Re: __register_frame_info & shared library compatibility

[Mark Kettenis <kettenis@wins.uva.nl>]

   From: Jeffrey A Law (law@cygnus.com)

   Back in 1997 we tried _very_ hard to convince Richard Kenner and Richard
   Stallman to keep the old "__register_frame_info" interface in libgcc.a for
   gcc2 for precisely this problem.

I think that you mean "__register_frame" instead of
"__register_frame_info".

   Against our recommendations, the interface was removed from gcc2.8.

The "__register_frame" interface was never included in any official
FSF release of gcc before 2.8.  Back then, egcs was still
"experimental" which was probably the reason why Kenner didn't want to
include the (broken) "__register_frame" interface that was part of
egcs 1.0 in gcc 2.8.  However, compatibility for the old
"__register_frame" was included in gcc 2.8.1.  This has not been
noticed by a lot of people since, where the "__register_frame_info"
and "__register_frame" functions are part of the same object module in
egcs's libgcc.a, they are in different modules in gcc's libgcc.a.
This was exactly why 

However, this issue is irrelevant for the current
"__register_frame_info & shared library compatibility" discussion.
The way "__register_frame_info" is referenced in 2.8 <= gcc <= 2.8.1
and 1.0.3 <= egcs <= 1.1.1 is in principle the same.  The problem is
indeed that egcs 1.1.2 now puts only a weak reference to
"__register_frame_info" in crtstuff.  This means that "du moment" one
recompiles a shared library that previously contained
"__register_frame_info" it probably does not anymore, and programs
linked with that library stop running.

Now, things get really complicated because of the egcs/Linux
``releases''.  In an attempt to fix problems the author has messed
around with the way "__register_frame_info" is used in the varied
egcs-1.1.1/Linux ``releases''.  This might mean that some people that
use these versions will experience the same problems, but report that
they're using egcs-1.1.1 instead of egcs-1.1.2.  IMHO we have to
prevent that this happens again for egcs-1.1.2, and discourage the
author to release any "fixed" version of egcs-1.1.2.

It is probably not a bad idea to revert the weak reference to
"__register_frame_info" patch in egcs-1.1.2.  It may result in larger
executables with glibc 2.0, but at least we get rid of the shared
library compatibility problem.  For glibc 2.1 things shouldn't matter
since "__register_frame_info" is exported from libc, which by default
every program and shared library is linked against.

Mark

P.S. I haven't tested this, but using

   "-Wl,-u __register_frame_info"

when rebuilding a shared library with egcs-1.1.2 (or egcs-1.1.1/Linux)
will probably avoid the problems discussed in this thread.