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Commit b9eab08d authored Nov 16, 2017 by Josh Poimboeuf Committed by Michael Ellerman Dec 11, 2017

powerpc/modules: Don't try to restore r2 after a sibling call



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>

parent a443bf6e

arch/powerpc/include/asm/code-patching.h

+1 −0

Original line number	Original line	Diff line number	Diff line
	@@ -33,6 +33,7 @@ int patch_branch(unsigned int *addr, unsigned long target, int flags);
	int patch_instruction(unsigned int *addr, unsigned int instr);		int patch_instruction(unsigned int *addr, unsigned int instr);

	int instr_is_relative_branch(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);		int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr);
	unsigned long branch_target(const unsigned int *instr);		unsigned long branch_target(const unsigned int *instr);
	unsigned int translate_branch(const unsigned int *dest,		unsigned int translate_branch(const unsigned int *dest,

arch/powerpc/kernel/module_64.c

+11 −1

Original line number	Original line	Diff line number	Diff line
	@@ -487,7 +487,17 @@ static bool is_early_mcount_callsite(u32 *instruction)
	restore r2. */		restore r2. */
	static int restore_r2(u32 instruction, struct module me)		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;		return 1;

	if (*instruction != PPC_INST_NOP) {		if (*instruction != PPC_INST_NOP) {

arch/powerpc/lib/code-patching.c

+5 −0

Original line number	Original line	Diff line number	Diff line
	@@ -302,6 +302,11 @@ int instr_is_relative_branch(unsigned int instr)
	return instr_is_branch_iform(instr) \|\| instr_is_branch_bform(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)		static unsigned long branch_iform_target(const unsigned int *instr)
	{		{
	signed long imm;		signed long imm;