time, if 209 <orderedlist>
143 <symbol>CONFIG_SYSFS</symbol> and <symbol>CONFIG_MODULES</symbol> 210 <listitem><para>As a kernel built-in:</para>
144 are enabled, by echo'ing a new config string to 211 <para>Use the kernel boot argument: <constant>kgdboc=&lt;tty-device&gt;,[baud]</constant></para></listitem>
145 <constant>/sys/module/&lt;driver&gt;/parameter/&lt;option&gt;</constant>. 212 <listitem>
146 The driver can be unconfigured by passing an empty string. You cannot 213 <para>As a kernel loadable module:</para>
147 change the configuration while the debugger is attached. Make sure 214 <para>Use the command: <constant>modprobe kgdboc kgdboc=&lt;tty-device&gt;,[baud]</constant></para>
148 to detach the debugger with the <constant>detach</constant> command 215 <para>Here are two examples of how you might formate the kgdboc
149 prior to trying unconfigure a kgdb I/O driver. 216 string. The first is for an x86 target using the first serial port.
217 The second example is for the ARM Versatile AB using the second
218 serial port.
219 <orderedlist>
220 <listitem><para><constant>kgdboc=ttyS0,115200</constant></para></listitem>
221 <listitem><para><constant>kgdboc=ttyAMA1,115200</constant></para></listitem>
222 </orderedlist>
150 </para> 223 </para>
224 </listitem>
225 </orderedlist></para>
226 </sect3>
227 <sect3 id="kgdbocArgs2">
228 <title>Configure kgdboc at runtime with sysfs</title>
229 <para>At run time you can enable or disable kgdboc by echoing a
230 parameters into the sysfs. Here are two examples:</para>
231 <orderedlist>
232 <listitem><para>Enable kgdboc on ttyS0</para>
233 <para><constant>echo ttyS0 &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
234 <listitem><para>Disable kgdboc</para>
235 <para><constant>echo "" &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
236 </orderedlist>
237 <para>NOTE: You do not need to specify the baud if you are
238 configuring the console on tty which is already configured or
239 open.</para>
240 </sect3>
241 <sect3 id="kgdbocArgs3">
242 <title>More examples</title>
243 <para>You can configure kgdboc to use the keyboard, and or a serial device
244 depending on if you are using kdb and or kgdb, in one of the
245 following scenarios.
246 <orderedlist>
247 <listitem><para>kdb and kgdb over only a serial port</para>
248 <para><constant>kgdboc=&lt;serial_device&gt;[,baud]</constant></para>
249 <para>Example: <constant>kgdboc=ttyS0,115200</constant></para>
250 </listitem>
251 <listitem><para>kdb and kgdb with keyboard and a serial port</para>
252 <para><constant>kgdboc=kbd,&lt;serial_device&gt;[,baud]</constant></para>
253 <para>Example: <constant>kgdboc=kbd,ttyS0,115200</constant></para>
254 </listitem>
255 <listitem><para>kdb with a keyboard</para>
256 <para><constant>kgdboc=kbd</constant></para>
257 </listitem>
258 </orderedlist>
259 </para>
260 </sect3>
261 <para>NOTE: Kgdboc does not support interrupting the target via the
262 gdb remote protocol. You must manually send a sysrq-g unless you
263 have a proxy that splits console output to a terminal program.
264 A console proxy has a separate TCP port for the debugger and a separate
265 TCP port for the "human" console. The proxy can take care of sending
266 the sysrq-g for you.
267 </para>
268 <para>When using kgdboc with no debugger proxy, you can end up
269 connecting the debugger at one of two entry points. If an
270 exception occurs after you have loaded kgdboc, a message should
271 print on the console stating it is waiting for the debugger. In
272 this case you disconnect your terminal program and then connect the
273 debugger in its place. If you want to interrupt the target system
274 and forcibly enter a debug session you have to issue a Sysrq
275 sequence and then type the letter <constant>g</constant>. Then
276 you disconnect the terminal session and connect gdb. Your options
277 if you don't like this are to hack gdb to send the sysrq-g for you
278 as well as on the initial connect, or to use a debugger proxy that
279 allows an unmodified gdb to do the debugging.
280 </para>
281 </sect2>
282 </sect1>
151 <sect1 id="kgdbwait"> 283 <sect1 id="kgdbwait">
152 <title>Kernel parameter: kgdbwait</title> 284 <title>Kernel parameter: kgdbwait</title>
153 <para> 285 <para>
@@ -162,103 +294,204 @@
162 </para> 294 </para>
163 <para> 295 <para>
164 The kernel will stop and wait as early as the I/O driver and 296 The kernel will stop and wait as early as the I/O driver and
165 architecture will allow when you use this option. If you build the 297 architecture allows when you use this option. If you build the
166 kgdb I/O driver as a kernel module kgdbwait will not do anything. 298 kgdb I/O driver as a loadable kernel module kgdbwait will not do
299 anything.
