View source for 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:

=={{anchor|DCSS}}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 [[Library (computer science)|shared libraries]] loadable in the system. 

IBM [[VM (operating system)|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 [[Dynamic-link library|DLL]]s by the loader. 

Some security extensions to [[Linux]]/[[X86 architecture|x86]] use rebasing to force the use of code addresses below <code>0x00ffffff</code> in order to introduce a <code>0x00</code> byte into all code pointers;{{cn|reason=I'm not disputing this, but I think a couple of sources discussing this in better details would be interesting here for some readers|date=July 2022}} This eliminates a certain class of [[buffer overflow]] security problems related to improper checking of [[null-terminated string]]s, common in the [[C (programming language)|C]] [[programming language]].

==Other uses==
* Rebasing is the act of moving [[changeset]]s to a different [[Branching (software)|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 (software)|Git]] and [[Darcs]] do this (but Darcs extends the concept and calls it "patch commutation").
* The [[daylight saving time]] (DST) rebasing tool TZMOVE.EXE contained in [[Microsoft Exchange Server|Microsoft Exchange]] and [[Microsoft Outlook|Outlook]] 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==
* {{cite book |author-last=Levine |author-first=John R. |author-link=John R. Levine |title=Linkers and Loaders |date=2000 |orig-year=October 1999 |edition=1 |publisher=[[Morgan Kaufmann]] |series=The Morgan Kaufmann Series in Software Engineering and Programming |location=San Francisco, USA |isbn=1-55860-496-0 |oclc=42413382 |pages=218 |url=https://www.iecc.com/linker/ |access-date=2020-01-12 |url-status=live |archive-url=https://archive.today/20121205032107/http://www.iecc.com/linker/ |archive-date=2012-12-05}} Code: [https://archive.today/20200114225034/https://linker.iecc.com/code.html][ftp://ftp.iecc.com/pub/linker/]{{dead link|date=May 2025|bot=medic}}{{cbignore|bot=medic}} Errata: [https://linker.iecc.com/<!-- https://archive.today/20200114224817/https://linker.iecc.com/ 2020-01-14 -->]
* {{Cite web |url=https://devblogs.microsoft.com/oldnewthing/20041217-00/?p=36953 |author-first=Raymond |author-last=Chen |author-link=Raymond Chen (Microsoft) |date=2004-12-17 |title=How did Windows 95 rebase DLLs? |work=The Old New Thing}}
* {{Cite web |title=Rebasing Win32 DLLs |author-first=Thiadmer |author-last=Riemersma |date=2000-12-01 |url=http://drdobbs.com/184416272 |work=[[Dr. Dobb's Journal]]}}
* {{Cite web |title=Optimizing DLL Loads|author=Mark Baker |date=2004-03-25 |url=http://drdobbs.com/184416922 |work=[[Dr. Dobb's Journal]]}}
* {{Cite journal |journal=[[MSDN Magazine]] |title=Improving Application Startup Time |author-first=Claudio |author-last=Caldato |url=http://msdn.microsoft.com/en-gb/magazine/cc163655.aspx#S6 |date=February 2006 |publisher=[[Microsoft Corporation]]}}
* {{Cite journal |journal=[[MSDN Magazine]] |title=The Performance Benefits of NGen |author-first=Surupa |author-last=Biswas |url=http://msdn.microsoft.com/en-us/magazine/cc163610.aspx#S5 |date=May 2006 |publisher=[[Microsoft Corporation]]}}
* {{Cite journal |journal=[[MSDN Magazine]] |title=An In-Depth Look into the Win32 Portable Executable File Format, Part 2 |author-first=Matt |author-last=Pietrek |author-link=Matt Pietrek |url=http://msdn.microsoft.com/en-us/magazine/cc301808.aspx |date=March 2002 |publisher=[[Microsoft Corporation]]}}
* {{Cite web |title=Rebasing Win32 DLLs: The Whole Story |author-first=Rüdiger R. |author-last=Asche |date=1995-09-18 |url=http://hyper.sunjapan.com.cn/~hz/win32/pagetest.htm |url-status=dead |archive-url=https://web.archive.org/web/20110707022420/http://hyper.sunjapan.com.cn/~hz/win32/pagetest.htm |archive-date=2011-07-07}}
* {{Cite book |title=Debugging applications: Microsoft |series=Microsoft programming series |author-first=John |author-last=Robbins |publisher=[[Microsoft Press]] |date=2000 |isbn=978-0-7356-0886-3 |pages=34{{ndash}}36}}
* {{Cite web |url=https://community.broadcom.com/symantecenterprise/communities/community-home/librarydocuments/viewdocument?DocumentKey=3d2a3ec7-0747-4add-a56d-809c3e54ff97&CommunityKey=1ecf5f55-9545-44d6-b0f4-4e4a7f5f5e68&tab=librarydocuments |date=2006-08-14 |title=Dynamic Linking in Linux and Windows, part two |author-first1=Reji |author-last1=Thomas |author-first2=Bhasker |author-last2=Reddy |publisher=[[Symantec Corp]]}}

[[Category:Computer libraries]]