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| The <strong>LLDB</strong> Debugger | |
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| <div class="post"> | |
| <h1 class ="postheader">Stack Frame and Thread Format</h1> | |
| <div class="postcontent"> | |
| <p>LLDB was recently modified to allow users to define the | |
| format of the information that generates the descriptions | |
| for threads and stack frames. Typically when your program stops | |
| at a breakpoint you will get a line that describes why | |
| your thread stopped:</p> | |
| <p><b><code>* thread #1: tid = 0x2e03, 0x0000000100000e85 a.out`main + 4, stop reason = breakpoint 1.1</code></b></p> | |
| <p>Stack backtraces frames also have a similar information line:</p> | |
| <p><code><b>(lldb)</b> thread backtrace | |
| <br><b>thread #1: tid = 0x2e03, stop reason = breakpoint 1.1 | |
| <br> frame #0: 0x0000000100000e85 a.out`main + 4 at test.c:19 | |
| <br> frame #1: 0x0000000100000e40 a.out`start + 52 | |
| </code></b></p> | |
| <p>The two format strings can currently be set using the <b>settings set</b> command:</p> | |
| <p><code><b>(lldb)</b> settings set frame-prompt STRING | |
| <br><b>(lldb)</b> settings set thread-prompt STRING | |
| </p></code> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <div class="post"> | |
| <h1 class ="postheader">Format Strings</h1> | |
| <div class="postcontent"> | |
| <p>So what is the format of the format strings? Format strings can | |
| contain plain text, control characters and variables that have access | |
| to the current program state.</p> | |
| <p>Normal characters are any text that doesn't contain a <code><b>'{'</b></code>, <code><b>'}'</b></code>, <code><b>'$'</b></code>, | |
| or <code><b>'\'</b></code> character.</p> | |
| <p>Variable names are found in between a <code><b>"${"</b></code> prefix, and | |
| end with a <code><b>"}"</b></code> suffix. In other words, a variable looks like | |
| <code>"<b>${frame.pc}</b>"</code>.</p> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <div class="post"> | |
| <h1 class ="postheader">Variables</h1> | |
| <div class="postcontent"> | |
| <p>A complete list of currently supported format string variables is listed below:</p> | |
| <table border="1"> | |
| <tr valign=top><td><b>Variable Name</b></td><td><b>Description</b></td></tr> | |
| <tr valign=top><td><b>file.basename</b></td><td>The current compile unit file basename for the current frame.</td></tr> | |
| <tr valign=top><td><b>file.fullpath</b></td><td>The current compile unit file fullpath for the current frame.</td></tr> | |
| <tr valign=top><td><b>frame.index</b></td><td>The frame index (0, 1, 2, 3...)</td></tr> | |
| <tr valign=top><td><b>frame.pc</b></td><td>The generic frame register for the program counter.</td></tr> | |
| <tr valign=top><td><b>frame.sp</b></td><td>The generic frame register for the stack pointer.</td></tr> | |
| <tr valign=top><td><b>frame.fp</b></td><td>The generic frame register for the frame pointer.</td></tr> | |
| <tr valign=top><td><b>frame.flags</b></td><td>The generic frame register for the flags register.</td></tr> | |
| <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> | |
| <tr valign=top><td><b>function.name</b></td><td>The name of the current function or symbol</td></tr> | |
| <tr valign=top><td><b>function.pc-offset</b></td><td>The program counter offset within the current function or symbol</td></tr> | |
| <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> | |
| <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> | |
| <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> | |
| <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> | |
| <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> | |
| <tr valign=top><td><b>module.file.basename</b></td><td>The basename of the current module (shared library or executable)</td></tr> | |
| <tr valign=top><td><b>module.file.fullpath</b></td><td>The basename of the current module (shared library or executable)</td></tr> | |
| <tr valign=top><td><b>process.file.basename</b></td><td>The basename of the file for the process</td></tr> | |
| <tr valign=top><td><b>process.file.fullpath</b></td><td>The fullname of the file for the process</td></tr> | |
| <tr valign=top><td><b>process.id</b></td><td>The process ID native the the system on which the inferior runs.</td></tr> | |
| <tr valign=top><td><b>process.name</b></td><td>The name of the process at runtime</td></tr> | |
| <tr valign=top><td><b>thread.id</b></td><td>The thread identifier for the current thread</td></tr> | |
| <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> | |
| <tr valign=top><td><b>thread.name</b></td><td>The name of the thread if the target OS supports naming threads</td></tr> | |
| <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> | |
| <tr valign=top><td><b>thread.stop-reason</b></td><td>A textual reason each thread stopped</td></tr> | |
| <tr valign=top><td><b>target.arch</b></td><td>The architecture of the current target</td></tr> | |
| </table> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <div class="post"> | |
| <h1 class ="postheader">Control Characters</h1> | |
| <div class="postcontent"> | |
| <p>Control characters include <b><code>'{'</code></b>, | |
| <b><code>'}'</code></b>, and <b><code>'\'</code></b>.</p> | |
| <p>The '{' and '}' are used for scoping blocks, and the '\' character | |