167 </para> 300 </para>
168 </sect1> 301 </sect1>
169 <sect1 id="kgdboc"> 302 <sect1 id="kgdbcon">
170 <title>Kernel parameter: kgdboc</title> 303 <title>Kernel parameter: kgdbcon</title>
171 <para> 304 <para> The kgdbcon feature allows you to see printk() messages
172 The kgdboc driver was originally an abbreviation meant to stand for 305 inside gdb while gdb is connected to the kernel. Kdb does not make
173 "kgdb over console". Kgdboc is designed to work with a single 306 use of the kgdbcon feature.
174 serial port. It was meant to cover the circumstance 307 </para>
175 where you wanted to use a serial console as your primary console as 308 <para>Kgdb supports using the gdb serial protocol to send console
176 well as using it to perform kernel debugging. Of course you can 309 messages to the debugger when the debugger is connected and running.
177 also use kgdboc without assigning a console to the same port. 310 There are two ways to activate this feature.
311 <orderedlist>
312 <listitem><para>Activate with the kernel command line option:</para>
313 <para><constant>kgdbcon</constant></para>
314 </listitem>
315 <listitem><para>Use sysfs before configuring an I/O driver</para>
316 <para>
317 <constant>echo 1 &gt; /sys/module/kgdb/parameters/kgdb_use_con</constant>
318 </para>
319 <para>
320 NOTE: If you do this after you configure the kgdb I/O driver, the
321 setting will not take effect until the next point the I/O is
322 reconfigured.
323 </para>
324 </listitem>
325 </orderedlist>
326 <para>IMPORTANT NOTE: You cannot use kgdboc + kgdbcon on a tty that is an
327 active system console. An example incorrect usage is <constant>console=ttyS0,115200 kgdboc=ttyS0 kgdbcon</constant>
328 </para>
329 <para>It is possible to use this option with kgdboc on a tty that is not a system console.
330 </para>
178 </para> 331 </para>
179 <sect2 id="UsingKgdboc"> 332 </sect1>
180 <title>Using kgdboc</title> 333 </chapter>
181 <para> 334 <chapter id="usingKDB">
182 You can configure kgdboc via sysfs or a module or kernel boot line 335 <title>Using kdb</title>
183 parameter depending on if you build with CONFIG_KGDBOC as a module
184 or built-in.
185 <orderedlist>
186 <listitem><para>From the module load or build-in</para>
187 <para><constant>kgdboc=&lt;tty-device&gt;,[baud]</constant></para>
188 <para> 336 <para>
189 The example here would be if your console port was typically ttyS0, you would use something like <constant>kgdboc=ttyS0,115200</constant> or on the ARM Versatile AB you would likely use <constant>kgdboc=ttyAMA0,115200</constant> 337 </para>
338 <sect1 id="quickKDBserial">
339 <title>Quick start for kdb on a serial port</title>
340 <para>This is a quick example of how to use kdb.</para>
341 <para><orderedlist>
342 <listitem><para>Boot kernel with arguments:
343 <itemizedlist>
344 <listitem><para><constant>console=ttyS0,115200 kgdboc=ttyS0,115200</constant></para></listitem>
345 </itemizedlist></para>
346 <para>OR</para>
347 <para>Configure kgdboc after the kernel booted; assuming you are using a serial port console:
348 <itemizedlist>
349 <listitem><para><constant>echo ttyS0 &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
350 </itemizedlist>
190 </para> 351 </para>
191 </listitem> 352 </listitem>
192 <listitem><para>From sysfs</para> 353 <listitem><para>Enter the kernel debugger manually or by waiting for an oops or fault. There are several ways you can enter the kernel debugger manually; all involve using the sysrq-g, which means you must have enabled CONFIG_MAGIC_SYSRQ=y in your kernel config.</para>
193 <para><constant>echo ttyS0 &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para> 354 <itemizedlist>
355 <listitem><para>When logged in as root or with a super user session you can run:</para>
356 <para><constant>echo g &gt; /proc/sysrq-trigger</constant></para></listitem>
357 <listitem><para>Example using minicom 2.2</para>
358 <para>Press: <constant>Control-a</constant></para>
359 <para>Press: <constant>f</constant></para>
360 <para>Press: <constant>g</constant></para>
194 </listitem> 361 </listitem>
195 </orderedlist> 362 <listitem><para>When you have telneted to a terminal server that supports sending a remote break</para>
196 </para> 363 <para>Press: <constant>Control-]</constant></para>
197 <para> 364 <para>Type in:<constant>send break</constant></para>
198 NOTE: Kgdboc does not support interrupting the target via the 365 <para>Press: <constant>Enter</constant></para>
199 gdb remote protocol. You must manually send a sysrq-g unless you 366 <para>Press: <constant>g</constant></para>
200 have a proxy that splits console output to a terminal problem and 367 </listitem>
201 has a separate port for the debugger to connect to that sends the 368 </itemizedlist>
202 sysrq-g for you. 369 </listitem>
370 <listitem><para>From the kdb prompt you can run the "help" command to see a complete list of the commands that are available.</para>
