linux-kernel - Re: [PATCH v2 2/5] ia64: reuse append_elf_note() and final

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Message-ID: <87mvge16gw.fsf@xmission.com>
Date:   Fri, 02 Dec 2016 13:22:39 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Hari Bathini <hbathini@...ux.vnet.ibm.com>
Cc:     Dave Young <dyoung@...hat.com>, linux-kernel@...r.kernel.org,
        fenghua.yu@...el.com, tony.luck@...el.com,
        linux-ia64@...r.kernel.org, kexec@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>, vgoyal@...hat.com
Subject: Re: [PATCH v2 2/5] ia64: reuse append_elf_note() and final_note() functions

Hari Bathini <hbathini@...ux.vnet.ibm.com> writes:

> Hi Dave,
>
>
> Thanks for the review.
>
>
> On Thursday 01 December 2016 10:26 AM, Dave Young wrote:
>> Hi Hari
>>
>> Personally I like V1 more, but split the patch 2 is easier for ia64
>> people to reivew.  I did basic x86 testing, it runs ok.
>>
>> On 11/25/16 at 05:24pm, Hari Bathini wrote:
>>> Get rid of multiple definitions of append_elf_note() & final_note()
>>> functions. Reuse these functions compiled under CONFIG_CRASH_CORE.
>>>
>>> Signed-off-by: Hari Bathini <hbathini@...ux.vnet.ibm.com>
>>> ---
>>>   arch/ia64/kernel/crash.c   |   22 ----------------------
>>>   include/linux/crash_core.h |    4 ++++
>>>   kernel/crash_core.c        |    6 +++---
>>>   kernel/kexec_core.c        |   28 ----------------------------
>>>   4 files changed, 7 insertions(+), 53 deletions(-)
>>>
>>> diff --git a/arch/ia64/kernel/crash.c b/arch/ia64/kernel/crash.c
>>> index 2955f35..75859a0 100644
>>> --- a/arch/ia64/kernel/crash.c
>>> +++ b/arch/ia64/kernel/crash.c
>>> @@ -27,28 +27,6 @@ static int kdump_freeze_monarch;
>>>   static int kdump_on_init = 1;
>>>   static int kdump_on_fatal_mca = 1;
>>>   -static inline Elf64_Word
>>> -*append_elf_note(Elf64_Word *buf, char *name, unsigned type, void *data,
>>> -		size_t data_len)
>>> -{
>>> -	struct elf_note *note = (struct elf_note *)buf;
>>> -	note->n_namesz = strlen(name) + 1;
>>> -	note->n_descsz = data_len;
>>> -	note->n_type   = type;
>>> -	buf += (sizeof(*note) + 3)/4;
>>> -	memcpy(buf, name, note->n_namesz);
>>> -	buf += (note->n_namesz + 3)/4;
>>> -	memcpy(buf, data, data_len);
>>> -	buf += (data_len + 3)/4;
>>> -	return buf;
>>> -}
>>> -
>>> -static void
>>> -final_note(void *buf)
>>> -{
>>> -	memset(buf, 0, sizeof(struct elf_note));
>>> -}
>>> -
>> The above IA64 version looks better than the functions in kexec_core.c
>> about the Elf64_Word type usage and the simpler final_note function.
>
> Hmmm.. Is void* better over Elf64_Word* to be agnostic of Elf32 or
> Elf64 type?

Both Elf64_Word and Elf32_Word result in a u32.  So I expect the right
solution is to add a definition of Elf_Word to include/linux/elf.h
and to make the buffer "Elf_Word *buf".

That way we preserve the alignment knowledge, while making the code
depend on 32bit or 64bit.

Eric