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Subject[PATCH v4 2/3] powerpc/modules: Don't try to restore r2 after a sibling call
Date
From: Josh Poimboeuf <jpoimboe@redhat.com>

When attempting to load a livepatch module, I got the following error:

module_64: patch_module: Expect noop after relocate, got 3c820000

The error was triggered by the following code in
unregister_netdevice_queue():

14c: 00 00 00 48 b 14c <unregister_netdevice_queue+0x14c>
14c: R_PPC64_REL24 net_set_todo
150: 00 00 82 3c addis r4,r2,0

GCC didn't insert a nop after the branch to net_set_todo() because it's
a sibling call, so it never returns. The nop isn't needed after the
branch in that case.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
---
arch/powerpc/kernel/module_64.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 39b01fd..9e5391f 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -489,6 +489,10 @@ static int restore_r2(u32 *instruction, struct module *me)
if (is_early_mcount_callsite(instruction - 1))
return 1;

+ /* Sibling calls don't return, so they don't need to restore r2 */
+ if (instruction[-1] == PPC_INST_BRANCH)
+ return 1;
+
if (*instruction != PPC_INST_NOP) {
pr_err("%s: Expect noop after relocate, got %08x\n",
me->name, *instruction);
--
2.9.3
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