[Lldb-commits] [lldb] r171477 - in /lldb/trunk/www: sidebar.incl symbolication.html

Greg Clayton gclayton at apple.com
Fri Jan 4 10:18:21 PST 2013

Author: gclayton
Date: Fri Jan  4 12:18:21 2013
New Revision: 171477

URL: http://llvm.org/viewvc/llvm-project?rev=171477&view=rev
Added a page that describes how to to manual symbolication with LLDB from the command line, from python, and also how to use the build in modules to do symbolication.

    lldb/trunk/www/symbolication.html   (with props)

Modified: lldb/trunk/www/sidebar.incl
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/www/sidebar.incl?rev=171477&r1=171476&r2=171477&view=diff
--- lldb/trunk/www/sidebar.incl (original)
+++ lldb/trunk/www/sidebar.incl Fri Jan  4 12:18:21 2013
@@ -17,6 +17,7 @@
         <li><a href="tutorial.html">Tutorial</a></li>
         <li><a href="lldb-gdb.html">GDB and LLDB command examples</a></li>
         <li><a href="formats.html">Frame and Thread Formatting</a></li>
+        <li><a href="symbolication.html">Symbolication</a></li>
         <li><a href="varformats.html">Variable Formatting</a></li>
         <li><a href="python-reference.html">Python Reference</a></li>
         <li><a href="scripting.html">Python Example</a></li>

Added: lldb/trunk/www/symbolication.html
URL: http://llvm.org/viewvc/llvm-project/lldb/trunk/www/symbolication.html?rev=171477&view=auto
--- lldb/trunk/www/symbolication.html (added)
+++ lldb/trunk/www/symbolication.html Fri Jan  4 12:18:21 2013
@@ -0,0 +1,323 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
+<link href="style.css" rel="stylesheet" type="text/css" />
+<title>Symbolicating with LLDB</title>
+    <div class="www_title">
+      The <strong>LLDB</strong> Debugger
+    </div>
+<div id="container">
+	<div id="content">
+  <!--#include virtual="sidebar.incl"-->
+		<div id="middle">
+    		<div class="post">
+    			<h1 class="postheader">Manual Symbolication with LLDB</h1>
+    			<div class="postcontent">
+    			    <p>LLDB is separated into a shared library that contains the core of the debugger,
+								and a driver that implements debugging and a command interpreter. LLDB can be
+								used to symbolicate your crash logs and can often provide more information than
+								other symbolication programs:
+							</p>
+								<ul>
+									<li>Inlined functions</li>
+									<li>Variables that are in scope for an address along with their locations</li>
+								</ul>
+							<p>The simplest form of symbolication is to just load an executable:</p>
+<code><pre><tt><b>(lldb)</b> target create --no-dependents --arch x86_64 /tmp/a.out
+							<p>We use the "--no-dependents" flag with the "target create" command so
+								that we don't load all of the dependent shared libraries from the current
+								OS. When we symbolicate, we are often symbolicating a binary that
+								was running on another system, and even though the main executable might
+								reference shared libraries in "/usr/lib", we often don't want to load
+								the versions on the current computer.</p>
+							<p>Using the "image list" command will show us a list of all shared libraries
+								associated with the current target. As expected, we currently only have a single
+								binary:
+							</p>
+							<code><pre><tt><b>(lldb)</b> image list
+[  0] 73431214-6B76-3489-9557-5075F03E36B4 0x0000000100000000 /tmp/a.out 
+      /tmp/a.out.dSYM/Contents/Resources/DWARF/a.out
+							<p>Now we can lookup an address:</p>
+<code><pre><tt><b>(lldb)</b> image lookup --address 0x100000aa3
+      Address: a.out[0x0000000100000aa3] (a.out.__TEXT.__text + 131)
+      Summary: a.out`main + 67 at main.c:13
+							<p>Since we haven't specified a slide or any load addresses for individual sections
+								in the binary, the address that we use here is a <b>file</b> address. A <b>file</b>
+								address refers to a virtual address as defined by each object file. 
