llvm dev - Dec 2018 - ABI change in LLVM 7.0.x release

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?

Thanks,
Tom

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

On Tue, Dec 4, 2018, 10:43 Tom Stellard via llvm-dev <
llvm-dev at lists.llvm.org wrote:
> 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.
>
I think we should go with 7.1.0 instead of 7.0.2, since 7.1.0 looks unusual
as opposed to 7.0.2, which looks like business as usual. This will help
people to notice that the ABI changed.
>
> How does this sound to everyone?
>
Sounds reasonable to me.

Jacob Lifshay
>
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On 12/5/18 4:06 AM, Jacob Lifshay via llvm-dev wrote:
On Tue, Dec 4, 2018, 10:43 Tom Stellard via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org> wrote:
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.
I think we should go with 7.1.0 instead of 7.0.2, since 7.1.0 looks unusual as
opposed to 7.0.2, which looks like business as usual. This will help people to
notice that the ABI changed.

+1 - ABI changes should increment the minor version number.

 -Hal

How does this sound to everyone?
Sounds reasonable to me.

Jacob Lifshay



_______________________________________________
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llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory
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Hi,

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?

https://reviews.llvm.org/rL347832

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
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
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On 12/05/2018 02:06 AM, Jacob Lifshay wrote:
> On Tue, Dec 4, 2018, 10:43 Tom Stellard via llvm-dev <llvm-dev at
lists.llvm.org <mailto:llvm-dev at lists.llvm.org> wrote:
> 
>     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.
> 
> I think we should go with 7.1.0 instead of 7.0.2, since 7.1.0 looks unusual
as opposed to 7.0.2, which looks like business as usual. This will help people
to notice that the ABI changed.
> 
This was my initial thought as well, but I'm not sure if this is technically
possible with our current system.  The shared object only contains the
major version in its name, so we would need some other changes.  I can look
into how feasible this would be.

-Tom
> 
>     How does this sound to everyone?
> 
> Sounds reasonable to me.
> 
> Jacob Lifshay
>