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Commit 84c08fd61e2d21702337e9fe366e97cdf09bf797

Authored by Jason Wessel
1 parent ada64e4c98
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

kgdb,docs: Update the kgdb docs to include kdb 

Update the kgdb docs to reflect the new directory structure and API.

Merge in the kdb shell information.

[Randy Dunlap <rdunlap@xenotime.net>: grammatical corrections]

CC: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

Showing 3 changed files with 532 additions and 178 deletions Side-by-side Diff

Documentation/DocBook/kgdb.tmpl
Diff comments   View file @ 84c08fd
... ... @@ -4,7 +4,7 @@
4 4  
5 5 <book id="kgdbOnLinux">
6 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 9 <authorgroup>
10 10 <author>
11 11  
... ... @@ -17,33 +17,8 @@
17 17 </affiliation>
18 18 </author>
19 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 20 <copyright>
46   - <year>2008</year>
  21 + <year>2008,2010</year>
47 22 <holder>Wind River Systems, Inc.</holder>
48 23 </copyright>
49 24 <copyright>
50 25  
51 26  
52 27  
53 28  
54 29  
55 30  
... ... @@ -69,41 +44,76 @@
69 44 <chapter id="Introduction">
70 45 <title>Introduction</title>
71 46 <para>
72   - kgdb is a source level debugger for linux kernel. It is used along
73   - with gdb to debug a linux kernel. The expectation is that gdb can
74   - be used to "break in" to the kernel to inspect memory, variables
75   - and look through call stack information similar to what an
76   - application developer would use gdb for. It is possible to place
77   - breakpoints in kernel code and perform some limited execution
78   - stepping.
  47 + The kernel has two different debugger front ends (kdb and kgdb)
  48 + which interface to the debug core. It is possible to use either
  49 + of the debugger front ends and dynamically transition between them
  50 + if you configure the kernel properly at compile and runtime.
79 51 </para>
80 52 <para>
81   - Two machines are required for using kgdb. One of these machines is a
82   - development machine and the other is a test machine. The kernel
83   - to be debugged runs on the test machine. The development machine
84   - runs an instance of gdb against the vmlinux file which contains
85   - the symbols (not boot image such as bzImage, zImage, uImage...).
86   - In gdb the developer specifies the connection parameters and
87   - connects to kgdb. The type of connection a developer makes with
88   - gdb depends on the availability of kgdb I/O modules compiled as
89   - builtin's or kernel modules in the test machine's kernel.
  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>.
90 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.
  72 + </para>
  73 + <para>
  74 + Two machines are required for using kgdb. One of these machines is
  75 + a development machine and the other is the target machine. The
  76 + kernel to be debugged runs on the target machine. The development
  77 + machine runs an instance of gdb against the vmlinux file which
  78 + contains the symbols (not boot image such as bzImage, zImage,
  79 + uImage...). In gdb the developer specifies the connection
  80 + parameters and connects to kgdb. The type of connection a
  81 + developer makes with gdb depends on the availability of kgdb I/O
  82 + modules compiled as built-ins or loadable kernel modules in the test
  83 + machine's kernel.
  84 + </para>
91 85 </chapter>
92 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 96 <para>
95 97 To enable <symbol>CONFIG_KGDB</symbol> you should first turn on
96 98 "Prompt for development and/or incomplete code/drivers"
97 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".
99 101 </para>
100 102 <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.
  108 + </para>
  109 + <para>
101 110 It is advised, but not required that you turn on the
102   - CONFIG_FRAME_POINTER kernel option. This option inserts code to
103   - into the compiled executable which saves the frame information in
104   - registers or on the stack at different points which will allow a
105   - debugger such as gdb to more accurately construct stack back traces
106   - while debugging the kernel.
  111 + <symbol>CONFIG_FRAME_POINTER</symbol> kernel option which is called "Compile the
  112 + kernel with frame pointers" in the config menu. This option
  113 + inserts code to into the compiled executable which saves the frame
  114 + information in registers or on the stack at different points which
  115 + allows a debugger such as gdb to more accurately construct
  116 + stack back traces while debugging the kernel.
107 117 </para>
108 118 <para>
109 119 If the architecture that you are using supports the kernel option
110 120  
111 121  
112 122  
113 123  
114 124  
115 125  
... ... @@ -116,38 +126,160 @@
116 126 this option.
