[Bug c++/21405] New: Template inlines have global visibility

[Bug c++/21405] New: Template inlines have global visibility

[mike at navi dot cx]

See http://gcc.gnu.org/ml/libstdc++/2005-04/msg00173.html

If you have code like:

std::string b = "bee";
std::string c = "see";

std::string a = b + c;

Then the string + operator overload will appear in the final ELF image with
GLOBAL WEAK visibility, meaning it can be bound to the wrong version of the
symbol at runtime (ie symbol versioning is ignored).

This is serious as it means you can't mix libraries that use different C++ ABIs
into the same image even if they only interact via C ABIs, something that the
GCC docs explicitly say will work!

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           Summary: Template inlines have global visibility
           Product: gcc
           Version: 3.4.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mike at navi dot cx
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug c++/21405] Template inlines have global visibility

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-05 22:27 -------
I don't know if this is really a vaild bug, as the standard requires the inline function as the same so it 
would be undefined if they are different.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug c++/21405] Template inlines have global visibility

[mike at navi dot cx]

------- Additional Comments From mike at navi dot cx  2005-05-05 22:39 -------
I don't understand what you mean. There's definitely a bug here because a
configuration that the docs say should work, causes mysterious crashes due to
mis-binds of symbols. I suspect building with -fvisibility-inlines-hidden can
resolve this problem but why is it not the default?

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug c++/21405] Template inlines have global visibility

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-05-05 22:40 -------
So here is the story really global templates have aways global visibility in C++ so this is not a bug in 
GCC or binutils.  This is a bug in how you think that you can use two different versions. 

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           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug c++/21405] Template inlines have global visibility

[mike at navi dot cx]

------- Additional Comments From mike at navi dot cx  2005-05-06 00:17 -------
No, there is very definitely a bug here even if it's just in the documentation.

The GCC docs say in very clear and unambiguous terms that this will work, by
design. Not by accident, by design. That's the whole point of applying symbol
versions to the standard C++ library.

It only affects methods that have been inlined into the headers. Methods that
are defined as external work correctly. So either:

a) No methods should be inlined

or

b) GCC should not emit them as GLOBAL WEAK so they can be overridden by other
definitions elsewhere in the image

The latter is what the new -fvisibility-inlines-hidden switch does. So why is it
not on by default?

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug c++/21405] Template inlines have global visibility

[chris at bubblescope dot net]

------- Additional Comments From chris at bubblescope dot net  2005-05-08 12:18 -------
Out of interest, where do the docs say that? (I'm not being sarcastic, just interested)

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug c++/21405] Template inlines have global visibility

[mike at navi dot cx]

------- Additional Comments From mike at navi dot cx  2005-05-08 12:38 -------
http://gcc.gnu.org/onlinedocs/libstdc++/abi.html

See the "testing multi-abi binaries" section at the bottom:

<quote>

A "C" application, dynamically linked to two shared libraries, liba, libb. The
dependent library liba is C++ shared library compiled with gcc-3.3.x, and uses
io, exceptions, locale, etc. The dependent library libb is a C++ shared library
compiled with gcc-3.4.x, and also uses io, exceptions, locale, etc.

[ ... snip ... ]

This resulting binary, when executed, will be able to safely use code from both
liba, and the dependent libstdc++.so.6, and libb, with the dependent libstdc++.so.5.

</quote>

A C++ program linked indirectly (via a C library) against another C++ library is
exactly the same scenario. This is the whole point of symbol versioning.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[bkoz at gcc dot gnu dot org]

------- Additional Comments From bkoz at gcc dot gnu dot org  2005-05-25 22:49 -------
Changing this to libstdc++, so we remember to track this.

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           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |libstdc++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[mike at navi dot cx]

------- Additional Comments From mike at navi dot cx  2005-05-31 13:23 -------
Reopening the bug, as Benjamin wishes to track it.

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           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2005-05-31 15:10 -------
You can't use -fvisibility-inlines-hidden or otherwise you'll get linker errors 
if the compiler later decides not to inline those functions. I don't think you 
can win.

