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* [Bug c++/15428] New: vtables shouldn't always be weak on Darwin
@ 2004-05-14 15:37 austern at apple dot com
2004-05-14 15:42 ` [Bug c++/15428] " pinskia at gcc dot gnu dot org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: austern at apple dot com @ 2004-05-14 15:37 UTC (permalink / raw)
To: gcc-bugs
Compiling this on Darwin, and looking at the .o file with 'nm -m', gives the following:
...
00000120 (__DATA,__datacoal_nt) weak external __ZTV1A
...
That is, the vtable is marked as weak. That's all as it should be: the ABI specification says that vtables
should always be weak. Unfortunately, on Darwin that's wrong.
It's wrong because of a limitation in Darwin's linker. Weak ("coalesced") symbols may not appear in the
table of contents of a static archive. So consider the following scenario:
1. The class is defined in a.h. The key method, A::~A(), is defined in a.cc.
2. a.cc gets compiled, and then gets put into a static archive libA.a.
3. Some other file, foo.cc, includes a.h and uses class A in a way that requires the definition of a vtable.
4. We link foo.o against libA.a.
foo.o will have an unresolved reference to _ZTV1A. There will be a perfectly good definition of it in
libA.a(a.o), but the linker won't find it because it won't be there in the table of contents. So even
though the user is doing everything right, the link will fail.
In the long run we should probably remove the Darwin linker's restriction. In the short run, however,
the linker is what it is.
What this means is that on Darwin we have to special-case vtables, just like we special-case members
of explicitly instantiated class templates with TARGET_EXPLICIT_INSTANTIATIONS_ONE_ONLY. (It's the
same issue.) On Darwin we have to mark vtables weak only if we believe that they will be emitted
everywhere they're needed. That is, we have to mark them weak if the class has no key method or if
the key method is inline, but leave them nonweak otherwise.
This is a bug in my code to enable linkonce support for Darwin, so this bug should be assigned to me
unless someone else desparately wants it.
--
Summary: vtables shouldn't always be weak on Darwin
Product: gcc
Version: 3.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: austern at apple dot com
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: powerpc-apple-darwin7.3.0
GCC host triplet: powerpc-apple-darwin7.3.0
GCC target triplet: powerpc-apple-darwin7.3.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15428
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/15428] vtables shouldn't always be weak on Darwin
2004-05-14 15:37 [Bug c++/15428] New: vtables shouldn't always be weak on Darwin austern at apple dot com
@ 2004-05-14 15:42 ` pinskia at gcc dot gnu dot org
2004-05-21 3:09 ` pinskia at gcc dot gnu dot org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-05-14 15:42 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-05-13 21:58 -------
Confirmed.
--
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|unassigned at gcc dot gnu |austern at apple dot com
|dot org |
Status|UNCONFIRMED |ASSIGNED
Ever Confirmed| |1
Keywords| |ABI, wrong-code
Last reconfirmed|0000-00-00 00:00:00 |2004-05-13 21:58:07
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15428
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/15428] vtables shouldn't always be weak on Darwin
2004-05-14 15:37 [Bug c++/15428] New: vtables shouldn't always be weak on Darwin austern at apple dot com
2004-05-14 15:42 ` [Bug c++/15428] " pinskia at gcc dot gnu dot org
@ 2004-05-21 3:09 ` pinskia at gcc dot gnu dot org
2004-06-03 23:15 ` cvs-commit at gcc dot gnu dot org
2004-06-03 23:37 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-05-21 3:09 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-05-20 01:18 -------
Patch here: <http://gcc.gnu.org/ml/gcc-patches/2004-05/msg01240.html>.
--
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |patch
Target Milestone|--- |3.5.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15428
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/15428] vtables shouldn't always be weak on Darwin
2004-05-14 15:37 [Bug c++/15428] New: vtables shouldn't always be weak on Darwin austern at apple dot com
2004-05-14 15:42 ` [Bug c++/15428] " pinskia at gcc dot gnu dot org
2004-05-21 3:09 ` pinskia at gcc dot gnu dot org
@ 2004-06-03 23:15 ` cvs-commit at gcc dot gnu dot org
2004-06-03 23:37 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: cvs-commit at gcc dot gnu dot org @ 2004-06-03 23:15 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From cvs-commit at gcc dot gnu dot org 2004-06-03 23:15 -------
Subject: Bug 15428
CVSROOT: /cvs/gcc
Module name: gcc
Changes by: austern@gcc.gnu.org 2004-06-03 23:15:02
Modified files:
gcc : ChangeLog defaults.h
gcc/config : darwin.h
gcc/cp : ChangeLog decl2.c
gcc/doc : tm.texi
Log message:
PR c++/15428
* default.h (TARGET_WEAK_NOT_IN_ARCHIVE_TOC): New name
for TARGET_EXPLICIT_INSTANTIATIONS_ONE_ONLY, with reversed sense.
* config/darwin.h (TARGET_WEAK_NOT_IN_ARCHIVE_TOC): Likewise.
* doc/tm.texi (TARGET_WEAK_NOT_IN_ARCHIVE_TOC): Rewrite
documentation to reflect the new macro name and to clarify its
meaning.
* cp/decl2.c (maybe_emit_vtables): If TARGET_WEAK_NOT_IN_ARCHIVE_TOC
is nonzero, and if we see a noninline definition of a key method,
make the vtables nonweak.
Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.3833&r2=2.3834
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/defaults.h.diff?cvsroot=gcc&r1=1.139&r2=1.140
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/config/darwin.h.diff?cvsroot=gcc&r1=1.80&r2=1.81
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&r1=1.4079&r2=1.4080
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/decl2.c.diff?cvsroot=gcc&r1=1.712&r2=1.713
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/doc/tm.texi.diff?cvsroot=gcc&r1=1.326&r2=1.327
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15428
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/15428] vtables shouldn't always be weak on Darwin
2004-05-14 15:37 [Bug c++/15428] New: vtables shouldn't always be weak on Darwin austern at apple dot com
` (2 preceding siblings ...)
2004-06-03 23:15 ` cvs-commit at gcc dot gnu dot org
@ 2004-06-03 23:37 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-06-03 23:37 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-06-03 23:37 -------
Fixed.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution| |FIXED
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15428
^ permalink raw reply [flat|nested] 5+ messages in thread
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2004-05-14 15:37 [Bug c++/15428] New: vtables shouldn't always be weak on Darwin austern at apple dot com
2004-05-14 15:42 ` [Bug c++/15428] " pinskia at gcc dot gnu dot org
2004-05-21 3:09 ` pinskia at gcc dot gnu dot org
2004-06-03 23:15 ` cvs-commit at gcc dot gnu dot org
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