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Add links to SLD from the LangRef.html doc 

Clean up the SLD document a LOT
Fill in a lot of details in the SLD document
update the formats for the object descriptors

llvm-svn: 10698
This commit is contained in:
Chris Lattner 2004-01-06 05:31:32 +00:00
parent 2007cec727
commit 941515cf67
2 changed files with 453 additions and 157 deletions
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49
llvm/docs/LangRef.html
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@ -95,6 +95,7 @@
<li><a href="#i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_debugger">Debugger intrinsics</a>
</ol>
</li>
</ol>
@ -1587,9 +1588,11 @@ an argument.</p>
<p>See the <a href="#int_varargs">variable argument processing</a>
section.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="intrinsics">Intrinsic Functions</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>LLVM supports the notion of an "intrinsic function". These
functions have well known names and semantics, and are required to
@ -1609,9 +1612,12 @@ required that they all be documented here if any are added.</p>
lowering pass to eliminate the intrinsic or all backends must support
the intrinsic function.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="int_varargs">Variable Argument
Handling Intrinsics</a> </div>
<div class="doc_subsection">
<a name="int_varargs">Variable Argument Handling Intrinsics</a>
</div>
<div class="doc_text">
<p>Variable argument support is defined in LLVM with the <a
href="#i_vanext"><tt>vanext</tt></a> instruction and these three
@ -1631,9 +1637,13 @@ used.</p>
href="#i_va_end">llvm.va_end</a>(sbyte* %aq)<br><br> ; Stop processing of arguments.<br> call void %<a
href="#i_va_end">llvm.va_end</a>(sbyte* %ap2)<br> ret int %tmp<br>}<br></pre>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_va_start">'<tt>llvm.va_start</tt>'
Intrinsic</a> </div>
<div class="doc_subsubsection">
<a name="i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> call va_list ()* %llvm.va_start()<br></pre>
@ -1650,9 +1660,12 @@ last argument of the function, the compiler can figure that out.</p>
<p>Note that this intrinsic function is only legal to be called from
within the body of a variable argument function.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_va_end">'<tt>llvm.va_end</tt>'
Intrinsic</a> </div>
<div class="doc_subsubsection">
<a name="i_va_end">'<tt>llvm.va_end</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> call void (va_list)* %llvm.va_end(va_list &lt;arglist&gt;)<br></pre>
@ -1669,9 +1682,12 @@ Calls to <a href="#i_va_start"><tt>llvm.va_start</tt></a> and <a
href="#i_va_copy"><tt>llvm.va_copy</tt></a> must be matched exactly
with calls to <tt>llvm.va_end</tt>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_va_copy">'<tt>llvm.va_copy</tt>'
Intrinsic</a> </div>
<div class="doc_subsubsection">
<a name="i_va_copy">'<tt>llvm.va_copy</tt>' Intrinsic</a>
</div>
<div class="doc_text">
<h5>Syntax:</h5>
<pre> call va_list (va_list)* %llvm.va_copy(va_list &lt;destarglist&gt;)<br></pre>
@ -1687,6 +1703,23 @@ element into the returned list. This intrinsic is necessary because the <tt><a
href="i_va_start">llvm.va_start</a></tt> intrinsic may be arbitrarily
complex and require memory allocation, for example.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="int_debugger">Debugger Intrinsics</a>
</div>
<div class="doc_text">
<p>
The LLVM debugger intrinsics (which all start with <tt>llvm.dbg.</tt> prefix),
are described in the <a
href="SourceLevelDebugging.html#format_common_intrinsics">LLVM Source Level
Debugging</a> document.
