From: Josh Poimboeuf jpoimboe@redhat.com
[ Upstream commit b9eab08d012fa093947b230f9a87257c27fb829b ]
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 Acked-by: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com Reviewed-and-tested-by: Kamalesh Babulal kamalesh@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- arch/powerpc/include/asm/code-patching.h | 1 + arch/powerpc/kernel/module_64.c | 12 +++++++++++- arch/powerpc/lib/code-patching.c | 5 +++++ 3 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h index 2015b072422c..b4ab1f497335 100644 --- a/arch/powerpc/include/asm/code-patching.h +++ b/arch/powerpc/include/asm/code-patching.h @@ -30,6 +30,7 @@ int patch_branch(unsigned int *addr, unsigned long target, int flags); int patch_instruction(unsigned int *addr, unsigned int instr);
int instr_is_relative_branch(unsigned int instr); +int instr_is_relative_link_branch(unsigned int instr); int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr); unsigned long branch_target(const unsigned int *instr); unsigned int translate_branch(const unsigned int *dest, diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c index 183368e008cf..99407cf12ad5 100644 --- a/arch/powerpc/kernel/module_64.c +++ b/arch/powerpc/kernel/module_64.c @@ -494,7 +494,17 @@ static bool is_early_mcount_callsite(u32 *instruction) restore r2. */ static int restore_r2(u32 *instruction, struct module *me) { - if (is_early_mcount_callsite(instruction - 1)) + u32 *prev_insn = instruction - 1; + + if (is_early_mcount_callsite(prev_insn)) + return 1; + + /* + * Make sure the branch isn't a sibling call. Sibling calls aren't + * "link" branches and they don't return, so they don't need the r2 + * restore afterwards. + */ + if (!instr_is_relative_link_branch(*prev_insn)) return 1;
if (*instruction != PPC_INST_NOP) { diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index d5edbeb8eb82..753d591f1b52 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -95,6 +95,11 @@ int instr_is_relative_branch(unsigned int instr) return instr_is_branch_iform(instr) || instr_is_branch_bform(instr); }
+int instr_is_relative_link_branch(unsigned int instr) +{ + return instr_is_relative_branch(instr) && (instr & BRANCH_SET_LINK); +} + static unsigned long branch_iform_target(const unsigned int *instr) { signed long imm;