[cfe-dev] AST modifications that apply to the binary

[John Brawn via cfe-dev]

By default a PluginASTAction will replace the main AST action (if you use -plugin pluginname on the
cc1 command line) or go after the main AST action (if you use -add-plugin pluginname on the cc1
command line), where the "main AST action" is "generate an object file" if using -c, "generate
assembly" is using -S, etc.

If you want the PluginASTAction to go before the main AST action, i.e. you want it to change the
AST in a way that will affect the compiled output, then define a getActionType method in the
PluginASTAction which returns AddBeforeMainAction.

John

From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org] On Behalf Of Ori Zaig via cfe-dev
Sent: 20 November 2016 16:49
To: cfe-dev at lists.llvm.org
Cc: Eran Jakoby
Subject: [cfe-dev] AST modifications that apply to the binary

Hi all

Is there any possible making AST modification that finally will be reflected in the binary?
I tried doing that via plugin, for instance changing a method name (let's say turn foo() to my_foo() ) such:

class FuncnameChangeVisitor : public RecursiveASTVisitor< FuncnameChangeVisitor > {
private:
                ASTContext *m_context;
public:
                /* some code */

                bool VisitFunctionDecl(FunctionDecl *f) {
                                DeclarationNameInfo newNameInfo(f->getNameInfo());
                                DeclarationName origName(f->getDeclName());
                                std::string newName("my_");
                                newName += origName.getAsString();
                                IdentifierInfo& newNameIdInfo(m_context->Idents.get(StringRef(newName.c_str())));
                                f->setDeclName(DeclarationName(&newNameIdInfo));
                                return true;
                }
};

class FuncnameChangeConsumer: public ASTConsumer {
private:
                FuncnameChangeVisitor m_visitor;
public:
                /* some code*/
                virtual void HandleTranslationUnit(ASTContext &Cntx) {
                                m_visitor.TraverseDecl(Cntx.getTranslationUnitDecl());
                }
};

class FuncnameChangeAction: public PluginASTAction {
                std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI, llvm::StringRef InFile) override {
                                return llvm::make_unique< FuncnameChangeConsumer >(CI, &CI.getSourceManager());
                }

                bool ParseArgs(const CompilerInstance &CI, const std::vector<std::string> &args) override {
                                return true;
                }
};

static FrontendPluginRegistry::Add< FuncnameChangeAction > reg("modify-func", "add my_ prefix to funtions");


But in vain... I understood that the IR and hence the binary are generated regardless the plugins

And if there isn't a way to do so, is there another way via Clang to make code-modifications that affect the binary, which are not source-to-source compilation?

Tnx

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