gcc10 cxx11 abi issue with CLING

[dan131riley]

DataFormats/FWLite/test/triggernames_cint.C is failing in gcc10 IBs with the error

IncrementalExecutor::executeFunction: symbol '_ZNK3edm12TriggerNames4sizeEv' unresolved while linking function '_GLOBAL__sub_I_cling_module_10'!
You are probably missing the definition of edm::TriggerNames::size() const
Maybe you need to load the corresponding shared library?
size = 47268205522688

The problem appears to be a change in cxx11 ABI propagation in gcc10. edm::TriggerNames::size() is defined as:

typedef std::vector<std::string> Strings;
Strings::size_type size() const;

If I run 'nm -C' on the resulting library and look for the routine, I get

000000000000aa50 T edm::TriggerNames::size[abi:cxx11]() const

and CLING doesn't find it. If I change the definition to:

std::vector<int>::size_type size() const;

I get

000000000000aa50 T edm::TriggerNames::size() const

and the test runs fine. If I do

std::vector<std::string>::size_type size() const;
std::vector<int>::size_type TriggerNames::size() const { return triggerNames_.size(); }

it compiles ok but fails at link time with a linker undefined reference

TriggerResultsByName.cc:(.text+0x8ee): undefined reference to `edm::TriggerNames::size[abi:cxx11]() const'

So in gcc10, std::vector<std::string>::size_type and std::vector<int>::size_type are the same type to the compiler but have different ABI linkage, and CLING doesn't know about this.

This appears to be new behavior in gcc10. but I haven't found it documented. It also seems weird to me, and may bite us in other ways.

[cmsbuild]

A new Issue was created by @dan131riley Dan Riley.

@Dr15Jones, @dpiparo, @silviodonato, @smuzaffar, @makortel, @qliphy can you please review it and eventually sign/assign? Thanks.

cms-bot commands are listed here

[makortel]

assign core

[cmsbuild]

New categories assigned: core

@Dr15Jones,@smuzaffar,@makortel you have been requested to review this Pull request/Issue and eventually sign? Thanks

[Dr15Jones]

Weird, I thought return values are not part of the ABI since they can be ignored.

[makortel]

Adding @vgvassilev in case the "old" version of LLVM (5) used for rootcling could play any role (we encountered a case where a piece of code failed to compile with rootcling in #30906).

[vgvassilev]

After a chat with @zygoloid we believe it is a bug in gcc. If T and U are the same type, then T size() const and U size() const are the same function, and must have the same mangling.

We should report this bug to gcc, if it was not reported.

[vgvassilev]

That's the godbolt link. The bug is present from gcc10 onward. Clang seems to agree with gcc9.

[makortel]

@dan131riley Could you follow up with gcc (if you didn't yet)?

In the meantime, the issue is worked round in #32528.

[dan131riley]

@makortel yes I'll followup with a gcc bug report, probably tomorrow

[dan131riley]

submitted https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98481

[makortel]

@dan131riley Given the (already merged) workaround #32528, is it still beneficial to keep this issue open or could we close it?

[dan131riley]

We have a workaround and an open bug report with the gcc developers, so there's no need to keep this ticket open.

[makortel]

+1

[cmsbuild]

This issue is fully signed and ready to be closed.

[dan131riley]

gcc devs agreed it’s a bug, fix and regression test are now on the gcc trunk.