+							</p>
+								<p>If we didn't use the "--no-dependents" option with "target create", we would
+								have loaded all dependent shared libraries:<p>
+									<code><pre><tt><b>(lldb)</b> image list
+[  0] 73431214-6B76-3489-9557-5075F03E36B4 0x0000000100000000 /tmp/a.out 
+      /tmp/a.out.dSYM/Contents/Resources/DWARF/a.out
+[  1] 8CBCF9B9-EBB7-365E-A3FF-2F3850763C6B 0x0000000000000000 /usr/lib/system/libsystem_c.dylib 
+[  2] 62AA0B84-188A-348B-8F9E-3E2DB08DB93C 0x0000000000000000 /usr/lib/system/libsystem_dnssd.dylib 
+[  3] C0535565-35D1-31A7-A744-63D9F10F12A4 0x0000000000000000 /usr/lib/system/libsystem_kernel.dylib 
+								<p>Now if we do a lookup using a <b>file</b> address, this can result in multiple
+									matches since most shared libraries have a virtual address space that starts at zero:</p>
+<code><pre><tt><b>(lldb)</b> image lookup -a 0x1000
+      Address: a.out[0x0000000000001000] (a.out.__PAGEZERO + 4096)
+      Address: libsystem_c.dylib[0x0000000000001000] (libsystem_c.dylib.__TEXT.__text + 928)
+      Summary: libsystem_c.dylib`mcount + 9
+      Address: libsystem_dnssd.dylib[0x0000000000001000] (libsystem_dnssd.dylib.__TEXT.__text + 456)
+      Summary: libsystem_dnssd.dylib`ConvertHeaderBytes + 38
+      Address: libsystem_kernel.dylib[0x0000000000001000] (libsystem_kernel.dylib.__TEXT.__text + 1116)
+      Summary: libsystem_kernel.dylib`clock_get_time + 102
+								<p>To avoid getting multiple file address matches, you can specify the
+									<b>name</b> of the shared library to limit the search:</p>
+<code><pre><tt><b>(lldb)</b> image lookup -a 0x1000 <b>a.out</b>
+      Address: a.out[0x0000000000001000] (a.out.__PAGEZERO + 4096)
+    			</div>
+         	<div class="postfooter"></div>
+        </div>
+    		<div class="post">
+    			<h1 class="postheader">Defining Load Addresses for Sections</h1>
+    			<div class="postcontent">
+    			    <p>When symbolicating your crash logs, it can be tedious if you always have to
+								fixup your addresses into file specified addresses. To avoid having to do any
+								conversion, you can set the load address for the sections of the modules in your target. 
+								Once you set any section load address locations, lookups will switch to using
+								<b>load</b> addresses. You can slide all sections in the executable by the same amount,
+								or set the <b>load</b> address if individual sections. The
+								"target moodules load" command allows us to set the <b>load</b> address for
+								the sections.
+							<p>Below is an example of sliding all sections in <b>a.out</b> by adding 0x123000 to each section's <b>file</b> address:</p>
+<code><pre><tt><b>(lldb)</b> target create --no-dependents --arch x86_64 /tmp/a.out
+<b>(lldb)</b> target modules load --file a.out --slide 0x123000
+							<p>It is often much easier to just specify the actual load location of each section by name. 
+								Crash logs on MacOSX actuall have a <b>Binary Images</b> section that specifies
+								that address of the __TEXT segments for each binary. Computing the slide can be tricky
+								for executables and you need to be careful to calculate the slide correctly. If you specify the
+								address of the __TEXT segment, you don't need to do any calculations. To specify
+								the load addresses of sections we can specify one or more section name + address pairs
+								in the "target modules load" command:</p>
+<code><pre><tt><b>(lldb)</b> target create --no-dependents --arch x86_64 /tmp/a.out
+<b>(lldb)</b> target modules load --file a.out __TEXT 0x100123000
+							<p>We specified that the <b>__TEXT</b> section is loaded at 0x100123000.
