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Subject: RE: [PATCH] rcu: shift 64-bit constant to avoid implicit 32 to 64 bit
 conversion
Date: Wed, 13 Nov 2024 04:31:28 +0100
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Thread-Topic: [PATCH] rcu: shift 64-bit constant to avoid implicit 32 to 64
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Andre Muezerie" <andremue@linux.microsoft.com>,
 "Honnappa Nagarahalli" <honnappa.nagarahalli@arm.com>
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> From: Andre Muezerie [mailto:andremue@linux.microsoft.com]
> Sent: Tuesday, 12 November 2024 23.03
>=20
> ../lib/rcu/rte_rcu_qsbr.c(101): warning C4334: '<<': result of 32-bit
>  shift implicitly converted to 64 bits (was 64-bit shift intended?)
> ../lib/rcu/rte_rcu_qsbr.c(107): warning C4334: '<<': result of 32-bit
>  shift implicitly converted to 64 bits (was 64-bit shift intended?)
> ../lib/rcu/rte_rcu_qsbr.c(145): warning C4334: '<<': result of 32-bit
>  shift implicitly converted to 64 bits (was 64-bit shift intended?)
>=20
> These warnings are being issued by the MSVC compiler. Since the result
> is
> being stored in a variable of type uint64_t, it makes sense to shift a
> 64-bit number instead of shifting a 32-bit number and then having the
> compiler to convert the result implicitly to 64 bits.
> UINT64_C was used in the fix as it is the portable way to define a 64-
> bit
> constant (ULL suffix is architecture dependent).
>=20
> Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>
> ---

As far as I can see, this is also a bugfix:
(1 << id), where id =3D thread_id & 0x3f, was incorrect when thread_id > =
0x1f.

Please add a Fixes tag, so backporting can be considered.

Reviewed-by: Morten Br=F8rup <mb@smartsharesystems.com>