</p>
</div>
<!-- *********************************************************************** -->
<hr>
<div class="doc_footer">

561
llvm/docs/SourceLevelDebugging.html
View File

@ -11,7 +11,8 @@
<ul>
<img src="venusflytrap.jpg" width=247 height=369 align=right>
<img src="venusflytrap.jpg" alt="A leafy and green bug eater"
width=247 height=369 align=right>
<li><a href="#introduction">Introduction</a></li>
<ol>
@ -29,25 +30,34 @@
<li><a href="#architecture">Architecture of the LLVM debugger</a></li>
<ol>
<li><a href="#arch_debugger">The Debugger and InferiorProcess classes</a></li>
<li><a href="#arch_info">The RuntimeInfo, ProgramInfo, and SourceLanguage classes</a></li>
<li><a href="#arch_llvm-db">The <tt>llvm-db</tt> tool</a></li>
<li><a href="#arch_todo">Short-term TODO list</a></li>
</ol>
<li><a href="#implementation">Debugging information implementation</a></li>
<li><a href="#format">Debugging information format</a></li>
<ol>
<li><a href="#impl_common_anchors">Anchors for global objects</a></li>
<li><a href="#impl_common_stoppoint">Representing stopping points in the source program</a></li>
<li><a href="#impl_common_lifetime">Object lifetimes and scoping</a></li>
<li><a href="#impl_common_descriptors">Object descriptor formats</a></li>
<li><a href="#format_common_anchors">Anchors for global objects</a></li>
<li><a href="#format_common_stoppoint">Representing stopping points in the source program</a></li>
<li><a href="#format_common_lifetime">Object lifetimes and scoping</a></li>
<li><a href="#format_common_descriptors">Object descriptor formats</a></li>
<ul>
<li><a href="#impl_common_source_files">Representation of source files</a></li>
<li><a href="#impl_common_globals">Representation of global objects</a></li>
<li><a href="#impl_common_localvars">Representation of local variables</a></li>
<li><a href="#format_common_source_files">Representation of source files</a></li>
<li><a href="#format_common_program_objects">Representation of program objects</a></li>
<li><a href="#format_common_object_contexts">Program object contexts</a></li>
</ul>
<li><a href="#impl_common_intrinsics">Other intrinsic functions</a></li>
<li><a href="#format_common_intrinsics">Debugger intrinsic functions</a></li>
<li><a href="#format_common_tags">Values for debugger tags</a></li>
</ol>
<li><a href="#impl_ccxx">C/C++ front-end specific debug information</a></li>
<li><a href="#ccxx_frontend">C/C++ front-end specific debug information</a></li>
<ol>
<li><a href="#impl_ccxx_descriptors">Object descriptor formats</a></li>
<li><a href="#ccxx_pse">Program Scope Entries</a></li>
<ul>
<li><a href="#ccxx_compilation_units">Compilation unit entries</a></li>
<li><a href="#ccxx_modules">Module, namespace, and importing entries</a></li>
</ul>
<li><a href="#ccxx_dataobjects">Data objects (program variables)</a></li>
</ol>
</ul>
@ -58,15 +68,15 @@
<div class="doc_text">
<p>This document is the central repository for all information pertaining to
debug information in LLVM. It describes how to use the <a
href="CommandGuide/llvm-db.html"><tt>llvm-db</tt> tool</a>, which provides a
powerful <a href="#llvm-db">source-level debugger</a> to users of LLVM-based
compilers. When compiling a program in debug mode, the front-end in use adds
LLVM debugging information to the program in the form of normal <a
href="LangRef.html">LLVM program objects</a> as well as a small set of LLVM <a
href="#implementation">intrinsic functions</a>, which specify the mapping of the
program in LLVM form to the program in the source language.
</p>
debug information in LLVM. It describes the <a href="#llvm-db">user
interface</a> for the <a href="CommandGuide/llvm-db.html"><tt>llvm-db</tt>
tool</a>, which provides a powerful <a href="#llvm-db">source-level debugger</a>
to users of LLVM-based compilers. It then describes the <a
href="#architecture">various components</a> that make up the debugger and the
libraries which future clients may use. Finally, it describes the <a
href="#format">actual format that the LLVM debug information</a> takes,
which is useful for those interested in creating front-ends or dealing directly
with the information.</p>
</div>
@ -100,7 +110,7 @@ LLVM should not put any restrictions of the flavor of the source-language, and
the debugging information should work with any language.</li>
<li>With code generator support, it should be possible to use an LLVM compiler
to compile a program to native machine code with standard debugging formats.
to compile a program to native machine code and standard debugging formats.
This allows compatibility with traditional machine-code level debuggers, like
GDB or DBX.</li>
@ -108,10 +118,10 @@ GDB or DBX.</li>
<p>
The approach used by the LLVM implementation is to use a small set of <a
href="#impl_common_intrinsics">intrinsic functions</a> to define a mapping
href="#format_common_intrinsics">intrinsic functions</a> to define a mapping
between LLVM program objects and the source-level objects. The description of
the source-level program is maintained in LLVM global variables in an <a
href="#impl_ccxx">implementation-defined format</a> (the C/C++ front-end
href="#ccxx_frontend">implementation-defined format</a> (the C/C++ front-end
currently uses working draft 7 of the <a
href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3 standard</a>).</p>
@ -207,14 +217,14 @@ scoping rules.</p>
<p>
After working with the debugger for a while, perhaps the nicest improvement
would be to add some sort of line editor, such as GNU readline (but that is
would be to add some sort of line editor, such as GNU readline (but one that is
compatible with the LLVM license).</p>
<p>
For someone so inclined, it should be straight-forward to write different
front-ends for the LLVM debugger, as the LLVM debugging engine is cleanly
seperated from the <tt>llvm-db</tt> front-end. A GUI debugger or IDE would be
an interesting project.
separated from the <tt>llvm-db</tt> front-end. A new LLVM GUI debugger or IDE
would be nice. :)
</p>
</div>
@ -252,18 +262,21 @@ a bug or, better yet, submit a patch to add it. :)</p>
<div class="doc_text">
<p><tt>llvm-db</tt> is the first LLVM debugger, and as such was designed to be
quick to prototype and build, and simple to extend. It is missing many many
features, though they should be easy to add over time (patches welcomed!).
