linux-kernel - Re: [PATCH 6/7] x86: kexec_file: clean up prepare_elf64

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Date:   Fri, 2 Mar 2018 13:39:45 +0800
From:   Dave Young <dyoung@...hat.com>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:     vgoyal@...hat.com, bhe@...hat.com, mpe@...erman.id.au,
        bauerman@...ux.vnet.ibm.com, prudo@...ux.vnet.ibm.com,
        kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 6/7] x86: kexec_file: clean up prepare_elf64_headers()

On 02/27/18 at 01:48pm, AKASHI Takahiro wrote:
> removing bufp variable in prepare_elf64_headers() makes the code simpler
> and more understandable.
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
> Cc: Dave Young <dyoung@...hat.com>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: Baoquan He <bhe@...hat.com>
> ---
>  arch/x86/kernel/crash.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index bfc37ad20d4a..a842fd847684 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -334,7 +334,7 @@ static int prepare_elf64_headers(struct crash_mem *cmem, int kernel_map,
>  	Elf64_Ehdr *ehdr;
>  	Elf64_Phdr *phdr;
>  	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
> -	unsigned char *buf, *bufp;
> +	unsigned char *buf;
>  	unsigned int cpu, i;
>  	unsigned long long notes_addr;
>  	unsigned long mstart, mend;
> @@ -359,9 +359,8 @@ static int prepare_elf64_headers(struct crash_mem *cmem, int kernel_map,
>  	if (!buf)
>  		return -ENOMEM;
>  
> -	bufp = buf;
> -	ehdr = (Elf64_Ehdr *)bufp;
> -	bufp += sizeof(Elf64_Ehdr);
> +	ehdr = (Elf64_Ehdr *)buf;
> +	phdr = (Elf64_Phdr *)(ehdr + 1);

phdr should start with ehdr + sizeof(Elf64_Ehdr);

>  	memcpy(ehdr->e_ident, ELFMAG, SELFMAG);
>  	ehdr->e_ident[EI_CLASS] = ELFCLASS64;
>  	ehdr->e_ident[EI_DATA] = ELFDATA2LSB;
> @@ -377,33 +376,30 @@ static int prepare_elf64_headers(struct crash_mem *cmem, int kernel_map,
>  
>  	/* Prepare one phdr of type PT_NOTE for each present cpu */
>  	for_each_present_cpu(cpu) {
> -		phdr = (Elf64_Phdr *)bufp;
> -		bufp += sizeof(Elf64_Phdr);
>  		phdr->p_type = PT_NOTE;
>  		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
>  		phdr->p_offset = phdr->p_paddr = notes_addr;
>  		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
>  		(ehdr->e_phnum)++;
> +		phdr++;
>  	}
>  
>  	/* Prepare one PT_NOTE header for vmcoreinfo */
> -	phdr = (Elf64_Phdr *)bufp;
> -	bufp += sizeof(Elf64_Phdr);
>  	phdr->p_type = PT_NOTE;
>  	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
>  	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
>  	(ehdr->e_phnum)++;
> +	phdr++;
>  
>  	/* Prepare PT_LOAD type program header for kernel text region */
>  	if (kernel_map) {
> -		phdr = (Elf64_Phdr *)bufp;
> -		bufp += sizeof(Elf64_Phdr);
>  		phdr->p_type = PT_LOAD;
>  		phdr->p_flags = PF_R|PF_W|PF_X;
>  		phdr->p_vaddr = (Elf64_Addr)_text;
>  		phdr->p_filesz = phdr->p_memsz = _end - _text;
>  		phdr->p_offset = phdr->p_paddr = __pa_symbol(_text);
> -		(ehdr->e_phnum)++;
> +		ehdr->e_phnum++;
> +		phdr++;
>  	}
>  
>  	/* Go through all the ranges in cmem->ranges[] and prepare phdr */
> -- 
> 2.16.2
> 

Thanks
Dave