117 127 </para>
118 128 <para>
119   - Next you should choose one of more I/O drivers to interconnect debugging
120   - host and debugged target. Early boot debugging requires a KGDB
121   - I/O driver that supports early debugging and the driver must be
122   - built into the kernel directly. Kgdb I/O driver configuration
123   - takes place via kernel or module parameters, see following
124   - chapter.
  129 + Next you should choose one of more I/O drivers to interconnect
  130 + debugging host and debugged target. Early boot debugging requires
  131 + a KGDB I/O driver that supports early debugging and the driver
  132 + must be built into the kernel directly. Kgdb I/O driver
  133 + configuration takes place via kernel or module parameters which
  134 + you can learn more about in the in the section that describes the
  135 + parameter "kgdboc".
125 136 </para>
126   - <para>
127   - The kgdb test compile options are described in the kgdb test suite chapter.
  137 + <para>Here is an example set of .config symbols to enable or
  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>
128 145 </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>
130 180 </chapter>
131   - <chapter id="EnableKGDB">
132   - <title>Enable kgdb for debugging</title>
133   - <para>
134   - In order to use kgdb you must activate it by passing configuration
135   - information to one of the kgdb I/O drivers. If you do not pass any
136   - configuration information kgdb will not do anything at all. Kgdb
137   - will only actively hook up to the kernel trap hooks if a kgdb I/O
138   - driver is loaded and configured. If you unconfigure a kgdb I/O
139   - driver, kgdb will unregister all the kernel hook points.
  181 + <chapter id="kgdbKernelArgs">
  182 + <title>Kernel Debugger Boot Arguments</title>
  183 + <para>This section describes the various runtime kernel
  184 + parameters that affect the configuration of the kernel debugger.
  185 + The following chapter covers using kdb and kgdb as well as
  186 + provides some examples of the configuration parameters.</para>
  187 + <sect1 id="kgdboc">
  188 + <title>Kernel parameter: kgdboc</title>
  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.
140 193 </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.
  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>
141 208 <para>
142   - All drivers can be reconfigured at run time, if
143   - <symbol>CONFIG_SYSFS</symbol> and <symbol>CONFIG_MODULES</symbol>
144   - are enabled, by echo'ing a new config string to
145   - <constant>/sys/module/&lt;driver&gt;/parameter/&lt;option&gt;</constant>.
146   - The driver can be unconfigured by passing an empty string. You cannot
147   - change the configuration while the debugger is attached. Make sure
148   - to detach the debugger with the <constant>detach</constant> command
149   - prior to trying unconfigure a kgdb I/O driver.
  209 + <orderedlist>
  210 + <listitem><para>As a kernel built-in:</para>
  211 + <para>Use the kernel boot argument: <constant>kgdboc=&lt;tty-device&gt;,[baud]</constant></para></listitem>
  212 + <listitem>
  213 + <para>As a kernel loadable module:</para>
  214 + <para>Use the command: <constant>modprobe kgdboc kgdboc=&lt;tty-device&gt;,[baud]</constant></para>
  215 + <para>Here are two examples of how you might formate the kgdboc
  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>
150 223 </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>
151 283 <sect1 id="kgdbwait">
152 284 <title>Kernel parameter: kgdbwait</title>
153 285 <para>
154 286  
155 287  
156 288  
157 289  
158 290  
159 291  
160 292  
161 293  
162 294  
163 295  
164 296  
165 297  
166 298  
167 299  
168 300  
169 301  
... ... @@ -162,111 +294,212 @@
162 294 </para>
163 295 <para>
164 296 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
166   - kgdb I/O driver as a kernel module kgdbwait will not do anything.
  297 + architecture allows when you use this option. If you build the
  298 + kgdb I/O driver as a loadable kernel module kgdbwait will not do
  299 + anything.
167 300 </para>
168 301 </sect1>
169   - <sect1 id="kgdboc">
170   - <title>Kernel parameter: kgdboc</title>
171   - <para>
172   - The kgdboc driver was originally an abbreviation meant to stand for
173   - "kgdb over console". Kgdboc is designed to work with a single
174   - serial port. It was meant to cover the circumstance
175   - where you wanted to use a serial console as your primary console as
176   - well as using it to perform kernel debugging. Of course you can
177   - also use kgdboc without assigning a console to the same port.
  302 + <sect1 id="kgdbcon">
  303 + <title>Kernel parameter: kgdbcon</title>
  304 + <para> The kgdbcon feature allows you to see printk() messages
  305 + inside gdb while gdb is connected to the kernel. Kdb does not make
  306 + use of the kgdbcon feature.
