linux-kernel - Re: [PATCH] RISC-V: Use GCC __builtin_prefetch() to implement prefetch()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20230726-washing-scoreless-12f0cca83365@wendy>
Date:   Wed, 26 Jul 2023 10:27:33 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     wang_yang <wang_yang6662023@....com>
CC:     <palmer@...belt.com>, <aou@...s.berkeley.edu>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        Wang Yang <yangwang@...iscas.ac.cn>
Subject: Re: [PATCH] RISC-V: Use GCC __builtin_prefetch() to implement
 prefetch()

Hey,

On Wed, Jul 26, 2023 at 03:47:32PM +0800, wang_yang wrote:
>  GCC's __builtin_prefetch() was introduced a long time ago, all supported GCC
>  versions have it.So this patch is to use it for implementing the prefetch.
> 
>  RISC-V Cache Management Operation instructions has been supported by GCC last
>  year.you can refer to
>  https://github.com/gcc-mirror/gcc/commit/3df3ca9014f94fe4af07444fea19b4ab29ba8e73

This should be in a Link: tag.

>  It is worth noting that CPU based on RISC-V should support Zicbop extension.

How do you intend determining whether the CPU supports Zicbop?

>  This has been already done on other architectures (see the commit:
>  https://github.com/torvalds/linux/commit/0453fb3c528c5eb3483441a466b24a4cb409eec5).

That's not how to describe commits, please see how that is done
elsewhere in the git history.

> 
> Signed-off-by: Wang Yang <yangwang@...iscas.ac.cn>

WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#6: 
 GCC's __builtin_prefetch() was introduced a long time ago, all supported GCC

ERROR: Missing Signed-off-by: line by nominal patch author 'wang_yang <wang_yang6662023@....com>'

> ---
>  arch/riscv/include/asm/processor.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index c950a8d9edef..f16d4c85ca5b 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -70,6 +70,17 @@ extern void start_thread(struct pt_regs *regs,
>  
>  extern unsigned long __get_wchan(struct task_struct *p);
>  
> +#define ARCH_HAS_PREFETCH
> +static inline void prefetch(const void *ptr)
> +{
> +	__builtin_prefetch(ptr, 0, 3);

As far as I can tell, this does not do anything and will be removed by
the compiler. Please take a look at how other extensions are implemented.

Also, why 3? (Your answer should be in the commit message)

Thanks,
Conor.

> +}
> +
> +#define ARCH_HAS_PREFETCHW
> +static inline void prefetchw(const void *ptr)
> +{
> +	__builtin_prefetch(ptr, 1, 3);
> +}
>  
>  static inline void wait_for_interrupt(void)
>  {
> -- 
> 2.34.1
> 

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)