[yocto] prelink support

[Mark Hatle]

On 6/20/16 7:24 AM, Kyle Russell wrote:
> It looks like the image-prelink support is still disabled in master because of
> an issue with IFUNC symbol relocation.
> 
> https://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/meta-poky/conf/local.conf.sample?id=8debfea81e69d038bd2d56314b272cb74f5582ed
> 
> Is there still a problem, or is it safe to reenable image-prelink?  I see a "Fix
> ARM IFUNC support" in the prelink-cross repo, but that appears to have been
> committed several months before image-prelink was disabled.  We'd like to enable
> image-prelink on a build off jethro.
> 
> Any help or links to a recent discussion thread would be helpful.  Thanks!
> 
> 

The ARM fix is for a different IFUNC problem.

Disabling the prelinker was caused by a serious of problems that started with a
fork failure traced back to shared library processing orders.

(For comments below, I'm referring to the repository:
http://git.yoctoproject.org/cgit/cgit.cgi/prelink-cross/)

The initial problem, IFUNC processing, showed that processing order of the
shared libraries could lead to a case where the wrong IFUNC was used.  We
believe this particular issues was fixed in the staging tree.

In the tree you'll see a cross_prelink_staging branch.  In that branch the fix
is commit ID: "8f55afd84b3580b1f1d6af904e8c2a39221055b7"  This fixes the 'fork'
issue by ensuring the proper sort order for shared library processing.  (This
was finally fixed in March.)

However with that we determined there was at least one more issue related to
section ordering.  The prelink test suite was failing due to various integrity
checks showing that once we prelinked something, we could not reverse the
process.  It has taken us months to identify the cause of the problem and the
solution.  (Cause BTW was a change in binutils-2.22 that no longer ensured that
the section order was sorted by offset order... a small amount of the prelink
processing needed to be changed to deal with that behavior.  It's taken far
longer to fix then we had ever expected.)

See commit (33be255d62af533189f1f7bc66c06602b703980a) in the
cross_prelink_staging branch.

With this commit, I think the two major issues have been resolved.  I've got a
small set of additional patches I need to put into place -- and then I have to
finish going through the regression suite to verify everything is working
properly.  (Seems like every time I get to this step, something else comes up
and I'm not getting it done...)

So if you've read this far, the point in all of this is that I THINK that the
cross_prelink_staging branch and current top commit
"33be255d62af533189f1f7bc66c06602b703980a" are working.  However, I've not
completed testing so I'm not sure of that yet.

If you can help with testing, you should modify your prelink recipe to use the
'cross_prelink_staging' branch, and the 33be255 commit.  Verify that this is
working for your use cases.  If you are using glib or graphical environments pay
particular attention to process startup messages that indicate failures.

If this IS working for you, I'd like a reply back with the architecture and
processor you are using so I can add that to my matrix.  (I'm traveling for the
next couple of days, and then should be back in the officer where I hope to
finish my regression testing, apply the last couple of patches from Gentoo
developers, regression test again and prepare a release version.)

Any help is appreciated, thanks for understanding why this is taking so long.

--Mark