crash when protocol buffers are used in .so

[fkusche]

Consider the following foo.cpp:

#include <dlfcn.h>
#include <stdio.h>
#include "p.pb.h"

int main()
{
    void* soHandle = dlopen( "./bar.so", RTLD_NOW );
    if( !soHandle ) {
        fprintf( stderr, "couldn't load bar.so\n" );
        return 1;
    }
    dlclose( soHandle );
    printf( "shutting down protobuf\n" );
    google::protobuf::ShutdownProtobufLibrary();

    return 0;
}

and bar.cpp:

int bar()
{
    return 0;
}

and p.proto:

package FooCfg;
message Msg {
     required int32 dummy = 2;
}

Compile the proto file: protoc --cpp_out=. p.proto
Compile foo to an executable: g++ -fPIC foo.cpp -ofoo -lprotobuf -ldl
Compile bar to a dll: g++ -fPIC -Wl,--unresolved-symbols=ignore-in-shared-libs -shared -o bar.so bar.cpp p.pb.cc -lprotobuf

running foo will produce a segmentation fault in ShutdownProtobufLibrary():

> gdb ./foo
GNU gdb (Debian 7.7.1+dfsg-5) 7.7.1
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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Reading symbols from ./foo...(no debugging symbols found)...done.
(gdb) r
Starting program: /home/pasu/devel/test/foo 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
shutting down protobuf

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff6698441 in ?? ()
(gdb) bt
#0  0x00007ffff6698441 in ?? ()
#1  0x00007ffff7af868b in google::protobuf::ShutdownProtobufLibrary() () from /usr/lib/x86_64-linux-gnu/libprotobuf.so.9
#2  0x00000000004008b1 in main ()
(gdb)

Without dlopening bar.so, there will be no segfault.
Also, when p.pb.cc is not compiled into bar.so.

Is this because of global constructors/destructors being executed?
How can this be solved?

[KjellKod]

@fkusche did you find out what it was? Any work around? I believe a project that I am working on is experiencing a very similar issue.

If we use .so then we see this crash. If we create it as a .a (static) then it doesn't happen.

[fkusche]

@KjellKod sorry for the late answer. No I did not find out anything more, unfortunately.

[xfxyjwf]

As protobuf has used some global variables, linking protobuf dynamically with dlopen across several modules are very problematic. I'm not aware of any good solution here.

[LocutusOfBorg]

Hello, if I'm correct this is making the vlc build segfault now
https://trac.videolan.org/vlc/ticket/18329