Re: Undefined symbols with exceptions for an egcs 1.1.1 cross-compiler

[Damian Gilmurray <dgilmurray at adaptivebroadband dot com>]

mrs@wrs.com (Mike Stump) writes:

> > To: egcs@egcs.cygnus.com
> > From: Damian Gilmurray <dgilmurray@adaptivebroadband.com>
> > Date: 05 Jan 1999 09:25:36 +0000
> 
> > In order to provide runtime support for exceptions, I've pulled libgcc2.c,
> > cp/exception.cc, cp/tinfo.cc and cp/tinfo2.cc from the distribution into a
> > C++ support library, compiling the .cc files with -frtti -fexceptions.
> 
> > __class_type_info type_info node
> 
> If you ask the compiler to not link with libgcc.a and libstdc++.a you
> should expect tons of these type of problem.  Maybe what you want to
> do is link against them, or at least more of them.  nm will tell you
> where things are defined.  Also, I suggest you let the libraries be
> built in the normal way.
> 

Mike,

Thanks for your reply. 

I've tracked down what I believe is the source of the problem.

These symbols were indeed being defined in tinfo.o and tinfo2.o but were
defined as common symbols. However, the cross-compiler is for an embedded
environment and in this environment we are using a bespoke linker (and
indeed bespoke runtime libraries, hence not linking in the full libgcc.a
and libstdc++). This linker cannot handle the resolution of common symbols
and therefore everything is compiled with -fno-common. However, when
compiling cp/tinfo.cc and cp/tinfo2.cc common symbols are generated for the
type_info nodes irrespective of the no-common flag. This is because the
code generation for type_info initialization in the function
synthesize_tinfo_fn() in cp/rtti.c ignores the no-common flag. With the
following patch:

*** rtti.c.orig      Fri Nov 13 19:45:38 1998
--- rtti.c    Wed Jan  6 18:44:15 1999
***************
*** 1074,1080 ****
    tdecl = get_tinfo_var (type);
    DECL_EXTERNAL (tdecl) = 0;
    TREE_STATIC (tdecl) = 1;
!   DECL_COMMON (tdecl) = 1;
    TREE_USED (tdecl) = 1;
    DECL_ALIGN (tdecl) = TYPE_ALIGN (ptr_type_node);
    cp_finish_decl (tdecl, NULL_TREE, NULL_TREE, 0, 0);
--- 1074,1081 ----
    tdecl = get_tinfo_var (type);
    DECL_EXTERNAL (tdecl) = 0;
    TREE_STATIC (tdecl) = 1;
!   if (!flag_no_common)
!     DECL_COMMON (tdecl) = 1;
    TREE_USED (tdecl) = 1;
    DECL_ALIGN (tdecl) = TYPE_ALIGN (ptr_type_node);
    cp_finish_decl (tdecl, NULL_TREE, NULL_TREE, 0, 0);

I can successfully link the application. I know very little about the
implementation of RTTI so please excuse any ignorance on my behalf but is
there a particular reason why the no-common flag is ignored here?

Regards,

Damian.

[ Damian P. Gilmurray             email:    dgilmurray@adaptivebroadband.com
    Adaptive Broadband Limited      www:    http://www.adaptivebroadband.com/
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