Messages in this thread |  | | Subject | Re: [PATCH 0/4] Compile kernel with -fwhole-program --combine | | From | David Woodhouse <> | | Date | Fri, 25 Aug 2006 09:55:16 +0100 |
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On Fri, 2006-08-25 at 08:01 +0200, Jan Engelhardt wrote: > >> Compiling files on their own (`make drivers/foo/bar.o`) seems to make > >> the optimization void. Sure, most people don't stop compiling in > >> between. Just a note > > > >Actually I'm not entirely sure what you write is true. It'll _build_ > >fs/jffs2/read.o, for example, but it still won't then use it when I make > >the kernel -- it'll just use fs/jffs2/jffs2.o which is built from all > >the C files with --combine. So the optimisation isn't lost. > > Umm then it spends double the time in compilation, doing: > > read.o <- read.c > foo.o <- foo.c > bar.o <- bar.c > built-in.o <- read.c foo.c bar.c
Only if you invoke make explicitly for read.o, foo.o and bar.o. If you just type 'make' then it won't build those.
> >So to overcome this, we use GCC's __attribute__((externally_visible)) > >which, as documented, just makes it global again -- undoing the effect > >of -fwhole-program just for this _one_ symbol. > > Interesting. __attribute__((visibility("default"))) does the same?
That much you can test for yourself without a fixed compiler. No, it doesn't.
-- dwmw2
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