jingham updated this revision to Diff 165614.
jingham added a comment.
I think this should address your concerns, though I did so more by reworking
the presentation, so you won't find inserts exactly at the places you pointed
out.
But I tried to make it clear that you only write the Resolver, and also gave
more examples of how the SearchFilter gets provided.
Repository:
rLLDB LLDB
https://reviews.llvm.org/D52065
Files:
www/python-reference.html
Index: www/python-reference.html
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</div>
</div>
+ </div>
+ <div class="post">
+ <h1 class ="postheader">Using the Python API's to create custom breakpoints</h1>
+ <div class="postcontent">
+
+ <p>Another use of the Python API's in lldb is to create a custom breakpoint resolver. This facility
+ was added in r51967.
+ </p>
+ <p>
+ It allows you to provide the algorithm which will be used in the breakpoint's
+ search of the space of the code in a given Target
+ to determine where to set the breakpoint locations - the actual places where the breakpoint will trigger.
+ To understand how this works you need to know a little about how lldb handles breakpoints.
+ </p>
+ <p>
+ In lldb, a breakpoint is composed of three parts, the Searcher, and the Resolver, which cooperate to determine
+ how breakpoint locations are set; and the the collection
+ of options which determine what happens when a location triggers. That last part includes the commands,
+ conditions, ignore counts, etc. All the options in this collection work identically for normal and scripted breakpoints,
+ so for our purposes only the Searcher and Resolver are relevant.
+ </p>
+ <p>
+ The Searcher's job is to traverse in a structured way the code in the current target. It
+ proceeds from the Target, to search all the Modules in the Target, in each Module it can recurse
+ into the Compile Units in that module, and within each Compile Unit it can recurse over the Functions
+ it contains.
+ </p>
+ <p>
+ The Searcher can be provided with a SearchFilter that it will use to restrict this search. For instance, if the
+ SearchFilter specifies a list of good Modules, the Searcher will not recurse into Modules that aren't on the list.
+ When you pass the <b>-s modulename</b> flag to <b>break set</b> you are creating a Module-based search filter.
+ When you pass <b>-f filename.c</b> to <b>break set -n</b> you are creating a file based search filter. If neither
+ of these is specified, the breakpoint will have a no-op search filter, so all parts of the program are searched
+ and all locations accepted.
+ </p>
+ <p>
+ The Resolver has two functions. The most important one is the callback it provides. This will get called at the appropriate time
+ in the course of the search. The callback is where the job of adding locations to the breakpoint gets done.
+ </p>
+ <p>
+ The other function is specifying to the Searcher at what depth in the above described recursion it wants to be
+ called. Setting a search depth also provides a stop for the recursion. For instance, if you request a Module depth
+ search, then the callback will be called for each Module as it gets added to the Target, but the searcher will not recurse into the
+ Compile Units in the module.
+ </p>
+ <p>
+ One other slight sublety is that the depth at which you get called back is not necessarily the depth at which the
+ the SearchFilter is specified. For instance, if you are doing symbol searches, it is convenient to use the Module
+ depth for the search, since symbols are stored in the module.
+ But the SearchFilter might specify some subset of CompileUnits, so not all the symbols you might find in each module
+ will pass the search. You don't need to
+ handle this situation yourself, since <b>SBBreakpoint::AddLocation</b> will only add locations that pass the Search Filter.
+ This API returns an SBError to inform you whether your location was added.
+ </p>
+ <p>
+ When the breakpoint is originally created, its Searcher will process all the currently loaded modules.
+ The Searcher will also visit any new modules as they are added to the target. This happens, for instance, when
+ a new shared library gets added to the target in the course of running, or on rerunning if any of the currently
+ loaded modules have been changed. Note, in the latter case, all the locations set in the old module will get
+ deleted and you will be asked to recreate them in the new version of the module when your callback gets called
+ with that module. For this reason, you shouldn't
+ try to manage the locations you add to the breakpoint yourself. Note that the Breakpoint takes care of
+ deduplicating equal addresses in AddLocation, so you shouldn't need to worry about that anyway.
+ </p>
+ <p>
+ At present, when adding a scripted Breakpoint type, you can only provide a custom Resolver, not a custom SearchFilter.
+ </p>
+ <p>
+ The custom Resolver is provided as a Python class with the following methods:
+ </p>
+</tt></pre></code>
+ <p><table class="stats" width="620" cellspacing="0">
+ <tr>
+ <td class="hed" width="10%">Name</td>
+ <td class="hed" width="10%">Arguments</td>
+ <td class="hed" width="80%">Description</td>
+ </tr>
+
+
+ <tr>
+ <td class="content">
+ <b>__init__</b>
+ </td>
+ <td class="content">
+ <b>bkpt: lldb.SBBreakpoint</b>
+ <b>extra_args: lldb.SBStructuredData</b>
+ </td>
+ <td class="content">
+ <p>
+ This is the constructor for the new Resolver.
