727 lines
38 KiB
HTML
Executable File
727 lines
38 KiB
HTML
Executable File
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<link href="style.css" rel="stylesheet" type="text/css" />
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<title>LLDB Tutorial</title>
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</head>
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<body>
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<div class="www_title">
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The <strong>LLDB</strong> Debugger
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</div>
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<div id="container">
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<div id="content">
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<!--#include virtual="sidebar.incl"-->
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<div id="middle">
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<div class="post">
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<h1 class ="postheader">Getting Started</h1>
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<div class="postcontent">
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<p>Here's a short precis of how to run lldb if you are familiar with the gdb command set.
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We will start with some details on lldb command structure and syntax to help orient you.</p>
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</div>
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<div class="postfooter"></div>
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<div class="post">
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<h1 class ="postheader">Command Structure</h1>
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<div class="postcontent">
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<p>Unlike gdb's command set, which is rather free-form, we tried to make
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the lldb command syntax fairly structured. The commands are all of the
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form:</p>
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<code color=#ff0000>
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<noun> <verb> [-options [option-value]] [argument [argument...]]
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</code>
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<p>The command line parsing is done before command execution, so it is
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uniform across all the commands. The command syntax for basic commands is very simple,
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arguments, options and option values are all white-space
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separated, and double-quotes are used to protect white-spaces in an argument.
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If you need to put a backslash or double-quote character
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in an argument you back-slash it in the argument. That makes the
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command syntax more regular, but it also means you may have to
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quote some arguments in lldb that you wouldn't in gdb.</p>
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<p>Options can be placed anywhere on the command line, but if the arguments
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begin with a "<code>-</code>" then you have to tell lldb that you're done with options
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for the current command by adding an option termination: "<code>--</code>"
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So for instance if you want to launch a process and give the "process launch" command
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the "<code>--stop-at-entry</code>" option, yet you want the
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process you are about to launch to be launched with the arguments
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"<code>-program_arg value</code>", you would type:</p>
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<code>
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(lldb) process launch --stop-at-entry -- -program_arg value
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</code>
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<p>We also tried to reduce the number of special purpose argument
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parsers, which sometimes forces the user to be a little more explicit
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about stating their intentions. The first instance you'll note of
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this is the breakpoint command. In gdb, to set a breakpoint, you
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might enter</p>
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<code>
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(gdb) break foo.c:12
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</code>
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<p>to break at line 12 of foo.c, and:</p>
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<code>
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(gdb) break foo
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</code>
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<p>to break at the function <code>foo</code>. As time went on, the parser that tells <code>foo.c:12</code>
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from <code>foo</code> from <code>foo.c::foo</code> (which means the function foo in the file
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foo.c) got more and more complex and bizarre, and especially in C++
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there are times where there's really no way to specify the function
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you want to break on. The lldb commands are more verbose but also more precise
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and allow for intelligent auto completion.
