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Greg Clayton198e8fe2010-10-04 02:33:45 +00001<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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Greg Claytonf9ab5ea2012-01-22 02:55:08 +00006<title>LLDB Stack and Frame Formats</title>
Greg Clayton198e8fe2010-10-04 02:33:45 +00007</head>
8
9<body>
10 <div class="www_title">
11 The <strong>LLDB</strong> Debugger
12 </div>
13
14<div id="container">
15 <div id="content">
16 <!--#include virtual="sidebar.incl"-->
17
18 <div id="middle">
19 <div class="post">
20 <h1 class ="postheader">Stack Frame and Thread Format</h1>
21 <div class="postcontent">
Enrico Granataf68ffcd2013-07-12 20:46:02 +000022 <p>LLDB has a facility to allow users to define the
Greg Clayton198e8fe2010-10-04 02:33:45 +000023 format of the information that generates the descriptions
24 for threads and stack frames. Typically when your program stops
25 at a breakpoint you will get a line that describes why
26 your thread stopped:</p>
27
28 <p><b><code>* thread #1: tid = 0x2e03, 0x0000000100000e85 a.out`main + 4, stop reason = breakpoint 1.1</code></b></p>
29
30 <p>Stack backtraces frames also have a similar information line:</p>
31
32 <p><code><b>(lldb)</b> thread backtrace
33 <br><b>thread #1: tid = 0x2e03, stop reason = breakpoint 1.1
34 <br>&nbsp;&nbsp;frame #0: 0x0000000100000e85 a.out`main + 4 at test.c:19
35 <br>&nbsp;&nbsp;frame #1: 0x0000000100000e40 a.out`start + 52
36 </code></b></p>
37
38 <p>The two format strings can currently be set using the <b>settings set</b> command:</p>
Jason Molendabc088c72011-08-25 02:46:44 +000039 <p><code><b>(lldb)</b> settings set frame-format STRING
40 <br><b>(lldb)</b> settings set thread-format STRING
Greg Clayton198e8fe2010-10-04 02:33:45 +000041 </p></code>
42
43 </div>
44 <div class="postfooter"></div>
45 </div>
46
47 <div class="post">
48 <h1 class ="postheader">Format Strings</h1>
49 <div class="postcontent">
50
51 <p>So what is the format of the format strings? Format strings can
52 contain plain text, control characters and variables that have access
53 to the current program state.</p>
54
55 <p>Normal characters are any text that doesn't contain a <code><b>'{'</b></code>, <code><b>'}'</b></code>, <code><b>'$'</b></code>,
56 or <code><b>'\'</b></code> character.</p>
57
58 <p>Variable names are found in between a <code><b>"${"</b></code> prefix, and
59 end with a <code><b>"}"</b></code> suffix. In other words, a variable looks like
60 <code>"<b>${frame.pc}</b>"</code>.</p>
61
62 </div>
63 <div class="postfooter"></div>
64 </div>
65
66 <div class="post">
67 <h1 class ="postheader">Variables</h1>
68 <div class="postcontent">
69
70 <p>A complete list of currently supported format string variables is listed below:</p>
71
72 <table border="1">
73 <tr valign=top><td><b>Variable Name</b></td><td><b>Description</b></td></tr>
74 <tr valign=top><td><b>file.basename</b></td><td>The current compile unit file basename for the current frame.</td></tr>
75 <tr valign=top><td><b>file.fullpath</b></td><td>The current compile unit file fullpath for the current frame.</td></tr>
76 <tr valign=top><td><b>frame.index</b></td><td>The frame index (0, 1, 2, 3...)</td></tr>
77 <tr valign=top><td><b>frame.pc</b></td><td>The generic frame register for the program counter.</td></tr>
78 <tr valign=top><td><b>frame.sp</b></td><td>The generic frame register for the stack pointer.</td></tr>
79 <tr valign=top><td><b>frame.fp</b></td><td>The generic frame register for the frame pointer.</td></tr>
80 <tr valign=top><td><b>frame.flags</b></td><td>The generic frame register for the flags register.</td></tr>
81 <tr valign=top><td><b>frame.reg.NAME</b></td><td>Access to any platform specific register by name (replace <b>NAME</b> with the name of the desired register).</td></tr>
Greg Clayton688082e2012-01-13 08:41:20 +000082 <tr valign=top><td><b>function.name</b></td><td>The name of the current function or symbol.</td></tr>
