Created attachment 1255725 [details]
minimal C reproducer extraceted from dbus code

Description of problem:
I run some of our test which use dbus and I found out that valgrinds test are failing on rawhide i386. There are some valgrind errors. And I can see then also in dbus unit tests.
 
==26500== Invalid read of size 4
==26500==    at 0x48A9100: _dbus_atomic_get (dbus-sysdeps-unix.c:2805)
==26500==    by 0x4859171: _dbus_connection_close_if_only_one_ref (dbus-connection.c:2152)
==26500==    by 0x4883340: handle_new_client_fd_and_unlock (dbus-server-socket.c:152)
==26500==    by 0x4883340: socket_handle_watch (dbus-server-socket.c:213)
==26500==    by 0x488FD9D: dbus_watch_handle (dbus-watch.c:758)
==26500==    by 0x10E868: _dbus_loop_iterate (dbus-mainloop.c:827)
==26500==    by 0x10C1EE: setup_connection (refs.c:270)
==26500==    by 0x4C0D6ED: ??? (in /usr/lib/libglib-2.0.so.0.5102.0)
==26500==    by 0x4C0D920: ??? (in /usr/lib/libglib-2.0.so.0.5102.0)
==26500==    by 0x4C0DB30: g_test_run_suite (in /usr/lib/libglib-2.0.so.0.5102.0)
==26500==    by 0x4C0DB5B: g_test_run (in /usr/lib/libglib-2.0.so.0.5102.0)
==26500==    by 0x10A953: main (refs.c:635)
==26500==  Address 0xfec7cbc8 is on thread 1's stack
==26500==  4 bytes below stack pointer

But I found out that problematic line is "__sync_synchronize ()".
So it's not bug in dbus but probably gcc. So I tried the same version of libdbus on fedora 25 and there was not any problem.


Version-Release number of selected component (if applicable):
sh$ rpm -q gcc valgrind
gcc-7.0.1-0.8.fc26.i686
valgrind-3.12.0-3.fc26.i686

How reproducible:
Deterministic on i686

Steps to Reproduce:
1. //Compile attached source code
   gcc -g3 dbus_minimal.c
2. // run the code with valgrind
   valgrind ./a.out


Actual results:
==10957== Memcheck, a memory error detector
==10957== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==10957== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==10957== Command: ./a.out
==10957== 
after inc:0
==10957== Invalid read of size 4
==10957==    at 0x804843C: _dbus_atomic_get (dbus_minimal.c:52)
==10957==    by 0x8048489: main (dbus_minimal.c:63)
==10957==  Address 0xfed38654 is on thread 1's stack
==10957==  4 bytes below stack pointer
==10957== 
after get:1
==10957== 
==10957== HEAP SUMMARY:
==10957==     in use at exit: 0 bytes in 0 blocks
==10957==   total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==10957== 
==10957== All heap blocks were freed -- no leaks are possible
==10957== 
==10957== For counts of detected and suppressed errors, rerun with: -v
==10957== ERROR SUMMARY: 3 errors from 1 contexts (suppressed: 0 from 0)

Expected results:
O error:

Here is an output from fedora rawhide x86_64

==10957== Memcheck, a memory error detector
==10957== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==10957== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==10957== Command: ./a.out
==10957== 
after inc:0
after get:1
==10957== 
==10957== HEAP SUMMARY:
==10957==     in use at exit: 0 bytes in 0 blocks
==10957==   total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==10957== 
==10957== All heap blocks were freed -- no leaks are possible
==10957== 
==10957== For counts of detected and suppressed errors, rerun with: -v
==10957== ERROR SUMMARY: 3 errors from 1 contexts (suppressed: 0 from 0)