Re: Symbol redefinition building 2.6.6 UML kernel

["H. J. Lu" <hjl at lucon dot org>]

On Wed, Jul 21, 2004 at 04:18:40PM -0700, Kevin P. Fleming wrote:
> I'm trying to help some members of the LFS team debug a problem building 
> a 2.6.6-based UML kernel. At this time, we cannot determine whether the 
> problem is actually the fault of "ld" or if we have a toolchain build 
> quality problem. The testing has been done with FSF 2.15 binutils and 
> HJL 2.15.90.0.1 binutils.
> 
> Here is the scenario:
> 
> - unpack a linux-2.6.6 kernel tarball
> - apply the 2.6.6 UML kernel patch (from 
> http://prdownloads.sourceforge.net/user-mode-linux/uml-patch-2.6.6-1.bz2)
> - run "make ARCH=um menuconfig" and turn off UML Networking Multicast 
> support
> - run "make ARCH=um linux"
> 
> On some of our systems, during the final link of vmlinux, there are 
> symbol redefinitions of the common functions from glibc that are also 
> present in the kernel. Primarily this includes the string functions, but 
> there are others.
> 
> I have followed this down to the object file "unmap_fin.o" (from 
> arch/um/kernel/tt) that is built; this object file is made by linking 
> "unmap.o" with the system's libc (glibc-CVS in our case) but producing a 
> relocatable object. This relocatable object is then linked into vmlinux 
> using the linker script at arch/um/uml.lds.S, which appears to just 
> "force" the contents of this file into the resulting kernel image as raw 
> data.
> 
> As best I can tell, during this final link step the linker should not be 
> paying attention to any exported symbols from this object file, but it 
> does. When it works properly, the symbol redefinitions do not occur and 
> the final link proceeds to completion.
> 
> We are concerned that we may be providing faulty toolchain build 
> instructions to our users, although we have not had problems building 
> hundreds of other packages. In fact, these same build instructions work 
> fine for the UML kernel on some of our testers' systems, just not all of 
> them.
> 
> Can anyone provide some assistance to us to try to isolate this problem? 
> Thanks in advance :-)

Please open a bug report at

http://sources.redhat.com/bugzilla/

and provide a pointer to a complete testcase. If you can show me how to
reproduce it, I will look into it.


H.J.