HOWTO: Use Source Profiler to Profile Dynamic-Link Libraries

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This article was previously published under Q179269

SUMMARY

The Microsoft Visual C++ Help discusses two ways to profile a dynamic-link library (DLL), but it does not indicate when to use each example. This article describes a general-purpose method of profiling DLLs.

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MORE INFORMATION

The first part of the Help on profiling a DLL describes the use of self- profiling DLLs, using the PREP option /OM. Self-profiling DLLs are not necessary, except when profiling DLLs that are dynamically loaded using the LoadLibrary instruction. Use the following batch file example (name it Profdll.bat) to profile a single DLL, accessed with LoadLibrary. Profdll.bat profiles a DLL with the assumption that the .exe file has not been prepared for profiling.

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Sample Batch File

   COPY %1.dll save
   PREP /OM %1.dll
   COPY %1._ll %1.dll
   PROFILE /I %1 /O %1 %2 %3 %4 %5 %6
   COPY save %1.dll
   PREP /M %1
   PLIST %1

If you have a main program (for example, Hearts.exe) that uses a DLL (for example, Cards.dll) and you want to profile only the DLL, you can run the batch file as:

   PROFDLL cards hearts

Note that the command above generates a warning message that the main program has not been prepared for profiling. You can ignore this message.

The second example batch file in the Help shows how to profile multiple DLLs as well as the calling executable. This example profiles an executable named "wingame" and two DLLs named "aliens" and "hiscore":

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Sample Batch File

   PREP /OM /FC wingame.exe aliens.dll hiscore.dll
   PROFILE wingame.exe
   PREP /M  wingame
   PLIST wingame >wingame.out

This method is most effective when the DLLs are loaded at run time, through the use of an import library. The Source Profiler, however, does not report any data for a dynamically loaded DLL if you use function profiling. The maximum number of DLLs that can be profiled this way is:

7 for Visual C++, versions 2.x and 4.x
15 for Visual C++, version 5.0
31 for Visual C++, version 6.0

When you combine import DLLs and LoadLibrary DLLs in a single executable, the Help is unclear about how to handle this. The first method provides information about a single DLL, and the second method does not work for all types of profiling.

You must combine these two methods when considering larger, more complex projects. First, create self-profiling objects for all items in the profile:

   PREP /OM /FT myfile.exe import1.dll loadlib1.dll ...

where "myfile.exe" is the executable program, "import1.dll" is a DLL called through an import library, and "loadlib1.dll" is a DLL called through the LoadLibrary and GetProcAddress functions.

Next, use the first method and copy the _LL files over all DLLs loaded using LoadLibrary:

   copy loadlib1.dll loadlib1.tmp
   copy loadlib1._ll loadlib1.dll

The rest of the procedure is the same as for most profiles:

   PROFILE myfile.exe
   PREP /M myfile
   PLIST myfile >> profile.out

Putting it all together, you can generalize the process as follows:

PREP /OM /[profiling type] exename dllname1 dllname2 ... where [profiling type] is either /FT, /FC, /FV, /LC, or /LV
If a DLL is loaded using LoadLibrary, copy the _LL file over the existing .dll file. You should backup the original DLL, just in case:
```
      copy dllname.dll dllname.tmp
      copy dllname._ll dllname.dll
						
```
where "dllname" is the name of the DLL accessed using LoadLibrary. Note that the _LL file is not created for /LC and /LV profiling types.
Run the remaining PROFILE, PREP, and PLIST steps as outlined above and in the Visual C++ Help.

You should not try to profile a DLL that may have been loaded at run time and dynamically in the same application.

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REFERENCES

Visual C++, version 5.0; Profiling DLLs from a Batch File; Profiling Multiple .dll and .exe Files

URL: mk:@ivt:vccore/F33/D36/S4D19E.HTM URL: mk:@ivt:vccore/F33/D36/S4D19F.HTM

Visual C++, versions 2.0, 2.1, 2.2, 4.0, 4.0a, 4.1, 4.2, 4.2b; search on: "Profiling DLLs from a batch file"; "Profiling multiple .dll and .exe files"

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