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<p>To set the same file and line breakpoint in LLDB you can enter either of:</p>
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<code>
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(lldb) breakpoint set --file foo.c --line 12
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<br>(lldb) breakpoint set -f foo.c -l 12
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</code>
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<p>To set a breakpoint on a function named <code>foo</code> in LLDB you can enter either of:</p>
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<code>
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(lldb) breakpoint set --name foo
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<br>(lldb) breakpoint set -n foo
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</code>
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<p>You can use the --name option multiple times to make a breakpoint on a set of functions as well. This is convenient
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since it allows you to set commmon conditions or commands without having to specify them multiple times:</p>
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<code>
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(lldb) breakpoint set --name foo --name bar
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</code>
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<p>Setting breakpoints by name is even more specialized in LLDB as you can specify
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that you want to set a breakpoint at a function by method name. To set a breakpoint
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on all C++ methods named <code>foo</code> you can enter either of:</p>
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<code>
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(lldb) breakpoint set --method foo
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<br>(lldb) breakpoint set -M foo
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</code>
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<p>To set a breakpoint Objective C selectors named <code>alignLeftEdges:</code> you can enter either of:</p>
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<code>
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(lldb) breakpoint set --selector alignLeftEdges:
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<br>(lldb) breakpoint set -S alignLeftEdges:
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</code>
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<p>You can limit any breakpoints to a specific executable image by using
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the "<code>--shlib <path></code>" ("<code>-s <path></code>" for short):</p>
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<code>
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(lldb) breakpoint set --shlib foo.dylib --name foo
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<br>(lldb) breakpoint set -s foo.dylib -n foo
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</code>
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<p>The <code>--shlib</code> option can also be repeated to specify several shared libraries.</p>
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<p>Suggestions on more interesting primitives of this sort are also very welcome.</p>
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<p>Just like gdb, the lldb command interpreter does a shortest unique
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string match on command names, so the following two commands will
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both execute the same command:</p>
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<code>
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(lldb) breakpoint set -n "-[SKTGraphicView alignLeftEdges:]"
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<br>(lldb) br s -n "-[SKTGraphicView alignLeftEdges:]"
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</code>
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<p>lldb also supports command completion for source file names, symbol
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names, file names, etc. Completion is initiated by a hitting a <b>TAB</b>.
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Individual options in a command can have different completers, so for
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instance the "<code>--file <path></code>" option in "breakpoint" completes to source files, the
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"<code>--shlib <path></code>" option to currently loaded shared libraries, etc. We can even do
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things like if you specify "<code>--shlib <path></code>", and are completing on "<code>--file <path></code>", we will only
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list source files in the shared library specified by "<code>--shlib <path></code>".</p>
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<p>The individual commands are pretty extensively documented. You can
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use the <code>help</code> command to get an overview of which commands are
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available or to obtain details about specific commands. There is also an
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<code>apropos</code> command that will search the help text for all commands
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for a particular word and dump a summary help string for each matching
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command.</p>
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<p>Finally, there is a mechanism to construct aliases for commonly used
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commands. So for instance if you get annoyed typing:</p>
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<code>
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(lldb) breakpoint set --file foo.c --line 12
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</code>
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<p>you can do:</p>
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<code>
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(lldb) command alias bfl breakpoint set -f %1 -l %2
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<br>(lldb) bfl foo.c 12
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</code>
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<p>We have added a few aliases for commonly used commands (e.g. "step",
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"next" and "continue") but we haven't tried to be exhaustive because
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in our experience it is more convenient to make the basic commands
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unique down to a letter or two, and then learn these sequences than
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to fill the namespace with lots of aliases, and then have to type them
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all the way out.</p>
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<p>However, users are free to customize lldb's command set however they
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like, and since lldb reads the file ~/.lldbinit at startup, you can
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store all your aliases there and they will be generally available to
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you. Your aliases are also documented in the help command so you can
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remind yourself of what you've set up.</p>
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<p> One alias of note that we do include by popular demand is a weak emulator
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of gdb's "break" command. It doesn't try to do everything that gdb's
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break command does (for instance, it doesn't handle <code>foo.c::bar</code>. But
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it mostly works, and makes the transition easier. Also by popular demand, it
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is aliased to <code>b</code>. If you actually want to learn the lldb command
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set natively, that means it will get in the way of the rest of the breakpoint
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commands. Fortunately, if you don't like one of our aliases, you an easily
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get rid of it by running (for example):</p>
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<code>
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(lldb) command unalias b
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</code>
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<p>I actually also do:</p>
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<code>
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(lldb) command alias b breakpoint
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</code>
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<p>so I can run the native lldb breakpoint command with just <code>b</code></p>
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<p>The lldb command parser also supports "raw" commands, where, after command options
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are stripped off, the rest of the command string is passed uninterpreted to the command.
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This is convenient for commands whose arguments might be some complex expression that would
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be painful to backslash protect.
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For instance the "expression" command is a "raw" command for obvious reasons. The
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"help" output for a command will tell you if it is "raw" or not, so you know what to expect.