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[mike at navi dot cx]

------- Additional Comments From mike at navi dot cx  2005-06-01 11:56 -------
So this feature is basically terminally broken and never worked in the first place?

How about if GCC supported a new attribute or something that made it emit
inlines for that class with a specific symbol version?

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[adam at gimp dot org]

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           What    |Removed                     |Added
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                 CC|                            |adam at gimp dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[matze at braunis dot de]

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           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matze at braunis dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[cristipp at excite dot com]

------- Comment #18 from cristipp at excite dot com  2006-03-22 19:10 -------
(In reply to comment #17)
> see the solution in 24660

I'm not sure I understand correctly: are all C++ template libraries supposed to
add 24660-style machinery?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[bkoz at gcc dot gnu dot org]

------- Comment #17 from bkoz at gcc dot gnu dot org  2006-03-22 04:51 -------

see the solution in 24660


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[pluto at agmk dot net]

------- Comment #16 from pluto at agmk dot net  2006-03-20 19:35 -------
(In reply to comment #15)
> see PR19664, PR20218, PR20297.

ops, this is the note for C#10.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[pluto at agmk dot net]

------- Comment #15 from pluto at agmk dot net  2006-03-20 19:34 -------
see PR19664, PR20218, PR20297.


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pluto at agmk dot net changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pluto at agmk dot net


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[cristipp at excite dot com]

------- Comment #14 from cristipp at excite dot com  2006-03-20 18:32 -------
The problem is not how the dynamic linker treats 'weak' symbols. The problem is
that template originating functions having no version numbers. It just happen
that template originating functions are also marked as weak (if I understand
correctly). In other words, if I have a regular C/C++ function, I can attach
version strings to it, whereas it I have a C++ template function I cannot
attach version strings to it, or more precisely to instances of it. I don't
really care whether symbols are 'weak' or 'strong', I only care of proper
versioning for *all* C++ symbols.

I believe that this situation was clearly described by the original bug
reporter 10 months ago. For some reason nobody seems to acknowledge that there
is a problem, the main line of reasoning so far being that 'C++ standard says
only unique (weak) names are valid'. However, that flies in the face of the
whole synmbol versioning mechanism, weak symbols or not. Afterall, versioning
for symbols was introduced precisely to allow multiple instances of the same
symbol to be valid in a shared object context.

Please feel free to correct me on any g++ internal details on which I am no
expert. However, the root problem is there and is a show-stopper for any
attempt of distributing pre-compiled C++ shared object binaries.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[hjl at lucon dot org]

------- Comment #13 from hjl at lucon dot org  2006-03-20 17:30 -------
FWIW, the current GNU binutils and glibc treat the weak definition in
shared libraries as strong. There is even a whole set of testsuite for
this in the GNU binutils.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[cristipp at excite dot com]

------- Comment #12 from cristipp at excite dot com  2006-03-20 17:07 -------
(In reply to comment #11)
> There is an one defintion rule in C++ unlike most other languages which have
> weak symbols.  And if you are working around it by using hidden symbols well
> you are asking to run into troubles.

I don't believe that C++ has to say (should say) anything that pertains to
shared libraries. Moreover, symbol versions were added as workarounds for
problems created by the ELF format semantics. This is a platform specific
problem, not a pure C++ problem. However, to have the gnu toolchain to properly
support C++ on ELF platforms, adding proper versioning for *all* symbols,
including template-originated symbols is a must. I'm not sure if this is a task
for g++ of for the linker or for both, but someone should eventually
acknowledge that there is a problem and start looking for solutions...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405

[Bug libstdc++/21405] Template inlines have global visibility

[pinskia at gcc dot gnu dot org]

------- Comment #11 from pinskia at gcc dot gnu dot org  2005-12-30 18:20 -------
There is an one defintion rule in C++ unlike most other languages which have
weak symbols.  And if you are working around it by using hidden symbols well
you are asking to run into troubles.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21405