[Bug lto/53808] New: Undefined symbol when building a library with lto

[Bug lto/53808] New: Undefined symbol when building a library with lto

[rafael.espindola at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

             Bug #: 53808
           Summary: Undefined symbol when building a library with lto
    Classification: Unclassified
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: rafael.espindola@gmail.com


The gcc lto plugin can drop a symbol that another translation unit has an
undefined reference to.

This might also be a bug in gcc (>= 4.6, with and without lto) producing an
undefined reference, the ABI is not very clear.

$ cat test.h
struct foo {
 virtual ~foo();
};
struct bar : public foo {
 virtual void zed();
};
$ cat def.cpp
#include "test.h"
void bar::zed() {
}
$ cat undef.cpp
#include "test.h"
void f() {
 foo *x(new bar);
 delete x;
}

Compile with:

$ ~/gcc/build/gcc/xgcc -B ~/gcc/build/gcc/ -c undef.cpp -o undef.o -O3 -fPIC
$ nm undef.o | grep D0
                U _ZN3barD0Ev

$ ~/gcc/build/gcc/xgcc -B ~/gcc/build/gcc/ -c def.cpp -o def.o -O3 -flto -fPIC
$ ~/gcc/build/gcc/xgcc -B ~/gcc/build/gcc/ def.o -o def.so -shared
-fuse-linker-plugin
$ readelf  -sDW def.so | grep bar
  12   7: 0000000000000931     5 OBJECT  WEAK   DEFAULT  13 _ZTS3bar
  11  10: 0000000000001ca0    40 OBJECT  WEAK   DEFAULT  24 _ZTV3bar
  13  14: 0000000000001cd0    24 OBJECT  WEAK   DEFAULT  24 _ZTI3bar
   8  15: 00000000000008b0    10 FUNC    GLOBAL DEFAULT  11 _ZN3bar3zedEv


Note that we have the vtable, but no the destructor.

$ g++ -shared -o foo.so undef.o def.so -Wl,-z,defs
undef.o:undef.cpp:function f(): error: undefined reference to 'bar::~bar()'

[Bug lto/53808] Undefined symbol when building a library with lto

[hubicka at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

Jan Hubicka <hubicka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-07-03
                 CC|                            |hubicka at gcc dot gnu.org
         AssignedTo|unassigned at gcc dot       |hubicka at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

[Bug lto/53808] Undefined symbol when building a library with lto

[rafael.espindola at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #1 from Rafael Avila de Espindola <rafael.espindola at gmail dot com> 2012-11-06 13:53:00 UTC ---
I can see two options for fixing this

1) producing a copy of the destructor when we devirtualize and not
devirtualizing if we cannot emit one.
2) making the destructor that is emitted with the vtable strong.

On the clang side John McCall likes the first option better
(http://lists.cs.uiuc.edu/pipermail/cfe-dev/2012-June/022606.html). Jason, what
do you think?

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> 2013-03-23 00:36:48 UTC ---
Created attachment 29709
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29709
partial (front end) patch

This patch causes the destructor to be created and marked as COMDAT, but for
some reason cgraph still isn't emitting it.

[Bug lto/53808] Undefined symbol when building a library with lto

[hubicka at ucw dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #3 from Jan Hubicka <hubicka at ucw dot cz> 2013-03-23 21:40:19 UTC ---
> This patch causes the destructor to be created and marked as COMDAT, but for
> some reason cgraph still isn't emitting it.
Thank you!.  I will work out why it is not emitted.

Honza

[Bug lto/53808] Undefined symbol when building a library with lto

[rafael.espindola at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #4 from Rafael Avila de Espindola <rafael.espindola at gmail dot com> ---
The equivalent clang bug (llvm.org/pr13124) just got fixed by avoiding the
devirtualization in this case.

Not sure how similar the issues are internally, but I summarized what I found
in clang in:

http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20130902/087810.html

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

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

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

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> ---
I just tried to reproduce the bug before checking my patch in for 4.9, and
couldn't; my patch seems to make no difference to the cgraph output for
def.cpp.  So I guess it isn't needed anymore.  Does that seem right to you?

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Jason Merrill from comment #6)
> I just tried to reproduce the bug before checking my patch in for 4.9, and
> couldn't; my patch seems to make no difference to the cgraph output for
> def.cpp.

...but it does make a difference to undef.cpp.  Never mind.

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Tue Feb 25 18:54:48 2014
New Revision: 208153

URL: http://gcc.gnu.org/viewcvs?rev=208153&root=gcc&view=rev
Log:
    PR lto/53808
    * class.c (clone_function_decl): Call note_vague_linkage_fn for
    defaulted virtual dtor.

Added:
    trunk/gcc/testsuite/g++.dg/opt/devirt4.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/class.c

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |4.9.0

--- Comment #9 from Jason Merrill <jason at gcc dot gnu.org> ---
Devirtualization + inlining of ~bar fixed for 4.9.