Because the (currently only) debugger backend (implemented in
"lib/Debugger/UnixLocalInferiorProcess.cpp") was designed to work without any
cooperation from the code generators, it suffers from the following inherent
limitations:</p>
<p><tt>llvm-db</tt> is designed to be modular and easy to extend. This
extensibility was key to getting the debugger up-and-running quickly, because we
can start with simple-but-unsophisicated implementations of various components.
Because of this, it is currently missing many features, though they should be
easy to add over time (patches welcomed!). The biggest inherent limitations of
<tt>llvm-db</tt> are currently due to extremely simple <a
href="#arch_debugger">debugger backend</a> (implemented in
"lib/Debugger/UnixLocalInferiorProcess.cpp") which is designed to work without
any cooperation from the code generators. Because it is so simple, it suffers
from the following inherent limitations:</p>
<p><ul>
<li>Running a program in <tt>llvm-db</tt> is a bit slower than running it with
<tt>lli</tt>.</li>
<tt>lli</tt> (i.e., in the JIT).</li>
<li>Inspection of the target hardware is not supported. This means that you
cannot, for example, print the contents of X86 registers.</li>
@ -281,10 +294,11 @@ supported.</li>
</ul></p>
<p>That said, it is still quite useful, and all of these limitations can be
eliminated by integrating support for the debugger into the code generators.
See the <a href="#future">future work</a> section for ideas of how to extend
the LLVM debugger despite these limitations.</p>
<p>That said, the debugger is still quite useful, and all of these limitations
can be eliminated by integrating support for the debugger into the code
generators, and writing a new <a href="#arch_debugger">InferiorProcess</a>
subclass to use it. See the <a href="#future">future work</a> section for ideas
of how to extend the LLVM debugger despite these limitations.</p>
</div>
@ -296,9 +310,48 @@ the LLVM debugger despite these limitations.</p>
<div class="doc_text">
<p>
TODO
</p>
<p>TODO: this is obviously lame, when more is implemented, this can be much
better.</p>
<p><pre>
$ <b>llvm-db funccall</b>
llvm-db: The LLVM source-level debugger
Loading program... successfully loaded 'funccall.bc'!
(llvm-db) <b>create</b>
Starting program: funccall.bc
main at funccall.c:9:2
9 -> q = 0;
(llvm-db) <b>list main</b>
4 void foo() {
5 int t = q;
6 q = t + 1;
7 }
8 int main() {
9 -> q = 0;
10 foo();
11 q = q - 1;
12
13 return q;
(llvm-db) <b>list</b>
14 }
(llvm-db) <b>step</b>
10 -> foo();
(llvm-db) <b>s</b>
foo at funccall.c:5:2
5 -> int t = q;
(llvm-db) <b>bt</b>
#0 -> 0x85ffba0 in foo at funccall.c:5:2
#1 0x85ffd98 in main at funccall.c:10:2
(llvm-db) <b>finish</b>
main at funccall.c:11:2
11 -> q = q - 1;
(llvm-db) <b>s</b>
13 -> return q;
(llvm-db) <b>s</b>
The program stopped with exit code 0
(llvm-db) <b>quit</b>
$
</pre></p>
</div>
@ -386,6 +439,8 @@ information about what these do, or try '<tt>help [command]</tt>' within
<li>set listsize</li>
<li>show language</li>
<li>set language</li>
<li>show args</li>
<li>set args [args]</li>
</ul>
<h2>TODO:</h2>
@ -415,19 +470,119 @@ information about what these do, or try '<tt>help [command]</tt>' within
<div class="doc_text">
<p><pre>
lib/Debugger
- UnixLocalInferiorProcess.cpp
<p>
The LLVM debugger is built out of three distinct layers of software. These
layers provide clients with different interface options depending on what pieces
of they want to implement themselves, and it also promotes code modularity and
good design. The three layers are the <a href="#arch_debugger">Debugger
interface</a>, the <a href="#arch_info">"info" interfaces</a>, and the
<a href="#arch_llvm-db"><tt>llvm-db</tt> tool</a> itself.
</p>
</div>
tools/llvm-db
- SourceLanguage interfaces
- ProgramInfo/RuntimeInfo
- Commands
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="arch_debugger">The Debugger and InferiorProcess classes</a>
</div>
</pre></p>
<div class="doc_text">
<p>
The Debugger class (defined in the <tt>include/llvm/Debugger/</tt> directory) is
a low-level class which is used to maintain information about the loaded
program, as well as start and stop the program running as necessary. This class
does not provide any high-level analysis or control over the program, only
exposing simple interfaces like <tt>load/unloadProgram</tt>,
<tt>create/killProgram</tt>, <tt>step/next/finish/contProgram</tt>, and
low-level methods for installing breakpoints.
