[cfe-dev] RFC: Only change libclang.so SONAME when the ABI changes

[Fāng-ruì Sòng via cfe-dev]

On Sat, Jun 26, 2021 at 3:29 AM Dimitry Andric via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
>
> On 26 Jun 2021, at 06:04, Tom Stellard via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> >
> > I would like to propose that we only change the SONAME of libclang.so
> > (this is the library that contains the C API for clang) when the ABI changes.
> > Currently, we change the SONAME whenever we bump the major version of LLVM,
> > but the C API tends to not change that often.
> >
> > This change will allow operating system maintainers to update the version
> > of libclang.so in their operating system without forcing rebuilds of
> > all programs that depend on it.
> >
> > The steps for implementing this change would be:
> >
> > - Hard-code the SONAME for libclang.so to libclang.so.13 (which is the current
> > SONAME).
> > - Hard-code the symbol versions to LLVM_13 (which is the current symbol version)
> >  for all existing symbols.
> > - Add a test case that checks if a new symbol has been added and ensures it has
> >  the correct symbol version.
> > - Add a buildbot that uses abi-compliance-checker[1] to ensure that ABI/API does
> >  not change unexpectedly.
> > - The next time the ABI of libclang.so is changed, the SOANME will be updated to
> >  libclang.so.$LLVM_MAJOR_VERSION.
> >
> > What do you think?

Is there an estimate how many packages use libclang.so ?

Symbol versioning seems fine for Linux glibc and FreeBSD.

> This sounds like a good plan in general (not only for libclang :), but
> how strict is this ABI check? Does *any* change (even like adding a new
> function) trigger an ABI check error?
>
> E.g., what are the criteria for bumping the version?
>
> -Dimitry

Sounds fine for libclang.so. (For C++ libLLVM-13git.so and
libclang-cpp.so, the ABI is changing very frequently, so I don't see
we could avoid DT_SONAME bump.)