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diff --git a/docs/libcurl/ABI.md b/docs/libcurl/ABI.md new file mode 100644 index 000000000..39134a1ae --- /dev/null +++ b/docs/libcurl/ABI.md @@ -0,0 +1,63 @@ +ABI - Application Binary Interface +================================== + + "ABI" describes the low-level interface between an application program and a + library. Calling conventions, function arguments, return values, struct + sizes/defines and more. + + [Wikipedia has a longer description](https://en.wikipedia.org/wiki/Application_binary_interface) + +## Upgrades + + In the vast majority of all cases, a typical libcurl upgrade does not break + the ABI at all. Your application can remain using libcurl just as before, + only with less bugs and possibly with added new features. You need to read + the release notes, and if they mention an ABI break/soname bump, you may have + to verify that your application still builds fine and uses libcurl as it now + is defined to work. + +## Version Numbers + + In libcurl land, you really can't tell by the libcurl version number if that + libcurl is binary compatible or not with another libcurl version. + +## Soname Bumps + + Whenever there are changes done to the library that will cause an ABI + breakage, that may require your application to get attention or possibly be + changed to adhere to new things, we will bump the soname. Then the library + will get a different output name and thus can in fact be installed in + parallel with an older installed lib (on most systems). Thus, old + applications built against the previous ABI version will remain working and + using the older lib, while newer applications build and use the newer one. + + During the first seven years of libcurl releases, there have only been four + ABI breakages. + + We are determined to bump the SONAME as rarely as possible. Ideally, we + never do it again. + +## Downgrades + + Going to an older libcurl version from one you're currently using can be a + tricky thing. Mostly we add features and options to newer libcurls as that + won't break ABI or hamper existing applications. This has the implication + that going backwards may get you in a situation where you pick a libcurl that + doesn't support the options your application needs. Or possibly you even + downgrade so far so you cross an ABI break border and thus a different + soname, and then your application may need to adapt to the modified ABI. + +## History + + The previous major library soname number bumps (breaking backwards + compatibility) have happened the following times: + + 0 - libcurl 7.1, August 2000 + + 1 - libcurl 7.5 December 2000 + + 2 - libcurl 7.7 March 2001 + + 3 - libcurl 7.12.0 June 2004 + + 4 - libcurl 7.16.0 October 2006 |