On Fri, Sep 20, 2013 at 07:15:29PM +0200, Jeroen Hofstee wrote: > Hello Tom, > > On 09/19/2013 11:16 PM, Tom Rini wrote: > >On Sat, Aug 24, 2013 at 01:55:38PM +0200, Jeroen Hofstee wrote: > > > >>The movt/movw instruction can be used to hardcode an > >>memory location in the instruction itself. The linker > >>starts complaining about this if the compiler decides > >>to do so: "relocation R_ARM_MOVW_ABS_NC against `a local > >>symbol' can not be used" and it is not support by U-boot > >>as well. Prevent their use by requiring word relocations. > >>This allows u-boot to be build at other optimalization > >>levels then -Os. > >> > >>Signed-off-by: Jeroen Hofstee <jer...@myspectrum.nl> > >>Cc: tiger...@viatech.com.cn > >>Cc: Albert ARIBAUD <albert.u.b...@aribaud.net> > >>--- > >> arch/arm/config.mk | 8 ++++++-- > >> 1 file changed, 6 insertions(+), 2 deletions(-) > >Is this also something we need for llvm? > > You guessed that right, for clang actually (llvm has > already been taught to not emit movw/movt pairs, > when requested not to do so). So with the > -mword-relocations || present I can teach clang to tell llvm > not to do it. > > I am not aware of any reason why gcc could not > decide to do the same in future releases. A pointer > comparison e.g. is of exactly the same size (afaik). > In this case U-boot will no longer compile without > mentioned flag.
OK. [snip] > >If there's some -O2 enabled gcc flag we want because of > >a measurable performance win, we should add it specifically to -Os. > > > First of all the default -Os is unchanged and I have no > intention to change it. -O2 won't build without the patch > last time I checked ;) > > Anyway, I like the flag since it helps to not special case > clang and it guarantees builds with gcc at all optimisation > levels, now and in the future. I don't care if it goes in this > release or the next one. Right, I'm OK picking this patch up then, on the grounds of making clang/llvm work now, and potentially keeping a future gcc happy. -- Tom
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