linux-kernel - Re: crossbuild fails in modpost

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Date:	Thu, 15 May 2008 21:19:26 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Sam Ravnborg <sam@...nborg.org>
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

Sam Ravnborg napsal(a):
> 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?

Well, the compiler is the same, but it's told to compile the kernel with 
-m64. It runs on x86_64 kernel and i386 userspace. It's debian i386 gcc 
package which understands x86_64 objects too. No SUBARCH option, it seems to 
default to x86_64.

> 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))

gcc gcc :)

>          cross_build := 1
>  endif
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