Re: [PATCH] module: set __jump_table alignment to 8

From: David Daney
Date: Thu Mar 02 2017 - 16:03:15 EST


On 03/02/2017 10:26 AM, Jessica Yu wrote:
+++ Steven Rostedt [02/03/17 13:11 -0500]:

Can I get an Ack from a module maintainer?

Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

Thanks!

Jessica

Thanks Jessica,

Can you also add scripts/module-common.lds to MAINTAINERS so that get_maintainers.pl will indicate that Jessica Yu and Rusty Russell be CCed on things like this in the future?



On Wed, 1 Mar 2017 14:04:53 -0800
David Daney <david.daney@xxxxxxxxxx> wrote:

For powerpc the __jump_table section in modules is not aligned, this
causes a WARN_ON() splat when loading a module containing a
__jump_table.

Strict alignment became necessary with commit 3821fd35b58d
("jump_label: Reduce the size of struct static_key"), currently in
linux-next, which uses the two least significant bits of pointers to
__jump_table elements.

Fix by forcing __jump_table to 8, which is the same alignment used for
this section in the kernel proper.

Signed-off-by: David Daney <david.daney@xxxxxxxxxx>
Tested-by: Sachin Sant <sachinp@xxxxxxxxxxxxxxxxxx>
---
scripts/module-common.lds | 2 ++
1 file changed, 2 insertions(+)

diff --git a/scripts/module-common.lds b/scripts/module-common.lds
index 73a2c7d..53234e8 100644
--- a/scripts/module-common.lds
+++ b/scripts/module-common.lds
@@ -19,4 +19,6 @@ SECTIONS {

. = ALIGN(8);
.init_array 0 : { *(SORT(.init_array.*)) *(.init_array) }
+
+ __jump_table 0 : ALIGN(8) { KEEP(*(__jump_table)) }
}