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The one thing you have to watch out for is that since raw commands still can have options,
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if your command string has dashes in it, you'll have to indicate these are not option
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markers by putting "--" after the command name, but before your command string.
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<p>lldb also has a built-in Python interpreter, which is accessible by
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the "script" command. All the functionality of the debugger is
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available as classes in the Python interpreter, so the more complex
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commands that in gdb you would introduce with the "define" command can
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be done by writing Python functions using the lldb-Python library,
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then loading the scripts into your running session and accessing them
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with the "script" command.</p>
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<p>Having given an overview of lldb's command syntax, we proceed to lay out the stages
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of a standard debug session.</p>
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</div>
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<div class="postfooter"></div>
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<div class="post">
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<h1 class ="postheader">Loading a program into lldb</h1>
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<div class="postcontent">
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<p>First we need to set the program to debug. As with gdb, you
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can start lldb and specify the file you wish to debug on the command line:</p>
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<code>
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$ lldb /Projects/Sketch/build/Debug/Sketch.app
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<br>Current executable set to '/Projects/Sketch/build/Debug/Sketch.app' (x86_64).
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</code>
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<p>or you can specify it after the fact with the "file" command:</p>
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<code>
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$ lldb
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<br>(lldb) file /Projects/Sketch/build/Debug/Sketch.app
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<br>Current executable set to '/Projects/Sketch/build/Debug/Sketch.app' (x86_64).
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</code>
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<p>
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</div>
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<div class="postfooter"></div>
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<div class="post">
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<h1 class ="postheader">Setting breakpoints</h1>
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<div class="postcontent">
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<p>We've discussed how to set breakpoints above. You can use <code>help breakpoint set</code>
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to see all the options for breakpoint setting. For instance, we might do:</p>
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<code>
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(lldb) breakpoint set --selector alignLeftEdges:
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<br>Breakpoint created: 1: name = 'alignLeftEdges:', locations = 1, resolved = 1
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</code>
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<p>You can find out about the breakpoints you've set with:</p>
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<pre><tt>(lldb) breakpoint list
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Current breakpoints:
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1: name = 'alignLeftEdges:', locations = 1, resolved = 1
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1.1: where = Sketch`-[SKTGraphicView alignLeftEdges:] + 33 at /Projects/Sketch/SKTGraphicView.m:1405, address = 0x0000000100010d5b, resolved, hit count = 0
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</tt></pre>
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<p>Note that setting a breakpoint creates a <i>logical</i> breakpoint, which could
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resolve to one or more <i>locations</i>. For instance, break by selector would
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set a breakpoint on all the methods that implement that selector in the classes in
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your program. Similarly, a file and line breakpoint might result in multiple
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locations if that file and line were inlined in different places in your code.</p>
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<p>The logical breakpoint has an integer id, and it's locations have an
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id within their parent breakpoint (the two are joined by a ".",
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e.g. 1.1 in the example above.) </p>
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<p>Also the logical breakpoints remain <i>live</i> so that if another shared library
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were to be loaded that had another implementation of the
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"<code>alignLeftEdges:</code>" selector, the new location would be added to
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breakpoint 1 (e.g. a "1.2" breakpoint would be set on the newly loaded
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selector).</p>
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<p>The other piece of information in the breakpoint listing is whether the
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breakpoint location was <i>resolved</i> or not. A location gets resolved when
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the file address it corresponds to gets loaded into the program you are
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debugging. For instance if you set a breakpoint in a shared library that
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then gets unloaded, that breakpoint location will remain, but it will no
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longer be <i>resolved</i>.</p>
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<p>One other thing to note for gdb users is that lldb acts like gdb with:</p>
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<code>
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(gdb) set breakpoint pending on
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</code>
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<p>That is, lldb will always make a breakpoint from your specification, even
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if it couldn't find any locations that match the specification. You can tell
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whether the expression was resolved or not by checking the locations field
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in "breakpoint list", and we report the breakpoint as "pending" when you
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set it so you can tell you've made a typo more easily, if that was indeed
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the reason no locations were found:</p>
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<code>
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(lldb) breakpoint set --file foo.c --line 12
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<br>Breakpoint created: 2: file ='foo.c', line = 12, locations = 0 (pending)
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<br>WARNING: Unable to resolve breakpoint to any actual locations.