  307 + </para>
  308 + <para>Kgdb supports using the gdb serial protocol to send console
  309 + messages to the debugger when the debugger is connected and running.
  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>
178 331 </para>
179   - <sect2 id="UsingKgdboc">
180   - <title>Using kgdboc</title>
  332 + </sect1>
  333 + </chapter>
  334 + <chapter id="usingKDB">
  335 + <title>Using kdb</title>
181 336 <para>
182   - You can configure kgdboc via sysfs or a module or kernel boot line
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>
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>
190 337 </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>
  351 + </para>
191 352 </listitem>
192   - <listitem><para>From sysfs</para>
193   - <para><constant>echo ttyS0 &gt; /sys/module/kgdboc/parameters/kgdboc</constant></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>
  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>
194 361 </listitem>
195   - </orderedlist>
  362 + <listitem><para>When you have telneted to a terminal server that supports sending a remote break</para>
  363 + <para>Press: <constant>Control-]</constant></para>
  364 + <para>Type in:<constant>send break</constant></para>
  365 + <para>Press: <constant>Enter</constant></para>
  366 + <para>Press: <constant>g</constant></para>
  367 + </listitem>
  368 + </itemizedlist>
  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>
196 381 </para>
197   - <para>
198   - NOTE: Kgdboc does not support interrupting the target via the
199   - gdb remote protocol. You must manually send a sysrq-g unless you
200   - have a proxy that splits console output to a terminal problem and
201   - has a separate port for the debugger to connect to that sends the
202   - sysrq-g for you.
  382 + </listitem>
  383 + <listitem>
  384 + <para>When you are done using kdb you need to consider rebooting the
  385 + system or using the "go" command to resuming normal kernel
  386 + execution. If you have paused the kernel for a lengthy period of
  387 + time, applications that rely on timely networking or anything to do
  388 + with real wall clock time could be adversely affected, so you
  389 + should take this into consideration when using the kernel
  390 + debugger.</para>
  391 + </listitem>
  392 + </orderedlist></para>
  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>
203 407 </para>
204   - <para>When using kgdboc with no debugger proxy, you can end up
205   - connecting the debugger for one of two entry points. If an
206   - exception occurs after you have loaded kgdboc a message should print
207   - on the console stating it is waiting for the debugger. In case you
208   - disconnect your terminal program and then connect the debugger in
209   - its place. If you want to interrupt the target system and forcibly
210   - enter a debug session you have to issue a Sysrq sequence and then
211   - type the letter <constant>g</constant>. Then you disconnect the
212   - terminal session and connect gdb. Your options if you don't like
213   - this are to hack gdb to send the sysrq-g for you as well as on the
214   - initial connect, or to use a debugger proxy that allows an
215   - unmodified gdb to do the debugging.
216   - </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>
218 433 </sect1>
219   - <sect1 id="kgdbcon">
220   - <title>Kernel parameter: kgdbcon</title>
221   - <para>
222   - Kgdb supports using the gdb serial protocol to send console messages
223   - to the debugger when the debugger is connected and running. There
224   - are two ways to activate this feature.
  434 + </chapter>
  435 + <chapter id="EnableKGDB">
  436 + <title>Using kgdb / gdb</title>
  437 + <para>In order to use kgdb you must activate it by passing
  438 + configuration information to one of the kgdb I/O drivers. If you
  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>
225 455 <orderedlist>
226   - <listitem><para>Activate with the kernel command line option:</para>
227   - <para><constant>kgdbcon</constant></para>
  456 + <listitem><para>Configure kgdboc</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>
228 466 </listitem>
229   - <listitem><para>Use sysfs before configuring an io driver</para>
230   - <para>
231   - <constant>echo 1 &gt; /sys/module/kgdb/parameters/kgdb_use_con</constant>
232   - </para>
233   - <para>
234   - NOTE: If you do this after you configure the kgdb I/O driver, the
235   - setting will not take effect until the next point the I/O is
236   - reconfigured.
237   - </para>
  467 + <listitem>
  468 + <para>Stop kernel execution (break into the debugger)</para>
  469 + <para>In order to connect to gdb via kgdboc, the kernel must
  470 + first be stopped. There are several ways to stop the kernel which
  471 + include using kgdbwait as a boot argument, via a sysrq-g, or running
  472 + the kernel until it takes an exception where it waits for the
  473 + debugger to attach.
