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Greg Claytone8ec5ac2012-11-16 23:50:32 +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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6<title>Debug Sybmols on Mac OS X</title>
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10 <div class="www_title">
11 The <strong>LLDB</strong> Debugger
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20 <div class="post">
21 <h1 class="postheader">Debug Symbols on MacOSX</h1>
22 <div class="postcontent">
23 <p>On MacOSX, debug symbols are often in stand alone bundles called <b>dSYM</b> files.
24 These are bundles that contain DWARF debug information and other resources related to
25 builds and debug info.</p>
26 <p>The DebugSymbols.framework framework helps locate dSYM files when given a UUID. It can
27 locate the symbols using a variety of methods:</p>
28 <ul>
29 <li>Spotlight</li>
30 <li>Explicit search paths</li>
31 <li>Implicit search paths</li>
32 <li>File mapped UUID paths</li>
33 <li>Running one or more shell scripts</li>
34 </ul>
35 <p>DebugSymbols.framework also has global defaults that can be modified to allow
36 all of the debug tools (lldb, gdb, sample, CoreSymbolication.framework) to easily
37 find important debug symbols. The domain for the DebugSymbols.framework defaults
38 is <b>com.apple.DebugSymbols</b>, and the defaults can be read, written or modified
39 using the <b>defaults</b> shell command:
40<code><pre><tt><b>% defaults read com.apple.DebugSymbols
41% defaults write com.apple.DebugSymbols KEY ...
42% defaults delete com.apple.DebugSymbols KEY</b>
43</tt></pre></code>
44
45 <p>The following is a list of the defaults key value
46 setting pairs that can be used to enhance symbol location:</p>
47 <table class="stats" width="620" cellspacing="0">
48 <tr>
49 <td class="hed" width="20%">Defaults Key</td>
50 <td class="hed" width="70%">Description</td>
51 </tr>
52
53 <tr>
54 <td class="content">
55 <b>DBGFileMappedPaths</b>
56 </td>
57 <td class="content">
58 This default can be specified as a single string, or an array of strings.
59 Each string represents a directory that contains file mapped UUID values
60 that point to dSYM files. See the "File Mapped UUID Directories" section
61 below for more details. Whenever DebugSymbols.framework is asked to lookup
62 a dSYM file, it will first look in any file mapped UUID directories
63 for a quick match.
64 </td>
65 </tr>
66 <td class="content" colspan="2">
67<code><pre><tt><b>% defaults write com.apple.DebugSymbols DBGFileMappedPaths -string /path/to/uuidmap1</b>
68<b>% defaults write com.apple.DebugSymbols DBGFileMappedPaths -array /path/to/uuidmap1
69 /path/to/uuidmap2</b>
70</tt></pre></code>
71 </tr>
72 <tr>
73 <td class="content">
74 <b>DBGShellCommands</b>
75 </td>
76 <td class="content">
77 This default can be specified as a single string, or an array of strings.
78 Specifies a shell script that will get run in order to find the dSYM.
79 The shell script will be run given a single UUID value as the shell
80 command arguments and the shell command is expected to return a property
81 list. See the property list format defined below.
82 </td>
83 </tr>
84 <td class="content" colspan="2">
85<code><pre><tt><b>% defaults write com.apple.DebugSymbols DBGShellCommands -string /path/to/script1</b>
86<b>% defaults write com.apple.DebugSymbols DBGShellCommands -array /path/to/script1
87 /path/to/script2</b>
88</tt></pre></code>
89 </td>
90 </tr>
91 <tr>
92 <td class="content">
93 <b>DBGSpotlightPaths</b>
94 </td>
95 <td class="content">
96 Specifies the directories to limit spotlight searches to as a string or array of strings. When any
97 other defaults are supplied to <b>com.apple.DebugSymbols</b>, spotlight
98 searches will be disabled unless this default is set to an empty array:
99 </td>
100 </tr>
101 <td class="content" colspan="2">
102<code><pre><tt><font color="green"># Specify an empty array to keep Spotlight searches enabled in all locations</font>
103<b>% defaults write com.apple.DebugSymbols DBGSpotlightPaths -array</b>
104
105<font color="green"># Specify an array of paths to limit spotlight searches to certain directories</font>
106<b>% defaults write com.apple.DebugSymbols DBGSpotlightPaths -array /path/dir1 /path/dir2</b>
107</tt></pre></code>
108 </td>
109 </tr>
110 </table>
111 </div>
112 <div class="postfooter"></div>
113 </div>
114 <div class="post">
115 <h1 class="postheader">Shell Script Property List Format</h1>
116 <div class="postcontent">
117<p>Shell scripts that are specified with the <b>DBGShellCommands</b> defaults key
118will be run in the order in which they are specified until a match is found.