</p>
<p>
The Debugger class is itself a wrapper around the lowest-level InferiorProcess
class. This class is used to represent an instance of the program running under
debugger control. The InferiorProcess class can be implemented in different
ways for different targets and execution scenarios (e.g., remote debugging).
The InferiorProcess class exposes a small and simple collection of interfaces
which are useful for inspecting the current state of the program (such as
collecting stack trace information, reading the memory image of the process,
etc). The interfaces in this class are designed to be as low-level and simple
as possible, to make it easy to create new instances of the class.
</p>
<p>
The Debugger class exposes the currently active instance of InferiorProcess
through the <tt>Debugger::getRunningProcess</tt> method, which returns a
<tt>const</tt> reference to the class. This means that clients of the Debugger
class can only <b>inspect</b> the running instance of the program directly. To
change the executing process in some way, they must use the interces exposed by
the Debugger class.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="arch_info">The RuntimeInfo, ProgramInfo, and SourceLanguage classes</a>
</div>
<div class="doc_text">
<p>
The next-highest level of debugger abstraction is provided through the
ProgramInfo, RuntimeInfo, SourceLanguage and related classes (also defined in
the <tt>include/llvm/Debugger/</tt> directory). These classes efficiently
decode the debugging information and low-level interfaces exposed by
InferiorProcess into a higher-level representation, suitable for analysis by the
debugger.
</p>
<p>
The ProgramInfo class exposes a variety of different kinds of information about
the program objects in the source-level-language. The SourceFileInfo class
represents a source-file in the program (e.g. a .cpp or .h file). The
SourceFileInfo class captures information such as which SourceLanguage was used
to compile the file, where the debugger can get access to the actual file text
(which is lazily loaded on demand), etc. The SourceFunctionInfo class
represents a... <b>FIXME: finish</b>. The ProgramInfo class provides interfaces
to lazily find and decode the information needed to create the Source*Info
classes requested by the debugger.
</p>
<p>
The RuntimeInfo class exposes information about the currently executed program,
by decoding information from the InferiorProcess and ProgramInfo classes. It
provides a StackFrame class which provides an easy-to-use interface for
inspecting the current and suspended stack frames in the program.
</p>
<p>
The SourceLanguage class is an abstract interface used by the debugger to
perform all source-language-specific tasks. For example, this interface is used
by the ProgramInfo class to decode language-specific types and functions and by
the debugger front-end (such as <a href="#arch_llvm-db"><tt>llvm-db</tt></a> to
evaluate source-langauge expressions typed into the debugger. This class uses
the RuntimeInfo &amp; ProgramInfo classes to get information about the current
execution context and the loaded program, respectively.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="arch_llvm-db">The <tt>llvm-db</tt> tool</a>
</div>
<div class="doc_text">
<p>
The <tt>llvm-db</tt> is designed to be a debugger providing an interface as <a
href="#llvm-db">similar to GDB</a> as reasonable, but no more so than that.
Because the <a href="#arch_debugger">Debugger</a> and <a
href="#arch_info">info</a> classes implement all of the heavy lifting and
analysis, <tt>llvm-db</tt> (which lives in <tt>llvm/tools/llvm-db</tt>) consists
mainly of of code to interact with the user and parse commands. The CLIDebugger
constructor registers all of the builtin commands for the debugger, and each
command is implemented as a CLIDebugger::[name]Command method.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="arch_todo">Short-term TODO list</a>
@ -455,11 +610,6 @@ level. Also, breakpoints should survive as much as possible across program
reloads.
</p>
<p>
<b>run (with args)</b> &amp; <b>set args</b>: These need to be implemented.
Currently run doesn't support setting arguments as part of the command. The
only tricky thing is handling quotes right and stuff.</p>
<p>
<b>UnixLocalInferiorProcess.cpp speedup</b>: There is no reason for the debugged
process to code gen the globals corresponding to debug information. The
@ -468,11 +618,16 @@ casts of the constant address of the LLVM objects for the descriptors. This
would also allow us to eliminate the mapping back and forth between physical
addresses that must be done.</p>
<p>
<b>Process deaths</b>: The InferiorProcessDead exception should be extended to
know "how" a process died, i.e., it was killed by a signal. This is easy to
collect in the UnixLocalInferiorProcess, we just need to represent it.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="implementation">Debugging information implementation</a>
<a name="format">Debugging information format</a>
</div>
<!-- *********************************************************************** -->
@ -497,32 +652,31 @@ piece of debugging information are deleted (for example, by the
become dead and be removed by the optimizer.</p>
<p>The debugger is designed to be agnostic about the contents of most of the
debugging information. It uses a source-language-specific module to decode the
information that represents variables, types, functions, namespaces, etc: this
allows for arbitrary source-language semantics and type-systems to be used, as
long as there is a module written for the debugger to interpret the information.
debugging information. It uses a <a href="#arch_info">source-language-specific
module</a> to decode the information that represents variables, types,
functions, namespaces, etc: this allows for arbitrary source-language semantics
and type-systems to be used, as long as there is a module written for the
debugger to interpret the information.
