Kamalesh Babulal wrote:
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Kamalesh Babulal <kamalesh@xxxxxxxxxxxxxxxxxx>
---
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;
+
This looks quite fragile, unless we know for sure that gcc will _always_
emit this instruction form for sibling calls with relocations.
As an alternative, does it make sense to do the following check instead?
if ((instr_is_branch_iform(insn) || instr_is_branch_bform(insn))
&& !(insn & 0x1))
- Naveen
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