Rebasing

This article is about computing activities. For the use of a new base for the CPI, see consumer price index.

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

• Levine, John R. (2000) [October 1999]. Linkers and Loaders. The Morgan Kaufmann Series in Software Engineering and Programming (1 ed.). San Francisco, USA: Morgan Kaufmann. p. 218. ISBN 1-55860-496-0. OCLC 42413382. Archived from the original on 2012-12-05. Retrieved 2020-01-12. Code: [1][2] Errata: [3]
• Chen, Raymond (2004-12-17). "How did Windows 95 rebase DLLs?". The Old New Thing.
• Riemersma, Thiadmer (2000-12-01). "Rebasing Win32 DLLs". Dr. Dobb's Journal.
• Mark Baker (2004-03-25). "Optimizing DLL Loads". Dr. Dobb's Journal.
• Caldato, Claudio (February 2006). "Improving Application Startup Time". MSDN Magazine. Microsoft Corporation.
• Biswas, Surupa (May 2006). "The Performance Benefits of NGen". MSDN Magazine. Microsoft Corporation.
• Pietrek, Matt (March 2002). "An In-Depth Look into the Win32 Portable Executable File Format, Part 2". MSDN Magazine. Microsoft Corporation.
• Asche, Rüdiger R. (1995-09-18). "Rebasing Win32 DLLs: The Whole Story". Archived from the original on 2011-07-07.
• Robbins, John (2000). Debugging applications: Microsoft. Microsoft programming series. Microsoft Press. pp. 34–36. ISBN 978-0-7356-0886-3.
• Thomas, Reji; Reddy, Bhasker (2006-08-14). "Dynamic Linking in Linux and Windows, part two". Symantec Corp.