linux-kernel - Re: [PATCH v2 1/5] elf: Define note name macros

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Message-ID: <Z3vrEYQVlff1+ZBW@e133380.arm.com>
Date: Mon, 6 Jan 2025 14:39:13 +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 1/5] elf: Define note name macros

On Sat, Jan 04, 2025 at 11:38:34PM +0900, Akihiko Odaki wrote:
> elf.h had a comment saying:
> > Notes used in ET_CORE. Architectures export some of the arch register
> > sets using the corresponding note types via the PTRACE_GETREGSET and
> > PTRACE_SETREGSET requests.
> > The note name for these types is "LINUX", except NT_PRFPREG that is
> > named "CORE".
> 
> However, NT_PRSTATUS is also named "CORE". It is also unclear what
> "these types" refers to.
> 
> To fix these problems, define a name for each note type. The added
> definitions are macros so the kernel and userspace can directly refer to
> them.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
>  include/uapi/linux/elf.h | 86 ++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 83 insertions(+), 3 deletions(-)
> 
> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
> index b44069d29cec..014b705b97d7 100644
> --- a/include/uapi/linux/elf.h
> +++ b/include/uapi/linux/elf.h
> @@ -372,8 +372,6 @@ typedef struct elf64_shdr {
>   * Notes used in ET_CORE. Architectures export some of the arch register sets
>   * using the corresponding note types via the PTRACE_GETREGSET and
>   * PTRACE_SETREGSET requests.
> - * The note name for these types is "LINUX", except NT_PRFPREG that is named
> - * "CORE".

Maybe most people would find it obvious, but is it worth saying what
the NT_ and NN_ macros are for?  They can easily be explained in terms
of the elfXX_note struct fields.

>   */
>  #define NT_PRSTATUS	1
>  #define NT_PRFPREG	2
> @@ -460,9 +458,91 @@ typedef struct elf64_shdr {
>  #define NT_LOONGARCH_HW_BREAK	0xa05   /* LoongArch hardware breakpoint registers */
>  #define NT_LOONGARCH_HW_WATCH	0xa06   /* LoongArch hardware watchpoint registers */
>  
> -/* Note types with note name "GNU" */
> +/* Note used in ET_EXEC and ET_DYN. */

May just "other notes"?  I think that the comment might bitrot
over time.

>  #define NT_GNU_PROPERTY_TYPE_0	5
>  
> +/* Note names */
> +#define NN_PRSTATUS	"CORE"

Can these be interleaved with the NT_ definitions?  I think this would
make the resulting header (and the diff) easier to read.

> +#define NN_PRFPREG	"CORE"

[...]

> +#define NN_GNU_PROPERTY_TYPE_0	"GNU"

[...]

Cheers
---Dave