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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>
This commit is contained in:
Josh Poimboeuf 2017-11-16 11:45:37 -06:00 committed by Michael Ellerman
parent a443bf6e8a
commit b9eab08d01
3 changed files with 17 additions and 1 deletions
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1
arch/powerpc/include/asm/code-patching.h
View File

@ -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 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,

12
arch/powerpc/kernel/module_64.c
View File

@ -487,7 +487,17 @@ 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) {

5
arch/powerpc/lib/code-patching.c
View File

@ -302,6 +302,11 @@ 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;