371 <para>Some useful commands in kdb include:
372 <itemizedlist>
373 <listitem><para>lsmod -- Shows where kernel modules are loaded</para></listitem>
374 <listitem><para>ps -- Displays only the active processes</para></listitem>
375 <listitem><para>ps A -- Shows all the processes</para></listitem>
376 <listitem><para>summary -- Shows kernel version info and memory usage</para></listitem>
377 <listitem><para>bt -- Get a backtrace of the current process using dump_stack()</para></listitem>
378 <listitem><para>dmesg -- View the kernel syslog buffer</para></listitem>
379 <listitem><para>go -- Continue the system</para></listitem>
380 </itemizedlist>
203 </para> 381 </para>
204 <para>When using kgdboc with no debugger proxy, you can end up 382 </listitem>
205 connecting the debugger for one of two entry points. If an 383 <listitem>
206 exception occurs after you have loaded kgdboc a message should print 384 <para>When you are done using kdb you need to consider rebooting the
207 on the console stating it is waiting for the debugger. In case you 385 system or using the "go" command to resuming normal kernel
208 disconnect your terminal program and then connect the debugger in 386 execution. If you have paused the kernel for a lengthy period of
209 its place. If you want to interrupt the target system and forcibly 387 time, applications that rely on timely networking or anything to do
210 enter a debug session you have to issue a Sysrq sequence and then 388 with real wall clock time could be adversely affected, so you
211 type the letter <constant>g</constant>. Then you disconnect the 389 should take this into consideration when using the kernel
212 terminal session and connect gdb. Your options if you don't like 390 debugger.</para>
213 this are to hack gdb to send the sysrq-g for you as well as on the 391 </listitem>
214 initial connect, or to use a debugger proxy that allows an 392 </orderedlist></para>
215 unmodified gdb to do the debugging. 393 </sect1>
394 <sect1 id="quickKDBkeyboard">
395 <title>Quick start for kdb using a keyboard connected console</title>
396 <para>This is a quick example of how to use kdb with a keyboard.</para>
397 <para><orderedlist>
398 <listitem><para>Boot kernel with arguments:
399 <itemizedlist>
400 <listitem><para><constant>kgdboc=kbd</constant></para></listitem>
401 </itemizedlist></para>
402 <para>OR</para>
403 <para>Configure kgdboc after the kernel booted:
404 <itemizedlist>
405 <listitem><para><constant>echo kbd &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
406 </itemizedlist>
216 </para> 407 </para>
217 </sect2> 408 </listitem>
409 <listitem><para>Enter the kernel debugger manually or by waiting for an oops or fault. There are several ways you can enter the kernel debugger manually; all involve using the sysrq-g, which means you must have enabled CONFIG_MAGIC_SYSRQ=y in your kernel config.</para>
410 <itemizedlist>
411 <listitem><para>When logged in as root or with a super user session you can run:</para>
412 <para><constant>echo g &gt; /proc/sysrq-trigger</constant></para></listitem>
413 <listitem><para>Example using a laptop keyboard</para>
414 <para>Press and hold down: <constant>Alt</constant></para>
415 <para>Press and hold down: <constant>Fn</constant></para>
416 <para>Press and release the key with the label: <constant>SysRq</constant></para>
417 <para>Release: <constant>Fn</constant></para>
418 <para>Press and release: <constant>g</constant></para>
419 <para>Release: <constant>Alt</constant></para>
420 </listitem>
421 <listitem><para>Example using a PS/2 101-key keyboard</para>
422 <para>Press and hold down: <constant>Alt</constant></para>
423 <para>Press and release the key with the label: <constant>SysRq</constant></para>
424 <para>Press and release: <constant>g</constant></para>
425 <para>Release: <constant>Alt</constant></para>
426 </listitem>
427 </itemizedlist>
428 </listitem>
429 <listitem>
430 <para>Now type in a kdb command such as "help", "dmesg", "bt" or "go" to continue kernel execution.</para>
431 </listitem>
432 </orderedlist></para>
218 </sect1> 433 </sect1>
219 <sect1 id="kgdbcon"> 434 </chapter>
220 <title>Kernel parameter: kgdbcon</title> 435 <chapter id="EnableKGDB">
221 <para> 436 <title>Using kgdb / gdb</title>
222 Kgdb supports using the gdb serial protocol to send console messages 437 <para>In order to use kgdb you must activate it by passing
223 to the debugger when the debugger is connected and running. There 438 configuration information to one of the kgdb I/O drivers. If you
224 are two ways to activate this feature. 439 do not pass any configuration information kgdb will not do anything
440 at all. Kgdb will only actively hook up to the kernel trap hooks
441 if a kgdb I/O driver is loaded and configured. If you unconfigure
442 a kgdb I/O driver, kgdb will unregister all the kernel hook points.
