1 ABI - Application Binary Interface 2 ================================== 3 4 "ABI" describes the low-level interface between an application program and a 5 library. Calling conventions, function arguments, return values, struct 6 sizes/defines and more. 7 8 [Wikipedia has a longer description](https://en.wikipedia.org/wiki/Application_binary_interface) 9 10 Upgrades 11 -------- 12 13 In the vast majority of all cases, a typical libcurl upgrade does not break 14 the ABI at all. Your application can remain using libcurl just as before, 15 only with less bugs and possibly with added new features. You need to read 16 the release notes, and if they mention an ABI break/soname bump, you may have 17 to verify that your application still builds fine and uses libcurl as it now 18 is defined to work. 19 20 Version Numbers 21 --------------- 22 23 In libcurl land, you really can't tell by the libcurl version number if that 24 libcurl is binary compatible or not with another libcurl version. 25 26 Soname Bumps 27 ------------ 28 29 Whenever there are changes done to the library that will cause an ABI 30 breakage, that may require your application to get attention or possibly be 31 changed to adhere to new things, we will bump the soname. Then the library 32 will get a different output name and thus can in fact be installed in 33 parallel with an older installed lib (on most systems). Thus, old 34 applications built against the previous ABI version will remain working and 35 using the older lib, while newer applications build and use the newer one. 36 37 During the first seven years of libcurl releases, there have only been four 38 ABI breakages. 39 40 We are determined to bump the SONAME as rarely as possible. Ideally, we 41 never do it again. 42 43 Downgrades 44 ---------- 45 46 Going to an older libcurl version from one you're currently using can be a 47 tricky thing. Mostly we add features and options to newer libcurls as that 48 won't break ABI or hamper existing applications. This has the implication 49 that going backwards may get you in a situation where you pick a libcurl that 50 doesn't support the options your application needs. Or possibly you even 51 downgrade so far so you cross an ABI break border and thus a different 52 soname, and then your application may need to adapt to the modified ABI. 53 54 History 55 ------- 56 57 The previous major library soname number bumps (breaking backwards 58 compatibility) have happened the following times: 59 60 0 - libcurl 7.1, August 2000 61 62 1 - libcurl 7.5 December 2000 63 64 2 - libcurl 7.7 March 2001 65 66 3 - libcurl 7.12.0 June 2004 67 68 4 - libcurl 7.16.0 October 2006 69