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</code>
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<p>You can delete, disable, set conditions and ignore counts either on all the
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locations generated by your logical breakpoint, or on any one of the particular locations
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your specification resolved to. For instance if we wanted to add a command
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to print a backtrace when we hit this breakpoint we could do:</p>
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<code>
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(lldb) breakpoint command add 1.1
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<br>Enter your debugger command(s). Type 'DONE' to end.
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<br>> bt
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<br>> DONE
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</code>
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<p>By default, the <code> breakpoint command add</code> command takes lldb command line commands.
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You can also specify this explicitly by passing the "<code>--command</code>" option.
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Use "<code>--script</code>" if you want to implement your breakpoint command using the Python script instead.</p>
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<p>This is an convenient point to bring up another feature of the lldb command help. Do:</p>
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<code>
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(lldb) help break command add
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<br>Add a set of commands to a breakpoint, to be executed whenever the breakpoint is hit.
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<br>
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<br>Syntax: breakpoint command add <cmd-options> <breakpt-id>
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<br> etc...
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</code>
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<p>When you see arguments to commands specified in the Syntax in angle
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brackets like <code><breakpt-id></code>, that indicates that
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that is some common argument type that you can get further help on from the command system.
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So in this case you could do:</p>
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<code>
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(lldb) help <breakpt-id>
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<br><breakpt-id> -- Breakpoint ID's consist major and minor numbers; the major
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<br> etc...
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</code>
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</div>
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<div class="postfooter"></div>
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<div class="post">
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<h1 class ="postheader">Setting watchpoints</h1>
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<div class="postcontent">
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<p>In addition to breakpoints, you can use <code>help watchpoint</code>
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to see all the commands for watchpoint manipulations. For instance, we might do the following to watch
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a variable called 'global' for write operation, but only stop if the condition '(global==5)' is true:</p>
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<pre><tt>(lldb) watch set var global
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Watchpoint created: Watchpoint 1: addr = 0x100001018 size = 4 state = enabled type = w
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declare @ '/Volumes/data/lldb/svn/ToT/test/functionalities/watchpoint/watchpoint_commands/condition/main.cpp:12'
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(lldb) watch modify -c '(global==5)'
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(lldb) watch list
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Current watchpoints:
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Watchpoint 1: addr = 0x100001018 size = 4 state = enabled type = w
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declare @ '/Volumes/data/lldb/svn/ToT/test/functionalities/watchpoint/watchpoint_commands/condition/main.cpp:12'
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condition = '(global==5)'
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(lldb) c
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Process 15562 resuming
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(lldb) about to write to 'global'...
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Process 15562 stopped and was programmatically restarted.
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Process 15562 stopped and was programmatically restarted.
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Process 15562 stopped and was programmatically restarted.
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Process 15562 stopped and was programmatically restarted.
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Process 15562 stopped
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* thread #1: tid = 0x1c03, 0x0000000100000ef5 a.out`modify + 21 at main.cpp:16, stop reason = watchpoint 1
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frame #0: 0x0000000100000ef5 a.out`modify + 21 at main.cpp:16
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13
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14 static void modify(int32_t &var) {
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15 ++var;
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-> 16 }
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17
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18 int main(int argc, char** argv) {
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19 int local = 0;
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(lldb) bt
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* thread #1: tid = 0x1c03, 0x0000000100000ef5 a.out`modify + 21 at main.cpp:16, stop reason = watchpoint 1
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frame #0: 0x0000000100000ef5 a.out`modify + 21 at main.cpp:16
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frame #1: 0x0000000100000eac a.out`main + 108 at main.cpp:25
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frame #2: 0x00007fff8ac9c7e1 libdyld.dylib`start + 1
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(lldb) frame var global
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(int32_t) global = 5
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(lldb) watch list -v
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Current watchpoints:
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Watchpoint 1: addr = 0x100001018 size = 4 state = enabled type = w
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declare @ '/Volumes/data/lldb/svn/ToT/test/functionalities/watchpoint/watchpoint_commands/condition/main.cpp:12'
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condition = '(global==5)'
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hw_index = 0 hit_count = 5 ignore_count = 0
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(lldb) </tt></pre>
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</div>
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<div class="postfooter"></div>
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<div class="post">
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<h1 class ="postheader">Starting or attaching to your Program</h1>
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<div class="postcontent">
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<p>To launch a program in lldb we use the "<code>process launch</code>" command or
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one of its built in aliases:</p>
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<code>
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(lldb) process launch
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<br>(lldb) run
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<br>(lldb) r
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</code>
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<p>You can also attach to a process by process ID or process name.
