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| <div class="www_title"> |
| The <strong>LLDB</strong> Debugger |
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| <div class="post"> |
| <h1 class="postheader">Debug Symbols on MacOSX</h1> |
| <div class="postcontent"> |
| <p>On MacOSX, debug symbols are often in stand alone bundles called <b>dSYM</b> files. |
| These are bundles that contain DWARF debug information and other resources related to |
| builds and debug info.</p> |
| <p>The DebugSymbols.framework framework helps locate dSYM files when given a UUID. It can |
| locate the symbols using a variety of methods:</p> |
| <ul> |
| <li>Spotlight</li> |
| <li>Explicit search paths</li> |
| <li>Implicit search paths</li> |
| <li>File mapped UUID paths</li> |
| <li>Running one or more shell scripts</li> |
| </ul> |
| <p>DebugSymbols.framework also has global defaults that can be modified to allow |
| all of the debug tools (lldb, gdb, sample, CoreSymbolication.framework) to easily |
| find important debug symbols. The domain for the DebugSymbols.framework defaults |
| is <b>com.apple.DebugSymbols</b>, and the defaults can be read, written or modified |
| using the <b>defaults</b> shell command: |
| <code><pre><tt><b>% defaults read com.apple.DebugSymbols |
| % defaults write com.apple.DebugSymbols KEY ... |
| % defaults delete com.apple.DebugSymbols KEY</b> |
| </tt></pre></code> |
| |
| <p>The following is a list of the defaults key value |
| setting pairs that can be used to enhance symbol location:</p> |
| <table class="stats" width="620" cellspacing="0"> |
| <tr> |
| <td class="hed" width="20%">Defaults Key</td> |
| <td class="hed" width="70%">Description</td> |
| </tr> |
| |
| <tr> |
| <td class="content"> |
| <b>DBGFileMappedPaths</b> |
| </td> |
| <td class="content"> |
| This default can be specified as a single string, or an array of strings. |
| Each string represents a directory that contains file mapped UUID values |
| that point to dSYM files. See the "File Mapped UUID Directories" section |
| below for more details. Whenever DebugSymbols.framework is asked to lookup |
| a dSYM file, it will first look in any file mapped UUID directories |
| for a quick match. |
| </td> |
| </tr> |
| <td class="content" colspan="2"> |
| <code><pre><tt><b>% defaults write com.apple.DebugSymbols DBGFileMappedPaths -string /path/to/uuidmap1</b> |
| <b>% defaults write com.apple.DebugSymbols DBGFileMappedPaths -array /path/to/uuidmap1 |
| /path/to/uuidmap2</b> |
| </tt></pre></code> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>DBGShellCommands</b> |
| </td> |
| <td class="content"> |
| This default can be specified as a single string, or an array of strings. |
| Specifies a shell script that will get run in order to find the dSYM. |
| The shell script will be run given a single UUID value as the shell |
| command arguments and the shell command is expected to return a property |
| list. See the property list format defined below. |
| </td> |
| </tr> |
| <td class="content" colspan="2"> |
| <code><pre><tt><b>% defaults write com.apple.DebugSymbols DBGShellCommands -string /path/to/script1</b> |
| <b>% defaults write com.apple.DebugSymbols DBGShellCommands -array /path/to/script1 |
| /path/to/script2</b> |
| </tt></pre></code> |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>DBGSpotlightPaths</b> |
| </td> |
| <td class="content"> |
| Specifies the directories to limit spotlight searches to as a string or array of strings. When any |
| other defaults are supplied to <b>com.apple.DebugSymbols</b>, spotlight |
| searches will be disabled unless this default is set to an empty array: |
| </td> |
| </tr> |
| <td class="content" colspan="2"> |
| <code><pre><tt><font color="green"># Specify an empty array to keep Spotlight searches enabled in all locations</font> |
| <b>% defaults write com.apple.DebugSymbols DBGSpotlightPaths -array</b> |
| |
| <font color="green"># Specify an array of paths to limit spotlight searches to certain directories</font> |
| <b>% defaults write com.apple.DebugSymbols DBGSpotlightPaths -array /path/dir1 /path/dir2</b> |
| </tt></pre></code> |
| </td> |
| </tr> |
| </table> |
| </div> |
| <div class="postfooter"></div> |
| </div> |
| <div class="post"> |
| <h1 class="postheader">Shell Script Property List Format</h1> |
| <div class="postcontent"> |
| <p>Shell scripts that are specified with the <b>DBGShellCommands</b> defaults key |
| will be run in the order in which they are specified until a match is found. |
| The shell script will be invoked with a single UUID string value like |
| "23516BE4-29BE-350C-91C9-F36E7999F0F1". The shell script must respond with a |
| property list being written to STDOUT. |
| The property list returned must contain UUID string values as the root key values, with |
