[Bug c++/42608] New: Undefined reference not reported in case of explicit template instantiation

[Bug c++/42608] New: Undefined reference not reported in case of explicit template instantiation

[bastien_emmanuel at yahoo dot fr]

The following code compiles without error and lead to a seg fault at runtime:

template <class U, class V>
struct A;

template <class V>
struct A<int, V> {
  void f();
};

template struct A<int, int>;

int main() {
  A<int, int> a;
  a.f();
  return 0;
}

Notice that there is no body defined for A<int, int>::f(). The correct link
error is reported when no explicit template instantiation is requested:

/tmp/ccycZSyE.o: In function `main':
testcase.cpp:(.text+0x10): undefined reference to `A<int, int>::f()'
collect2: ld returned 1 exit status

$g++ -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 4.4.2-7'
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls
--enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc
--with-arch-32=i486 --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.2 (Debian 4.4.2-7)


-- 
           Summary: Undefined reference not reported in case of explicit
                    template instantiation
           Product: gcc
           Version: 4.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bastien_emmanuel at yahoo dot fr
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-01-04 14:19 -------
Confirmed.

Starting with GCC 4.4 we emit:

        .size   main, .-main
        .weak   _ZN1AIiiE1fEv
        .weak   _ZN1AIiiE1fEv
        .weak   _ZN1AIiiE1fEv
        .ident  "GCC: (Debian 4.4.2-8) 4.4.2"
        .section        .note.GNU-stack,"",@progbit

huh.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |wrong-code
      Known to work|                            |4.3.4
   Last reconfirmed|0000-00-00 00:00:00         |2010-01-04 14:19:25
               date|                            |
            Summary|Undefined reference not     |[4.4/4.5 Regression]
                   |reported in case of explicit|Undefined reference not
                   |template instantiation      |reported in case of explicit
                   |                            |template instantiation
   Target Milestone|---                         |4.4.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[jason at gcc dot gnu dot org]

-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jason at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2010-01-04 14:19:25         |2010-01-05 23:02:12
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[jason at gcc dot gnu dot org]

------- Comment #2 from jason at gcc dot gnu dot org  2010-01-05 23:14 -------
This was broken by

    2008-08-19  Rafael Espindola  <espindola@google.com>

          * varasm.c (weak_decls): Move earlier in the file.
          (assemble_external): Add weak decls to the weak_decls list.
          (declare_weak): Don't add decls to the weak_decls list.

Before this change only declarations explicitly marked weak became weak
references, but after this change any C++ vague linkage function which isn't
defined in the current translation unit becomes a weak reference.


-- 

jason at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |espindola at gcc dot gnu dot
                   |                            |org, jason at gcc dot gnu
                   |                            |dot org
         AssignedTo|jason at gcc dot gnu dot org|unassigned at gcc dot gnu
                   |                            |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2010-01-07 14:47 -------
I wonder if the C++ FE should diagnose this as invalid anyway?


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[jason at gcc dot gnu dot org]

------- Comment #4 from jason at gcc dot gnu dot org  2010-01-07 19:50 -------
No, there's no way for the front end to know that f isn't instantiated in
another translation unit.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[jakub at gcc dot gnu dot org]

------- Comment #5 from jakub at gcc dot gnu dot org  2010-01-08 12:06 -------
Yeah, there are several reasons why DECL_WEAK may be set, but only when it is
because of weak attribute or #pragma weak we want to add it to weak_decls.
For vague linkage, or weakref attribute we don't want to do that.

I wonder whether we couldn't add weak attribute in apply_pragma_weak and just
add to weak_decls decls that have that attribute.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[jakub at gcc dot gnu dot org]

------- Comment #6 from jakub at gcc dot gnu dot org  2010-01-08 13:42 -------
Created an attachment (id=19507)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19507&action=view)
gcc45-pr42608.patch

Untested fix.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[jakub at gcc dot gnu dot org]

------- Comment #7 from jakub at gcc dot gnu dot org  2010-01-14 22:41 -------
Subject: Bug 42608

Author: jakub
Date: Thu Jan 14 22:41:02 2010
New Revision: 155919

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=155919
Log:
        PR c++/42608
        * varasm.c (declare_weak): Add weak attribute to decl if it
        doesn't have one already.
        (assemble_external): Only add decls to weak_decls if they also
        have weak attribute.

        * g++.dg/template/instantiate11.C: New test.

Added:
    trunk/gcc/testsuite/g++.dg/template/instantiate11.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/varasm.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[jakub at gcc dot gnu dot org]

------- Comment #8 from jakub at gcc dot gnu dot org  2010-01-14 22:47 -------
Subject: Bug 42608

Author: jakub
Date: Thu Jan 14 22:46:43 2010
New Revision: 155921

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=155921
Log:
        PR c++/42608
        * varasm.c (declare_weak): Add weak attribute to decl if it
        doesn't have one already.
        (assemble_external): Only add decls to weak_decls if they also
        have weak attribute.

        * g++.dg/template/instantiate11.C: New test.

Added:
    branches/gcc-4_4-branch/gcc/testsuite/g++.dg/template/instantiate11.C
Modified:
    branches/gcc-4_4-branch/gcc/ChangeLog
    branches/gcc-4_4-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_4-branch/gcc/varasm.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608

[Bug c++/42608] [4.4/4.5 Regression] Undefined reference not reported in case of explicit template instantiation

[jakub at gcc dot gnu dot org]

------- Comment #9 from jakub at gcc dot gnu dot org  2010-01-14 23:20 -------
Fixed.


-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42608