LTO setup

[Fabio Coatti]

In data martedì 2 febbraio 2016 13:01:06, Markus Trippelsdorf ha scritto:

> > 3) the most problematic one: whenever a static lib (.a) is produced,
> > compilations depending on it always fails, complaining about missing
> > symbols. I tried every "solution" that I found (placing plugin in right
> > directory, using wrappers for ar/nm/ranlib and so on, to no avail.
> > some examples are plib (plib.sourceforge.net) qtdeclarative, etc.
> > It seems that many symbols are not present in lto-built libs, however I'm
> > not able to fix the issue, so I'm wondering if this could be an issue
> > with my setup or the package itself that can't be built with LTO. Again,
> > a very short test case to check if my setup is fine would be really
> > helpful.
> 
> This should be fixed by the symlink in lib/bfd-plugins.

Thanks for your answer; I've followed your advices (and others on the blog) 
and I think I can assume that lto is applied: using git-shell the size is 
greatly reduced when compiling with lto turned on. I created the symlink as 
suggested.

However, I see a behaviour that I can't understand with static libs (.a).

As example, I built plib both with lto and without.
The result puzzles me:
LTO
size 531792 
nm libplibfnt.a | wc -l: 105

NO-LTO
size 153604
nm libplibfnt.a | wc -l: 809

The size can be justified by this error:
x86_64-pc-linux-gnu-strip: /var/tmp/portage/media-libs/plib-1.8.5-
r1/image/usr/lib64/st1bAIiB/slMODinst.o: plugin needed to handle lto object

I get many of them, so it is likely that object files are not stripped; however 
the issue is that exported symbols are far less in LTO build, and, as example, 
flightgear fails to compile due to missing symbols; it builds fine with plib 
compiled without lto.

I guess I have something else to fix :)

-- 
Fabio