linux-kernel - Re: [-next] FATAL: drivers/gpu/drm/udl/udl: sizeof(struct usb_device_id)=24 is not a modulo of the size of section __mod_usb_device

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Date:	Sun, 17 Jun 2012 16:00:57 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	Andreas Schwab <schwab@...ux-m68k.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	USB list <linux-usb@...r.kernel.org>,
	linux-kernel@...r.kernel.org,
	Linux-Next <linux-next@...r.kernel.org>,
	linux-kbuild <linux-kbuild@...r.kernel.org>,
	Linux/m68k <linux-m68k@...r.kernel.org>
Subject: Re: [-next] FATAL: drivers/gpu/drm/udl/udl: sizeof(struct usb_device_id)=24 is not a modulo of the size of section __mod_usb_device_table=44.

Andreas Schwab <schwab@...ux-m68k.org> writes:
> Bjørn Mork <bjorn@...k.no> writes:
>
>> AFAIK (which admittedly is not much wrt cross building) there is no way
>> we can make the host built file2alias know the proper aligment for the
>> structure in the target built modules.  That's the background for this
>> fix: 
>>
>> commit 4ce6efed48d736e3384c39ff87bda723e1f8e041
>> Author: Sam Ravnborg <sam@...nus.ravnborg.org>
>> Date:   Sun Mar 23 21:38:54 2008 +0100
>>
>>     kbuild: soften modpost checks when doing cross builds
>
> This is not a fix in any sense of the word.  modpost can only work
> properly if its view of the device_id structures matches *exactly* that
> of the target.

You are absolutely correct, of course.  I am starting to believe Greg is
correct.  Cross building works mostly by pure luck :-)

I found that the reason the change I referred to above didn't kick in
was because CONFIG_DEBUG_SECTION_MISMATCH was set, causing modpost to be
called from scripts/Makefile.build without the "-c" option:

 # Do section mismatch analysis for each module/built-in.o
 ifdef CONFIG_DEBUG_SECTION_MISMATCH
   cmd_secanalysis = ; scripts/mod/modpost $@
 endif


But as you point out: The whole "soften modpost check" concept is bogus.
It just cannot work.  And I just verified it doing a m68k allmodconfig
build without CONFIG_DEBUG_SECTION_MISMATCH.  modpost will bail out
unless host and target aligment matches:

  scripts/mod/modpost -m -a -o /usr/local/src/build-tmp/linux/Module.symvers    -S  -c -s
drivers/media/video/gspca/gspca_sunplus: struct usb_device_id is 24 bytes.  The last of 55 is:
0x04 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 
FATAL: drivers/media/video/gspca/gspca_sunplus: struct usb_device_id is not terminated with a NULL entry!
make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2


So the prosed fix from Greg is certainly the correct one, until someone
rewrites modpost to be completely cross build safe.


Bjørn
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