+ </p>
+ <p>
+ <b>bkpt</b> is the breakpoint owning this Resolver.
+ </p>
+ <p>
+ <b>extra_args</b> is an SBStructuredData object that the user can pass in when creating instances of this
+ breakpoint. It is not required, but is quite handy. For instance if you were implementing a breakpoint on some
+ symbol name, you could write a generic symbol name based Resolver, and then allow the user to pass
+ in the particular symbol in the extra_args
+ </td>
+ </tr>
+
+ <tr>
+ <td class="content">
+ <b>__callback__</b>
+ </td>
+ <td class="content">
+ <b>sym_ctx: lldb.SBSymbolContext</b>
+ </td>
+ <td class="content">
+ This is the Resolver callback.
+ The <b>sym_ctx</b> argument will be filled with the current stage
+ of the search.
+ </p>
+ <p>
+ For instance, if you asked for a search depth of lldb.eSearchDepthCompUnit, then the
+ target, module and compile_unit fields of the sym_ctx will be filled. The callback should look just in the
+ context passed in <b>sym_ctx</b> for new locations. If the callback finds an address of interest, it
+ can add it to the breakpoint with the <b>SBBreakpoint::AddLocation</b> method, using the breakpoint passed
+ in to the <b>__init__</b> method.
+ </td>
+ </tr>
+ <tr>
+ <td class="content">
+ <b>__get_depth__</b>
+ </td>
+ <td class="content">
+ <b>None</b>
+ </td>
+ <td class="content">
+ Specify the depth at which you wish your callback to get called. The currently supported options are:
+ <dl>
+ <dt>lldb.eSearchDepthModule</dt>
+ <dt>lldb.eSearchDepthCompUnit</dt>
+ <dt>lldb.eSearchDepthFunction</dt>
+ </dl>
+ For instance, if you are looking
+ up symbols, which are stored at the Module level, you will want to get called back module by module.
+ So you would want to return <b>lldb.eSearchDepthModule</b>. This method is optional. If not provided the search
+ will be done at Module depth.
+ </td>
+ </tr>
+ <tr>
+ <td class="content">
+ <b>get_short_help</b>
+ </td>
+ <td class="content">
+ <b>None</b>
+ </td>
+ <td class="content">
+ This is an optional method. If provided, the returned string will be printed at the beginning of
+ the description for this breakpoint.
+ </td>
+ </tr>
+ </table>
+
+ <p>To define a new breakpoint command defined by this class from the lldb command line, use the command:</p>
+
+<code><pre><tt>(lldb) <strong>breakpoint set -P MyModule.MyResolverClass</strong>
+</tt></pre></code>
+ <p>You can also populate the extra_args SBStructuredData with a dictionary of key/value pairs with:</p>
+
+<code><pre><tt>(lldb) <strong>breakpoint set -P MyModule.MyResolverClass -k key_1 -v value_1 -k key_2 -v value_2</strong>
+</tt></pre></code>
+ <p>Although you can't write a scripted SearchFilter, both the command line and the SB API's for adding a
+ scripted resolver allow you to specify a SearchFilter restricted to certain modules or certain compile
+ units. When using the command line to create the resolver, you can specify a Module specific SearchFilter
+ by passing the <b>-s ModuleName</b> option - which can be specified multiple times.
+ You can also specify a SearchFilter restricted to certain
+ compile units by passing in the <b>-f CompUnitName</b> option. This can also be specified more than
+ once. And you can mix the two to specify "this comp unit in this module". So, for instance,
+ </p>
+
+<code><pre><tt>(lldb) <strong>breakpoint set -P MyModule.MyResolverClass -s a.out</strong>
+</tt></pre></code>
+ <p>
+ will use your resolver, but will only recurse into or accept new locations in the module a.out.
+ </p>
+
+ <p>Another option for creating scripted breakpoints is to use the <b>SBTarget.CreateBreakpointFromScript</b> API.
+ This one has the advantage that you can pass in an arbitrary SBStructuredData object, so you can
+ create more complex parametrizations.
+ SBStructuredData has a handy SetFromJSON method which you can use for this purpose.
+ Your __init__ function gets passed this SBStructuredData object.
+ This API also allows you to directly provide the list of Modules and the list of CompileUnits that will
+ make up the SearchFilter. If you pass in empty lists, the breakpoint will use the default "search everywhere,accept
+ everything" filter.
+ </p>
+
+ </div>
<div class="post">
<h1 class ="postheader">Using the Python API's to create custom stepping logic</h1>
<div class="postcontent">
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