Why rebase dlls

Move these libraries near the system DLLs msvcrt. For more information, see the Dependency Walker website. This is an example heap configuration used by Sun GlassFish Enterprise Server for heavy server-centric applications, on Windows, as set in the domain.

If you attempt to run the. Then the loader maps the first DLL to the 0x memory address. But now, when the loader attempts to map the second DLL into the process' address space, it can't possibly map it at the module's preferred base address. It must relocate the DLL module, placing it somewhere else. As seen, both DLLs have the same base address and only one will be loaded at that address and the other needs to be reallocated.

Relocating an executable or DLL module is an absolutely horrible process, and you should take measures to avoid it. Let's see why. Suppose that the loader relocates the second DLL to address 0x In that case, the code that changes the " i " variable to 5 should be:. If the code from the file's image without changing the address is allowed to execute, some 4-byte value in the first DLL module will be overwritten with the value 5. This can't possibly be allowed. The loader must somehow fix this code.

There will be multiple copies in the page file. The cost of this dynamic relocation is what rebasing attempts to avoid. Consequently, a DLL will load at its preferred base address only in the case of an astonishing coincidence. Does a DLL being loaded away from its preferred base address incur a relocation penalty?

But what if the DLL is relocated for some other reason? For example, it could be that the ASLR-chosen base address is not available in the process, because the process already allocated something else at that location. In that case, a traditional relocation must take place, and you pay the relocation penalty. These large dlls will magnify the effects. They are so large that I had to write a program to produce the source code for them. There is no installer for the program. Just unzip into a folder.

If you copy additional dlls into the same folder, these will also become available to the tool. Start up the tool, select the two dlls and load them. The tool makes use of published APIs, when applicable, but also uses some unpublished kernel interfaces to obtain information or request system modifications. The tool understands the differences between versions of the operating system and adjusts to those differences.

The tool will run on Windows and above. The bit version only supports bit dlls, but it can be run on x86 or x64 systems. The bit version supports 64 bit dlls and may only be run on x64 systems. TMurgent has a bunch of tools on this page. Usually they are free, unless you are a Software Vendor. Tools for performance have a segregated list here. Site Login Log in Register. Log in Username. Remember Me.

Log in. Click for short video. New E-book. Get The Book. Click for video. New Class. Updated Training Class for This is an intense hour hands-on class.