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Message-ID: <20200612220158.GA13279@pi3.com.pl>
Date: Sat, 13 Jun 2020 00:01:58 +0200
From: Adam Zabrocki <pi3@....com.pl>
To: lkrg-users@...ts.openwall.com
Subject: Re: RE: ISRA optimized functions
Hey,
On Fri, Jun 12, 2020 at 08:38:35PM +0200, Adam Zabrocki wrote:
> On Fri, Jun 12, 2020 at 07:03:06PM +0200, Mikhail Morfikov wrote:
> > On 12/06/2020 16:07, Adam Zabrocki wrote:
> > > As you can see, even CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE is configured, so this
> > > is "lowlatency" kernel, and CONSTPROP optimization is enforced in various
> > > places (590 funtions was optimized using this method), function "lookup_fast"
> > > is not touched. This is Ubuntu 20.xx kernel package.
> > > The main reason why you have that problem is unusual and specific kernel
> > > configuration which allows for such optimization.
> >
> > But the kernel config I have is the same I had with gcc9 -- nothing has changed
> > here, and in the case of gcc9 I also have lookup_fast without the constprop,
> > which I already mentioned. So something has changed in gcc10 itself, and I don't
> > know what that would be. Maybe you could try building a kernel with gcc10 and
> > check whether you also have this issue? In this way we could confirm that
> > there's a problem with gcc10.
> >
>
> Using GCC version 10.0.1, exactly:
>
> gcc version 10.0.1 20200411 (experimental) [master revision bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566] (Ubuntu 10-20200411-0ubuntu1)
>
> Kernel:
> $ cat /proc/version
> Linux version 5.7.0-g4 (root@oi3) (gcc version 10.0.1 20200411 (experimental) [master revision bb87d5cc77d:75961caccb7:f883c46b4877f637e0fa5025b4d6b5c9040ec566] (Ubuntu 10-20200411-0ubuntu1), GNU ld (GNU Binutils for Ubuntu) 2.34) #28 SMP PREEMPT Fri Jun 12 18:09:14 UTC 2020
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> $ cat /proc/kallsyms |grep lookup_fast|head -1
> 0000000000000000 t lookup_fast
> $
>
>
> However, as I mentioned in my previous emails, I need to discuss and research
> more in details if adding such non-standard kernel configuration / compilation
> support makes sense from LKRG perspective. Maybe it does, maybe not.
>
> Thanks,
> Adam
>
I've been talking with Alexander, and I've pushed support for CONSTPROP. You
can check if that works for you.
Thanks,
Adam
--
pi3 (pi3ki31ny) - pi3 (at) itsec pl
http://pi3.com.pl
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