linux-kernel - Re: crossbuild fails in modpost

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Message-ID: <20080515174015.GA24024@uranus.ravnborg.org>
Date:	Thu, 15 May 2008 19:40:15 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Michael Buesch <mb@...sch.de>,
	Gordon Farquharson <gordonfarquharson@...il.com>
Subject: Re: crossbuild fails in modpost

On Thu, May 15, 2008 at 07:35:39PM +0200, Sam Ravnborg wrote:
> On Thu, May 15, 2008 at 07:12:34PM +0200, Jiri Slaby wrote:
> > Well, let's fix sam's email.
> > 
> > Jiri Slaby napsal(a):
> > >Hi,
> > >
> > >probably
> > >4ce6efed48d736e3384c39ff87bda723e1f8e041
> > >kbuild: soften modpost checks when doing cross builds
> > >
> > >causes build failures on x86_64 kernel build on 32 bit machine:
> > >
> > >make -f /local/xslaby/hid/scripts/Makefile.modpost
> > >YYYYYYYYYYYYYY x86_64 x86_64
> > >  scripts/mod/modpost -m -a -o /local/xslaby/buhid/Module.symvers    -S 
> > >-K /local/xslaby/buhid/Module.markers -M 
> > >/local/xslaby/buhid/Module.markers   -s
> > >XXXXXXXXXXXXXXXXXX 20: 0 (2), 4 (4), 8 (4), 12 (8)
> > >FATAL: drivers/hid/hid-apple: sizeof(struct hid_device_id)=20 is not a 
> > >modulo of the size of section __mod_hid_device_table=648.
> > >Fix definition of struct hid_device_id in mod_devicetable.h
> > >make[2]: *** [__modpost] Error 1
> > >make[1]: *** [modules] Error 2
> > >make: *** [sub-make] Error 2
> > >
> > >after sticking echo into:
> > > __modpost: $(modules:.ko=.o) FORCE
> > >+       @echo YYYYYYYYYYYYYY $(KBUILD_BUILDHOST) $(ARCH)
> > >        $(call cmd,modpost) $(wildcard vmlinux) $(filter-out FORCE,$^)
> > >
> 
> Your machine claims it is a x86_64 and you are building for a x86_64
> according to the following line:
> > >YYYYYYYYYYYYYY x86_64 x86_64
> 
> So it looks to me that you are building for 64 bit on a 64 bit machine.
> So when you write:
>  on x86_64 kernel build on 32 bit machine:
> 
> I assume you try to say that your HOSTCC is 32 bit and your
> kernel cc is 64 bit (or something similar).
> 
> The commit you reference loosen up the check so we do not do the
> check if we _know_ that the host and the target system differs.
> The only thing I can imagine right now to solve your issue would
> be to skip the check if we do not use the same gcc for target and host?

So something like this (entirely untested):

--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -65,7 +65,7 @@ modules   := $(patsubst %.o,%.ko, $(wildcard $(__modules:.ko=.o)))
 # Stop after building .o files if NOFINAL is set. Makes compile tests quicker
 _modpost: $(if $(KBUILD_MODPOST_NOFINAL), $(modules:.ko:.o),$(modules))
 
-ifneq ($(KBUILD_BUILDHOST),$(ARCH))
+ifneq ($(CC),$(HOSTCC))
         cross_build := 1
 endif
 

Only powerpc (and ppc) does seems to do the wrong thing
and fiddle with CC:

powerpc/Makefile:override CC    += -m$(CONFIG_WORD_SIZE)

So for most users this is OK.
(If it works as expected).

	Sam
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