versioning of _Unwind_*() symbols

[H. J. Lu]

On Wed, Apr 21, 2004 at 12:34:30PM -0700, Mark Mitchell wrote:
> 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.
> 

If we are building a shared library with DT_NEEDED pointed to the
unwind library called "libgcc_s.so.1", how can another compiler use
their unwind library, saying libmyunwind, with this DSO? If the C++
ABI covers unwind with shared library and executable, it should also
specify how the unwind library should be handled at link time as well
as at run time.


H.J.