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

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Message-ID: <75a9224f-8c8a-da15-3ad7-f49fe3c36cf@inria.fr>
Date: Thu, 30 Oct 2025 14:38:47 +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:

> >> 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;
> >>         }
> …>> 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:
> …
>
> Would you like to acknowledge that undesirable difference displays were generated anyhow
> for these test cases?

Sure.

>
>
> >> Would you like to reconsider implementation details accordingly?
>
> Are we looking for corresponding software improvements?

If time permits.

julia