DragonFly added DT_GNU_HASH support to rtld

[Konstantin Belousov]

On Sun, Mar 11, 2012 at 10:59:00AM +0100, John Marino wrote:
> Hi Konstantin,
> 
> It seems that no BSD supported DT_GNU_HASH despite this option being 
> available on the base binutils (FreeBSD's 2.17.50 binutils supports it). 
>  This gnu extension is a big performance improvement over the specified 
> SysV hash.
> 
> The guy porting libreoffice to pkgsrc was finding -Wl,--hash-style=gnu 
> to be the default build for that package.  Indeed, using the standard 
> hash results in very long startup times for something like Writer (> 8 
> seconds launched from a SSD)
> 
> The result is that we brought in DT_GNU_HASH support to our real-time 
> linker this weekend.  We're still waiting to see how that improves 
> libreoffice startup times.
> 
> full commit:
> >http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/7629c6317998f850ebca23c296822ba08af09e5b
> 
> 
> Modification to base compiler so all system libs and binaries can take 
> advantage of it:
> >http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/4687ecd9561d76f3d02ccb4f7adeecd5e3afdd8f
> 
> 
> For a while, binaries with dynamic symbol tables will have both types of 
> hashes embedded.  At some point in the future, we may switch over to 
> only generating the GNU hash.  This will break forward compatibility, 
> but that happens rather frequently for other reasons anyway.
> 
> I was a bit surprised FreeBSD didn't already have this functionality 
> given the performance benefits, so hopefully these DragonFly commits 
> will be interesting for you.
> 

I finally ported the Dragonfly commit to FreeBSD. There were several
changes reverted in dragonfly version of the extracted matched_symbol()
function which were restored. I also blindly converted all non-x86
arches.

The matched_symbol() extraction is the good opportunity to apply the
style(9) formatting to the large chunk of rtld code.

Any testers, esp. on non-x86 architectures, are welcome. You would need
to modify gcc spec file for you architecture, see corresponding x86
changes in contrib/gcc/config/i386.

For me, patch successfully worked on the machine were I disabled sysv
hashes at all.

http://people.freebsd.org/~kib/misc/rtld-gnu_hash.1.patch
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