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #10 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Feb 26 21:32:41 2014
New Revision: 208184

URL: http://gcc.gnu.org/viewcvs?rev=208184&root=gcc&view=rev
Log:
    PR c++/60347
    PR lto/53808
    * class.c (clone_function_decl): Don't note_vague_linkage_fn.
    * init.c (build_vtbl_address): Do it here.

Added:
    trunk/gcc/testsuite/g++.dg/template/dtor9.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/class.c
    trunk/gcc/cp/init.c

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #11 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Mon Jun 30 20:20:55 2014
New Revision: 212174

URL: https://gcc.gnu.org/viewcvs?rev=212174&root=gcc&view=rev
Log:
    PR c++/61659
    PR lto/53808
gcc/cp
    * decl2.c (maybe_emit_vtables): Mark all vtable entries if
    devirtualizing.
    * init.c (build_vtbl_address): Don't mark destructor.
    * class.c (finish_struct_1): Add all classes to keyed_classes
    if devirtualizing.
libstdc++-v3/
    * libsupc++/cxxabi.h (class __pbase_type_info): __pointer_catch
    is pure, not inline.

Added:
    trunk/gcc/testsuite/g++.dg/opt/devirt5.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/class.c
    trunk/gcc/cp/decl2.c
    trunk/gcc/cp/init.c
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/libsupc++/cxxabi.h

[Bug lto/53808] Undefined symbol when building a library with lto

[rafael.espindola at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #12 from Rafael Avila de Espindola <rafael.espindola at gmail dot com> ---
Note that this bug is present once more when -fno-use-all-virtuals is used.
With the original testcase gcc again produces an undefined reference to
_ZN3barD0Ev.

Is -fno-use-all-virtuals intended to be an abi breaking option? If so it would
be nice to document that.

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #13 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Jul 30 17:27:14 2014
New Revision: 213307

URL: https://gcc.gnu.org/viewcvs?rev=213307&root=gcc&view=rev
Log:
    PR lto/53808
    PR c++/61659
    * pt.c (push_template_decl_real): Set DECL_COMDAT on templates.
    (check_explicit_specialization): Clear it on specializations.
    * decl.c (duplicate_decls, start_decl): Likewise.
    (grokmethod, grokfndecl): Set DECL_COMDAT on inlines.
    * method.c (implicitly_declare_fn): Set DECL_COMDAT.  Determine
    linkage after setting the appropriate flags.
    * tree.c (decl_linkage): Don't check DECL_COMDAT.
    * decl2.c (mark_needed): Mark clones.
    (import_export_decl): Not here.

Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl.c
    trunk/gcc/cp/decl2.c
    trunk/gcc/cp/method.c
    trunk/gcc/cp/pt.c
    trunk/gcc/cp/tree.c
    trunk/gcc/testsuite/g++.dg/opt/devirt4.C

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #14 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Jul 30 21:29:25 2014
New Revision: 213311

URL: https://gcc.gnu.org/viewcvs?rev=213311&root=gcc&view=rev
Log:
    PR lto/53808
    PR c++/61659
    * pt.c (push_template_decl_real): Don't set DECL_COMDAT on friends.

Added:
    trunk/gcc/testsuite/g++.dg/template/friend56.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #15 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Tue Aug 19 17:29:41 2014
New Revision: 214177

URL: https://gcc.gnu.org/viewcvs?rev=214177&root=gcc&view=rev
Log:
    PR lto/53808
    PR c++/61659
    * decl.c (maybe_commonize_var): Don't use DECL_COMDAT to trigger
    comdat_linkage.

Added:
    trunk/gcc/testsuite/g++.dg/abi/spec1.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/decl.c

[Bug lto/53808] Undefined symbol when building a library with lto

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53808

--- Comment #16 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Wed Sep 10 14:27:40 2014
New Revision: 215131

URL: https://gcc.gnu.org/viewcvs?rev=215131&root=gcc&view=rev
Log:
    PR lto/53808
    PR c++/61659
    * decl2.c (note_comdat_fn): New.
    (set_comdat): New.
    (cp_write_global_declarations): Call set_comdat.
    * method.c (implicitly_declare_fn): Call note_comdat_fn.
    * pt.c (tsubst_decl) [FUNCTION_DECL]: Likewise.
    * decl2.c (mark_needed): Mark clones.
    (import_export_decl): Not here.

Added:
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/abi/no-weak1.C
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/abi/spec1.C
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/opt/devirt5.C
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/template/friend56.C
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/template/spec38.C
Modified:
    branches/gcc-4_9-branch/gcc/cp/ChangeLog
    branches/gcc-4_9-branch/gcc/cp/cp-tree.h
    branches/gcc-4_9-branch/gcc/cp/decl2.c
    branches/gcc-4_9-branch/gcc/cp/method.c
    branches/gcc-4_9-branch/gcc/cp/pt.c
    branches/gcc-4_9-branch/gcc/testsuite/g++.dg/opt/devirt4.C