| a dictionary for each UUID. The dictionaries can contain one or more of the following keys: |
| |
| <table class="stats" width="620" cellspacing="0"> |
| <tr> |
| <td class="hed" width="20%">Key</td> |
| <td class="hed" width="70%">Description</td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>DBGArchitecture</b> |
| </td> |
| <td class="content">A textual architecture or target triple like "x86_64", "i386", or "x86_64-apple-macosx". |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>DBGBuildSourcePath</b> |
| </td> |
| <td class="content">A path prefix that was used when building the dSYM file. The debug information will |
| contain paths with this prefix. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>DBGSourcePath</b> |
| </td> |
| <td class="content">A path prefix for where the sources exist after the build has completed. Often when |
| building projects, build machines will host the sources in a temporary directory while building, then |
| move the sources to another location for archiving. If the paths in the debug info don't match where |
| the sources are currently hosted, then specifying this path along with the <b>DBGBuildSourcePath</b> |
| will help the developer tools always show you sources when debugging or symbolicating. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>DBGDSYMPath</b> |
| </td> |
| <td class="content">A path to the dSYM mach-o file inside the dSYM bundle. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>DBGSymbolRichExecutable</b> |
| </td> |
| <td class="content">A path to the symbol rich executable. Binaries are often stripped after |
| being built and packaged into a release. If your build systems saves an unstripped executable |
| a path to this executable can be provided. |
| </td> |
| </tr> |
| <tr> |
| <td class="content"> |
| <b>DBGError</b> |
| </td> |
| <td class="content">If a binary can not be located for the supplied UUID, a user readable error |
| can be returned. |
| </td> |
| </tr> |
| </table> |
| |
| <p>Below is a sample shell script output for a binary that contains two architectures: |
| <code><pre><tt> |
| <?xml version="1.0" encoding="UTF-8"?> |
| <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> |
| <plist version="1.0"> |
| <dict> |
| <key>23516BE4-29BE-350C-91C9-F36E7999F0F1</key> |
| <dict> |
| <key>DBGArchitecture</key> |
| <string>i386</string> |
| <key>DBGBuildSourcePath</key> |
| <string>/path/to/build/sources</string> |
| <key>DBGSourcePath</key> |
| <string>/path/to/actual/sources</string> |
| <key>DBGDSYMPath</key> |
| <string>/path/to/foo.dSYM/Contents/Resources/DWARF/foo</string> |
| <key>DBGSymbolRichExecutable</key> |
| <string>/path/to/unstripped/executable</string> |
| </dict> |
| <key>A40597AA-5529-3337-8C09-D8A014EB1578</key> |
| <dict> |
| <key>DBGArchitecture</key> |
| <string>x86_64</string> |
| <key>DBGBuildSourcePath</key> |
| <string>/path/to/build/sources</string> |
| <key>DBGSourcePath</key> |
| <string>/path/to/actual/sources</string> |
| <key>DBGDSYMPath</key> |
| <string>/path/to/foo.dSYM/Contents/Resources/DWARF/foo</string> |
| <key>DBGSymbolRichExecutable</key> |
| <string>/path/to/unstripped/executable</string> |
| </dict> |
| </dict> |
| </plist> |
| </tt></pre></code> |
| |
| <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 |
| script that has high latency or takes a long time to download unless this |
| is really what you want. This can slow down debug sessions in LLDB and GDB, symbolication |
| with CoreSymbolication or Report Crash, with no visible feedback to the user. You can |
| quickly return a plist with a single <b>DBGError</b> key that indicates a timeout |
| has been reached. You might also want to exec new processes to do the downloads so |
| that if you return an error that indicates a timeout, your download can still proceed |
| after your shell script has exited so subsequent debug sessions can use the cached files. |
| It is also important to track when a current download is in progress in case you get multiple requests for the same UUID so |
| that you don't end up downloading the same file simultaneously. Also you will want |
| to verify the download was successful and then and only then place the file into the |
| cache for tools that will cache files locally. |
| </div> |
| <div class="postfooter"></div> |
| </div> |
| <div class="post"> |
| <h1 class="postheader">Embedding UUID property lists inside the dSYM bundles</h1> |
| <div class="postcontent"> |
| <p>Since dSYM files are bundles, you can also place UUID info plists files inside |
| your dSYM bundles in the <b>Contents/Resources</b> directory. One of the main |
| reasons to create the UUID plists inside the dSYM bundles |
| is that it will help LLDB and other developer tools show you source. LLDB currently |
| knows how to check for these plist files so it can automatically remap the source |