443 </para>
444 <para> All kgdb I/O drivers can be reconfigured at run time, if
445 <symbol>CONFIG_SYSFS</symbol> and <symbol>CONFIG_MODULES</symbol>
446 are enabled, by echo'ing a new config string to
447 <constant>/sys/module/&lt;driver&gt;/parameter/&lt;option&gt;</constant>.
448 The driver can be unconfigured by passing an empty string. You cannot
449 change the configuration while the debugger is attached. Make sure
450 to detach the debugger with the <constant>detach</constant> command
451 prior to trying to unconfigure a kgdb I/O driver.
452 </para>
453 <sect1 id="ConnectingGDB">
454 <title>Connecting with gdb to a serial port</title>
225 <orderedlist> 455 <orderedlist>
226 <listitem><para>Activate with the kernel command line option:</para> 456 <listitem><para>Configure kgdboc</para>
227 <para><constant>kgdbcon</constant></para> 457 <para>Boot kernel with arguments:
458 <itemizedlist>
459 <listitem><para><constant>kgdboc=ttyS0,115200</constant></para></listitem>
460 </itemizedlist></para>
461 <para>OR</para>
462 <para>Configure kgdboc after the kernel booted:
463 <itemizedlist>
464 <listitem><para><constant>echo ttyS0 &gt; /sys/module/kgdboc/parameters/kgdboc</constant></para></listitem>
465 </itemizedlist></para>
228 </listitem> 466 </listitem>
229 <listitem><para>Use sysfs before configuring an io driver</para> 467 <listitem>
230 <para> 468 <para>Stop kernel execution (break into the debugger)</para>
231 <constant>echo 1 &gt; /sys/module/kgdb/parameters/kgdb_use_con</constant> 469 <para>In order to connect to gdb via kgdboc, the kernel must
232 </para> 470 first be stopped. There are several ways to stop the kernel which
233 <para> 471 include using kgdbwait as a boot argument, via a sysrq-g, or running
234 NOTE: If you do this after you configure the kgdb I/O driver, the 472 the kernel until it takes an exception where it waits for the
235 setting will not take effect until the next point the I/O is 473 debugger to attach.
236 reconfigured. 474 <itemizedlist>
237 </para> 475 <listitem><para>When logged in as root or with a super user session you can run:</para>
476 <para><constant>echo g &gt; /proc/sysrq-trigger</constant></para></listitem>
477 <listitem><para>Example using minicom 2.2</para>
478 <para>Press: <constant>Control-a</constant></para>
479 <para>Press: <constant>f</constant></para>
480 <para>Press: <constant>g</constant></para>
238 </listitem> 481 </listitem>
239 </orderedlist> 482 <listitem><para>When you have telneted to a terminal server that supports sending a remote break</para>
240 </para> 483 <para>Press: <constant>Control-]</constant></para>
241 <para> 484 <para>Type in:<constant>send break</constant></para>
242 IMPORTANT NOTE: Using this option with kgdb over the console 485 <para>Press: <constant>Enter</constant></para>
243 (kgdboc) is not supported. 486 <para>Press: <constant>g</constant></para>
487 </listitem>
488 </itemizedlist>
244 </para> 489 </para>
245 </sect1> 490 </listitem>
246 </chapter> 491 <listitem>
247 <chapter id="ConnectingGDB"> 492 <para>Connect from from gdb</para>
248 <title>Connecting gdb</title>
249 <para>
250 If you are using kgdboc, you need to have used kgdbwait as a boot
251 argument, issued a sysrq-g, or the system you are going to debug
252 has already taken an exception and is waiting for the debugger to
253 attach before you can connect gdb.