  474 + <itemizedlist>
  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>
238 481 </listitem>
239   - </orderedlist>
  482 + <listitem><para>When you have telneted to a terminal server that supports sending a remote break</para>
  483 + <para>Press: <constant>Control-]</constant></para>
  484 + <para>Type in:<constant>send break</constant></para>
  485 + <para>Press: <constant>Enter</constant></para>
  486 + <para>Press: <constant>g</constant></para>
  487 + </listitem>
  488 + </itemizedlist>
240 489 </para>
241   - <para>
242   - IMPORTANT NOTE: Using this option with kgdb over the console
243   - (kgdboc) is not supported.
244   - </para>
245   - </sect1>
246   - </chapter>
247   - <chapter id="ConnectingGDB">
248   - <title>Connecting gdb</title>
  490 + </listitem>
  491 + <listitem>
  492 + <para>Connect from from gdb</para>
249 493 <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.
  494 + Example (using a directly connected port):
254 495 </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>
261   - Example (using a serial port):
262   - </para>
263 496 <programlisting>
264 497 % gdb ./vmlinux
265 498 (gdb) set remotebaud 115200
266 499 (gdb) target remote /dev/ttyS0
267 500 </programlisting>
268 501 <para>
269   - Example (kgdb to a terminal server on tcp port 2012):
  502 + Example (kgdb to a terminal server on TCP port 2012):
270 503 </para>
271 504 <programlisting>
272 505 % gdb ./vmlinux
273 506  
... ... @@ -283,7 +516,84 @@
283 516 communications. You do this prior to issuing the <constant>target
284 517 remote</constant> command by typing in: <constant>set debug remote 1</constant>
285 518 </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>
286 527 </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
  584 +1 idle process (state I) and
  585 +27 sleeping system daemon (state M) processes suppressed,
  586 +use 'ps A' to see all.
  587 +Task Addr Pid Parent [*] cpu State Thread Command
  588 +
  589 +0xc78291d0 1 0 0 0 S 0xc7829404 init
  590 +0xc7954150 942 1 0 0 S 0xc7954384 dropbear
  591 +0xc78789c0 944 1 0 0 S 0xc7878bf4 sh
  592 +(gdb)
  593 + </programlisting></informalexample>
  594 + </para>
  595 + </sect1>
  596 + </chapter>
287 597 <chapter id="KGDBTestSuite">
288 598 <title>kgdb Test Suite</title>
289 599 <para>
290 600  
291 601  
292 602  
293 603  
294 604  
295 605  
296 606  
297 607  
298 608  
... ... @@ -309,34 +619,36 @@
309 619 </para>
310 620 </chapter>
311 621 <chapter id="CommonBackEndReq">
312   - <title>KGDB Internals</title>
  622 + <title>Kernel Debugger Internals</title>
313 623 <sect1 id="kgdbArchitecture">
314 624 <title>Architecture Specifics</title>
315 625 <para>
316   - Kgdb is organized into three basic components:
  626 + The kernel debugger is organized into a number of components:
317 627 <orderedlist>
318   - <listitem><para>kgdb core</para>
  628 + <listitem><para>The debug core</para>
319 629 <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:
321 631 <itemizedlist>
322   - <listitem><para>All the logic to implement the gdb serial protocol</para></listitem>
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>
  632 + <listitem><para>A generic OS exception handler which includes
  633 + sync'ing the processors into a stopped state on an multi-CPU
  634 + system.</para></listitem>
324 635 <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>
326 637 <listitem><para>The logic to perform safe memory reads and writes to memory while using the debugger</para></listitem>
327 638 <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>
328 640 </itemizedlist>
329 641 </para>
330 642 </listitem>
331   - <listitem><para>kgdb arch specific implementation</para>
  643 + <listitem><para>kgdb arch-specific implementation</para>
332 644 <para>
333 645 This implementation is generally found in arch/*/kernel/kgdb.c.
