// -*- mode: c++ -*-
// Copyright (c) 2010 Google Inc. All Rights Reserved.
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//
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// 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__