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When attaching to a process by name, lldb also supports the "<code>--waitfor</code>" option which waits for the
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next process that has that name to show up, and attaches to it</p>
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<code>
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(lldb) process attach --pid 123
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<br>(lldb) process attach --name Sketch
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<br>(lldb) process attach --name Sketch --waitfor
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</code>
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<p>After you launch or attach to a process, your process might stop
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somewhere:</p>
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<code>
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(lldb) process attach -p 12345
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<br>Process 46915 Attaching
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<br>Process 46915 Stopped
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<br>1 of 3 threads stopped with reasons:
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<br>* thread #1: tid = 0x2c03, 0x00007fff85cac76a, where = libSystem.B.dylib`__getdirentries64 + 10, stop reason = signal = SIGSTOP, queue = com.apple.main-thread
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</code>
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|
|
|
<p>Note the line that says "<code>1 of 3 threads stopped with reasons:</code>" and the
|
|
lines that follow it. In a multi-threaded environment it is very
|
|
common for more than one thread to hit your breakpoint(s) before the
|
|
kernel actually returns control to the debugger. In that case, you
|
|
will see all the threads that stopped for some interesting reason
|
|
listed in the stop message.</p>
|
|
|
|
</div>
|
|
<div class="postfooter"></div>
|
|
|
|
<div class="post">
|
|
<h1 class ="postheader">Controlling your Program</h1>
|
|
<div class="postcontent">
|
|
|
|
|
|
<p>After launching, we can continue until we hit our breakpoint. The primitive
|
|
commands for process control all exist under the "thread" command:</p>
|
|
|
|
<code>
|
|
(lldb) thread continue
|
|
<br>Resuming thread 0x2c03 in process 46915
|
|
<br>Resuming process 46915
|
|
<br>(lldb)
|
|
</code>
|
|
|
|
<p>At present you can only operate on one thread at a time, but the
|
|
design will ultimately support saying "step over the function in
|
|
Thread 1, and step into the function in Thread 2, and continue Thread
|
|
3" etc. When we eventually support keeping some threads running while
|
|
others are stopped this will be particularly important. For
|
|
convenience, however, all the stepping commands have easy aliases.
|
|
So "thread continue" is just "c", etc.</p>
|
|
|
|
<p>The other program stepping commands are pretty much the same as in gdb.
|
|
You've got:</p>
|
|
|
|
<pre><tt>(lldb) thread step-in // The same as gdb's "step" or "s"
|
|
(lldb) thread step-over // The same as gdb's "next" or "n"
|
|
(lldb) thread step-out // The same as gdb's "finish" or "f"
|
|
</tt></pre>
|
|
|
|
<p>By default, lldb does defined aliases to all common gdb process control
|
|
commands ("<code>s</code>", "<code>step</code>", "<code>n</code>", "<code>next</code>", "<code>finish</code>").
|
|
If we have missed any, please add them to your <code>~/.lldbinit</code> file
|
|
using the "<code>command alias</code>" command.