119The shell script will be invoked with a single UUID string value like
120"23516BE4-29BE-350C-91C9-F36E7999F0F1". The shell script must respond with a
Greg Clayton5ee8d642012-11-19 17:38:24 +0000121property list being written to STDOUT.
122The property list returned must contain UUID string values as the root key values, with
123a dictionary for each UUID. The dictionaries can contain one or more of the following keys:
Greg Claytone8ec5ac2012-11-16 23:50:32 +0000124
125 <table class="stats" width="620" cellspacing="0">
126 <tr>
127 <td class="hed" width="20%">Key</td>
128 <td class="hed" width="70%">Description</td>
129 </tr>
130 <tr>
131 <td class="content">
132 <b>DBGArchitecture</b>
133 </td>
134 <td class="content">A textual architecture or target triple like "x86_64", "i386", or "x86_64-apple-macosx".
135 </td>
136 </tr>
137 <tr>
138 <td class="content">
139 <b>DBGBuildSourcePath</b>
140 </td>
141 <td class="content">A path prefix that was used when building the dSYM file. The debug information will
142 contain paths with this prefix.
143 </td>
144 </tr>
145 <tr>
146 <td class="content">
147 <b>DBGSourcePath</b>
148 </td>
149 <td class="content">A path prefix for where the sources exist after the build has completed. Often when
150 building projects, build machines will host the sources in a temporary directory while building, then
151 move the sources to another location for archiving. If the paths in the debug info don't match where
152 the sources are currently hosted, then specifying this path along with the <b>DBGBuildSourcePath</b>
153 will help the developer tools always show you sources when debugging or symbolicating.
154 </td>
155 </tr>
156 <tr>
157 <td class="content">
158 <b>DBGDSYMPath</b>
159 </td>
160 <td class="content">A path to the dSYM mach-o file inside the dSYM bundle.
161 </td>
162 </tr>
163 <tr>
164 <td class="content">
165 <b>DBGSymbolRichExecutable</b>
166 </td>
167 <td class="content">A path to the symbol rich executable. Binaries are often stripped after
168 being built and packaged into a release. If your build systems saves an unstripped executable
169 a path to this executable can be provided.
170 </td>
171 </tr>
172 <tr>
173 <td class="content">
174 <b>DBGError</b>
175 </td>
176 <td class="content">If a binary can not be located for the supplied UUID, a user readable error
177 can be returned.
