Re: "gdb vmlinux" gives wrong symbol addresses

[Vivek Goyal <vgoyal at in dot ibm dot com>]

On Fri, Aug 18, 2006 at 02:48:37PM -0400, Daniel Jacobowitz wrote:
> On Fri, Aug 18, 2006 at 02:38:07PM -0400, Vivek Goyal wrote:
> > Following are two outputs.
> > 
> > vmlinux linked without option --emit-relocs
> > 
> > (gdb) p &linux_banner
> > $1 = (char (*)[162]) 0xc0344000
> > 
> > vmlinux linked with option --emit-relocs
> > 
> > (gdb) p &linux_banner
> > $1 =  (char (*)[162]) 0x8068a000
> 
> Stick a 1 in front of that and it should be obvious what the problem
> is.  The address has been doubled.
> 

Oh. Thanks.

> The debug section has been fully resolved, but relocations are also
> applied to it, moving all addresses up even further.  I don't have
> any good idea on how to detect this case.  We originally handled
> relocations for shared libraries with unrelocated debug sections;
> but this is a fully relocated section which still has relocation
> information.
> 
> Did we change all binutils targets to resolve relocations in debug
> sections?  I don't really remember.  If so, maybe we should drop
> support for shared libraries with this problem, and only apply
> relocations to debug info for ET_REL objects.
> 

In this case file type is ET_EXEC and not even ET_DYN or ET_REL. 
Probably we should not be applying relocations at least for file
types ET_EXEC as relocations have already been processed.

We are looking at making i386 kernel relocatable by retaining
relocation information in fully linked executable and later using
that info to relocate the kernel at run time. Eric already has
posted working patches. In this context I can not debung kernel core
using gdb if this problem persists.

Thanks
Vivek