Re: [PATCH v2] rcu: shift 64-bit constant to avoid implicit 32 to 64 bit conversion

[David Marchand <david.marchand@redhat.com>]

On Wed, Nov 13, 2024 at 5:24 PM Andre Muezerie
<andremue@linux.microsoft.com> wrote:
>
> ../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?)
>
> 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).
>
> From reading the code this is also a bugfix:
> (1 << id), where id = thread_id & 0x3f, was wrong when thread_id > 0x1f.
>
> Fixes: 64994b56cfd7 ("rcu: add RCU library supporting QSBR mechanism")
>
> Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Morten Brørup <mb@smartsharesystems.com>

Just a nit, EAL provides a macro:
lib/eal/include/rte_bitops.h:#define RTE_BIT64(nr) (UINT64_C(1) << (nr))


Does this change allow to build the rcu library with MSVC?
I see it is disabled in meson.


-- 
David Marchand