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

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Message-ID: <abda1fe0-af59-4fa9-a1ec-efda0f63b3f1@web.de>
Date: Thu, 30 Oct 2025 14:35:36 +0100
From: Markus Elfring <Markus.Elfring@....de>
To: Julia Lawall <julia.lawall@...ia.fr>, cocci@...ia.fr
Cc: 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?

>> 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?


>> Would you like to reconsider implementation details accordingly?

Are we looking for corresponding software improvements?

Regards,
Markus