c++/7320: g++ 3.2 relocation problem
snyder@fnal.gov
snyder@fnal.gov
Mon Jul 15 17:32:00 GMT 2002
>Number: 7320
>Category: c++
>Synopsis: g++ 3.2 relocation problem
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Mon Jul 15 16:46:00 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: scott snyder
>Release: 3.2 20020715 (experimental)
>Organization:
>Environment:
System: Linux karma 2.4.9-13 #1 Tue Oct 30 20:11:04 EST 2001 i686 unknown
Architecture: i686
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../egcs/configure --prefix=/usr/local/egcs --enable-threads=posix --enable-long-long --enable-languages=c,c++,f77 : (reconfigured) : (reconfigured) : (reconfigured) : (reconfigured) : (reconfigured) : (reconfigured) : (reconfigured) : (reconfigured) : (reconfigured)
>Description:
In recent versions of gcc, i've been having difficulties
building shared libraries. Sometimes, when i try to use a type
from the library in a dynamic_cast, i get a link warning about
an unresolved relocation, and the dynamic_cast fails at run time ---
it looks like in the call to the dynamic_cast, the argument that
is supposed to be the typeinfo for the destination gets pointed
at the beginning of the shared library from which it comes.
To be complete, i should mention that the as and ld versions i'm using
are as follows:
GNU assembler 2.12.90.0.14 20020627
GNU ld version 2.12.90.0.14 20020627
I have seen the same problem with different binutils versions, though.
An example (consisting of three source files) is below.
Here's how i build it:
$ g++ -fPIC -c y4.cc
$ g++ -fPIC -shared -o yy.so y4.o
$ g++ -g -fPIC y3.cc -o y3 yy.so
/usr/local/egcs/bin/ld: /tmp/ccqQJ3Fn.o(.text+0x41): unresolvable relocation against symbol `typeinfo for xtype'
/usr/local/egcs/bin/ld: /tmp/ccqQJ3Fn.o(.text+0x4b): unresolvable relocation against symbol `typeinfo for xatomic'
$
Note the relocation errors for the typeinfo objects.
It then crashes if i try to run it:
$ ./y3
Segmentation fault
$
Older versions of gcc (from about a month ago) do not show this behavior.
By a binary search, i found the change which introduced this problem:
2002-06-30 Nathan Sidwell <nathan@codesourcery.com>
* cp-tree.h (CPTI_TINFO_DECL_TYPE): Replace with ...
(CPTI_TYPE_INFO_PTR_TYPE): ... this.
(tinfo_decl_type): Replace with ...
(type_info_ptr_type): ... this.
(import_export_tinfo): Declare.
(tinfo_decl_p): Rename to ...
(unemitted_tinfo_decl_p): ... this.
* decl2.c (import_export_decl): Break out tinfo handling into ...
(import_export_tinfo): ... here. New function.
(finish_file): Adjust.
* rtti.c (TINFO_REAL_NAME): New macro.
(init_rtti_processing): Create the tinfo types.
(get_tinfo_decl_dynamic): Use type_info_ptr_type, get_tinfo_ptr.
(get_tinfo_decl): Adjust.
(get_tinfo_ptr): New function.
(get_type_id): Use it.
(tinfo_base_init): Create vtable decl here, if it doesn't exist.
(ptr_initializer): Use get_tinfo_ptr.
(ptm_initializer): Likewise.
(synthesize_tinfo_var): Break into ...
(get_pseudo_ti_init): ... this. Just create the initializer.
(get_pseudo_ti_desc): .. and this.
(create_real_tinfo_var): Remove.
(create_pseudo_type_info): Don't create the vtable decl here.
(get_vmi_pseudo_type_info): Remove.
(create_tinfo_types): Adjust.
(tinfo_decl_p): Rename to ...
(unemitted_tinfo_decl_p): ... here. Adjust.
(emit_tinfo_decl): Adjust. Create the initializer.
I found that if i make this change, the problem goes away.
This is probably not the correct fix, though.
Index: rtti.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/cp/rtti.c,v
retrieving revision 1.138
diff -u -p -r1.138 rtti.c
--- rtti.c 5 Jul 2002 10:40:47 -0000 1.138
+++ rtti.c 15 Jul 2002 23:31:47 -0000
@@ -342,6 +342,7 @@ get_tinfo_decl (type)
TREE_STATIC (d) = 1;
DECL_EXTERNAL (d) = 1;
SET_DECL_ASSEMBLER_NAME (d, name);
+ DECL_COMDAT (d) = 1;
cp_finish_decl (d, NULL_TREE, NULL_TREE, 0);
pushdecl_top_level (d);
>How-To-Repeat:
- y3.cc --------------------------------------------------------
#include "y.hh"
extern "C" int printf (...);
int main ()
{
xtype* p = get_atomic_type ();
xatomic* pp = dynamic_cast<xatomic*> (p);
printf ("%x\n", pp);
return 0;
}
- y4.cc --------------------------------------------------------
#include "y.hh"
xatomic* get_atomic_type ()
{
return new xatomic ();
}
xatomic::~xatomic () {}
xtype::~xtype () {}
- y.hh ---------------------------------------------------------
#ifndef Y_HH
#define Y_HH
struct xtype
{
virtual ~xtype ();
};
struct xatomic
: public xtype
{
~xatomic ();
};
xatomic* get_atomic_type ();
#endif
----------------------------------------------------------------
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
More information about the Gcc-bugs
mailing list