|
|
|
|
<p>lldb also supported the <i>step by instruction</i> versions:</p>
|
|
<pre><tt>(lldb) thread step-inst // The same as gdb's "stepi" / "si"
|
|
(lldb) thread step-over-inst // The same as gdb's "nexti" / "ni"
|
|
</tt></pre>
|
|
|
|
<p>Finally, lldb has a <i>run until line or frame exit</i> stepping mode:</p>
|
|
|
|
<code>
|
|
(lldb) thread until 100
|
|
</code>
|
|
|
|
<p>This command will run the thread in the current frame till it reaches line 100 in
|
|
this frame or stops if it leaves the current frame. This is a pretty
|
|
close equivalent to gdb's "<code>until</code>" command.</p>
|
|
|
|
<p>A process, by default, will share the lldb terminal with the inferior
|
|
process. When in this mode, much like when debugging with gdb, when
|
|
the process is running anything you type will go to the STDIN of the
|
|
inferior process. To interrupt your inferior program, type CTRL+C.</p>
|
|
|
|
<p>If you attach to a process, or launch a process with the "<code>--no-stdin</code>"
|
|
option, the command interpreter is always available to enter commands. This
|
|
might be a little disconcerting to gdb users when always have an <code>(lldb)</code>
|
|
prompt. This allows you to set a breakpoint, etc without having to explicitly interrupt
|
|
the program you are debugging:</p>
|
|
|
|
<code>
|
|
(lldb) process continue
|
|
<br>(lldb) breakpoint set --name stop_here
|
|
</code>
|
|
|
|
<p>There are many commands that won't work while running, and the command
|
|
interpreter should do a good job of letting you know when this is the
|
|
case. If you find any instances where the command interpreter isn't
|
|
doing its job, please file a bug. This way of operation will set us
|
|
up for a future debugging mode called <i>thread centric debugging</i>.
|
|
This mode will allow us to run all threads and only stop the threads
|
|
that are at breakpoints or have exceptions or signals.</p>
|
|
|
|
<p>The commands that currently work while running include
|
|
interrupting the process to halt execution ("<code>process interrupt</code>"),
|
|
getting the process status ("<code>process status</code>"),
|
|
breakpoint setting and clearing ("<code> breakpoint [set|clear|enable|disable|list] ...</code>"),
|
|
and memory reading and writing ("<code> memory [read|write] ...</code>").
|
|
</p>
|
|
|
|
<p>The question of disabling stdio when running brings up a good opportunity to
|
|
show how to set debugger properties in general.
|
|
If you always want to run in the <code>--no-stdin</code> mode, you can set this
|
|
as a generic process property using the lldb "<code>settings</code>" command,
|
|
which is equivalent to gdb's "<code>set</code>" command. For instance,
|
|
in this case you would say:</p>
|
|
|
|
<code>
|
|
(lldb) settings set target.process.disable-stdio true
|
|
</code>
|
|
|
|
<p>Over time, gdb's "<code>set</code> command became a wilderness of disordered options,
|
|
so that there were useful options that even experienced gdb users didn't know about
|
|
because they were too hard to find. We tried to organize the settings hierarchically
|
|
using the structure of the basic entities in the debugger. For the most part anywhere
|
|
you can specify a setting on a generic entity (threads, for example) you can also apply
|
|
the option to a particular instance, which can also be convenient at times.
|
|
You can view the available settings with "<code>settings list</code>" and
|
|
there is help on the settings command explaining how it works more generally.</p>
|
|
|
|
</div>
|
|
<div class="postfooter"></div>
|
|
|
|
<div class="post">
|
|
<h1 class ="postheader">Examining Thread State</h1>
|
|
<div class="postcontent">
|
|
|
|
<p>Once you've stopped, lldb will choose a current thread, usually the
|
|
one that stopped "for a reason", and a current frame in that thread (on stop this is always the bottom-most frame).