83 <tr valign=top><td><b>function.name-with-args</b></td><td>The name of the current function with arguments and values or the symbol name.</td></tr>
Greg Clayton198e8fe2010-10-04 02:33:45 +000084 <tr valign=top><td><b>function.pc-offset</b></td><td>The program counter offset within the current function or symbol</td></tr>
85 <tr valign=top><td><b>line.file.basename</b></td><td>The line table entry basename to the file for the current line entry in the current frame.</td></tr>
86 <tr valign=top><td><b>line.file.fullpath</b></td><td>The line table entry fullpath to the file for the current line entry in the current frame.</td></tr>
87 <tr valign=top><td><b>line.number</b></td><td>The line table entry line number for the current line entry in the current frame.</td></tr>
88 <tr valign=top><td><b>line.start-addr</b></td><td>The line table entry start address for the current line entry in the current frame.</td></tr>
89 <tr valign=top><td><b>line.end-addr</b></td><td>The line table entry end address for the current line entry in the current frame.</td></tr>
90 <tr valign=top><td><b>module.file.basename</b></td><td>The basename of the current module (shared library or executable)</td></tr>
91 <tr valign=top><td><b>module.file.fullpath</b></td><td>The basename of the current module (shared library or executable)</td></tr>
92 <tr valign=top><td><b>process.file.basename</b></td><td>The basename of the file for the process</td></tr>
93 <tr valign=top><td><b>process.file.fullpath</b></td><td>The fullname of the file for the process</td></tr>
94 <tr valign=top><td><b>process.id</b></td><td>The process ID native the the system on which the inferior runs.</td></tr>
95 <tr valign=top><td><b>process.name</b></td><td>The name of the process at runtime</td></tr>
96 <tr valign=top><td><b>thread.id</b></td><td>The thread identifier for the current thread</td></tr>
97 <tr valign=top><td><b>thread.index</b></td><td>The unique one based thread index ID which is guaranteed to be unique as threads come and go.</td></tr>
98 <tr valign=top><td><b>thread.name</b></td><td>The name of the thread if the target OS supports naming threads</td></tr>
99 <tr valign=top><td><b>thread.queue</b></td><td>The queue name of the thread if the target OS supports dispatch queues</td></tr>
100 <tr valign=top><td><b>thread.stop-reason</b></td><td>A textual reason each thread stopped</td></tr>
Jim Ingham1586d972011-12-17 01:35:57 +0000101 <tr valign=top><td><b>thread.return-value</b></td><td>The return value of the latest step operation (currently only for step-out.)</td></tr>
Greg Clayton198e8fe2010-10-04 02:33:45 +0000102 <tr valign=top><td><b>target.arch</b></td><td>The architecture of the current target</td></tr>
Enrico Granataf68ffcd2013-07-12 20:46:02 +0000103 <tr valign=top><td><b>target.script:<i>python_func</i></b></td><td>Use a Python function to generate a piece of textual output</td></tr>
104 <tr valign=top><td><b>process.script:<i>python_func</i></b></td><td>Use a Python function to generate a piece of textual output</td></tr>
105 <tr valign=top><td><b>thread.script:<i>python_func</i></b></td><td>Use a Python function to generate a piece of textual output</td></tr>
106 <tr valign=top><td><b>frame.script:<i>python_func</i></b></td><td>Use a Python function to generate a piece of textual output</td></tr>
Greg Clayton198e8fe2010-10-04 02:33:45 +0000107 </table>
108
109 </div>
110 <div class="postfooter"></div>
111 </div>
112
113 <div class="post">
114 <h1 class ="postheader">Control Characters</h1>
115 <div class="postcontent">
116
117 <p>Control characters include <b><code>'{'</code></b>,
118 <b><code>'}'</code></b>, and <b><code>'\'</code></b>.</p>
119
120 <p>The '{' and '}' are used for scoping blocks, and the '\' character
121 allows you to desensitize control characters and also emit non-printable
122 characters.
