linux-kernel - Re: [cocci] [RFC] Increasing usage of direct pointer assignments from memcpy() calls with SmPL?

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Message-ID: <aa99eded-be51-af3b-414-7c3bbaddea4a@inria.fr>
Date: Thu, 30 Oct 2025 13:31:49 +0100 (CET)
From: Julia Lawall <julia.lawall@...ia.fr>
To: Markus Elfring <Markus.Elfring@....de>
cc: cocci@...ia.fr, LKML <linux-kernel@...r.kernel.org>, 
    kernel-janitors@...r.kernel.org, Miaoqian Lin <linmq006@...il.com>
Subject: Re: [cocci] [RFC] Increasing usage of direct pointer assignments
 from memcpy() calls with SmPL?



On Thu, 30 Oct 2025, Markus Elfring wrote:

> > If you have a concern, you have to say what it is.  It doesn't seem it is
> > about the running time, so why do you include that information?
>
> How will remaining open issues be resolved?
>
>
> > I should not have to repeat your experiment
>
> It would be nice if further software users would occasionally reproduce
> presented data processing possibilities.
>
>
> >                                             to figure out what you are
> > asking about.
>
> I “accidentally” tried also the following SmPL script variants out.
>
> A)
> @replacement3@
> expression object, size, source, target;
> @@
>  target =
> -object; memcpy(target, source, size)
> +object; memcpy(object, source, size)
>  ;
>
> Markus_Elfring@...ne:…/Projekte/Linux/next-analyses> time /usr/bin/spatch --max-width 100 --no-loops …/Projekte/Coccinelle/janitor/use_memcpy_assignment3.cocci arch/arm64/kvm/arm.c
> …
> @@ -2600,8 +2600,8 @@ static int __init init_hyp_mode(void)
>                         goto out_err;
>                 }
>
> -               page_addr = page_address(page);
> -               memcpy(page_addr, CHOOSE_NVHE_SYM(__per_cpu_start), nvhe_percpu_size());
> +               page_addr =memcpy(page_address(page), CHOOSE_NVHE_SYM(__per_cpu_start),
> +                                 nvhe_percpu_size());page_address(page);
>                 kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu] = (unsigned long)page_addr;
>         }
>
>
> real    0m0,578s
> user    0m0,524s
> sys     0m0,047s
>
>
>
> B)
> @replacement4@
> expression object, size, source, target;
> @@
> -target = object; memcpy(target, source, size)
> +target = object; memcpy(object, source, size)
>  ;
>
> Markus_Elfring@...ne:…/Projekte/Linux/next-analyses> time /usr/bin/spatch --max-width 100 --no-loops …/Projekte/Coccinelle/janitor/use_memcpy_assignment4.cocci arch/arm64/kvm/arm.c
> …
> @@ -2600,8 +2600,8 @@ static int __init init_hyp_mode(void)
>                         goto out_err;
>                 }
>
> +               memcpy(page_address(page), CHOOSE_NVHE_SYM(__per_cpu_start), nvhe_percpu_size());
>                 page_addr = page_address(page);
> -               memcpy(page_addr, CHOOSE_NVHE_SYM(__per_cpu_start), nvhe_percpu_size());
>                 kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu] = (unsigned long)page_addr;
>         }

Not sure what is the point of all this.  Try:

- target = object; memcpy(target, source, size);
+ target = memcpy(target, source, size);

Then it will add newlines in the argument of memcpy if needed to stay in a
reasonable number of columns.

julia

>
>
> real    0m0,565s
> user    0m0,533s
> sys     0m0,032s
>
>
>
> Would you like to reconsider implementation details accordingly?
>
> Regards,
> Markus
>