Rebasing

In computing, rebasing is one of the following:

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; 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 Microsoft 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

Further reading

• John R. Levine (2000). Linkers and loaders. The Morgan Kaufmann Series in Software Engineering and Programming. Morgan Kaufmann. p. 218. ISBN 978-1-55860-496-4. 
• Raymond Chen (2004-12-17). "How did Windows 95 rebase DLLs?". The Old New Thing. 
• Thiadmer Riemersma (2000-12-01). "Rebasing Win32 DLLs". Dr. Dobb's Journal. 
• Mark Baker (2004-03-25). "Optimizing DLL Loads". Dr. Dobb's Journal. 
• Claudio Caldato (February 2006). "Improving Application Startup Time". MSDN Magazine. Microsoft Corporation. 
• Surupa Biswas (May 2006). "The Performance Benefits of NGen". MSDN Magazine. Microsoft Corporation. 
• Matt Pietrek (March 2002). "An In-Depth Look into the Win32 Portable Executable File Format, Part 2". MSDN Magazine. Microsoft Corporation. 
• Ruediger R. Asche (1995-09-18). "Rebasing Win32 DLLs: The Whole Story". 
• John Robbins (2000). Debugging applications: Microsoft. Microsoft programming series. Microsoft Press. pp. 34–36. ISBN 978-0-7356-0886-3. 
• Reji Thomas and Bhasker Reddy (2006-08-14). "Dynamic Linking in Linux and Windows, part two". Symantec Corp.