[Bug c++/80947] New: Different visibility for the lambda and its capture list members with -fvisibility=hidden

[vladz at scylladb dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80947

            Bug ID: 80947
           Summary: Different visibility for the lambda and its capture
                    list members with -fvisibility=hidden
           Product: gcc
           Version: 6.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vladz at scylladb dot com
  Target Milestone: ---

I'm trying to compile a C++14 program using standard g++-6 and g++-7 compilers
coming with Ubuntu 16.04:

g++-6 (Ubuntu/Linaro 6.3.0-18ubuntu2~16.04) 6.3.0 20170519
g++-7 (Ubuntu 7.1.0-5ubuntu2~16.04) 7.1.0

The error I get with both of them is the same.

The issue doesn't reproduce with the
g++ (Ubuntu 5.4.1-2ubuntu1~16.04) 5.4.1 20160904

The issue doesn't reproduce when I use -fvisibility=default.

The error looks as follows:


g++-6 -MD -MT build/release/gms/versioned_value.o -MF
build/release/gms/versioned_value.o.d -std=gnu++1y -g  -Wall -Werror
-fvisibility-inlines-hidden -fvisibility=hidden  -pthread
-I/home/vladz/work/urchin/seastar -I/home/vladz/work/urchin/seastar/fmt
-I/home/vladz/work/urchin/seastar/build/release/gen  -march=nehalem -fconcepts
-Ifmt -DBOOST_TEST_DYN_LINK -Wno-overloaded-virtual -DFMT_HEADER_ONLY
-DHAVE_GCC6_CONCEPTS -DHAVE_HWLOC -DHAVE_NUMA -DHAVE_LZ4_COMPRESS_DEFAULT  -O2
-I/usr/include/jsoncpp -DBOOST_TEST_DYN_LINK  -Wno-maybe-uninitialized
-Wno-tautological-compare -Wno-missing-braces
-Wno-error=deprecated-declarations -DHAVE_LIBSYSTEMD=1 -I. -I build/release/gen
-I seastar -I seastar/build/release/gen -c -o
build/release/gms/versioned_value.o gms/versioned_value.cc
In file included from ./utils/exponential_backoff_retry.hh:25:0,
                 from ./sstables/compaction_manager.hh:32,
                 from ./database.hh:67,
                 from ./repair/repair.hh:31,
                 from ./message/messaging_service.hh:34,
                 from gms/versioned_value.cc:39:
/home/vladz/work/urchin/seastar/core/sleep.hh: In instantiation of ‘struct
seastar::sleep(std::chrono::duration<_Rep,
_Period>)::sleeper::sleeper(std::chrono::duration<_Rep, _Period>) [with Clock =
std::chrono::_V2::steady_clock; Rep = long int; Period = std::ratio<1l,
1000l>]::<lambda()>’:
/home/vladz/work/urchin/seastar/core/sleep.hh:48:47:   required from
‘seastar::sleep(std::chrono::duration<_Rep,
_Period>)::sleeper::sleeper(std::chrono::duration<_Rep, _Period>) [with Clock =
std::chrono::_V2::steady_clock; Rep = long int; Period = std::ratio<1l,
1000l>]’
/home/vladz/work/urchin/seastar/core/sleep.hh:52:5:   required from
‘seastar::future<> seastar::sleep(std::chrono::duration<_Rep, _Period>) [with
Clock = std::chrono::_V2::steady_clock; Rep = long int; Period = std::ratio<1l,
1000l>]’
./utils/exponential_backoff_retry.hh:45:36:   required from here
/home/vladz/work/urchin/seastar/core/sleep.hh:48:24: error:
‘seastar::sleep(std::chrono::duration<_Rep,
_Period>)::sleeper::sleeper(std::chrono::duration<_Rep, _Period>) [with Clock =
std::chrono::_V2::steady_clock; Rep = long int; Period = std::ratio<1l,
1000l>]::<lambda()>’ declared with greater visibility than the type of its
field ‘seastar::sleep(std::chrono::duration<_Rep,
_Period>)::sleeper::sleeper(std::chrono::duration<_Rep, _Period>) [with Clock =
std::chrono::_V2::steady_clock; Rep = long int; Period = std::ratio<1l,
1000l>]::<lambda()>::<this capture>’ [-Werror=attributes]
             : tmr([this] { done.set_value(); })
                        ^
cc1plus: all warnings being treated as errors


Error message implies that the visibility of the lambda in question is  greater
than the visibility of the capture list value "this".

Since lambdas are translated into the classes with the operator()(...)  and (it
seems like) captured values are translated into the fields of this class it
looks like for some reason the visibility of that class is higher than the one
of those fields.

Another workaround that would make the error go away is to explicitly use the
__attribute__ ((visibility ("hidden"))) or __attribute__ ((visibility
("default"))) for the sleeper struct.

Attached is an *.ii value generated by g++-6