linux-kernel - Re: [PATCH] kexec: Avoid calculating array size twice

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Date:   Thu, 1 Jun 2023 18:40:16 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Simon Horman <horms@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kexec: Avoid calculating array size twice

On 05/25/23 at 04:26pm, Simon Horman wrote:
> Avoid calculating array size twice in kexec_purgatory_setup_sechdrs().
> Once using array_size(), and once open-coded.
> 
> Flagged by Coccinelle:
> 
>   .../kexec_file.c:881:8-25: WARNING: array_size is already used (line 877) to compute the same size

Amazingly smart. Thanks.

Acked-by: Baoquan He <bhe@...hat.com>

> 
> No functional change intended.
> Compile tested only.
> 
> Signed-off-by: Simon Horman <horms@...nel.org>
> ---
>  kernel/kexec_file.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index f989f5f1933b..3f5677679744 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -867,6 +867,7 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
>  {
>  	unsigned long bss_addr;
>  	unsigned long offset;
> +	size_t sechdrs_size;
>  	Elf_Shdr *sechdrs;
>  	int i;
>  
> @@ -874,11 +875,11 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
>  	 * The section headers in kexec_purgatory are read-only. In order to
>  	 * have them modifiable make a temporary copy.
>  	 */
> -	sechdrs = vzalloc(array_size(sizeof(Elf_Shdr), pi->ehdr->e_shnum));
> +	sechdrs_size = array_size(sizeof(Elf_Shdr), pi->ehdr->e_shnum);
> +	sechdrs = vzalloc(sechdrs_size);
>  	if (!sechdrs)
>  		return -ENOMEM;
> -	memcpy(sechdrs, (void *)pi->ehdr + pi->ehdr->e_shoff,
> -	       pi->ehdr->e_shnum * sizeof(Elf_Shdr));
> +	memcpy(sechdrs, (void *)pi->ehdr + pi->ehdr->e_shoff, sechdrs_size);
>  	pi->sechdrs = sechdrs;
>  
>  	offset = 0;
>