linux-kernel - Re: [PATCH v3 5/6] s390/crash: Use note name macros

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Message-ID: <2ad7234d-bfc5-49e3-abe6-7a85d992329d@daynix.com>
Date: Thu, 9 Jan 2025 14:29:19 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Dave Martin <Dave.Martin@....com>
Cc: Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Eric Biederman <ebiederm@...ssion.com>,
 Kees Cook <kees@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
 Mark Brown <broonie@...nel.org>, Baoquan He <bhe@...hat.com>,
 Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
 kexec@...ts.infradead.org, binutils@...rceware.org, devel@...nix.com
Subject: Re: [PATCH v3 5/6] s390/crash: Use note name macros

On 2025/01/08 22:50, Dave Martin wrote:
> On Wed, Jan 08, 2025 at 01:53:51PM +0900, Akihiko Odaki wrote:
>> On 2025/01/08 1:17, Dave Martin wrote:
>>> Hi,
>>>
>>> On Tue, Jan 07, 2025 at 09:45:56PM +0900, Akihiko Odaki wrote:
>>>> Use note name macros to match with the userspace's expectation.
>>>>
>>>> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
>>>> ---
>>>>    arch/s390/kernel/crash_dump.c | 62 ++++++++++++++++---------------------------
>>>>    1 file changed, 23 insertions(+), 39 deletions(-)
>>>>
>>>> diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
>>>
>>> [...]
> 
>>>> +#define NT_INIT(buf, type, desc) \
>>>> +	(nt_init_name((buf), NT_ ## type, &(desc), sizeof(desc), NN_ ## type))
> 
> [...]
> 
>>> (Note also, the outer parentheses and the parentheses around (buf)
>>> appear redundant -- although harmless?)
>>
>> They only make a difference in trivial corner cases and may look needlessly
>> verbose.
> 
> (In case there was a misunderstanding here, I meant that some
> parentheses can be removed without affecting correctness:
> 
> #define NT_INIT(buf, type, desc) \
> 	nt_init_name(buf, NT_ ## type, &(desc), sizeof(desc), NN_ ## type))
> 
> It still doesn't matter though -- and some people do prefer to be
> defensive anyway and err on the side of having too many parentheses
> rather than too few.)

Well, being very pedantic, there are some cases where these parentheses 
have some effect.

If you omit the outer parentheses, the following code will have 
different consequences:
a->NT_INIT(buf, PRSTATUS, desc)

The parentheses around buf will make difference for the following code:
#define COMMA ,
NT_INIT(NULL COMMA buf, PRSTATUS, desc)

But nobody will write such code.

Regards,
Akihiko Odaki