linux-kernel - Re: [PATCH v2 5/5] crash: Remove KEXEC_CORE_NOTE

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Message-ID: <Z3vuBTiQvnRvv9DQ@e133380.arm.com>
Date: Mon, 6 Jan 2025 14:51:49 +0000
From: Dave Martin <Dave.Martin@....com>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: 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, devel@...nix.com
Subject: Re: [PATCH v2 5/5] crash: Remove KEXEC_CORE_NOTE_NAME

Hi,

On Sat, Jan 04, 2025 at 11:38:38PM +0900, Akihiko Odaki wrote:
> Now KEXEC_CORE_NOTE_NAME is only used at one place and it does not seem
> to provide any value anymore. Replace the remaining usage with the
> literal and remove the macro.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
>  arch/s390/kernel/crash_dump.c | 2 +-
>  include/linux/kexec.h         | 2 --
>  include/linux/vmcore_info.h   | 1 -
>  3 files changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
> index cd0c93a8fb8b..4a9817489e35 100644
> --- a/arch/s390/kernel/crash_dump.c
> +++ b/arch/s390/kernel/crash_dump.c
> @@ -253,7 +253,7 @@ static const char *nt_name(Elf64_Word type)
>  	const char *name = "LINUX";
>  
>  	if (type == NT_PRPSINFO || type == NT_PRSTATUS || type == NT_PRFPREG)
> -		name = KEXEC_CORE_NOTE_NAME;
> +		name = "CORE";

If I've understood the code here correctly, the note type is supplied
at all the nt_init() and nt_size() call sites, so instead of this hack
can we wrap those in macros that get the formal name from elf.h rather
than guessing it here?  e.g.:

#define nt_size(..., note, ...) \
	__nt_size(..., NT ## _ ## note, NN ## _ ## note, ...)

etc.

The compiler is quite likely to fold away most of the implied
duplication of code (it would be interesting to look at the compiler
output) -- but anyway, this is super-slow-path: nobody expects realtime
response when the kernel has crashed.

[...]

Cheers
---Dave