</p>
<p>
To provide basic functionality, the LLVM debugger does have to make some
assumptions about the source-level language being debugged, though it keeps
these to a minimum. The only common features that the LLVM debugger assumes
exist are <a href="#impl_common_source_files">source files</a>, <a
href="#impl_common_globals">global objects</a> (aka methods, messages, global
variables, etc), and <a href="#impl_common_localvars">local variables</a>.
These abstract objects are used by the debugger to form stack traces, show
information about local variables, etc.
exist are <a href="#format_common_source_files">source files</a>, and <a
href="#format_program_objects">program objects</a>. These abstract objects are
used by the debugger to form stack traces, show information about local
variables, etc.
<p>This section of the documentation first describes the representation aspects
<a href="#impl_common">common to any source-language</a>. The next section
describes the data layout conventions used by the <a href="#impl_ccxx">C and C++
front-ends</a>.</p>
common to any source-language. The <a href="#ccxx_frontend">next section</a>
describes the data layout conventions used by the C and C++ front-ends.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="impl_common_anchors">Anchors for global objects</a>
<a name="format_common_anchors">Anchors for global objects</a>
</div>
<div class="doc_text">
@ -542,8 +696,8 @@ So far, the following names are recognized as anchors by the LLVM debugger:
</p>
<p><pre>
%<a href="#impl_common_source_files">llvm.dbg.translation_units</a> = linkonce global {} {}
%<a href="#impl_common_globals">llvm.dbg.globals</a> = linkonce global {} {}
%<a href="#format_common_source_files">llvm.dbg.translation_units</a> = linkonce global {} {}
%<a href="#format_program_objects">llvm.dbg.globals</a> = linkonce global {} {}
</pre></p>
<p>
@ -560,7 +714,7 @@ deleted.
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="impl_common_stoppoint">
<a name="format_common_stoppoint">
Representing stopping points in the source program
</a>
</div>
@ -574,8 +728,9 @@ front-end inserts calls to the <tt>%llvm.dbg.stoppoint</tt> intrinsic function
at every point in the program where the debugger should be able to inspect the
program (these correspond to places the debugger stops when you "<tt>step</tt>"
through it). The front-end can choose to place these as fine-grained as it
would like (for example, before every subexpression was evaluated), but it is
recommended to only put them after every source statement.</p>
would like (for example, before every subexpression evaluated), but it is
recommended to only put them after every source statement that includes
executable code.</p>
<p>
Using calls to this intrinsic function to demark legal points for the debugger
@ -585,21 +740,22 @@ transformations, these calls simply look like calls to an external function,
which they must assume to do anything (including reading or writing to any part
of reachable memory). On the other hand, it does not impact many optimizations,
such as code motion of non-trapping instructions, nor does it impact
optimization of subexpressions, or any other code between the stop points.</p>
optimization of subexpressions, code duplication transformations, or basic-block
reordering transformations.</p>
<p>
An important aspect of the calls to the <tt>%llvm.dbg.stoppoint</tt> intrinsic
is that the function-local debugging information is woven together with use-def
chains. This makes it easy for the debugger to, for example, locate the 'next'
stop point. For a concrete example of stop points, see <a
href="#impl_common_lifetime">the next section</a>.</p>
stop point. For a concrete example of stop points, see the example in <a
href="#format_common_lifetime">the next section</a>.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="impl_common_lifetime">Object lifetimes and scoping</a>
<a name="format_common_lifetime">Object lifetimes and scoping</a>
</div>
<div class="doc_text">
@ -642,25 +798,25 @@ void %foo() {
%X = alloca int
%Y = alloca int
%Z = alloca int
<a name="#icl_ex_D1">%D1</a> = call {}* %llvm.dbg.func.start(<a href="#impl_common_globals">%lldb.global</a>* %d.foo)
%D2 = call {}* <a href="#impl_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D1, uint 2, uint 2, <a href="#impl_common_source_files">%lldb.compile_unit</a>* %file)
<a name="#icl_ex_D1">%D1</a> = call {}* %llvm.dbg.func.start(<a href="#format_program_objects">%lldb.global</a>* %d.foo)
%D2 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D1, uint 2, uint 2, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
%D3 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D2, ...)
<i>;; Evaluate expression on line 2, assigning to X.</i>
%D4 = call {}* <a href="#impl_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D3, uint 3, uint 2, <a href="#impl_common_source_files">%lldb.compile_unit</a>* %file)
%D4 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D3, uint 3, uint 2, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
%D5 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D4, ...)
