Re: [XenPPC] PHDR link failure testcase

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On Aug 16, 2006, at 10:00 PM, Tony Breeds wrote:

> On Wed, Aug 16, 2006 at 08:10:20AM -0400, Jimi Xenidis wrote:
>
> > Thanks for getting to the bottom of this Tony.
> >
> > > As it's empty the linker decides to start a
> > > 3rd segment rather than waste disk space.
> > Hmm, what is "empty"?
> By empty I mean "filled with 0s", which I believe is because all the
> per_cpu variables are initialised at runtime.
so why does LONG(0) (from option (2)) fix this?
> > >  Initially the linker guessed
> > > it would need 2 segments, but due to this decision it actually  
> > > uses 3,
> > > causeing the abort.
> > >
> > > Aparently the newer (read current CVS) tools don't abort here but do
> > > the right thing.
> > What _is_ the "right thing"?
> Use 3 PHDRS.
Ok.

> > Perhaps, this is just mythology/warm-n-fuzzy for me, but I really
> > like having 1 PHDR.
> > Lemmy collect my thoughts and come up with a rational reason.
> Sure.  Wouldn't that mean that everything will end up being in a
> read/write/execute PHDR.  Do we care about that?
Not really its not like we protect any of it :) and the section  
separation still exits
after-all we all (kernels/xen) link with -N/--omagic, which does not  
page align the data sections which has always implied a single PHDR.   
Besides, the more I do this the less I trust FW and bootloaders so a  
single segment is just cleaner.
> Placing everything in one PHDR would look like:
>
> ---
> diff -r 279843441136 xen/arch/powerpc/xen.lds.S
> --- a/xen/arch/powerpc/xen.lds.S        Wed Aug 16 17:19:38 2006 -0500
> +++ b/xen/arch/powerpc/xen.lds.S        Thu Aug 17 11:30:50 2006 +1000
> @@ -10,11 +10,15 @@ SEARCH_DIR("=/usr/local/lib64"); SEARCH_
>  SEARCH_DIR("=/usr/local/lib64"); SEARCH_DIR("=/lib64"); SEARCH_DIR 
> ("=/usr/lib64"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/ 
> lib"); SEARCH_DIR("=/usr/lib");
>  /* Do we need any of these for elf?
>     __DYNAMIC = 0;    */
> +PHDRS
> +{
> +  text PT_LOAD FILEHDR PHDRS;
> +}
I think this is all we need, not other changes are required.

>  SECTIONS
>  {
>    /* Read-only sections, merged into text segment: */
>    PROVIDE (__executable_start = 0x10000000); . = 0x10000000 +  
> SIZEOF_HEADERS;
Actually the above line should just be:
   PROVIDE (__executable_start = .);

We always specific the link address on the command line and not that  
we define PHDRS there is no need for SIZEOF_HEADERS (as the linker  
docs indicate)
I'm pretty sure the rest of the changes are unnecessary.

-JX



> -  .interp         : { *(.interp) }
> +  .interp         : { *(.interp) } :text
>    .hash           : { *(.hash) }
>    .dynsym         : { *(.dynsym) }
>    .dynstr         : { *(.dynstr) }
> @@ -121,7 +125,7 @@ SECTIONS
>    __inithcall_end = .;
>
>    __per_cpu_start = .;
> -  .data.percpu : { *(.data.percpu) } :text
> +  .data.percpu : { *(.data.percpu) }
>    __per_cpu_data_end = .;
>    . = __per_cpu_start + (NR_CPUS << PERCPU_SHIFT);
>    . = ALIGN(STACK_SIZE);
>
> Yours Tony
>
>    linux.conf.au       http://linux.conf.au/ || http:// 
> lca2007.linux.org.au/
>    Jan 15-20 2007      The Australian Linux Technical Conference!
>
>
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