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

[Tom Stellard via cfe-dev]

On 6/26/21 3:28 AM, Dimitry Andric 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?
> 
> 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?
> 

New functions don't trigger an ABI check error.  The things I've seen
it flag in the past are: function signature changes, struct size changes,
and enum value changes.

-Tom

> E.g., what are the criteria for bumping the version?
> 
> -Dimitry
>