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 // -*- mode: c++ -*-

 // Copyright (c) 2010 Google Inc. All Rights Reserved.

 //

 // Redistribution and use in source and binary forms, with or without

 // modification, are permitted provided that the following conditions are

 // met:

 //

 //     * Redistributions of source code must retain the above copyright

 // notice, this list of conditions and the following disclaimer.

 //     * Redistributions in binary form must reproduce the above

 // copyright notice, this list of conditions and the following disclaimer

 // in the documentation and/or other materials provided with the

 // distribution.

 //     * Neither the name of Google Inc. nor the names of its

 // contributors may be used to endorse or promote products derived from

 // this software without specific prior written permission.

 //

 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 // Original author: Jim Blandy <jimb@mozilla.com> <jimb@red-bean.com>

 // dwarf2reader::CompilationUnit is a simple and direct parser for

 // DWARF data, but its handler interface is not convenient to use.  In

 // particular:

 //

 // - CompilationUnit calls Dwarf2Handler's member functions to report

 //   every attribute's value, regardless of what sort of DIE it is.

 //   As a result, the ProcessAttributeX functions end up looking like

 //   this:

 //

 //     switch (parent_die_tag) {

 //       case DW_TAG_x:

 //         switch (attribute_name) {

 //           case DW_AT_y:

 //             handle attribute y of DIE type x

 //           ...

 //         } break;

 //       ...

 //     } 

 //

 //   In C++ it's much nicer to use virtual function dispatch to find

 //   the right code for a given case than to switch on the DIE tag

 //   like this.

 //

 // - Processing different kinds of DIEs requires different sets of

 //   data: lexical block DIEs have start and end addresses, but struct

 //   type DIEs don't.  It would be nice to be able to have separate

 //   handler classes for separate kinds of DIEs, each with the members

 //   appropriate to its role, instead of having one handler class that

 //   needs to hold data for every DIE type.

 //

 // - There should be a separate instance of the appropriate handler

 //   class for each DIE, instead of a single object with tables

 //   tracking all the dies in the compilation unit.

 //

 // - It's not convenient to take some action after all a DIE's

 //   attributes have been seen, but before visiting any of its

 //   children.  The only indication you have that a DIE's attribute

 //   list is complete is that you get either a StartDIE or an EndDIE

 //   call.

 //

 // - It's not convenient to make use of the tree structure of the

 //   DIEs.  Skipping all the children of a given die requires

 //   maintaining state and returning false from StartDIE until we get

 //   an EndDIE call with the appropriate offset.

 //

 // This interface tries to take care of all that.  (You're shocked, I'm sure.)

 //

 // Using the classes here, you provide an initial handler for the root

 // DIE of the compilation unit.  Each handler receives its DIE's

 // attributes, and provides fresh handler objects for children of

 // interest, if any.  The three classes are:

 //

 // - DIEHandler: the base class for your DIE-type-specific handler

 //   classes.

 //

 // - RootDIEHandler: derived from DIEHandler, the base class for your

 //   root DIE handler class.

 //

 // - DIEDispatcher: derived from Dwarf2Handler, an instance of this

 //   invokes your DIE-type-specific handler objects.

 //

 // In detail:

 //

 // - Define handler classes specialized for the DIE types you're

 //   interested in.  These handler classes must inherit from

 //   DIEHandler.  Thus:

 //

 //     class My_DW_TAG_X_Handler: public DIEHandler { ... };

 //     class My_DW_TAG_Y_Handler: public DIEHandler { ... };

 //

 //   DIEHandler subclasses needn't correspond exactly to single DIE

 //   types, as shown here; the point is that you can have several

 //   different classes appropriate to different kinds of DIEs.

 //

 // - In particular, define a handler class for the compilation

 //   unit's root DIE, that inherits from RootDIEHandler:

 //

 //     class My_DW_TAG_compile_unit_Handler: public RootDIEHandler { ... };

 //

 //   RootDIEHandler inherits from DIEHandler, adding a few additional

 //   member functions for examining the compilation unit as a whole,

 //   and other quirks of rootness.

 //

 // - Then, create a DIEDispatcher instance, passing it an instance of

 //   your root DIE handler class, and use that DIEDispatcher as the

 //   dwarf2reader::CompilationUnit's handler:

 //

 //     My_DW_TAG_compile_unit_Handler root_die_handler(...);

 //     DIEDispatcher die_dispatcher(&root_die_handler);

 //     CompilationUnit reader(sections, offset, bytereader, &die_dispatcher);

 //

 //   Here, 'die_dispatcher' acts as a shim between 'reader' and the

 //   various DIE-specific handlers you have defined.

