how did BSD libc make binary compatibility promise beetween freebsd version?

[Matthew Seaman]

On 19/08/2016 15:39, kang joni wrote:
> As the title suggest, I usually compile my linux code from old debian
> squeeze to run for either centos 6 or debian wheezy and these distros
> later version and adjusting some app rpath and clang libc++ runtime
> libs to point local relative file path via origin method. Is there any
> easy guideline to follow when working on bsd libc version? I feels do
> not like on how libc emulation method as it seems complex
> configuration fine tuning for starter BSD like me.

FreeBSD promises /forward/ ABI compatibility for the whole of one major
version's lifetime.  That means that if you want to run your application
on a mixture of 10.1, 10.2 and 10.3 machines, then you should compile it
under 10.1.

This is modified by the use of versioned symbols in recent releases:
effectively libc contains multiple copies of certain symbols where there
have been ABI-breaking changes, so you can run something compiled for
10.1 on an 11.0 system and dynamically link against the
same copy of libc.  The use of versioned symbols applies to the most
important shared libraries provided by the base system, but not all, and
it doesn't apply to any shared libraries provided from the ports as far
as I am aware.  So while it will normally 'just work' for safeties' sake
you'll still need to test cross compatibility and may still need to
install compat libraries or compile code separately for each different
major OS version.

See: https://people.freebsd.org/~deischen/symver/freebsd_versioning.txt
for a much fuller explanation of symbol versioning.

	Cheers,

	Matthew

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