+								Now that we have defined where sections have been loaded in our target, 
+								any lookups we do will now use <b>load</b> addresses so we don't have to
+								do any math on the addresses in the stack backtraces, we can just use the
+								raw addresses:</p>
+<code><pre><tt><b>(lldb)</b> image lookup --address 0x100123aa3
+      Address: a.out[0x0000000100000aa3] (a.out.__TEXT.__text + 131)
+      Summary: a.out`main + 67 at main.c:13
+    			</div>
+         	<div class="postfooter"></div>
+        </div>
+    		<div class="post">
+    			<h1 class="postheader">Loading Multiple Executables</h1>
+    			<div class="postcontent">
+    			    <p>You often have more than one executable involved when you need to symbolicate
+								a crash log. When this happens, you create a target for the main executable
+								or one of the shared libraries, then add more modules to the target using the
+								"target modules add" command.<p>
+							<p>Lets say we have a Darwin crash log that contains the following images:
+<code><pre><tt>Binary Images:
+    <font color=blue>0x100000000</font> -    0x100000ff7 <A866975B-CA1E-3649-98D0-6C5FAA444ECF> /tmp/a.out
+ <font color=green>0x7fff83f32000</font> - 0x7fff83ffefe7 <8CBCF9B9-EBB7-365E-A3FF-2F3850763C6B> /usr/lib/system/libsystem_c.dylib
+ <font color=red>0x7fff883db000</font> - 0x7fff883e3ff7 <62AA0B84-188A-348B-8F9E-3E2DB08DB93C> /usr/lib/system/libsystem_dnssd.dylib
+ <font color=purple>0x7fff8c0dc000</font> - 0x7fff8c0f7ff7 <C0535565-35D1-31A7-A744-63D9F10F12A4> /usr/lib/system/libsystem_kernel.dylib
+							<p>First we create the target using the main executable and then add any extra shared libraries we want:</p>
+<code><pre><tt><b>(lldb)</b> target create --no-dependents --arch x86_64 /tmp/a.out
+<b>(lldb)</b> target modules add /usr/lib/system/libsystem_c.dylib
+<b>(lldb)</b> target modules add /usr/lib/system/libsystem_dnssd.dylib
+<b>(lldb)</b> target modules add /usr/lib/system/libsystem_kernel.dylib
+							<p>If you have debug symbols in stand alone files, such as dSYM files on MacOSX, you can specify their paths using the <b>--symfile</b> option for the "target create" (recent LLDB releases only) and "target modules add" commands:</p>
+<code><pre><tt><b>(lldb)</b> target create --no-dependents --arch x86_64 /tmp/a.out <b>--symfile /tmp/a.out.dSYM</b>
+<b>(lldb)</b> target modules add /usr/lib/system/libsystem_c.dylib <b>--symfile /build/server/a/libsystem_c.dylib.dSYM</b>
+<b>(lldb)</b> target modules add /usr/lib/system/libsystem_dnssd.dylib <b>--symfile /build/server/b/libsystem_dnssd.dylib.dSYM</b>
+<b>(lldb)</b> target modules add /usr/lib/system/libsystem_kernel.dylib <b>--symfile /build/server/c/libsystem_kernel.dylib.dSYM</b>
+							<p>Then we set the load addresses for each __TEXT section using (note the colors of the load addresses above and below) the first address from the Binary Images section for each image:</p>
+<code><pre><tt><b>(lldb)</b> target modules load --file a.out <font color=blue>0x100000000</font>
+<b>(lldb)</b> target modules load --file libsystem_c.dylib <font color=green>0x7fff83f32000</font>
+<b>(lldb)</b> target modules load --file libsystem_dnssd.dylib <font color=red>0x7fff883db000</font>
+<b>(lldb)</b> target modules load --file libsystem_kernel.dylib <font color=purple>0x7fff8c0dc000</font>
+							<p>Now any stack backtraces that haven't been symbolicated can be symbolicated using "image lookup"
+								with the raw backtrace addresses.</p>
+							<p>Given the following raw backtrace:</p>
+<code><pre><tt>Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
+0   libsystem_kernel.dylib        	0x00007fff8a1e6d46 __kill + 10
+1   libsystem_c.dylib             	0x00007fff84597df0 abort + 177
+2   libsystem_c.dylib             	0x00007fff84598e2a __assert_rtn + 146
+3   a.out                         	0x0000000100000f46 main + 70
+4   libdyld.dylib                 	0x00007fff8c4197e1 start + 1
+						<p>We can now symbolicate the <b>load</b> addresses:<p>
+<code><pre><tt><b>(lldb)</b> image lookup -a 0x00007fff8a1e6d46
+<b>(lldb)</b> image lookup -a 0x00007fff84597df0
+<b>(lldb)</b> image lookup -a 0x00007fff84598e2a
+<b>(lldb)</b> image lookup -a 0x0000000100000f46
+    			</div>
+         	<div class="postfooter"></div>
+        </div>
+    		<div class="post">
+    			<h1 class="postheader">Getting Variable Information</h1>
+    			<div class="postcontent">