<i>;; Evaluate expression on line 3, assigning to Y.</i>
%D6 = call {}* <a href="#impl_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D5, uint 5, uint 4, <a href="#impl_common_source_files">%lldb.compile_unit</a>* %file)
%D6 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D5, uint 5, uint 4, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
<a name="#icl_ex_D1">%D7</a> = call {}* %llvm.region.start({}* %D6)
%D8 = call {}* %llvm.dbg.DEFINEVARIABLE({}* %D7, ...)
<i>;; Evaluate expression on line 5, assigning to Z.</i>
%D9 = call {}* <a href="#impl_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D8, uint 6, uint 4, <a href="#impl_common_source_files">%lldb.compile_unit</a>* %file)
%D9 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D8, uint 6, uint 4, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
<i>;; Code for line 6.</i>
%D10 = call {}* %llvm.region.end({}* %D9)
%D11 = call {}* <a href="#impl_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D10, uint 8, uint 2, <a href="#impl_common_source_files">%lldb.compile_unit</a>* %file)
%D11 = call {}* <a href="#format_common_stoppoint">%llvm.dbg.stoppoint</a>({}* %D10, uint 8, uint 2, <a href="#format_common_source_files">%lldb.compile_unit</a>* %file)
<i>;; Code for line 8.</i>
<a name="#icl_ex_D1">%D12</a> = call {}* %llvm.region.end({}* %D11)
@ -672,7 +828,7 @@ void %foo() {
This example illustrates a few important details about the LLVM debugging
information. In particular, it shows how the various intrinsics used are woven
together with def-use and use-def chains, similar to how <a
href="#impl_common_anchors">anchors</a> are used with globals. This allows the
href="#format_common_anchors">anchors</a> are used with globals. This allows the
debugger to analyze the relationship between statements, variable definitions,
and the code used to implement the function.</p>
@ -681,21 +837,24 @@ In this example, two explicit regions are defined, one with the <a
href="#icl_ex_D1">definition of the <tt>%D1</tt> variable</a> and one with the
<a href="#icl_ex_D7">definition of <tt>%D7</tt></a>. In the case of
<tt>%D1</tt>, the debug information indicates that the function whose <a
href="#impl_common_globals">descriptor</a> is specified as an argument to the
href="#format_program_objects">descriptor</a> is specified as an argument to the
intrinsic. This defines a new stack frame whose lifetime ends when the region
is ended by <a href="#icl_ex_D12">the <tt>%D12</tt> call</a>.</p>
<p>
Representing the boundaries of functions with regions allows normal LLVM
interprocedural optimizations to change the boundaries of functions without
having to worry about breaking mapping information between LLVM and source-level
functions. In particular, the inlining optimization requires no modification to
support inlining with debugging information: there is no correlation drawn
between LLVM functions and their source-level counterparts.</p>
Using regions to represent the boundaries of source-level functions allow LLVM
interprocedural optimizations to arbitrarily modify LLVM functions without
having to worry about breaking mapping information between the LLVM code and the
and source-level program. In particular, the inliner requires no modification
to support inlining with debugging information: there is no explicit correlation
drawn between LLVM functions and their source-level counterparts (note however,
that if the inliner inlines all instances of a non-strong-linkage function into
its caller that it will not be possible for the user to manually invoke the
inlined function from the debugger).</p>
<p>
Once the function has been defined, the <a
href="#impl_common_stoppoint">stopping point</a> corresponding to line #2 of the
href="#format_common_stoppoint">stopping point</a> corresponding to line #2 of the
function is encountered. At this point in the function, <b>no</b> local
variables are live. As lines 2 and 3 of the example are executed, their
variable definitions are automatically introduced into the program, without the
@ -708,10 +867,9 @@ introduced because they go out of scope at the same point in the program: line
In contrast, the <tt>Z</tt> variable goes out of scope at a different time, on
line 7. For this reason, it is defined within <a href="#icl_ex_D7">the
<tt>%D7</tt> region</a>, which kills the availability of <tt>Z</tt> before the
code for line 8 is executed. Through the use of LLVM debugger regions,
arbitrary source-language scoping rules can be supported, as long as they can
only be nested (ie, one scope cannot partially overlap with a part of another
scope).
code for line 8 is executed. In this way, regions can support arbitrary
source-language scoping rules, as long as they can only be nested (ie, one scope
cannot partially overlap with a part of another scope).
</p>
<p>
@ -719,7 +877,7 @@ It is worth noting that this scoping mechanism is used to control scoping of all
declarations, not just variable declarations. For example, the scope of a C++
using declaration is controlled with this, and the <tt>llvm-db</tt> C++ support
routines could use this to change how name lookup is performed (though this is
not yet implemented).
not implemented yet).
</p>
</div>
@ -727,41 +885,46 @@ not yet implemented).
