Rebasing

Short description: Process of modifying data based on one reference to another

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In computing, rebasing is the process of modifying data based on one reference to another. It can be one of the following:

## Contents

* 1 Shared libraries
* 2 Other uses
* 3 See also
* 4 Further reading

## Shared libraries

Rebasing is the process of creating a shared library image in such a way that it is guaranteed to use virtual memory without conflicting with any other shared libraries loadable in the system.

IBM VM/370 discontinuous saved segments (DCSS) were an early example of this technique, though not called rebasing. The technique is used extensively on Win32 platforms to avoid the overhead of address relocation of system DLLs by the loader.

Some security extensions to Linux/x86 use rebasing to force the use of code addresses below `0x00ffffff` in order to introduce a `0x00` byte into all code pointers;[citation needed] This eliminates a certain class of buffer overflow security problems related to improper checking of null-terminated strings, common in the C programming language.

## Other uses

* Rebasing is the act of moving changesets to a different branch when using a revision control system or in some systems, by synchronizing a branch with the originating branch by merging all new changes in the latter to the former. For example, Git and Darcs do this (but Darcs extends the concept and calls it "patch commutation").
* The mechanism that the Microsoft Exchange or Outlook daylight saving time (DST) rebasing tool TZMOVE.EXE uses to recalculate and reschedule appointment dates that are affected by DST.

## See also

* Relocation (computing)
* Position-independent code
* Portable Executable (PE)
* High memory area (HMA)
* Dynamic dead code elimination

## Further reading

* Linkers and Loaders. The Morgan Kaufmann Series in Software Engineering and Programming (1 ed.). San Francisco, USA: Morgan Kaufmann. 2000. pp. 218. ISBN 1-55860-496-0. OCLC 42413382. https://www.iecc.com/linker/. Retrieved 2020-01-12. Code: [1][2] Errata: [3]
* "How did Windows 95 rebase DLLs?". The Old New Thing. 2004-12-17. http://blogs.msdn.com/b/oldnewthing/archive/2004/12/17/323556.aspx.
* "Rebasing Win32 DLLs". Dr. Dobb's Journal. 2000-12-01. http://drdobbs.com/184416272.
* Mark Baker (2004-03-25). "Optimizing DLL Loads". Dr. Dobb's Journal. http://drdobbs.com/184416922.
* "Improving Application Startup Time". MSDN Magazine (Microsoft Corporation). February 2006. http://msdn.microsoft.com/en-gb/magazine/cc163655.aspx#S6.
* "The Performance Benefits of NGen". MSDN Magazine (Microsoft Corporation). May 2006. http://msdn.microsoft.com/en-us/magazine/cc163610.aspx#S5.
* "An In-Depth Look into the Win32 Portable Executable File Format, Part 2". MSDN Magazine (Microsoft Corporation). March 2002. http://msdn.microsoft.com/en-us/magazine/cc301808.aspx.
* "Rebasing Win32 DLLs: The Whole Story". 1995-09-18. http://hyper.sunjapan.com.cn/~hz/win32/pagetest.htm.
* Debugging applications: Microsoft. Microsoft programming series. Microsoft Press. 2000. pp. 34–36. ISBN 978-0-7356-0886-3.
* "Dynamic Linking in Linux and Windows, part two". Symantec Corp. 2006-08-14. http://www.symantec.com./connect/articles/dynamic-linking-linux-and-windows-part-two.

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