|
|
Many the commands for inspecting state work on this current
|
|
thread/frame.</p>
|
|
|
|
<p>To inspect the current state of your process, you can start with the
|
|
threads:</p>
|
|
|
|
<pre><tt>(lldb) thread list
|
|
Process 46915 state is Stopped
|
|
* thread #1: tid = 0x2c03, 0x00007fff85cac76a, where = libSystem.B.dylib`__getdirentries64 + 10, stop reason = signal = SIGSTOP, queue = com.apple.main-thread
|
|
thread #2: tid = 0x2e03, 0x00007fff85cbb08a, where = libSystem.B.dylib`kevent + 10, queue = com.apple.libdispatch-manager
|
|
thread #3: tid = 0x2f03, 0x00007fff85cbbeaa, where = libSystem.B.dylib`__workq_kernreturn + 10
|
|
</tt></pre>
|
|
|
|
<p>The * indicates that Thread 1 is the current thread. To get a
|
|
backtrace for that thread, do:</p>
|
|
|
|
<pre><tt>(lldb) thread backtrace
|
|
thread #1: tid = 0x2c03, stop reason = breakpoint 1.1, queue = com.apple.main-thread
|
|
frame #0: 0x0000000100010d5b, where = Sketch`-[SKTGraphicView alignLeftEdges:] + 33 at /Projects/Sketch/SKTGraphicView.m:1405
|
|
frame #1: 0x00007fff8602d152, where = AppKit`-[NSApplication sendAction:to:from:] + 95
|
|
frame #2: 0x00007fff860516be, where = AppKit`-[NSMenuItem _corePerformAction] + 365
|
|
frame #3: 0x00007fff86051428, where = AppKit`-[NSCarbonMenuImpl performActionWithHighlightingForItemAtIndex:] + 121
|
|
frame #4: 0x00007fff860370c1, where = AppKit`-[NSMenu performKeyEquivalent:] + 272
|
|
frame #5: 0x00007fff86035e69, where = AppKit`-[NSApplication _handleKeyEquivalent:] + 559
|
|
frame #6: 0x00007fff85f06aa1, where = AppKit`-[NSApplication sendEvent:] + 3630
|
|
frame #7: 0x00007fff85e9d922, where = AppKit`-[NSApplication run] + 474
|
|
frame #8: 0x00007fff85e965f8, where = AppKit`NSApplicationMain + 364
|
|
frame #9: 0x0000000100015ae3, where = Sketch`main + 33 at /Projects/Sketch/SKTMain.m:11
|
|
frame #10: 0x0000000100000f20, where = Sketch`start + 52
|
|
</tt></pre>
|
|
|
|
<p>You can also provide a list of threads to backtrace, or the keyword
|
|
"all" to see all threads:</p>
|
|
|
|
<code>
|
|
(lldb) thread backtrace all
|
|
</code>
|
|
|
|
<p>You can select the current thread, which will be used by default in all the commands in
|
|
the next section, with the "thread select" command:</p>
|
|
|
|
<code>
|
|
(lldb) thread select 2
|
|
</code>
|
|
|
|
<p>where the thread index is just the one shown in the "<code>thread list</code>" listing.
|
|
|
|
</div>
|
|
<div class="postfooter"></div>
|
|
|
|
<div class="post">
|
|
<h1 class ="postheader">Examining Stack Frame State</h1>
|
|
<div class="postcontent">
|
|
|
|
|
|
<p>The most convenient way to inspect a frame's arguments and local variables is to use the "<code>frame variable</code>" command:</p>
|
|
|
|
<code>
|
|
(lldb) frame variable
|
|
<br>self = (SKTGraphicView *) 0x0000000100208b40
|
|
<br>_cmd = (struct objc_selector *) 0x000000010001bae1
|
|
<br>sender = (id) 0x00000001001264e0
|
|
<br>selection = (NSArray *) 0x00000001001264e0
|
|
<br>i = (NSUInteger) 0x00000001001264e0
|
|
<br>c = (NSUInteger) 0x00000001001253b0
|
|
</code>
|
|
|
|
<p>As you see above, if you don't specify any variable names, all arguments
|
|
and locals will be shown. If you call "<code>frame variable</code>"
|
|
passing in the names of a particular local(s), only those variables
|
|
will be printed. For instance:
|
|
</p>
|
|
|
|
<code>
|
|
(lldb) frame variable self
|
|
<br>(SKTGraphicView *) self = 0x0000000100208b40
|
|
</code>
|
|
|
|
<p>You can also pass in a path to some subelement of one of the available locals,
|
|
and that sub-element will be printed. For instance:
|
|
</p>
|
|
|
|
<code>
|
|
<br>(lldb) frame variable self.isa
|
|
<br>(struct objc_class *) self.isa = 0x0000000100023730
|
|
</code>
|
|
|
|
<p>The "<code>frame variable</code>" command is not a full expression
|
|
parser but it does support a few simple operations like &, *, ->, [] (no overloaded
|
|
operators). The array brackets can be used on pointers to treat pointers
|
|
as arrays:</p>
|
|
|
|
<code>
|
|
(lldb) frame variable *self
|
|
<br>(SKTGraphicView *) self = 0x0000000100208b40
|
|
<br>(NSView) NSView = {
|
|
<br>(NSResponder) NSResponder = {
|
|
<br>...
