linux-kernel - Re: [PATCH 6/6] genksyms: use uint32_t instead of unsigned long for calculating CRC

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Message-ID: <20250103083435.1785f86e@pumpkin>
Date: Fri, 3 Jan 2025 08:34:35 +0000
From: David Laight <david.laight.linux@...il.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] genksyms: use uint32_t instead of unsigned long for
 calculating CRC

On Fri,  3 Jan 2025 16:30:43 +0900
Masahiro Yamada <masahiroy@...nel.org> wrote:

> Currently, 'unsigned long' is used for intermediate variables when
> calculating CRCs.
> 
> The size of 'long' differs depending on the architecture: it is 32 bits
> on 32-bit architectures and 64 bits on 64-bit architectures.
> 
> The CRC values generated by genksyms represent the compatibility of
> exported symbols. Therefore, reproducibility is important. In other
> words, we need to ensure that the output is the same when the kernel
> source is identical, regardless of whether genksyms is running on a
> 32-bit or 64-bit build machine.
> 
> Fortunately, the output from genksyms is not affected by the build
> machine's architecture because only the lower 32 bits of the
> 'unsigned long' variables are used.
> 
> To make it even clearer that the CRC calculation is independent of
> the build machine's architecture, this commit explicitly uses the
> fixed-width type, uint32_t.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
> 
>  scripts/genksyms/genksyms.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/scripts/genksyms/genksyms.c b/scripts/genksyms/genksyms.c
> index e2cd3dcb469f..8b0d7ac73dbb 100644
> --- a/scripts/genksyms/genksyms.c
> +++ b/scripts/genksyms/genksyms.c
>...
> -	printf("#SYMVER %s 0x%08lx\n", name, crc);
> +	printf("#SYMVER %s 0x%08lx\n", name, (unsigned long)crc);

That should use PRIu32, but the whole patch could just use 'unsigned int'.
No one is going to try to build this where 'int' is 16bit.
All the hex constants assume that int is 32bits as well.

	David