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

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Date:   Wed, 25 Jan 2023 08:46:09 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Song Liu <song@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Nicholas Piggin <npiggin@...il.com>,
        live-patching@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/2] powerpc/module_64: Fix "expected nop" error on
 module re-patching

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