|
|
<br>
|
|
<br>(lldb) frame variable &self
|
|
<br>(SKTGraphicView **) &self = 0x0000000100304ab
|
|
<br>
|
|
<br>(lldb) frame variable argv[0]
|
|
<br>(char const *) argv[0] = 0x00007fff5fbffaf8 "/Projects/Sketch/build/Debug/Sketch.app/Contents/MacOS/Sketch"
|
|
</code>
|
|
|
|
<p>The frame variable command will also perform "object printing" operations on
|
|
variables (currently we only support ObjC printing, using the object's "description" method.
|
|
Turn this on by passing the -o flag to frame variable:</p>
|
|
|
|
<code>
|
|
(lldb) frame variable -o self
|
|
(SKTGraphicView *) self = 0x0000000100208b40 <SKTGraphicView: 0x100208b40>
|
|
</code>
|
|
|
|
<p>You can select another frame to view with the "<code>frame select</code>" command</p>
|
|
|
|
<code>
|
|
(lldb) frame select 9
|
|
<br>frame #9: 0x0000000100015ae3, where = Sketch`function1 + 33 at /Projects/Sketch/SKTFunctions.m:11
|
|
</code>
|
|
|
|
<p>You can also move up and down the stack by passing the "<code>--relative</code>" ("<code>-r</code>")
|
|
option. And we have built-in aliases "<code>u</code>" and "<code>d</code>" which
|
|
behave like their gdb equivalents.
|
|
|
|
<p>If you need to view more complex data or change program data, you can
|
|
use the general "expression" command. It takes an expression and
|
|
evaluates it in the scope of the currently selected frame. For instance:</p>
|
|
|
|
<code>
|
|
(lldb) expr self
|
|
<br>$0 = (SKTGraphicView *) 0x0000000100135430
|
|
<br>(lldb) expr self = 0x00
|
|
<br>$1 = (SKTGraphicView *) 0x0000000000000000
|
|
<br>(lldb) frame var self
|
|
<br>(SKTGraphicView *) self = 0x0000000000000000
|
|
</code>
|
|
|
|
<p>You can also call functions:</p>
|
|
|
|
<code>
|
|
(lldb) expr (int) printf ("I have a pointer 0x%llx.\n", self)
|
|
<br>$2 = (int) 22
|
|
<br>I have a pointer 0x0.
|
|
</code>
|
|
|
|
<p>As I said above, "expression" is one of the "raw" commands. So
|
|
you don't have to quote your whole expression, nor backslash protect quotes,
|
|
etc...</p>
|
|
|
|
<p>Finally, the results of the expressions are stored in persistent variables
|
|
(of the form $[0-9]+) that you can use in further expressions, like:</p>
|
|
|
|
<code>
|
|
(lldb) expr self = $0
|
|
<br>$4 = (SKTGraphicView *) 0x0000000100135430
|
|
</code>
|
|
<p>
|
|
</div>
|
|
<div class="postfooter"></div>
|
|
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|