[llvm-dev] ABI change in LLVM 7.0.x release

Kristina Brooks via llvm-dev llvm-dev at lists.llvm.org
Wed Dec 5 06:54:40 PST 2018


While on topic of ABI changes, could I request that this (only the first
part which bumped the constant number up for OS targets) be merged into
an ABI breaking release?


This is only the LLVMSupport part of the patch, the Clang half depends on
it but that is more of a feature thing so it's better left for 8.x.x. I'm
mentioning this because there was some confusion w/r Debian merging this
patch into their 7.x.x fork before it went into trunk which caused ABI
breakage for anyone who relied on the last enum member to determine
the size.

Thank you.
- Kristina

Hans Wennborg via llvm-dev wrote:
> On Tue, Dec 4, 2018 at 7:43 PM Tom Stellard <tstellar at redhat.com> wrote:
>> Hi,
>> Fixing http://llvm.org/PR39427 in the release_70 branch, will change
>> the ABI of a clang built libLLVM-7.so so that it is no longer compatible
>> with the 7.0.0 release.  libLLVM-7.so built by gcc will not be affected
>> by this fix.
>> Changing the ABI is something we aren't supposed to do in stable releases,
>> but this fixes an ABI difference between clang and gcc built
>> libLLVM-7.so that is impacting many users, including Linux distributions,
>> so an ABI change for clang only seems like the least bad solution in this case.
>> I am proposing that we hold this fix out of 7.0.1 and instead ship it in
>> a special 7.0.2 (or maybe 7.1.0 ?) release, so that users that want to
>> are still able to get all the bug-fixes without the ABI changes.
>> How does this sound to everyone?
> I think this sounds reasonable. The important thing is that the fix
> gets shipped, and if we do e.g. both 7.0.1 and 7.0.2 (I'm not sure
> what version numbers would be best to use) that should hopefully serve
> everyone well.
> Thanks,
> Hans
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