LTO setup

[Fabio Coatti]

In data martedì 2 febbraio 2016 19:54:22, Markus Trippelsdorf ha scritto:
> On 2016.02.02 at 18:35 +0100, Fabio Coatti wrote:

> > 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.
> 
> The libplibfnt.a should only contain compressed GIMPLE code when build
> with -flto.
> 
> See also https://gcc.gnu.org/wiki/LinkTimeOptimizationFAQ


ok, thanks; I'm still struggling to understand why the linking fails, even 
with your suggestion. It would be useful a way to list symbols present in a .o 
and .a file, to make sure that object files are created fine.
>From what I read, gcc-nm (or even nm in latest versions) should do that, 
however running it on libplibfnt.a (to use the same examples) shows only few 
symbols, way fewer than on no-lto build.
So, now my question is: is it ok for nm not to show all the symbols or should 
it show also those related to gimple code?
Interesting enough, "strings" run against libplibfnt.a shows all symbols, but 
with some differences:

If I grep strings for a symbols shown by nm, like this:
# nm /usr/lib/libplibfnt.a | grep ZN7fntFontC2Ev
00000000 T _ZN7fntFontC2Ev
         U _ZN7fntFontC2Ev

I get the following result:
# strings /usr/lib/libplibfnt.a | grep ZN7fntFontC2Ev
_ZN7fntFontC2Ev
.gnu.lto__ZN7fntFontC2Ev.73e0594a6663c7f3

while doing the same for asymbol not shown by nm:
strings /usr/lib/libplibfnt.a | grep ZL23Fixed8x13_Character_12

I get the following output (for a lto-built lib)
# strings /usr/lib/libplibfnt.a | grep ZL23Fixed8x13_Character_123
.gnu.lto__ZL23Fixed8x13_Character_123.78e9fac11ab52f79

Quite different, as it is shown only as .gnu.lto

does this means that the lib itself is built correctly with lto flag, and it is 
a problem in the build phase of the program requiring the static lib? If this 
is the case, the behaviour of nm, not showng .lto symbols is it correct?

Many thanks.


-- 
Fabio