| allows you to desensitize control characters and also emit non-printable | |
| characters. | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <div class="post"> | |
| <h1 class ="postheader">Desensitizing Characters in the format string</h1> | |
| <div class="postcontent"> | |
| <p>The backslash control character allows your to enter the typical | |
| <b><code>"\a"</code></b>, <b><code>"\b"</code></b>, <b><code>"\f"</code></b>, <b><code>"\n"</code></b>, | |
| <b><code>"\r"</code></b>, <b><code>"\t"</code></b>, <b><code>"\v"</code></b>, <b><code>"\\"</code></b>, characters | |
| and along with the standard octal representation <b><code>"\0123"</code></b> | |
| and hex <b><code>"\xAB"</code></b> characters. This allows you to enter | |
| escape characters into your format strings and will | |
| allow colorized output for terminals that support color. | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <div class="post"> | |
| <h1 class ="postheader">Scoping</h1> | |
| <div class="postcontent"> | |
| <p>Many times the information that you might have in your prompt might not be | |
| available and you won't want it to print out if it isn't valid. To take care | |
| of this you can enclose everything that <b>must</b> resolve into a scope. A scope | |
| is starts with <code><b>'{'</code></b> and ends with | |
| <code><b>'}'</code></b>. For example in order to only display | |
| the current frame line table entry basename and line number when the information | |
| is available for the current frame: | |
| <p><b><code>"{ at {$line.file.basename}:${line.number}}"</code></b></p> | |
| <p>Broken down this is: | |
| <ul> | |
| <li>The start the scope <p><b><code>"{"</code></b></p></li> | |
| <li> format whose content will only be displayed if all information is available: | |
| <p><b><code>"at {$line.file.basename}:${line.number}"</code></b></p></li> | |
| <li>end the scope: <p><b><code>"}"</code></b></p></li> | |
| </ul> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <div class="post"> | |
| <h1 class ="postheader">Making the Frame Format</h1> | |
| <div class="postcontent"> | |
| <p>The information that we see when stopped in a frame: | |
| <p><b><code>frame #0: 0x0000000100000e85 a.out`main + 4 at test.c:19</code></b></p> | |
| <p>can be displayed with the following format:</p> | |
| <p><b><code>"frame #${frame.index}: ${frame.pc}{ ${module.file.basename}`${function.name}{${function.pc-offset}}}{ at ${line.file.basename}:${line.number}}\n"</code></b></p> | |
| <p>This breaks down to: | |
| <ul> | |
| <li>Always print the frame index and frame PC: | |
| <p><b><code>"frame #${frame.index}: ${frame.pc}"</code></b></p> | |
| <li>only print the module followed by a tick if there is a valid | |
| module for the current frame: | |
| <p><b><code>"{ ${module.file.basename}`}"</code></b></p> | |
| <li>print the function name with optional offset:</p> | |
| <p><b><code>"{${function.name}{${function.pc-offset}}}"</code></b></p> | |
| <li>print the line info if it is available:</p> | |
| <p><b><code>"{ at ${line.file.basename}:${line.number}}"</code></b></p> | |
| <li>then finish off with a newline:</p> | |
| <p><b><code>"\n"</code></b></p> | |
| </ul> | |
| </div> | |
| <div class="postfooter"></div> | |
| </div> | |
| <div class="post"> | |
| <h1 class ="postheader">Making Your Own Formats</h1> | |
| <div class="postcontent"> | |
| <p>When modifying your own format strings, it is useful | |
| to start with the default values for the frame and | |
| thread format strings. These can be accessed with the | |
| <b><code>"settings show"</code></b> command: | |
| <p><b><code>(lldb)</b> settings show thread-format | |
| <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 = ${thread.queue}}\n' | |
| <br><b>(lldb)</b> settings show frame-format | |
| <br>frame-format (string) = 'frame #${frame.index}: ${frame.pc}{ ${module.file.basename}`${function.name}{${function.pc-offset}}}{ at ${line.file.basename}:${line.number}}\n' | |
| </code></p> | |
| <p>When making thread formats, you will need surround any | |
| of the information that comes from a stack frame with scopes (<b>{</b> <i>frame-content</i> <b>}</b>) | |
| as the thread format doesn't always want to show frame information. | |
| When displaying the backtrace for a thread, we don't need to duplicate | |
| the information for frame zero in the thread information: | |
| <p><code><b>(lldb)</b> thread backtrace | |
| <br>thread #1: tid = 0x2e03, stop reason = breakpoint 1.1 2.1 | |
| <br> frame #0: 0x0000000100000e85 a.out`main + 4 at test.c:19 | |
| <br> frame #1: 0x0000000100000e40 a.out`start + 52 | |
| </code> | |
| </p> | |
| <p>The frame related variables are: | |
| <ul> | |
| <li><code><b>${file.*}</b></code></li> | |
| <li><code><b>${frame.*}</b></code></li> | |
| <li><code><b>${function.*}</b></code></li> | |
| <li><code><b>${line.*}</b></code></li> | |
| <li><code><b>${module.*}</b></code></li> | |
| </ul> | |
| </p> | |
| <p>Looking at the default format for the thread, and underlining | |
| the frame information: | |
| <p><code>'thread #${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' | |
| </code></p> | |
| <p>We can see that all frame information is contained in scopes so | |
| that when the thread information is displayed in a context where | |
| we only want to show thread information, we can do so. | |
| </div> | |
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