C++ Types: Introduction

As announced previously, the upcoming 0.9.7 version of the Profiler represents a milestone in the development road map. We’re excited to present to you an awesome set of new features. In fact, the ground to cover is so vast that one post is not nearly enough. Throughout this week I’ll write some posts to cover the basics and this will allow for enough time to beta test the new version before reaching a release candidate.

Let’s start with an awesome image:

Presentation

Does it look like a Clang based tool to parse C++ sources and extract type information? If yes, then that’s exactly it!

To sum it up very briefly, the Profiler is now able to extract C++ types such as classes and structures and use these types both in the UI and in Python.

Add structure dialog

Of course, there’s much more to it. The layout of C++ types is a complex matter and doesn’t just involve supporting simple data structures. This post is just an introduction, the next ones will focus on topics such as: endianness, pointers, arrays, sub-structures, unions, bit-fields, inheritance, virtual tables, virtual inheritance, anonymous types, alignment, packing and templates. Yes, you read correctly: templates. :)

And apart from the implications of C++ types themselves, there’s the SDK part of the Profiler which will also require some dedicated posts. In this introduction I’m going to show a very simple flow and one of the many possible use cases.

You probably have noticed that the code in the screenshot above belongs to WinNT.h. Let’s see how to import the types in this header quickly. Usually we could parse all the headers of a framework with a few clicks, but while Clang is ideal to parse both Linux and OS X sources, it has difficulty with some Visual C++ extensions which are completely invalid C++ code. So rather than importing the whole Windows SDK we just limit ourselves to a part of WinNT.h.

I have added some predefines for Windows types (we could also include WinDef.h):

#define BYTE unsigned char
#define WORD unsigned short
#define DWORD unsigned int
#define __int64 long long
#define LONG long
#define CHAR char
#define WCHAR short
#define ULONGLONG unsigned long long
#define UNALIGNED
#define SHORT short
#define NTAPI
#define VOID void
#define PVOID void *
#define BOOL unsigned int
#define BOOLEAN unsigned int

Then I just copied the header into the import tool. Usually this isn’t necessary, because we can set up the include directories from the UI and then just use #include directives, but since we need to modify the header to remove invalid C++ extensions, it makes sense to paste it.

The beginning of the code:

HEADER_START("WinNT");
 
typedef struct _GUID {
    unsigned long  Data1;
    unsigned short Data2;
    unsigned short Data3;
    unsigned char  Data4[ 8 ];
} GUID;
 
typedef GUID CLSID;
 
typedef struct _IMAGE_DOS_HEADER {      // DOS .EXE header
    WORD   e_magic;                     // Magic number
    WORD   e_cblp;                      // Bytes on last page of file
    WORD   e_cp;                        // Pages in file
    WORD   e_crlc;                      // Relocations
    WORD   e_cparhdr;                   // Size of header in paragraphs
    WORD   e_minalloc;                  // Minimum extra paragraphs needed
    WORD   e_maxalloc;                  // Maximum extra paragraphs needed
    WORD   e_ss;                        // Initial (relative) SS value
    WORD   e_sp;                        // Initial SP value
    WORD   e_csum;                      // Checksum
    WORD   e_ip;                        // Initial IP value
    WORD   e_cs;                        // Initial (relative) CS value
    WORD   e_lfarlc;                    // File address of relocation table
    WORD   e_ovno;                      // Overlay number
    WORD   e_res[4];                    // Reserved words
    WORD   e_oemid;                     // OEM identifier (for e_oeminfo)
    WORD   e_oeminfo;                   // OEM information; e_oemid specific
    WORD   e_res2[10];                  // Reserved words
    LONG   e_lfanew;                    // File address of new exe header
  } IMAGE_DOS_HEADER, *PIMAGE_DOS_HEADER;
 
// etc. etc.

Did you notice the HEADER_START macro?

HEADER_START("WinNT");

This tells our parser that the C++ types following this directive will be dumped into the header “WinNT.cphdr”. This file is relative to the header directory, a sub-directory of the user data directory. A HEADER_END directive does also exist, it equals to invoking the start directive with an empty string. To give you a better idea how these directives work take a look at this snippet:

// the types in A.h won't be dumped to a header file
 
#include <A.h>
 
HEADER_START("BC");
 
// the types of B.h and C.h will end up in BC.cphdr
#include <B.h>
#include <C.h>
 
HEADER_END();
 
// what follows is not dumped to a header file

If you specify the “#” string in the start directive, the types which follow will be dumped to the ‘this’ header. This is a special header which lives in the current project, so that you can pass the Profiler project to a colleague and it will already contain the necessary types without having to send extra files.

Back to the importing process, we click on ‘Import’ and that’s it. If Clang encounters C++ errors, we can fix them thanks to the diagnostic information:

Diagnostic information

We can explore the created header file from the ‘Explore’ tab.

Explore header

Now let’s use the header to analyze a PE file inside of a Zip archive.

Add structure to layout

Please notice that I’m adding the types with a packing of 1: PE structures are pragma packed to 1.

What you see applied to the hex view, is a layout. In a layout you can insert structures or intervals (a segment of data with a description and a color).

A layout can even be created programmatically and be attached to a hex view as we’ll see in some other post. The implementation of layouts in the Profiler is quite cool, because they are standalone objects. Layouts are not really bound to a hex view: a view just chooses to be attached to a layout. This means that you can share a single layout among different hex views and changes will reflect in all attached views.

Multi-view layout

And while I didn’t mention it, the table view below on the left is the layout inspector. Its purpose is to let you inspect the structures associated to a layout at a particular position. Since layouts allow for overlapping structures, the inspector shows all structures associated in the current range.

Multi-structure inspection

But what if you go somewhere else and return to the hex view? The layout will be gone. Of course, you could press Ctrl+Alt+L and re-attach the layout to the view. There are other two options: navigate back or create a bookmark!

Bookmark

The created bookmark when activated will jump to the right entry and associate the layout for us. Remember that changing the name of a layout invalidates the bookmark.

That’s all for now. And we’ve only scraped the surface… :)

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