178 </td>
179 </tr>
180 </table>
181
182<p>Below is a sample shell script output for a binary that contains two architectures:
183<code><pre><tt>
184&lt;?xml version="1.0" encoding="UTF-8"?&gt;
185&lt;!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;
186&lt;plist version="1.0"&gt;
187&lt;dict&gt;
188 &lt;key&gt;23516BE4-29BE-350C-91C9-F36E7999F0F1&lt;/key&gt;
189 &lt;dict&gt;
190 &lt;key&gt;DBGArchitecture&lt;/key&gt;
191 &lt;string&gt;i386&lt;/string&gt;
192 &lt;key&gt;DBGBuildSourcePath&lt;/key&gt;
193 &lt;string&gt;/path/to/build/sources&lt;/string&gt;
194 &lt;key&gt;DBGSourcePath&lt;/key&gt;
195 &lt;string&gt;/path/to/actual/sources&lt;/string&gt;
196 &lt;key&gt;DBGDSYMPath&lt;/key&gt;
197 &lt;string&gt;/path/to/foo.dSYM/Contents/Resources/DWARF/foo&lt;/string&gt;
198 &lt;key&gt;DBGSymbolRichExecutable&lt;/key&gt;
199 &lt;string&gt;/path/to/unstripped/exectuable&lt;/string&gt;
200 &lt;/dict&gt;
201 &lt;key&gt;A40597AA-5529-3337-8C09-D8A014EB1578&lt;/key&gt;
202 &lt;dict&gt;
203 &lt;key&gt;DBGArchitecture&lt;/key&gt;
204 &lt;string&gt;x86_64&lt;/string&gt;
205 &lt;key&gt;DBGBuildSourcePath&lt;/key&gt;
206 &lt;string&gt;/path/to/build/sources&lt;/string&gt;
207 &lt;key&gt;DBGSourcePath&lt;/key&gt;
208 &lt;string&gt;/path/to/actual/sources&lt;/string&gt;
209 &lt;key&gt;DBGDSYMPath&lt;/key&gt;
210 &lt;string&gt;/path/to/foo.dSYM/Contents/Resources/DWARF/foo&lt;/string&gt;
211 &lt;key&gt;DBGSymbolRichExecutable&lt;/key&gt;
212 &lt;string&gt;/path/to/unstripped/exectuable&lt;/string&gt;
213 &lt;/dict&gt;
214&lt;/dict&gt;
215&lt;/plist&gt;
216</tt></pre></code>
217
Greg Clayton5ee8d642012-11-19 17:38:24 +0000218<p>There is no timeout imposed on a shell script when is it asked to locate a dSYM file, so be careful to not make a shell
219script that has high latency or takes a long time to download unless this
220is really what you want. This can slow down debug sessions in LLDB and GDB, symbolication
221with CoreSymbolication or Report Crash, with no visible feedback to the user. You can
222quickly return a plist with a single <b>DBGError</b> key that indicates a timeout
223has been reached. You might also want to exec new processes to do the downloads so
224that if you return an error that indicates a timeout, your download can still proceed
225after your shell script has exited so subsequent debug sessions can use the cached files.
226It is also important to track when a current download is in progress in case you get multiple requests for the same UUID so
227that you don't end up downloading the same file simultaneously. Also you will want
228to verify the download was successful and then and only then place the file into the
229cache for tools that will cache files locally.
Greg Claytone8ec5ac2012-11-16 23:50:32 +0000230 </div>
231 <div class="postfooter"></div>
232 </div>
233 <div class="post">
234 <h1 class="postheader">Embedding UUID property lists inside the dSYM bundles</h1>
235 <div class="postcontent">
236<p>Since dSYM files are bundles, you can also place UUID info plists files inside
237your dSYM bundles in the <b>Contents/Resources</b> directory. One of the main
238reasons to create the UUID plists inside the dSYM bundles
239is that it will help LLDB and other developer tools show you source. LLDB currently
240knows how to check for these plist files so it can automatically remap the source
241location information in the debug info.
242
243<p>If we take the two UUID values from the returns plist above, we can split
244them out and save then in the dSYM bundle:
245
246<code><pre><tt><b>% ls /path/to/foo.dSYM/Contents/Resources</b>
24723516BE4-29BE-350C-91C9-F36E7999F0F1.plist
248A40597AA-5529-3337-8C09-D8A014EB1578.plist
249
250<b>% cat /path/to/foo.dSYM/Contents/Resources/23516BE4-29BE-350C-91C9-F36E7999F0F1.plist</b>
251&lt;?xml version="1.0" encoding="UTF-8"?&gt;
252&lt;!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"&gt;
253&lt;plist version="1.0"&gt;
254&lt;dict&gt;
255 &lt;key&gt;DBGArchitecture&lt;/key&gt;
256 &lt;string&gt;i386&lt;/string&gt;
257 &lt;key&gt;DBGBuildSourcePath&lt;/key&gt;
258 &lt;string&gt;/path/to/build/sources&lt;/string&gt;
259 &lt;key&gt;DBGSourcePath&lt;/key&gt;
260 &lt;string&gt;/path/to/actual/sources&lt;/string&gt;
261 &lt;key&gt;DBGDSYMPath&lt;/key&gt;
262 &lt;string&gt;/path/to/foo.dSYM/Contents/Resources/DWARF/foo&lt;/string&gt;
263 &lt;key&gt;DBGSymbolRichExecutable&lt;/key&gt;
264 &lt;string&gt;/path/to/unstripped/exectuable&lt;/string&gt;
265&lt;/dict&gt;
266&lt;/plist&gt;
267</tt></pre></code>
268
269<p>Note that the output is very close to what is needed by shell script output,
270so making the results of your shell script will be very easy to create by
271combining two plists into a single one where you take the UUID and use it a
272 string key, and the value is the contents of the plist.
