[linux-dvb] Re: scan doesn't compile

[Holger Waechtler <holger@convergence.de>]

Johannes Stezenbach wrote:
> On Tue, Oct 29, 2002 at 04:05:25PM +0100, Holger Waechtler wrote:
> 
>>Stefan Hußfeldt wrote:
>>
>>>scan from todays (CVS) DVB package doesn't compile:
>>>
>>>|[root@zaphod scan]# make
>>>|gcc -M -g -Wall -O0 -I/usr/src/linux-2.4.19-16mdksmp/include 
>>>-I../../include scan.c dump.c > .depend
>>>|gcc -g -Wall -O0 -I/usr/src/linux-2.4.19-16mdksmp/include -I../../include 
>>>-c scan.c -o scan.o
>>>|In file included from /usr/include/linux/prefetch.h:13,
>>>|                 from /usr/include/linux/list.h:6,
>>>|                 from scan.c:13:
>>>|/usr/include/asm/processor.h:55: `CONFIG_X86_L1_CACHE_SHIFT' undeclared 
>>>here (not in a function)
>>>|/usr/include/asm/processor.h:55: requested alignment is not a constant
>>>|make: *** [scan.o] Fehler 1
>>>
>>>|[root@zaphod scan]# rpm -q kernel-headers
>>>|kernel-headers-2.4.18-41mdk
>>>
>>>|[root@zaphod scan]# cat /etc/redhat-release 
>>>|Mandrake Linux release 9.0 (dolphin) for i586
>>
>>Your kernel include files are screwed up. /usr/include/linux, 
>>/usr/include/asm have to refer to the same kernel source. You should use 
>>header files of a recent kernel.
> 
> 
> AFAIK the header files in /usr/include/linux and asm must match
> the glibc installed in the system. Replacing them with newer
> ones is not recommended. Sometimes it's necessary to supply
> newer driver API header files to use new ioctls (like for the
> DVB driver ;-), but in general you should leave the system
> header files alone.

in /usr/include/linux and /usr/include/asm right. But to compile 
additional drivers you always need the include files for the currently 
installed header, that's why the DVB driver (and the scan utility too) 
used the includes from /us/src/linux-$(KERNELRELEASE)/include/.

The files from /usr/include/linux and /usr/include/asm were used by gcc 
as fallback because the actual includes were not found. Maybe we should 
add -nostdinc to the CFLAGS, then compilation is rejected and the 
fallbacks from /usr/include will never be used.


> What scan.c does to use linux/list.h is simply illegal.

(illegal but working:)
It was a quick hack to get a linked list implementation and would have 
worked fine if your kernel headers would had been installed correctly.

(Anyway, it's clean now - your computer science teacher should be happy 
too;)

When you don't install the include files for your currently running 
kernel (and compile everything that talks directly to the kernel against 
these header files, applications as well as driver modules) you always 
risk oopses and segfaults because nobody guarantees that data layout 
does not changes between kernel revisions.

Holger



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