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11 The <strong>LLDB</strong> Debugger
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19 <div class="post">
20 <h1 class ="postheader">Stack Frame and Thread Format</h1>
21 <div class="postcontent">
22 <p>LLDB was recently modified to allow users to define the
23 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>
39 <p><code><b>(lldb)</b> settings set frame-prompt STRING
40 <br><b>(lldb)</b> settings set thread-prompt STRING
41 </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>
82 <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.pc-offset</b></td><td>The program counter offset within the current function or symbol</td></tr>
84 <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>
85 <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>
86 <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>
87 <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>
88 <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>
89 <tr valign=top><td><b>module.file.basename</b></td><td>The basename of the current module (shared library or executable)</td></tr>
90 <tr valign=top><td><b>module.file.fullpath</b></td><td>The basename of the current module (shared library or executable)</td></tr>
91 <tr valign=top><td><b>process.file.basename</b></td><td>The basename of the file for the process</td></tr>
92 <tr valign=top><td><b>process.file.fullpath</b></td><td>The fullname of the file for the process</td></tr>
93 <tr valign=top><td><b>process.id</b></td><td>The process ID native the the system on which the inferior runs.</td></tr>
94 <tr valign=top><td><b>process.name</b></td><td>The name of the process at runtime</td></tr>
95 <tr valign=top><td><b>thread.id</b></td><td>The thread identifier for the current thread</td></tr>
96 <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>
97 <tr valign=top><td><b>thread.name</b></td><td>The name of the thread if the target OS supports naming threads</td></tr>
98 <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>
99 <tr valign=top><td><b>thread.stop-reason</b></td><td>A textual reason each thread stopped</td></tr>
100 <tr valign=top><td><b>target.arch</b></td><td>The architecture of the current target</td></tr>
101 </table>
102
103 </div>
104 <div class="postfooter"></div>
105 </div>
106
107 <div class="post">
108 <h1 class ="postheader">Control Characters</h1>
109 <div class="postcontent">
110
111 <p>Control characters include <b><code>'{'</code></b>,
112 <b><code>'}'</code></b>, and <b><code>'\'</code></b>.</p>
113
114 <p>The '{' and '}' are used for scoping blocks, and the '\' character
115 allows you to desensitize control characters and also emit non-printable
116 characters.
117
118 </div>
119 <div class="postfooter"></div>
120 </div>
121
122 <div class="post">
123 <h1 class ="postheader">Desensitizing Characters in the format string</h1>
124 <div class="postcontent">
125 <p>The backslash control character allows your to enter the typical
126 <b><code>"\a"</code></b>, <b><code>"\b"</code></b>, <b><code>"\f"</code></b>, <b><code>"\n"</code></b>,
127 <b><code>"\r"</code></b>, <b><code>"\t"</code></b>, <b><code>"\v"</code></b>, <b><code>"\\"</code></b>, characters
128 and along with the standard octal representation <b><code>"\0123"</code></b>
129 and hex <b><code>"\xAB"</code></b> characters. This allows you to enter
130 escape characters into your format strings and will
131 allow colorized output for terminals that support color.
