linux-kernel - Re: [RFC PATCH 3/4] riscv: Introduce is_compat

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Date: Tue, 26 Dec 2023 16:24:55 -0300
From: Leonardo Bras Soares Passos <leobras@...hat.com>
To: Andy Chiu <andy.chiu@...ive.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Eric Biederman <ebiederm@...ssion.com>, 
	Kees Cook <keescook@...omium.org>, Oleg Nesterov <oleg@...hat.com>, 
	Conor Dooley <conor.dooley@...rochip.com>, Greg Ungerer <gerg@...nel.org>, 
	Vincent Chen <vincent.chen@...ive.com>, Xiao Wang <xiao.w.wang@...el.com>, 
	Charlie Jenkins <charlie@...osinc.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Alexandre Ghiti <alexghiti@...osinc.com>, Kemeng Shi <shikemeng@...weicloud.com>, 
	David Hildenbrand <david@...hat.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, 
	Qinglin Pan <panqinglin2020@...as.ac.cn>, Greentime Hu <greentime.hu@...ive.com>, 
	Björn Töpel <bjorn@...osinc.com>, 
	Clément Léger <cleger@...osinc.com>, 
	Guo Ren <guoren@...nel.org>, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH 3/4] riscv: Introduce is_compat_thread() into compat.h

On Sat, Dec 23, 2023 at 1:26 AM Andy Chiu <andy.chiu@...ive.com> wrote:
>
> On Fri, Dec 22, 2023 at 3:46 PM Leonardo Bras <leobras@...hat.com> wrote:
> >
> > task_user_regset_view() makes use of a function very similar to
> > is_compat_task(), but pointing to a any thread.
> >
> > In arm64 asm/compat.h there is a function very similar to that:
> > is_compat_thread(struct thread_info *thread)
> >
> > Copy this function to riscv asm/compat.h and make use of it into
> > task_user_regset_view().
> >
> > Also, introduce a compile-time test for CONFIG_COMPAT and simplify the
> > function code by removing the #ifdef.
> >
> > Signed-off-by: Leonardo Bras <leobras@...hat.com>
> > ---
> >  arch/riscv/include/asm/compat.h | 8 ++++++++
> >  arch/riscv/kernel/ptrace.c      | 6 +++---
> >  2 files changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm/compat.h
> > index 91517b51b8e27..da4b28cd01a95 100644
> > --- a/arch/riscv/include/asm/compat.h
> > +++ b/arch/riscv/include/asm/compat.h
> > @@ -20,6 +20,14 @@ static inline int is_compat_task(void)
> >         return test_thread_flag(TIF_32BIT);
> >  }
> >
> > +static inline int is_compat_thread(struct thread_info *thread)
> > +{
> > +       if (!IS_ENABLED(CONFIG_COMPAT))
> > +               return 0;
> > +
> > +       return test_ti_thread_flag(thread, TIF_32BIT);
> > +}
> > +
>
> Does it make sense to use a #ifdef CONFIG_COMPAT clause to group
> is_compat_thread() and is_compat_flag()? For example,

Hello Andy,

Sure, it does make sense.

But I honestly think that using IS_ENABLED() instead of #ifdef +
multiple same-named functions works better for code reading, at least
for small functions such as these.

Does this make sense?

Thanks for reviewing!
Leo


>
> #ifdef CONFIG_COMPAT
> static inline int is_compat_thread(struct thread_info *thread)
> {
>  return test_ti_thread_flag(thread, TIF_32BIT);
> }
> static inline int is_compat_task(void)
> {
>  return is_compat_thread(current);
> }
> #else
> static inline int is_compat_thread(struct thread_info *thread) { return 0; }
> static inline int is_compat_task(void) { return 0; }
> #endif
>
> >  struct compat_user_regs_struct {
> >         compat_ulong_t pc;
> >         compat_ulong_t ra;
> > diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
> > index 2afe460de16a6..f362832123616 100644
> > --- a/arch/riscv/kernel/ptrace.c
> > +++ b/arch/riscv/kernel/ptrace.c
> > @@ -374,14 +374,14 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
> >
> >         return ret;
> >  }
> > +#else
> > +static const struct user_regset_view compat_riscv_user_native_view = {};
> >  #endif /* CONFIG_COMPAT */
> >
> >  const struct user_regset_view *task_user_regset_view(struct task_struct *task)
> >  {
> > -#ifdef CONFIG_COMPAT
> > -       if (test_tsk_thread_flag(task, TIF_32BIT))
> > +       if (is_compat_thread(&task->thread_info))
> >                 return &compat_riscv_user_native_view;
> >         else
> > -#endif
> >                 return &riscv_user_native_view;
> >  }
> > --
> > 2.43.0
> >
>