Bruce Cran [mailto:br...@cran.org.uk] wrote:
]Sent: Wednesday, July 08, 2015 05:12 PM
]To: edk2-devel@lists.sourceforge.net
]Subject: Re: [edk2] [PATCH] BaseTools/GCC: allow unused but set variables
]
]On Wed, Jul 08, 2015 at 10:43:38PM +0200, Laszlo Ersek wrote:
]
]> I think it would make a difference if -flto *actually* worked, but from
]> a quick google search, I think it either doesn't work with gcc-4.8 at
]> all, *or* the edk2 build system would have to use FLTO-aware binutils
]> and linker wrappers (or parameters). I have no clue how to set that up.
]> So for now we'll have to stick with MDEPKG_NDEBUG I guess.
]
]I've been trying to get -flto working this week, but without success (yet!).
]I'm currently running into a problem of ld (built from source) apparently not
]knowing about the lto plugin (and passing the liblto.so file via -plugin causes
]an assert failure), but I'll keep trying.
Last year I spent some time to get gcc -flto working properly with EDK2.
At that time, the people here were busy with other things and there didn't
seem to be a lot of interest in gcc link time optimization. So I never
submitted a patch. Maybe it is time to revive this effort. Here is what I
found:
http://notabs.org/uefi/gcc-lto.htm
So 6 conditions need to be met for ghcc link time optimization to work
properly with EDK2:
1) Add -flto to the compile flags
2) Use gcc to launch ld instead of invoking ld directly
3) Include the compile flags on the link command line
4) Use gcc-ar in place of ar when building static libraries
5) Library code that resolves helper function calls generated by the
compiler must be compiled without the -flto flag
6) These libraries must be prefixed with -Wl,-plugin-opt=-pass-through= on
the link command line.
A patch from late 2014 is here:
http://sourceforge.net/projects/edk2developertoolsforwindows/files/Patches/Link%20Time%20Optimization/
Thanks,
Scott
]Also, in terms of edk2-related resources, if anyone's interested I've been
]running doxygen on the sources and putting the results in
]http://bluestop.org/edk2/docs - the log files contain the tons of warnings the
]tool generates, while the directories (http://bluestop.org/edk2/docs/trunk,
]http://bluestop.org/edk2/docs/UDK2014.SP1 etc.)
]contain the API docs themselves. I started generating them since I noticed
]feishare.com hadn't been updated for a couple of years and wasn't aware of any
]other sites hosting a copy.
]
]--
]Bruce
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