334 646 As an example, arch/x86/kernel/kgdb.c contains the specifics to
335 647 implement HW breakpoint as well as the initialization to
336 648 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:
338 650 <itemizedlist>
339   - <listitem><para>contains an arch specific trap catcher which
  651 + <listitem><para>contains an arch-specific trap catcher which
340 652 invokes kgdb_handle_exception() to start kgdb about doing its
341 653 work</para></listitem>
342 654 <listitem><para>translation to and from gdb specific packet format to pt_regs</para></listitem>
343 655  
344 656  
... ... @@ -347,11 +659,35 @@
347 659 </itemizedlist>
348 660 </para>
349 661 </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>
350 686 <listitem><para>kgdb I/O driver</para>
351 687 <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:
353 689 <itemizedlist>
354   - <listitem><para>configuration via builtin or module</para></listitem>
  690 + <listitem><para>configuration via built-in or module</para></listitem>
355 691 <listitem><para>dynamic configuration and kgdb hook registration calls</para></listitem>
356 692 <listitem><para>read and write character interface</para></listitem>
357 693 <listitem><para>A cleanup handler for unconfiguring from the kgdb core</para></listitem>
358 694  
359 695  
... ... @@ -416,15 +752,15 @@
416 752 underlying low level to the hardware driver having "polling hooks"
417 753 which the to which the tty driver is attached. In the initial
418 754 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
420 756 single character while in an atomic context. When kgdb makes an I/O
421 757 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
423   - certainly possible to extend kgdboc to work with non-uart based
  758 + core which in turn uses the call back in the UART driver. It is
  759 + certainly possible to extend kgdboc to work with non-UART based
424 760 consoles in the future.
425 761 </para>
426 762 <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>
428 764 #ifdef CONFIG_CONSOLE_POLL
429 765 .poll_get_char = serial8250_get_poll_char,
430 766 .poll_put_char = serial8250_put_poll_char,
... ... @@ -434,7 +770,7 @@
434 770 <constant>#ifdef CONFIG_CONSOLE_POLL</constant>, as shown above.
435 771 Keep in mind that polling hooks have to be implemented in such a way
436 772 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
438 774 to normal when the debugger detaches. You need to be very careful
439 775 with any kind of lock you consider, because failing here is most
440 776 going to mean pressing the reset button.
... ... @@ -450,6 +786,10 @@
450 786 <listitem><para>Tom Rini<email>trini@kernel.crashing.org</email></para></listitem>
451 787 </orderedlist>
452 788 In March 2008 this document was completely rewritten by:
  789 + <itemizedlist>
  790 + <listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem>
  791 + </itemizedlist>
  792 + In Jan 2010 this document was updated to include kdb.
453 793 <itemizedlist>
454 794 <listitem><para>Jason Wessel<email>jason.wessel@windriver.com</email></para></listitem>
455 795 </itemizedlist>
Documentation/kernel-parameters.txt
Diff comments   View file @ 84c08fd
... ... @@ -58,6 +58,7 @@
58 58 ISAPNP ISA PnP code is enabled.
59 59 ISDN Appropriate ISDN support is enabled.
60 60 JOY Appropriate joystick support is enabled.
  61 + KGDB Kernel debugger support is enabled.
61 62 KVM Kernel Virtual Machine support is enabled.
62 63 LIBATA Libata driver is enabled
63 64 LP Printer support is enabled.
64 65  
... ... @@ -1120,12 +1121,15 @@
1120 1121 use the HighMem zone if it exists, and the Normal
1121 1122 zone if it does not.
1122 1123  
1123   - kgdboc= [HW] kgdb over consoles.
  1124 + kgdboc= [KGDB,HW] kgdb over consoles.
1124 1125 Requires a tty driver that supports console polling,
1125 1126 or a supported polling keyboard driver (non-usb).
1126 1127 Serial only format: <serial_device>[,baud]
1127 1128 keyboard only format: kbd
1128 1129 keyboard and serial format: kbd,<serial_device>[,baud]
  1130 +
  1131 + kgdbwait [KGDB] Stop kernel execution and enter the
  1132 + kernel debugger at the earliest opportunity.
1129 1133  
1130 1134 kmac= [MIPS] korina ethernet MAC address.
1131 1135 Configure the RouterBoard 532 series on-chip
include/linux/kgdb.h
Diff comments   View file @ 84c08fd
... ... @@ -204,6 +204,17 @@
204 204 */
205 205 extern 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 + */
  215 +extern void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc);
  216 +
  217 +
207 218 /* Optional functions. */
208 219 extern int kgdb_validate_break_address(unsigned long addr);
209 220 extern int kgdb_arch_set_breakpoint(unsigned long addr, char *saved_instr);
... ... @@ -264,7 +275,6 @@
264 275  
265 276 extern unsigned long __weak kgdb_arch_pc(int exception, struct pt_regs *regs);
266 277  
267   -extern void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long pc);
268 278 extern int kgdb_register_io_module(struct kgdb_io *local_kgdb_io_ops);
269 279 extern void kgdb_unregister_io_module(struct kgdb_io *local_kgdb_io_ops);
270 280 extern struct kgdb_io *dbg_io_ops;