254 </para>
255 <para>
256 If you are not using different kgdb I/O driver other than kgdboc,
257 you should be able to connect and the target will automatically
258 respond.
259 </para>
260 <para> 493 <para>
261 Example (using a serial port): 494 Example (using a directly connected port):
262 </para> 495 </para>
263 <programlisting> 496 <programlisting>
264 % gdb ./vmlinux 497 % gdb ./vmlinux
@@ -266,7 +499,7 @@
266 (gdb) target remote /dev/ttyS0 499 (gdb) target remote /dev/ttyS0
267 </programlisting> 500 </programlisting>
268 <para> 501 <para>
269 Example (kgdb to a terminal server on tcp port 2012): 502 Example (kgdb to a terminal server on TCP port 2012):
270 </para> 503 </para>
271 <programlisting> 504 <programlisting>
272 % gdb ./vmlinux 505 % gdb ./vmlinux
@@ -283,6 +516,83 @@
283 communications. You do this prior to issuing the <constant>target 516 communications. You do this prior to issuing the <constant>target
284 remote</constant> command by typing in: <constant>set debug remote 1</constant> 517 remote</constant> command by typing in: <constant>set debug remote 1</constant>
285 </para> 518 </para>
519 </listitem>
520 </orderedlist>
521 <para>Remember if you continue in gdb, and need to "break in" again,
522 you need to issue an other sysrq-g. It is easy to create a simple
523 entry point by putting a breakpoint at <constant>sys_sync</constant>
524 and then you can run "sync" from a shell or script to break into the
525 debugger.</para>
526 </sect1>
527 </chapter>
528 <chapter id="switchKdbKgdb">
529 <title>kgdb and kdb interoperability</title>
530 <para>It is possible to transition between kdb and kgdb dynamically.
531 The debug core will remember which you used the last time and
532 automatically start in the same mode.</para>
533 <sect1>
534 <title>Switching between kdb and kgdb</title>
535 <sect2>
536 <title>Switching from kgdb to kdb</title>
537 <para>
538 There are two ways to switch from kgdb to kdb: you can use gdb to
539 issue a maintenance packet, or you can blindly type the command $3#33.
540 Whenever kernel debugger stops in kgdb mode it will print the
541 message <constant>KGDB or $3#33 for KDB</constant>. It is important
542 to note that you have to type the sequence correctly in one pass.
543 You cannot type a backspace or delete because kgdb will interpret
544 that as part of the debug stream.
545 <orderedlist>
546 <listitem><para>Change from kgdb to kdb by blindly typing:</para>
547 <para><constant>$3#33</constant></para></listitem>
548 <listitem><para>Change from kgdb to kdb with gdb</para>
549 <para><constant>maintenance packet 3</constant></para>
550 <para>NOTE: Now you must kill gdb. Typically you press control-z and
551 issue the command: kill -9 %</para></listitem>
552 </orderedlist>
553 </para>
554 </sect2>
555 <sect2>
556 <title>Change from kdb to kgdb</title>
557 <para>There are two ways you can change from kdb to kgdb. You can
558 manually enter kgdb mode by issuing the kgdb command from the kdb
559 shell prompt, or you can connect gdb while the kdb shell prompt is
560 active. The kdb shell looks for the typical first commands that gdb
561 would issue with the gdb remote protocol and if it sees one of those
562 commands it automatically changes into kgdb mode.</para>
563 <orderedlist>
564 <listitem><para>From kdb issue the command:</para>
565 <para><constant>kgdb</constant></para>
566 <para>Now disconnect your terminal program and connect gdb in its place</para></listitem>
567 <listitem><para>At the kdb prompt, disconnect the terminal program and connect gdb in its place.</para></listitem>
568 </orderedlist>
569 </sect2>
570 </sect1>
571 <sect1>
572 <title>Running kdb commands from gdb</title>
573 <para>It is possible to run a limited set of kdb commands from gdb,
574 using the gdb monitor command. You don't want to execute any of the
575 run control or breakpoint operations, because it can disrupt the
576 state of the kernel debugger. You should be using gdb for
577 breakpoints and run control operations if you have gdb connected.
578 The more useful commands to run are things like lsmod, dmesg, ps or
579 possibly some of the memory information commands. To see all the kdb
580 commands you can run <constant>monitor help</constant>.</para>
581 <para>Example:
582 <informalexample><programlisting>
583(gdb) monitor ps
5841 idle process (state I) and
58527 sleeping system daemon (state M) processes suppressed,
586use 'ps A' to see all.
