Re: ABI compatibility between versions

[Rich Felker <dalias@libc.org>]

On Tue, Feb 26, 2019 at 12:18:06AM +0100, Alexander Revin wrote:
> Hi all,
> 
> I know this have been briefly discussed here before, but still: does
> musl guarantee in some way that executable/library compiled against
> one musl version will work with  another (for example, 1.18 and 1.21)
> ?
> 
> I remember there were concerns against embedding versioning
> information in musl like glibc does, but is there a way to somehow
> ensure the stability between releases?

It guarantees that there is no ABI mismatch. That's not entirely the
same as guaranteeing that it will work. If the application was relying
on a bug in an old version to function, or was poking at some
accidentally-exposed libc internals not defined as a public interface,
it's possible that updating libc.so will expose this bug in the
application.

This is different from the glibc approach, which is to use symbol
versioning to attempt to retain "bug-compatibility" with the version
of glibc the application was linked with. Such a system forces new
application binaries that want to be able to run on systems with old
glibc to link against the old glibc, and thereby get the buggy
behaviors even if they're running on a system without the bugs. Myself
and most of the musl community I'm aware of consider this entirely
unreasonable, and that's why musl doesn't do it.

Rich