 //

 // - When you call reader.Start(), die_dispatcher behaves as follows,

 //   starting with your root die handler and the compilation unit's

 //   root DIE:

 //

 //   - It calls the handler's ProcessAttributeX member functions for

 //     each of the DIE's attributes.

 //

 //   - It calls the handler's EndAttributes member function.  This

 //     should return true if any of the DIE's children should be

 //     visited, in which case:

 //

 //     - For each of the DIE's children, die_dispatcher calls the

 //       DIE's handler's FindChildHandler member function.  If that

 //       returns a pointer to a DIEHandler instance, then

 //       die_dispatcher uses that handler to process the child, using

 //       this procedure recursively.  Alternatively, if

 //       FindChildHandler returns NULL, die_dispatcher ignores that

 //       child and its descendants.

 // 

 //   - When die_dispatcher has finished processing all the DIE's

 //     children, it invokes the handler's Finish() member function,

 //     and destroys the handler.  (As a special case, it doesn't

 //     destroy the root DIE handler.)

 // 

 // This allows the code for handling a particular kind of DIE to be

 // gathered together in a single class, makes it easy to skip all the

 // children or individual children of a particular DIE, and provides

 // appropriate parental context for each die.

 #ifndef COMMON_DWARF_DWARF2DIEHANDLER_H__

 #define COMMON_DWARF_DWARF2DIEHANDLER_H__

 #include <stack>

 #include <string>

 #include "common/dwarf/types.h"

 #include "common/dwarf/dwarf2enums.h"

 #include "common/dwarf/dwarf2reader.h"

 #include "common/using_std_string.h"

 namespace dwarf2reader {

 // A base class for handlers for specific DIE types.  The series of

 // calls made on a DIE handler is as follows:

 //

 // - for each attribute of the DIE:

 //   - ProcessAttributeX()

 // - EndAttributes()

 // - if that returned true, then for each child:

 //   - FindChildHandler()

 //   - if that returns a non-NULL pointer to a new handler:

 //     - recurse, with the new handler and the child die

 // - Finish()

 // - destruction

 class DIEHandler {

  public:

   DIEHandler() { }

   virtual ~DIEHandler() { }

   // When we visit a DIE, we first use these member functions to

   // report the DIE's attributes and their values.  These have the

   // same restrictions as the corresponding member functions of

   // dwarf2reader::Dwarf2Handler.

   //

   // Since DWARF does not specify in what order attributes must

   // appear, avoid making decisions in these functions that would be

   // affected by the presence of other attributes. The EndAttributes

   // function is a more appropriate place for such work, as all the

   // DIE's attributes have been seen at that point.

   //

   // The default definitions ignore the values they are passed.

   virtual void ProcessAttributeUnsigned(enum DwarfAttribute attr,

                                         enum DwarfForm form,

                                         uint64 data) { }

   virtual void ProcessAttributeSigned(enum DwarfAttribute attr,

                                       enum DwarfForm form,

                                       int64 data) { }

   virtual void ProcessAttributeReference(enum DwarfAttribute attr,

                                          enum DwarfForm form,

                                          uint64 data) { }

   virtual void ProcessAttributeBuffer(enum DwarfAttribute attr,

                                       enum DwarfForm form,

                                       const char* data,

                                       uint64 len) { }

   virtual void ProcessAttributeString(enum DwarfAttribute attr,

                                       enum DwarfForm form,

                                       const string& data) { }

   virtual void ProcessAttributeSignature(enum DwarfAttribute attr,

                                          enum DwarfForm form,

                                          uint64 signture) { }

   // Once we have reported all the DIE's attributes' values, we call

   // this member function.  If it returns false, we skip all the DIE's

   // children.  If it returns true, we call FindChildHandler on each

   // child.  If that returns a handler object, we use that to visit

   // the child; otherwise, we skip the child.

   //

   // This is a good place to make decisions that depend on more than

   // one attribute. DWARF does not specify in what order attributes

   // must appear, so only when the EndAttributes function is called

   // does the handler have a complete picture of the DIE's attributes.

   //

   // The default definition elects to ignore the DIE's children.

   // You'll need to override this if you override FindChildHandler,

   // but at least the default behavior isn't to pass the children to

   // FindChildHandler, which then ignores them all.

   virtual bool EndAttributes() { return false; }

   // If EndAttributes returns true to indicate that some of the DIE's

   // children might be of interest, then we apply this function to

   // each of the DIE's children.  If it returns a handler object, then

   // we use that to visit the child DIE.  If it returns NULL, we skip

   // that child DIE (and all its descendants).

   //

   // OFFSET is the offset of the child; TAG indicates what kind of DIE

   // it is.