587Task Addr Pid Parent [*] cpu State Thread Command
588
5890xc78291d0 1 0 0 0 S 0xc7829404 init
5900xc7954150 942 1 0 0 S 0xc7954384 dropbear
5910xc78789c0 944 1 0 0 S 0xc7878bf4 sh
592(gdb)
593 </programlisting></informalexample>
594 </para>
595 </sect1>
286 </chapter> 596 </chapter>
287 <chapter id="KGDBTestSuite"> 597 <chapter id="KGDBTestSuite">
288 <title>kgdb Test Suite</title> 598 <title>kgdb Test Suite</title>
@@ -309,34 +619,36 @@
309 </para> 619 </para>
310 </chapter> 620 </chapter>
311 <chapter id="CommonBackEndReq"> 621 <chapter id="CommonBackEndReq">
312 <title>KGDB Internals</title> 622 <title>Kernel Debugger Internals</title>
313 <sect1 id="kgdbArchitecture"> 623 <sect1 id="kgdbArchitecture">
314 <title>Architecture Specifics</title> 624 <title>Architecture Specifics</title>
315 <para> 625 <para>
316 Kgdb is organized into three basic components: 626 The kernel debugger is organized into a number of components:
317 <orderedlist> 627 <orderedlist>
318 <listitem><para>kgdb core</para> 628 <listitem><para>The debug core</para>
319 <para> 629 <para>
320 The kgdb core is found in kernel/kgdb.c. It contains: 630 The debug core is found in kernel/debugger/debug_core.c. It contains:
321 <itemizedlist> 631 <itemizedlist>
322 <listitem><para>All the logic to implement the gdb serial protocol</para></listitem> 632 <listitem><para>A generic OS exception handler which includes
323 <listitem><para>A generic OS exception handler which includes sync'ing the processors into a stopped state on an multi cpu system.</para></listitem> 633 sync'ing the processors into a stopped state on an multi-CPU
634 system.</para></listitem>
324 <listitem><para>The API to talk to the kgdb I/O drivers</para></listitem> 635 <listitem><para>The API to talk to the kgdb I/O drivers</para></listitem>
325 <listitem><para>The API to make calls to the arch specific kgdb implementation</para></listitem> 636 <listitem><para>The API to make calls to the arch-specific kgdb implementation</para></listitem>
326 <listitem><para>The logic to perform safe memory reads and writes to memory while using the debugger</para></listitem> 637 <listitem><para>The logic to perform safe memory reads and writes to memory while using the debugger</para></listitem>
327 <listitem><para>A full implementation for software breakpoints unless overridden by the arch</para></listitem> 638 <listitem><para>A full implementation for software breakpoints unless overridden by the arch</para></listitem>
639 <listitem><para>The API to invoke either the kdb or kgdb frontend to the debug core.</para></listitem>
328 </itemizedlist> 640 </itemizedlist>
329 </para> 641 </para>
330 </listitem> 642 </listitem>
331 <listitem><para>kgdb arch specific implementation</para> 643 <listitem><para>kgdb arch-specific implementation</para>
332 <para> 644 <para>
333 This implementation is generally found in arch/*/kernel/kgdb.c. 645 This implementation is generally found in arch/*/kernel/kgdb.c.
