prelink: is it worth it?

[yersinia]

On Thu, Jul 9, 2009 at 5:06 PM, Jakub Jelinek <jakub at redhat.com> wrote:

> On Thu, Jul 09, 2009 at 10:32:01AM -0400, Matthew Miller wrote:
> > Apparently there was some fun with prelink breaking everything in rawhide
> > recently: <https://bugzilla.redhat.com/show_bug.cgi?id=509655>. I didn't
> > notice, because like Pete Zaitcev says in the comments, removing prelink
> is
> > one of the first things I do.
> >
> > I see it as adding unnecessary complexity and fragility, and it makes
> > forensic verification difficult. Binaries can't be verified without being
> > modified, which is far from ideal. And the error about dependencies
> having
> > changed since prelinking is disturbingly frequent.
> >
> > On the other hand, smart people have worked on it. It's very likely that
> > those smart people know things I don't. I can't find any good numbers
> > anywhere demonstrating the concrete benefits provided by prelink. Is
> there
> > data out there? Pretty charts and graphs would be nice. The only things
> I've
> > been able to find are old and not very impressive:
> >
> >    <http://crast.us/james/articles/prelink.php>
> >    <
> http://smackerelofopinion.blogspot.com/2009/06/does-prelinking-speed-up-boot-times.html
> >
> >    <http://reallylongword.org/prelink-2/>
>
> Say on x86-64 F11 (with /etc/prelink.conf.d/nss-prelink.conf removed):
> LD_DEBUG=statistics /usr/lib64/openoffice.org3/program/swriter.bin
>     11799:
>     11799:     runtime linker statistics:
>     11799:       total startup time in dynamic loader: 18632372 clock
> cycles
>     11799:                 time needed for relocation: 2975643 clock cycles
> (15.9%)
>     11799:                      number of relocations: 0
>     11799:           number of relocations from cache: 1527
>     11799:             number of relative relocations: 0
>     11799:                time needed to load objects: 13190177 clock
> cycles (70.7%)
> LD_USE_LOAD_BIAS=0 LD_DEBUG=statistics
> /usr/lib64/openoffice.org3/program/swriter.bin
>     11817:
>     11817:     runtime linker statistics:
>     11817:       total startup time in dynamic loader: 145813250 clock
> cycles
>     11817:                 time needed for relocation: 129375884 clock
> cycles (88.7%)
>     11817:                      number of relocations: 42207
>     11817:           number of relocations from cache: 126013
>     11817:             number of relative relocations: 149959
>     11817:                time needed to load objects: 15248893 clock
> cycles (10.4%)
> The former is how long it takes before swriter.bin starts up when
> prelinked,
> the latter tells it not to use prelink information and do normal
> relocation.
> Try this on any other GUI app that links against dozens of shared
> libraries.


Perfect. this is the key point for me. If i mantain server only, not desktop
client, without X and the like,
no problem to disable it. Isn't right ? I have already do this, for security
reason due to centralizzated integrity checker, on +300 production RHEL
machine.

Regards

>
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