Re: [Xen-devel] Re: [Xen-staging] [xen-unstable] [LINUX] Support creating ELF note segments in the kernel ELF image.

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Tue, 2006-08-22 at 08:47 -0400, Jimi Xenidis wrote:
> On Aug 22, 2006, at 7:22 AM, Xen staging patchbot-unstable wrote:
> 
> > # HG changeset patch
> > # User Ian Campbell <ian.campbell@xxxxxxxxxxxxx>
> > # Date 1156245643 -3600
> > # Node ID a4550b7488400c44a9f27c92115c8e364493837a
> > # Parent  cd4e7ace4e58d9e35c08ccaa4677c6b6d0cf137b
> > [LINUX] Support creating ELF note segments in the kernel ELF image.
> >
> [snip]
> > diff -r cd4e7ace4e58 -r a4550b748840 linux-2.6-xen-sparse/arch/i386/ 
> > kernel/vmlinux.lds.S
> > --- a/linux-2.6-xen-sparse/arch/i386/kernel/vmlinux.lds.S   Tue Aug  
> > 22 11:34:46 2006 +0100
> > +++ b/linux-2.6-xen-sparse/arch/i386/kernel/vmlinux.lds.S   Tue Aug  
> > 22 12:20:43 2006 +0100
> > @@ -12,6 +12,12 @@ OUTPUT_ARCH(i386)
> >  OUTPUT_ARCH(i386)
> >  ENTRY(phys_startup_32)
> >  jiffies = jiffies_64;
> > +
> > +PHDRS {
> > +   text PT_LOAD FLAGS(5);  /* R_E */
> > +   data PT_LOAD FLAGS(7);  /* RWE */
> 
> Are you sure you want to explicitly create a data segment that was  
> not there before?

I'm note 100% sure since this is a patch backported -mm but I think that
may have been part of the intention.

> > +   note PT_NOTE FLAGS(4);  /* R__ */
> 
> FLAGS() should be zero. The NOTE segment(s) are usually for the ELF  
> interpreter and not software accessible to the program.
> If it is your intention for this to be accessible by your program  
> then you need a symbolic reference to it and it probably should not  
> be in a segment all on its own.

We want to replace the __xen_guest string with a selection of ELF notes
so these are for the use of the interpreter (i.e. the domain builder). I
guess the flags is largely immaterial in this context but perhaps 0
would be a more sensible value, I'll mention it upstream...

BTW the reason for this is that the __xen_guest stuff was unpalatable
for the upstream merge, plus the notes is a nicer interface anyway,
IMHO...

Ian.


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