132
133 </div>
134 <div class="postfooter"></div>
135 </div>
136
137 <div class="post">
138 <h1 class ="postheader">Scoping</h1>
139 <div class="postcontent">
140 <p>Many times the information that you might have in your prompt might not be
141 available and you won't want it to print out if it isn't valid. To take care
142 of this you can enclose everything that <b>must</b> resolve into a scope. A scope
143 is starts with <code><b>'{'</code></b> and ends with
144 <code><b>'}'</code></b>. For example in order to only display
145 the current frame line table entry basename and line number when the information
146 is available for the current frame:
147
148 <p><b><code>"{ at {$line.file.basename}:${line.number}}"</code></b></p>
149
150 <p>Broken down this is:
151 <ul>
152 <li>The start the scope <p><b><code>"{"</code></b></p></li>
153 <li> format whose content will only be displayed if all information is available:
154 <p><b><code>"at {$line.file.basename}:${line.number}"</code></b></p></li>
155 <li>end the scope: <p><b><code>"}"</code></b></p></li>
156 </ul>
157
158 </div>
159 <div class="postfooter"></div>
160 </div>
161
162 <div class="post">
163 <h1 class ="postheader">Making the Frame Format</h1>
164 <div class="postcontent">
165 <p>The information that we see when stopped in a frame:
166
167 <p><b><code>frame #0: 0x0000000100000e85 a.out`main + 4 at test.c:19</code></b></p>
168
169 <p>can be displayed with the following format:</p>
170
171 <p><b><code>"frame #${frame.index}: ${frame.pc}{ ${module.file.basename}`${function.name}{${function.pc-offset}}}{ at ${line.file.basename}:${line.number}}\n"</code></b></p>
172
173 <p>This breaks down to:
174
175 <ul>
176 <li>Always print the frame index and frame PC:
177
178 <p><b><code>"frame #${frame.index}: ${frame.pc}"</code></b></p>
179
180 <li>only print the module followed by a tick if there is a valid
181 module for the current frame:
182
183 <p><b><code>"{ ${module.file.basename}`}"</code></b></p>
184
185 <li>print the function name with optional offset:</p>
186 <p><b><code>"{${function.name}{${function.pc-offset}}}"</code></b></p>
187
188 <li>print the line info if it is available:</p>
189
190 <p><b><code>"{ at ${line.file.basename}:${line.number}}"</code></b></p>
191
192 <li>then finish off with a newline:</p>
193
194 <p><b><code>"\n"</code></b></p>
195 </ul>
196
197 </div>
198 <div class="postfooter"></div>
199 </div>
200
201 <div class="post">
202 <h1 class ="postheader">Making Your Own Formats</h1>
203 <div class="postcontent">
204
205 <p>When modifying your own format strings, it is useful
206 to start with the default values for the frame and
207 thread format strings. These can be accessed with the
208 <b><code>"settings show"</code></b> command:
209
210 <p><b><code>(lldb)</b> settings show thread-format
211 <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 = ${thread.queue}}\n'
212 <br><b>(lldb)</b> settings show frame-format
213 <br>frame-format (string) = 'frame #${frame.index}: ${frame.pc}{ ${module.file.basename}`${function.name}{${function.pc-offset}}}{ at ${line.file.basename}:${line.number}}\n'
214 </code></p>
215
216
Greg Clayton9d49e0e2010-10-04 03:06:05 +0000217 <p>When making thread formats, you will need surround any
218 of the information that comes from a stack frame with scopes (<b>{</b> <i>frame-content</i> <b>}</b>)
219 as the thread format doesn't always want to show frame information.
220 When displaying the backtrace for a thread, we don't need to duplicate
221 the information for frame zero in the thread information:
222
223 <p><code><b>(lldb)</b> thread backtrace
224 <br>thread #1: tid = 0x2e03, stop reason = breakpoint 1.1 2.1
225 <br>&nbsp;&nbsp;frame #0: 0x0000000100000e85 a.out`main + 4 at test.c:19
226 <br>&nbsp;&nbsp;frame #1: 0x0000000100000e40 a.out`start + 52
227 </code>
228 </p>
229
230 <p>The frame related variables are:
231 <ul>
232 <li><code><b>${file.*}</b></code></li>
233 <li><code><b>${frame.*}</b></code></li>
234 <li><code><b>${function.*}</b></code></li>
235 <li><code><b>${line.*}</b></code></li>
236 <li><code><b>${module.*}</b></code></li>
237 </ul>
238 </p>
239
240 <p>Looking at the default format for the thread, and underlining
241 the frame information:
242 <p><code>'thread #${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'
243 </code></p>
244 <p>We can see that all frame information is contained in scopes so
245 that when the thread information is displayed in a context where
246 we only want to show thread information, we can do so.
247
Greg Clayton198e8fe2010-10-04 02:33:45 +0000248 </div>
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