[Bug c++/60731] New: dynamic library not getting reinitialized on multiple calls to dlopen()

[Bug c++/60731] New: dynamic library not getting reinitialized on multiple calls to dlopen()

[tim.moloney at mrsl dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

            Bug ID: 60731
           Summary: dynamic library not getting reinitialized on multiple
                    calls to dlopen()
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tim.moloney at mrsl dot com

Created attachment 32518
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32518&action=edit
Example showing failure to initialize a dynamic library after multiple calls to
dlopen().

If a dynamic library is loaded multiple times via dlopen(), subsequent loads do
not correctly initialize static variables under the following conditions:
1) A class/struct with a constructor
2) with an inlined function
3) containing a static variable.
Please run the attached example.
  # tar xf gcc_static_issue.tgz
  # cd gcc_static_issue
  # make
  # ./test_static
  Expected behavior (as on RHEL5, g++ 4.1.2):
  Type 'q' to exit or enter to reload/run the DLL
  count:1

  count:1

  count:1

  count:1

  count:1
  q
  #
Actual behavior (as on RHEL6 and RHEL7beta, g++ 4.4.7 and 4.8.2, respectively):
  Type 'q' to exit or enter to reload/run the DLL
  count:1

  count:2

  count:3

  count:4

  count:5
  q
  #

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-04-02
      Known to work|                            |4.4.7
   Target Milestone|---                         |4.7.4
            Summary|dynamic library not getting |[4.7/4.8/4.9 Regression]
                   |reinitialized on multiple   |dynamic library not getting
                   |calls to dlopen()           |reinitialized on multiple
                   |                            |calls to dlopen()
     Ever confirmed|0                           |1
      Known to fail|                            |4.5.4, 4.8.2, 4.9.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Works up to GCC 4.4, fails since GCC 4.5.  It's not clear what makes the
difference here.

Btw, with LD_DEBUG=all I see


     10389:     opening file=./static.so [0]; direct_opencount=2
     10389:
     10389:     symbol=routine;  lookup in file=./static.so [0]
     10389:     binding file ./static.so [0] to ./static.so [0]: normal symbol
`routine'
count:2

     10389:     opening file=./static.so [0]; direct_opencount=3
     10389:
     10389:     symbol=routine;  lookup in file=./static.so [0]
     10389:     binding file ./static.so [0] to ./static.so [0]: normal symbol
`routine'
count:3

so the dlclose call does nothing.  While in the working case:

     10438:
     10438:     file=./static.so [0];  dynamically loaded by ./test_static [0]
     10438:     file=./static.so [0];  generating link map
     10438:       dynamic: 0x00007ffff6ffede0  base: 0x00007ffff6dfd000   size:
0x00000000002020a8
     10438:         entry: 0x00007ffff6dfdb10  phdr: 0x00007ffff6dfd040  phnum:
                 7
....
     10438:     calling init: ./static.so
     10438:
     10438:     opening file=./static.so [0]; direct_opencount=1
     10438:
     10438:     symbol=routine;  lookup in file=./static.so [0]
     10438:     binding file ./static.so [0] to ./static.so [0]: normal symbol
`routine'
count:1
     10438:
     10438:     calling fini: ./static.so [0]
     10438:
     10438:
     10438:     file=./static.so [0];  destroying link map

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
We hit

void
_dl_close (void *_map)
{
  struct link_map *map = _map;

  /* First see whether we can remove the object at all.  */
  if (__builtin_expect (map->l_flags_1 & DF_1_NODELETE, 0))
    {
      assert (map->l_init_called);
      /* Nope.  Do nothing.  */
      return;

the DF_1_NODELETE flag is set already after the first dlopen call which sets
it via do_lookup_x for the STB_GNU_UNIQUE symbol _ZGVZ16make_static_stayvE3smp

                  if (map->l_type == lt_loaded)
                    /* Make sure we don't unload this object by
                       setting the appropriate flag.  */
                    ((struct link_map *) map)->l_flags_1 |= DF_1_NODELETE;

so this either points to a "bad" design on the guard code for initializing
'smp' or to a weakness in the dynamic loader which doesn't handle unloading
of objects which define any(?) STB_GNU_UNIQUE symbol.  Note the above is
guarded with

              if ((type_class & ELF_RTYPE_CLASS_COPY) != 0)
                enter (entries, size, new_hash, strtab + sym->st_name, ref,
                       undef_map);
              else
                {
                  enter (entries, size, new_hash, strtab + sym->st_name, sym,
                         map);

                  if (map->l_type == lt_loaded)
                    /* Make sure we don't unload this object by
                       setting the appropriate flag.  */
                    ((struct link_map *) map)->l_flags_1 |= DF_1_NODELETE;
                }

thus if this were referenced via a copy relocation it would work.

Jason?

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Right, it was a deliberate choice in ld.so to suppress dlclose of DSOs that use
STB_GNU_UNIQUE, which causes problems with some code that relies on
reinitialization with dlclose/dlopen.  As Ian says in

http://gcc.gnu.org/ml/gcc-help/2011-05/msg00450.html

this seems excessive; you only need to avoid unloading files that are
satisfying symbol references in another DSO.  But I guess checking for that was
deemed too slow.

If you're using the gold linker, you can link with --no-gnu-unique to avoid the
use of STB_GNU_UNIQUE.

I suppose I should add a compiler flag to turn it off, too...

