linux-kernel - Re: [PATCH v5 01/19] scripts: move genksyms crc32 implementation to a common include

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Message-ID: <CAK7LNARVK1ZpGXZVTAynuo7CDjgB4uT5bQzcGiWseZfaEu7Tvw@mail.gmail.com>
Date: Sat, 16 Nov 2024 18:08:23 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Matthew Maurer <mmaurer@...gle.com>, 
	Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>, 
	Petr Pavlu <petr.pavlu@...e.com>, Daniel Gomez <da.gomez@...sung.com>, Neal Gompa <neal@...pa.dev>, 
	Hector Martin <marcan@...can.st>, Janne Grunau <j@...nau.net>, Miroslav Benes <mbenes@...e.cz>, 
	Asahi Linux <asahi@...ts.linux.dev>, Sedat Dilek <sedat.dilek@...il.com>, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-modules@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v5 01/19] scripts: move genksyms crc32 implementation to a
 common include

On Thu, Nov 14, 2024 at 2:54 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> Hi,
>
> On Mon, Nov 11, 2024 at 8:06 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > On Thu, Oct 31, 2024 at 2:01 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> > >
> > > To avoid duplication between host programs, move the crc32 code to a
> > > shared header file.
> >
> >
> > Only the motivation to use this long table is to keep compatibility
> > between genksyms and gendwarfksyms.
> > I do not think this should be exposed to other programs.
> >
> >
> > If you avoid the code duplication, you can do
> >
> > // scripts/gendwarfksyms/crc.c
> > #include "../genksyms/crc.c"
>
> Sure, that sounds reasonable. I'll change this in the next version.


BTW, is it necessary to share the same crc function
between genksyms and gendwarfksyms?

If CONFIG_GENKSYMS and CONFIG_GENDWARFKSYMS
were able to produce the same CRC, it would be a good motivation
to share the same function.
However, as far as I tested, gendwarfksyms generates different CRC values.

When a distro migrates to CONFIG_GENDWARFKSYMS,
the new kernel cannot load old modules built with CONFIG_GENKSYMS.

So, there is no need to share the old code.
Another solution might be to use crc32() provided by zlib, for example.
It requires another external library, but this already depends on
libdw and libelf.










>
> > > Suggested-by: Petr Pavlu <petr.pavlu@...e.com>
> > > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> > > Acked-by: Neal Gompa <neal@...pa.dev>
> >
> > Does this Ack add any value?
> >
> > Acked-by is meaningful only when it is given by someone who
> > maintains the relevant area or has established a reputation.
> >
> > $ git grep "Neal Gompa"
> > $ git shortlog -n -s | grep "Neal Gompa"
> >      2 Neal Gompa
> >
> > His Ack feels more like "I like it" rather than a qualified endorsement.
>
> Like Neal explained, an Ack from a potential user of this feature
> seemed relevant, but if you don't think it's meaningful, I can
> certainly drop it.

Tested-by is more suitable if he wants to leave something.




--
Best Regards
Masahiro Yamada