Re: [PATCH 1/12] i386: Distinguish absolute symbols

Vivek Goyal
2006-10-09T13:49:54Z

On Mon, Oct 09, 2006 at 09:35:26AM +0200, Gerd Hoffmann wrote:
> >> looks odd. What's the point in putting a gap before __smp_alt_end? Moving
> >> __smp_alt_end to before the ALIGN doesn't prevent the warning.
> >>
>
> > Please find attached a patch for the same. I am also copying Gerd Hoffmann,
> > who introduced this ALIGN. Gerd, can you please confirm that above ALIGN()
> > is not required and the patch attached should be fine.
>
> The data between __smp_alt_start and __smp_alt_end will be released at
> boot time in some cases (UP machine, kernel without CPU_HOTPLUG, ...).
>
> Releasing memory works at page granularity only, thats why I added the
> alignment. I think you can't simply drop it.
>
> > o There seems to be one extra ALIGN(4096) before symbol __smp_alt_end. The
> > only usage of __smp_alt_end is to mark the end of smp alternative
> > sections so that this memory can be freed. As a physical page is freed
> > one has to just make sure that there is no other data on the same page
> > where __smp_alt_end is pointing. There is already a ALIGN(4096) after
> > this section which should take care of the above issue. Hence it looks
> > like the ALIGN(4096) before __smp_alt_end is redundant and not required.
>
> Hmm, ok, it should work then. How about adding a comment to make sure
> the align after __smp_alt_end doesn't get dropped by accident?
>

Thanks Gerd. I have put a comment to make things more clear. Please find
attahched the attached regenerated patch.

o There seems to be one extra ALIGN(4096) before symbol __smp_alt_end. The
only usage of __smp_alt_end is to mark the end of smp alternative
sections so that this memory can be freed. As a physical page is freed
one has to just make sure that there is no other data on the same page
where __smp_alt_end is pointing. There is already a ALIGN(4096) after
this section which should take care of the above issue. Hence it looks
like the ALIGN(4096) before __smp_alt_end is redundant and not required.

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
---

linux-2.6.19-rc1-vivek/arch/i386/kernel/vmlinux.lds.S | 8 ++++++--
1 files changed, 6 insertions(+), 2 deletions(-)

diff -puN arch/i386/kernel/vmlinux.lds.S~i386-remove-unnecessary-align-option arch/i386/kernel/vmlinux.lds.S
--- linux-2.6.19-rc1/arch/i386/kernel/vmlinux.lds.S~i386-remove-unnecessary-align-option 2006-10-09 09:39:00.000000000 -0400
+++ linux-2.6.19-rc1-vivek/arch/i386/kernel/vmlinux.lds.S 2006-10-09 09:43:22.000000000 -0400
@@ -112,11 +112,15 @@ SECTIONS
}
.smp_altinstr_replacement : AT(ADDR(.smp_altinstr_replacement) - LOAD_OFFSET) {
*(.smp_altinstr_replacement)
- . = ALIGN(4096);
__smp_alt_end = .;
}

- /* will be freed after init */
+ /* will be freed after init
+ * Following ALIGN() is required to make sure no other data falls on the
+ * same page where __smp_alt_end is pointing as that page might be freed
+ * after boot. Always make sure that ALIGN() directive is present after
+ * the section which contains __smp_alt_end.
+ */
. = ALIGN(4096); /* Init code and data */
.init.text : AT(ADDR(.init.text) - LOAD_OFFSET) {
__init_begin = .;
_