   //

   // The default definition skips all children.

   virtual DIEHandler *FindChildHandler(uint64 offset, enum DwarfTag tag) {

     return NULL;

   }

   // When we are done processing a DIE, we call this member function.

   // This happens after the EndAttributes call, all FindChildHandler

   // calls (if any), and all operations on the children themselves (if

   // any). We call Finish on every handler --- even if EndAttributes

   // returns false.

   virtual void Finish() { };

 };

 // A subclass of DIEHandler, with additional kludges for handling the

 // compilation unit's root die.

 class RootDIEHandler: public DIEHandler {

  public:

   RootDIEHandler() { }

   virtual ~RootDIEHandler() { }

   // We pass the values reported via Dwarf2Handler::StartCompilationUnit

   // to this member function, and skip the entire compilation unit if it

   // returns false.  So the root DIE handler is actually also

   // responsible for handling the compilation unit metadata.

   // The default definition always visits the compilation unit.

   virtual bool StartCompilationUnit(uint64 offset, uint8 address_size,

                                     uint8 offset_size, uint64 cu_length,

                                     uint8 dwarf_version) { return true; }

   // For the root DIE handler only, we pass the offset, tag and

   // attributes of the compilation unit's root DIE.  This is the only

   // way the root DIE handler can find the root DIE's tag.  If this

   // function returns true, we will visit the root DIE using the usual

   // DIEHandler methods; otherwise, we skip the entire compilation

   // unit.

   //

   // The default definition elects to visit the root DIE.

   virtual bool StartRootDIE(uint64 offset, enum DwarfTag tag) { return true; }

 };

 class DIEDispatcher: public Dwarf2Handler {

  public:

   // Create a Dwarf2Handler which uses ROOT_HANDLER as the handler for

   // the compilation unit's root die, as described for the DIEHandler

   // class.

   DIEDispatcher(RootDIEHandler *root_handler) : root_handler_(root_handler) { }

   // Destroying a DIEDispatcher destroys all active handler objects

   // except the root handler.

   ~DIEDispatcher();

   bool StartCompilationUnit(uint64 offset, uint8 address_size,

                             uint8 offset_size, uint64 cu_length,

                             uint8 dwarf_version);

   bool StartDIE(uint64 offset, enum DwarfTag tag);

   void ProcessAttributeUnsigned(uint64 offset,

                                 enum DwarfAttribute attr,

                                 enum DwarfForm form,

                                 uint64 data);

   void ProcessAttributeSigned(uint64 offset,

                               enum DwarfAttribute attr,

                               enum DwarfForm form,

                               int64 data);

   void ProcessAttributeReference(uint64 offset,

                                  enum DwarfAttribute attr,

                                  enum DwarfForm form,

                                  uint64 data);

   void ProcessAttributeBuffer(uint64 offset,

                               enum DwarfAttribute attr,

                               enum DwarfForm form,

                               const char* data,

                               uint64 len);

   void ProcessAttributeString(uint64 offset,

                               enum DwarfAttribute attr,

                               enum DwarfForm form,

                               const string &data);

   void ProcessAttributeSignature(uint64 offset,

                                  enum DwarfAttribute attr,

                                  enum DwarfForm form,

                                  uint64 signature);

   void EndDIE(uint64 offset);

  private:

   // The type of a handler stack entry.  This includes some fields

   // which don't really need to be on the stack --- they could just be

   // single data members of DIEDispatcher --- but putting them here

   // makes it easier to see that the code is correct.

   struct HandlerStack {

     // The offset of the DIE for this handler stack entry.

     uint64 offset_;

     // The handler object interested in this DIE's attributes and

     // children.  If NULL, we're not interested in either.

     DIEHandler *handler_;

     // Have we reported the end of this DIE's attributes to the handler?

     bool reported_attributes_end_;

   };

   // Stack of DIE attribute handlers.  At StartDIE(D), the top of the

   // stack is the handler of D's parent, whom we may ask for a handler

   // for D itself.  At EndDIE(D), the top of the stack is D's handler.

   // Special cases:

   //

   // - Before we've seen the compilation unit's root DIE, the stack is

   //   empty; we'll call root_handler_'s special member functions, and

   //   perhaps push root_handler_ on the stack to look at the root's

   //   immediate children.

   //

   // - When we decide to ignore a subtree, we only push an entry on

   //   the stack for the root of the tree being ignored, rather than

   //   pushing lots of stack entries with handler_ set to NULL.

   std::stack<HandlerStack> die_handlers_;

   // The root handler.  We don't push it on die_handlers_ until we

   // actually get the StartDIE call for the root.

   RootDIEHandler *root_handler_;

 };

 } // namespace dwarf2reader

 #endif  // COMMON_DWARF_DWARF2DIEHANDLER_H__