netdev - Re: [PATCH] soreuseport: use "unsigned int" in __reuseport

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 4 Apr 2017 14:36:02 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Craig Gallek <kraigatgoog@...il.com>
Cc:     David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] soreuseport: use "unsigned int" in __reuseport_alloc()

On Mon, Apr 3, 2017 at 4:56 PM, Craig Gallek <kraigatgoog@...il.com> wrote:
> On Sun, Apr 2, 2017 at 6:18 PM, Alexey Dobriyan <adobriyan@...il.com> wrote:
>> Number of sockets is limited by 16-bit, so 64-bit allocation will never
>> happen.
>>
>> 16-bit ops are the worst code density-wise on x86_64 because of
>> additional prefix (66).
> So this boils down to a compiled code density vs a
> readability/maintainability argument?  I'm not familiar with the 16
> bit problem you're referring to, but I'd argue that using the
> self-documenting u16 as an input parameter to define the range
> expectations is more useful that the micro optimization that this
> change may buy you in the assembly of one platform.  Especially given
> that this is a rare-use function.

It's not a problem as in "create trouble".
16-bit operations are the worst on x86_64: they require additional prefix,
compiler often has to extend it to 32-bit to do anything useful
(MOVZX = 1 cycle, 3 bytes) because of cast-everything-to-int
behaviour enabled by the language.