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64 lines
2.4 KiB
Markdown
64 lines
2.4 KiB
Markdown
ABI - Application Binary Interface
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==================================
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"ABI" describes the low-level interface between an application program and a
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library. Calling conventions, function arguments, return values, struct
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sizes/defines and more.
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[Wikipedia has a longer description](https://en.wikipedia.org/wiki/Application_binary_interface)
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## Upgrades
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In the vast majority of all cases, a typical libcurl upgrade does not break
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the ABI at all. Your application can remain using libcurl just as before,
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only with less bugs and possibly with added new features. You need to read
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the release notes, and if they mention an ABI break/soname bump, you may have
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to verify that your application still builds fine and uses libcurl as it now
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is defined to work.
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## Version Numbers
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In libcurl land, you really can't tell by the libcurl version number if that
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libcurl is binary compatible or not with another libcurl version.
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## Soname Bumps
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Whenever there are changes done to the library that will cause an ABI
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breakage, that may require your application to get attention or possibly be
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changed to adhere to new things, we will bump the soname. Then the library
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will get a different output name and thus can in fact be installed in
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parallel with an older installed lib (on most systems). Thus, old
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applications built against the previous ABI version will remain working and
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using the older lib, while newer applications build and use the newer one.
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During the first seven years of libcurl releases, there have only been four
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ABI breakages.
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We are determined to bump the SONAME as rarely as possible. Ideally, we
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never do it again.
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## Downgrades
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Going to an older libcurl version from one you're currently using can be a
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tricky thing. Mostly we add features and options to newer libcurls as that
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won't break ABI or hamper existing applications. This has the implication
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that going backwards may get you in a situation where you pick a libcurl that
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doesn't support the options your application needs. Or possibly you even
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downgrade so far so you cross an ABI break border and thus a different
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soname, and then your application may need to adapt to the modified ABI.
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## History
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The previous major library soname number bumps (breaking backwards
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compatibility) have happened the following times:
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0 - libcurl 7.1, August 2000
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1 - libcurl 7.5 December 2000
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2 - libcurl 7.7 March 2001
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3 - libcurl 7.12.0 June 2004
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4 - libcurl 7.16.0 October 2006
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