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Re: [PATCH v2] xen/config.h: Move BITS_PER_* definitions from asm/config.h to xen/config.h
- To: Jan Beulich <jbeulich@xxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 28 Mar 2025 08:45:21 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 28 Mar 2025 08:45:39 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28/03/2025 7:49 am, Jan Beulich wrote:
> On 27.03.2025 18:33, Oleksii Kurochko wrote:
>> BITS_PER_* values can be defined in a common way using compiler-provided
>> macros.
>> Thus, these definitions are moved to xen/config.h to reduce duplication
>> across
>> architectures.
>>
>> Additionally, *_BYTEORDER macros are removed, as BITS_PER_* values now come
>> directly from the compiler environment.
>>
>> The arch_fls() implementation for Arm and PPC is updated to use BITS_PER_INT
>> instead of a hardcoded value of 32.
>>
>> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> albeit ...
>
>> --- a/xen/include/xen/config.h
>> +++ b/xen/include/xen/config.h
>> @@ -98,4 +98,14 @@
>> #define ZERO_BLOCK_PTR ((void *)-1L)
>> #endif
>>
>> +#define BYTES_PER_LONG __SIZEOF_LONG__
> ... I remain unconvinced that we actually need this (yet then not its sibling
> for int). All uses I can spot could be replaced by sizeof(long).
Perhaps, but that's orthogonal to centralising the definition. It can
be deferred.
> This (and its
> sibling) would be needed only for #if uses, and there I would then wonder why
> we couldn't use __SIZEOF_LONG__ directly, now that we assume its universally
> available.
Looking at the usages, sizeof(long) would be best, and shortest.
While we do have a whole bunch of constants which are universally
available now, I still want to use the more normal terms where
possible. e.g. the difference between __BYTE_ORDER__ and BYTE_ORDER is
relevant for the code shared with userspace, and using BYTE_ORDER across
Xen is the cleaner option.
~Andrew
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