Re: versioning of _Unwind_*() symbols

[Mark Mitchell <mark at codesourcery dot com>]

Daniel Jacobowitz wrote:

> On Wed, Apr 21, 2004 at 12:15:16PM -0700, Mark Mitchell wrote:
>  
>
> > > While we are on it, binaries compiled by gcc may reference gcc
> > > personality functions, which only come with gcc. That means when you
> > > mix them with other compilers, you have to do something like
> > >
> > > # icc .... find the right gcc personality functions
> > >
> > > How can we address this?
> > >
> > >
> > >      
> > The presonality routines should be either (a) included in the shared 
> > object or executable, or (b)  the shared object or executable should 
> > have a dependency on a shared object providing that personality routine.
> >    
>
> It seems to me that we need to sit down and think about what kinds of
> "compatibility" are really guaranteed by the ABI before we make any
> changes in this area.  For instance, we currently satisfy references to
> the unwind symbols (on ELF platforms, this is) by adding a DT_NEEDED
> referring to "libgcc_s.so.1".  Does that violate the ABI?  If not,
> perhaps versioning the symbols doesn't either.
No, that doesn't violate the ABI.  The is built atop whatever other ABIs 
are on the platform.  On  IA32 GNU/Linux (say), ELF with DT_NEEDED is 
part of the system ABI, so using it is just fine.  Your program can 
depend on whatever shared objects it wants to, including libgcc.

The C++ runtime support library (containing __cxa_* and _Unwind_*) is 
special; the ABI specifically is designed to allow any compiler to 
generate code that will work with any support library.  I don't think 
the use of versioned symbols allows that; it means, concretely, that 
Intel would have to emit references to versioned symbols in the code 
that icc generates.  That didn't use to be the case, and it shouldn't be 
the case now.

--
Mark Mitchell
CodeSourcery, LLC
(916) 791-8304
mark@codesourcery.com