| location information in the debug info. |
| |
| <p>If we take the two UUID values from the returns plist above, we can split |
| them out and save then in the dSYM bundle: |
| |
| <code><pre><tt><b>% ls /path/to/foo.dSYM/Contents/Resources</b> |
| 23516BE4-29BE-350C-91C9-F36E7999F0F1.plist |
| A40597AA-5529-3337-8C09-D8A014EB1578.plist |
| |
| <b>% cat /path/to/foo.dSYM/Contents/Resources/23516BE4-29BE-350C-91C9-F36E7999F0F1.plist</b> |
| <?xml version="1.0" encoding="UTF-8"?> |
| <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> |
| <plist version="1.0"> |
| <dict> |
| <key>DBGArchitecture</key> |
| <string>i386</string> |
| <key>DBGBuildSourcePath</key> |
| <string>/path/to/build/sources</string> |
| <key>DBGSourcePath</key> |
| <string>/path/to/actual/sources</string> |
| <key>DBGDSYMPath</key> |
| <string>/path/to/foo.dSYM/Contents/Resources/DWARF/foo</string> |
| <key>DBGSymbolRichExecutable</key> |
| <string>/path/to/unstripped/executable</string> |
| </dict> |
| </plist> |
| </tt></pre></code> |
| |
| <p>Note that the output is very close to what is needed by shell script output, |
| so making the results of your shell script will be very easy to create by |
| combining two plists into a single one where you take the UUID and use it a |
| string key, and the value is the contents of the plist. |
| |
| |
| </div> |
| <div class="postfooter"></div> |
| </div> |
| <div class="post"> |
| <h1 class="postheader">File Mapped UUID Directories</h1> |
| <div class="postcontent"> |
| <p>File Mapped directories can be used for efficient dSYM file lookups for |
| local or remote dSYM files. The UUID is broken up by splitting the first |
| 20 hex digits into 4 character chunks, and a directory is created for each |
| chunk, and each subsequent directory is created inside the previous one. |
| A symlink is then created whose name is the last 12 hex digits in the deepest |
| directory. The symlinks value is a full path to the mach-o files inside the |
| dSYM bundle which contains the DWARF. Whenever DebugSymbols.framework is asked |
| to lookup a dSYM file, it will first look in any file mapped UUID directories |
| for a quick match if the defaults are appropriately set. |
| |
| <p>For example, if we take the sample UUID plist inforamtion from above, we |
| can create a File Mapped UUID directory cache in <b>~/Library/SymbolCache/dsyms/uuids</b>. |
| We can easily see how things are laid out: |
| |
| <code><pre><tt><b>% find ~/Library/SymbolCache/dsyms/uuids -type l</b> |
| ~/Library/SymbolCache/dsyms/uuids/2351/6BE4/29BE/350C/91C9/F36E7999F0F1 |
| ~/Library/SymbolCache/dsyms/uuids/A405/97AA/5529/3337/8C09/D8A014EB1578 |
| </tt></pre></code> |
| |
| <p>The last entries in these file mapped directories are symlinks to the actual dsym mach file in the dsym bundle: |
| |
| <code><pre><tt><b>% ls -lAF ~/Library/SymbolCache/dsyms/uuids/2351/6BE4/29BE/350C/91C9/F36E7999F0F1</b> |
| ~/Library/SymbolCache/dsyms/uuids/2351/6BE4/29BE/350C/91C9/F36E7999F0F1@ -> ../../../../../../dsyms/foo.dSYM/Contents/Resources/DWARF/foo |
| </tt></pre></code> |
| <p>Then you can also tell DebugSymbols to check this UUID file map cache using: |
| |
| <code><pre><tt><b>% defaults write com.apple.DebugSymbols DBGFileMappedPaths ~/Library/SymbolCache/dsyms/uuids</b> |
| </tt></pre></code> |
| |
| |
| </div> |
| <div class="postfooter"></div> |
| </div> |
| <div class="post"> |
| <h1 class="postheader">dSYM Locating Shell Script Tips</h1> |
| <div class="postcontent"> |
| |
| <p>One possible implementation of a dSYM finding shell script is to have the script |
| download and cache files locally in a known location. Then create a UUID map |
| for each UUID value that was found in a local UUID File Map cache so the next query for the dSYM |
| file will be able to use the cached version. So the shell script is used to |
| initially download and cache the file, and subsequent accesses will use the |
| cache and avoid calling the shell script. |
| |
| <p>Then the defaults for DebugSymbols.framework will entail enabling your shell script, |
| enabling the file mapped path setting so that already downloaded dSYMS fill quickly |
| be found without needing to run the shell script every time, and also leaving spotlight enabled |
| so that other normal dSYM files are still found: |
| |
| <code><pre><tt><b>% defaults write com.apple.DebugSymbols DBGShellCommands /path/to/shellscript |
| % defaults write com.apple.DebugSymbols DBGFileMappedPaths ~/Library/SymbolCache/dsyms/uuids |
| % defaults write com.apple.DebugSymbols DBGSpotlightPaths -array</b> |
| </tt></pre></code> |
| |
| Hopefully this helps explain how DebugSymbols.framework can help any company |
| implement a smart symbol finding and caching with minimal overhead. |
| </p> |
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