334 As an example, arch/x86/kernel/kgdb.c contains the specifics to 646 As an example, arch/x86/kernel/kgdb.c contains the specifics to
335 implement HW breakpoint as well as the initialization to 647 implement HW breakpoint as well as the initialization to
336 dynamically register and unregister for the trap handlers on 648 dynamically register and unregister for the trap handlers on
337 this architecture. The arch specific portion implements: 649 this architecture. The arch-specific portion implements:
338 <itemizedlist> 650 <itemizedlist>
339 <listitem><para>contains an arch specific trap catcher which 651 <listitem><para>contains an arch-specific trap catcher which
340 invokes kgdb_handle_exception() to start kgdb about doing its 652 invokes kgdb_handle_exception() to start kgdb about doing its
341 work</para></listitem> 653 work</para></listitem>
342 <listitem><para>translation to and from gdb specific packet format to pt_regs</para></listitem> 654 <listitem><para>translation to and from gdb specific packet format to pt_regs</para></listitem>
@@ -347,11 +659,35 @@
347 </itemizedlist> 659 </itemizedlist>
348 </para> 660 </para>
349 </listitem> 661 </listitem>
662 <listitem><para>gdbstub frontend (aka kgdb)</para>
663 <para>The gdbstub is located in kernel/debug/gdbstub.c. It contains:</para>
664 <itemizedlist>
665 <listitem><para>All the logic to implement the gdb serial protocol</para></listitem>
666 </itemizedlist>
667 </listitem>
668 <listitem><para>kdb frontend</para>
669 <para>The kdb debugger shell is broken down into a number of
670 components. The kdb core is located in kernel/debug/kdb. There
671 are a number of helper functions in some of the other kernel
672 components to make it possible for kdb to examine and report
673 information about the kernel without taking locks that could
674 cause a kernel deadlock. The kdb core contains implements the following functionality.</para>
675 <itemizedlist>
676 <listitem><para>A simple shell</para></listitem>
677 <listitem><para>The kdb core command set</para></listitem>
678 <listitem><para>A registration API to register additional kdb shell commands.</para>
679 <para>A good example of a self-contained kdb module is the "ftdump" command for dumping the ftrace buffer. See: kernel/trace/trace_kdb.c</para></listitem>
680 <listitem><para>The implementation for kdb_printf() which
681 emits messages directly to I/O drivers, bypassing the kernel
682 log.</para></listitem>
683 <listitem><para>SW / HW breakpoint management for the kdb shell</para></listitem>
684 </itemizedlist>
685 </listitem>
350 <listitem><para>kgdb I/O driver</para> 686 <listitem><para>kgdb I/O driver</para>
351 <para> 687 <para>
352 Each kgdb I/O driver has to provide an implemenation for the following: 688 Each kgdb I/O driver has to provide an implementation for the following:
353 <itemizedlist> 689 <itemizedlist>
354 <listitem><para>configuration via builtin or module</para></listitem> 690 <listitem><para>configuration via built-in or module</para></listitem>
355 <listitem><para>dynamic configuration and kgdb hook registration calls</para></listitem> 691 <listitem><para>dynamic configuration and kgdb hook registration calls</para></listitem>
356 <listitem><para>read and write character interface</para></listitem> 692 <listitem><para>read and write character interface</para></listitem>
357 <listitem><para>A cleanup handler for unconfiguring from the kgdb core</para></listitem> 693 <listitem><para>A cleanup handler for unconfiguring from the kgdb core</para></listitem>
@@ -416,15 +752,15 @@
416 underlying low level to the hardware driver having "polling hooks" 752 underlying low level to the hardware driver having "polling hooks"
417 which the to which the tty driver is attached. In the initial 753 which the to which the tty driver is attached. In the initial
418 implementation of kgdboc it the serial_core was changed to expose a 754 implementation of kgdboc it the serial_core was changed to expose a
419 low level uart hook for doing polled mode reading and writing of a 755 low level UART hook for doing polled mode reading and writing of a
420 single character while in an atomic context. When kgdb makes an I/O 756 single character while in an atomic context. When kgdb makes an I/O
421 request to the debugger, kgdboc invokes a call back in the serial 757 request to the debugger, kgdboc invokes a call back in the serial
422 core which in turn uses the call back in the uart driver. It is 758 core which in turn uses the call back in the UART driver. It is
423 certainly possible to extend kgdboc to work with non-uart based 759 certainly possible to extend kgdboc to work with non-UART based
424 consoles in the future. 760 consoles in the future.
425 </para> 761 </para>
426 <para> 762 <para>
427 When using kgdboc with a uart, the uart driver must implement two callbacks in the <constant>struct uart_ops</constant>. Example from drivers/8250.c:<programlisting> 763 When using kgdboc with a UART, the UART driver must implement two callbacks in the <constant>struct uart_ops</constant>. Example from drivers/8250.c:<programlisting>
428#ifdef CONFIG_CONSOLE_POLL 764#ifdef CONFIG_CONSOLE_POLL
429 .poll_get_char = serial8250_get_poll_char, 765 .poll_get_char = serial8250_get_poll_char,
430 .poll_put_char = serial8250_put_poll_char, 766 .poll_put_char = serial8250_put_poll_char,
@@ -434,7 +770,7 @@
434 <constant>#ifdef CONFIG_CONSOLE_POLL</constant>, as shown above. 770 <constant>#ifdef CONFIG_CONSOLE_POLL</constant>, as shown above.
