151 lines
5.1 KiB
ReStructuredText
151 lines
5.1 KiB
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=============
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Clang Plugins
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=============
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Clang Plugins make it possible to run extra user defined actions during a
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compilation. This document will provide a basic walkthrough of how to write and
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run a Clang Plugin.
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Introduction
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============
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Clang Plugins run FrontendActions over code. See the :doc:`FrontendAction
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tutorial <RAVFrontendAction>` on how to write a ``FrontendAction`` using the
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``RecursiveASTVisitor``. In this tutorial, we'll demonstrate how to write a
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simple clang plugin.
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Writing a ``PluginASTAction``
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=============================
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The main difference from writing normal ``FrontendActions`` is that you can
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handle plugin command line options. The ``PluginASTAction`` base class declares
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a ``ParseArgs`` method which you have to implement in your plugin.
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.. code-block:: c++
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bool ParseArgs(const CompilerInstance &CI,
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const std::vector<std::string>& args) {
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for (unsigned i = 0, e = args.size(); i != e; ++i) {
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if (args[i] == "-some-arg") {
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// Handle the command line argument.
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}
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}
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return true;
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}
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Registering a plugin
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====================
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A plugin is loaded from a dynamic library at runtime by the compiler. To
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register a plugin in a library, use ``FrontendPluginRegistry::Add<>``:
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.. code-block:: c++
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static FrontendPluginRegistry::Add<MyPlugin> X("my-plugin-name", "my plugin description");
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Putting it all together
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=======================
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Let's look at an example plugin that prints top-level function names. This
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example is also checked into the clang repository; please also take a look at
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the latest `checked in version of PrintFunctionNames.cpp
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<http://llvm.org/viewvc/llvm-project/cfe/trunk/examples/PrintFunctionNames/PrintFunctionNames.cpp?view=markup>`_.
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.. code-block:: c++
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#include "clang/Frontend/FrontendPluginRegistry.h"
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#include "clang/AST/ASTConsumer.h"
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#include "clang/AST/AST.h"
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#include "clang/Frontend/CompilerInstance.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace clang;
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namespace {
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class PrintFunctionsConsumer : public ASTConsumer {
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public:
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virtual bool HandleTopLevelDecl(DeclGroupRef DG) {
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for (DeclGroupRef::iterator i = DG.begin(), e = DG.end(); i != e; ++i) {
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const Decl *D = *i;
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if (const NamedDecl *ND = dyn_cast<NamedDecl>(D))
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llvm::errs() << "top-level-decl: \"" << ND->getNameAsString() << "\"\n";
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}
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return true;
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}
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};
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class PrintFunctionNamesAction : public PluginASTAction {
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protected:
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ASTConsumer *CreateASTConsumer(CompilerInstance &CI, llvm::StringRef) {
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return new PrintFunctionsConsumer();
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}
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bool ParseArgs(const CompilerInstance &CI,
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const std::vector<std::string>& args) {
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for (unsigned i = 0, e = args.size(); i != e; ++i) {
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llvm::errs() << "PrintFunctionNames arg = " << args[i] << "\n";
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// Example error handling.
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if (args[i] == "-an-error") {
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DiagnosticsEngine &D = CI.getDiagnostics();
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unsigned DiagID = D.getCustomDiagID(
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DiagnosticsEngine::Error, "invalid argument '" + args[i] + "'");
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D.Report(DiagID);
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return false;
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}
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}
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if (args.size() && args[0] == "help")
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PrintHelp(llvm::errs());
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return true;
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}
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void PrintHelp(llvm::raw_ostream& ros) {
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ros << "Help for PrintFunctionNames plugin goes here\n";
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}
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};
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}
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static FrontendPluginRegistry::Add<PrintFunctionNamesAction>
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X("print-fns", "print function names");
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Running the plugin
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==================
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To run a plugin, the dynamic library containing the plugin registry must be
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loaded via the :option:`-load` command line option. This will load all plugins
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that are registered, and you can select the plugins to run by specifying the
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:option:`-plugin` option. Additional parameters for the plugins can be passed with
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:option:`-plugin-arg-<plugin-name>`.
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Note that those options must reach clang's cc1 process. There are two
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ways to do so:
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* Directly call the parsing process by using the :option:`-cc1` option; this
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has the downside of not configuring the default header search paths, so
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you'll need to specify the full system path configuration on the command
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line.
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* Use clang as usual, but prefix all arguments to the cc1 process with
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:option:`-Xclang`.
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For example, to run the ``print-function-names`` plugin over a source file in
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clang, first build the plugin, and then call clang with the plugin from the
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source tree:
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.. code-block:: console
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$ export BD=/path/to/build/directory
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$ (cd $BD && make PrintFunctionNames )
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$ clang++ -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS \
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-D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -D_GNU_SOURCE \
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-I$BD/tools/clang/include -Itools/clang/include -I$BD/include -Iinclude \
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tools/clang/tools/clang-check/ClangCheck.cpp -fsyntax-only \
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-Xclang -load -Xclang $BD/lib/PrintFunctionNames.so -Xclang \
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-plugin -Xclang print-fns
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Also see the print-function-name plugin example's
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`README <http://llvm.org/viewvc/llvm-project/cfe/trunk/examples/PrintFunctionNames/README.txt?view=markup>`_
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