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="impl_common_descriptors">Object descriptor formats</a>
<a name="format_common_descriptors">Object descriptor formats</a>
</div>
<div class="doc_text">
<p>
The LLVM debugger expects the descriptors for global objects to start in a
The LLVM debugger expects the descriptors for program objects to start in a
canonical format, but the descriptors can include additional information
appended at the end. All LLVM debugging information is versioned, allowing
backwards compatibility in the case that the core structures need to change in
some way. The lowest-level descriptor are those describing <a
href="#impl_common_source_files">the files containing the program source
code</a>, all other descriptors refer to them.
appended at the end that is source-language specific. All LLVM debugging
information is versioned, allowing backwards compatibility in the case that the
core structures need to change in some way. Also, all debugging information
objects start with a <a href="#format_common_tags">tag</a> to indicate what type
of object it is. The source-language is allows to define its own objects, by
using unreserved tag numbers.</p>
<p>The lowest-level descriptor are those describing <a
href="#format_common_source_files">the files containing the program source
code</a>, as most other descriptors (sometimes indirectly) refer to them.
</p>
</div>
<!----------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="impl_common_source_files">Representation of source files</a>
<a name="format_common_source_files">Representation of source files</a>
</div>
<div class="doc_text">
<p>
Source file descriptors were roughly patterned after the Dwarf "compile_unit"
object. The descriptor currently is defined to have the following LLVM
type:</p>
Source file descriptors are patterned after the Dwarf "compile_unit" object.
The descriptor currently is defined to have at least the following LLVM
type entries:</p>
<p><pre>
%lldb.compile_unit = type {
uint, <i>;; Tag: <a href="#tag_compile_unit">LLVM_COMPILE_UNIT</a></i>
ushort, <i>;; LLVM debug version number</i>
ushort, <i>;; Dwarf language identifier</i>
sbyte*, <i>;; Filename</i>
sbyte*, <i>;; Working directory when compiled</i>
sbyte*, <i>;; Producer of the debug information</i>
{}* <i>;; Anchor for llvm.dbg.translation_units</i>
sbyte* <i>;; Producer of the debug information</i>
}
</pre></p>
@ -770,13 +933,16 @@ These descriptors contain the version number for the debug info, a source
language ID for the file (we use the Dwarf 3.0 ID numbers, such as
<tt>DW_LANG_C89</tt>, <tt>DW_LANG_C_plus_plus</tt>, <tt>DW_LANG_Cobol74</tt>,
etc), three strings describing the filename, working directory of the compiler,
and an identifier string for the compiler that produced it, and the <a
href="#impl_common_anchors">anchor</a> for the descriptor. Here is an example
and an identifier string for the compiler that produced it. Note that actual
compile_unit declarations must also include an <a
href="#format_common_anchors">anchor</a> to <tt>llvm.dbg.translation_units</tt>,
but it is not specified where the anchor is to be located. Here is an example
descriptor:
</p>
<p><pre>
%arraytest_source_file = internal constant %lldb.compile_unit {
<a href="#tag_compile_unit">uint 17</a>, ; Tag value
ushort 0, ; Version #0
ushort 1, ; DW_LANG_C89
sbyte* getelementptr ([12 x sbyte]* %.str_1, long 0, long 0), ; filename
@ -789,78 +955,126 @@ descriptor:
%.str_3 = internal constant [12 x sbyte] c"llvmgcc 3.4\00"
</pre></p>
<p>
Note that the LLVM constant merging pass should eliminate duplicate copies of
the strings that get emitted to each translation unit, such as the producer.
</p>
</div>
<!----------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="impl_common_globals">Representation of global objects</a>
<a name="format_program_objects">Representation of program objects</a>
</div>
<div class="doc_text">
<p>
The LLVM debugger needs to know what the source-language global objects, in
order to build stack traces and other related activities. Because
source-languages have widly varying forms of global objects, the LLVM debugger
only expects the following fields in the descriptor for each global:
The LLVM debugger needs to know about some source-language program objects, in
order to build stack traces, print information about local variables, and other
related activities. The LLVM debugger differentiates between three different
types of program objects: subprograms (functions, messages, methods, etc),
variables (locals and globals), and others. Because source-languages have
widely varying forms of these objects, the LLVM debugger expects only a few
fields in the descriptor for each object:
</p>
<p><pre>
%lldb.global = type {
<a href="#impl_common_source_files">%lldb.compile_unit</a>*, <i>;; The translation unit containing the global</i>
sbyte*, <i>;; The global object 'name'</i>
[type]*, <i>;; Source-language type descriptor for global</i>
{}* <i>;; The anchor for llvm.dbg.globals</i>
%lldb.object = type {
uint, <i>;; <a href="#format_common_tag">A tag</a></i>
<i>any</i>*, <i>;; The <a href="#format_common_object_contexts">context</a> for the object</i>
sbyte* <i>;; The object 'name'</i>
}
</pre></p>
<p>
The first field contains a pointer to the translation unit the function is
defined in. This pointer allows the debugger to find out which version of debug
information the function corresponds to. The second field contains a string
that the debugger can use to identify the subprogram if it does not contain
explicit support for the source-language in use. This should be some sort of
unmangled string that corresponds to the function somehow.
