Re: [PATCH 2/2] powerpc/module_64: Fix "expected nop" error on module re-patching

Josh Poimboeuf
2023-01-25T16:46:23Z

On Tue, Jan 24, 2023 at 10:09:56PM -0800, Song Liu wrote:
> > @@ -514,9 +515,18 @@ static int restore_r2(const char *name, u32 *instruction, struct module *me)
> > if (!instr_is_relative_link_branch(ppc_inst(*prev_insn)))
> > return 0;
> >
> > - if (*instruction != PPC_RAW_NOP()) {
> > + /*
> > + * For livepatch, the restore r2 instruction might have already been
> > + * written previously, if the referenced symbol is in a previously
> > + * unloaded module which is now being loaded again. In that case, skip
> > + * the warning and the instruction write.
> > + */
> > + if (insn_val == PPC_INST_LD_TOC)
> > + return 0;
>
> Do we need "sym->st_shndx == SHN_LIVEPATCH" here?

My original patch had that check, but I dropped it for simplicity.

In the non-livepatch case, the condition should never be true, but it
doesn't hurt to check it anyway.

--
Josh