+    			    <p>If you add the --verbose flag to the "image lookup --address" command, 
+								you can get verbose information which can often include the locations
+								of some of your local variables:
+<code><pre><tt>><b>(lldb)</b> image lookup --address 0x100123aa3 --verbose
+      Address: a.out[0x0000000100000aa3] (a.out.__TEXT.__text + 110)
+      Summary: a.out`main + 50 at main.c:13
+       Module: file = "/tmp/a.out", arch = "x86_64"
+  CompileUnit: id = {0x00000000}, file = "/tmp/main.c", language = "ISO C:1999"
+     Function: id = {0x0000004f}, name = "main", range = [0x0000000100000bc0-0x0000000100000dc9)
+     FuncType: id = {0x0000004f}, decl = main.c:9, clang_type = "int (int, const char **, const char **, const char **)"
+       Blocks: id = {0x0000004f}, range = [0x100000bc0-0x100000dc9)
+               id = {0x000000ae}, range = [0x100000bf2-0x100000dc4)
+    LineEntry: [0x0000000100000bf2-0x0000000100000bfa): /tmp/main.c:13:23
+       Symbol: id = {0x00000004}, range = [0x0000000100000bc0-0x0000000100000dc9), name="main"
+     Variable: id = {0x000000bf}, name = "path", type= "char [1024]", location = DW_OP_fbreg(-1072), decl = main.c:28
+     Variable: id = {0x00000072}, name = "argc", type= "int", <b>location = r13</b>, decl = main.c:8
+     Variable: id = {0x00000081}, name = "argv", type= "const char **", <b>location = r12</b>, decl = main.c:8
+     Variable: id = {0x00000090}, name = "envp", type= "const char **", <b>location = r15</b>, decl = main.c:8
+     Variable: id = {0x0000009f}, name = "aapl", type= "const char **", <b>location = rbx</b>, decl = main.c:8
+    			    <p>The interesting part is the variables that are listed. The variables are
+								the parameters and local variables that are in scope for the address that
+								was specified. These variable entries have locations which are shown in bold
+								above. Crash logs often have register information for the first frame in each
+								stack, and being able to reconstruct one or more local variables can often
+								help you decipher more information from a crash log than you normally would be
+								able to. Note that this is really only useful for the first frame, and only if
+								your crash logs have register information for your threads.
+    			</div>
+         	<div class="postfooter"></div>
+        </div>
+    		<div class="post">
+    			<h1 class="postheader">Using Python API to Symbolicate</h1>
+    			<div class="postcontent">
+    			    <p>All of the commands above can be done through the python script bridge. The code below
+								will recreate the target and add the three shared libraries that we added in the darwin
+								crash log example above:
+<code><pre><tt>triple = "x86_64-apple-macosx"
+platform_name = None
+add_dependents = False
+target = lldb.debugger.CreateTarget("/tmp/a.out", triple, platform_name, add_dependents, lldb.SBError())
+if target:
+	<font color=green># Get the executable module</font>
+	module = target.GetModuleAtIndex(0)
+	target.SetSectionLoadAddress(module.FindSection("__TEXT"), 0x100000000)
+	module = target.AddModule ("/usr/lib/system/libsystem_c.dylib", triple, None, "/build/server/a/libsystem_c.dylib.dSYM")
+	target.SetSectionLoadAddress(module.FindSection("__TEXT"), 0x7fff83f32000)
+	module = target.AddModule ("/usr/lib/system/libsystem_dnssd.dylib", triple, None, "/build/server/b/libsystem_dnssd.dylib.dSYM")
+	target.SetSectionLoadAddress(module.FindSection("__TEXT"), 0x7fff883db000)
+	module = target.AddModule ("/usr/lib/system/libsystem_kernel.dylib", triple, None, "/build/server/c/libsystem_kernel.dylib.dSYM")
+	target.SetSectionLoadAddress(module.FindSection("__TEXT"), 0x7fff8c0dc000)
+	load_addr = 0x00007fff8a1e6d46
+	<font color=green># so_addr is a section offset address, or a lldb.SBAddress object</font>
+	so_addr = target.ResolveLoadAddress (load_addr)
+	<font color=green># Get a symbol context for the section offset address which includes
+	# a module, compile unit, function, block, line entry, and symbol</font>
+	sym_ctx = so_addr.GetSymbolContext (lldb.eSymbolContextEverything)
+	print sym_ctx
+    			</div>
+         	<div class="postfooter"></div>
+        </div>
+	<div class="post">
+    			<h1 class="postheader">Use Builtin Python module to Symbolicate</h1>
+    			<div class="postcontent">
+    			    <p>LLDB includes a module in the "lldb" package named "lldb.utils.symbolication". 
