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Re: [PATCH v2][4.17?] core-parking: fix build with gcc12 and NR_CPUS=1
- To: Julien Grall <julien@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 24 Oct 2022 09:26:00 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>
- Delivery-date: Mon, 24 Oct 2022 07:26:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 22.10.2022 17:30, Julien Grall wrote:
> Is this intended for 4.17?
Well, yes, it was meant to be - it has been ...
> On 09/09/2022 15:30, Jan Beulich wrote:
... well over a month since it was sent.
>> --- a/xen/arch/x86/sysctl.c
>> +++ b/xen/arch/x86/sysctl.c
>> @@ -157,7 +157,7 @@ long arch_do_sysctl(
>> long (*fn)(void *);
>> void *hcpu;
>>
>> - switch ( op )
>> + switch ( op | -(CONFIG_NR_CPUS == 1) )
> This code is quite confusing to read and potentially risky as you are
> are relying the top bit of 'op' to never be 1. While I am expecting this
> will ever be the case, this will be a "fun" issue to debug if this ever
> happen. So I would suggest to check CONFIG_NR_CPUS == 1 separately.
You're aware that we use this pattern in a few other places already (I
guess in my local tree I have one or two which aren't upstream yet)? Just
grep for "switch[^_].*[|]" to see them. Also note that it's not just the
top bit of "op" - we merely assume "op" will never be ~0. Personally I
prefer this way of coding the logic, but if at least one of the other x86
maintainers agreed with you, I'd be okay to switch to using a separate
if().
Jan
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