Re: [PATCH] Allow kmscon to be cross-compiled

[Thierry Reding <thierry.reding@gmail.com>]

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On Mon, Sep 09, 2013 at 12:48:08PM +0200, David Herrmann wrote:
> Hi
> 
> On Mon, Sep 9, 2013 at 12:27 PM, Thierry Reding
> <thierry.reding@gmail.com> wrote:
> > The genshader and genunifont utilities are run during the build process
> > to generate source files. In order for that to work when cross-compiling
> > the files need to be built using the native compiler instead of the
> > cross-compiler.
> >
> > Add the AX_PROG_CC_FOR_BUILD m4 macro which defines various *_FOR_BUILD
> > variables that are the native equivalents of CC, CFLAGS, LDFLAGS, etc.
> > Override CC, CFLAGS and LDFLAGS for genshader and genunifont and their
> > object files so that they will be built natively and can be executed
> > during the build.
> 
> Thanks a lot! Looks all good, few comments below. I think I will apply
> it as is, anyway. New bugfix-release is planned for this week, too.
> 
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> >  Makefile.am                |  16 ++++--
> >  configure.ac               |   3 +-
> >  m4/ax_prog_cc_for_build.m4 | 125 +++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 139 insertions(+), 5 deletions(-)
> >  create mode 100644 m4/ax_prog_cc_for_build.m4
> >
> > diff --git a/Makefile.am b/Makefile.am
> > index 7019290..f1b4435 100644
> > --- a/Makefile.am
> > +++ b/Makefile.am
> > @@ -445,8 +445,12 @@ EXTRA_DIST += $(SHADERS)
> >  CLEANFILES += src/static_shaders.c
> >  genshader_SOURCES = src/genshader.c
> >
> > -src/static_shaders.c: $(SHADERS) genshader$(EXEEXT)
> > -       $(AM_V_GEN)./genshader$(EXEEXT) src/static_shaders.c $(SHADERS)
> > +src/static_shaders.c: $(SHADERS) genshader$(BUILD_EXEEXT)
> > +       $(AM_V_GEN)./genshader$(BUILD_EXEEXT) src/static_shaders.c $(SHADERS)
> > +
> > +genshader$(BUILD_EXEEXT) $(genshader_OBJECTS): CC = $(CC_FOR_BUILD)
> > +genshader$(BUILD_EXEEXT) $(genshader_OBJECTS): CFLAGS = $(CFLAGS_FOR_BUILD)
> > +genshader$(BUILD_EXEEXT): LDFLAGS = $(LDFLAGS_FOR_BUILD)
> 
> Just wondering, isn't this going to break if $BUILD_EXEEXT != $EXEEXT
> I mean, noinst_PROGRAMS generates build-rules for $EXEEXT, not for
> $BUILD_EXEEXT, so a dependency on "genshader$(BUILD_EXEEXT)" won't do
> anything if it differs from $EXEEXT. But maybe I am just missing
> something and automake creates rules for both?

That's a good point. And yes, I think it would break if both extensions
differed. On the other hand I have no idea on how to make automake
generate rules for $(BUILD_EXEEXT). I don't think it can.

Interestingly, I mistakenly used genshader$(EXEEXT) initially, but that
causes automake to spew out warnings that these "rules" (which aren't
really rules at all) were overriding previous commands for the same
target. So while $(BUILD_EXEEXT) is the right extension to use, it also
works around a shortcoming in automake. Another shortcoming of automake
will cause this to break when doing MinGW->Unix and Unix->MinGW cross-
builds...

A different approach of this patch was to move genshader and genunifont
to a tools subdirectory with a separate Makefile.am and overwrite the
CC, CFLAGS and LDFLAGS variables in that directory only, but automake
doesn't accept that either because CFLAGS is considered a user variable
and therefore can't be overwritten.

I think this is as good as it gets for now. I've tried to fix this kind
of problem in automake several times but never managed to. Perhaps it's
time to move on to something like SCons...

Thierry

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