123
124 </div>
125 <div class="postfooter"></div>
126 </div>
127
128 <div class="post">
129 <h1 class ="postheader">Desensitizing Characters in the format string</h1>
130 <div class="postcontent">
131 <p>The backslash control character allows your to enter the typical
132 <b><code>"\a"</code></b>, <b><code>"\b"</code></b>, <b><code>"\f"</code></b>, <b><code>"\n"</code></b>,
133 <b><code>"\r"</code></b>, <b><code>"\t"</code></b>, <b><code>"\v"</code></b>, <b><code>"\\"</code></b>, characters
134 and along with the standard octal representation <b><code>"\0123"</code></b>
135 and hex <b><code>"\xAB"</code></b> characters. This allows you to enter
136 escape characters into your format strings and will
137 allow colorized output for terminals that support color.
138
139 </div>
140 <div class="postfooter"></div>
141 </div>
142
143 <div class="post">
144 <h1 class ="postheader">Scoping</h1>
145 <div class="postcontent">
146 <p>Many times the information that you might have in your prompt might not be
147 available and you won't want it to print out if it isn't valid. To take care
148 of this you can enclose everything that <b>must</b> resolve into a scope. A scope
149 is starts with <code><b>'{'</code></b> and ends with
150 <code><b>'}'</code></b>. For example in order to only display
151 the current frame line table entry basename and line number when the information
152 is available for the current frame:
153
154 <p><b><code>"{ at {$line.file.basename}:${line.number}}"</code></b></p>
155
156 <p>Broken down this is:
157 <ul>
158 <li>The start the scope <p><b><code>"{"</code></b></p></li>
159 <li> format whose content will only be displayed if all information is available:
160 <p><b><code>"at {$line.file.basename}:${line.number}"</code></b></p></li>
161 <li>end the scope: <p><b><code>"}"</code></b></p></li>
162 </ul>
163
164 </div>
165 <div class="postfooter"></div>
166 </div>
167
168 <div class="post">
169 <h1 class ="postheader">Making the Frame Format</h1>
170 <div class="postcontent">
171 <p>The information that we see when stopped in a frame:
172
173 <p><b><code>frame #0: 0x0000000100000e85 a.out`main + 4 at test.c:19</code></b></p>
174
175 <p>can be displayed with the following format:</p>
176
177 <p><b><code>"frame #${frame.index}: ${frame.pc}{ ${module.file.basename}`${function.name}{${function.pc-offset}}}{ at ${line.file.basename}:${line.number}}\n"</code></b></p>
178
179 <p>This breaks down to:
180
181 <ul>
182 <li>Always print the frame index and frame PC:
183
184 <p><b><code>"frame #${frame.index}: ${frame.pc}"</code></b></p>
185
186 <li>only print the module followed by a tick if there is a valid
187 module for the current frame:
188
189 <p><b><code>"{ ${module.file.basename}`}"</code></b></p>
190
191 <li>print the function name with optional offset:</p>
192 <p><b><code>"{${function.name}{${function.pc-offset}}}"</code></b></p>
193
194 <li>print the line info if it is available:</p>
195
196 <p><b><code>"{ at ${line.file.basename}:${line.number}}"</code></b></p>
197
198 <li>then finish off with a newline:</p>
199
200 <p><b><code>"\n"</code></b></p>
201 </ul>
202
203 </div>
204 <div class="postfooter"></div>
205 </div>
206
207 <div class="post">
208 <h1 class ="postheader">Making Your Own Formats</h1>
209 <div class="postcontent">
210
211 <p>When modifying your own format strings, it is useful
212 to start with the default values for the frame and
213 thread format strings. These can be accessed with the
214 <b><code>"settings show"</code></b> command:
215
216 <p><b><code>(lldb)</b> settings show thread-format
217 <br>thread-format (string) = 'thread #${thread.index}: tid = ${thread.id}{, ${frame.pc}}{ ${module.file.basename}`${function.name}{${function.pc-offset}}}{, stop reason = ${thread.stop-reason}}{, name = ${thread.name}}{, queue = ${thread.queue}}\n'
218 <br><b>(lldb)</b> settings show frame-format
219 <br>frame-format (string) = 'frame #${frame.index}: ${frame.pc}{ ${module.file.basename}`${function.name}{${function.pc-offset}}}{ at ${line.file.basename}:${line.number}}\n'
220 </code></p>
221
222
Greg Clayton9d49e0e2010-10-04 03:06:05 +0000223 <p>When making thread formats, you will need surround any
224 of the information that comes from a stack frame with scopes (<b>{</b> <i>frame-content</i> <b>}</b>)
225 as the thread format doesn't always want to show frame information.
