How to compare binary images of the same project builds

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SUMMARY

Sometimes you may need to compare the build images (EXE, DLL, etc.) of the same project that were built at different times. Since the images contain time and date stamps, a plain file compare reports the differences between the images. You can use the DUMPBIN utility to generate the correct file compare.

MORE INFORMATION

The time and date stamps can be removed from the built image without removing relevant information (code and data) using the /RAWDATA switch available in the DUMPBIN utility. Any file compare utility can then be used on the DUMPBIN output as follows:
   DUMPBIN  /RAWDATA  MyApp.EXE > first.txt
				
If Myapp.exe is built again at a different time, then use DUMPBIN as follows:
   DUMPBIN  /RAWDATA  MyApp.EXE > second.txt
				
You can now compare first.txt and second.txt using a file compare utility like:
       FC /B first.txt second.txt
				
Run DUMPBIN in the resident directory of the image. The above procedure applies to the Release build only because the Debug build records the time and date stamp on the images (irrespective of /Zi or /Z7) and DUMPBIN does not remove this information. If the predefined macros __DATE__ and __TIME__ are used in the source, the time and date stamp recorded in the images will not be removed by DUMPBIN for the Release build. Under these circumstances, you may use the /DISASM switch. However, the /DISASM switch removes the time and date stamp, as well as the initialized data. This means that you will not get a true image compare.

NOTE: There is no guarantee that Visual C++ will generate the same binary image when building the same source files on successive builds. However, you are guaranteed that the EXE (or DLL) will behave in precisely the same manner under execution, all other things being equal. Compile and link options and link order play a role in whether two binary images will compare equally.

If you follow the procedures outlined above and the two images compare equally, then the images are the same. If the two images do not compare equally, then there is still uncertainty as to whether the images are the same or not.

The resource section of the executable contains date/time stamps. In the resource section of the executable, there is a header for each type of resource (for example, string table, dialog, icon). Each of these headers contains a date/time stamp.

Use the Microsoft Portable Executable and Common Object File Format Specification from the MSDN Library to alter the date/time stamps so that they won't be a factor in the comparison or ignore the resources section in the comparison.

To identify the section containing the differences, run the WinDiff utility shipped with Visual C++:
   WINDIFF first.txt second.txt
				
The section containing the differences will start with a line similar to the following (although the number may be different):
   RAW DATA #5
				
Then, compare this with the output from the following:
   dumpbin /headers MyApp.exe
				
You should find a header that starts with the following:
   SECTION HEADER #5
      .rsrc name
				
Because the section number matches the section with the differences in the raw data (in this example, the section number is 5), then the differences occur in the section named ".rsrc". This is the name of the resource section.

The Export Directory Table has a date/time stamp as well. This is typically located in the .rdata section (Visual C++ 4.2 and later) or the .edata section (earlier than Visual C++ 4.2). This table exists only if you export symbols from the PE image.

The Import Directory Table also has a date/time stamp. This is typically located in the .idata section. One of these tables exists for each DLL to which the image refers. This date/time stamp is zero unless the image is bound. Once the image is bound, the date/time stamp is set to the date/time stamp of the DLL from where the symbols are imported.

Once again, please refer to the Microsoft Portable Executable and Common Object File Format Specification in the MSDN Library for information on how to locate the date/time information in an image.

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Article ID: 164151 - Last Review: October 26, 2007 - Revision: 3.1
APPLIES TO
  • Microsoft Visual C++ 2.0 Professional Edition
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