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

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Message-ID: <ZHh3u+9H/OBHFKlC@MiWiFi-R3L-srv>
Date:   Thu, 1 Jun 2023 18:49:31 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Simon Horman <horms@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     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 06/01/23 at 06:40pm, Baoquan He wrote:
> 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>

Just noticed Andrew has picked this one, please ignore this.

> 
> > 
> > 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;
> > 
>