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Thus this is a bug in the dynamic loader as well.  Please file a bug against
glibc on sourceware.org/bugzilla.

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |MOVED

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
And actually it might be considered a non-bug in GCC but a consequence of
implementing a requirement.  Jason posted a patch that implements a workaround
for the dynamic linker issue.

Closing as moved - please open a bugreport against glibc.

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Mon Apr  7 13:27:39 2014
New Revision: 209186

URL: http://gcc.gnu.org/viewcvs?rev=209186&root=gcc&view=rev
Log:
    PR c++/60731
    * common.opt (-fno-gnu-unique): Add.
    * config/elfos.h (USE_GNU_UNIQUE_OBJECT): Check it.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/common.opt
    trunk/gcc/config/elfos.h
    trunk/gcc/doc/invoke.texi

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Mon Apr  7 13:27:45 2014
New Revision: 209187

URL: http://gcc.gnu.org/viewcvs?rev=209187&root=gcc&view=rev
Log:
    PR c++/60731
    * lib/gcc-dg.exp (dg-build-dso): New.
    (gcc-dg-test-1): Handle dg-do-what "dso".
    * lib/target-supports.exp (add_options_for_dlopen): New.
    (check_effective_target_dlopen): Use it.
    * g++.dg/dso/dlclose1.C: New.
    * g++.dg/dso/dlclose1-dso.cc: New.

Added:
    trunk/gcc/testsuite/g++.dg/dso/
    trunk/gcc/testsuite/g++.dg/dso/dlclose1-dso.cc
    trunk/gcc/testsuite/g++.dg/dso/dlclose1.C
Modified:
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/lib/gcc-dg.exp
    trunk/gcc/testsuite/lib/target-supports.exp

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[neleai at seznam dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

Ondrej Bilka <neleai at seznam dot cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |neleai at seznam dot cz

--- Comment #9 from Ondrej Bilka <neleai at seznam dot cz> ---
I started to looking what STB_UNIQUE purpose is so I have several questions.

First does suggestion below really work?
http://gcc.gnu.org/ml/gcc-help/2011-05/msg00450.html

Say you have foo.so with unique symbol foo and function 

bar *getfoo() {
  return (void *) &foo;
}

which gets loaded and unloaded like

void *h = dlopen("foo.so",RTLD_NOW);
bar *p1 = dlsym(h,"getfoo")();
dlclose(h);
foo->baz();
h = dlopen("foo.so",RTLD_NOW);
bar *p2 = dlsym(h,"getfoo")();
dlclose(h);

Are p1 and p2 supposed to point to same object?
Also is foo->baz(); legal or not? If its so we cannot call destructors.

There could be fix to add zombie state where we call destructors but not free
memory so we can reinitialize object at same address but I need to know that
calling destructor is always intended behaviour.

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Ondrej Bilka from comment #9)
> First does suggestion below really work?
> http://gcc.gnu.org/ml/gcc-help/2011-05/msg00450.html

I don't see why it wouldn't.

> void *h = dlopen("foo.so",RTLD_NOW);
> bar *p1 = dlsym(h,"getfoo")();
> dlclose(h);
> foo->baz();
> h = dlopen("foo.so",RTLD_NOW);
> bar *p2 = dlsym(h,"getfoo")();
> dlclose(h);
> 
> Are p1 and p2 supposed to point to same object?
> Also is foo->baz(); legal or not? If its so we cannot call destructors.

I don't think a program can reasonably rely on either of these.

> There could be fix to add zombie state where we call destructors but not
> free memory so we can reinitialize object at same address but I need to know
> that calling destructor is always intended behaviour.

That sounds fine to me.

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

--- Comment #12 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Dave Johansen from comment #11)
> Can this please be reopened? It was determined in the glibc bugzilla that
> this is a gcc problem because of the incorrect setting of unique flag.

The setting is not incorrect, nor is it an optimization; it is necessary to fix
the behavior of RTLD_LOCAL with multiple loaded objects depending on the same
library, since the glibc developers rejected the other approach that I
suggested (https://www.sourceware.org/ml/libc-alpha/2002-05/msg00222.html).

If you don't need this handling, in 4.9 you can use -fno-gnu-unique to disable
it.  I'll go ahead and backport that switch to 4.8 as well.

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

--- Comment #13 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Fri Jun 13 16:39:37 2014
New Revision: 211648

URL: https://gcc.gnu.org/viewcvs?rev=211648&root=gcc&view=rev
Log:
    PR c++/60731
    * common.opt (-fno-gnu-unique): Add.
    * config/elfos.h (USE_GNU_UNIQUE_OBJECT): Check it.

Modified:
    branches/gcc-4_8-branch/gcc/ChangeLog
    branches/gcc-4_8-branch/gcc/common.opt
    branches/gcc-4_8-branch/gcc/config/elfos.h
    branches/gcc-4_8-branch/gcc/doc/invoke.texi

[Bug c++/60731] [4.7/4.8/4.9 Regression] dynamic library not getting reinitialized on multiple calls to dlopen()

[davejohansen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60731

--- Comment #14 from Dave Johansen <davejohansen at gmail dot com> ---
Could you please point me to how I can reproduce the issue with "RTLD_LOCAL
with multiple loaded objects depending on the same library"? I would like to
see if I can reproduce that issue with clang++ and icpc.
Thanks,
Dave