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

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Date: Sat, 23 Dec 2023 12:25:44 +0800
From: Andy Chiu <andy.chiu@...ive.com>
To: Leonardo Bras <leobras@...hat.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 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,

#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
>