Prelinking apps

Scott James Remnant scott at
Wed Oct 20 07:10:33 CDT 2004

On Wed, 2004-10-20 at 12:57 +0100, Colin Watson wrote:

> On Wed, Oct 20, 2004 at 12:34:28PM +0100, Scott James Remnant wrote:
> > On Wed, 2004-10-20 at 01:35 +0200, Tollef Fog Heen wrote:
> > > * Scott James Remnant 
> > > | descent scott% LD_DEBUG=statistics /lib/tls/i686/cmov/ /usr/bin/gedit
> > > 
> > > After a bit of discussion with Daniel Jacobowitz, it seems your method
> > > of checking is a bit flawed.  You need to run just LD_DEBUG=statistics
> > > /usr/bin/gedit, else you will get relocations nonetheless (as you can
> > > see -- the prelinking should have reduced the number of relocations to
> > > 0).
> > 
> > How curious ... Why doesn't prelinking work when you use the TLS-enabled
> > link loader?
> Daniel said that if you run the loader by hand as above, the kernel
> moves it to a different address from the one prelink expects, which
> breaks prelinking.
Just the link-loader?  You can't move the binary itself, as those aren't
PIC and have fixed load addresses.  I'm surprised that does break
pre-linking, but oh well.

I'm still a bit amused that I missed the fact the relocations weren't 0
in the second run; though in the first run only 121 relocations were
performed (the rest came from the cache).

So the benefit is the loss of 121 load-time relocations, and about 5500
runtime relocations (which are even harder to measure benefit-wise).
I'm still going to stand by my assertion that this isn't won't give a
noticeable speed improvement, but without the broken statistics this
time <g>

> > Does this mean that any TLS-enabled application, even when prelinked,
> > isn't going to benefit anyway?
> > 
> > The reason you need to use that link loader is because the default i386
> > one doesn't know about the hyper-accurate timer in the i686, so you
> > can't use it for any useful stats.
> Is there no way to use the TLS loader other than by running it manually?
Only by linking with it in the first place.

Have you ever, ever felt like this?
Had strange things happen?  Are you going round the twist?
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