The first field contains a tag for the descriptor. The second field contains
either a pointer to the descriptor for the containing <a
href="#format_common_source_files">source file</a>, or it contains a pointer to
another program object whose context pointer eventually reaches a source file.
Through this <a href="#format_common_object_contexts">context</a> pointer, the
LLVM debugger can establish the debug version number of the object.</p>
<p>
The third field contains a string that the debugger can use to identify the
object if it does not contain explicit support for the source-language in use
(ie, the 'unknown' source language handler uses this string). This should be
some sort of unmangled string that corresponds to the object, but it is a
quality of implementation issue what exactly it contains (it is legal, though
not useful, for all of these strings to be null).
</p>
<p>
Note again that descriptors can be extended to include source-language-specific
information in addition to the fields required by the LLVM debugger. See the <a
href="#impl_ccxx_descriptors">section on the C/C++ front-end</a> for more
information.
</p>
</div>
<!----------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="impl_common_localvars">Representation of local variables</a>
</div>
<div class="doc_text">
<p>
href="#ccxx_descriptors">section on the C/C++ front-end</a> for more
information. Also remember that global objects (functions, selectors, global
variables, etc) must contain an <a href="format_common_anchors">anchor</a> to
the <tt>llvm.dbg.globals</tt> variable.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="impl_common_intrinsics">Other intrinsic functions</a>
<a name="format_common_object_contexts">Program object contexts</a>
</div>
<div class="doc_text">
<p><pre>
Allow source-language specific contexts, use to identify namespaces etc
Must end up in a source file descriptor.
Debugger core ignores all unknown context objects.
</pre></p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="format_common_intrinsics">Debugger intrinsic functions</a>
</div>
<div class="doc_text">
<p><pre>
Define each intrinsics, as an extension of the language reference manual.
llvm.dbg.stoppoint
llvm.dbg.region.start
llvm.dbg.region.end
llvm.dbg.function.start
llvm.dbg.declare
</pre></p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="format_common_tags">Values for debugger tags</a>
</div>
<div class="doc_text">
<p>
Happen to be the same value as the similarly named Dwarf-3 tags, this may change
in the future.
</p>
</p>
<p><pre>
<a name="tag_compile_unit">LLVM_COMPILE_UNIT</a> : 17
<a name="tag_subprogram">LLVM_SUBPROGRAM</a> : 46
<a name="tag_variable">LLVM_VARIABLE</a> : 52
<!-- <a name="tag_formal_parameter">LLVM_FORMAL_PARAMETER : 5-->
</pre></p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="impl_ccxx">C/C++ front-end specific debug information</a>
<a name="ccxx_frontend">C/C++ front-end specific debug information</a>
</div>
<div class="doc_text">
@ -871,18 +1085,32 @@ that is effectively identical to <a
href="http://www.eagercon.com/dwarf/dwarf3std.htm">Dwarf 3.0</a> in terms of
information content. This allows code generators to trivially support native
debuggers by generating standard dwarf information, and contains enough
information for non-dwarf targets to translate it other as needed.</p>
information for non-dwarf targets to translate it as needed.</p>
<p>
TODO: document extensions to standard debugging objects, document how we
represent source types, etc.
The basic debug information required by the debugger is (intentionally) designed
to be as minimal as possible. This basic information is so minimal that it is
unlikely that <b>any</b> source-language could be adequately described by it.
Because of this, the debugger format was designed for extension to support
source-language-specific information. The extended descriptors are read and
interpreted by the <a href="#arch_info">language-specific</a> modules in the
debugger if there is support available, otherwise it is ignored.
</p>
<p>
This section describes the extensions used to represent C and C++ programs.
Other languages could pattern themselves after this (which itself is tuned to
representing programs in the same way that Dwarf 3 does), or they could choose
to provide completely different extensions if they don't fit into the Dwarf
model. As support for debugging information gets added to the various LLVM
source-language front-ends, the information used should be documented here.
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="impl_ccxx_descriptors">Object Descriptor Formats</a>
<a name="ccxx_pse">Program Scope Entries</a>
</div>
<div class="doc_text">
@ -891,6 +1119,41 @@ represent source types, etc.
</p>
</div>
<!----------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="ccxx_compilation_units">Compilation unit entries</a>
</div>
<div class="doc_text">
<p>
Translation units do not add any information over the standard <a
href="#format_common_source_files">source file representation</a> already
expected by the debugger. As such, it uses descriptors of the type specified,
with a trailing <a href="#format_common_anchors">anchor</a>.
</p>
</div>
<!----------------------------------------------------------------------------->
<div class="doc_subsubsection">
<a name="ccxx_modules">Module, namespace, and importing entries</a>
</div>
<div class="doc_text">
<p>
</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="ccxx_dataobjects">Data objects (program variables)</a>
</div>
<div class="doc_text">
<p>
</p>
</div>
<!-- *********************************************************************** -->