linux-kernel - Re: [PATCH 08/11] kexec_file: Simplify kexec_purgatory_setup

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Date:   Fri, 9 Mar 2018 10:54:03 +0100
From:   Philipp Rudo <prudo@...ux.vnet.ibm.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     kexec@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        AKASHI Takahiro <takahiro.akashi@...aro.org>
Subject: Re: [PATCH 08/11] kexec_file: Simplify
 kexec_purgatory_setup_sechdrs 2

Hi Dave,

On Fri, 9 Mar 2018 11:18:05 +0800
Dave Young <dyoung@...hat.com> wrote:

> Hi,
> 
> On 02/26/18 at 04:16pm, Philipp Rudo wrote:
> > The main loop currently uses quite a lot of variables to update the section
> > headers. Some of them are unnecessary. So clean them up a little.
> >   
> 
> It looks better to use some patch subject eg below:
> "Remove unnecessary variables in kexec_purgatory_setup_sechdrs"

ok, done. I also renamed the patch before and after. The subjects now
are

kexec_file: Remove mis-use of sh_offset field during purgatory load
kexec_file: Remove unneeded variables in kexec_purgatory_setup_sechdrs 
kexec_file: Remove unneeded for-loop in kexec_purgatory_setup_sechdrs

Thanks
Philipp

 
> > Signed-off-by: Philipp Rudo <prudo@...ux.vnet.ibm.com>
> > ---
> >  kernel/kexec_file.c | 34 ++++++++++++----------------------
> >  1 file changed, 12 insertions(+), 22 deletions(-)
> > 
> > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > index bb31a3b627c2..746b91e46e34 100644
> > --- a/kernel/kexec_file.c
> > +++ b/kernel/kexec_file.c
> > @@ -724,12 +724,8 @@ static int kexec_purgatory_setup_kbuf(struct purgatory_info *pi,
> >  static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
> >  					 struct kexec_buf *kbuf)
> >  {
> > -	unsigned long curr_load_addr;
> > -	unsigned long load_addr;
> >  	unsigned long bss_addr;
> >  	unsigned long offset;
> > -	unsigned char *buf_addr;
> > -	unsigned char *src;
> >  	Elf_Shdr *sechdrs;
> >  	int i;
> >  
> > @@ -762,20 +758,18 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
> >  						sechdrs[i].sh_offset;
> >  	}
> >  
> > -	/* Load SHF_ALLOC sections */
> > -	buf_addr = kbuf->buffer;
> > -	load_addr = curr_load_addr = kbuf->mem;
> > -	bss_addr = load_addr + kbuf->bufsz;
> > +	offset = 0;
> > +	bss_addr = kbuf->mem + kbuf->bufsz;
> >  	kbuf->image->start = pi->ehdr->e_entry;
> >  
> >  	for (i = 0; i < pi->ehdr->e_shnum; i++) {
> >  		unsigned long align;
> > +		void *src, *dst;
> >  
> >  		if (!(sechdrs[i].sh_flags & SHF_ALLOC))
> >  			continue;
> >  
> >  		align = sechdrs[i].sh_addralign;
> > -
> >  		if (sechdrs[i].sh_type == SHT_NOBITS) {
> >  			bss_addr = ALIGN(bss_addr, align);
> >  			sechdrs[i].sh_addr = bss_addr;
> > @@ -783,31 +777,27 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
> >  			continue;
> >  		}
> >  
> > -		curr_load_addr = ALIGN(curr_load_addr, align);
> > -		offset = curr_load_addr - load_addr;
> > -		/* We already modifed ->sh_offset to keep src addr */
> > -		src = (char *)sechdrs[i].sh_offset;
> > -		memcpy(buf_addr + offset, src, sechdrs[i].sh_size);
> > -
> > +		offset = ALIGN(offset, align);
> >  		if (sechdrs[i].sh_flags & SHF_EXECINSTR &&
> >  		    pi->ehdr->e_entry >= sechdrs[i].sh_addr &&
> >  		    pi->ehdr->e_entry < (sechdrs[i].sh_addr
> >  					 + sechdrs[i].sh_size)) {
> >  			kbuf->image->start -= sechdrs[i].sh_addr;
> > -			kbuf->image->start += curr_load_addr
> > +			kbuf->image->start += kbuf->mem + offset;
> >  		}
> >  
> > -		/* Store load address and source address of section */
> > -		sechdrs[i].sh_addr = curr_load_addr;
> > +		src = (void *)sechdrs[i].sh_offset;
> > +		dst = pi->purgatory_buf + offset;
> > +		memcpy(dst, src, sechdrs[i].sh_size);
> > +
> > +		sechdrs[i].sh_addr = kbuf->mem + offset;
> >  
> >  		/*
> >  		 * This section got copied to temporary buffer. Update
> >  		 * ->sh_offset accordingly.
> >  		 */
> > -		sechdrs[i].sh_offset = (unsigned long)(buf_addr + offset);
> > -
> > -		/* Advance to the next address */
> > -		curr_load_addr += sechdrs[i].sh_size;
> > +		sechdrs[i].sh_offset = (unsigned long)dst;
> > +		offset += sechdrs[i].sh_size;
> >  	}
> >  
> >  	return 0;
> > -- 
> > 2.13.5
> >   
> 
> Thanks
> Dave
>