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Re: [XenPPC] PHDR link failure testcase

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.


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;    */

I think this is all we need, not other changes are required.

   /* 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.


-  .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);

Yours Tony

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