+								This module contains a lot of helper functions that simplify symbolication
+								by allowing you to create objects that represent symbolication class objects such as:
+								<ul>
+									<li>lldb.utils.symbolication.Address</li>
+									<li>lldb.utils.symbolication.Section</li>
+									<li>lldb.utils.symbolication.Image</li>
+									<li>lldb.utils.symbolication.Symbolicator</li>
+								</ul>
+							<p>Another package that is distributed on MacOSX builds on LLDB is the "lldb.macosx.crashlog"
+								module. This packages subclasses many of the above symbolication class objects. The module
+								installs a new "crashlog" command into the lldb command interpreter so that you can use
+								it to parse and symbolicate MacOSX crash logs:</p>
+<code><pre><tt><b>(lldb)</b> script import lldb.macosx.crashlog
+"crashlog" and "save_crashlog" command installed, use the "--help" option for detailed help
+<b>(lldb)</b> crashlog --help
+Usage: crashlog [options] <FILE> [FILE ...]
+Symbolicate one or more darwin crash log files to provide source file and line
+information, inlined stack frames back to the concrete functions, and
+disassemble the location of the crash for the first frame of the crashed
+thread. If this script is imported into the LLDB command interpreter, a
+"crashlog" command will be added to the interpreter for use at the LLDB
+command line. After a crash log has been parsed and symbolicated, a target
+will have been created that has all of the shared libraries loaded at the load
+addresses found in the crash log file. This allows you to explore the program
+as if it were stopped at the locations described in the crash log and
+functions can  be disassembled and lookups can be performed using the
+addresses found in the crash log.
+  -h, --help            show this help message and exit
+  -v, --verbose         display verbose debug info
+  -g, --debug           display verbose debug logging
+  -a, --load-all        load all executable images, not just the images found
+                        in the crashed stack frames
+  --images              show image list
+  --debug-delay=NSEC    pause for NSEC seconds for debugger
+  -c, --crashed-only    only symbolicate the crashed thread
+                        set the depth in stack frames that should be
+                        disassembled (default is 1)
+  -D, --disasm-all      enabled disassembly of frames on all threads (not just
+                        the crashed thread)
+                        the number of instructions to disassemble before the
+                        frame PC
+                        the number of instructions to disassemble after the
+                        frame PC
+  -C NLINES, --source-context=NLINES
+                        show NLINES source lines of source context (default =
+                        4)
+  --source-frames=NFRAMES
+                        show source for NFRAMES (default = 4)
+  --source-all          show source for all threads, not just the crashed
+                        thread
+  -i, --interactive     parse all crash logs and enter interactive mode
+						<p>The source for the "symbolication" and "crashlog" modules are available in SVN:
+						<br><a href="http://llvm.org/svn/llvm-project/lldb/trunk/examples/python/symbolication.py">symbolication.py</a>
+						<br><a href="http://llvm.org/svn/llvm-project/lldb/trunk/examples/python/crashlog.py">crashlog.py</a>
+    			</div>
+         	<div class="postfooter"></div>
+        </div>

Propchange: lldb/trunk/www/symbolication.html
    svn:executable = *

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