Re: Don't use INTDEF/INTUSE in unwind-dw2-fde.c (bug 14132)

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Tue, 28 Oct 2014, Carlos O'Donell wrote:

> > 2014-10-22  Joseph Myers  <joseph@codesourcery.com>
> > 
> > 	[BZ #14132]
> > 	* sysdeps/generic/unwind-dw2-fde.c
> 
> <off topic>
> Is this file shared with libgcc and should it be listed here?
> 
> https://sourceware.org/glibc/wiki/SharedSourceFiles

It's not shared in the sense of being useful to have a single version that 
works in both places.  This file is in glibc purely for binary 
compatibility with binaries built with old glibc and GCC versions (from 
before symbol versioning, when glibc accidentally re-exported various 
symbols from libgcc) - so there is no use in it supporting newer unwind 
info features generated by newer GCC (unwinding from thread cancellation 
uses the copy of the unwinder in shared libgcc, not this compat copy).  
But those unwinder files did originate from libgcc, yes.

It might be possible to eliminate those copies by making libc on affected 
architectures dlopen shared libgcc at startup and use the functions from 
there in the same way as done for thread cancellation, but that might not 
be desirable given most binaries wouldn't need it (really you'd want it to 
be dlopened only for binaries referencing those symbols; lazy opening is 
problematic for error reporting).

All the symbols conditioned on EXPORT_UNWIND_FIND_FDE in elf/Versions 
really ought to be compat symbols, although they aren't at present (see 
the note on the wiki todo list about reviewing exported symbols starting 
with '_' in general).

> .. and while I'm thinking about it, should the soft-fp code be 
> listed in our `SharedSourceFiles` wiki page?

Yes, it's shared, with the glibc version getting copied verbatim to 
libgcc.  I still need to implement one feature for the glibc version 
(FP_TO_INT_ROUND) before it has all the features needed to replace the old 
fork of the code in the Linux kernel (replacing the kernel version will 
also be a lot of work, given the various interface changes since it 
diverged over 10 years ago).

-- 
Joseph S. Myers
joseph@codesourcery.com