273
274
275 </div>
276 <div class="postfooter"></div>
277 </div>
278 <div class="post">
279 <h1 class="postheader">File Mapped UUID Directories</h1>
280 <div class="postcontent">
281<p>File Mapped directories can be used for efficient dSYM file lookups for
282local or remote dSYM files. The UUID is broken up by splitting the first
28320 hex digits into 4 character chunks, and a directory is created for each
284chunk, and each subsequent directory is created inside the previous one.
285A symlink is then created whose name is the last 12 hex digits in the deepest
286directory. The symlinks value is a full path to the mach-o files inside the
287dSYM bundle which contains the DWARF. Whenever DebugSymbols.framework is asked
288to lookup a dSYM file, it will first look in any file mapped UUID directories
289for a quick match if the defaults are appropriately set.
290
291<p>For example, if we take the sample UUID plist inforamtion from above, we
292can create a File Mapped UUID directory cache in <b>~/Library/SymbolCache/dsyms/uuids</b>.
293We can easily see how things are laid out:
294
295<code><pre><tt><b>% find ~/Library/SymbolCache/dsyms/uuids -type l</b>
296~/Library/SymbolCache/dsyms/uuids/2351/6BE4/29BE/350C/91C9/F36E7999F0F1
297~/Library/SymbolCache/dsyms/uuids/A405/97AA/5529/3337/8C09/D8A014EB1578
298</tt></pre></code>
299
300<p>The last entries in these file mapped directories are symlinks to the actual dsym mach file in the dsym bundle:
301
302<code><pre><tt><b>% ls -lAF ~/Library/SymbolCache/dsyms/uuids/2351/6BE4/29BE/350C/91C9/F36E7999F0F1</b>
303~/Library/SymbolCache/dsyms/uuids/2351/6BE4/29BE/350C/91C9/F36E7999F0F1@ -> ../../../../../../dsyms/foo.dSYM/Contents/Resources/DWARF/foo
304</tt></pre></code>
305<p>Then you can also tell DebugSymbols to check this UUID file map cache using:
306
307<code><pre><tt><b>% defaults write com.apple.DebugSymbols DBGFileMappedPaths ~/Library/SymbolCache/dsyms/uuids</b>
308</tt></pre></code>
309
310
311 </div>
312 <div class="postfooter"></div>
313 </div>
314 <div class="post">
315 <h1 class="postheader">dSYM Locating Shell Script Tips</h1>
316 <div class="postcontent">
317
318<p>One possible implementation of a dSYM finding shell script is to have the script
319download and cache files locally in a known location. Then create a UUID map
320for each UUID value that was found in a local UUID File Map cache so the next query for the dSYM
321file will be able to use the cached version. So the shell script is used to
322initially download and cache the file, and subsequent accesses will use the
323cache and avoid calling the shell script.
324
325<p>Then the defaults for DebugSymbols.framework will entail enabling your shell script,
326enabling the file mapped path setting so that already downloaded dSYMS fill quickly
327be found without needing to run the shell script every time, and also leaving spotlight enabled
328so that other normal dSYM files are still found:
329
330<code><pre><tt><b>% defaults write com.apple.DebugSymbols DBGShellCommands /path/to/shellscript
331% defaults write com.apple.DebugSymbols DBGFileMappedPaths ~/Library/SymbolCache/dsyms/uuids
332% defaults write com.apple.DebugSymbols DBGSpotlightPaths -array</b>
333</tt></pre></code>
334
335Hopefully this helps explain how DebugSymbols.framework can help any company
336implement a smart symbol finding and caching with minimal overhead.
337</p>
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