Re: [PATCH RFC v2 riscv/for-next 5/5] riscv: align arch_static_branch function

[Guo Ren <guoren@kernel.org>]

On Wed, Sep 14, 2022 at 10:24 PM Jessica Clarke <jrtc27@jrtc27.com> wrote:
>
> On 13 Sept 2022, at 10:42, Andy Chiu <andy.chiu@sifive.com> wrote:
> >
> > runtime code patching must be done at a naturally aligned address, or we
> > may execute on a partial instruction.
> >
> > Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
> > Reviewed-by: Greentime Hu <greentime.hu@sifive.com>
> > ---
> > arch/riscv/include/asm/jump_label.h | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/jump_label.h b/arch/riscv/include/asm/jump_label.h
> > index 38af2ec7b9bf..729991e8f782 100644
> > --- a/arch/riscv/include/asm/jump_label.h
> > +++ b/arch/riscv/include/asm/jump_label.h
> > @@ -18,6 +18,7 @@ static __always_inline bool arch_static_branch(struct static_key *key,
> >                                              bool branch)
> > {
> >       asm_volatile_goto(
> > +             "       .align          2                       \n\t"
>
> .align is a horrible directive whose meaning changes between
> architectures and requires careful thought, especially when the
> argument is a power of 2. Better to use .balign 4, or .p2align 2 if you
> really want to for some reason.
Do we really need to align here? Should it be naturally done by the compiler?

>
> Jess
>
> >               "       .option push                            \n\t"
> >               "       .option norelax                         \n\t"
> >               "       .option norvc                           \n\t"
> > @@ -39,6 +40,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key,
> >                                                   bool branch)
> > {
> >       asm_volatile_goto(
> > +             "       .align          2                       \n\t"
> >               "       .option push                            \n\t"
> >               "       .option norelax                         \n\t"
> >               "       .option norvc                           \n\t"
> > --
> > 2.36.0
> >
> >
> > _______________________________________________
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> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>


-- 
Best Regards
 Guo Ren

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