226 When displaying the backtrace for a thread, we don't need to duplicate
227 the information for frame zero in the thread information:
228
229 <p><code><b>(lldb)</b> thread backtrace
230 <br>thread #1: tid = 0x2e03, stop reason = breakpoint 1.1 2.1
231 <br>&nbsp;&nbsp;frame #0: 0x0000000100000e85 a.out`main + 4 at test.c:19
232 <br>&nbsp;&nbsp;frame #1: 0x0000000100000e40 a.out`start + 52
233 </code>
234 </p>
235
236 <p>The frame related variables are:
237 <ul>
238 <li><code><b>${file.*}</b></code></li>
239 <li><code><b>${frame.*}</b></code></li>
240 <li><code><b>${function.*}</b></code></li>
241 <li><code><b>${line.*}</b></code></li>
242 <li><code><b>${module.*}</b></code></li>
243 </ul>
244 </p>
245
246 <p>Looking at the default format for the thread, and underlining
247 the frame information:
248 <p><code>'thread #${thread.index}: tid = ${thread.id}<u><b>{</b>, ${frame.pc}<b>}{</b> ${module.file.basename}`${function.name}{${function.pc-offset}}<b>}</b></u>{, stop reason = ${thread.stop-reason}}{, name = ${thread.name}}{, queue = ${thread.queue}}\n'
249 </code></p>
250 <p>We can see that all frame information is contained in scopes so
251 that when the thread information is displayed in a context where
252 we only want to show thread information, we can do so.
253
Enrico Granataf68ffcd2013-07-12 20:46:02 +0000254 <p>For both thread and frame formats, you can use ${target.script:<i>python_func</i>}, ${process.script:<i>python_func</i>} and ${thread.script:<i>python_func</i>}
255 (and of course ${frame.script:<i>python_func</i>} for frame formats)<br/>
256 In all cases, the signature of <i>python_func</i> is expected to be:<br/>
257 <p><code>
258 def <i>python_func</i>(<i>object</i>,unused):<br/>
259 &nbsp;&nbsp;&nbsp;&nbsp;...<br/>
260 &nbsp;&nbsp;&nbsp;&nbsp;return <i>string</i><br/></code>
261 <p>Where <i>object</i> is an instance of the SB class associated to the keyword you are using.
262
263 <p>e.g. Assuming your function looks like<br/><code><p>
264 def thread_printer_func (thread,unused):<br/>
265 &nbsp;&nbsp;return "Thread %s has %d frames\n" % (thread.name, thread.num_frames)<br/></code><p>
266
267 And you set it up with <code><br/><b>(lldb)</b> settings set thread-format "${thread.script:thread_printer_func}"<br/></code>
268 you would see output like:
269 </p>
270 <code>* Thread main has 21 frames</code>
Greg Clayton198e8fe2010-10-04 02:33:45 +0000271 </div>
272 <div class="postfooter"></div>
273 </div>
274
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Greg Clayton688082e2012-01-13 08:41:20 +0000279</html>