435 Keep in mind that polling hooks have to be implemented in such a way 771 Keep in mind that polling hooks have to be implemented in such a way
436 that they can be called from an atomic context and have to restore 772 that they can be called from an atomic context and have to restore
437 the state of the uart chip on return such that the system can return 773 the state of the UART chip on return such that the system can return
438 to normal when the debugger detaches. You need to be very careful 774 to normal when the debugger detaches. You need to be very careful
439 with any kind of lock you consider, because failing here is most 775 with any kind of lock you consider, because failing here is most
440 going to mean pressing the reset button. 776 going to mean pressing the reset button.
@@ -453,6 +789,10 @@
453 <itemizedlist> 789 <itemizedlist>
454 <listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem> 790 <listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem>
455 </itemizedlist> 791 </itemizedlist>
792 In Jan 2010 this document was updated to include kdb.
793 <itemizedlist>
794 <listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem>
795 </itemizedlist>
456 </para> 796 </para>
457 </chapter> 797 </chapter>
458</book> 798</book>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 3845e3a84a52..bdce359820bb 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -58,6 +58,7 @@ parameter is applicable:
58 ISAPNP ISA PnP code is enabled. 58 ISAPNP ISA PnP code is enabled.
59 ISDN Appropriate ISDN support is enabled. 59 ISDN Appropriate ISDN support is enabled.
60 JOY Appropriate joystick support is enabled. 60 JOY Appropriate joystick support is enabled.
61 KGDB Kernel debugger support is enabled.
61 KVM Kernel Virtual Machine support is enabled. 62 KVM Kernel Virtual Machine support is enabled.
62 LIBATA Libata driver is enabled 63 LIBATA Libata driver is enabled
63 LP Printer support is enabled. 64 LP Printer support is enabled.
@@ -1120,13 +1121,16 @@ and is between 256 and 4096 characters. It is defined in the file
1120 use the HighMem zone if it exists, and the Normal 1121 use the HighMem zone if it exists, and the Normal
1121 zone if it does not. 1122 zone if it does not.
1122 1123
1123 kgdboc= [HW] kgdb over consoles. 1124 kgdboc= [KGDB,HW] kgdb over consoles.
1124 Requires a tty driver that supports console polling, 1125 Requires a tty driver that supports console polling,
1125 or a supported polling keyboard driver (non-usb). 1126 or a supported polling keyboard driver (non-usb).
1126 Serial only format: <serial_device>[,baud] 1127 Serial only format: <serial_device>[,baud]
1127 keyboard only format: kbd 1128 keyboard only format: kbd
1128 keyboard and serial format: kbd,<serial_device>[,baud] 1129 keyboard and serial format: kbd,<serial_device>[,baud]
1129 1130
1131 kgdbwait [KGDB] Stop kernel execution and enter the
1132 kernel debugger at the earliest opportunity.
1133
1130 kmac= [MIPS] korina ethernet MAC address. 1134 kmac= [MIPS] korina ethernet MAC address.
1131 Configure the RouterBoard 532 series on-chip 1135 Configure the RouterBoard 532 series on-chip
1132 Ethernet adapter MAC address. 1136 Ethernet adapter MAC address.
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index 5b37df00000d..407edb1e0c4d 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -204,6 +204,17 @@ kgdb_arch_handle_exception(int vector, int signo, int err_code,
204 */ 204 */
205extern void kgdb_roundup_cpus(unsigned long flags); 205extern void kgdb_roundup_cpus(unsigned long flags);
206 206
207/**
208 * kgdb_arch_set_pc - Generic call back to the program counter
209 * @regs: Current &struct pt_regs.
210 * @pc: The new value for the program counter
211 *
212 * This function handles updating the program counter and requires an
213 * architecture specific implementation.
214 */
215extern void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc);
216
217
207/* Optional functions. */ 218/* Optional functions. */
208extern int kgdb_validate_break_address(unsigned long addr); 219extern int kgdb_validate_break_address(unsigned long addr);
209extern int kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr); 220extern int kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr);
@@ -264,7 +275,6 @@ extern struct kgdb_arch arch_kgdb_ops;
264 275
265extern unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs); 276extern unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs);
266 277
267extern void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc);
268extern int kgdb_register_io_module(struct kgdb_io *local_kgdb_io_ops); 278extern int kgdb_register_io_module(struct kgdb_io *local_kgdb_io_ops);
269extern void kgdb_unregister_io_module(struct kgdb_io *local_kgdb_io_ops); 279extern void kgdb_unregister_io_module(struct kgdb_io *local_kgdb_io_ops);
270extern struct kgdb_io *dbg_io_ops; 280extern struct kgdb_io *dbg_io_ops;
generated by cgit v1.2.2 (git 2.25.0) at 2025-12-09 10:39:53 -0500